Accurate and real-time tracking of multiple moving targets remains a fundamental challenge in radar-based indoor sensing, particularly when the number of targets is unknown or varies over time. This paper presents a real-time motion tracking system RTCtrack that operates directly on signal variations induced by human movement. At each time step, the method extracts significant variation points relative to a static baseline and incrementally groups them into coherent trajectories without requiring prior knowledge of the number of targets. A tail-based spatial association strategy enables robust path formation, while weak or inconsistent clusters are automatically removed based on activity level. To maintain tracking stability in evolving environments, an adaptive baseline update mechanism replaces the reference signal when persistent global deviations are detected. RTCtrack is evaluated using a public indoor radar dataset involving multiple individuals moving independently. Simulation results show that the system reliably identifies and tracks multiple motion paths in real time without knowing the exact number of targets. Comparisons with video-based ground truth confirm strong spatial and temporal alignment, demonstrating its effectiveness for radar sensing and passive human motion tracking.

The Internet-of-Things (IoT) networks comprise of the wired, the wireless terrestrial and the satellite networks. The satellite IoT networks can cover areas that are not reachable by the wired and the wireless terrestrial networks. A Self-Organizing Time Division Multiplexing Access (SOTDMA medium access control (MAC) protocol is used for the Satellite Automatic Identification System (S-AIS). This paper analyzes and derives the detection probabilities of the ship vessels from a AIS satellite for the S-AIS with a Decollision Algorithm (S-AIS-DA) as well as with Spot Beam (S-AIS-SB) or both (S-AIS-DA-SB). A simple probabilistic model is used to capture the packet error ratios in these schemes. Numerical results show that the performance gains in the number of ship vessels that can be detected can be up to 132% for the S-AIS-DA scheme that can decode up to 4 packets over a basic S-AIS scheme and up to 131% for the S-AIS-DA-SB scheme that can decode up to 4 packets and with 6 spot beams over the S-AIS-SB scheme. The percentage losses of number of ship vessels that can be detected for these schemes with packet loss ratios as compared with these schemes without packet loss ratios are about 1.1%, 1.1% and 2.9% for a decollision algorithm that can decode in an access slot up to one, two and three packets, respectively. On the other hand, the percentage drops in the detection probabilities of the S-AIS-DA scheme with packet error ratios over that of the S-AIS-DA scheme without packet error ratios and the S-AIS-DA-SB scheme with packet error ratios over that of the S-AIS-DA-SB scheme without packet error ratios for detecting up to 3 packets are 4.6% and 3.8%, respectively.

We analyze the performance of a Satellite Slot Carrier-Sense TDMA (SCTDMA) medium access control (MAC) protocol with a decollision algorithm for future maritime VHF Data Exchange System (VDES) in this paper. The key contribution of this paper is the theoretical analysis of this MAC protocol which will be used in the future maritime communication networks — VDES. The key parameter in this proposed MAC protocol is the maximum number of packets that can be recovered by a decollision algorithm. The larger this number, the higher the throughput performance of this proposed MAC protocol. The throughputs and the corresponding offered load points for the maximum normalized throughputs of the proposed MAC protocol are derived and investigated. Both finite packet arrival population and infinite packet arrival population models are modeled, derived and analyzed with new results. Numerical results show that the maximum normalized throughput gain of the proposed MAC protocol can be at least 5.3 times that of the Slotted Aloha MAC protocol for both finite and infinite population models with a decollision algorithm that can recovered up to 4 packet transmissions in an access slot of a frame.

Rise in wireless data traffics requires innovative interference management techniques to meet the demand. Transmit cooperation among multiple base stations has been proposed as a solution to this challenge and improve throughput. For base stations equipped with massive MIMO arrays, a proposed subspace encoding technique can decouple the joint multicell resource allocation problems into independent problems for each cell. The subspace encoding in the multicell environment is analytically equivalent to a reduction of degrees of freedom in a single cell broadcast channel. Hence, the resulting computational and conceptual simplicity can be exploited to arrive at the optimal resource allocation for maximum throughput.

Traditional cellular systems have depended on coverage areas partitioned into disjoint cells where each user is served by a single base station, without any cooperation. To deal with the resulting inter-cell interference, this work combines the advantages of CoMP along with detection and broadcasting techniques with different channel output suitable for massive MIMO. Two novel interference management techniques, viz. Centralised Interference Cancellation (CIC) and Distributed Interference Cancellation (DIC) to optimise power allocation in a cooperative framework have been proposed. The schemes point out the trade off between achievable performance and computational complexity. Since large number of antennas require mathematical manipulation of big random matrices, a suboptimal two layer decoding method is proposed which combines selection diversity with least mean square filtering.

