The Wireless Smart Utility Network Field Area Network (Wi-SUN FAN) relies on IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) to construct large-scale multi-hop IP networks. However, local parent selection can concentrate traffic through a few relays, increase path depth, and amplify packet loss. We propose a centralized route-construction framework that aggregates neighbor reports at the border router and applies zero-suppressed decision diagram (ZDD) to enumerate all Destination-Oriented Directed Acyclic Graph (DODAG)-consistent spanning structures under global constraints such as hop bounds and per-parent child limits. From this feasible set, routes are chosen according to a network-wide objective and then minimized for total relay count. In a 75-router, 4 km × 4 km simulation with realistic Wi-SUN PHY/MAC and propagation settings, the selected routes improve end-to-end success rate and latency, achieving approximately 90% end-to-end packet delivery ratio (PDR) at low offered load. By optimizing globally before installation, our approach produces shallow DODAGs that reduce hop counts while balancing relay load, resulting in a substantial improvement in communication reliability.

This paper presents a comprehensive wideband indoor propagation characterization via real-world experiments at 105.8 GHz with a 4 GHz bandwidth in a lecture hall environment. Utilizing a double-directional channel sounding system with rotating horn antennas, we measure power angular delay profiles (PADPs) at multiple receiver (RX) positions. Our study derives a path loss model, delay characteristics, and angle characteristics, including path loss exponent, root mean square (RMS) delay spread (DS), K-factor, RMS azimuth angle spread of arrival (ASA), and RMS azimuth angle spread of departure (ASD). We compared these results with the 3GPP indoor hotspot (InH) office model (up to 100 GHz), highlighting both similarities and differences in propagation characteristics. Notably, the path loss exponent was found to be 1.49, which is lower than the 1.73 observed in the 3GPP InH-Office LoS model. Moreover, there were positive correlations between the above spread values and transmitter (TX)-RX distance, and negative correlations between K-factor and TX-RX distance, which were not considered in the 3GPP InH-Office LoS model. Furthermore, our analysis revealed a strong negative correlation in RMS ASA vs K-factor and RMS ASD vs K-factor, which are not accounted for in the current 3GPP InH office model. These findings emphasize the need to consider such correlations in accurate propagation models in lecture hall scenarios at the 105 GHz sub-terahertz band.

This study presents the world's fastest three-dimensional double-directional channel sounding system operating at 105 GHz with a null-to-null bandwidth of 4 GHz. The developed channel sounding system allows a full scan of the 105 GHz multipath channel in both azimuth and elevation angles of the transmitter (TX) and receiver (RX) directional antennas. The developed channel sounding system is calibrated with an anechoic measurement in that the path loss of the observed line-of-sight ray coincides with the free-space path loss. Moreover, the anechoic measurement verifies the performance of the channel sounding system, where the peak width at the half-power in delay domain is lower than 0.5 ns, and the peak width at the half-power in angular domain is approximately 10° in the azimuth plane for both TX and RX.

Full-duplex cellular (FDC), which incorporates inband full-duplex (IBFD) into a cellular system, is a candidate scheme to enhance the spectral efficiency of the mobile communication system. To realize FDC, it is necessary to reduce self-interference (SI) and control inter-user interference (IUI) by appropriate user scheduling. Many researchers have studied various technologies to overcome them, but there are few studies to demonstrate the effectiveness of IBFD with actual equipment, which works in real time. In this paper, we develop a 5G-based real-time FDC prototype, which has functions of digital SI cancellation, collecting IUI information, and flexibly changing user scheduling in real time. In addition, this system can transmit and receive arbitrary data using 5G signals even in FD operation. We evaluate its fundamental effectiveness by experiment and show that IBFD can nearly double the UL and DL throughput.

In this paper, we developed and demonstrated a highly spectral-efficient private 5G standalone system using open-source 5G software and software-defined radio. We introduced an innovative waveform shaping technique for downlink (DL) transmissions and a dynamic bandwidth adaptation scheduler for uplink (UL) communications within the 5G base station. These methods substantially reduce out-of-band emissions (OOBE), making high-speed transmission possible even under stringent interference requirements, with only a minimal 18% throughput reduction and no need for device modifications. Notably, our developed prototype ensures complete compatibility with existing 5G systems, allowing commercial off-the-shelf devices, such as smartphones, to connect seamlessly. Experiments in an anechoic chamber using a smartphone have shown that high-data-rate transmission (240.5 Mbps at DL and 43.9 Mbps at UL) can be achieved while suppressing OOBE by 25dB at DL and 11dB at UL.

In-band full-duplex (IBFD) is gaining attention due to its improved spectral utilization efficiency towards 6G. A dynamic full-duplex cellular (DDC) system has been proposed to gradually introduce IBFD into the current time-division duplex-based 5G system. In addition, the DDC system with transmission (Tx) and reception (Rx) separation has been proposed to reduce self-interference at base stations. However, previous studies have not considered a multi-cell environment. In this study, we propose a DDC system with separated and distributed Rx antennas for a multi-cell environment equipped with directional antennas to reduce inter-cell interference.

In fifth-generation (5G) cellular vehicle-to-everything (C-V2X) communication, single-hop communication where a one-hop relay is established among vehicles, roadside units (RSUs), and base stations (BSs) has attracted attention for enabling pervasive and reliable packet delivery in urban inter sections environments and expressways. Regarding C-V2X single-hop communication, a signal-to-noise ratio (SNR)-based routing protocol has been proposed, where SNR between vehicles, RSUs, and BSs is used to assess communication paths as a metric. However, owing to blockage events between communication nodes, SNR values between nodes may fluctuate sharply; therefore, the conventional methods that use an instant SNR as a metric cannot ensure stable communication against blockage events. This paper proposes a novel blockage prediction-based 5G C-V2X routing method that enables the selection of links that remain stable over time. Specifically, assuming that future line-of-sight (LOS) conditions between nodes are available from on-vehicle camera images, we develop a routing method that avoids non-LOS paths to prevent communication failures in single-hop transmission. Moreover, we propose a blockage prediction-based scheduling method, ensuring packet transmission only in the LOS conditions for further reliable packet delivery. Our system-level simulation in an intersection environment defined by 3GPP demonstrates that the proposed blockage prediction-based routing protocol outperforms the conventional SNR-based routing protocol in terms of packet reception ratio.

Wireless Smart Utility Network Field Area Network (Wi-SUN FAN) is a profile of Wi-SUN, a wireless communication standard for Internet of Things (IoT) devices, designed for applications requiring large-scale, outdoor, mesh-based communication networks such as smart metering systems. Wi-SUN FAN adopts the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) as its network-layer routing protocol. RPL is primarily designed for communication among fixed nodes, which poses challenges for constructing optimal communication routes in mobile communication environments. To address this issue, research has been conducted to improve the routing method for realizing mobile communications based on Wi-SUN FAN. However, the previous study has the disadvantage of requiring adjustments to time constraint parameters related to route construction when nodes move, and is unable to accommodate speeds above a certain level. In this paper, we propose a routing method that solves this problem by optimizing the generation of control frames and eliminating time constraints on route updates for mobile communication system using Wi-SUN FAN that is independent of speed. We compare and evaluate conventional method (i.e. RPL), modified method in the previous study, and proposed method for route control methods using computer simulations. The results show that the proposed method optimizes control frames and enables the construction of reliable communication routes even under high-speed mobility, and the transmission success rate when the mobile node moves at 19 m/s is improved by a factor of approximately 2.9 compared to the conventional method.

In this paper, we show that there is an excellent possibility that 5G can be operated as a spectrum-sharing system in the 15 GHz band of the frequency range 3 (FR3). First, we consider how much spectrum resource can be secured in the 15 GHz band and show that it can ensure a 550 MHz bandwidth in many places and a 190–510 MHz bandwidth in urban areas. Next, we propose a phase noise model for the 15 GHz band, evaluate the block error rate characteristics of various sub carrier spacings (SCSs) using link-level simulation, and show no effect of phase noise if the SCS is 30 kHz or more. Finally, the interference immunity of the 5G new radio is evaluated, and it is found that the required SIR is approximately 10 dB and that each 5G base station could achieve coverage of approximately 700 m in radius.

Sidelink communication has evolved as a distributed device-to-device (D2D) communication system within the third-generation partnership project (3GPP) for the advancements in next-generation distributed autonomous systems. However, the current sidelink communication system basically being considered for operation at microwave band is not suitable for distributed wireless networking with a Gbit/s-level data rate. In this context, we have conceptualized a millimeter wave (mmWave) sidelink-based wireless personal area network (WPAN) to enable high-speed distributed wireless networking among indoor proximate devices. Particularly, inspired by the notion of “common-mode signaling (CMS)” in the IEEE 802.15.3c/11ad mmWave WPAN standards, we proposed an innovative physical sidelink broadcast channel (PSBCH) coined CMS- PSBCH to reach a robust inter-node control signaling to maintain a connection under harsh mmWave channel characteristics. As a sequential study, this paper proposes a robust signal detection and timing synchronization scheme tailored for CMS-PSBCH to lead a successful detection and demodulation, thereby providing a complete set of robust synchronization signal block (SSB) for the sidelink-based mmWave WPAN. Our link-level evaluation shows that the proposed scheme effectively detects synchronization signals and symbol timing even under the signal-to-noise ratio (SNR) of −18 dB. Moreover, the proposed scheme leads to successful demodulation of CMS- PSBCH payload for various multipath channels for a wideband indoor short-range communication scenario at the 60 GHz band.

Toward 6G, cell-free networks (CFN) are attracting attention as a solution to the problem of poor communication quality at the cell edge. In CFN, many access points are densely deployed and cooperatively operated as distributed MIMO systems. In uplink communication in CFN, transmit power control (TPC) is required to mitigate interference and ensure fairness between users. In this paper, we propose an open-loop TPC algorithm for CFN and evaluate its performance by computer simulation. As a result, an improvement of 55.0% in the fifth percentile spectral efficiency is achieved compared to the case without TPC while maintaining a higher average spectral efficiency.

MmWave is currently attracting attention for its significant role in next-generation communication systems such as the fifth generation and sixth generation mobile networks. In this paper, we propose a novel temporal statistical channel model based on our recently conducted indoor short-range propagation measurements at the 60 GHz band. We constructed the channel model compatibly with the New York University channel simulator (NYUSIM) channel model framework which adopts the unique time cluster spatial lobe approach, which lacks both parameter definitions and suitable channel modeling and regeneration framework for indoor short-range communication applications. The channel regeneration simulations demonstrate that our proposed model exhibits good agreement with experimental data in almost all channel parameters, including the number of time clusters, cluster sub-path numbers, inter-cluster delay, and more. Additionally, the proposed model shows better alignment with experimental data in terms of the root mean squared delay spread, compared to existing models.

This paper proposes a comprehensive 3GPPcompatible channel model with statistical enhancement tailored for indoor short-range device-to-device (D2D) communications operating in the frequency range (FR) of $52.6-71.0 \mathrm{GHz}$ termed FR2-2. Regardless of the existence of various channel models at this band for indoor communications, there will be a need for developing a channel model compatible with and understandable from the current 3GPP stochastic channel model (SCM) to facilitate the discussion in the 3GPP for developing such FR2-2 short-range D2D communication framework based on the fifth-generation (5G) new radio (NR). Indeed, such a futuristic vision can be foreseen from the fact that the 3GPP is discussing the evolution of sidelink, referred to as a D2D communication framework; however, there are no 3GPP SCM-compatible channel models applicable to FR2-2 short-range D2D communications. To fill this void, we propose the channel model coined 3GPPCompFR2-InS that allows us to generate channel impulse responses (CIRs) for computer simulations, which is suitable for various indoor short-range D2D communication scenarios while retailing the similarity in terms of the implementation policy of the 3GPP SCM. 3GPPCompFR2-InS is verified based on the real-world measurements at the $\mathbf{6 0 ~ G H z}$ band from the viewpoint of both the validity of the channel model parameters and that of the statistical behavior of the generated CIRs.

This study analyzes the omnidirectional power delay profile (PDP) characteristics at the 105 GHz band in a personal office desktop area by conducting a multipath propagation measurement. In those days, for the 6th generation communication system, there is a demand for a wider bandwidth, and exploring sub-terahertz (sub-THz) is attracting huge interest. However, the omnidirectional multipath propagation characteristics at the 105 GHz band for a personal desktop environment has not been investigated yet regardless of the potential feasibility of the wireless personal area network (WPAN) communication systems operating at this band in a personal desktop area. In this study, we first conduct a measurement of omnidirectional PDPs for the 105 GHz and 60 GHz bands in a personal desktop environment. The comparison of these two bands unveils an affinity in terms of delay-domain multipath characteristics, where the delay spread difference is less than 1 ns. Moreover, this study derives an appropriate guard interval (GI) length to be 20 ns at most for the personal desktop environment, which is compared with those in the internationally standardized 60 GHz WPAN communication systems. These two comparisons with 60 GHz bands provide evidence for the feasibility of 105 GHz wideband WPAN communication systems, which can be designed analogously from 60 GHz WPAN communication systems.

To meet increasing demands for higher-rate communication, exploring the sub-terahertz (THz) band is attracting huge attention. The first standardization of a sub-THz communication was performed at the IEEE 802.15.3d task group, which designed an ultra-wideband short-range communication operating in a 300 GHz band. However, to alleviate hardware challenges, the usage of a much lower-sub-THz band around 100 GHz should also be considered. Moreover, in terms of the advantage of using shared signal processing circuits with the 5G new radio (NR), the frame format should be designed in a compatible manner with the commercially pervasive 5G NR, which cannot be reached by IEEE 802.15.3d. Motivated by these backgrounds, this paper proposes a 5G NR-based ultra-wideband short-range communication operating in a low sub-THz band that lies in 90–110 GHz. This can be achieved by using 5G NR sidelink communication with the bandwidth expansion to several GHz, and no changes are made for the frame format to retain compatibility. This study conducts a performance evaluation of such a 5G NR sidelink system with a 4 GHz bandwidth by using a channel model at the 93–97 GHz band recently developed for device-to-device short-range communications. The evaluation reveals that the proposed communication system using the 5G NR sidelink can achieve the required block error rate (BLER) equal of 0.1 for both control and user-data transmissions even when a 4 GHz bandwidth is utilized. Moreover, it is shown that transmission at a meter-level distance is feasible even when an omnidirectional antenna in an azimuth plane is used.

The increasing demand for faster and more efficient communication technologies has highlighted the in-band full-duplex (IBFD) cellular system as a key advancement for the upcoming 6th-generation mobile communication (6G) systems. Due to the limited availability and high demand for frequency resources, maximizing the utilization of existing frequencies is crucial. The dynamic full-duplex cellular (DDC) system addresses this challenge by introducing IBFD, which simultaneously transmits and receives signals on the same in-band frequency, thereby having the potential to double the spectrum efficiency. However, existing studies on the DDC system have been evaluated using system-level simulations that simplify physical layer processing and focus solely on the MAC layer scheduler, leaving their practical applicability to actual 5G systems undetermined. To address this gap, we present a DDC system emulator developed using OpenAirInterface (OAI), which emulates the complete 5G system from the physical layer to the 5G core network. We propose higher-layer signaling to facilitate IBFD transmission within the DDC system and create a single-cell emulator to evaluate its applicability for future cellular systems beyond 5G. Our results indicate that the DDC system can enhance spectral efficiency while maintaining compatibility with existing 5G infrastructure, paving the way for future 6G implementations. Specifically, our evaluation example shows a 19% increase in downlink throughput, underscoring the practical advantages of the DDC system.

This study conducts a wideband multi-path propagation measurement at the 95 GHz sub-terahertz band for short-range communication in a conference room desktop scenario. Regardless of the fact that the current 3rd generation partnership (3GPP) stochastic channel model (SCM) targets the frequency up to 100 GHz for various scenarios, neither detailed measurements at the 95 GHz band nor a compatible channel modeling/generation framework for indoor short-range communication scenarios have been conducted. To fill these voids, based on a real-world measurement at 95 GHz with a bandwidth of 4 GHz, this study analyzes the multi-path propagation characteristics and yields the following insights for developing a 3GPP SCM-compatible channel generation framework at this band. First, the exponential power decay with delay time and quasi-uniform azimuth angles of arrival (AAoAs) are observed, which should be revisited to develop a channel generation framework. Secondly, distribution models for root mean squared (RMS) delay/AAoA spreads and omnidirectional path loss model are derived, which serves as a foundation for developing a channel generation framework at this band. Moreover, these established models are compared with the recently conducted measurement results at the 60 GHz band in the same scenario, shedding light on the hypothesis that the models for these parameters at the 60 GHz can be generalized for the 95 GHz band.

With advancements in distributed autonomous systems (e.g., vehicles, sensors, and robots) in the 5G/6G era, sidelink communication technology has evolved as a distributed communication system in the third-generation partnership project (3GPP). However, the current sidelink communication design focusing on information dissemination or point-to-point communication with a low rate is not suitable for rapid development of such autonomous systems. Instead, based on sidelink, developing distributed wireless personal area networks (WPANs) with a drastically higher rate for transmitting user data is essential. The overarching goal of this study is to explore the possibility of sidelink communication evolution to 1) form a distributed and autonomous WPAN and 2) support millimeter wave (mmWave) bands. Our core idea is to merge several design concepts of the precedented mmWave WPAN standards, i.e., IEEE 802.15.3c/11ad, into the sidelink communications, thereby bridging the gap between the two separated systems. This paper presents the anatomy of the IEEE 802.15.3c/11ad system with a focus on the formation of mmWave WPANs among distributed nodes and their operation. In addition, the current status of sidelink communication system design is highlighted, along with the missing building blocks, which are required to develop 3GPP sidelink-based mmWave WPAN systems. Simulation results shed light on merging IEEE 802.15.3c/11ad concepts into 3GPP sidelink communication regarding a control data transmission scheme, which should be designed to enhance robustness and is a crucial step for subsequent high-rate user data transmission.

This study proposes a heterogeneous in-band full-duplex (Het-IBFD) system for the simultaneous transmission of the Wi-SUN field area network (Wi-SUN FAN) 1.1 signal using IEEE 802.15.4-2020-compliant orthogonal frequency division multiplexing (OFDM) and reception of the Wi-SUN FAN 1.0 signal using IEEE 802.15.4g-compliant frequency-shift keying (FSK). Furthermore, we propose a simple and highly accurate digital self-interference (SI) canceller to realize the proposed system, focusing on the difference between the spectrum of the IEEE 802.15.4g FSK and IEEE 802.15.4-2020 OFDM. The proposed Het-IBFD system using the proposed digital SI canceler is evaluated using computer simulations under the conditions of one-path Rayleigh fading for the desired communication channel and Rice fading for the SI channel. If no quantization noise effect is considered and the Rice factor is 5 dB, the communication quality of the FSK in Het-IBFD can achieve the required packet error rate (PER) of the wireless smart ubiquitous network (Wi-SUN) system. This is realized using the proposed digital SI canceller when the sum of the pathloss and antenna/analog SI cancelation level is more than 39 dB. If the quantization noise effect is considered with the 12-bit acrlong ADC and the Rice factor is 20 dB, the communication quality of the FSK in Het-IBFD can achieve the required PER of the Wi-SUN system using the proposed digital SI canceller when the sum of the pathloss and antenna/analog SI cancelation level is more than 52 dB.

Towards flexible channel measurements of millimeter wave (mmWave) communications, this paper proposes a time-alignment algorithm of multiple power delay profiles (PDPs) separately measured with different antenna rotation angles. To characterize mmWave channels, capturing both delay time and angular property of multi-path components is necessary, which requires multiple PDP measurements with antenna rotations and alignment of the delay time with respect to a standard time, e.g., time of departure or the arrival time of a line-of-sight ray. While this alignment conventionally requires hardware synchronization between the transmitter and the receiver, this study turns this synchronization into the softwarelized post-processing to eliminate any nuisances incurred by the hardware synchronizations during measurements. To this end, we propose a time of arrival (ToA) estimation method of a maximum power peak in PDPs unsynchronized among different antenna rotation angles, which can be performed without any hardware synchronizations. The core idea is to align the time of the PDPs so that the powers between adjacent antenna rotation angles are highly correlated to each other because the ground-truth time-aligned PDP should possess such higher correlations. This paper formulates this problem as maximum-likelihood estimations; thereby deriving the algorithm to reach this objective. The experimental results based on real measurements demonstrate the feasibility of the time-alignment of the unsynchronized PDPs by comparing to the results by raytracing simulation.

This paper first summarizes the specifications of standardized wireless personal area networks (WPANs) and wireless local-area networks (WLANs) using the 60 GHz band, for example IEEE 802.15.3c and 802.11ad standards, and the significance of the standardization, together with the standardization transition of third-generation partnership project (3GPP)-based public wireless communication systems and other radio systems in the 2010s. The concept of a virtual community network (VCN) using a millimeter-wave wireless communication system in the 6G era is then proposed based on the 3GPP-based orthogonal frequency-division multiple access (OFDMA) system. Moreover, by using a latest propagation characteristics model of the 60-GHz propagation characteristics in 3GPP, we evaluated the block error rate (BLER) performance of the proposed VCN by changing the parameters of the physical layer such as the subcarrier spacing (SCS) through computer simulation. The results showed that a transmission distance of 5 m per terminal could be achieved even with a low-gain antenna, demonstrating the feasibility of a VCN based on the high-density installation of many terminals in a room.

This paper reports a first wideband indoor channel measurement at the 105 GHz sub-terahertz (sub-THz) band and analyzes the multipath characteristics in terms of the omnidirectional path-loss and angular characteristics. The measurement campaigns with the 4 GHz bandwidth are performed focusing on indoor short-range communication scenarios in a conference room, corridor, and office room, which have been considered in the primary 60 GHz communication systems standardized by the IEEE 802.15.3c/11ad. Moreover, to draw full understanding to scale the 60 GHz indoor channel models and 60 GHz system designs for the 105 GHz band, we also conduct 60 GHz channel measurements in the same environment with few modifications in the channel-sounding system and performed the comparison between these two bands. Based on these measurements, we demonstrate the affinity that exists between 105 GHz and 60 GHz bands in terms of path loss exponent and angular characteristics of multipath components, shedding light on the hypothesis that several system designs of the 60 GHz communication systems (e.g., beam switching for non-line-of sight conditions) can be applied to the 105 GHz sub-THz communication systems.

Currently, orthogonal frequency division multiplexing (OFDM), standardized in IEEE 802.15.4, has attracted attention as a transmission scheme for higher data rates, long-distance transmissions, and mobile communications for the expansion of Internet of Things (IoT) applications as well as for legacy IoT applications, such as smart metering systems and home-area networks. In particular, receiving schemes using IEEE 802.15.4-based OFDM have been actively examined to realize mobile communication. Previous studies used the long training field (LTF) and pilot subcarriers for channel estimation of multipath fading, achieving mobile communication with data rates of 100 Kb/s or above at moving speeds of up to 40 km/h in an urban environment. In a previous study, channel estimates were obtained by repeating channel estimates from the LTF and pilot subcarriers in the time domain and by interpolating the estimates in the frequency domain. This study proposes a receiving scheme for IEEE 802.15.4 OFDM aimed at high-speed mobile IoT communication systems. In the time axis direction, the proposed scheme obtains channel estimates in the same manner as previous schemes. However, in the frequency axis, the proposed scheme obtains the channel estimates by copying estimates of neighboring subcarriers according to the coherence bandwidth of the multipath fading channel to update the channel estimates frequently. Computer simulation results show that the proposed scheme, including delay spread estimation can achieve mobile communication with a data rate of 100 Kb/s at moving speed of 200 km/h in the urban environment.

In this study, to evaluate large-scale IoT applications comprising numerous radio devices, we developed a wireless emulator that can evaluate various radio communication systems in cyberspace, without requiring actual radio devices, in addition to verifying transmission performance in an operation similar to actual operations. Because the wireless emulator can separately and independently operate each radio node by porting software that realizes protocols other than the physical layer on the actual radio device to the emulator, the software can be implemented in the actual radio device as it is after completing the emulation. Furthermore, in the emulator, the topology of the network can be altered freely in cyberspace. Moreover, because the simulation of the physical layer is analyzed independently in the emulator, various applications can be evaluated, regardless of mobile and fixed communications. In this study, the Wi-SUN FAN system was adopted as the evaluation example of the wireless communication system using this emulator, star and tree topologies with Wi-SUN FAN nodes were formed in cyberspace, and transmission characteristics, such as average packet transmission success rate and average delay time, were evaluated. The characteristics were compared with the computer simulation results without actual operations and were consistent.

In-band full-duplex (IBFD) is a technique for transmitting and receiving signals simultaneously using the same frequency and time slot. Ideally, by adopting IBFD, the frequency utilization efficiency can be twice than that of the half-duplex. In this study, we focus on a full-duplex cellular (FDC) system, where the base station (BS) allows for the superimposition of downlink (DL) communications with other user equipment (UE) on the uplink (UL) communications and the superimposition of UL communications with other UE on DL communications by applying IBFD. The BS needs to identify the UE whose signals do not degrade DL communication quality in the FDC. Moreover, self-interference (SI) of the BS (i.e., interference when the transmitted signal interferes with its own received signal in IBFD) should not degrade the UL communication quality. This paper summarizes the system configuration and research and development items on the dynamic-duplex cellular system that is generally operated in half-duplex. It adaptively performs IBFD only for UEs whose signal does not interfere with other users. In addition, this paper summarizes the development of a monitoring system for the interference from UEs and the development of digital and analog SI canceller applicable to a BS. The developed BS can reduce SI by more than 35 dB in the RF and more than 20 dB in the digital parts.

