mmWave CS (chirp sequence) radar is one of the most widely used automotive sensors for ADAS (Advanced Driving Assistance System) and autonomous driving. It offers various advantages, including high resolution, cost-effectiveness, and robustness in all-weather and ambient light environment. However, as mmWave radar density increases, the potential for inter-radar interference rises, which leads to degraded target detection accuracy. Deep learning technologies have shown significant promise in mitigating inter-radar interference. However, this enhancement often comes with the high computational complexity. In this paper, we propose a ConvMixer based interference suppression method, which is primarily composed of patch embedding and depth-wise separatable convolution. The effectiveness of the proposed ConvMixer-based approach is verified and analyzed using simulated data, demonstrating superior performance in terms of SNR, correlation coefficient, phase difference, detection rate, and processing time compared to the state-of-the-art approaches.

Yi Hong is an Associate Professor in the ECSE DEPT at Monash University. She served as a member of the Australian Research Council College of Experts (2018-20) and she was the Director of Graduate Research (2016-18) of the ECSE Department at Monash University. She is a Senior Member of IEEE, the IET Fellow, and a member of IEEE Communications Society, IEEE Information Theory Soceity, and IEEE Vehicular Technology Society. She was the Tutorial Chair of 2021 IEEE International Symposium on Information Theory, Melbourne. She was the General co-Chair of 2014 IEEE Information Theory Workshop at Hobart, Tasmania; the Technical Program Committee Chair of the 2011 Australian Communication Theory workshop, Melbourne; the Publicity Chair of 2009 IEEE Information Theory Workshop at Taromina, Sicily; and Technical Program Committee Member of various IEEE leading conferences. She is currently the Associate Editor (AE) of IEEE Transactions on Green Communications and Networking (TGCN). She served as the AE for IEEE Wireless Communications Letters (WCL) and Transactions on Emerging Telecommunications Technologies (ETT). She received the NICTA-ACoRN Early Career Researcher award at AUSCTW Adelaide 2007. She leads a group of research students and postdocs working on communications technology, wireless security, and coding techniques for wireless communications and networking as well as SSD storage.

Next generation wireless communications such as B5G (Beyond 5G)/6G and wireless LAN are expected to support sensing function in addition to broadband wireless access to support new applications, and radar-communication integration is becoming a hot topic nowadays. This paper compares radar communication integration approaches, i.e. FMCW (Frequency Modulated Continuous Wave) radar-based, OFDM (Orthogonal Frequency Division Multiplexing) radar-based and PMCW (Pulse Modulation Continuous Wave) radar-based approach, and proposes radar-communication integration system based on PMCW radar using Zadoff-Chu sequence which is CAZAC (Constant Amplitude Zero Auto Correlation) sequence, i.e. constant amplitude and zero auto correlation, suitable for PMCW radar applications. This paper describes basic design issues such as signal format, maximum detection range and range resolution and shows correlation detection performance of the proposed PMCW radar when filtering is applied.

Due to its ease of deployment and high mobility, unmanned aerial vehicles (UAVs) have gained great popularity for a variety of applications. To conduct high-level and complicated tasks such as search/rescue missions and target identification, deep learning functions at UAVs are required. To this end, distributed learning methods such as federated learning (FL) and split learning (SL) have been proposed. In this paper, we investigate the SL assisted image classification task in a multi-UAV system for applications such as area exploration and object detection. Specifically, the whole deep learning model is cut into the UAV-side model and BS (base station)-side model. Each UAV performs forward propagation on UAV-side model by using the locally gathered images, and sends the smashed data to the BS. The BS performs forward and backward propagation based on the smashed data, and sends back the gradients of the cut layer to the UAVs, which is used for the backward propagation of the UAV-side model. The performance was evaluated using an aerial perspective geographic dataset, and the effectiveness of the proposed system was validated by comparing with FL-based and centralized learning methods. It was found that SL can significantly reduce computation time at UAV compared with FL, and is particularly effective with non-IID (independent and identically distributed) dataset. SL also requires less data during the training initial phase and has a faster convergence speed compared to centralized learning.