In this paper, we propose a dynamic bandwidth control based medium access control (DBC-MAC) protocol for CWPAN/IEEE 802.11aj networks, which consists of operations like network establishment, network termination, channel splitting and channel expansion. The proposed DBC-MAC protocol solves the coexistence problem between CWPAN/IEEE 802.11aj networks and IEEE 802.11ad networks that are operating in the same or overlapping 60 GHz band and also supports the backward compatibility with the legacy IEEE 802.11ad stations. Performance evaluations show that the DBC-MAC protocol under CWPAN/IEEE 802.11aj networks outperforms the fixed channel bandwidth mechanism under IEEE 802.11ad networks for specific performance metrics.

In this paper, we propose a spatial reuse strategy for millimeter-wave (mmWave) wireless personal area networks (WPANs) with directional antennas. By this strategy, two or more transmissions can be appropriately scheduled for spatial sharing based on the beamforming (BF) information. Moreover, we analyze the performance of this strategy with consideration of the difference between idealistic and realistic directional antennas. Simulation results show that the strategy efficiency is related to antenna types, configurations and network topologies, and that the spatial multiplexing gain can be increased accordingly.

Transmit power of a femtocell access point (FAP) is a key design parameter in two-tier networks. When the FAP is near the macrocell edge, existing transmit power design based on the strongest interference from the macrocell base station (MBS) may not be appropriate. This paper proposes three criteria for FAP transmit power control, two of which taking into account the interference from neighbor MBSs. Particularly, the proposed transmit power control based on the sum interference criterion is suitable for an FAP located near the macrocell edge and outperforms an existing criterion under the target FAP coverage.

A good approximate analytical formulation of the saturated throughput of a Cooperative MAC (CoopMAC) is presented via a two-dimensional discrete-time Markov chain rather than using an approximation. A helper node is used to relay packets from the source node to the destination node within a coverage via a faster two-hop link if possible. The analytical model is formulated with a number of data rates and their corresponding distances. The critical probabilities that at least a helper node exists in different regions to relay packets are explicitly derived through areas of the intersection of the coverages of the source and destination nodes using different data rates to the helper node. By using the weighted sum of the probabilities of the statistics of each of the stations, the saturated throughput of CoopMAC protocol is explicitly derived. Numerical results of the saturated throughput show that the agreement between the simulation and the new analytical results for CoopMAC is very good.

Orthogonal Frequency Division Multiplexing (OFDM) technique serves as an important architecture for very high data rate short range wireless communication systems from Ultra-Wideband (UWB) to 60GHz millimeter wave systems for Wireless Personal Area Networks (WPANs). One of the bottleneck in implementing these high data rate systems is the demanding requirement for high-speed and high-precision Analog-to-Digital Converters (ADCs), as these ADCs are either not available yet, or are very costly and power hungry. This motivates the hardware implementation to use lower precision ADC to simplify the implementation complexity. However, using lower precision ADC will degrade the entire system performance significantly from frequency offset and channel estimation to demodulation and decoding. In this paper, we address the important problem at the front end of an OFDM system, i.e., Carrier Frequency Offset (CFO) and channel estimation problem when using lower precision ADC. We propose joint CFO and channel estimation algorithm using low precision ADC with feedback dither control. Our simulation result shows that it is possible to approach the CFO and channel estimation performance with full precision ADC by using low precision ADC with feedback dither control.

Analytical formulations of the throughput of multi-channel medium access control (MAC) protocols are presented. Both multi-channel multi-rate MAC and multi-channel CoopMAC protocols are considered. A discrete time Markov chain is used to model the number of nodes communicating with the AP in the multi-channel multi-rate MAC protocol, while another discrete time Markov chain is used to model the number of data channels used in the multi-channel CoopMAC protocol. The throughput of the multi-channel multi-rate MAC protocol is expressed as a function of the number of data channels, the channel transmission rate and the solutions to the first Markov chain, while the throughput of the multi-channel CoopMAC protocol is expressed as a function of the number of data channels, the channel transmission rates, and the solutions to the latter Markov chain. The first Markov chain only considers direct one-hop links communications in the multi-channel multi-rate MAC, while the latter Markov chain accounts not only the direct one-hop links communications but also for faster two-hop relaying links communications in the multi-channel CoopMAC as well. Numerical results of the throughput corresponding to typical values are presented. The results also clearly demonstrate the advantage of our proposed multi-channel CoopMAC protocol over a multi-channel multi-rate MAC protocol.