In this study, we developed a USB-type radio board equipped with a wireless smart ubiquitous network (Wi-SUN) field area network (FAN) wireless module capable of performing multi-hops for hundreds of units and an integrated evaluation board to evaluate the transmission performance of Wi-SUN FAN with hundreds of wireless devices in the laboratory. The USB-type radio board achieves low power consumption by controlling the operation of the Wi-SUN FAN wireless module mounted on the board from the outside. Therefore, this study measured the current consumption characteristics. Furthermore, fundamental evaluations of the transmission performance, such as the network configuration time and packet transmission success rate, were performed by configuring a large-scale wireless evaluation system with tree and star topologies using 100 USB-type radio boards and the integrated evaluation boards. A transmission success rate of 95% or higher was achieved continuously for 12 h when all terminals sent a UDP data with a packet length of 200 bytes to the border router of Wi-SUN FAN with a data rate of 100 kbps at the intervals of 150 s.

This paper proposes a concept of large-scale emulation and evaluation environment of wireless communication systems. The environment can build radio nodes called virtual node by software in cyberspace and provide interaction among the virtual nodes and the reconfigurable physical radio devices that are connected to the environment from the outside. The environment therefore enables preliminary investigations and evaluations for the highly advanced and complicated wireless systems in the future. Moreover, in the radio interactive emulation, the radio propagation parameters based on the preliminary obtained models are suitably referred. The proposed wireless emulation environment enables wireless emulations required in the six typical wireless systems that are further developed and promoted in B5G/6G society. The paper shows evaluation and consideration of the fundamental performances for the proposed wireless emulation environment that includes numerical investigation for the interconnection performances between the virtual nodes and the reconfigurable physical radio devices, as well as fundamental operation for the wireless emulation with suitable visualization functions.

Full-duplex cellular (FDC) system, which introduces in-band full-duplex (IBFD) to the cellular system, has been paid attention to for increasing spectral efficiency in 5G and 6G systems. IBFD causes new interferences, such as self-interference (SI), because uplink (UL) and downlink (DL) communications are performed simultaneously on the same frequency resources; however, if the new interferences problem can be overcome, IBFD can ideally improve spectral efficiency up to twice that of half-duplex (HD) system. Many SI cancellations have been proposed; however, to the best of our knowledge, there has been no study of digital SI cancellation for application of IBFD to the 5G system by taking into account the 5G signal configuration and the impact on the performance of low-density parity-check (LDPC) code. In this paper, we propose a digital SI cancellation for applying to the 5G-based orthogonal frequency division multiplexing (OFDM) signal. First, we propose a demodulation reference signal (DMRS) configuration to improve the estimation accuracy of the SI channel. Second, the noise power estimation scheme using the proposed DMRS configuration is also proposed for decoding 5G adopted LDPC. Finally, the proposed scheme is evaluated by computer simulations, and we found that the communication quality in IBFD operation becomes equivalent to that in HD operation by applying the proposed digital SI cancellation.

The Internet of Things (IoT) has been increasingly realizing communication among diverse devices, in addition to sensors and meters. IoT is equipped with communication functions and entails interconnection via the Internet to collect and use various data. Wireless smart ubiquitous network (Wi-SUN) conforms to the international standard IEEE 802.15.4, and it has therefore been considered a wireless communication standard for IoT. The Wi-SUN uses frequency-shift keying (FSK), standardized in IEEE 802.15.4, and achieves a typical data rate of 100 kbps. However, when Wi-SUN is used in other IoT applications to realize smart cities and smart factories, communications with higher data transmission rates and longer distances are required. Orthogonal frequency division multiplexing (OFDM), standardized in IEEE 802.15.4, has been used as a transmission method to satisfy the associated requirements. In this study, the fundamental transmission characteristics of IEEE 802.15.4 OFDM were first evaluated through computer simulations and laboratory experiments by employing developed evaluation boards. Next, the outdoor transmission performance of IEEE 802.15.4 OFDM was evaluated using the developed evaluation boards. Experimental results indicate that IEEE 802.15.4 OFDM can yield the same transmission distance as that of FSK using a smaller transmit power to achieve the packet error rate (PER) smaller than 10%.

International Telecommunications Research Institute International (ATR) and Kyoto University (Kyoto Univ.) have jointly promoted a wireless COE (Center of Excellence) program with the support of the Ministry of Internal Affairs and Communications since 2019. The objectives of the program are to create technologies related to resilient radio resource utilization and to accelerate the development of SMEs, start-ups and young talents to lead the wireless technology of the future. In order to achieve the objectives, we have mainly conducted three activities: the concurrent promotion of R&D projects, the construction and operation of open wireless R&D facilities, and the assignment of mentors and their R&D support. Through three-year promotion of the activities with mutual collaboration, we got outcomes and lessons learned. In this paper, we report the overall picture of the program and current status we got through the activities so far.

In-band full-duplex (IBFD), which ideally leads to a doubling of spectral efficiency, has been attracting much attention as a promising technology for the beyond 5G and 6G cellular systems. As a method for introducing IBFD to cellular systems, the dynamic duplex cellular (DDC) system has been proposed. In the DDC system, IBFD is applied if it does not degrade the quality of existing half-duplex (HD) communications. However, the conventional DDC system has not established sufficient improvement of user throughput due to the residual self-interference (SI) at the base station (BS). In this paper, we propose a DDC system with distributed receive-only base stations based on the concept of distributed antenna systems to reduce the impact of the SI. In the proposed system, the radio unit (RU) of the BS is separated into transmit-only RU (TRU) and receive-only RU (RRU), and the TRU and multiple RRUs are spatially distributed in the cell. The effectiveness by the proposed system is evaluated by computer simulation in the single-cell environment.

Wireless technology that can conFigure wide-area IoT systems with high data rates is required toward 6G. To further expand area coverage, it is necessary to improve the data rate of the conventional machine type communications (MTC) such as LTE-M and mMTC at the edge of the coverage area. In this paper, we propose an orthogonal frequency division multiplexing (OFDM) with symbol-edges truncating transmission (STTOFDM) for data rate enhancement. In the proposed STT-OFDM scheme, only a part of the cyclic prefix (CP)-OFDM symbols, which is the legacy communication scheme adopted to 4G and 5G, is transmitted. On the receiver side, zeros are inserted where the no transmission took place at the transmitter side before normal OFDM demodulation is performed. The energy per one-symbol transmission is expected to be reduced by the proposed STTOFDM. We evaluate the achievable throughput and show the usefulness of the proposed STT-OFDM scheme. The proposed STT-OFDM can improve the throughput of the CP-OFDM by about 1.5 times even in low SNR environments.

Radio communication systems using the frequency-shift keying (FSK) scheme standardized by the IEEE 802.15.4g standard can realize low-power consumption and highly reliable communications and are mainly adopted for smart metering as part of the Internet of Things (IoT). However, smart metering has recently broadened its application expectations, with broadband and long-distance communications now required. To fulfill these requirements, orthogonal frequency-division multiplexing (OFDM) has been incorporated into the IEEE 802.15.4g and 802.15.4x standards. However, comprehensive transmission performance analysis of OFDM under static and multipath fading environments has not been conducted. In this article, we first evaluated the packet error rate (PER) of OFDM assuming fixed communications using computer simulations. We then evaluated the transmission distance of OFDM and showed that OFDM can communicate at transmission distances up to 3.0 times longer than those specified in IEEE 802.15.4g FSK. Next, the PER in a mobile communication environment was evaluated using computer simulations. When only the long training field (LTF) was used to estimate multipath radio channels, the required PER of 10% was not achieved, even in a mobile communication environment at a speed of several km/h. To solve this problem, we proposed a receiving scheme which included a new channel estimation scheme. This scheme successively utilized not only the LTF but also pilot signals inserted into the transmitter to estimate radio propagation characteristics. Computer simulation results showed that the required PER was achieved even in a mobile communication environment at 30–40 km/h by using the proposed scheme.

In-band full-duplex (IBFD) systems are attracting attention as a key technology for ideally doubling channel capacity for beyond 5G and 6G. First, we propose an analytical model of the effect of$N$-bit analog-to-digital converter (A/D) quantization noise on channel capacity quasi-upper limit of the desired signal at the base station of the IBFD systems. We derive averaged and peak powers of input signal to$N$-bit A/D and quantization noise power of$N$-bit A/D to formulate uplink (UL) channel capacity quasi-upper limit. Numerical analysis results by the proposed analytical model show that the UL channel capacity quasi-upper limit degrades by 16% and 80% in the 12- and 8-bit A/D, respectively. Second, we propose digital signal-processing (DSP)-assisted dual- and quad-A/Ds to reduce the quantization noise effect in IBFD systems. When A/D resolution bit is 8-bit, the proposed DSP-assisted dual- and quad-A/Ds improve the UL channel capacity quasi-upper limit by up to 92.3 and 192%, respectively, compared to conventional A/D for peak-to-average power ratio condition of 15 dB and analog self-interference (SI) cancellation capability of 30 dB. The proposed dual- and quad-A/Ds can reduce the burden on the analog SI cancellation circuitry by 6 and 12 dB, respectively.

Currently, in-band full-duplex (IBFD) has attracted much attention and has been researched for the beyond 5G systems. IBFD enables simultaneous operation of downlink (DL) and uplink (UL) communications at the same frequency and ideally doubles spectrum efficiency compared with the conventional half-duplex. In recent years, the dynamic-duplex cellular (DDC) system has been proposed to flexibly expand the system capacity with IBFD. However, previous studies of the DDC system were based on the LTE (Long-Term Evolution) system in the sub-6 GHz band. In this paper, we propose a 5G new radio-based DDC system to add UL communications to the DL subframes by considering the antenna directivity in the super high frequency (SHF) band.

The full-scale operation of the 5th generation mobile communication (5G) system was started in several countries. In Japan, in addition to the 5G nationwide public network service provided by telecommunications carriers, the local 5G (i.e., a private 5G network self-operated by various entities to flexibly configure and use a dedicated network within their buildings or premises) is attracting attention. As the local 5G systems become more widespread in the future, many local 5G systems will need to coexist in nearby areas. Therefore, estimating operational area of local 5G systems and avoiding interference between them will be important. Conventionally, the free-space propagation (FS) and the extended-Hata (EH) models are well-known as radio propagation estimation methods. However, they have problems to calculate the radio protection area from the interference and cause wasteful protection area setting or the lack of the radio protection. In this paper, we propose two novel methods for estimating the radio protection area to achieve both high spectrum efficiency and interference protection. In the proposed methods, the effect of single-knife edge diffraction is considered to the conventional models. The proposed methods are evaluated by using measurement results of actual radio propagation experiments in the campus field of Kyoto University.

In recent years, the Wi-SUN field area network (FAN), a wireless multi-hop communication standard, has emerged in smart city infrastructures. Wi-SUN FAN adopts the Internet protocol version 6 (IPv6) routing protocol for low power and lossy networks (RPL) as its routing protocol in the network layer. RPL is originally developed for fixed nodes, such as smart metering devices. Nevertheless, as smart city infrastructures develop, mobile nodes' deployment becomes inevitable, and the Wi-SUN FAN needs to support the routing of mobile nodes. This paper evaluates the delivery rate of data packets from a mobile node to the network's gateway under RPL by computer simulations. The results specify that the slow parent handover deteriorates the delivery rate. Then, we propose a routing algorithm that considers the mobile node's movement to achieve reliable mobile communication in the Wi-SUN FAN. The computer simulation results show that the proposed routing algorithm increases the delivery rate by up to 80.7% compared to the original RPL.

To further improve spectral efficiency for current wireless communication systems, we propose a new lazy learning-based cancellation approach to suppress self-interference (SI) sent from a base station and enable in-band full-duplex (IBFD) transmissions in cellular networks. Differ from the existing IBFD systems based on traditional approaches, our proposal consists of two phases: an offline phase for database generation and an online phase for data transmission. In the offline phase, the output before a 0/1 decision is previously measured without the desired signal input and recorded to a database with self-defined feature vectors (FVs). In the online phase, for the same system architecture with the desired signal input, a suitable result is sought from the generated database with the help of a learning method and the use of FV; then, the result is assigned as a value of SI cancellation. Computer simulation results indicate that the proposed cancellation approaches can achieve about 134 dB SI suppression and thus enables the IBFD transmissions in the considered systems.

To improve the spectral efficiency of the 5th generation mobile communication system (5G) and beyond, the universal time-domain windowed orthogonal frequency division multiplexing (UTW-OFDM) has been proposed. Particularly, the simplified UTW-OFDM is highly compatible with the conventional cyclic-prefix-based OFDM (CP-OFDM). It can strongly suppress out-of-band emission (OOBE) with a simple configuration of multiplying a time window with a long transition length. However, in the simplified UTW-OFDM, multiplication of the time window causes inter-carrier interference (ICI), which degrades the communication quality, especially for higher-order modulation schemes such as 64QAM. In this paper, firstly, we investigate the applicability of the simplified UTW-OFDM to 5G. Next, an ICI canceller is proposed for the simplified UTW-OFDM-applied 5G system to improve the communication quality. In the proposed method, an optimal ICI cancellation weight is designed by taking the noise enhancement suppression into account. The proposed method improves communication quality while achieving stronger OOBE suppression. In the case of 64QAM, the simplified UTW-OFDM can suppress the PSD at the channel edge by up to 45.0 dB compared to that of CP-OFDM.

This paper proposes an inter-user interference (IUI) reduction scheme applying successive interference cancellation (SIC) to expand the in-band full-duplex (IBFD)-applicable area in the dynamic-duplex cellular (DDC) system. If the received power of the IUI is stronger than that of the desired signal at the user equipment for downlink communication (DL-UE), the IUI component is firstly demodulated and decoded in the proposed scheme. Then, a replica signal of the IUI is generated. Finally, we can obtain the IUI-reduced desired signal by subtracting the replica signal of the IUI from the received signal. By applying the proposed scheme to the DDC system, the IBFD-applicable area can be expanded. The proposed scheme is evaluated by the link-level and the system-level simulations to show the IUI reduction and the IBFD-applicable area expansion performances. From the evaluation results, it is found that the IBFD-inapplicable area can reduce from 33.9% to 8.0%, namely the IBFD-applicable area can expand by 25.9%, by applying the proposed scheme to the DL-UE.

Wireless smart ubiquitous network (Wi-SUN) has been applied to various wireless Internet of things (IoT) networks. In Wi-SUN, IEEE 802.15.4g-based frequency shift keying (FSK) modulation is adopted as a low-power consumption physical layer. On the other hand, IEEE 802.15.4g/4x-based orthogonal frequency division multiplexing (OFDM) is one of the candidates for the next-generation physical layer of Wi-SUN to meet the increasing demand for high-speed transmission due to the diversification of applications. In the next-generation Wi-SUN, the existing FSK-based system and the new-generation OFDM-based system will be operated in the same field. In this paper, we consider the construction of an in-band full-duplex (IBFD) communication system using these heterogeneous wireless communication systems, assuming that the base station (BS) transmits the OFDM signal while receiving the FSK signal simultaneously. To realize the IBFD-based FSK and OFDM hybrid Wi-SUN base station, we propose a high-efficiency demodulation scheme based on successive interference cancellation (SIC) scheme using characteristics of the FSK spectrum and the OFDM pilot arrangement. The proposed scheme improves the self-interference (SI) channel estimation accuracy by about 20 dB and improves the bit error rate (BER) characteristics of the FSK signal in the IBFD system to the same level as the BER of the half-duplex (HD).

Wi-SUN FAN (wireless smart utility network field area network) is a technical specification of Wi-SUN that introduced multi-hop M2M (machine-to-machine) transmission for advanced smart city infrastructure. To construct a multihop network, the RPL (IPv6 routing protocol for low power and lossy networks) and the ETX (expected transmission count) are adopted as routing protocol and routing metric, respectively, in Wi-SUN FAN. The combination of the RPL and the ETX may cause a node to change its parent frequently. If a node selects a parent with lower link quality, communication reliability becomes lower. To avoid the frequent parent changing problem, parent candidates of each node should be selected appropriately. In this paper, we propose two schemes to select parent candidates for each node (i.e., optimized RSL (received signal level) threshold scheme and MAC (media access control) address filtering scheme) to stabilize the multi-hop routing construction in the Wi-SUN FAN systems. The proposed schemes are experimentally evaluated in a real field in an office building using the IoT-GWs (internet of things gateways) with Wi-SUN FAN module. By using the optimized RSL threshold scheme, the number of parent changes can be reduced by up to 96% compared to the case with unoptimized RSL threshold. Also, the number of parent changes can be reduced by up to 77% with the proposed MAC address filtering scheme compared to without the proposed scheme.

In this paper, we propose a heterogeneous wireless management scheme for a home area network (HAN) system. The HAN system integrates multiple wireless systems (e.g., the Wi-Fi operating in the 2.4 GHz-band and the Wi-SUN field area network (Wi-SUN FAN) operating in the sub-GHz-band) for the in-home health care management system. The system assumes a medical care and proactive health management, and a variety of data such as the vital data, the environment data, and the user activity data are collected to a coordinator by using IoT gateways (IoT-GWs). For the transmission scheme between the loT-GWs, we compare two schemes; the conventional FAN scheme and the proposed fast-path scheme. In the FAN scheme, all of the measured data are collected by using the Wi-SUN FAN multi-hop transmission. On the other hand, the proposed fast-path scheme uses both the Wi-Fi and the Wi-SUN FAN, and a part of the data is offloaded to the Wi-Fi from the Wi-SUN FAN. These two schemes are evaluated by computer simulations. In the case that only the vital and environmental data are collected to the coordinator, these data can be collected with the end-to-end (E2E) transmission success rate of 98 % in the proposed fast-path scheme compared with 92 % in the conventional FAN scheme.

In this paper, we propose a dependable source routing scheme for multi-hop networks based on the receiver-initiated media access control (MAC) protocol. In the proposed scheme, multiple candidates of relay terminals can be loaded in routing information, so the route is not specified uniquely. The following two effects are expected to the proposed scheme. The first is the improvement of communication reliability by avoiding disturbed link. Second is the improvement of the delay and current consumption by shortening the waiting time for communication timings. To show the effectiveness of the proposed scheme, we conduct computer simulations that suppose a multi-hop network based on the feathery receiver-initiated transmission (F-RIT) protocol in stable channel conditions. In the evaluation, the data are collected by polling communications, and the proposed scheme is applied to downlink communications. The results show the effectiveness of the proposed scheme that improves the delay by up to 41.3%and current consumption by up to 13.5% under a specific condition for the evaluation.

The wireless smart utility network (Wi-SUN) gets attention as one of the promising wireless networks for the machine-to-machine (M2M) and Internet of Things (IoT) systems. The resource-limited monitoring and management (RLMM) is a profile of the Wi-SUN for the non-Internet protocol (non-IP)-based networks in resource-poor environments. The coordinated sampled listening (CSL) is one of the IEEE 802.15.4e-based low-power media access control (MAC) protocols, and it is a candidate protocol for the RLMM systems. To construct the CSL-based RLMM systems in a variable environment, the communication characteristics should be evaluated theoretically and experimentally. In this paper, we designed a practical CSL protocol for the implementation, and a theoretical analysis scheme to evaluate communication characteristics of the practical CSL is proposed considering with the effect of Acknowledgement (ACK) frames. Furthermore, the practical CSL protocol is demonstrated experimentally using 30 actual Wi-SUN dongles in a radio anechoic chamber. The proposed theoretical analysis results agree well with not only computer simulation results but also experimental results. It means that the proposed theoretical analysis scheme has high practicality and reliability under actual environments. The experimental and theoretical results show that a high communication success rate of over 90 % can be achieved when the data generation rate is lower than 5.0 × 10−3s−1.

The wireless smart ubiquitous network (Wi-SUN) has been attracting much attention as one of the candidates of wireless sensor networks (WSNs) for the Internet-of-Things (IoT). In considering that the Wi-SUN is applied to the IoT system in the environment where the power supply cannot be easily secured, such as structure monitoring systems, it is imperative to establish the technology enabling the Wi-SUN system to operate with only a battery for a prolonged time. The key enabling technology for the low operation in the Wi-SUN system is a low-power media access control (MAC) protocol. The coordinated sampled listening (CSL) protocol is one of the standardized low-power MAC protocol. In this paper, we demonstrate the feasibility of the CSL-based protocol and verify its detailed characteristics by implementing the CSL-based protocol into the actual Wi-SUN dongles to construct the CSL-based low-power networks. The experimental and computer simulation results demonstrate the feasibility and reliability of the CSL-based protocol.

In this paper, a novel cancellation scheme named superposition cancellation technique is proposed by using a superposition modulation technique for the single carrier fullduplex (FD) system. The proposed scheme utilizes the features that a single carrier with the Nyquist filter has no inter-symbol interference (ISI) and the phase-shift keying (PSK) modulation symbol has a constant amplitude to perform the self-interference (SI) cancellation. The proposed scheme can be applied in combination with other conventional cancellation schemes. This means that the cancellation requirement for the conventional cancellation schemes can be mitigated. From the feasibility study with theoretical evaluation and computer simulations, the proposed scheme achieves about 40 dB SI cancellation.

The wireless smart ubiquitous network (Wi-SUN) field area network (FAN) attracts attention as a wireless communication standard for large-scale Internet of Things (IoT) systems. Currently, frequency shift keying (FSK) defined in IEEE 802.15.4 is adopted in the physical layer of the Wi-SUN FAN. To improve the network performance toward next-generation IoT systems, a data rate enhancement scheme for FSK has been proposed. However, there is no evaluation of data rate improvement effect by adopting the data rate enhanced FSK on the transmission characteristics of the Wi-SUN FAN. Besides, introducing the data rate enhanced FSK causes the bandwidth to increase. For multiple systems to coexist in limited frequency bands, it is necessary to achieve high spectral efficiency even when the Wi-SUN FAN adopts the data rate enhanced FSK. In this paper, we evaluate the transmission characteristics of the Wi-SUN FAN adopting the high-speed FSK of 600 kbps by computer simulations. The simulation results show that the system throughput improves by 2.5 times, but the bandwidth also increases by 2.5 times compared to the existing system. Furthermore, we propose highly-dense frequency hopping based on a novel channel arrangement scheme to improve spectral efficiency and compatibility with the existing system design while the data rate enhanced FSK is adopted. The evaluation results show that the system throughput in the proposed scheme is 2.4 times of the existing system while using less than half of the bandwidth compared to the conventional channel arrangement scheme.

IEEE 802.22 is a standardized WRAN (Wireless Regional Area Network) system that operates in TVWS (TV White Spaces) and aims to achieve an effective spectrum utilization. Since IEEE 802.22 offers excellent propagation characteristics in the UHF (Ultra High Frequency) band, it is expected to support a cost-effective wireless communication system in rural areas. To provide a long-distance wireless communication, it is important for the receiver design to compensate a multipath fading attributed to large differences in path lengths, while existing multipath fading channel profiles applicable to IEEE 802.22 has generalization and statistical limitations. To generally and stochastically reproduce the multipath propagation characteristics in an actual wide area environment, an algorithm to obtain a statistical channel model extracted from the field experiment data is required. In this study, we develop a novel channel modeling algorithm based on the conventional S-V (Saleh-Valenzuela) modeling algorithm that offers an approach to model and reproduce the multipath characteristics in an actual environment. The proposed channel modeling algorithm applies a dynamic GEV (Generalized Extreme Value) distribution fitting for the amplitude fluctuation of individual arrival cluster. We also evaluate the channel reproduction performance of the proposed algorithm by computer simulation using channel modeling factors calculated from the experiment result with a FE (Fading Emulator). As a result, by applying the proposed algorithm, the multipath fading characteristics measured in the experiment can be modeled, and its reproducibility is confirmed with regard to relative path power distribution, rms delay spread distribution, and BER characteristics.

Wireless smart utility network field area network (Wi-SUN FAN), which configures very large-scale multi-hop networks, has been standardized to promote interoperable open standards for machine-to-machine (M2M) communication. In the media access control (MAC) layer, Wi-SUN FAN adopts a carrier sense multiple access with collision avoidance (CSMA/CA) and a channel hopping (CH) to avoid interferences between devices. A channel schedule controls the operational channel of CH and it is dominant for both unicast and broadcast transmission performances. In this paper, the impact of channel schedule on the network performance is studied to enhance the unicast transmission throughput. The transmission throughput of a Wi-SUN FAN system in four multiple tandem topologies are evaluated by computer simulations in various channel schedule schemes. The simulation results show that by adopting CH and setting the broadcast interval (BI) coefficient to the optimal value that depends on the network topology, higher unicast throughput can be achieved and the transmission interval of broadcast control frames can be preserved at 131 s. In the case of a multiple tandem topology that consists of 33 devices, by adopting CH and setting the BI coefficient to be 30, the unicast throughput increases by up to 12.2% compared to the case of default parameter configuration recommended in Wi-SUN FAN standard.

Wireless Smart Utility Network Field Area Network (Wi-SUN FAN) is one of the Wi-SUN profiles that is expected to be adopted by many smart devices in advanced smart city infrastructures to provide Machine-to-Machine (M2M) communication in Low power and Lossy Networks (LLNs). The physical and data link layer of Wi-SUN FAN systems is complied with IEEE 802.15.4-2015 to perform multi-hop data transmission. Currently, the implementation of Wi-SUN FAN devices has been initiated. However, the Wi-SUN FAN devices face a serious problem of very slow network configuration. In this paper, the multi-hop network configuration time of the current Wi-SUN FAN devices is measured by the experiment to analyze the factors that cause the slow configuration. The optimization scheme to accelerate the configuration process is discussed and the instant response configuration scheme that further reduces the configuration time is proposed. In addition, the computer simulation is performed to study the trade-off relationship between the configuration time and the percentage of time used in the configuration process. Finally, the appropriate values of the configuration parameters that can complete the configuration process in each hop within 1 minute while minimally deteriorate the transmission performance in both conventional and proposed configuration schemes are determined.

The enhanced universal filtered-DFTs-OFDM (eUF-DFTs-OFDM) has been proposed for reducing the out-of-band emission (OOBE) drastically with low peak-to-average power ratio (PAPR). However, this scheme has high complexity due to the time-domain convolution of LPF. In this paper, we propose a new time-domain windowing function for the universal time-domain windowed-DFTs-OFDM (UTW-DFTs-OFDM) to reduce the OOBE with low PAPR and low implementation complexity by using a time response of the LPF for the eUF-DFTs-OFDM. The performance of the proposed time-domain window function is evaluated by simulation in terms of OOBE, PAPR, block error rate (BLER), and implementation complexity with the LTE uplink parameters. As a result, we achieve almost same performance as the eUF-DFTs-OFDM with the significant reduction of the number of multipliers used for wave-shaping.

