Wireless sensor networks (WSNs) are meant to monitor natural and man-made phenomena, made of simple low cost sensors interconnected via low data rate communication links to survey wide areas. In this paper, we investigate the trade-off arising from spectrum occupation and packet delivery time in professionally installed wide area WSNs (WA-WSNs). We study two types of network topologies, namely star and mesh topologies, based on the recent IEEE 802.15.4k and multi-channel multi-radio IEEE 802.15.4g standards, respectively. We perform extensive packet level simulations of the mesh topology network, while keeping the star network as a benchmark. Our contribution is threefold. First, we address connectivity in the mesh network by deploying additional relay nodes, when necessary, to enable also each node with at least two independent route alternatives. Second, our simulation results show that the mesh topology requires 20% more spectrum to deliver the whole set of sensed data to the traffic sink compared with the star topology network under delivery time constraints. Finally, we show that only 10% of the nodes in the mesh network actually need additional spectrum and multiple radio transceivers to keep the delay bounded by that of the star topology.

In this paper, we evaluate the performance of a low-complexity 60 GHz system in a realistic non-line-of sight indoor environment. We consider a single-carrier transmission system that does not employ equalization, but only uses forward error correction. The channel model was created from measurements in a conference room in which a non-line-of-sight environment is created through a human-sized blocking object, and in which beamforming is applied at the receiver to track and obtain reflected paths. We obtained the bit error rate performance using channel impulse responses obtained from measurements and from the resulting channel model. Our evaluation indicates that the system can achieve the target bit error rate. As a result, we not only verified the new channel model but also show that complex equalization methods are not necessary to achieve reliable communication in indoor 60 GHz scenarios.

In this work, we evaluate preamble patterns of IEEE P802.15.4k Low Energy Critical Infrastructure Monitoring Networks (LECIM) DSSS PHY. Due to energy constraints of the P802.15.4k systems, preambles should have robust performance to realize high throughput at low Eb/No situations. Our results reveal that the detection performances of the proposed 2-octet and 4-octet preambles are not adequate. For the case of 4-octet preamble, the main drawback is poor pattern design. To improve the performance of the 4-octet preamble, we propose a novel pattern. The new 4-octet preamble pattern achieves the required detection rate of 10-3at the target Eb/No of 4 dB. For the case of the 2-octet preamble, its length is the limiting factor. We focus on the receiver side techniques. We propose using aperture and flywheel techniques to improve detection. Using these techniques, target detection rate is achieved and higher throughputs at low Eb/No values are enabled.

In order to solve the problem of multi-Gbps transmission in 60 GHz band - communication interruption by human body crossing, this paper proposes a method to increase reflected waves by installing artificial reflector(s) in two-dimensional arrangement and shows a good improvement of disconnection probability reduction to 1/4 (by one artificial reflector) and to 1/16 (by two reflectors). The interruption by human crossing is modeled and locations of transmitters and receivers are set on any grid of sub-partitioned rooms by grid (room sizes are defined by IEEE 802.11ad) to get statistically meaningful data. The computer simulations have been carried out with various TX and RX antenna HPBWs (Half Power Beam Width), several receiver sensitivities corresponding to 3Gbps to 0.5Gbps transmissions and by assuming a fixed TX antenna direction and a beam-forming receiver antenna that can track the incoming reflected wave(s) in case of LOS (Line of sight) path interruption. The simulation results show that disconnection probability reduction from about 80% to 20-10% by setting an artificial reflector to generate an additional reflected path and a reduction to 5% by setting two artificial reflectors when the TX and RX antennas' HPBWs are 30degree and the receiver sensitivity is -55.0dBm. The improvements by the proposed method are generally applicable to similar indoor communications environments.

In this paper, group training protocols for beamforming of multiple devices are proposed in the context of the IEEE 802.15.3c standard using single carrier. The standard defined sector and beam-level training sequences function well if only the establishment of one or two communication links is required, but in the case of, e.g. interactive gaming or conference room environment it can lead to considerable inefficiency. The proposed group training protocols address the cases where two or more devices need to carry out beamforming in order to communicate with each other. Moreover, the group training method exploits the knowledge that the personal area network coordinator already has on the associated devices. The standard defined beamforming protocol and the group training proposals are evaluated using varying superframe lengths in both symmetric and asymmetric antenna systems. The results show that group training can reduce the time to achieve beam-level synchronization considerably even when only two devices need to connect while staying compliant with the standard.