Analog beamforming with low-resolution phase shifters is a key technique for 5G networks due to its superior hardware complexity and power consumption advantages. However, the optimal beamforming coordination is an extremely challenging issue in a downlink multi-antenna base station and single-antenna user equipment scenario. To avoid using global channel state information and reduce the communication overhead, in this paper, we propose a deep reinforcement learning based distributed analog beamforming approach to improve the energy efficiency for a downlink multiple-input and single-output (MISO) system. Specifically, each base station trains a neural network to steer its beamformer by phase shifters according to its local and obtained neighbouring information, with the purpose of maximizing its own energy efficiency and minimizing the negative impacts to its neighbouring cells. We evaluate the performance of the proposed approach by simulations, and validate its superiority by comparing with baseline schemes.

5G NR (New Radio) employs OFDMA (Orthogonal Frequency Division Multiple Access) for both uplink and downlink where sub-carrier spacing can be modified. To enable flexible uplink access for IoT (Internet of Things) in beyond 5G, it is required to accommodate various types of mobile terminals from low to high-speed transmission. When sub-channel spacing is different and/or transmission timing is asynchronous in adjacent channels, OFDMA signals will not be orthogonal with each other and channel filtering is required to reduce ACI (Adjacent channel interference). Supposing joint use of OW-DFTs-OFDM (Overlap-Windowed Discrete Fourier Transform spreading OFDM) signals for low PAPR (Peak to Average Power Ratio) and FFT (Fast Fourier Transform) based filter-bank for flexible channel filtering, this paper discusses FFT-based frequency domain filter design for receiving multi-channel OW-DFTs-OFDM signals to avoid performance degradation due to ACI and ISI (Inter-Symbol Interference).

In recent years, to cope with the rapid growth in mobile data traffic, increasing the capacity of cellular networks is receiving more and more attention. To this end, offloading the current LTE‐advanced or 5G system’s data traffic from licensed spectrum to the unlicensed spectrum that is used by WiFi systems, i.e., LTE‐Licensed‐Assisted‐Access (LTE‐LAA), has been extensively investigated. In the current LTE‐LAA system, a Listen‐Before‐Talk (LBT) approach is implemented, which requires the LTE user also perform carrier sense before the transmission. However, fair LTE‐WiFi coexistence is still hard to guarantee due to their unbalanced frame sizes and traffic loads. In the LTE‐LAA system, the optimal channel selection and subframe number adjustment are the keys to realize efficient spectrum utilization and fair system coexistence. To this end, in this paper, we propose a reinforcement learning‐based joint channel/subframe selection scheme for LTE‐LAA. The proposed approach is implemented at the LTE access points with zero knowledge of the WiFi systems. The results of extensive simulations verify that the proposed approach can significantly improve the fairness and packet loss rate compared with baseline schemes.

After a disaster occurred, it is extremely important to reconstruct the network and provide the communication services to the victims immediately. Deploying MDRU (Movable and Deployable Resource Unit) in the disaster area, along with multiple access points to extend the service area of MDRU is a very promising solution. In this kind of heterogeneous disaster response networks, it is of great importance to minimize the packet delay from user terminals by performing optimal radio access control. In this paper, we propose a deep reinforcement learning based radio access control mechanism, which enables the smart relay selection and transmitting power control. We evaluate the performance by extensive simulations, and validate the superiority of the proposed mechanism by comparing with baseline schemes.

In recent years, to cope with the rapid growth in mobile data traffic, increasing the capacity of cellular networks is receiving much attention. To this end, offloading the current LTE-advance or the future 5G system's data traffic from licensed spectrum to unlicensed spectrum that used by WiFi system has been proposed. In the current LTE-WiFi coexistence standard, a Listen-Before-Talk (LBT) approach is adopted to make the LTE system senses the medium before a transmission. However, the channel selection and subframe adjustment issues are still open to realize fair coexistence between co-located LTE and WiFi networks. In this paper, we propose a reinforcement learning based joint channel/subframe selection scheme for fair LTE-WiFi coexistence. The proposed approach is distributedly implemented at LTE Access Points (APs) with zero knowledge of the WiFi systems. Extensive simulations have been performed, and the results verified that the proposed approach can achieve better fairness and packet loss rate compared with baseline schemes.