In this paper, we propose an analysis scheme of the feathery receiver-initiated transmission (F-RIT) protocol for low power wireless smart utility network (Wi-SUN) system. The proposed analysis scheme is developed taking the turnaround time that deteriorates the transmission performance in implemented protocol under interference environments into account. The proposed theoretical analysis result and simulation result on the Wi-SUN Japan utility telemetering association (JUTA) profile-compliant F-RIT protocol for evaluation shows same tendency. Furthermore, the Wi-SUN JUTA profile-compliant F-RIT protocol is evaluated experimentally using actual Wi-SUN dongles. The experiments under interference environment demonstrate that the collision due to the turnaround time occurs in actual, and it is verified that the theoretical analysis by the proposed analysis scheme is efficient to evaluate the protocol generally.

IBFD (In-Band Full-Duplex) has attracted renewed attentions in recent years along with the improvement of self-interference cancellation technologies because IBFD can ideally double the system capacity. Although there have been various reports applying IBFD to the cellular system, some impair the compatibility with the conventional LTE (Long-Term Evolution) system and some are not evaluated in practical scenario such as a multi-cell environment. In this paper, we propose an advanced DDC (Dynamic-Duplex Cellular) system applying IBFD to all cells in a multi-cell environment. The proposed system suppresses inter-cell interferences among all cells and enhances the system capacity with proper scheduling and power control without information exchange among neighboring cells while maintaining compatibility with the conventional TD (Time division Duplex)-LTE system. Practicality of the proposed DDC system is also evaluated by computer simulation with regard to the enhancement of the user throughput.

Currently, the IAB (Integrated Access and Backhaul) system that offers effective relaying architecture between Donor and UEs (User Equipments) via Node has been discussed in 3GPP for various use cases including mobile relaying scenarios. For applying the IAB system to mobile systems, sub-6 GHz band is used for BL (Backhaul Link) to support wide coverage, and it is preferred to use the same frequency for both BL and AL (Access Link) due to the serious spectrum resource shortage below 6 GHz. However, since the frequency resource is divided into four links by the combination of BL/AL and UL/DL (Uplink/Downlink), system capacity of the sub-6GHz IAB system will be degraded. In this paper, we propose DDC (Dynamic full- Duplex Cellular)-IAB that applies IBFD (In-band Full-duplex) to the sub-6 GHz IAB system to enhance the system capacity. With the system level simulation in a multi-cell environment, the proposed DDC-IAB system improves UL UPT (User Perceived Throughput) between UE and Node and between UE and Donor by 90.2 % and 34.9 %, respectively, and also improves DL UPT between Donor and UE by 39.6 % compared to HD (Half-duplex)-IAB system.

The IEEE 802.22 system was standardized in 2011 as a fixed wireless communication system for regional area networks using TV white-spaces (TVWS). Due to its wide coverage area of 10-30 km, the IEEE 802.22 system is expected as a backbone wireless network system in developing countries as well as a public safety broadband communication system even in leading countries. This wide coverage enables a reduction of the number of base stations, resulting in the initial-cost saving compared to other communication systems. However, previously prototyped IEEE 802.22-based devices have not been deployed for social demonstrations, because there still have difficulties in cost and procurement due to the costly design such as FPGA-based baseband signal processing and specially customized RF components to comply with the strict spectrum limitations by some leading countries. In this paper, we prototype compact and lightweight IEEE 802.22-based radio equipment by applying mixed design using an FPGA and a DSP. Measured transmission spectrum conforms to Ofcom and FCC regulations with a transmit power of +30 dBm and +24 dBm, respectively. Also, measured receiver sensitivity achieves the requirement of the IEEE 802.22 system, and a maximal UDP throughput of 14.86 Mbit/s was obtained on the conditions of PHY mode 16 with a 6 MHz channel bandwidth and a 1/4 CP length.

In this paper, an enhanced universal filtered (UF)-DFT-spread-OFDM (eUF-DFTs-OFDM) is proposed. The conventional UF-DFTs-OFDM can drastically reduce the out-of-band emission (OOBE), which has been the problem of the conventional cyclic prefix (CP)-DFTs-OFDM. However, the conventional UF-DFTs-OFDM degrades the communication quality in long-delay multipath environment due to the frequency-domain ripples derived from extending the rise and fall time of the LPF corresponding to the guard interval (GI). On the contrary, the proposed eUF-DFTs-OFDM achieves significantly low OOBE and high communication quality even in the long-delay multi-path fading environment by applying the CP and the LPF with short rise and fall time. The advantages of the proposed eUF-DFTs-OFDM are discussed by simulating the characteristics of the OOBE, peak-to-average power ratio (PAPR) and block error rate (BLER) with the LTE uplink parameters. As a result, it is confirmed that the proposed eUF-DFTs-OFDM is capable of suppressing the OOBE at the channel edge by 40 dB compared to the conventional CP-DFTs-OFDM. Moreover, the proposed eUF-DFTs-OFDM can improve the ES/N0to achieve BLER= 10-3by about 2 dB for QPSK and 16QAM compared to the conventional UF-DFTs-OFDM. Especially for 64QAM, the proposed eUF-DFTs-OFDM can achieve BLER = 10-3at an ES/N0of 30 dB, even though BLER characteristics of the conventional UF-DFTs-OFDM results in error floor.

The 5G system requires flexible and ultrahigh-efficient spectrum usage, while spectrum efficiency is limited by using the conventional LTE and LTE-Advanced based on cyclic prefix-based orthogonal frequency division multiplexing (CP-OFDM) due to the high out-of-band emission (OOBE). Therefore, new-waveforms for reducing the OOBE are required to improve spectrum efficiency and the authors have proposed universal time-domain windowed OFDM (UTW-OFDM) as one of the new-waveforms for the 5G system. The UTW-OFDM has many advantages such as low-OOBE, low-complexity and high-compatibility with conventional CP-OFDM-based systems. In this paper, we developed a UTW converter enabling a proposed UTW-OFDM-based LTE-downlink (DL) system in real time. By applying the UTW converter to the off-the-shelf LTE-DL system, feasibility of the proposed UTW-OFDM is experimentally evaluated. The experimental results show that the UTW-OFDM suppresses power spectrum density at the channel-edge by about 20 dB and 18 dB for QPSK and 64QAM, respectively, without any throughput deterioration compared to the conventional CP-OFDM-based LTE-DL signal.

This paper proposes a load balancing algorithm for a layer 2 routing (L2R) protocol of IEEE 802.15.4/4g/4e based wireless smart utility network (Wi-SUN) systems to achieve low-power consumption mesh networking. In the conventional link quality based routing method scheme discussed in IEEE 802.15.10 Draft 01, the fairness of cumulative number of sending packets has not effectively been achieved. Therefore, it may cause that many terminals send packets to a certain terminal. In the proposed method, the number of sendings is used to select the path of routing as well as link quality. The performance of the proposed routing method is evaluated by computer simulation. As the result, the proposed scheme can improve the maximum sending ratio that evaluates the cumulative number of sending packets by 59% with no degradation of the average sending times and end-to-end success rate (E2E-SR) compared with the conventional routing scheme that is one of the candidate schemes discussed in IEEE 802.15.10 Draft 01.

In this paper, we propose an enhanced universal filtered orthogonal frequency division multiplexing (eUF- OFDM) to achieve low out-of-band emission (OOBE) while maintaining high communication quality under the long-delay multipath fading environment by combinedly using a cyclic prefix (CP) and a filter with short-transition time. The proposed eUF- OFDM can suppress the OOBE at channel-edge by 25 dB compared to the conventional OFDM. Furthermore, the proposed eUFOFDM improves the signal-to-noise ratio (SNR) to achieve block-error-rate (BLER) = 10-3by 1.3 dB compared to the conventional UF-OFDM under the long- delay multipath fading mobile environment.

In this paper, a novel broadcast protocol is proposed for the receiver initiated transmission (RIT) media access control (MAC) protocol based wireless smart utility network (Wi-SUN) systems. The RIT protocol adopted by IEEE 802.15.4e achieves the low power consumption by switching the short wake-up state and the long sleep state, however, the protocol does not support broadcasting because terminals with the protocol are in the sleep state mostly. In the proposed protocol, terminals follow to adjusted periodical listening instructions that are unicasted, and the broadcasting frame transmitted at the periodical timing. Computer simulations are carried out to evaluate the required time for the layer 2 (L2) address resolution, as a typical case of the proposed broadcast protocol. The evaluation shows broadcasting is achieved by the proposed protocol and it is found that the average required time to finish the L2 address resolution is about 16s when a personal area network coordinator (PANC) performs broadcasting with repeat listen interval of 5.0s and the number of terminals is 100. Also, the evaluation results show that the proposed protocol has the flexibility that achieves broadcasting without setting parameters regardless of the number of terminals. By the proposed RIT based broadcast system, very low-power consumption internet protocol (IP) transmission in the Wi-SUN can be implemented within the permissible delay.

In this paper, the effectiveness and feasibility of the feathery receiver initiated transmission (F-RIT) protocol based wireless smart utility network (Wi-SUN) systems are proved experimentally by developing the actual modules and experimental evaluations. The experimental results show that the F-RIT based Wi-SUN systems can achieve over 90% transmission success rate under the practical automatic meter infrastructure (AMI) specified conditions. Additionally, the transmission failure factors in the experimental results are analyzed for the further improvement of the F-RIT protocol. The results of the analysis indicate that the timeout problem is the main factor of the transmission failures in the F-RIT based Wi-SUN systems.

This paper presents the experimental performance evaluation results of the IEEE 802.15.4/4g/4e Smart Utility Networks (SUN) in applications suited for outdoor environment. SUN is an advanced wireless communications network designed for reliable, low data rate, and low energy consumption networks for command-and-control applications like utility service, sensor network, and so on. IEEE 802.15.4g/4e is the international standard for SUN supported by multiple utility providers and product vendors. In this paper, a comprehensive field test was conducted by employing the implementation we have developed to evaluate the performance of the SUN devices based on IEEE 802.15.4/4g/4e standard. The output power of the implementation is 250 mW for extended range, reducible to 20 mW for short-range scalability and battery preservation. Results showed that in an outdoor line-of-sight environment, the achievable one-hop range of a 50 kbps SUN device was 450 m. Next, in a non-line-of-sight environment involving typical residential concrete building, the communications could be established penetrating obstructions to reach above the 11th storey, reaching the performance degradation limits at the 20th storey. Next, the network of the SUN system was proven to be capable of supporting a typical multihop tree network in a dense populated building, meeting the required performance by the standard.

This paper proposes novel two carrier frequency offset (CFO) estimation schemes to introduce inexpensive oscillators and operate under mobile multipath environments in wide area Wi-SUN systems based on IEEE 802.15.4g. One of the proposed schemes using a moving average low-pass filter (LPF) can compensate CFO within ±20 ppm at 920 MHz completely with simple configuration under condition of mobile and multipath fading environment. The second proposed scheme using the same LPF of the first scheme and artificially designed frequency offset can compensate larger CFO within ±30 ppm at 920 MHz.

This paper proposes a novel ultra-low-power media access control (MAC) protocol, called the feathery-receiver initiated transmission protocol (F-RIT), complied with RIT in the IEEE 802.15.4e standard (15.4e). The proposed F-RIT protocol uses compacted 15.4e MAC frames to reduce power consumption. Additionally, a simplified channel sampling process, called pre-carrier sense (Pre-CS), is introduced to the proposed F-RIT instead of carrier sense multiple access with collision avoidance (CSMA/CA) in 15.4e RIT to improve time utilization efficiency per a channel. The proposed F-RIT can improve the success rate by more than 5-fold relative to the coordinated sampled listening (CSL) protocol, another low-power-consumption protocol of 15.4e, in an environment containing 100 terminals, where each terminal transmits its signal for 100 ms, and the data transmission data occurring 0.01 s−1per a terminal.

This paper presents measurement and analysis results of power delay profiles and fading characteristics for “Public Broadband Wireless Communication (PBB) System” in VHF band. The PBB system was proposed to utilize a portion of vacant spectrum in VHF band due to the frequency reallocation plan in Japan, and the system was standardized as ARIB STD-T103 as well as IEEE802.16n. The purpose of this study is to evaluate the applicability of the system for non-line-of-sight urban environment and characterize the 200 MHz band broad band radio channel. The measurement is conducted by using a developed device which is compliant with the ARIB STD-T103 as a transceiver, and received signal is captured as complex IQ signals by using a signal analyzer. In order to obtain the power delay profile, impulse responses are analyzed by calculating sliding correlation between reference signal and measured signals. For the evaluation of delay characteristics, RMS delay spread is calculated using the power delay profile. In addition, fading characteristics is also shown to confirm the behavior of VHF band mobile propagation channel.

We have implemented a hierarchical mesh (HM) based routing protocol for data collection in an indoor environment. Devices are autonomously organized into a hierarchy based on a metric used to evaluate links between two devices, and end-to-end paths. The HM-based routing is implemented at the link layer over the MAC layer in a working WPAN (IEEE 802.15.4) and uses MAC addresses. A mesh root initiates the construction of the HM and acts as the data collector of the network. Data collection can begin as soon as the HM topology is established and does not require additional route establishment signaling. Devices select a next hop from a neighbor table and do not need to have knowledge of the entire path. We observe efficient routing with limited link layer retransmissions through our experiments. Additionally, the use of data concatenation reduces the number of transmissions in the network as well as the probability of collisions, providing a promising solution in high density and high traffic applications.

This paper proposes an universal time-domain windowed orthogonal frequency division multiplexing (UTW-OFDM) as a novel physical layer signal format for the next generation communications systems such as the 5th generation mobile communication (5G) systems. Most of the conventional wireless communication systems such as the 4th generation mobile communication (4G) systems and WLAN are based on OFDM that has advantage in terms of spectrum efficiency in a band. However, OFDM has also drawbacks such as high out-of-band spectrum emission. Novel physical layer signal formats should be developed to overcome such drawbacks of OFDM for the 5G systems and so on. The proposed UTW-OFDM has high backward compatibility with conventional OFDM based systems such as Long term evolution (LTE) downlink and the out-of-band power emission can be reduced by over 44 dB compared to the conventional OFDM.

In this paper, diversity receiver performance at base station for VHF-band broadband mobile communication systems is examined by using measurement results. Diversity gain of two RX antennas for link budget calculation has been calculated by using a selective combining and an equal gain combining schemes. By analyzing the diversity gain statistically, it is found that the diversity gain of selective combining and its variation are increased in larger antenna separation and shorter transmission range. On the other hand, the diversity gain of equal gain combining and its variation are decreased in larger antenna separation and in shorter transmission range. In addition, a path loss model has been developed for a link budget design. The path loss model parameters are extracted for over 1 km transmission range. By considering the path loss model with analytically-extracted constant diversity gains for BS antenna separation lengths of 1, 5, and 10 wavelengths, the system service coverage can be estimated.

Wireless Smart Utility Network (Wi-SUN) combining TV White Space (TVWS), which leverages the benefits of TVWS for Wi-SUN with a view to improvement associated with coverage, bandwidth, scalability of current Wi-SUN, receives overwhelming attention. The recently released standard IEEE 802.15.4m details techniques to enable Wireless Personal Area Network (WPAN) work in TVWS. We develop the first IEEE 802.15.4m compliant TVWS-Wi-SUN system, including the system design and prototype implementation. Furthermore, a series of laboratory experiments are performed to characterize the developed prototype transceiver performance. Any differences in performance between simulation and laboratory experiments are emphasized and analyzed. Laboratory experiment results provide the strong evidence that the developed prototype transceiver fulfills the requirements defined by IEEE 802.15.4m. Additionally, our work lays out a solid foundation for the practical application of the TVWS-Wi-SUN system.

TV White Spaces (TVWS) technology allows wireless devices to opportunistically use locally-available TV channels enabled by a geolocation database. The UK regulator Ofcom has initiated a pilot of TVWS technology in the UK. This paper concerns a large- scale series of trials under that pilot. The purposes are to test aspects of white space technology, including the white space device and geolocation database interactions, the validity of the channel availability/powers calculations by the database and associated interference effects on primary services, and the performances of the white space devices, among others. An additional key purpose is to perform research investigations such as on aggregation of TVWS resources with conventional resources and also aggregation solely within TVWS, secondary coexistence issues and means to mitigate such issues, and primary coexistence issues under challenging deployment geometries, among others. This paper provides an update on the trials, giving an overview of their objectives and characteristics, some aspects that have been covered, and some early results and observations.

Utilization of the TV white-spaces (TVWS), which are spatially or temporally unused frequency in TV bands, is promising technology to alleviate spectrum resource shortage. Services using the TVWS have been already started in the U.S.A., and the TVWS pilot program has been performed and test operation of qualified white-spaces database (WSDB) has been started by the Ofcom in the U.K. Authors have developed TVWS LTE (Long Term Evolution) system with white-space devices (WSDs) licensed by the Ofcom and WSDB qualified by also the Ofcom, and participated in the pilot program performed in the U.K. In this paper, developed TVWS LTE system is summarized and field experiment of throughput measurement is performed in the London urban area is described. As a result of the field experiment, maximum downlink throughput of 45.4 Mbps in the FDD mode and 19.5 Mbps in the TDD mode were obtained under the condition of SISO with a signal bandwidth of 20 MHz. This is the first report on the field experiment of the TVWS LTE system aiming for practical use.

This paper performs the world's first IEEE 802.11af based Wireless Local Area Networks (WLAN) operating in TV White Space (TVWS) indoor experiment in the Ofcom TVWS pilot program of the UK. The prototype system consists of TVWS Database (WSDB), Registered Location Secure Server (RLSS), and two prototype hardware for an Access Point (AP) and a Station (STA). The developed WSDB qualified by Ofcom TVWS pilot program of the UK. The prototype hardware meets to the transmission spectrum regulation of the European Telecommunication Standards Institute (ETSI). By using the developed system, a trial indoor experiment performed in the building of the King's College London (KCL), Denmark Hill Campus in London, UK. The prototype system and the experiment results show an effectiveness of the IEEE 802.11af and indicate the way to the practical application.

An IEEE 802.11af indoor trial experiment has been conducted in the Ofcom pilot program of the United Kingdom. This paper describes an indoor propagation characterization and throughput estimation method using prototype devices based on the IEEE 802.11af standard. Since the IEEE 802.11af is recent technology for TV white space (TVWS) spectrum sharing, indoor propagation measurements at TVWS band for WLAN usage are very seldom in the previous researches. Path loss model parameters has been extracted for each line-of-sight (LoS) and non-LoS (NLoS) situation on the same floor. Also a fluctuation of measured path loss is analyzed using the log-normal and the extreme value distributions. A developed path loss model is useful for the location design of access points and the interference risk estimation for IEEE 802.11af devices. As another modeling, a throughput estimation model has been developed using the exponential distribution derived from the cumulative probability distribution (CDF) of measured throughputs. By combination of the developed path loss model and the throughput estimation model, throughput can be estimated as a function in each LoS and NLoS situation.

This study evaluates the performance of a practical IEEE 802.15.4/4e/4g low‐rate (LR) wireless personal area network (WPAN) with multiple physical (PHY) layers and multi‐hop capabilities for smart utility networks, machine‐to‐machine networks and other advanced sensor networks. The proposal includes realistic design considerations addressing demands of practical applications, country‐specific regulatory requirements and technical specification in international standards. A cross‐layer open system interconnection model from the application, transport, network, medium access control, down to the multiple PHY layers is constructed based on the specification in IEEE 802.15.4 LR‐WPAN and other layer‐specific standards. Employing the cross‐layer model, extensive computer simulations were conducted to investigate the performance of the LR‐WPAN system in this application domain. As a result, the authors have successfully verified the simulated achievable average throughput in both PHY layer designs, multi‐rate and multi‐regional frequency shift keying (MR‐FSK) and multi‐rate and multi‐regional orthogonal frequency division multiplexing (MR‐OFDM) with the theoretical throughput by calculation. Secondly, in a multi‐PHY environment with the presence of 30 interferer devices, throughput degradation of the victim system is observed within 30%. Furthermore, when interferer devices transmit frames with interval beyond 1 s, the degradation to the victim system becomes negligible. Thirdly, MR‐FSK PHY has a simpler design with higher energy‐efficiency, whereas MR‐OFDM PHY is more complicated with more resilience to interference. They have found an interference tolerance capability difference of 15 dB between the MR‐FSK and MR‐OFDM systems. Fourthly, comparing with their single‐hop counterparts, multi‐hop systems have lower average throughput in MR‐FSK by 25% and MR‐OFDM by 10%. Finally, comparing with networks with periodical beacon transmissions, asynchronous networks have more inferior average throughput of 20% in MR‐FSK and 3% in MR‐OFDM, with the advantage of longer battery lifespan.

Demand for wireless communication has increased significantly, on the other hand, the frequency band available for wireless communication is scarce. Use of wireless communication in the TV white spaces (TVWS) has been promoted in various countries, and primary user protection is mandatory. Particularly, very strict transmit spectrum mask is configured by FCC in USA. In order to effective use of TVWS, this paper proposes a transmit power control method based on adaptive time-domain windowing processing for orthogonal frequency division multiplexing (OFDM) based wireless communication systems operating in TVWS. The proposed transmit power control scheme provides the appropriate transmit spectrum to meet the required transmit spectrum mask regulation and the maximum throughput under the given environment without any special processing at the receiver side. The proposed scheme will contribute to the realization of the wireless communication systems operating in the TVWS.

This paper proposes a novel routing protocol named Hierarchical Mesh Tree Protocol (HMTP) that achieves efficient routing at the MAC layer for multi-hop data collection in ad-hoc networks, wireless sensor networks, intelligent transportation system networks, etc. The proposed protocol enables the self-organization of a network into a hierarchical mesh tree topology. The mesh tree topology is used to select the optimal route from a terminal to the root of the tree among the different branches available in order to yield an efficient, scalable and robust routing. The HMTP also enables the terminals to autonomously maintain and update the network mesh tree topology. The hierarchical mesh tree (HMT) alleviates the drawbacks of the conventional cluster-tree proposed in the IEEE 802.15.4 standard and the quasi-mesh tree proposed in the IEEE 802.15.4m standard. The simulations results show that HMTP drastically improves the data collection performance in comparison with the mentioned conventional tree-based routing protocols.

Some important issues remain to be better resolved before sensing technologies can be widely used in applications. For the reason, spectrum sensing is not selected as the mandatory solution for protection of primary users in current FCC regulations on usage of TV white space (TVWS). In this work, we introduce a sensing prototype for detection of Japanese digital TV signals. The prototype targets at fulfilling the strict FCC sensing requirement under reasonable interference. Moreover, efforts are made to improve physical features and cost-performance ratio. Computer simulation and hardware tests are conducted to evaluate performance of the sensing prototype under adjacent channel interference and co-channel interference. The results verify that the prototype has improved robustness for sensing under interference.

This study introduces a white space device (WSD) prototype developed for the white space technology trial organised by Infocomm Development Authority of Singapore (Singapore Trial). A draft regulation was issued by the Infocomm Development Authority for the Singapore Trial. To meet the strict requirements on some performance criteria defined in the draft regulation, some solutions on designs of the system and algorithm are developed and adopted to the WSD prototype. The prototype has a complete design of hardware and software to realise real‐time and intelligent operations of periodical spectrum sensing and database access, dynamic frequency selection and non‐continuous transmission featured with low adjacent channel power leakage and power control. During the Singapore Trial, tests were conducted to check the above cognitive radio (CR) technologies and CR‐enabled operations. The official test results verify the effectiveness of implemented system and algorithm designs.

Cognitive radio technology improves radio resource usage by reconfiguring the wireless connection settings according to the optimum decisions, which are made on the basis of the collected context information. This paper focuses on optimization algorithms for decision making to optimize radio resource usage in heterogeneous cognitive wireless networks. For networks with centralized management, we proposed a novel optimization algorithm whose solution is guaranteed to be exactly optimal. In order to avoid an exponential increase of computational complexity in large-scale wireless networks, we model the target optimization problem as a minimum cost-flow problem and find the solution of the problem in polynomial time. For the networks with decentralized management, we propose a distributed algorithm using the distributed energy minimization dynamics of the Hopfield–Tank neural network. Our algorithm minimizes a given objective function without any centralized calculation. We derive the decision-making rule for each terminal to optimize the entire network. We demonstrate the validity of the proposed algorithms by several numerical simulations and the feasibility of the proposed schemes by designing and implementing them on experimental cognitive radio network systems.

This paper proposes a low-power multi-hop data frame transmission scheme to create a long-lived smart utility network (SUN), as standardized by IEEE 802.15 TG4g/4e. In the proposed scheme, low energy superframe structure with turned-off beacons are employed to reduce power wastage, thereby providing effective sleep periods for each device. Moreover, multi-hop frame transmission is easily realized by constructing a tree-shaped topology with incoming and outgoing superframes. Furthermore, in the proposed system, effective frame aggregation technology exploiting such low energy superframe structure is employed in order to solve the bottle neck problems that seriously degrade utility data collection performance in SUN. The results of computer simulations confirm that the proposed scheme enables a greater than 90% frame success rate without error control while holding a less than 0.4% active period ratio in feasible SUN usage situations.