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.

This paper presents a physical and MAC layer analysis of the recently introduced IEEE 802.15.3c standard for multi Gbps communication at 60 GHz. We find the optimal beamwidth of the transmitting antenna, achieving a trade-off between the Piconet Coordinator discovery and the duration of the contention access period (CAP) of the IEEE 802.15.3c MAC superframe. To find the optimal beamwidth, we first analyze the link budget of 60 GHz based directional communication, to identify the transmitting and receiving antenna gain, and hence the minimum beamwidth required to achieve a specific bit error probability (BEP) for a given distance between transmitter and receiver. We introduce a more efficient method for analytically modeling the binary exponential backoff (BEB) process during the CSMA/CA based CAP of the superframe, using a 1-dimentional Markov chain. Numerical results for the required antenna gain and optimal beamwidth, demonstrate the usefulness of our analysis technique.

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.

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.

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.

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.

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.

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.

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.

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.

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 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).

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.

The 19 papers in this special issue focus on the push beyond giga-bit-per-second (Gbps) data rates, in order to more rapidly access data on personal devices, as well as potentially replace all the cables going into a device, including the video cable. This issue beings together the state-of-the-art, across multiple disciplines, for achieving Gbps WPAN capability.

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 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.

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.

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.

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.

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.

We propose a neurodynamical approach to a large scale optimization problem in the cognitive wireless clouds, in which a huge number of mobile terminals with multiple different air interfaces autonomously utilize the most appropriate infrastructure wireless networks, by sensing available wireless networks, selecting the most appropriate one, and reconfiguring themselves with seamless handover to the target networks. In order to deal with such a cognitive radio network, the game theory has been applied in order to analyze stability of the dynamical systems consisting of the mobile terminals' distributed behaviours, but it is not based on fundamental optimization property. As more natural optimization dynamical system model suitable for large-scale complex systems, we introduce the mutual connection neural network dynamics which converges to an optimal state with always decreasing property of its energy function. In this paper, we apply such a neurodynamics to optimization problem in radio access technology selection. We composed a neural network which solves the problems, and showed that it is possible to improve total average throughput only by distributed and autonomous neuron updates on the terminal side.

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.

Proposed PHY layer schemes are evaluated using the channel model that corresponds to each usage model in IEEE802.15.3c standardization process. NICT has contributed TSV model to the IEEE802.15.3c channel model subgroup. The model developed by NICT has been selected as the model for the evaluation of mandatory simulations. This paper describes the channel model for millimeter-wave band developed for the TG3c.

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.

We show that a symbol-by-symbol detector is the optimal MLSE demodulator for Gaussian minimum-shift keying (GMSK) (BT=0.3) on both AWGN and a class of weakly dispersive multipath fading channels. Furthermore, it is shown that, for the remaining weakly dispersive channels, a 2 state Viterbi equalizer is optimum. As an illustration of the importance of this result, a receiver is proposed which can reduce the power consumption of GSM handsets using conditional equalization, as more than 70% of the time the channel is considered to be weakly dispersive.

Diversity combining methods for mobile satellite communication systems employing convolutional encoding and soft-decision Viterbi decoding are evaluated. Computer simulation clarifies that the pre-Viterbi-decoding maximal ratio combining method has better performance than other methods in Rician fading channels. The simulation results agree with the Pe (bit error probability) performance derived from the numerical analysis for slow fading using the approximate Pe performance of Viterbi decoding in AWGN (additive white Gaussian noise) channels and the probability density function of Rician fading. Applying this diversity method to the multi-beam mobile satellite communication systems, a satellite beam diversity reception scheme is proposed. A computer simulation result shows that the proposed scheme decreases the packet error rate of the control signals to less than 1/100 around the satellite beam boundary.>