Constructing Radio Environment Map (REM) accurately and cost-efficiently is of great importance to realize dynamic spectrum access. Two kinds of approaches are widely investigated recently, i.e., radio propagation model based approaches and sensor monitoring based approaches. However, these existing approaches are suffering from either inaccurate spectrum availability or high deployment cost. To this end, outsourcing the spectrum sensing task to mobile users that are outfitted with spectrum sensors could greatly reduce the operator's expenditure, and meanwhile, achieve a satisfactory accuracy. The key of crowdsourced REM construction is to attract user participation. In this paper, we propose a novel online incentive mechanism for constructing a fine-grained REM with crowdsourcing in a realistic scenario, where the mobile users arrive and leave in an online manner. The proposed mechanism is proven to satisfy the truthfulness, individual rationality, computational efficiency and consumer sovereignty. Evaluation results demonstrate that the proposed mechanism outperforms the baseline schemes substantially.

Broadband wireless systems need to achieve high spectrum efficiency as well as high power efficiency of HPA (High Power Amplifier). When HPA is used with low output back-off (OBO), increased ACLP (Adjacent Channel Leakage Power) results in significant ACI (Adjacent Channel Interference) especially in TDD (Time Division Duplexing) wireless systems due to a near-far problem. In order to solve this ACLP problem of HPA at a mobile terminal, this paper proposes a novel HPA linearization system using amplitude reference pilot signal which is used to measure input-output characteristics of HPA of a mobile terminal at a base station. It describes design and performance of amplitude reference pilot signal and shows ACLP improvement to confirm the feasibility of the proposed HPA linearization system.

Recently, multi-band WLAN becomes a promising solution to increase the spectral efficiency, where 60GHz band provides ultra-high speed transmission and 2.4/5GHz band is used for maintaining the connectivity. For multi-band WLAN end-users, in order to detect the service area of different bands, their RF units need to be turned on all the time, which leads to substantial energy consumption overhead. To solve this problem, this paper proposes an energy efficient learning-based 60GHz band coverage prediction approach by taking into consideration the strong reflected waves in indoor environment. The simulation results demonstrate that the proposed approach could greatly improve the reliability of the prediction compared to the existing approaches.

As IoT (Internet of Things) is one of the most promising applications in 5G and beyond, a new waveform to enable flexible uplink access is strongly required to accommodate various IoT applications. OFDMA (Orthogonal Frequency Division Multiple Access) based approaches such as FBMC (Filter Bank Multi Carrier) are proposed to achieve low ACLP (Adjacent Channel Leakage Power) however, they have some drawbacks such as high PAPR (Peak to Average Power Ratio) and heavy signal processing for channel filtering. This paper proposes overlap-windowed DFTs-OFDM (Discrete Fourier Transform spreading-OFDM) with overlap FFT filter-bank for flexible uplink access in 5G and beyond. The proposed scheme employs overlap windowing at the transmitter side to achieve low ACLP and overlap FFT filter-bank on the receiver side to reduce ACI (Adjacent Channel Interference) even in the case of asynchronous uplink access. This paper also describes performance evaluation results of the proposed scheme.

5G systems are expected to employ C/U (Control/User)-plane split and massive deployment of small cells for high frequency reuse at SHF bands such as 28GHz band in conjunction with a macro cell using traditional UHF bands to meet increasing demand for higher capacity. In 5G multi-band cellular networks, an energy efficient SHF band cell discovery technique is required since SHF band cells will be deployed on a hot-spot basis. This paper proposes Kriging-based RSSI (Received signal strength indication) prediction for cell coverage discovery using spectrum database in 5G multi-band cellular networks. This paper also describes performance evaluation results of the Kriging-based RSSI prediction using ray-tracing simulation and demonstrates the feasibility of the proposed RSSI prediction method.