This paper presents the evaluation on energy consumption of power saving mechanisms in recent IEEE 802.15.4 Low-Rate Wireless Personal Area Network (LR-WPAN) systems. The LR-WPAN applications share a common system requirement of high energy efficiency through power saving mechanisms to prolong battery lifespan. First, the recent IEEE 802.15.4 standard amendments including, but not limited to IEEE 802.15.4/4e/4f/4g/4j/4k/4m and their targeted applications are listed and discussed. Then, the applications are categorized based on different energy consumption models which are interconnected with the radio operations of the proposed power saving mechanisms. Next, addressing pervasive demands and respective energy consumption models in multiple application scenarios, three power saving mechanisms for LR-WPAN are proposed and evaluated taking into consideration realistic parameters. As a result, it is found that the power saving mechanisms are capable of supporting battery lifespan up to typically 3 years. Out of the three proposed mechanisms, two are found to be more suitable for deployment of symmetrical energy consumption model where all devices share similar burden of radio operations, while one is found to be otherwise, optimized for asymmetrical energy consumption model where some devices have larger burden as compared to others.

This paper reports measurements and characterizations of broadband indoor Television White Space (TVWS) channel with center frequency of 670 MHz. The measurements have been carried out in small- and medium-size mixed office and lab indoor environments recently. Channel multipath delay spread of both line-of-sight (LOS) and non-LOS (NLOS) connections are identified by using BPSK signaling of 20-Mbps data rate. The root-mean-square (RMS) delay spreads are found between 20 ns to 32 ns for LOS and 32 ns to 41 ns for NLOS in small-size office and lab environment, and is found about 38 ns for LOS and 39 ns for NLOS in medium-size indoor environment. A general complex low-pass impulse response model is proposed based on our findings and the classic Saleh-Valenzuela (S-V) channel model. With the proposed channel impulse response model, ray clusters may appear before and after the strongest cluster and rays may exist on both sides of the strongest ray in a cluster. Model parameters are extracted from the measurement results. Extensive simulation results show that the model fits the measurements well.

Cognitive radio technology, which enables an efficient use of spectrum, is expected as one of solutions for a spectrum shortage problem. Recently, spectrum sharing type cognitive radio technology in TV white-spaces has been actively promoted worldwide and technical specifications have been advanced in international standardization activities such as IEEE802.11af and IEEE802.22. These standardizing systems tend to secure more frequency channels for existing systems by simply converting their native frequency band to TV white-spaces for data traffic offload. As one of the simplest technologies to realize wireless communications in TV white-spaces, we proposed a frequency conversion system using a UHF converter. In this paper, we prototyped a tablet-type portable TV band device, which can communicate in TV band with IEEE802.11b/g-based communication systems by using the UHF converter. Also, physical features of our prototyped tablet terminal are summarized and the RF transmitter and receiver performance and spurious response are characterized.

This paper presents the performance analysis of an IEEE 802.15.4g multi-hop orthogonal frequency division multiplexing (OFDM) system in a network with multiple physical (PHY) layer design. Identified usage models for the IEEE 802.15.4g standard are low energy wireless sensor network and smart grid/utility network applications. For that, a total of three PHY layer designs under a unified medium access control (MAC) are specified to address different market segments. The multi-PHY layer architecture has an advantage of covering a wide range of pervasive use case scenarios, at the expense of inter-PHY interference (IPI) among respective PHY layers. This paper focuses on the OFDM PHY that promises high data rate and superior propagation performance. To enable optimized operation in the targeted applications, a multi-hop MAC layer design is specified to extend the operating range of the network, while low energy features are designed to increase energy efficiency of the system. Additionally, an IPI mitigation technique is also developed to combat IPI generated from the interfering network. As a result, it is found that the average throughput of a multi-hop OFDM network is 8% lower than that of a single-hop OFDM network, but with larger achievable operating range. Secondly, with the proposed IPI mitigation technique, no degradation among devices with different PHY layer designs is observed to take place. Thirdly, with the energy-efficient non-beacon-enabled mode, devices are consuming less power, at the expense of immunity reduction against interferer.

This paper presents the network performance analysis of a low energy IEEE 802.15.4/4e/4m LR-WPAN operating in TV White Space. An energy-efficient mechanism optimizing the tradeoff between device sleep time and synchronization strategy is utilized to reduce the total power consumption in a non-beacon-enabled network. To evaluate the performance of the network, we have modeled a cross-layer system starting from the application, transport, network layers, to the MAC layer where the energy-efficient mechanism resides, to the PHY layer where the FSK PHY resides, down to the propagation channel where the VHF/UHF channels applies. Extensive computer simulations were conducted to investigate the performance of this low energy LR-WPAN system. As a result, we have found that a device may consume up to 40% and 2% of its total operation time to perform channel scanning and transmission, respectively. Applying the proposed energy-efficient mechanism, the achievable reduction of channel scanning time and transmission time are 20% and 1% respectively. We have also observed that the average residual battery capacity can be most effectively preserved when the number of devices in the network reaches approximately 30.

TV White Spaces (TVWS) indicate frequency bands, which were reserved for licensed terrestrial TV broadcasting and open to unlicensed use under regulatory conditions. One important regulation which is common in all regulatory domains is no harmful interference should be received by licensed devices. On the other hand, interference between unlicensed devices is usually not regulated. As a result IEEE 802 LMSC started 802.19.1 standardization project to enable coexistence between unlicensed devices. In this paper we are investigating the throughput performance of heterogeneous and independently operating networks under the control of a 802.19.1 based system. The simulations are done with networks based on 802.11 and 802.22 standards. Our results indicate that the coexistence system and its protocols are stable and they increase the throughput of 802.11 based networks %30 percent if 3 TV channels are available.

Driven by the progress of regulations of TVWS worldwide, IEEE 802.11 started a new Task Group af (TGaf) to pursue extension of traditional Wi-Fi to TV White Spaces (TVWS). Wi-Fi in TVWS offers longer distance and broader bandwidth; while maintaining the same user experience of traditional Wi-Fi systems. It is therefore regarded as one of most promising technologies to exploit the market derived from the new regulations of VHF/UHF bands. In this paper, we present the world's first prototype system of Wi-Fi in TVWS based on the TGaf draft specification. The prototype system verifies the PHY and MAC design of TGaf and the database query protocols that is needed for TVWS operation but not in the scope of TGaf. It is demonstrated that, with sufficiently defined MAC protocol and PHY that meets sharp transmission spectrum mask, the developed prototype supports video streaming on single TV channel while well coexisting with primary TV services in the vicinity.

This paper analyzes the performance of a realistic multi-PHY layer IEEE 802.15.4g Smart Utility Networks (SUN) design and proposes a coexistence approach for multi-PHY interference management. Technical details of the design such as network architecture, mechanism protocols, signal formats, device interfaces, regulatory requirements and channel characterization are implemented following the IEEE 802.15.4g SUN specification. The performance evaluation is conducted in a cross-layer computer simulation based on the MAC (medium access control) and multi-PHY technical specification in the standard with realistic application scenarios and channel characteristics. To manage the interference in the system, a Multi-PHY Management (MPM) protocol is proposed and evaluated. The MPM is adopted in the current IEEE 802.15.4g standard. As a result, the coexistence mechanism is observed to be able to improve the victim throughput performance up to 25%. It is also found that the throughput degradation in a non-beacon-enabled network is 50% worse than the degradation in a beacon-network.

Following the standard approach envisioned by the Federal Communication Commission (FCC), we consider database as a tool to plan the utilization of VHF/UHF spectrum by White Space (WS) radios. Our approach, however, differs from the one adopted by the aforementioned regulatory body in the sense that the algorithms loaded into the database are not limited to processing broadcaster information, i.e., effective antenna height, effective isotropic radiated power (EIRP), and simplistic terrain information, i.e., antenna height above average terrain (HAAT). We utilize detailed regional topography data in order to predict the primary contour and WS radios service area in a more realistic fashion through Fresnel diffraction theory. The contour calculated based on our algorithms are overlaid on Google Earth software, therefore, creating a very flexible and interactive tool for TVWS prediction.

Considerable efforts have been made by research entities in the world to develop sensing prototypes for digital TV (DTV) signals that can fulfill the FCC sensing requirement. FCC official test results for some sensing prototypes have shown that adjacent channel interference (ACI), which truly exists in real sensing world for DTV signals, has significantly increased the difficulty of fulfilling the FCC sensing requirement. In this work, we aim at developing a real-time sensing prototype that achieves robust sensing under ACI. A partial (channel) bandwidth based feature detection (PB-FD) method is proposed, which not only exploits identical features of DTV standards, namely the DVB-T and ISDB-T, to produce high process gain in detection, but also significantly mitigates the ACI produced by transmission power leakage. The PB-FD is specified to the center segment based FD when it is implemented into a sensing prototype to detect ISDB-T. Computer simulation results verify that PB-FD achieves superior performance over the optimal conventional sensing method, especially when sensing is performed under ACI. The PB-FD is then implemented into a sensing prototype. Hardware performance tests are performed to detect ISDB-T at FCC required threshold level of -114 dBm/6MHz under a moderate level of ACI. The test results indicate that above 0.9 detection probability and below 0.01 false alarm probability are achieved by the sensing prototype.

By increase of various radio access network (RAN) services, available spectrum resources for mobile communications get decrease, and efficient use of the radio resource is becoming a very important issue. In order to optimize the radio resource usage and maxmize the throughput and quality of service (QoS), the link aggregation technologies to utilize multiple different available RANs have been studied. However, in such heterogeneous wireless networks, it is difficult to improve the throughput by their aggregation because of the differences among the QoSs of the different RANs. In this paper, we propose an autonomous parameter optimization scheme using a machine learning algorithm, which maximize the throughput of the heterogeneous RAN aggregation system. We evaluate the performance of the proposed scheme implemented on a cognitive wireless network system called Cognitive Wireless Cloud (CWC) system, connected to real wireless network services, such as HSDPA, WiMAX and W-CDMA. Our experimental results of the proposed system show that the aggregation throughput can be improved with increase of the training samples, which are collected autonomously.

Both spectrum regulators and standardization organizations are making efforts to realize licensed exempt utilization of TV white space (TVWS). One of major concerns in the usage of TVWS is the potential interference imposed by a TV band device (TVBD) to primary users (PU) in TV bands. Spectrum sensing is used as one important solution for protection of PU. In this work, we aim at developing a real-time sensing prototype that fulfills FCC regulation requirement for sensing only TVBD. To overcome the sensing challenges arising from adjacent channel interference (ACI) in real sensing world, a partial bandwidth based feature detection (PB-FD) method is proposed, which can be used to detect many types of OFDM based signals. When the PB-FD is applied to detect DTV signals of Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) standard, it is specified to detect the centre segment of ISDB-T spectrum. In this paper, we present the sensing algorithm and its simulation results, major system features and performance of the sensing prototype. Hardware performance test for sensing ISDB-T signals under ACI is performed. A sensing performance of above 0.9 detection probability with a false alarm probability of 0.01 is achieved for signal level ≥-114dBm/6MHz, with a sensing time equals to 0.6 second for sensing one channel.

Motivated by the large interest in the white space radio systems research, design, and standardization, IEEE Standards Committee on Dynamic Spectrum Networks (IEEE DySPAN-SC) of the IEEE Communications Society Standards Board has started to consider standardization of white space radio systems. IEEE 1900.7 working group (WG) of the IEEE DySPAN-SC is currently developing draft standard for “Radio Interface for White Space Dynamic Spectrum Access Radio Systems Supporting Fixed and Mobile Operation.” This paper describes the current status of the IEEE 1900.7 WG focusing on use cases and associated network topology options and requirements.1

AMPHIBIA is a framework which enables dynamic virtual network provisioning over wired and wireless networks for providing diverse services by coordinated reconfiguration in both sides of wired and wireless networks, exploiting the emerging network virtualization and cognitive radio technologies. AMPHIBIA introduces a new concept of a virtual cognitive base station (vCBS), a cognitive base station built on the virtualized infrastructure. The target applications of AMPHIBIA include flexible and rapid deployment of mobile services, end-to-end QoS, efficient wireless and wired resource utilization, and green networking. In prior work, we proposed a basic framework design of AMPHIBIA and a service model. In this paper, we show the implementation and prototype system of AMPHIBIA including the implementation of a cognitive virtualization manager (CVM), which is responsible for coordinated reconfiguration. We implement the AMPHIBIA prototype as an extension of CoreLab, a flexible software-based virtual router platform. Specifically, we develop vCBS by incorporating cognitive radio functionalities into a CoreLab virtual machine (VM). We also implement CVM and a reconfiguration manager of cognitive radio as external entities to enhance CoreLab. We confirm the basic behavior of the prototype and demonstrate with a set of simple typical scenarios that a VM-based virtual network including vCBS can be dynamically created, expanded, and deleted, and mobile streaming services can be flexibly deployed on the virtual network on an on-demand basis. We also demonstrate that AMPHIBIA can create and reconfigure a vCBS in about 51 seconds, and can timely operate the successive handover of a mobile terminal.

This paper proposes an energy-efficient beaconless synchronization mechanism for SUN operating in the TVWS. From the aspects of fulfilling the pervasive yet stringent requirements of low-energy wireless meters and TVWS regulations, the proposed mechanism is able to prolong battery lifespan beyond the required level for wireless smart meters, and is compliant to the specific network architecture and communication protocols demanded by the TVWS rules. In the MAC layer, a novel design for low duty cycle beaconless synchronization/data exchange is specified. In the PHY layer, the transceiver and realistic channel models applicable to the IEEE 802.15.4g SUN is constructed. Actual data from chip vendors of the wireless meter industry are also included to facilitate a more practical investigation. All the above are combined for performance evaluation to quantify the energy-efficiency and error performance of the proposed mechanism. As a result, it is found that the proposed mechanism enables battery lifespan of more than 10 years in most typical cases. For the system to achieve a ten-year battery lifespan at data transmission interval of 15 minutes, it is recommended that the system duty factor to be controlled in the order of 10-4, and that transmitted data frames to be limited within the length of 50 octets.

In this paper, we describe the design challenges of a recently developed television white space (TVWS) device prototype and how those were resolved. The prototype, which includes the following components: a cognitive management entity (CME), a sensing module, a geolocation device, a TV band database, a transmitter and a receiver, was designed to take part in Singapore TVWS test trial. The major features the prototype has are: cognitive functionality, spectrum sensing and database access. The technical challenges faced during its development are described in terms of wide dynamic range, adjacent channel rejection and synchronization issues of the spectrum sensor, baseband vs intermediate frequency based sensing, non white environmental noise, security regarding database access and troubles inherent in wireless environment. Performance of the prototype is also presented in terms of cognitive operations such as, success of TV signals and other incumbent detection through database access and sensing, time required for database access, sensing, channel selection, channel switching etc. Discussion regarding setting a reasonable sensing target is also presented.

This paper proposes a generic enhanced beaconless synchronization mechanism for industrial standard IEEE 802.15.4g Smart Utility Networks (SUN) in multiple regulatory domains globally. IEEE 802.15.4g has specified different regulatory domains for SUN applications, each with a distinctive set of channelization and corresponding operating parameters such as center frequency, channel width and channel spacing. This has added new challenges not limited to, but particularly in beaconless synchronization mechanism supporting low energy consumption demands in conventional IEEE 802.15.4 low rate wireless personal area networks (WPANs). This paper first provides the updates in the SUN technical specification, identifies the challenges due to the effort of addressing multi-regional governing regulatory demands and then proposes a generic solution to tackle the problem. This simple but straightforward approach is preferable in industrial applications with strict energy efficiency requirement. The proposed beaconless synchronization mechanism has outlined two metrics with conflicting interest, namely required time to achieve synchronization and effective bandwidth for data communication. As a result, it is found that as the input radio resource increases, the effective communication bandwidth increases exponentially, while the required time for synchronization increases only linearly.

Consulting to geo-location database is one of the approaches for secondary user (SU) to obtain the list of available channels for its operation. Each regulator may require the SU to send different types of information to the geo-location database in order to calculate the channel availability. However existing methods consume time and introduce heavy load to the database due to the procedures of checking overlapping between protected contours and SU's operation areas in order to protect primary users (PU) from harmful interference. By submitting SU's preferred channels to database the calculation time and database's load will be reduced significantly. The additional information can also help the database manages spectrum usage so that it can provide recommendation to other SUs.

This paper presents the analysis on communication range and interference range of the IEEE 802.15.4g Smart Utility Networks (SUN). Firstly, error performance analysis corresponding to different propagation environments based on realistic measurement is conducted. Secondly, the effective communication range of SUN devices in these propagation channels are presented and discussed. Thirdly, in the presence of an interfering SUN device, the interference range between the victim and interfering devices are also studied. As a result, we have found that the achievable communication range of SUN devices in the GHz-order bands, the higher-UHF bands and the lower-UHF bands are 33m, 65m and 104m respectively. The critical interferer-to-victim distance below which, causing intolerable degradation to the victim receiver, is found to be 20m for typical urban and 35m for hilly rural environment. Finally, the analysis results are compared with the requirements based on the survey on utility metering device deployment conditions.

Moving forward based on the current spectrum regulations and industrial standardization for unlicensed usage of TV white space, we postulate a potential deployment scenario and describe the management procedure of coexisting secondary user (SU) networks under the interference constraints to the primary user (PU) receivers. For the quantitative evaluation of coexistence we first introduce a new parameter named quality of coexistence (QoC), which is utilized to measure the benefits achieved by a novel coexistence scheme also proposed in this paper, namely, interference-constrained time slot splitting and allocation. Furthermore, on the basis of a system model we obtain the optimal SU networks time slot allocation ratios by maximizing the aforementioned QoC, therefore, leading to an efficient spectrum usage by SUs without incurring harmful interference to the PUs. Finally, we simulate a coexistence scenario in TV white space in order to compare the proposed scheme with other schemes that select a single SU network to operate based on simplistic criteria. It can be seen that when the SU network employs adaptive transmit power control (TPC), the medium value of QoC is doubled by using the optimal time slot allocation, resulting in significant improvement in coexistence.

In this paper, we present a coexistence protocol design to provide coexistence solution among dissimilar or independently operated autonomous decision-making networks in a wireless communication environment over, specifically but not limited to, TV white space (TVWS) frequency bands. The designed coexistence protocol for the information service has three main functionalities: (1) To collect basic information of subscribed TVWS networks; (2) To support generating neighbor lists for the TVWS networks based on the geography information or propagation parameters; (3) To provide the necessary information for TVWS networks to make coexistence decisions. Both theoretical analysis and simulation results shows that the designed coexistence protocol ensures harmonious communication among multiple dissimilar networks and finally achieves coexistence over a particular area with a limited white space channel resource.

This paper discusses a way to determine which devices interfere with each other in order to provide efficient information for coexistence control among dissimilar or independently operated networks in wireless communication environment over, specifically but not limited to, TV white space (TVWS) frequency bands. We refer this as coexistence neighbor discovery in TVWS. Coexistence neighbor discovery is a key algorithm for coexistence control system, which provides the necessary input for coexistence manager or for TVWS networks or devices subscribing for coexistence information service to make coexistence decisions. It therefore significantly impacts the complexity and accuracy of coexistence decision-making. In this paper the potential interference between two networks are statistically evaluated. The 90% confidential interference level that 90% of devices inside communication area receives interference equal or less than is taken as a potential interference of two networks. This value is then compared with the tolerable interference level of a device to determine interference relationship of two networks. The simulation results show the rational to select 90% as confidential interference level, the accuracy of the proposed algorithm was also approved in this paper.

This paper proposes a hybrid SDMA/TDMA scalable heuristic scheduling scheme for throughput enhancement in practical multi-Gbps millimeter-wave systems with directional antenna. A theoretical cross layer design framework is proposed taking into consideration the MAC layer, PHY layer and millimeter-wave propagation channels based on actual measurements. The proposed generalized framework can be well suited into two of the most prominent industrial wireless communication standards, namely IEEE 802.15.3c WPAN and IEEE 802.11ad WLAN. Employing the developed theoretical framework, evaluation for throughput and error performance is conducted with validation of computer simulations. Firstly, it is found that the proposed STDMA scheme is capable of improving system throughput in the order of typically 4 to 8dB. Secondly, the proposed scheduling scheme offers superior design flexibility through its scalability features, with the optimum heuristic order observed at the 13-th order, a reasonably low value considering the performance enhancement that can be obtained. Lastly, the typical allowable interference in a network due to coexisting communication links sharing the same time slot is recommended to be controlled below -20dB. Numerical results other then the typical findings are detailed in the paper.

In heterogeneous wireless network environment, various radio access networks (RANs) are available for mobile terminals which have multiple wireless network interfaces to connect to each different RAN. However, it is very difficult to improve the throughput by aggregating different RANs, which have different quality of service (QoS) in the throughput, the delay, the packet loss, and so on. In this paper, we propose a traffic allocation control scheme using a machine learning algorithm to improve the link aggregation throughput in such heterogeneous wireless networks. We introduce the support vector machine, which has an advantage on generalization to have good performance for unknown input patterns. By our experiments using a cognitive wireless network system, called Cognitive Wireless Clouds, it is clarified that our proposed scheme improves the throughput higher than the conventional methods based on the throughput of each RAN.

This paper proposes a space-time scheduling algorithm that improves the throughput performance of millimeter-wave wireless personal/local area network(mmWave WPAN/WLAN) systems. The upcoming mmWave WPAN/WLAN systems are designed to support high definition TV (HDTV) transmission, high speed wireless docking and gaming, etc. These data-rate-greedy applications require Gbits/s or even multi-Gbits/s transmission capacity which can be provided by the mmWave bands. Directional antenna are preferred in these bands to compensate high path loss. However the narrowed transmission angle of directional antenna makes the system susceptible to blockage of human body or furniture. Consequently, the throughput performance is compromised and may not meet the requirement of the targeting applications. Cooperative relay with time slot sharing is a solution to guarantee throughput under such situation. Compared with lower frequency bands, it is easier in mmWave bands to share time slot between the direct path and relay path, due to less co-channel interference constrained by path loss. In this paper, we propose a space-time scheduling algorithm to assist cooperative relay. The algorithm is based on graph theory and designed to find optimized relay station and time slot to maximize the system throughput. Computer simulations demonstrate over 25 percent throughput improvement is achieved under conference room None-line-of-sight (NLOS) environment with human blockage. The achieved performance meets the requirement of uncompressed HDTV transmission.

In this paper we analyze mechanisms of coexistence between different cognitive radio systems operating as secondary users in white space frequency bands. In particular, our focus is coexistence mechanisms that can be provided by IEEE 802.19.1 coexistence system. IEEE 802.19.1 standard is at the early stage of its development. At this stage it is very important to consider different design directions and focus areas. This paper presents results of performance evaluation of the IEEE 802.19.1 coexistence system based on simulation. We believe that simulation results shown in this paper and analysis of these results are very important for the future of both IEEE 802.19.1 standard and products based on this standard.

To cope with the increasingly diversifying services, QoS, and network architectures, network virtualization is a promising technology that enables the concurrent deployment of multiple network technologies on a shared network. However, traditional research on network virtualization preliminarily focuses on a wired environment and network virtualization for a wireless environment is not well studied. Considering that in near-future, various wireless technologies will play the most important role in access networks and multi-mode wireless terminals will become more popular, it is crucial to extend the concept of network virtualization to wireless networks. We refer to building such extended virtual networks as "end-to-end slicing". The key technical challenges for such extension are (1) abstraction of heterogeneous wireless access networks for maximizing radio frequency utilization and (2) isolation of wireless resources such as radio frequencies, throughput, or name spaces for accommodating multiple virtual networks on a single wireless access network. In this paper, we tackle the first challenge and propose a Cognitive Virtualization Platform, called AMPHIBIA, which enables end-to-end slicing over heterogeneous wired and wireless networks. AMPHIBIA is a platform to provide independent virtual networks each of which can be configured for the corresponding service and to coordinate the resource management in both sides of wired and wireless networks, exploiting the network virtualization and cognitive radio technology. AMPHIBIA is motivated by the shared property of "reconfigurability" of network virtualization and cognitive radio, and provides network operators with the capability of cooperative resource allocation over wired and wireless networks. In other words, AMPHIBIA virtualizes a cognitive base station to dynamically configure a wireless access network for each virtual network. In this paper, we first show the basic architecture of AMPHIBIA from the perspective of network virtualization. Then we show the hardware and software design of prototype system.

This paper describes the challenges of frequency channel selection for WLANs operating in the TV White Space (TVWS) and proposes a dynamic frequency selection (DFS) technique as a solution. Based on the statistics gained from past usage experience of channels, of the TVWS channels' vacancies and channel occupation by the adjacent WLANs, each WLAN evaluates and prioritize the channels independently using a priority function. Then by selecting the channel of the highest priority among vacant channels, each WLAN can quickly find a channel in the low interference regime and whose vacancy is adaptive to its traffic load distribution as well. Performance of the proposed DFS is evaluated through simulation using QualNet, based on TVWS channels with realistic feature and by setting the weight factors of different metrics in the priority function to different values. The evaluation results show that compared to conventional DFS, the proposed DFS avoids adjacent APs selecting the same channel and reduces channel switch rate, and is more adaptive to diverse environments. As a consequence, it maximally reduces total time consumption of channel switch by 40% than random selection.

This paper presents the system design method to determine the modulation and coding schemes according to the given usage models of single carrier transmission in millimeter wave Wireless LAN systems. Various modulation and coding combinations are compared and analyzed based on the BER performance over both AWGN and fading channels. The effects of hardware impairments including power amplifier non-linear effects and phase noise, etc., are considered as well. The system design strategy provides a guideline for the selection of modulation and coding schemes in practical which can fulfill the realistic system requirements.

This paper investigates effectiveness of distributed radio access network (RAN) selection schemes to optimize radio resource usage, for the realistic heterogeneous wireless networks, in which the distribution of the base stations are non-uniform and the non-cognitive legacy terminals also connect to the same RANs. Our proposed algorithm is based on mutually-connected and higher-order neural networks, which can directly optimize any objective functions of entire heterogeneous wireless networks, by completely distributed procedure. Our simulation results show that the proposed scheme is effective even for non-uniform heterogeneous wireless network environments, especially for higher-order and complex optimization problems. Such improvements in the proposed method also can be seen also for the cases that the legacy non-cognitive terminals co-exist in the same heterogeneous wireless networks.