This paper proposes a very low power consumption ADPCM voice codec LSIC. The developed LSIC satisfies CCITT recommendation G.721 completely and is suitable for realizing the high-quality voice signal transmission expected from personal communication systems in fading environments. By employing a time sharing signal processing, a very low power consumption (only 500 /spl mu/W) for ADPCM codec core has been achieved. Moreover, the LSIC has a novel click noise detection function and erroneous received signals are suppressed digitally according to the click noise detection information. This makes it possible to improve the voice transmission quality significantly in fading environments, for instance, the MOS (mean opinion score) evaluation is improved by 0.5 points compared with that of the conventional scheme.

Portability of services will be one of the key elements of personal communications since it will enable us to communicate with everyone, anytime and anywhere. Mobile communications are reviewed in conjunction with radio and network technologies. The most important and often overlooked condition: customer requirements will be discussed by comparing the cordless phone and cellular phone approaches toward personal communications systems (PCS). A perspective view of PCS through PHS field tests in Japan will be given with survey data on acceptable tariff and what customers really want. An example of portable terminal development will be described to meet these customers requirements: high quality voice transmission, longer talk time, small and light weight through 1-chip LSIC implementation.

This paper presents a low power coherent /spl pi//4-shift QPSK demodulator LSIC for personal communication systems in Japan. The developed LSIC, implemented on a CMOS 0.8 /spl mu/m standard cell with 2-V operation, achieves better frame error rate performance and lower power consumption than conventional demodulators. It uniquely employs (1) a reverse-modulation carrier recovery scheme with a -/spl pi//4 signal-phase rotator and a band-width-varied carrier filter, (2) a clock recovery scheme using initial clock phase estimation, (3) a fully digital orthogonal detection scheme suitable for low power consumption, and (4) a burst detection scheme using phase information in preamble. Performance evaluation confirms that the demodulator LSIC reduces the irreducible frame error rate by 40%, and achieves an Eb/No improvement of 3 dB at the frame error rate of 10% compared with differential detection under the Rayleigh fading channel common in personal communication.

A /spl pi//4-shift QPSK digital modulator LSIC consisting of a digital pulse shaping filter and a baseband quadrature modulator is newly developed. By employing a novel digital filter configuration, the required filter memory is reduced to just 1/2048th that of the conventional modulator. Moreover, since the proposed baseband modulation scheme does not employ a complex multiplier or a quadrature modulator with multipliers, a compact and low power consumption modulator is realized.

The paper proposes a half chip offset QPSK (quadrature phase shift keying) modulation CDMA (code division multiple access) scheme coupled with time diversity and high-coding-gain FEC (forward error correction) for wireless LAN (local area network) systems. It is clarified that the proposed scheme realizes compact spectrum characteristics in hard limited channels and excellent Pe performance for high-speed data transmission with simple hardware configuration. The experimental results show that by employing time diversity with FEC, the half chip offset QPSK CDMA scheme realizes a required Eb/No of 14.2 dB at a Pe of 10/sup -5/ in Rician fading environments with fD of 10 Hz and delay spread of 40 nsec.

An advanced, high-speed, and universal-coding-rate Viterbi decoder VLSI implementation is presented. Two novel circuit design schemes have been proposed: scarce state transition (SST) decoding and direct high-coding-rate convolutional code generation and variable-rate decoding. SST makes it possible to omit the final decision circuit and to reduce the required path memory length without degrading error probability performance. Moreover, the power consumption of the SST Viterbi decoder is significantly reduced when implemented as a CMOS device. These features overcome the speed limits of high-speed and high-coding-gain Viterbi decoder VLSIs in the rate one-half mode imposed by the thermal limitation. The other Viterbi decoding scheme makes it possible to realize a simple and variable coding-rate forward-error-correction circuit by changing only the branch metric calculation ROM tables. By employing these schemes, high-speed (25-Mb/s) and universal-coding-rate Viterbi decoder VLSIs have been developed.>