In spectrum sharing system, an exclusion zone is defined to protect both primary and secondary users from interference. Reducing the size of exclusion zone is critical for efficiently utilizing the fallow spectrum. In this paper, we propose a novel crowdsourcing augmented exclusion zone refinement framework. In our framework, a barter-like exchange model using spectrum access right is employed to incentivize the secondary users (SUs) to participate in the crowdsourcing. We further design a truthful auction mechanism to select the SUs and determine their access time in a computationally efficient way. We perform simulations to validate the proposed mechanism, and compare it with two baseline schemes.

To improve the spectrum utilization efficiency, radio propagation model based spectrum database is widely investigated recently. However, it is prone to offer inaccurate and stale spectrum availability since the empirical models do not count for local environment details. One promising solution is to incorporate real- time spectrum measurement into the quasi-static spectrum database. In this paper, we propose a novel fine-grained incentive mechanism for sensing augmented spectrum database. We first present a reverse auction framework, which minimizes the operator's total expenditure subject to the quality requirement of each spot that needs to be augmented. Then we propose a practical incentive mechanism to solve the auction problem, which is proven to be truthful, individual rational and computationally efficient. Simulation results demonstrate that the proposed mechanism could save noticeable expenditure compared to two baseline schemes.

Spectrum occupancy rate (SOR) is an important parameter for spectrum utilization efficiency in terms of frequency and time. We have proposed a novel spectrum occupancy rate (SOR) measurement method based on least square error (LSE) estimation of Gaussian noise CDF (Cumulative Probability Distribution Function) to improve SOR measurement accuracy in low SNR conditions, and its validity has been confirmed by computer simulations. This paper describes experimental setup of SOR measurement system and experimental performance evaluation results in AWGN (Additive White Gaussian Noise) channel and frequency selective fading channel. The experimental results are compared with computer simulation results.

Ultra multi-level modulation such as 1024/4096QAM can achieve higher spectrum efficiency of 10/12 bit/s/Hz than 8 bit/s/Hz achieved by 256QAM in current WLAN/LTE standards, however BER (Bit Error Rate) performance is significantly degraded due to very small reference phase error for coherent detection. This paper proposes ultra-multi-amplitude-level BPSK (Binary Phase Shift Keying) based SSB-DFTs-OFDM (Single Side Band Discrete Fourier Transform spreading Orthogonal Frequency Division Multiplexing) to achieve higher spectrum efficiency. Theoretical analysis and computer simulation results reveal the proposed multi-amplitude-level BPSK based SSB-DFTs-OFDM is more robust to reference phase error for coherent detection, and lower PAPR (Peak to Average Power Ratio) than conventional 1024/4096QAM.

As link quality in 60GHz WLAN is significantly affected by moving human body shadowing, it is required to introduce shadowing countermeasures such as diversity and fast session transfer. For performance evaluation of these techniques in various environments, we need a deterministic shadowing model for ray-tracing simulations rather than a traditional empirical shadowing model based on experimental data. With this motivation, this paper proposes a twin cylinder model for moving human body shadowing in 60GHz WLAN, where three knife edges for diffraction loss calculation are derived from geometrical positions of a moving human body, a transmitter and a receiver. It is confirmed that calculated results using the proposed model agrees to measured results.

OFDM (Orthogonal Frequency Division Multiplexing) has been widely accepted in various wireless systems such as cellular systems and wireless LAN because of its robustness to frequency selective fading. However it has a drawback of large PAPR (Peak to Average Power Ratio) since it is a multi-carrier transmission scheme. In order to apply DFTs-OFDM (DFT spreading OFDM) for low PAPR, DC offset error robustness is also required to avoid BER performance degradation due to DC offset error for cost-effective wireless terminal implementation. This paper proposes a modified DFTs-OFDM with DC subcarrier shift to cope with low PAPR and DC offset error robustness. Computer simulation results confirm that BER performance is not degraded by DC offset error and low PAPR is maintained. It is also demonstrated that application of the proposed DFTs-OFDM to wireless LANs can reduce HPA output back-off while keeping adjacent channel leakage power (ACLP).