This paper presents the performance analysis of a realistic Smart Utility Network (SUN) system with low duty signaling design. The main focus of this paper is to evaluate the performance of the SUN system based on the specifications in an on-going industrial standardization activity, the IEEE 802.15.4g. For this purpose, a theoretical framework is constructed to model the transceiver with low duty signals over a realistic SUN channel based on actual measurements. The theoretical framework provides the models of multiple access interference (MAI) and inter-symbol interference (ISI). To align the analysis with actual industrial requirements, the developed framework is substituted with parameters from the IEEE 802.15.4g specifications. As a result, it is found that the low duty system (i.e. 0.1%) is capable of supporting up to 100 users in a single network. Additionally, by reducing the duty factor (e.g. from 1% to 0.1%), a 2-digit performance improvement (e.g. bit error rate (BER)=10-5to BER=10-7) can be achieved as compared to the requirement of IEEE 802.15.4g specifications (i.e. BER ≈ 10-5).

An exact closed-form expression is developed for the probability density function (PDF) of the sum of independent but not necessarily identically distributed Nakagami-m random variables. By utilizing the newly developed PDF and the associated developments, new exact expressions of the bit error probability are presented for predetection equal gain combining diversity.

Wireless personal area networks (WPANs) usually have very limited coverage. In this paper, we focus on methods to extend this range through multi-hop communication crossing several inter-connected WPANs called piconets. Multi-hop communication between piconets is possible through the bridge devices. While extending the range of WPANs, bridge devices become the capacity bottlenecks for these connected piconets. Therefore, an unoptimized resource allocation mechanism involving the bridges could degrade system performance severely. In this work we propose a novel resource allocation mechanism that outperforms other schemes proposed so far. Moreover, our scheme is QoS aware due to its cross-layer design. In our proposed scheme, resource allocation cooperates with the route discovery process to mitigate collisions due to inter-piconet resource reservations. Simulation results show that our approach significantly increases network capacity. This work is expected to pave the way for QoS support in WPANs.

In cognitive radio networks, secondary users need to conduct spectrum sensing to properly detect the presence of primary signals that may have much lower power than noise plus interference power. In such a case, time-varying noise plus interference, which is briefly called noise uncertainty in this paper, can substantially degrade the sensing reliability of hard information combining (HIC) and soft information combining (SIC). To improve the sensing reliability in the circumstance with heavy noise uncertainty, we propose an adaptive two thresholds based energy detection and a two stage HIC based cooperative decision for cooperative spectrum sensing. The proposed sensing technique has shown better performance than conventional HIC and comparable performance with SIC when a small number of sensing nodes are used in spectrum sensing.

This paper proposes a scalable heuristic spatial time division multiple access (STDMA) time-slot scheduling algorithm for millimeter-wave wireless personal area network (WPAN) with spatial division multiple access (SDMA) through directional antenna system. A detailed cross layer design is proposed including the medium access control (MAC) layer and the physical (PHY) layer designs. The proposed hybrid STDMA/SDMA scheduling engine possesses the capability of flexible throughput-enhancement employing different levels (i.e. heuristic order) of algorithm complexity. Firstly, it is found that the scheduling engine with exhaustive searching algorithm is able to improve up to 9-fold of the achievable system throughput. Secondly, it is determined that heuristic order of 5 is sufficient to provide optimum throughput enhancement with minimized system complexity. Thirdly, the analysis of required overhead to perform the STDMA scheduling engine is also discussed.

Recently, various wireless networks are emerging and it leads to spectrum congestions. Cognitive radio, which allows users of the emerging wireless networks to opportunistically utilize the unused bands of the existing primary systems, can alleviate this problem. As one of the emerging wireless networks, 802.16 networks are suggested to explore TV “White Space” and then it is necessary to study cognitive operations of this network. In this paper, we propose enhanced frame structure and new channel accessing algorithms to enable cognitive operation of the WiMAX Mesh networks. With the novel algorithms for dynamically accessing the frequency channels for the control messages transmissions, no extra common control channels and operations of mesh clusters are needed, thus the spectrum resource can be saved and the network operation becomes simpler. The performance of the algorithms and the MAC protocol are analyzed theoretically and evaluated numerically. Results show that our algorithms can achieve, e.g., 3 times gain, in getting control messages received by neighbors, when compared to the scheme of mesh clusters. It also shows that with the parameter values presented, the normalized saturation throughput can be, e.g., as high as 75%.

Spectrum sensing is a key component of cognitive radio (CR) system to understand its radio frequency (RF) environment. One critical challenge in spectrum sensing is detection of weak signals in particular in an indoor environment. Distributed spectrum sensing can address this shortcoming by providing a combined data from spatially distributed sensors. This approach often achieves higher sensitivity in comparison to a single standalone sensor by exploiting the inherent spatial diversity of the cooperating sensors. The overall system performance of distributed sensing, however, depends both on the quality of sensing at the individual sensors and the forwarding scheme from the sensors to the data fusion center (FC). In this aspect the choice of appropriate media access (MAC) control plays significant role. We can improve the system performance by optimizing the MAC and the spectrum sensing parameters jointly. In this paper we propose such cross layer approach to yield an enhanced distributed spectrum sensing scheme. To demonstrate our idea, we provide computer simulation by considering energy detection based distributed spectrum sensors and some of the 802.15.4 MAC specification assumptions.

In this paper, we propose a spacial time slot scheduling algorithm for relay operation to improve the throughput performance of millimeter-wave wireless personal area network (mmWave WPAN) systems which employ directional antenna. The upcoming mmWave WPAN is designed for high definition TV (HDTV) transmission, high speed wireless docking and gaming, etc. Based on the fact that the significant path loss of millimeter-wave environments provides good space isolation, we have proposed a coexistence mechanism by sharing time slots for relay with direct transmission to guarantee throughput for the above data-rate-greedy applications. This paper is an extension that addresses spacial time slot scheduling for relay operation taking the effect of directional antenna into consideration. We model the throughput maximization with scheduling as an integer optimization and solve it by transforming the problem to a max-weight matching problem of a bipartite graph. We propose a scheduling algorithm based on the Kuhn-Munkres algorithm which can be used to solve the max weight matching problem. Simulation results show that there is up to 25% throughput improvement achieved compared with random scheduling method.

In order to realize very high throughput wireless local area network (WLAN) systems, which demand multi Gbps capacities/bitrates, the IEEE802.11.TGad (Next generation WLAN standard at 60GHz band) is in the standardization process. To evaluate and select the proposed physical layer modulation and coding schemes in the standardization process, channel models for each specified usage model are required. In this paper, suitable impulse channel models for that purpose are proposed. Propagation measurements are carried out in a living room environment in the 60GHz band. To cover various usage cases, line-of-sight (LOS) and non-line-of-site (NLOS) scenarios and three different signal transmission polarization types are examined, and each channel model's parameters are extracted by statistical analysis. These channel models are useful in designing systems for millimeter-wave wireless communications.

This paper addresses the issues of coexistence for cognitive radio networks including both the coexistence between primary users (PUs) and secondary users (SUs), as well as the coexistence among SUs. The coexistence between SUs and PUs addresses the interference from SUs to PUs, whereas, the coexistence among SUs addresses sharing of identified spectrum opportunity among SUs to achieve efficient spectrum usage. In this study, we first introduce a new parameter named as quality of coexistence (QoC), which is defined as the ratio of quality of SU transmission over the negative interference to PUs. Assuming that a time slot of spectrum opportunity has been found by multiple SUs, we partition this time slot into subslots and allocate time slots and transmit power to multiple SUs to maximize the QoC. This leads to a "wise" spectrum usage among SUs and minimized interference to PUs. In this study we assume that the SUs have multiple antennas and employ fixed transmit power control (fixed-TPC). By using the approximation of the approximation to the distribution of weighted sum of chi-square random variable (RV) we develop the analytical model for the time slot allocation among SUs. Results show that both the time slot and transmit power allocation can be optimized for achieving the maximum QoC. In a particular scenario the QoC can be increased by 30%.

Millimeter wave (mmWave) wireless personal area networks (WPANs) could provide multi-Gbps based data rate for short range communications. However, this ultra high data rate is sensitive to the co-channel interference (CCI). In this paper we use synchronization frame (sync frame) to mitigate possible interference between WPANs. Sync frames could be simply considered as the copies of beacons, which are relayed via the devices associated with the piconet. By using sync frames, the possible CCI could be reduced by increasing per WPAN coverage range, but meanwhile, the spatial reuse capability is also reduced. Therefore, in this work, we are motivated to investigate the optimized beacon/sync frame range at different link distances and its effect to throughput. Simulation results in 60 GHz system for a 2.5 m link indicate that, sync frames can double the guaranteed throughput. For guaranteed throughput of 1.4 Mbps at a 3.5 m link, beacon range can be 35\% reduced. Another contribution of the paper is investigating the effect of CCI in 60 GHz systems with spreading 2 and 4. Our results indicate a limited increase in robustness at high CCI situation compared to non spreading cases.

This paper develops a cross layer model for both interference and coexistence analysis of a multi-Gbps millimeter-wave wireless personal area network (WPAN) system with directional antennas. The model takes into consideration realistic 60 GHz propagation channel and high-speed physical layer design in actual WPAN network scenario. The model facilitates the analysis of directional interference and coexistence unique to the millimeter-wave frequency band. Employing the developed model, we found that in order to generate minimum interference to the victim receiver, the interferer has to be angularly located at least 1.3 times the victim's beamwidth away from the victim's antenna pointing direction, and/or the interferer's antenna has to be angularly pointing towards at least 1.3 times its beamwidth away from the location of the victim. Additionally, to mitigate interference and still maintain the desired link connectivity, the victim receiver may shift its antenna beam away from the location of the interferer, as much as the angle between the victim's antenna pointing direction and the interferer's location minus 1.3 times the victim's beamwidth. Lastly, we have also introduced the quantification of coexistence availability between interfering and desired links, taking into consideration requirements and parameters in the physical layer.

In this paper, we proposes the pro-active beamforming (BF) protocol realized in media access control (MAC) layer following IEEE 802.15.3c criteria for millimeter-wave 60GHz wireless personal area networks (60GHz WPANs). The pro-active BF may be used when the piconet controller (PNC) is the source of data to one or multiple devices (DEVs). It allows multiple DEVs to train their own receiver antennas for optimal reception from the PNC with lower overhead. The pro-active BF realizes part of BF operation in association process, extending the system's BF capability. It also enables DEVs to associate with PNC with directional antenna pattern, thus enlarges the coverage area of a piconet. Since it may train multiple users simultaneously based on the proposed multi-resolution codebooks, it significantly decreases the BF set-up time and mitigates the high path loss of 60GHz WPAN systems. Simulation results show that the proposed pro-active BF further reduce more than 20% of the BF set-up time comparing with on-demand BF in the multiple DEVs scenarios. It is completely compliant to IEEE 802.15.3c, and adopted by IEEE 802.15.3c as an important compliment to the on-demand BF to realize Giga-bit-per-second (Gbps) communication in WPAN Systems.

There is a lack of high-speed and low-cost wireless network at sea to meet the increasing need of maritime users. With this observation, we have envisaged a WiMAX mesh network for high-speed ship-to-ship/shore communications. Analysis of interference range in such maritime WiMAX mesh networks is presented in this paper. And based on the findings, scheduling transmission of MAC control messages and data packets within three-hop neighborhood is investigated for the purpose of minimizing interference. A model is developed for analysis of the interference range in maritime environment. With parameter values that are derived from measurements at sea, we show that by scheduling among three-hop neighborhood the probability a transmission being interfered by a concurrent transmission drops about 30%. Simulation results show that, with the simulation settings in this paper, by scheduling among three-hop neighborhood, the initial packet delay and the average packet delay can be reduced by about 17% and 15.6% in sea state 3.0, respectively. In sea state 6.0, the performance improvement in initial packet delay and average packet delay are about 45% and 19.3%, respectively.

Closed-form expressions of the precisely accurate error probability are given for equal gain diversity in generalized fading distributions, namely ¿-¿ and ¿-¿, considered by da Costa and Yacoub.

This paper proposes a spatial time-division multiple access (STDMA) throughput enhancement scheme for a multiGbps millimeter-wave (mmWave) wireless personal area network (WPAN) system. The system design includes in the medium access control (MAC) layer, an interference-monitoring mechanism and a heuristic TDMA time-slot scheduling engine, and in the physical (PHY) layer, a Reed-Solomon (RS) coded phase-shift keying (PSK) system with selective Rake reception over a realistic 60 GHz multipath propagation channel. The theoretical analysis of the throughput and error performance is verified by Monte Carlo simulations. Firstly, it is found that the proposed STDMA scheme is capable of improving system throughput as much as 100%. Secondly, the co-channel interference (CCI) in a communication link has to be controlled at/below -15 dB in order to achieve the optimum system throughput. Lastly, different tolerable CCI levels to meet respective application requirements are determined.

An adaptive power control scheme for cognitive radio system (CRS) in Rayleigh fading channel is proposed. The transmit power of a secondary user (SU) is adjusted in Rayleigh fading to maximize the constant output signal-to-noise ratio (SNR) at an SU receiver while keeping the interference to a primary user (PU) under given constraints. To calculate the maximum constant output SNR at the SU receiver under the interference constraints of the PUs, we develop an analytical model for the distribution of the interference to PUs while considering the detection performance at the SUs. The analytical model takes into account of the use of multiple antennas and includes a single antenna scenario as a special case. The proposed scheme is compared with a straightforward fixed power control scheme for the CRS in terms of bit-error-rate (BER). Results show that the proposed adaptive power control scheme outperforms the fixed power control scheme. For example, when the BER is 10 3 the adaptive power control scheme with two transmit antennas and two receive antennas has a 3-dB improvement in SNR as compared with the fixed power control scheme.

In this paper, we propose a feasible beamforming (BF) scheme realized in media access control (MAC) layer following the guidelines of the IEEE 802.15.3c criteria for millimeterwave 60 GHz wireless personal area networks (60 GHz WPANs). The proposed BF targets to minimize the BF set-up time and mitigates the high path loss of 60 GHz WPAN systems. It is based on designed multi-resolution codebooks, which generate three kinds of patterns of different half power beam widths (HPBWs): quasi-omni pattern, sector and beam. These three kinds of patterns are employed in the three stages of the BF protocol, namely device-to-device (DEV-to-DEV) linking, sector-level searching and beam-level searching. All the three stages can be completed within one superframe, which minimizes the potential interference to other systems during BF set-up period. In this paper, we show some example codebooks and provide the details of BF procedure. Simulation results show that the setup time of the proposed BF protocol is as small as 2% when compared to the exhaustive searching protocol. The proposed BF is a complete design, it re-uses commands specified in IEEE 802.15.3c, completely compliant to the standard; It has thus been adopted by IEEE 802.15.3c as an optional functionality to realize Giga-bit-per-second (Gbps) communication in WPAN Systems.

This paper proposes the virtual time-slot allocation (VTSA) scheme for throughput enhancement to realize a Gbps-order time division multiple access (TDMA) wireless personal area network (WPAN) system in a realistic millimeter-wave residential multipath environment. Conventional TDMA system allocates each time-slot to only one communication link, which is insufficient to achieve Gbps-order throughput, particularly in severe channel conditions of multipath environment. In this paper, the proposed VTSA scheme enables a single time-slot to be reused for multiple communication links simultaneously (hence the name virtual), thus significantly increases system throughput. However, this generates co-channel interference (CCI) among the communication links occupying the same time-slot. The proposed cross layer VTSA scheme is therefore designed to be able to schedule the sharing of time-slots among multiple communication links, and at the same time monitor to minimize performance degradation due to CCI. Two time-slot reuse methods are proposed and compared in this paper, namely the minimum-CCI slotting method and the random slotting method. As a result, it is found that the VTSA scheme is capable of increasing the system throughput as much as approximately 30% in the additive white Gaussian noise (AWGN), line-of-sight (LOS) and the non-line-of-sight (NLOS) multipath channel. It is also found that the minimum-CCI slotting method has 10% better performance as compared to the random slotting method.

Cognitive radio(CR) has become an enabling technology to realize dynamic spectrum access through its spectrum sensing and reconfigurable capability. Robust and reliable spectrum sensing is needed to discover spectrum opportunity. Single cognitive radios often fail to provide such reliable information due to their inherent sensitivity limitation. Primary signals that are subject to detection by cognitive radios may become weak due to several factors such as fading and shadowing. One approach to alleviate this problem is to perform the spectrum sensing by using multiple CRs or multiple spectrum sensors. This approach known as distributed sensing because sensing is carried out through cooperation of spatially distributed sensors. In distributed sensing, sensors should perform spectrum sensing and forward the result to a destination where data fusion is carried out. In this paper we introduce a concept of a dual-purpose spectrum sensor that can combine the sensing and communication functions. The dual-purpose sensor reuses its detection hardware for both functions resulting in a less hardware complexity. We consider IEEE802.15.4a UWB PHY for communication and energy detection for spectrum sensing.

This paper studies the throughput of IEEE mmWave-WPAN based on the hybrid multiple access of CSMA/CA and TDMA. To study the throughput, we make a novel analytical model for the hybrid multiple access. Our throughput analysis shows that the throughput is highly affected by the access time of CSMA/CA. A larger access time of CSMA/CA will cause a lower data transmission time in TDMA, while a lower access time of CSMA/CA will also cause a higher collision that leads to increase the unused time for data transmission. This paper provides the approximated optimum access time of CSMA/CA maximizing the throughput. Furthermore, this paper introduces a private channel release time method for reducing collisions that highly improves the throughput of the mmWave-WPAN.

There is a lack of broadband wireless network in sea to meet the increasing needs of modern maritime users and we have envisaged WiMAX mesh networks for high-speed and low-cost ship-to-ship/shore communications. In such a maritime WiMAX mesh network, due to the long transmission distance and the distributed scheduling among two-hop neighbors, a single frequency channel may not be sufficient to provide the required bandwidth. An effective solution is to employ multiple frequency channels, by which the network capacity can be greatly increased. This paper presents operation of multi-channel transmission in maritime WiMAX mesh networks including allocation of minislots and frequency channels. The operation is based on a distributed adaptive time slots allocation and use of availability tables tracing minislots status. In the design, routing information is delivered in control subframe portion, and then the spreading of routing information can be speed up and less overhead in control slots can be used to describe and broadcast the availabilities of the minislots. Simulation results show that with the proposed scheme, by multi-channel transmission, the network performance can be improved in average packet delay and packets delivery ratio.

Transmitted reference Ultra-wideband (TR-UWB) system in conjunction with autocorrelation receivers (AcR) is a popular low cost and low complexity radio system for low and mid-data rate applications. The scheme is in general robust against multipath fading. At the receiver front-end, however, both the desired UWB signal and narrowband interference (NBI) can enter to the radio receiver in which case several co-terms and cross-terms are produced after correlation. Previous studies provided an approximate data model of TR-UWB under NBI. However, analytically computed covariance matrix based on the approximate data model showed inferior performance to that of the estimated covariance matrix when used to compute bit error rate (BER) by using linear minimum mean squared error (MMSE) method. In this paper we provide an improved data model taking into account some of the neglected factors in the previous data model derivation. Finally, we show that the analytic covariance matrix derived from the improved data model achieves a closely matching BER with that achieved by the estimated covariance matrix.

To achieve ultra high data rate communications in 60 GHz Wireless Personal Area Networks (WPANs), frame aggregation is devised in IEEE 802.15.3c to increase the MAC transmission efficiency. In this work, we propose a novel statistical model to analyze the behavior of two types of frame aggregation mechanisms: standard frame aggregation and low latency frame aggregation. Through our model, we could fully understand the performance of the frame aggregation mechanisms in terms of transmission delay and system capacity. The accuracy of our model is validated by extensive simulations. Our work provides valuable insights for ultra high performance transmission using 60 GHz radio.

In this paper, we propose a solution to resolve link blockage problem in 60 GHz WPANs. Line-of-Sight (LOS) link is easily blocked by a moving person, which is concerned as one of the severe problems in 60 GHz systems. Beamforming is a feasible technique to resolve link blockage by switching the beam path from LOS link to a Non-LOS (NLOS) link. We propose and evaluate two kinds of Beam Switching (BS) mechanisms: instant decision based BS and environment learning based BS. We examine these mechanisms in a typical indoor WPAN scenario. Extensive simulations have been carried out, and our results reveal that combining angle-of-arrival with the received signal to noise ratio could make better decision for beam switching. Our work provides valuable observations for beam switching during point-to-point communication using 60 GHz radio.

The current radio operational environment is characterized by its heterogeneity, which includes multiple operators, services, radio access technologies, network topologies, radio equipment, and frequency bands. While each radio access technology has mechanisms for efficient usage of the assigned spectrum, there is a need for the new intelligent management system, which can have capability to optimize spectrum usage across different radio access technologies and operators. In IEEE the standardization of such new management system has been performed under the Working Group 1900.4 of the Standards Coordinating Committee 41. The IEEE standard 1900.4 "Architectural Building Blocks Enabling Network-Device Distributed Decision Making for Optimized Radio Resource Usage in Heterogeneous Wireless Access Networks" was published in February 2009. Currently, two more projects are active in Working Group 1900.4. The first project is P1900.4.1 "Interfaces and Protocols Enabling Distributed Decision Making for Optimized Radio Resource Usage in Heterogeneous Wireless Networks." The second project is P1900.4a "Architecture and Interfaces for Dynamic Spectrum Access Networks in White Space Frequency Bands." The purpose of this paper is to give overview of the current status of the IEEE projects P1900.4.1 and P1900.4a.1

This paper introduces a network concept to handle heterogeneous and spectrum sharing (white space) type radio access networks, cognitive wireless cloud (CWC). This paper explains the overview, the system architecture, and the feasibility studies. As for the feasibility studies, network implementation and the development of new base station and terminal that suit for the CWC have done by using the technologies of cognitive radio and software defined radio technologies.

We propose a distributed radio resource usage optimization algorithm to satisfy users' QoS requirements in heterogeneous wireless networks. Our optimization algorithm is based on the mutually connected neural network dynamics, which can be run distributively and autonomously, and does not require centralized computation. We define an optimization problem to satisfy QoS requirements of users' applications, and compose a neural network to solve the problem autonomously. Since the objective function of the defined problem becomes higher order function, we apply a higher order neural network model that minimizes higher order energy function by its distributed and autonomous updating. By computer simulation, the proposed method has been shown effective to optimize such a problem, without any centralized computation.

This paper proposes a method to estimate locations of neighboring APs near a specified AP without using absolute location measured by the GPS. This estimation contributes to reduce handover latency between APs and improve communication quality. The method does not require terminals to have the GPS because it's not supported by all existing terminals. The estimation utilizes relative location of APs calculated using the spring model where RSSI and detection probability of APs are applied. Simulation results show that the nearest three APs can be estimated with probability of around 30%. The relative location is expected to be applied to enhance communication quality on mobile terminals.

This paper presents a study on the fading behavior in wideband 60 GHz-Millimeter-wave (MMW) wireless system. The evaluation is carried out based on a two-ray propagation model, with considering the large propagation loss of the multi-reflected waves other than the first reflected wave at 60 GHz-millimeter-wave. The study focuses on the strong fading effect due to the large variation of antenna location compared to the short wavelength (about 5 mm) and the wide frequency range (about 9 GHz) in such MMW wireless system. The influence of the polarization mismatch of antenna is also investigated. To reduce the fading, we employ the technique of space diversity by introducing two or more antennas in receiving side. We perform an optimization of the locations (heights) for these antennas. From the simulation results, we obtain some optimal heights with which the fading effect can be reduced in less than 3 dB. The simulation results also reveal how the polarization mismatch, in two different cases of antenna rotations, influences the system performance, and how space diversity reduce the fading as well. The antenna used in simulation is a planar patch antenna which is considered suitable for portable wireless handset. The radiation pattern is obtained from electromagnetic simulation. This paper demonstrates that by employing multiple antennas with optimized antenna locations can significantly reduce the fading for the 60 GHz-MMW wireless system.

This paper details the current work status of the ETSI Reconfigurable Radio Systems (RRS) Technical Committee (TC) and gives an outlook on the future evolution. In particular, Software Defined Radio (SDR) related study results are presented with a focus on SDR architectures for Mobile Devices (MD), such as mobile phones, etc., as well as for Reconfigurable Base Stations (RBS). For MDs, a novel architecture is presented enabling the usage of SDR principles in a mass market context. Cognitive Radio (CR) principles within ETSI RRS are concentrated on two topics, a Cognitive Pilot Channel (CPC) proposal and a Functional Architecture (FA) for Management and Control of Reconfigurable Radio Systems, including Dynamic Self-Organising Planning and Management, Dynamic Spectrum Management, Joint Radio Resource Management, etc. Finally, study results are indicated which are targeting a SDR/CR security framework

This paper studies the system throughput of the 802.15.3c WPAN by considering the different wireless multiple access methods of CSMA/CA and hybrid CSMA/CA and TDMA. We construct an analytical model to study the throughput and the conducted analysis clearly shows the system throughput of the 802.15.3c WPAN upon both CSMA/CA and hybrid CSMA/CA and TDMA. We have found that CSMA/CA-TDMA can achieve much higher throughput compared to CSMA/CA, especially as the increase in the contending devices of a network.

In order to clarify the dual antenna offset channel model needed to transmit multi gigabit/sec streams with directional Tx and Rx antennas at 60 GHz, the paper describes the measurement results of vertical, horizontal and circular polarized signal transmission using co-polarized and cross-polarized directional antennas. Measurement results show that the number of strong reflection waves depends on the polarization type and that the power of cross-polarized wave transmission is very small. These results are useful for developing the novel indoor millimeter-wave channel model that considers AoD, AoA and polarization type.

0.4-5.2 GHz broadband quadrature mixer (QMIX) and quadrature modulator (QMOD) using static frequency divider for multiband transceiver, and multimode transceiver IC having a low spurious local oscillator (LO) configuration using 2fLO switching circuit are described. Configurations of the fabricated RF-IC's and their measurement results for the multiband multimode transceiver are shown in this paper.