This paper proposes a full digital modem employing a reverse-modulation type carrier recovery scheme for offset type modulation schemes. The full digital modem employs a wave forming filter for reverse-modulation of offset type modulated signals to increase the extracted carrier signal-to-noise ratio. The proposed modem achieves both high speed carrier acquisition and low carrier slipping rate simultaneously which other methods cannot achieve. Computer simulation results show that the proposed modem applied to OQPSK systems achieves a low carrier slipping rate performance of less than 1.0*10/sup -7/ event/symbol at an Eb/No of 4 dB with negligible bit error rate degradation. The proposed modem can be implemented in all-digital circuits and suitable for LSI implementation.>

In order to increase the channel capacity of CDMA (code division multiple access) mobile/personal communication systems, an inter-channel interference cancellation (IIC) technique is proposed. By employing one or few additional interference cancellation circuits, it makes it possible to increase allowable error of the TXPC (transmission power control) at the mobile/personal terminals. The experimental results show that by employing the proposed IIC scheme, Pe performance degradation due to a desired and an undesired signal power ratio of -20 dB (20 dB of TXPC control error) can be improved to only 1.5 dB at Pe=10/sup -3/.>

The authors discuss the possibility of transmitting synchronous digital hierarchy (SDH) signals through two-link nonlinear satellite channels. Transmitting such high bit rate signals through a standard 54 MHz or 36 MHz transponder bandwidth requires the use of high-level modulation schemes. The techniques and technologies needed to make the use of 16-ary quadrature amplitude modulation (QAM) and 64-ary QAM transmissions feasible for future satellite communication systems are examined. It is shown that it is possible to transmit a synchronous transport module-level 1 (STM-1) signal through a standard 54 or 36 MHz transponder bandwidth using 16-ary QAM or 64-ary QAM transmission, respectively, for the 6/4 GHz band. However, for higher frequency bands, due to high fade margins needed to achieve the high availability and performance for SDH systems, is not practical to transmit the STM-1 signal through such standard transponder bandwidths.>

In order to realize a higher-code-gain forward error correction scheme in mobile satellite communication systems, a novel concatenated coding scheme employing soft decision decoding for not only inner codes but also outer codes (double soft decision, or DSD, concatenated forward error correction scheme) is proposed. Soft-decision outer decoding can improve the bit error probability of inner decoded data. In this scheme, likelihood information from an inner Viterbi decoder is used in the decoding of outer codes. A technique using the path memory circuit status 1.0 ratio for likelihood information is proposed, and is shown to be the most reliable even though it requires the simplest hardware among the alternative methods. A computer simulation clarifies that the DSD scheme improves Pe performance to one-third of that of the conventional hard-decision outer decoding. Moreover, to reduce the interleaving delay time in fading channels or inner decoded data of concatenated codes, a parallel forward error correction scheme is proposed.>

The authors propose a satellite video signal transmission system that uses a time division multiple access (TDMA) scheme for digital video signal transmission and a code division multiple access (CDMA) scheme for voice signal transmission from a video signal reception-only earth station (backward voice signal transmission). The adoption of a TDMA scheme makes it possible to transmit video signals from various places and to communicate in multipoint-to-(multi)point mode. For backward voice channel transmission from video signal reception-only earth stations, a superposed CDMA voice signal transmission over TDMA video signals by using the same transponder is proposed. The employment of high coding gain forward error correction and development of a cochannel interference cancellation technique have made it possible for the proposed system to transmit a practical number of voice channels. The performance of the proposed system has been experimentally evaluated and the results show the proposed scheme can transmit about 20 CDMA voice channels simultaneously.>

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 DCF (dual carrier filter) reverse-modulation-type carrier recovery circuit is proposed to achieve a low carrier skipping rate and satisfactory phase tracking performance for coherent detection of PSK (phase shift keying) signals in fast Rician fading channels. The proposed scheme employs both narrow and wide bandwidth carrier filters simultaneously for the reverse-modulation-type carrier recovery circuit. It is clarified by computer simulation that the Pe performance of a QPSK (quadriphase shift keying) modem employing the proposed scheme shows an improvement of 1.5 dB in required E/sub s//N/sub O/ at Pe=10/sup 4/ (after Viterbi decoding (R=7/8, K=7), C/M (direct-to-multipath signal power ratio)=10 dB, interleaving size=64*64), compared with conventional coherent detection employing the reverse modulation tank-limiter scheme or the Costas loop scheme.>