This paper describes performance evaluation results of SSB (Single Side Band) transmission of DFTs-OFDM (Discrete Fourier Transform Spreading Orthogonal Frequency Division Multiplexing) using multi-level BPSK (Binary Phase Shift Keying) through nonlinear HPA (High Power Amplifier). SSB-DFTs-OFDM is generated by eliminating USB (Upper Side Band) or LSB (Lower Side Band) spectrum in frequency domain after DFT spreading of multi-level BPSK signals, thus Hilbert transformer is not necessary to generate SSB signals. The simulation results show that SSB-DFTs-OFDM achieves almost the same PAPR (Peak to Average Power Ratio) and ACLP (adjacent channel power leakage) as conventional DFTs-OFDM and lower PAPR and ACLP than OFDM and required bandwidth can be reduced by half when BPSK modulation is employed. Furthermore, SSB-DFTs-OFDM using multi-level BPSK shows less error floor and/or Eb/N0 degradation compared with conventional DFTs-OFDM using QAM modulation in some cases when HPA OBO (Output Back Off) is small. SSB-DFTs-OFDM is an attractive alternative to DFTs-OFDM for WLAN and cellular applications.

A cyclostationarity based feature detection by calculating autocorrelation function for OFDM signal with cyclic prefix is proposed as a spectrum sensing scheme for dynamic spectrum access. However, this approach cannot be applied to single carrier modulation signals without cyclic prefix. This paper proposes a novel spectrum sensing scheme for single carrier modulation signals using clock timing extraction based feature detection, where envelope detection is used for clock timing extraction and an overlap FFT filter-bank is used to receive the primary signals using the designated frequency band. This paper also evaluates false-alarm and miss-detection probability performance of the proposed scheme and compares with those of the conventional energy detection scheme by computer simulation.

Satellite and terrestrial integrated mobile communication systems (STICS) is proposed to secure communications services anytime and anywhere. In the case of natural disasters or special event, it is required for satellite systems to allocate the frequency resources to a specific area as much as possible. Dynamic channel assignment is one of the attractive solutions to achieve the flexible and efficient utilization of the frequency resources. Although dynamic channel assignment can increase the bandwidth per satellite cell, smaller frequency reuse factor results in larger inter-cell interference and the link quality degradation. To solve this problem, this paper proposes centralized dynamic channel assignment based on interference measurement with link quality threshold control for multi-beam mobile satellite communications networks. It also shows the performance evaluation results by computer simulations regarding the blocking rate and the link quality.

An orthogonal polarization based MIMO transmission scheme is proposed to achieve over 10Gbps transmission for advanced 60GHz WLAN. As the proposed MIMO transmission scheme uses V(Vertical)/H(Horizontal) polarization directional antennas, stable 2×2 MIMO transmission is enabled even in LOS (line-of-sight) environment. A ray-tracing method is employed for computer simulation to evaluate channel capacity and BER performance of the proposed scheme in indoor conference room environments. The simulation results confirm that the proposed orthogonal polarization based MIMO transmission scheme achieves higher channel capacity than the conventional MIMO transmission using the same polarization antenna. Furthermore, this paper shows that BER performance depends on the location of transmitter and receiver as well as the beam-width of the directional antenna. BER performance is significantly degraded when the antenna height of the transmitter is the same as that of the receiver. On the other hand, better BER performance can be achieved when the antenna height difference is large.

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.

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.

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.