This paper investigates the interference mitigation capability of a millimeter-wave wireless personal area network (WPAN) in a realistic 60 GHz channel. The interference mitigation mechanism employs farther-reaching beacon signals and device-relayed synchronization command frames (sync frames) to further extend the protection range of the victim (a.k.a. primary) network. Firstly, it is found that the sync frame is capable of extending the 'interference-free' region as a function of network-controller-to-device distance and the location of the interferer. Secondly, it is found that in the interference-free region extended by the beacon/sync frame, the probability of interference is near zero. Finally, interference, when taking place, impacts high speed (3~5 Gbps) links 5~8 dB more significantly than their low speed (1~3 Gbps) counterparts.

This paper addresses the transmit power control with multiple antennas. A theoretical comparison of transmit diversity and beamforming techniques in the presence of fading correlation at an antenna array and handoff is presented. The objective is to investigate transmit power of both system and investigate the effect of array perturbations that exist in practical applications of antenna arrays. The perturbations are modeled as additive random errors, following complex Gaussian multivariate distribution, to the antenna array steering vectors. Using the outage probability of the instantaneous channel capacity and transmitter power as performance measures, we conclude that by overlooking array perturbations the performance evaluation tends to underestimate and overestimate, respectively, the transmit diversity and beamforming systems in practical application environments.

User-centric dynamic spectrum access (DSA) in heterogeneous cognitive networks is an approach which allows cognitive radio (CR) to select and utilize radio resource according to user preferences. Defining a utility function corresponding to different preferences is required for the implementation and evaluation of a user-centric DSA scheme. This paper proposes a numerical representation method of common user preferences, and a numerical representation method of user satisfaction corresponding to multiple preferences. User satisfaction is defined based on the amount of received service and the perceived fairness to the service, it is used as a utility function to evaluate the affects of a user-centric DSA scheme to network load and to the fairness of resource sharing among CRs.

In this paper, we propose a radio resource allocation (RRA) scheme for multiuser multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing access (OFDMA) systems in order to achieve the optimal system throughput. The proposed RRA algorithm adaptively schedules 3-dimension (3-D) (space, frequency and time) slots to different users according to various channel state information (CSI). Different from most of conventional RRA algorithms, the proposed algorithm joins scheduling process with power allocation, that is, iteratively allocating total transmit power into resource block (RB) during 3-D slot assignment. The power allocation is an extension of the space-frequency waterfilling algorithm, and is adapted to an equivalent 1-D single input single output (SISO) channels. The equivalent SISO channels are obtained from the original 3-D RBs in the sense of the same maximum achievable throughput. The proposed algorithm was confirmed in the Worldwide interoperability for Microwave Access (WiMAX) systems following IEEE 802.16e media access control (MAC) protocols. It is shown that the proposed RRA algorithm significantly simplifies the scheduling process and achieves more throughput than round robin (RR) scheme.

We envisage extending the coverage of existing terrestrial wireless broadband wireless networks to the sea so that cost-efficient wireless access is available to the ships near the shore. The coverage extension is achieved through a multi-hop WiMAX wireless mesh networks where ships, maritime beacons and buoys are the nodes. In such a multi-hop network, routing protocol plays an important role in ensuring reliable end-to-end packet delivery. Compared to AOMDV and OLSR, AODV has been found as a more suitable routing protocol in terms of average packet delay, packet delivery ratio, and implementation complexity. AODV requires route request messages being broadcast during route discovery process. However, WiMAX mesh MAC protocol is not efficient in supporting broadcast of data packets that carry the route request. This inefficiency is due to need of performing the three-way-handshaking process in reserving a data slot before transmitting each route request. As a result, AODV suffers from large initial packet delay and average packet delay. In view of the problem, this paper proposes a method to efficiently deliver the AODV routing messages by piggybacking them on the existing WiMAX mesh MAC control messages. As such, the three-way-handshaking is avoided leading to a faster transmission of routing messages. Simulation results confirm that the proposed scheme can lead to an improvement in initial packet delay, weighted average delay, and packet delivery ratio.

In this paper we present preamble design for millimeter-wave single carrier wireless personal area networks. Several factors are considered for a successful preamble design, such as sequence complexity, operation range, associated delay, robustness to frequency offset. Complementary Golay sequences are selected, which combine flexibility and performance. Simulation results indicate at optimum threshold level, it is possible to reduce both false alarm probability and misdetection probability less than 10-3in non-line-of-sight channels.

Recent studies on spectrum sensing for cognitive radio (CR) reveal that sensing based on single CR may not provide reliable information due to the fact that signals degrade as a result of fading and shadowing. Hence, spectrum sensing based on multiple CR has been considered. In this paper we investigate a distributed sensing based on multiple spectrum sensors where the sensors are located outside the CR. Depending on the channel conditions between sensors (sensor- to-sensor channel) and between the sensor and the radio (user-channel), we explore three different modes of sensing where sensors provide the sensing information either cooperatively or independently. Computer simulation results are provided to validate the concepts.

In this paper we investigate spectrum sensing for cognitive radio (CR) by using multiple spectrum sensors. We explore sensing schemes based on soft information combining, hard information combining and a two-stage detection scheme that uses both soft information combining and hard information combining. The two-stage detection scheme is shown to provide improved performance compared to sensing based on either hard information combining or soft information combining alone with a trade-off of sensing time. Computer simulation results are provided to validate the concept.

We have designed and implemented a radio access network selection algorithm for heterogeneous wireless network environment, in which mobile terminals can adaptively and seamlessly handover among different radio access technologies. We propose a radio resource usage optimization algorithm without centralized computation on the network side, which is based on the Hopfield neural network dynamics whose energy function autonomously minimizes by distributed update of each neuron. We have implemented the proposed algorithm on an experimental heterogeneous wireless network system, which includes functionalities defined in IEEE 1900.4. First, we show that the proposed algorithm can optimize fairness of the throughput by numerical simulation. Then, we show that our algorithm works correctly and optimizes radio resource usage also on the experimental wireless network by distributed handover decisions on the terminal side.

In this paper, we propose a method to reduce the scan time using detection probability calculated from reports from multiple terminals. The detection probability is a probability that any of two APs (APiand APj) are found at the same time under the condition when APiis found. By using this method, terminals can omit to scan some of channels which are apparently lower in probability that available APs are found. Our simulation results show that the scan time has been reduced by more than 40% compared with a RSSI based AP selection method. The proposed method is expected to improve the quality of service of real-time applications on mobile terminals.

This paper proposes a framework to collect bandwidth information from terminals, analyze them statistically, and feed back to terminals in order to increase usable bandwidth in terminals keeping coexistence with legacy WiFi systems. This coexistence feature enables practical integration of the proposed framework with the legacy WiFi systems including Internet. By introducing two-level transmission via components categorized into radio access network side and core network side, replacement or modification on existing systems is not required for deployment of the proposed framework. The feedback is transmitted using multicast from APs to terminals in order to reduce message traffic, but the transmission from the server to APs is unicast because the current Internet does not fully support the IP multicasting. The proposed algorithm increases minimum throughput among all terminals by more than twice at maximum per terminal as well as total network throughput by 30% on average, compared with random selection method.

Multi-Input-Multi-Output (MIMO) is an emerging technology for the 4th-generation mobile communication systems due to the capability of high-speed data transmission. There have been only a few literatures regarding MIMO propagation characteristics under outdoor condition, and most of which have focused only on 2 GHz bands for existing cellular systems. However, since 3.4-3.6 GHz band will be allocated as one of frequency bands for the 4th-generation mobile communication systems, the channel characteristics at this band should be carefully considered. This report presents the outdoor MIMO channel characteristics measured by a 2×2 MIMO channel sounding system at the center frequency of 3.35 GHz in urban environment. In this measurement system, the 9-stage PN signals are transmitted by controlling the transmission timing in each transmitter, and hence, the complex MIMO channel impulse responses can be obtained by using same PN sequence in the receiver. From the measured MIMO channel characteristics, we computed the channel capacity based on each eigenvalue that was obtained through singular value decomposition (SVD). In addition, we evaluated the channel capacity for line-of-site (LOS) and non-line-of-site (NLOS) environments with respect to the antennas distance.

We envisage extending radio coverage of the existing terrestrial wireless broadband networks to the sea to provide ships with high speed connection to the Internet. This is achieved by forming a WiMAX-based maritime wireless mesh network where ships are network nodes connected to the land station across multiple hops. In such a wireless mesh network, routing protocol plays an important role in providing efficient and reliable communications. This paper proposes a routing protocol, called MRPT (MAC-based Routing Protocol for TRITON), that piggybacks routing information on WiMAX mesh MAC control messages. This provides proactiveness and readily available multi-path for traffic from ship to land station. For traffic from land station to ship, the proposed routing protocol uses a bitmap encoding to efficiently inform land station of the constructed routing tree. Simulation results confirm that MRPT outperforms AODV, AOMDV and OLSR in terms of delay and throughput.

In this paper, we propose a deflection routing scheme for throughput improvement to realize Gbps millimeter-wave wireless personal area network (mmWave WPAN) system. The upcoming mmWave WPAN system is designed to support transmission of uncompressed high definition TV (HDTV), high speed wireless downloading and docking etc. These data-rate-greedy applications require Gbps-order throughput which can be met by the capability of mmWave PHY. However, because of the ad-hoc formed network topology, it is easily happening that the line-of-sight (LOS) path may be blocked, while the non-line-of-sight (NLOS) path is not sufficient to guarantee Gbps throughput due to signal degradation. In this paper, we propose a cross-layer deflection routing (DR) scheme to solve the issue. When the direct path is blocked, the source device finds a relay to form deflection route, send the data to the destination through this alternative route. To avoid throughput degradation due to the consumption of extra time for relay operation, the deflection route is designed to share time slots with other transmissions on direct path. Two routing algorithms are proposed, namely random fit DR (RFDR) and best fit DR (BFDR). They search appropriate relay and time slots that provides sufficient isolation of co-channel interference (CCI) between the transmissions on direct path and deflection route. Computer simulations show that, in realistic 60 GHz environment, Gbps-order system throughput is achieved under blocking condition. There is up to 35% system throughput improvement compared to the conventional relay scheme.

This paper studies communication channel assignment in IEEE 802.15.3 WPANs. We clarify the channel interference problems as well as introduce an interesting channel interference caused by a hidden PNC in IEEE 802.15.3 WPANs. In this paper, we propose a predictive channel assignment method (PCAM) to efficiently avoid the channel interference among piconets and to minimize throughput degradation by channel interference. The basic idea of the proposed method is to synchronize the communication channel time among the piconets residing in the channel interference area, to predict the future channel interference time and to make a schedule of the communication channel time to minimize throughput degradation. The obtained results show that the proposed PCAM highly improves the system throughput by avoiding channel interference compared to the existing method of IEEE 802.15.3 WPANs.

Inter-symbol/frame interference analysis is presented for pulsed direct sequence (DS) and hybrid direct sequence time hopping (DS/TH) ultra-wideband (UWB) communications considering a frequency selective Nakagami fading channel. Following the analysis, error rate expressions are developed and performance comparison is presented for the systems. It is found that the performance of pulsed DS system may depend on pulse repetition rate (PRR), number of combined paths by Rake receiver and the channel profile in a kind of unpredictable manner. For low PRR, the DS system performs better than DS/TH irrespective of the channel profile. For medium to high PRR, DS and DS/TH systems may perform comparably in a channel with a single decaying profile. However, if the channel contains more than one decaying profiles like as in Saleh-Valenzuela model, the performance of DS may drastically degrade and perform worse than DS/TH at some values of PRRs. The performance of DS/TH is relatively less influenced by the shape of the channel profile. Theoretical results are verified by simulations.

In order to realize intra-car multimedia communications systems composed of entertainment which requires several hundred Mbps to 1 Gbps capacity and monitoring signal transmission between many parts of the car which requires high reliability and low latency, this paper proposes a millimeter wave system which has high capacity and low latency transmission capability. To clarify the feasibility of millimeter wave systems applications to intra-car multimedia communications, propagation characteristics inside a car have been extensively measured and analyzed. The proposed system sets a car navigator as the center of Intra-car multimedia communications with an Omni antenna and receivers are assumed at front seats, back seats and the luggage space behind the back seats in a typical SUV (Sports Utility Vehicle). The measured results show i. Front seat communications are no worry with simple single carrier (SC) modems without any equalizer, ii. Back seats communications may need beam forming capability for better receive signal power (an Omni antenna system still works with a simple SC modem with a simple rake receiver but without any equalizer, iii. "Luggage space communications may require a directive / beam forming antenna for better receive signal power. The maximum delay spread observed is 6 to 7 ns and no equalizer necessity has been found for Omni antenna receivers inside a car. Further advancement to beam forming antenna will have only 1 - 2 ns maximum delay spread inside a car. Thus, this paper has proved the feasibility of millimeter wave intra-car multimedia communications system by employing a simple single carrier modem without any equalizers but with simple rake receivers.

This paper investigates the impact of adjacent channel interference (ACI) and co-channel interference (CCI) on the error performance and throughput of a multi-Gbps millimeter-wave wireless personal area network (WPAN) system in both residential multipath line-of-sight (LOS) and non-LOS (NLOS) environment. It is found that the ACI that causes 0.5dB degradation in signal-to-noise ratio (SNR) for BPSK, QPSK, 8-PSK and 16-QAM systems are 13, 7, 0 and -6 dB respectively. And the CCI that causes similar SNR degradation for BPSK, QPSK, 8-PSK and 16-QAM are -18, -20, -26 and -29 dB respectively. Additionally, multipath NLOS environment in the presence of ACI is found to cause an extra 5 dB degradation on error performance as compared to ACI in LOS environment. On the other hand, CCI in both LOS and NLOS environment display approximately similar impact on error performance. In extremely low ACI/CCI environment, the maximum achievable throughput for BPSK, QPSK, 8-PSK and 16-QAM in NLOS environment are 1.1, 2.2, 3.4 and 4.6Gbps respectively. Then as ACI/CCI increases, the throughput of 16-QAM decreases the most rapidly, followed by 8-PSK, QPSK and pi/2-BPSK. It is also found that system tolerance against ACI/CCI can be increased by employing modulation schemes with lower modulation level, at the expense of lower maximum achievable throughput.

This paper presents throughput and error performance analysis of the proposed space-time resource management (STRM) scheme for a multi-Gbps millimeter-wave system. The proposed STRM allows multiple peer-to-peer communication links to occupy the same time-division-multiple-access (TDMA) time slot, in contrary to the conventional TDMA system that allocates only one time slot to one communication link. In this paper, theoretical analysis is conducted to investigate the achievable throughput in the presence of co-channel interference (CCI) generated by communication links co-sharing the same time slot. Firstly, it is found that the upper bound of the achievable throughput increases linearly with the number of communication links sharing the same time slot. Secondly, by presenting a parameter that manages the allowable CCI in the network, the system throughput can be optimized. The optimum preset allowable CCI values are found to be in the range of -13dB¿CCI¿-11dB. Lastly, it is also found that in a millimeterwave band system, a victim system with transmitter-receiver separation of 1-meter can achieve its targeted bit error rate (BER) provided that the interferer is 6 meters away.

The function of a cognitive radio system (CRS) can be classified as cognitive engine (CE) and sensing. The CE fulfills spectrum analysis and decision making of spectrum access. The sensing function is realized by either a CR node or distributed spectrum sensors. In this paper, we propose a sensing architecture, which adds new functional entities, sensing controller (SC) and sensing information processor (SIP) inside CE and sensing, respectively. Based on the architecture, we give a use case where sensing is realized by distributed sensors. Selection of these sensors is performed in Rayleigh fading channel to improve the detection performance and save power consumption. Using analytical analysis we prove the benefits of sensor selection. Results show that using energy detection with 5000 symbols in - 15 dB signal-to-noise ratio (SNR) environment, we can reduce the false alarm rate from 0.95 to 0.1 while keeping 99% protection to primary users by selecting among ten sensors. Results also show that it is beneficial perform selection based on user channel.

AbstraAbThis study addresses detection of primary users (PUs) for cognitive radio system (CRS) with distributed spectrum sensors (DSSs) in Rayleigh fading environment. Two sensing schemes using DSSs that employ energy detection (ED) are investigated as cooperative sensing and collaborative sensing. For the cooperative sensing, each DSS makes hard decision after sensing and transmits the information by on-off keying (OOK) singling to a secondary user (SU) that performs data fusion. In collaborative sensing DSSs exchange the hard decision information after sensing and make data fusion at a selected DSS. Then, the selected DSS transmits the decision information to the SU with OOK signaling. In this paper, a closed-form expression for the probability of detection (PD) of ED with selective combining (SC) in Rayleigh fading environment is derived. Applying this expression to the PU detection problem, analytical models for evaluating the two sensing schemes are obtained. Results show that at 5-dB signal-to-noise ratio (SNR) and using 3 DSSs, the PD is increased from 0.02 to 0.3 and 0.4 by collaborative sensing and collaborative sensing, respectively.

A cognitive radio system (CRS) senses the radio spectrum environment and adaptively use unoccupied spectrum resource. The CRS should optimize between two conflicting goals for different applications. One is the minimization of interference to primary users and the other is the maximization of usage of spectrum opportunities of the secondary users. In this paper, we propose a dual-level management scheme that performs spectrum analysis and access decision making at both network level and terminal level. Using this scheme, secondary users obtain the distribution of the silent period and control their sensing performance. A closed-form optimal threshold is obtained using the maximum a posteriori (MAP) rule based on the distribution of the silent period of primary users. Furthermore, applying this optimal detection threshold, we set up an analytical model to study the tradeoff between protection to primary users and spectrum usage of secondary users. Results show that the optimal threshold changes according to the duration of sensing. Furthermore, increasing the duration of sensing might not necessarily improve the protection to primary users. Using this analytical model, the scheme chooses sensing period conditioned on the distribution of silent period of licensed users to improve the usage of unoccupied spectrum while limiting the collision between primary users and secondary users for different application purposes.

The paper presents a signal-to-noise ratio (SNR) mapping scheme for single-carrier (SC) frequency domain equalization (FDE) based millimeter-wave wireless personal area networks (WPANs). The effective SNR, defined as an average SNR over whole data frame after equalization, is a one-to-one mapper of the SNR in practical scenario in the sense of the same bit error rate (BER) performance. As the mapping is based on theoretical calculation instead of the simulation on a specific channel model, the defined effective SNR is suitable to be used as a metric, such as threshold for link adaptation, because it decides system BER performance just based on theoretical BER performance of AWGN channel instead of channel-model dependent SNR-BER table. The close form of effective SNR is proposed. A link adaptation method based on the defined effective SNR is given to show how our defined effective SNR simplifies system design. Both theoretical analysis and simulation results show that the defined effective SNR is channel-model independent and it is accuracy enough with variance of mapping error lower than 1 dB, it is therefore useful, especially for the system possibly involved in several different wireless communication scenarios.

Abstract-The paper proposes a codebook design to support beamforming mechanism in a wide band millimeter-wave 60 GHz wireless personal area networks (60 GHz WPANs) in a realistic millimeter-wave environment. The codebooks are designed symmetrically in order to mitigate the possible beam shift due to the large differences of wave lengthes at different sub-bands of a wide band communication system. In order to provide a high data rate and high performance with minimum power consumption in 60 GHz systems, the codebooks are generated with 90 degree phase resolution without amplitude adjustment. The codebooks are designed for different numbers of antenna elements, supporting a multitude of antenna configurations. The paper provides codebook design mechanism, some example codebooks and some analysis on antenna gain loss due to phase shift errors of phase shifters. Simulation results shows that: (1) To keep the gain loss at the intersections of any two patterns inside the codebook lower than ldB, the number of patterns inside the codebook shall be at least 2 times of the number of antenna elements used for pattern generation; (2) The designed codebooks are robust to phase shift errors: the gain loss is lower than ldB with only 10% outage probability when standard deviation of phase shift errors at phase shifters is 0.5 [28.6 degree]. The proposed codebooks are a feasible design, they are the key basis of the beamforming protocol in 60 GHz WPANs (IEEE 802.15.3c).

Non-coherent UWB receivers provide robustness against multi path fading at low complexity. The analog front-end of these receivers, however, is susceptible to narrowband interference (NBI), thus requiring NBI mitigation capability. NBI identification and NBI parameter estimation is the first step towards implementing effective NBI mitigation. We propose an NBI detection and its center frequency identification method for multichannel autocorrelation receivers (AcR) as used by transmitted-reference (TR) UWB systems. We evaluate the performance of the method by computer simulations.

We envisage extending radio coverage of the existing terrestrial wireless broadband networks to the sea to provide ships with cost-efficient high-speed connection to the Internet. This is achieved by forming a WiMAX based maritime wireless mesh network where ships are network nodes connected to the land station across multiple hops. In such a maritime wireless mesh network, time slot allocation is an important issue as it affects the performance in terms of throughout and delay. This papers proposes a distributed adaptive time slot allocation (DATSA) scheme for WiMAX mesh MAC protocol. DATSA is a distributed scheme that allocates time slots robustly by taking into consideration difference between radio reception range and interference range, and latency in scheduling control messages. DATSA has a method to monitor reception quality of an allocated time slot, in order to detect the effect of topology changes due to ship mobility, etc. Based on the monitoring outcome, the method adaptively changes the time slot allocation if necessary. We have evaluated DATSA through random event simulation using QualNet. The simulation results confirm that DATSA outperforms the original WiMAX mesh MAC protocol that has no adaptive time slot allocation, in terms of throughput, average packet delay, and packet delivery ratio.

In this paper, we propose a cross-layer deflect routing scheme that improves effective throughput of multi-hop millimeter-wave wireless personal area network (mmWave WPAN) system. The upcoming mmWave WPAN is designed to provide Gbps-order transmission capability, targeting applications like high definition TV (HDTV) transmission, high speed wireless docking and gaming etc. Adopting multi-hop relay offers solutions to the issues existing in mmWave WPAN system such as limited coverage range caused by the significant path loss, dramatic communication link change due to the unexpected blockage of the line-of-sight (LOS) path etc. However, multi-hop relay on the other hand decreases the effective throughput because of the required extra time. As a result, the compromised throughput may not be able to support the above applications which are greedy for data rate. Inspired by the fact that the significant path loss of millimeter-wave environment can provide good space isolation, our proposed scheme manages to improve the multi-hop throughput by sharing time slots for relay path with direct path for other transmissions. We also propose two algorithms, namely random fit deflect routing (RFDR) and best lit deflect routing (BFDR), to find the relay path on which the interference due to time slot sharing is low enough to guarantee the concurrent transmissions. Computer simulations show that, in realistic 60 GHz environment, the effective multi-hop throughput can be improved up to 45%.

An exact expression of error rate is developed for maximal ratio combining (MRC) in an independent but not necessarily identically distributed frequency selective Nakagami fading channel taking into account inter-symbol, co-channel and adjacent channel interferences (ISI, CCI and ACI respectively). The characteristic function (CF) method is adopted. While accurate analysis of MRC performance cannot be seen in frequency selective channel taking ISI (and CCI) into account, such analysis for ACI has not been addressed yet. The general analysis presented in this paper solves a problem of past and present interest, which has so far been studied either approximately or in simulations. The exact method presented also lets us obtain an approximate error rate expression based on Gaussian approximation (GA) of the interferences. It is shown, especially while the channel is lightly faded, has fewer multipath components and a decaying delay profile, the GA may be substantially inaccurate at high signal-to-noise ratio.

This paper proposes a virtual time-slot allocation (VTSA) throughput enhancement scheme with multiple modulation methods to realize a multi-Gbps time division multiple access (TDMA) wireless personal area network (WPAN) system in a realistic millimeter-wave residential multipath environment. The VTSA scheme allows multiple communication links in the network to simultaneously use the same time-slot, thus increases system throughput. Additionally, by coupling to higher-order modulation schemes, higher data rate can be achieved. The combination of both is found to be capable of realizing a multi- Gbps WPAN system. However, the employment of the VTSA scheme causes the generation of co-channel interference (CCI) in the system, and CCI is found to affect the modulation schemes differently. This paper investigates the tradeoff parameters between varying CCI due to the employment of the VTSA scheme, and the higher-order modulations applied. As a result, it is found that the VTSA scheme is capable of increasing 30% of the system throughput. It is also found that in low CCI environment, 16QAM offers the highest achievable system throughput, whereas when CCI becomes higher, the more-robust BPSK offers the highest throughput.

This paper proposes a new channel model for millimeter wave (60 GHz) for indoor applications, power amplifier and phase noise models at 60 GHz, an optimal global channelization over 9 GHz bandwidth, common mode signaling to bridge SC (single carrier) and OFDM (orthogonal frequency division multiplex) camps, and a robust payload as well as a header and preamble design for single carrier for practical applications. The computer simulations have validated these new proposals for WPAN (wireless personal are network) design and significantly contributed a lot to global (IEEE802.15.3c) standardization which will be closed in the near future by issuing system specifications.

In this paper, we propose a deflection routing scheme that improves effective throughput (defined as the successfully transmitted bits over the duration between two available sequential time slots) of millimeter-wave wireless personal area network (mmWave WPAN) systems. The upcoming mmWave WPAN is based on dynamic time division multiple access (TDMA) and designed to guarantee Gbps-order transmission capability for high definition TV (HDTV) transmission, high speed wireless docking and gaming, etc. The decode-and-forward (DF) type of relay offers a simple solution to the issues of mmWave WPAN systems, such as limited coverage range and unexpected blockage. However, due to the required extra time, DF relay on the other hand decreases the effective throughput, and may not be sufficient to satisfy the requirement of the above data-rate-greedy applications. Inspired by the fact that the significant path loss of a millimeter-wave environment can provide good space isolation, we propose a deflection routing scheme to improve the effective throughput by sharing time slots for direct path with relay path. Based on the sub-exhaustive search, a routing algorithm, named as best fit deflection routing (BFDR), has been developed to find the relay path with the least interference that maximizes the system throughput. To reduce the computational complexity of the BFDR, we have also developed a sub-optimal algorithm named as random fit deflection routing (RFDR). The RFDR algorithm finds the sub-optimized relay path, where the interference may not be the least but is sufficiently low to guarantee the concurrent transmissions. Computer simulations show that, in realistic 60 GHz environments, the effective system throughput can be improved up to 28% under grid topology and 35% under random topology. RFDR achieves almost the same order of throughput improvement with only 10% of the computational complexity of BFDR.