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.>

A DCF (dual carrier filter) reverse-modulation-type carrier recovery circuit is proposed to achieve a low carrier skipping rate and satisfactory phase tracking performance for coherent detection of PSK (phase shift keying) signals in fast Rician fading channels. The proposed scheme employs both narrow and wide bandwidth carrier filters simultaneously for the reverse-modulation-type carrier recovery circuit. It is clarified by computer simulation that the Pe performance of a QPSK (quadriphase shift keying) modem employing the proposed scheme shows an improvement of 1.5 dB in required E/sub s//N/sub O/ at Pe=10/sup 4/ (after Viterbi decoding (R=7/8, K=7), C/M (direct-to-multipath signal power ratio)=10 dB, interleaving size=64*64), compared with conventional coherent detection employing the reverse modulation tank-limiter scheme or the Costas loop scheme. >

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.>

An appropriate sampling of devices and architectures for onboard TDMA (Time Division Multiple Access) equipment, burst modems, baseband switches, and SCPC (Single Channel per Carrier) multicarrier demodulators from the present to the year 2000 are selected and presented along with device technology development trends, in terms of minimizing onboard weight and power consumption. The results show that at the present time (equivalent to around the year 1990 for onboard use), onboard TDMA equipment with a clock rate of lower than 100 MHz can be reasonably realized by parallel-processed CMOS/BULK LSIC's, while for TDMA equipment with clock rates of higher than 100 MHz, bipolar devices are more appropriate. The boundary clock rate is not so rigid, and toward the year 2000, the boundary will move up to about 200 MHz. Moreover, around the year 2000, GaAs devices will be more widely used for onboard high-bit rate TDMA. It is shown that for carrier frequencies up to 2 GHz, modem implementation in monolithic microwave IC's is most suitable. Moreover, it is found that coherent demodulation will not entail a big penalty in hardware size and power consumption, because of implementing carrier recovery circuits using IC's and LSIC's. As potential baseband switch configurations, a singleT-stage andT-S-Tarchitecture are compared, and suitable throughputs and TDMA frame lengths for each architecture are clarified. For SCPC multicarrier demodulators, the selection of demodulation schemes depends on the number of channels available for regeneration onboard the satellite. Therefore, in this paper, for years 1990, 1995, and 2000, the total weight and power consumption for several suitable onboard multicarrier demodulation schemes are studied as a function of the number of channels to be regenerated.

A new modulation technique, cross-correlated phase-shift keying (XPSK), is introduced. XPSK is a band-limited offset QPSK modulation technique which has an almost constant envelope. In XPSK modulators, a controlled amount of cross correlation between the in-phase (I) and quadrature (Q) channels is introduced.IandQcross correlation reduce the envelope fluctuation Of the intersymbol-interference and jitter-free OQPSK (IJF-OQPSK) modulation scheme, introduced by Feher et al. [1], [2], from 3 dB to approximately 0 dB, thus further improving the performance of IJF-OQPSK systems in nonlinear radio systems [7], [14]. It is shown that the baseband signal of the modulator, theP_{e} = f(E_{b}/N_{0})performance, and the spectral characteristics of nonlinearly amplified (hard-limited or saturated) radio systems of XPSK and tamed frequency modems (TFM) are practically the same. The XPSK demodulator is a conventional OQPSK demodulator, the TFM demodulator requires a somewhat more complex signal processor. For this reason, the XPSK approach may lead to significant demodulator hardware cost savings, particularly in point-to-multipoint distribution systems such as broadcast systems. Simulation results for linear and nonlinear (saturated amplifier) systems operated in an adjacent-channel interference environment (in addition to thermal noise) are presented. Measurement results performed on a 128 kbit/s rate hardware-prototype modem are also reported. Experimental eye diagram and power spectrum density measurement results are in close agreement with the computer simulation results.