The wide area ubiquitous network (WAUN), which is used for transmitting and receiving information for sensors and actuators, is proposed and the feasibility study of a new wireless network for the WAUN is described. The WAUN is designed to satisfy the requirements of many new applications using sensors and actuators, which are wirelessly connected to the IP network. One of the basic requirements for the wireless system of the WAUN is wide coverage larger than several km with low wireless terminal output power of 10 mW To meet this requirement, an experimental wireless system, which uses a powerful FEC and the diversity technique, for use in WAUNs is designed, and its feasibility is evaluated by field experiments. The experimental results demonstrate the feasibility of the WAUN. That is, the 10 mW transmission power wireless terminal communicates with the access point (base station) 5 km away

This paper proposes a packet multiplexing transmission technique for wireless ad-hoc networks. Furthermore, we present and discuss our network and architecture concept. Preliminary numerical estimations show that the proposed multiplexing technique may not only increase the throughput, but also suppress the average end-to-end delay degradation in a multi-hop environment

We propose a new 5/25-GHz dual-band wireless LAN for high-capacity broadband communications. In Japan, the 25/27-GHz band has been allocated for nomadic wireless access systems to increase system capacity and achieve transmission rates higher than 100 Mbit/s. We will describe the application areas and regulatory requirements of 25/27-GHz band systems, and then describe the concept of 5/25-GHz dual-band OFDM-based wireless LAN systems. We will examine the transmission performance of 25-GHz OFDM-based systems on the basis of our experimental results. We will then discuss a prototype 5/25-GHz dual-band WLAN card and demonstrate the feasibility of compact mobile terminals.

This paper describes a prototype software defined radio (SDR) transceiver on a distributed and heterogeneous hybrid programmable architecture; it consists of a central processing unit (CPU), digital signal processors (DSPs), and pre/postprocessors (PPPs), and supports both Personal Handy Phone System (PHS), and IEEE 802.11 wireless local area network (WLAN). It also supports system switching between PHS and WLAN and over-the-air (OTA) software downloading. In this paper, we design an IEEE 802.11 WLAN around the SDR; we show the software architecture of the SDR prototype and describe how it handles the IEEE 802.11 WLAN protocol. The medium access control (MAC) sublayer functions are executed on the CPU, while the physical layer (PHY) functions such as modulation/demodulation are processed by the DSPs; higher speed digital signal processes are run on the PPP implemented on a field-programmable gate array (FPGA). The most difficult problem in implementing the WLAN in this way is meeting the short interframe space (SIFS) requirement of the IEEE 802.11 standard; we elucidate the potential weakness of the current configuration and specify a way of implementing the IEEE 802.11 protocol that avoids this problem. This paper also describes an experimental evaluation of the prototype for WLAN use, the results of which agree well with computer-simulation results.

The spread of the Internet has given rise to strong demands for real-time services such as voice and streaming video. Since these services require guarantees that may include transmission rate, delay, and delay variance, the network, including the wireless access networks, must offer QoS (quality of service) guarantees. However, no radio access system fully supports QoS controls. IEEE 802.11e is one scheme that uses an access control mechanism for QoS support. The scheme is based on a distributed access control method, CSMA (carrier sense multiple access). Since it employs EDCA (enhanced distributed channel access) for priority differentiation, terminals with large traffic loads can throttle the throughput of priority terminals because EDCA is essentially decentralized control. This paper proposes a back pressure traffic control method that avoids this problem and supports QoS guarantees as well as describe its characteristics.

This paper describes an SDM-COFDM (space division multiplexed-coded orthogonal frequency division multiplexing) prototype employing a hierarchical ICI (inter-channel interference) canceller for MIMO (multi-input multi-output)-based broadband wireless access systems. The prototype has two types of ICI cancellers: multiplicative and subtractive. The multiplicative canceller multiplies the received signals by the estimated inverse propagation coefficient matrix. In addition, the subtractive one generates ICI replicas, subtracts the replicas from the received symbols, weights the subtracted signals by the estimated propagation coefficients, and combines them to obtain diversity gain. Experimental results show that the newly developed prototype with 2/spl times/2 antennas obtains a 1.4 dB improvement in required CNR at the PER of 0.1 compared to that achieved with only the multiplicative canceller. It achieves more than 100 Mbit/s per 18 MHz bandwidth by using 64QAM with the coding rate of 3/4 in frequency selective fading environments.