This paper studies the throughput of the IEEE 802.15.3c millimeter-wave (mm-Wave) WPAN system that is based on the hybrid multiple access of CSMA/CA and TDMA. In order to study the throughput of this system, we construct a novel analytical model by considering hybrid multiple access. Our throughput analysis shows that the throughput is significantly affected by the length of access time of CSMA/CA. A large length of access time of CSMA/CA will cause a low data transmission time in TDMA, while a short length of access time of CSMA/CA will cause a large number of data transmission collisions in CSMA/CA. The failure of data transmission channel release due to the collisions will lead to an increase in the unused data transmission time in TDMA. In order to improve the throughput, we introduce a private channel-release time to avoid the failure of data transmission channel release and provide the optimum access time of CSMA/CA, thereby maximizing the throughput. The proposed method can significantly improve the throughput of the IEEE 802.15.3c mm-wave WPAN system.

In order to realize a vehicle area network for multimedia entertainment systems, which demand capacities of up to 1 Gbps, and vehicle control links between many parts of the car, which demand high reliability and low latency, this paper proposes a millimeter-wave system that offers high capacity and low latency transmission. Propagation measurement results show the maximum delay spread of 6 - 7 ns can be achieved with omni antennas without complicated equalizers. Feasible advances in beam forming antenna performance will reduce the maximum delay spread inside the car to only 1 - 2 ns. This paper proves that millimeter-wave vehicle area networks can support multimedia communications as well as control links by employing a basic single carrier modem with simple rake receivers; no equalization is needed.

This paper investigates the impact of adjacent channel interference (ACI) and co-channel interference (CCI) on error performance and throughput of a multi-Gbps millimeterwave wireless personal area network (WPAN) system in a realistic residential line-of-sight (LOS) and non-line-of-sight (NLOS) multipath environment. The main contribution of this paper is providing a multi-Gbps WPAN system design in the challenging multipath environment in the presence of ACI/CCI. Based on the investigation results, we have provided ACI/CCI rejection as a reference for victim receiver protection design. In the NLOS environment, the ACI rejection (i.e. ACI that causes 0.5 dB degradation in the required signal-to-noise ratio (SNR) to achieve bit error rate (BER) of 10-6) for pi/2-BPSK, QPSK, 8 PSK and 16 QAM are 13, 7, 0 and -6dB respectively. And the CCI rejection for similar modulation schemes are -18, -20, -26 and -29 respectively. Secondly, we have clarified the LOS-NLOS relationship of the ACI/CCI impact to system performance. ACI in multipath NLOS environment causes an additional 5 dB degradation to error performance as compared to ACI in the LOS environment. CCI on the other hand, has similar impact on error performance in both LOS and NLOS environment. Thirdly, we have clarified the relationship between modulation spectral efficiency and robustness against ACI/CCI. In an environment with no or low ACI/CCI, the maximum achievable throughput for pi/2-BPSK, QPSK, 8 PSK and 16 QAM in LOS environment are 1.2, 2.5, 3.8 and 5 Gbps respectively. In NLOS environment, the achievable throughput decreases to 1, 1.9, 2.8 and 3.8 Gbps respectively. As ACI/CCI increases, the throughput of higherorder modulation schemes such as 16 QAM decreases the most rapidly, followed by 8 PSK and QPSK. The throughput for pi/2-BPSK has the highest tolerance against increasing ACI/CCI, at the expense of lower maximum achievable throughput.

This paper proposes a virtual time-slot allocation (VTSA) scheme for throughput enhancement to realize a multi-Gbps time division multiple access (TDMA) wireless personal area network (WPAN) system in a realistic millimeter-wave residential multipath environment. TDMA system without time-slot-reuse mechanism conventionally allocates one TDMA time-slot to only one communication link at a time. In the proposed VTSA scheme, taking advantage on the large path loss in the millimeterwave band, a single TDMA time-slot can be reallocated and reused by multiple communication links simultaneously (hence the name virtual), thus significantly increasing system throughput. On the other hand, allowing multiple communication links to occupy the same time-slot causes the generation of co-channel interference (CCI). The cross layer VTSA scheme is therefore designed to be able to maximize the throughput improvement by adaptively scheduling the sharing of time-slots, and at the same time monitor the potential performance degradation due to CCI. As a result, it is found that the VTSA scheme is capable of improving system throughput as much as 30% in both AWGN and multipath channels (line-of-sight (LOS) and non-line-of-sight (NLOS) environment). Additionally, by coupling with higher-order modulation schemes, the system is able to achieve up to a maximum throughput of 3.8 Gbps. It is also observed that higher-order modulations although have higher maximum achievable throughput in low CCI environment, the tolerance against increasing CCI is considerably lower than that of the lower-order modulations.

In order to realize high speed, long range, reliable transmission in millimeter-wave 60 GHz wireless personal area networks (60 GHz WPANs), we propose a beamforming (BF) protocol realized in media access control (MAC) layer on top of multiple physical layer (PHY) designs. The proposed BF protocol targets to minimize the BF set-up time and to mitigate the high path loss of 60 GHz WPAN systems. It consists of 3 stages, namely the device (DEV) to DEV linking, sector-level searching and beam-level searching. The division of the stages facilitates significant reduction in setup time as compared to BF protocols with exhaustive searching mechanisms. The proposed BF protocol employs discrete phase-shifters, which significantly simplifies the structure of DEVs as compared to the conventional BF with phase-and-amplitude adjustment, at the expense of a gain degradation of less than 1 dB. The proposed BF protocol is a complete design and PHY-independent, it is applicable to different antenna configurations. Simulation results show that the setup time of the proposed BF protocol is as small as 2% when compared to the exhaustive searching protocol. Furthermore, based on the codebooks with four phases per element, around 15.1 dB gain is achieved by using eight antenna elements at both transmitter and receiver, thereby enabling 1.6 Gbps-data-streaming over a range of three meters. Due to the flexibility in supporting multiple PHY layer designs, the proposed protocol has been adopted by the IEEE 802.15.3c as an optional functionality to realize Gbps communication systems.

Implementing dynamic spectrum assignment and access technologies in heterogeneous wireless networks may lead to considerable improvement in spectrum usage and quality of service. In this paper we evaluate the performance of SINR-based dynamic spectrum assignment and access algorithms using simulation. We compare network capacity values gained using these two algorithms with the one gained using SINR-based vertical handover algorithm. We show that dynamic spectrum assignment and access algorithms have considerable gain in network capacity compared to handover algorithm. These performance evaluation results prove the efficiency of the dynamic spectrum assignment and access technologies.

In this paper, dynamic spectrum access scenario where cognitive terminal having multi-homing capability dynamically access frequency bands assigned to different radio access networks is considered. For this scenario, QoS-guaranteed load-balancing dynamic spectrum access algorithm is proposed. For each cognitive terminal, this algorithm selects wireless access nodes to connect to. Also, it selects amount of data to transmit via each connection. Performance of the proposed dynamic spectrum access algorithm is compared to SINR-based and load-balancing vertical handover algorithms using simulation. It is shown that the proposed load-balancing dynamic spectrum access algorithm has considerable network capacity gain compared to both load-balancing and SINR-based vertical handover algorithms. Compared to load-balancing handover algorithm, this gain is equal to 10-40% depending on traffic rate per cognitive terminal.

High-definition video streaming and peripheral device communication on wireless access are promising applications of multi-gigabit 60-GHz wireless personal area networks (WPANs). For such different requirements, a frame design methodology is required which is different from that applied for the conventional wireless local area network (WLANs) and WPANs. This paper proposes a novel frame design methodology on PHY layer for the multi-gigabit 60-GHz WPANs supporting those applications. The proposed methodology is that preamble and header are designed to be further protected against payload, on the basis of 2-digit improvements in synchronization error probability and header error rate over payload bit error rate. In addition, the paper describes frame structures for control and data-communication in accordance with the proposed methodology. Performance evaluation is done by computer simulation to validate the proposed methodology. These frame structure designed by the proposed metrology has been applied in IEEE 802.15.3c WPANs systems.

A small-size software defined cognitive radio equipment that consists of a hardware platform and a software platform have been introduced. The hardware platform consists of a multiband/tunable RF unit with multiple switching circuits, signal processing unit consists of FPGA and CPU boards. The software platform consists of several managers that manage spectrum sensing and reconfiguration of communication systems and is worked on the Linux. The developed cognitive radio prototype combined by hardware and software platforms senses the signal level (RSSI) over 400 MHz-6 GHz bands and moreover identifies the system by using reconfiguration of software packages and checks RSSI, BER, connectivity, and so on. The software packages can configure specified wireless communication systems and consist of physical layer, MAC/DLC layer, IP layer, and application layer part of the systems. This paper also describes the sensing time and reconfiguration time.

The wireless sensor networks, which collect various data from a physical environment, are usually defined as an ad hoc network consisted of a huge number of tiny wireless sensor nodes whose computing power and battery capacity are limited. Because it is difficult to replace all of batteries on such a huge number of sensor nodes, maximization of the lifetime of the network has been one of the important research issues. To optimize such a network with a huge number of the sensor nodes, autonomous and decentralized computing and reconfiguration schemes can be considered suitable. Therefore, in this paper, we propose a routing reconfiguration method based on an autonomous optimization dynamics of the mutually connected neural network which minimizes its own energy function with autonomous and distributed computing. We show that the proposed method can optimize the routes for maximizing the lifetime of the sensor network, without any centralized computing nodes.

In order to design a simple and highly accurate channel estimator for wireless personal area network systems, this paper proposes Golay sequence aided channel estimation. To evaluate the performance of proposed channel estimation, bit error rate performance of single-carrier transmission with frequency-domain equalization has been analyzed by computer simulation. When 8PSK modulation and Reed-Solomon coding RS(255, 239) as forward error correction are used, the proposed Golay sequence aided channel estimation works very well in millimeter-wave and non line-of-sight fading environments with a 1.8 dB degradation of Eb/N0at 10-6of bit error rate against the ideal channel estimation, which is practically acceptable. Moreover, comparing with Chu sequence aided channel estimation, the proposed Golay sequence aided channel estimation improves 0.4 dB of Eb/N0at the bit error rate while achieving much less hardware than Chu sequence aided one, which is very important for mobile terminal applications.

Because of the unknown position of devices in ad-hoc network, it is difficult for the MAC to discover other devices by using directional antenna. This device discovery procedure needs extra signaling and costs considerable time, especially if there are a lot of devices. In this paper, on top of IEEE 802.15.3 MAC, we introduce the ultra superframe concept and propose an on-demand device discovery mechanism that significantly reduces signaling overhead, therefore speeds up the device discovery process and increases channel efficiency. Computer simulations show that, assuming up to 64 uniformly distributed devices, this MAC enhancement accomplishes device discovery procedure within 200 ms while keeping channel efficiency over 70% under 60 GHz channel environment.

This paper details a novel approach of developing a low-cost and high speed maritime ship-to-ship/shore mesh network to complement or replace satellite communications in narrow water channels or traffic lanes close to shorelines. To design the system, we gathered requirements from typical users of the system. We then carried out preliminary studies such as radio channel propagation over sea water, ship movement patterns, ship rocking and its effect on radio transmission and network connectivity to determine the feasibility of using a mesh network for maritime networks. We present the architecture and detail some of our routing and scheduling design considerations that address the unique challenges of the maritime environment and provide us with framework for providing fair and equal opportunity access to users.

Multiple access analysis is presented for pulsed direct sequence (DS) and hybrid DS time hopping (DS/TH) ultra-wideband (UWB) communications considering a Saleh-Valenzuela type clustered frequency selective Nakagami fading channel. A general analytical framework is developed for modeling the multiple access interference (MAI) in low-duty systems that is substantially complicated than analysis of more commonly known DS-code division multiple access (CDMA). Using Rake receiver with maximal ratio combining (MRC), we are able to produce a simple error rate expression for general number of combined paths. The theoretical results are then used for performance evaluation and comparison of the two systems. Results show that in multiple access environment, a DS/TH system may gain many fold performance improvement as compared to a DS system.

This paper investigates the adjacent channel interference (ACI) resistance of a multi-Gbps single carrier wireless personal area network (WPAN) operating in the 60 GHz millimeter-wave band. The significance of performance degradation due to ACI is investigated corresponding to varying factors such as types of modulation and radio frequency (RF) hardware impairments. The level of modulation scheme is found to change the system resistance against ACI considerably. RF hardware impairments such as power amplifier (PA) non-linearity and phase-locked loop (PLL) phase noise are also major factors affecting ACI generation. The tolerable ACI for WPAN system design is defined as the ACI that causes 0.5 dB degradation in required signal to noise ratio (SNR) at bit error rate (BER)=10-6. It is found that for a system employing pi/2 binary phase shift keying (BPSK) with PA output backoff (OBO)=3 dB, ACI=13.5 dB causes 0.5 dB BER degradation. For systems employing quadrature phase shift keying (QPSK) modulation, the tolerable ACI with PA OBO=3 dB and 5 dB are observed at 9 dB and 15 dB, respectively. For modulation schemes with higher levels such as the 16-quadrature amplitude modulation (QAM) system with PA OBO=3 dB and 5 dB, the tolerable ACI of 1 dB and 5 dB are observed. Next, the maximum ACI resistance is defined as the tolerable ACI by the system before the BER performance degrades and saturates towards 0.5. The performance of pi/2-BPSK system with PA OBO=3 dB has maximum resistance against ACI up to 25 dB before the BER saturates towards 0.5. Similar performance can be observed in QPSK system, but with PA OBO increased to 5 dB. Systems with 16-QAM are found to saturate to BER=0.5 beyond ACI=10 dB. Additionally, the presence of PLL phase noise is found to severely compromise the system performance particularly those with higher modulation levels. ACI as low as 0 dB is found to cause error floor to 16-QAM systems.

This paper proposes a user-centric access point selection scheme to minimize the number of unnecessary reconfigurations of cognitive terminal. In this scheme, number of terminal reconfigurations is defined based on the dwell-time of terminal which is estimated from user’s mobility and coverage area of the access point (AP). Each terminal selects one AP from a candidate list that is generated based on user’s preferences. Information needed for the selection scheme is obtained from both network-side and terminal-side entities. Four different algorithms are investigated in order to find the best combination of dwell-time and other parameter such as load of APs, to minimize the number of reconfigurations and to achieve load balancing for Radio Access Networks simultaneously.

The multi-Gbps wireless personal area network (WPAN) operating at 60-GHz is being standardized in the task group of IEEE 802.15.3c. To deal with the multi-path delay spread in non-line-of-sight (NLOS) environments, single-carrier frequency-domain equalization (SC-FDE), a.k.a., single-carrier block transmission (SCBT), is used in the physical (PHY) layer design. The low-density parity-check (LDPC) coding is considered as the high-performance channel coding scheme due to its good tradeoff between performance and complexity. A series of structured LDPC designs with very short codeword length of 576 are being adopted in one of the major proposals for IEEE 802.15.3c. The short codeword length helps to reduce the decoding complexity of LDPC. We evaluated the 576- length structured LDPC codes in SC-FDE system and found they have very good fixed point decoding performance. They are very promising in supporting ultra high-data-rate transmission with low complexity in 60-GHz WPAN (IEEE 802.15.3c).

The multi-Gbps wireless personal area network (WPAN) using 60-GHz is being standardized in the task group of IEEE 802.15.3c. In the physical (PHY) layer design, there are two competitive techniques, one is orthogonal frequency division multiplexing (OFDM) and the other is single-carrier frequency-domain equalization (SC-FDE), a.k.a., single-carrier block transmission (SCBT). This paper compared the performance of low-density parity-check (LDPC) coded OFDM and SC-FDE under hardware impairments including analog-to-digital converter (ADC) resolution, non-linear distortion induced by 60- GHz power amplifier (PA), and phase noise of 60-GHz PLL circuits. The simulation results show that SC-FDE has much better performance than OFDM under hardware impairments of 60-GHz devices and circuits.

This paper introduces the concept, features and architecture of a software defined cognitive radio system: Cognitive Wireless Clouds (CWC) that can realize user-centric and scalable network based on unique cognitive spectrum access, cross-network signaling, network optimization, and fast reconfiguration methods. Then, this paper shows results of feasibility studies on a software defined cognitive radio (SDCR) terminal that can access to the CWC. This includes the configuration of the SDCR terminal and a measurement data for spectrum sensing period and reconfiguration period by using software packages of W-CDMA and IEEE802.11a.

New services on trains are attracting a great deal of attention throughout Europe and Asia where trains are one of the most important forms of transportation. We introduced two information services on bullet-trains; Internet access and video. There are three technical challenges posed by seamless handover at 300 hn/h, aggregation of multiple access, and attack-tolerant communications. We proposed a network architecture to solve them based on the requirements of these services. Due to its extendibility and flexibility, new services that will be introduced in the future can be integrated easily. We are currently developing a tested for experimental evaluations.

This paper proposes an air interface for ultra high-speed millimeter wave (60 GHz) systems which have been under standardization process at IEEE 802.15.3c: the proposed channel plan permits ease of portable device implementation employing the major crystal oscillator used in CDMA cellar phones. The proposed transmission modes offer much greater scalability, covering from several tens Mbps to over 4 Gbps. The proposed preamble employs Golay codes, providing sufficient robustness against wireless environment being subject to the characteristics of millimeter wave with reduced hardware complexity. Common mode is a novel technique to communicate with single carrier (SC) and OFDM camps with multi rates up to around 1.5 Gbps. This technique gives the proposed systems easy expandability from SC to OFDM or other SCs and vice versa.

A software defined cognitive radio prototype that consists of a hardware platform and a software platform has been developed. The hardware platform consists of a multi-band antenna supported from UHF band and 2-5 GHz band, multiband RF unit, signal processing unit consists of FPGA and CPU boards. The software platform consists of several managers that manage spectrum sensing and reconfiguration of communication systems by changing software packages. The software packages (called as "waveform") configure specified wireless communication systems and consist of physical layer, MAC/DLC layer, IP layer, and application layer part of the systems. This paper introduces the configuration of the hardware and software platforms and addresses a measurement result of spectrum sensing period and reconfiguration period by using software packages of W-CDMA and IEEE802.11a.

We propose a new space division multiplexing-orthogonal frequency division multiplexing system using reduced-complexity-and-latency detection and channel estimation algorithms. It is important to reduce a latency from receiver processing because the latency degrades performances of wireless systems in a mobile fading environment. In this paper, we evaluate and discuss bit error rate performance and computational complexity of the proposed system. From simulation results, we observe that our proposed estimation scheme improves the accuracy more than conventional minimum mean square error based schemes, and that the proposed system outperforms a maximum likelihood detection based system in a mobile fading environment. Moreover, we confirm that the proposed system is superior to the conventional schemes from the points of not only the performance but also the complexity.

To achieve ultra high speed (several gigabits/s) transmission over 60 GHz system efficiently, this paper proposes Automatic Device Discover (ADD) and frame aggregation. The computer simulation results show good feasibility of handling directional antenna for ultra high speed transmission and highly efficient transmission up to 87 percent over 4.094 Gbps PHY-SAP with 8PSK modulation.

The millimeter-wave 60-GHz wireless personal area network (WPAN) is being standardized by the IEEE 802.15 Alternative PHY Task Group 3c (IEEE 802.15.3c). The physical (PHY) layer design targets data rates of multi-giga bits per second (multi-Gbps). In this paper, two physical (PHY) layer designs based on single-carrier frequency-domain equalization (SC-FDE) and orthogonal frequency division multiplexing (OFDM) were compared in packet error rate (PER) and throughput. The performance evaluation and comparison were conducted with the non-linear distortion, induced by the 60-GHz power amplifier (PA), taken into account. It was shown that the PHY layer design based on SC-FDE has much better PER performance and higher throughput than the one based on OFDM. The SC-FDE based PHY layer design exhibits itself as a strong candidate for the 60-GHz WPAN (IEEE 802.15.3c) standard.

The paper proposed a multi-layer space-time block coded orthogonal frequency division multiplexing (multilayer STBC OFDM) scheme. It combines the spatial diversity and spatial multiplexing in order to exploit the benefits of both techniques. The transmit antennas are divided into several layers and each layer is encoded by STBC. The antennas transmit OFDM signals in order to deal with frequency-selective fading channels. In addition to exhaustive detection scheme which applies the same detection at each subcarrier independently, the subcarrier correlation was exploited to develop two subcarrier-grouping based detection schemes. The subcarriers bound into the same group share the same detection parameters, e.g., layer detection order or nulling matrices, which are obtained at the center subcarrier of that group. The proposed schemes can significantly reduce the complexity with very small performance loss. The simulation results show that compared with exhaustive detection scheme, the propose detection scheme is capable of reducing 51.79% complexity with only 0.5dB performance loss for 4times4 system, and reducing 69.96% complexity with only 1.0dB performance loss for 6times6 system.

In the past years we have been focusing on developing DPC-OF/TDMA (dynamic parameter controlled orthogonal frequency and time division multiple access) system (Harada et al., 2003) which targets at beyond 100 Mbps data rate. In this paper, we extend DPC-OF/TDMA to support higher data rates with the same bandwidth of its original version. The evolved DPC-OF/TDMA is based on our newly proposed multi-layer STBC OFDM (multi-layer space-time block coded orthogonal frequency division multiplexing) scheme. This scheme combines the spatial diversity and spatial multiplexing in order to exploit the benefits of both techniques. To evaluate the performance of the evolved DPC-OF/TDMA, we conduct simulations under different MIMO antenna configurations. As the packet error rate (PER) is required to be 1.0e-2 with Eb/No lower than 20.0dB, the evolved DPC-OF/TDMA can reach data rate of 921.6Mbps while the bandwidth is 128MHz. The achieved average spectral efficiency is 7.2bit/s/Hz.

This paper discusses system design strategies and performance evaluation for adaptive modulation techniques used in new and up-and-coming wireless access systems. After a brief discussion on basic modulation parameter (MP) settings as well as functionalities specific for adaptive modulation systems, this paper discusses how to design a narrowband time-division multiple-access/time-division duplex (TDMA/TDD)-based adaptive modulation system and confirms through laboratory experiments that the narrowband TDMA/TDD-based adaptive modulation system dramatically enhances system robustness to multipath fading and flexibility in throughput and transmission quality control. Next, as an extension to many fields of application for adaptive modulation, this paper discusses subcarrier-level adaptive modulation for orthogonal frequency-division multiplexing (OFDM)-based one-cell reuse broadband cellular systems. One key result is that nonsubcarrier transmit power control (TPC) applied adaptive modulation systems can achieve almost the same performance as subcarrier TPC applied adaptive modulation systems provided that the required signal-to-noise-plus-interference power ratio increment in the MP sets is designed to be sufficiently small. Finally, this paper explains the dynamic parameter controlled OFDM/TDMA system as an example of a practical scheme for one-cell reuse broadband wireless access systems. The analysis confirms that this adaptive system can achieve a spatial reuse efficiency defined by (average throughput in multicell conditions)/(average throughput in single cell conditions) of 0.8 as well as an average media access control payload throughput of about 150 Mb/s using about 100 MHz of bandwidth.

Abstract R&D on new generation mobile network has attracted a growing interest over the world on the background of rapid market growth for 2nd and 3rd generation cellular networks and wireless LANs/MANs. The National Institute of Information and Communications Technology (NICT) started the New Generation Mobile Network Project in April 2002, and has developed fundamental technologies to enable seamless and secure integration of various wireless access networks such as existing cellular networks, wireless LANs, home networks, intelligent transport systems (ITS), the Beyond‐3G (B3G) cellular and other wireless access systems. This paper overviews the achievements of the project focusing on network and access technologies. Copyright © 2007 John Wiley & Sons, Ltd.

3.4-4.2 and 4.4-4.9 GHz microwave bands are regarded as promising candidates in the possible frequency bands that can be assigned to the 4G mobile communication systems. In order to contribute to the frequency allocation, we conducted radio propagation experiments by use of 3.35 GHz carrier frequency in macro-cellular environments. For the experiments, we developed a measurement system calculating received signal power and delay power profiles by employing 215-1 PN sequences with a sampling rate of 160 Msample/s, which enables the high accuracy of radio propagation measurements. This paper describes an outline of the radio propagation experiments, and presents the results of rms delay spread distribution, in addition to the evaluation of two propagation models: Walfisch-Ikegami (WI) and extended WI models

We propose a new multiple-QR-decomposition assisted group detection (multi-QRD-GD) algorithm for the development of reduced-complexity-and-latency multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) receivers. In addition, we investigate an effect of adaptive grouping (AG) based on received signal-to-noise power ratio for multi-QRD-GD. In this paper, we describe the functions of the multi-QRD-GD algorithm and AG scheme. Then, we compare bit error rate (BER) performances of the proposed multi-QRD-GD and conventional detection algorithms by computer simulations. In addition, we compare the computational complexities of the algorithms

We propose a multi-layer space-time block coded orthogonal frequency division multiplexing (multi-layer STBC OFDM) scheme. It combines the spatial diversity and spatial multiplexing in order to exploit the benefits of both techniques. The transmit antennas are divided into several layers and each layer is encoded by STBC. The antennas transmit OFDM signals in order to deal with frequency-selective fading channels. In addition to exhaustive detection scheme which applies the same detection at each subcarrier independently, we exploit the subcarrier correlation to develop a subcarrier-grouping based detection scheme (SGD scheme). The subcarriers bound into the same group share the same detection parameters, e.g., layer detection order which is obtained at the center subcarrier of that group. This feature can significantly reduce the detection complexity with very small performance loss. The simulation results show that compared with exhaustive detection scheme, the proposed SGD scheme is capable of reducing 36.13% complexity with less than 1.0 dB performance loss for 4times4 system, and reducing 52.44% complexity with about 1.3 dB performance loss for 6times6 system, respectively

During these years we have been focusing on developing ultra high-data-rate wireless access systems. One of such kind of systems is called DPC-OF/TDMA (dynamic parameter controlled orthogonal frequency and time division multiple access) which targets at beyond 100 Mbps data rate. In order to support higher data rates, e.g., several hundreds of mega bps or even giga bps, it is necessary to evolve DPC-OF/TDMA on MIMO-OFDM (multiple-input multiple-output orthogonal frequency division multiplexing) platform. In this paper, we propose two MIMO-OFDM evolution schemes for DPC-OF/TDMA: M1 scheme and M2 scheme. M1 scheme is based on the combination of V-BLAST (vertical Bell laboratories layered space-time architecture) and OFDM. It invests all transmit antennas on multiplexing while exploits no diversity in the transmitter. M2 scheme is based on multi-layer space-time block coded OFDM (multi-layer STBC OFDM). This scheme achieves compromise between multiplexing and diversity in the transmitter. We conduct exhaustive simulations and find that each evolution scheme has its own prevailing area. When the receive diversity order is limited, M2 scheme has better performance since it embeds transmit diversity; as the receive diversity order increases, the performance gap between the two schemes shrinks and finally M1 scheme prevails in performance. Therefore, the proper choice depends on the system configuration, i.e., the numbers of transmit and receive antennas

We propose a multi-layer space-time block coded orthogonal frequency division multiplexing (multi-layer STBC OFDM) scheme. It combines the spatial diversity and spatial multiplexing in order to exploit the potentials of both techniques. The transmit antennas are divided into different layers and each layer is composed of a small number of antennas. These antennas transmit OFDM signals in order to deal with frequency- selective fading channels. In each layer, Alamouti's space-time codes are applied at individual subcarriers to provide spatial diversity gain. Exhaustive simulations are conducted to compare the proposed scheme with the full-multiplexing V-BLAST OFDM under the same spectral efficiency condition. We find each scheme has its own prevailing area. When the receive diversity order is limited, the proposed Multi-Layer STBC OFDM has better performance since it embeds transmit diversity; as the receive diversity order increases, the performance gap between the two schemes shrinks and finally V-BLAST OFDM prevails in performance. Therefore, the proper choice depends on the system configuration, i.e., the numbers of transmit and receive antennas.

This paper proposes a channel estimation technique for multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM)/time division multiple access (TDMA) (MIMO-OFDM/TDMA) cellular systems based on the dynamic parameter controlled-OF/TDMA (DPC-OF/TDMA) systems. In the proposed scheme, impulse responses of all the transmit antennas are multiplexed in the time domain using a carrier interferometry (CI) signal, which is equivalent to an impulse signal, and each impulse response is discriminated using a time window with the length of the maximum delay time of delayed paths, in order to estimate a channel state information (CSI) using only 64 subcarriers. Computer simulation confirms that the proposed channel estimation scheme is effective even in the case of 64 subcarriers under MIMO and multi-cell conditions

In one-cell-frequency-reuse MIMO (multi input multi output) - OFDMA based TDMA (OF/TDMA) systems, we face a problem that communication is blocked by interferences from adjacent cells. To solve this problem, an AMC (adaptive modulation and coding) scheme that is controlled by estimating DUR (desired signal to undesired signal power ratio) would be most promising. However, there is no accurate DUR estimation method using spreading codes for OF/TDMA systems due to the asynchronous FFT so far. In this paper, we propose a novel DUR estimation method by adding IFFT and time-window and introducing CI (carrier interferometry). The proposed DUR estimation method can separate the desired signal from a received signal even if FFT is asynchronous

In an AMS/OFDM system, base station is in control of the modulation level of each subcarrier, and then, adaptive modulated packet is transmitted from the base station to the mobile station. In this case, the mobile station is required the modulation level information (MLI) to demodulate the received packet. The MLI is generally transmitted as a data symbol, therefore, the throughput is degraded. In an OFDM, the channel response at a particular subcarrier frequency is not supposed to be totally different from its neighboring frequencies, and hence, they mast have correlation which depends on the coherence bandwidth of the channel B/sub c/. If we could assign the same modulation level for coherently faded subcarrier block, MLI is required only one time for each subcarrier block. Moreover, we can assign the data on the empty space of pilot signals for increasing the total transmission. In this paper, we propose an adaptive subcarrier block modulation with differentially modulated pilot symbol assistance for downlink OFDM using uplink delay spread.

The next-generation wireless access system named DPC-OF/TDMA, which is capable of achieving 100 Mbps carrier bit rate under high mobility environment, has been proposed and is being developed. For the realization of this system, large size of cellular zone is required in order to increase system capacity. However, propagation delays between an access point (AP) and mobile stations (MSs) managed by the AP increase as the cellular zone size is large. These increased propagation delays falls system throughput. In this paper, application of PR-DSMA, which is robust against large propagation delays, to the MAC layer protocol of DPC-OF/DMA is proposed to solve this problem. This paper also conducts performance evaluation in terms of Automatic Request control (ARQ) and cell radius by computer simulation.

In this paper, we propose a wireless access scheme supporting data transmission beyond 1 Gbps with the system bandwidth of 160MHz for the indoor wireless applications. This ultra high-data-rate wireless access scheme is based on the multiple-input multiple-out and orthogonal frequency division multiplexing (MIMO-OFDM) techniques. The Bell laboratories layered space-time architecture (V-BLAST) is used for transmitting signals of different antennas at the same subcarrier. The receiver is based on the zero-forcing decision-feedback-equalization (ZF-DFE) detection method at individual subcarriers. The frame/slot structures are also introduced. A 512-point IFFT is used to generate OFDM signals at each transmit antenna. Two antenna configurations are investigated: One is with 4 transmit antennas (TX) and 8 receive antennas (RX); the other is with 6 TX and 8 RX. We use a typical indoor multipath channel to evaluate the proposed scheme. The simulation results show that several data rates beyond 1 Gbps can be achieved by using the proposed scheme when the packet error rates (PER) are required to be under 1.0e-2 with Eb/No no larger than 20.0 dB. The achieved highest data rate satisfying these requirements is 1.728 Gbps with the average spectral efficiency being equivalent to 10.8 bit/s/Hz.

This paper proposes a channel estimation technique for the dynamic parameter controlled - orthogonal frequency and time division multiple access (DPC-OF/TDMA) system. In the proposed scheme, channel impulse response that represents channel state information (CSI) is measured using a carrier interferometry (CI) which is equivalent to impulse transmission. Moreover, because the minimum unit (subchannel block) of subcarriers to be allocated to each terminal is 64 subcarriers, to achieve high accuracy of the estimated CSI with a spreading factor of 64, code-multiplexed pilot signal is applied to identify base station (BS) in the cell search process, and CSI between a terminal and each transmit antenna element in the BS is detected using a time-domain-multiplexed CI signal for ease of extension of the DPC-OF/TDMA to multi-input multi-output (IMO) systems. Furthermore, we will also propose a CSI estimation scheme flexible to the plural subchannel block assignment cases. Conmputer simulation confirms that the proposed scheme can estimate the CSI regardless of the number of subchannel blocks assigned to each terminal.

In this paper, we propose an adaptive power distribution algorithm which aims at improving the spectral efficiency in orthogonal frequency division multiplexing (OFDM) under the condition that the target bit error rate (BER) should be maintained and the transmit power threshold should not be exceeded. This algorithm is based on an iterative mechanism. In every iteration, the power and the corresponding number of bits are distributed to the subcarrier at which there is a modulation mode demanding the minimum average incremental transmit power per incremental bit to guarantee the pre-designated bit error rate (BER) performance. The iterative procedure terminates once the transmit power threshold is reached. The performance investigations show the proposed adaptive power distribution algorithm always outperforms the scheme of equal power distribution in a large dynamic range of transmit power threshold. Moreover, the performance improvement is very large when the transmit power threshold is required to be low.

The combination of OFDM and multiple antennas in either the transmitter or receiver is attractive to increase a diversity gain. However, multiple antennas system requires an antenna separation of 510 /spl lambda/ to keep the correlation coefficient below 0.7 for the space diversity, so this may be difficult to implement in a mobile station with high mobility. Recently, the polarization transmit diversity is considered in a mobile station. However, polarization transmit diversity requires twice transmit powers to compare with the conventional transmit diversity, since only vertically polar antenna cannot receive the horizontal signal components. In this paper, we express the cross correlation of each polarization antenna and the cross polarization discrimination (XPD) of multiple polarization antennas with simple model, and we propose a wideband OFDM using Alamouti coded heterogeneous polarization antennas for reducing the previous problem. From the simulated results, the proposed system shows better BER performance than that of the conventional STBC/OFDM.

We propose a new generation mobile communication system that can realize 100 Mbps carrier bit rate under high mobility environment and can access the IP network easily. The new system is based on dynamic parameter controlled orthogonal frequency and time division multiple access (DPC-OF/TDMA) in which users share "slots" that use a certain number of subcarriers and a certain number of OFDM symbols. To access the slots, mobile stations use a packet-reservation-based protocol: packet reservation dynamic time-slotted multiple access (PR-DSMA). In addition, to avoid cochannel interference from adjacent cells and increase frequency utilization efficiency, we use an adaptive modulation scheme that is based on an interference detection algorithm. We mention the concept and the basic transmission performance of the proposed system.

This paper proposes a novel time alignment control (TAC) for uplink dynamic parameter controlled orthogonal frequency and time division multiple access (DPC-OF/TDMA), which has been suggested for development of new generation mobile communication system. The purpose of the proposed TAC is reducing an influence of multiple access interference (MAI) by propagation delays (PDs) due to differences of distances between accessing mobile stations (MSs) and an access point (AP). The proposed TAC estimates PDs of all MSs and informs the estimates to them. MSs accessing to AP control their transmission timings according to the informed estimates and compensate PDs. This paper examines the uplink DPC-OF/TDMA with the proposed TAC in term of slot error rate (SER) performances by computer simulation. The result shows that the proposed TAC performs precisely to compensate PDs, and that the uplink DPC-OF/TDMA with proposed TAC enables an equivalent performance to an ideal one under no PDs condition.

The link adaptation scheme in the current IEEE 802.11a technical specifications only consider channel variation in the time-domain, and assume all the data subcarriers use the same modulation mode and coding rate once the transmission data rate is determined. However, in the frequency-selective fading scenario, the BER performance is severely degraded by OFDM subcarriers where deep fading occurs. We propose a frequency-domain link adaptation scheme for IEEE 802.11a, which is based on a modified adaptive bit and power loading algorithm and a modified pilot pattern. Simulation results show our proposal can greatly improve performance when perfect channel information is obtainable. We also investigate the performance of the proposed scheme in two channel mismatch situations, and show it is capable of achieving large performance gain in the most favorable environment for IEEE 802.11a, the low mobile speed environment.

We propose a combinational scheme of adaptive beamforming and adaptive loading for orthogonal frequency division multiplexing (OFDM). Two adaptive beamforming schemes based on least mean square (LMS) algorithm and pre-FFT combining are used to obtain the space diversity gain. Their difference, which lies in either the frequency-domain or time-domain pilot vector is used in the beamforming. In order to counter the severe frequency-selective fading which is inevitable in broadband wireless communications, we use the frequency-domain adaptive loading to load the bits and transmit power to the individual subcarriers. The performance investigations show that the combinational scheme based on the adaptive beamforming and adaptive loading is very effective in improving the performance of OFDM packet transmission.

The link adaptation scheme in the current orthogonal frequency division multiplexing (OFDM) systems such as IEEE802.11a only consider the channel variation in the time-domain, and assume all the data subcarriers use the same modulation mode and transmit power once the data rate is determined. However, in the frequency-selective fading environments, the error probability performance of OFDM is severely degraded by the subcarriers where the deep fading occurs. In order to deal with this issue, we propose a coded frequency-domain link adaptation scheme for OFDM packet transmission in the time division duplex (TDD) mode. This scheme is based on the concatenation of the channel coding and the adaptive bit and power loading. The simulation results show the proposed scheme can significantly improve the packet error rate (PER) performance compared with other schemes. Further investigations also show that it can contribute to large performance gain even in the challenging high-speed environments.

We measured path loss in a macro cellular environment in 5 GHz band. In this paper, existing propagation models for path loss prediction in UHF band are applied to 5 GHz band, and the estimates are compared with the measured data. From the results of the comparison, we describe the differences between the measured and the estimated data.

OpenMP has attracted widespread interest because it is an easy-to-use parallel programming model for shared memory multiprocessor systems. Implementation of a "cluster-enabled" OpenMP compiler is presented. Compiled programs are linked to the page-based software distributed-shared-memory system, SCASH, which runs on PC clusters. This allows OpenMP programs to be run transparently in a distributed memory environment. The compiler converts programs written for OpenMP into parallel programs using the SCASH static library, moving all shared global variables into SCASH shared address space at runtime. As data mapping has a great impact on the performance of OpenMP programs compiled for software distributed-shared-memory, extensions to OpenMP directives are defined for specifying data mapping and loop scheduling behavior, allowing data to be allocated to the node where it is to be processed. Experimental results of benchmark programs on PC clusters using both Myrinet and fast Ethernet are reported.

Increasingly large-scale clusters of PC/WS continue to become majority platform in HPC field. Such a commodity cluster environment, there may be incremental upgrade due to several reasons, such as rapid progress in processor technologies, or user needs and it may cause the performance heterogeneity between nodes from which the application programmer will suffer as load imbalances. To overcome these problems, some dynamic load balancing mechanisms are needed. In this paper, we report our ongoing work on dynamic load balancing extension to Omni/SCASH which is an implementation of OpenMP on Software Distributed Shared Memory, SLASH. Using our dynamic load balancing mechanisms, we expect that programmers can have load imbalances adjusted automatically by the runtime system without explicit definition of data and task placements in a commodity cluster environment with possibly heterogeneous performance nodes.

RHiNET-2/NI is a network interface for a parallel and distributed computing system with network connected PCs. The core of the network interface is an ASIC network controller chip Martini, which provides low-latency and large-bandwidth communication. Evaluation results show that it achieves almost full bandwidth of the 66MHz/64bit PCI bus, which is much larger than that of Myrinet-2000. The performance of a small prototype parallel system achieves almost linear speed up.

A flexible symbol-timing synchronization method is a one that uses a common sampling clock to find synchronization points for radio communication systems that have different symbol rates. This method estimates synchronization points from state patterns calculated using the symbol rate, sampling clock, and number of observed symbols. Decreasing the number of state pattern is one of best ways to reduce the amount of device resources needed to store the patterns. In this paper, we propose a new pattern generation method in which the number of generated patterns does not increase when the sampling clocks of the communications systems are different. To show the feasibility of this method for symbol-timing synchronization, we analyzed a relationship between the number of samples and the number of state patterns and calculated the BER (bit error rate) in AWGN (additive white Gaussian noise) and one-path flat Rayleigh fading environments by computer simulation.

We propose a new simple timing synchronization method for the orthogonal frequency division multiplexing (OFDM) packet transmission systems in this paper. The conventional synchronization method adopts to calculate signal correlation by multiplication employing the feature of preamble or cyclic prefix in burst packet. However, multiplication circuit makes volume of digital signal processing (DSP) larger and more complex. In order to design a low-complex receiver, we replace the complex process by multiplication with the simple one by subtraction in the proposed method. We evaluated the performance of the proposed method from view points of timing offset mean, variance and bit error rate (BER) performance by computer simulation. Adopting simpler process, the proposed method shows that it can acquire quite smaller variance of timing offset and has equivalent BER performance to the conventional method under both slow and fast multipath fading environments.

The paper proposes a system configuration for a private mobile network that is constructed by several mobile terminals and needs no base station infrastructure, as in ad hoc networks. This configuration uses an autonomous packet routing algorithm that provides an intelligent wireless network structure. Our packet routing algorithm senses the preferred paths for packet transmission, which are dynamically generated among terminals according to traffic conditions. We discuss the entire system configuration where such a packet routing algorithm is suitably supported by the lower layer protocols, such as control sequence configuration, transmission frame format, and transmission schemes. We assume the VHF band transmission that is widely used for private systems and assume the slotted-ALOHA based packet transmission protocol. One of the most significant goals of our system is to achieve IP based service transmission on limited bandwidth. Essential logical channel signal introduction and effective slot format are investigated.

Over-the-air reconfiguration is a key characteristic of software defined radio communication systems. It offers great advantages in terms of cost-effective software deployment to a large number of user terminals. It also enables manufacturers and service providers to introduce additional features in hardware components after their shipment. Even though automatic repeat request (ARQ) or forward error correction (FEC) schemes are used for error control in transmission of configuration data (CD), the received configuration data may not be error free, therefore, the erroneous CD result in implementation of faulty circuits. In order to reduce the effects of the CD error, fault-tolerant processing is provided in circuits to be reconfigured over the air. We designed fault-tolerant digital filters based on redundant residue number arithmetic. A computer simulation model is described and simulation results are presented for the filters operating in the presence of simulated hardware failures.

A prototype of a wireless transmission system has been developed that can transmit multimedia-information data at a maximum rate of 4.608 Mb/s in the 5.2-GHz carrier frequency band. It is based on a multicode transmission scheme that uses cyclic shifted-and-extended M-sequences and is designed for applications such as intelligent transport systems (ITS) and future broadband mobile communication systems. The proposed scheme is highly robust against high-speed multipath fading. The transmission performance of the prototype system was measured in field trials at an outdoor ITS experimental course. The real-time data-transmission rate between the base and mobile stations was 4.608 Mb/s at a vehicle speed of 80 km/h.

This paper proposes a new amplitude and phase compensation scheme for OFDM packet transmission systems in order to compensate severe and time-variant fluctuation of the received signal amplitude and phase under fast fading environment. The proposed scheme, in addition to the conventional scheme that averages and updates the estimated propagation characteristics on each subchannel, detects subchannels that are momentarily distorted by noise and inter-carrier-interference (ICI) over the fast frequency-selective channels, or by the sudden intercept owing to the shadowing effects. The information of the detected subchannel is used to improve accuracy of the compensation when update the estimated propagation characteristics. The performance of the proposed OFDM packet transmission system was evaluated from several aspects by computer simulation. As a result, by using the proposed scheme, packet error rate (PER) is improved under a high-mobility environment in comparison with the conventional scheme.

We newly propose a protocol stack of a multiservice terminal that can handle conventional wireless communication systems as a seamless network. To confirm the feasibility of our proposed stack, we developed a demonstration system that realizes a seamless communication between Japanese Personal Handy Phone system (PHS) and wireless LAN system based on IEEE802.11b, and measured transmission characteristics included the received-signal power of the wireless LAN signal at the multiservice terminal, time-variant state of the multiservice terminal, and the response time when "ping" commands are sent to a server.

This paper proposes a radio-on-fiber (ROF) based road-vehicle communication system. In the proposed system, several radio base stations (RBSs) are connected with one control station (CS) by an ROF technology. All RBSs use the same frequency band of millimeter-waves to communicate with mobile stations (MSs). Consequently, one virtual large cellular zone based on the millimeter wave band can be constructed using several RBSs controlled by one CS. Based on the virtual large cellular zone, handover is performed. However, in one virtual cellular zone, interference occurs at the boundaries between adjacent cellular zones by RBSs. To overcome the interference, we use code division multiplexing as a modulation scheme to communicate between MSs and RBSs. The feasibility is confirmed by developing an experimental testbed and performing field trials for the downlink, and we discuss the effect of RBS cell size.

In order to quantify the performance degradation of software radio communication systems due to faults of digital circuits which are configured by over-the-air download of configuration data, a 16-QAM demodulator with LUT-based reconfigurable square root raised cosine filters is designed. After over-the-air download of configuration data and reconfiguration is completed at the 16-QAM demodulator, BER performance of the reconfigured demodulator in an AWGN channel is evaluated by computer simulations. Furthermore, we develop a new radio transmission scheme of the configuration data. Our results show that 25 percent reduction in the number of symbols to transmit configuration data can be achieved without significant BER degradations.

We propose an access protocol that enables effective radio resource utilization in the road-vehicle communication (RVC) system. The proposed access protocol is based on reservation slotted ALOHA and the dynamic data slot assignment scheme, and thereby improves transmission performances. In the proposed access protocol, a base station broadcasts channel usage information to mobile terminals. Each mobile terminal sends a request packet or data packets according to the information. The base station dynamically assigns data slots to each terminal. In this paper, transmission performances of the proposed access protocol applied to a radio-on-fiber (ROF) based road-vehicle seamless communication system are evaluated by using computer simulations. From the result, it is confirmed that the proposed access protocol improves system capacity compared with the conventional slotted ALOHA protocols.

A radio-on-fiber (ROF) based road-vehicle communication system is described in which several radio base stations (RBSs) communicate with a control station (CS) over ROF connections. The RBSs use the same millimeter-wave frequency band to communicate with mobile stations (MSs). The result is one large virtual cellular zone encompassing several RBSs controlled by one CS. However, in one virtual cellular zone, interference arises at the bound between adjacent cellular zones because the RBSs in each zone transmit their signals using the same frequency band. To minimize this interference, code division multiplexing is used to modulate the signals sent between the MSs and RBSs. Testing using an experimental course demonstrated that by using this system, we can achieve an error-free continuous communication system with a maximum transmission rate of 4.608 Mbps.

Proposes a scheme to realize a high-performance communication facility using a commodity network. This scheme does not require any special hardware or hardware-specific device drivers in order to adapt to many kinds of network interface cards (NICs). In this scheme, a reliable lightweight network protocol is handled directly on a data link layer called by a network device driver. An interrupt reaping technique is proposed to eliminate the hardware interrupt overhead when an application waits for a message. PM/Ethernet, an instance of the scheme, is implemented on Linux with minimal modification to the Linux kernel, and existing network device drivers are used without any modification. Using Pentium III 500-MHz PCs on Packet Engine's G-NIC II Gigabit Ethernet NIC, it achieves 77.5 MB/s bandwidth and 37.6 /spl mu/s round-trip time latency compared to that of TCP/IP, which achieves 46.7 MB/s bandwidth and 89.6 /spl mu/s round-trip time latency. The NAS parallel benchmark IS results show that MPI on PM/Ethernet achieves 75% better performance than MPI on TCP/IP and is 7.8% slower than that of MPI on Myrinet PM.

This paper proposes an autonomous relay access algorithm that provides an intelligent wireless network structure for an inter-vehicle communication system. The proposed algorithm introduces a special classification among mobile terminals and assigns terminals to one of several terminal groups, which are adaptively and autonomously constructed according to traffic conditions. The proposed algorithm uses the terminal groups to conduct relay access transmission among terminals, and achieves a higher rate of successful inter-terminal transmission. Computer simulation confirms that the proposed algorithm can achieve a lower blocking probability than an algorithm without a relay access scheme.

This paper introduces a high performance communication middle layer, called PM2, for hetero-geneous network environments. PM2 currently supports Myrinet, Ethernet, and SMP. Binary code written in PM2 or written in a communication library, such as MPICH-SCore on top of PM2, may run on any combination of those networks without re-compilation. According to a set of NAS parallel benchmark results, MPICH-SCore performance is better than dedicated communication libraries such as MPICH-BIP/SMP and MPICH-GM when running some benchmark programs.

A high performance communication facility, called the GigaE PM, has been designed and implemented for parallel applications on clusters of computers using a Gigabit Ethernet. The GigaE PM provides not only a reliable high bandwidth and low latency communication function, but also supports existing network protocols such as TCP/IP. In the design of the GigaE PM, it is assumed that the Gigabit Ethernet card used has a dedicated processor and its program can be modied. A reliable communication mechanism for a parallel application is implemented on the rmware while existing network protocols are handled by an operating system kernel. A prototype system has been implemented using an Essential Communications Gigabit Ethernet card. The performance results show that a 48.3 s round trip time for a four byte user message, and 56.7 MBytes/sec bandwidth for a 1,468 byte message have been achieved on Intel Pentium II 400 MHz PCs. We have implemented MPICH-PM on top of the GigaE PM, and evaluat...

An adaptive zone configuration system for land mobile communications was examined using a developed circular, 8-element array antenna. Simulations were performed to investigate the effectiveness of the adaptive zone configuration system compared with the present omni directional zone system. It was found that the adaptive zone configuration system was more effective than the omni zone system in controlling the blocking rate (BR) and the ratio of the mean power of the communication zone.

This paper proposes a new parallel transmission scheme using cyclic codes generated from a modified M-sequence, which is biased with constant direct current (dc) on a M-sequence and inserted guard chips before and after this biased M-sequence. In the proposed system, the orthogonality of codes is kept not only between parallel transmission channels but also between direct and delayed waves within the guard chips. In this paper we apply a code and chip timing joint recovery scheme based on the feature of the guard chips of a modified M-sequence and evaluate the bit error rate performances by computer simulations. As a result, the proposed system can transmit several Mbps with better quality in comparison with conventional multi-code code division multiplexing (CDM) transmission.

This paper proposes an OFDM-based wireless ATM transmission system. In the proposed system, the guard bits, which are cyclically extended by repeating information bits, are inserted before and after serial-parallel converted wireless ATM data bits for OFDM transmission, and these bits are applied for the wireless ATM frame synchronization and the decision of the DFT (discrete Fourier transform) start point at the receiver. In addition, the cyclically extended PN sequence is inserted in some of the proposed OFDM transmission subchannels with the fixed interval to estimate phase rotation, frequency offset and delay characteristics. This proposed system does not need to equip the "bit by bit " guard interval insertion and removal circuits which are needed in a conventional OFDM system. It is easy to estimate phase rotation, frequency offset and delay characteristics, and the synchronization of wireless ATM cell is also easy. In this paper, moreover, the bit error rate (BER) and the ATM cell error rate (CER) of this wireless ATM transmission scheme are evaluated by computer simulations.