We have successfully fabricated a prototype software defined radio (SDR) transceiver that supports both Japanese PHS and IEEE 802.11 wireless LAN (WLAN). In this paper, we design an IEEE 802.11 WLAN around the SDR with its distributed and heterogeneous hybrid programmable architecture. The most difficult problem in implementing the WLAN in this way is how to meet the SIFS requirement in the IEEE 802.11 standard. This paper shows the hardware and software architecture of the prototype and how it can support the protocol processing of the IEEE 802.11 WLAN. The hybrid programmable architecture is a sophisticated combination of a general-purpose microprocessor (CPU), digital signal processors (DSPs), and programmable hardware (FPGAs). The MAC layer functions are executed on the CPU, and the PHY layer functions such as MODEM are processed by the DSP; higher-speed digital signal processes are run on the FPGA. This paper also describes an experimental evaluation of the prototype for IEEE 802.11 WLAN use.

This paper introduces a novel SDM-COFDM (space division multiplexed-coded orthogonal frequency division multiplexing) prototype for MIMO (multi-input multi-output) channel-based broadband wireless access systems. The developed prototype reduces the inter-channel interference in the SDM transmission by suing a simple feed-forward compensator that simply multiplies the received data symbols by the estimated inverse propagation coefficient matrix at each OFDM subcarrier. Moreover, in order to improve the accuracy of estimating the inverse propagation coefficient matrix, the STC (space-time coded) preamble and the common AFC (automatic frequency control) circuit have been implemented. Furthermore, the likelihood weighting, based on SNR (signal to noise power ratio) of each OFDM subcarrier, is used to improve the error correction performance of soft decision Viterbi decoding. Experimental results show that the prototype with 2/spl times/2 antennas achieves double the transmission bit rate without expanding the occupied frequency bandwidth, while achieving SISO (single-input single-output) transmission quality in fading environments. The prototype offers 108 Mbit/s per 20 MHz by using 64 QAM with the coding rate of 3/4.

A software defined radio (SDR) prototype based on a multiprocessor architecture (MPA) is developed. Software for Japanese personal handy phone system (PHS) of a 2G mobile system, and IEEE 802.11 wireless LAN, which has a much wider bandwidth than the 2G systems, is successfully implemented. A newly developed flexible-rate pre-/post-processor (FR-PPP) achieves the flexibility and wideband performance that the platform needs. This paper shows the design of the SDR prototype and evaluates its performance by experiments that include PHS processor load and processing delay characteristics and wireless LAN processor load and throughput characteristics.

This paper proposes space division multiplexed coded orthogonal frequency division multiplexing (SDM-COFDM) scheme using inter-channel interference canceller for multi-input multi-output (MIMO) channels. It reduces the degradation due to inter-channel interference in SDM transmission with a feed-forward canceller multiplying the received symbols by the estimated propagation inverse matrix for each OFDM subcarrier. Moreover, the proposed likelihood-weighting scheme, which is based on each subcarrier's signal-to-noise power ratio (SNR), enhances the error correction performance or soft decision Viterbi decoding. Computer simulation shows that the SDM-COFDM scheme achieves more than 100 Mbit/s per 20 MHz in frequency selective fading environments with the same carrier-to-noise ratio (CNR) as the single channel COFDM.

This paper discusses wireless and IP integrated system architectures for broadband mobile multimedia services. Possible wireless IP network architectures are given and discussed, taking mobility support into account. This paper also proposes a new ATM-based wireless IP network architecture with handover capability for broadband mobile multimedia services.

Automatic Repeat reQuest (ARQ) for the transmission of data blocks using TDMA/TDD is considered. Simulations for two ARQ schemes that perform well under the constraint of finite control channel capacity are shown. The simulations show that Modified Partial Selective Repeat superIMposEd on gbn ARQ (Modified PRIME ARQ) shows superior performance compared to the other ARQ scheme.

Wireless communications are expected to be the dominant mode of access technology in the next century. Besides voice, a new range of services such as multimedia, high-speed data, etc. are being offered for delivery over wireless networks. Mobility will be seamless, realizing the concept of persons being in contact anywhere, at any time. Two developments are likely to have a substantial impact on the mobile communications systems deployed in the twenty-first century: the adoption of International Mobile Telecommunications-2000 and wireless asynchronous transfer mode (ATM). They are two different but cooperative approaches to providing high-speed wireless access. The limitations of the radio-frequency spectrum and radio channel propagation impose special constraints on the technologies of systems to be deployed. To make future mobile systems globally acceptable, standardization efforts are underway in the International Telecommunications Union and the ATM Forum. This paper reviews the international standardization efforts, the challenges to the technologies imposed by the radio spectrum limitations, radio channel propagation-induced distortions, and possible solutions. Evolution, migration, and architecture issues also are discussed.

This paper proposes a network architecture of ATM wireless access with mobility support for mobile access to ATM-based multimedia networks. ATM wireless access aims at ATM-based transport capability with mobility for multimedia services by wireless media in private ATM LAN/WAN environments as well as public environments. This paper discusses network and protocol architecture issues for supporting mobility in a wireless ATM network. It describes the required network control functions and function assignment in wireless ATM, and gives examples of call control procedures.

Wireless ATM (asynchronous transfer mode) is used to provide nomadic and seamless access to ATM based networks. Wireless ATM can offer multiple connections supporting various types of services. For CBR (constant bit rate) and VBR (variable bit rate) services, time-sensitive QoS (quality of services) are important, unlike other services such as ABR (available bit rate). For CBR and VBR services, the peak bandwidth needs to be assigned to meet CDV (cell delay variation) requirements. For time-insensitive services, assigning the peak bandwidth wastes radio resources since the average bandwidth of such services is generally much lower than the peak bandwidth. This paper proposes a QoS oriented buffer control algorithm to satisfy CDV requirements while maximizing radio resource utilization. The proposed scheme needs less total bandwidth than the sum of the peak bandwidths required for all connections.

The authors propose a TDMA (time-division multiple-access) satellite communication system suitable for both basic and primary ISDN services in addition to B-channel transmission lines among ISDN switches. To provide these services economically and efficiently, the proposed system uses an offset quadrature phase-shift keying (QPSK) burst model coupled with high-coding gain and rate-forward-error correction, demand assignment technology for each data burst, and a transmission and reception transponder (carrier) hopping scheme. To realize cost-effective transmission and subscriber lines and to increase the reliability of TDMA terminals, the major functions of TDMA terminals have been implemented in large-scale integrated circuits (LSICs), monolithic ICs (MICs) and hybrid ICs (HICs). The experimental results show narrow spectrum transmission with little bit error probability degradation for the offset QPSK burst modem and perfect operation of demand assignment and carrier hopping capability of the system.>

A system concept of a common alternative routing system is proposed for reducing total network costs by integrating satellite communications into public-switched networks, where satellite systems carry overflow traffic from terrestrial systems through common satellite channels. This concept has been realized by a satellite communication system called DYANET (dynamic channel assigning and routing satellite aided digital networks), which provides trunk circuits in combination with terrestrial systems. The key technologies developed for DYANET are a centralized network control system and a transponder hopping demand assignment TDMA (time-division multiple-access) system, to assure single-hop connection and to use satellite channel efficiently. The authors describe the system concept and configuration, the network control system, and the results of its commercial use.>

An architecture is proposed for TDMA (time division multiple access) equipment and functional-module realization in microelectronics to increase reliability and to reduce hardware size and development time. The approach described basically involves digitization of analog circuits (allowing their realization using digital LSI circuits) and analog IC implementation for high-speed circuits. In order to use general-purpose LSI circuits and ICs, TDMA equipment is reconfigured into a hardware-oriented and simplified architecture. Using this architecture and optimal function assigning to each module, six types of general-purpose synchronization unit LSI circuits have been developed in addition to eleven types of LSI circuits and ICs, i.e. three types of digital LSI circuits, four types of MAICs (monolithic analog ICs), and four types of HICs (hybrid ICs) for a burst modem. As a result of this LSI circuit and IC implementation, the hardware size of TDMA equipment has been reduced to one-fifth of the conventional size, and maintenance-free capability has been achieved.>