In this paper, a class of quasi-orthogonal space-time block codes (Q-STBC) is proposed for systems with two transmit antennas and three time slots, where the Alamouti code is not applicable due to the odd time slots. The proposed Q-STBC codes achieve rate one and full diversity with low complexity maximum likelihood decoding. The Q-STBC design also shows excellent properties in other practical aspects, such as the compatibility with the single antenna transmission mode, low power fluctuation, and low receiver decoding and transmitter encoding complexity.

In the uplink, while macrocell mobile stations (mMSs) are synchronized to the macrocell base station (mBS), their signals will arrive asynchronously at the femtocell base station (fBS). For OFDMA, if the timing misalignment among the mMSs is greater than the cyclic prefix duration, intersymbol interference (ISI) and intercarrier interference (ICI) will occur in the received signal at the femtocell. In this paper, we show that the average performance of closed access OFDMA femtocell under timing misalignment depends on its distance to the mBS and on the number of mMSs. Simulation results show performance degradations in ergodic capacity and symbol error rate due to ISI and ICI induced by timing misalignment of the mMSs.

In this paper, a class of quasi-orthogonal space- time block codes (Q-STBC) is proposed for systems with 2 antennas and 3 time slots, where the orthogonal Alamouti code can not be applied due to the odd, also known as Orphan, symbol problem inherited in the 3GPP frame structure. The proposed codes can achieve rate one and full diversity with lower complexity maximum likelihood detection. The design also takes into consideration other issues, such as the power fluctuation, the compatibility with single antenna transmission mode, the receiver and transmitter complexity etc.

In this paper, a class of quasi-orthogonal space-time block codes (Q-STBC) is proposed for systems with 2 antennas and 3 time slots, where the orthogonal Alamouti code can not be applied due to the “odd symbol” problem inherited in the 3GPP frame structure. The proposed codes can achieve rate one and full diversity with lower complexity maximum likelihood detection. The design takes into consideration the signal power fluctuation and minimizes the potential peak-to-average ratio (PAPR) in the transmitted signals. The application to Single Carrier Frequency Division Multiple Access (SC-FDMA) has been investigated further. A transmission scheme is proposed to preserve the good PAPR property of SC-FDMA. In addition, linear and iterative decoding algorithms are proposed to simplify the receiver complexity. Simulations have been conducted to demonstrate the superior performance.

Indoor localization is becoming an important application for wireless sensor networks. In order to determine sensors location, ranging packets need to be transmitted. Therefore, a good scheduling scheme is needed in order to avoid collision during packet transmission. Current wireless cellular network allows sensors inside the network to transmit without packet collision by using frequency reuse method or assigning different orthogonal code sequences to every individual sensor so that they can transmit at the same time. One of the drawbacks in the earlier method is the requirement for a large frequency band that must be wide enough to allocate frequencies to all the sensors inside a network. For the latter method, there is a limited number of code sequences that can be assigned to all the sensors inside the network. Therefore in this paper, we first proposed a time scheduling method for ranging packet transmission to avoid packet collision in order to locate a large number of people or objects inside an indoor environment at the same time. The proposed method allows sensors to transmit at different time slot. They are able to use the same frequency across the entire network and interference between neighboring cells is avoided. In addition, frequency guard band is no longer required, therefore, it is bandwidth saving. This makes the system to be scalable to large network coverage, low cost and simple to operate. Secondly, we modified our localization method to suit this time scheduling scheme so that it can perform both offline and online localization for a multi-cell indoor environment.

A common scenario of cognitive radio system consists of a primary network and a secondary network. In our paper, we generalized the scenario to a primary network with the coexistence of multiple secondary networks. An approximate analytical formulation of the saturated throughput of multiple secondary cognitive carrier sense multiple access with collision avoidance (CSMA/CA) networks in the presence of a primary network is presented. Each of these secondary cognitive networks uses a quiet period in a superframe structure to sense the primary network. The longer the sensing time, the lower the probability of false alarm for a fixed detection probability. Numerical results of the saturated throughputs of two secondary cognitive CSMA/CA networks corresponding to typical parameter values are presented. These values are derived from IEEE 802.11n MAC and WiMedia MAC. These results show that the saturated throughputs of these networks can be maximized for certain probabilities of false alarm with sufficient protection of the primary network. These probabilities of false alarm give rise to the corresponding sensing times for these secondary cognitive networks. It is also shown that for some scenarios, the saturated throughputs of these cognitive networks with sensing can be significantly better than those without sensing. The effects of varying the data rates of these networks are also studied.

Coexistence between networks is an emerging challenge in the 60 GHz unlicensed band. An approximate analytical formulation of the saturated throughput of a cognitive IEEE 802.15.3c MAC in the directional contention access period (D-CAP) in the presence of contention time allocation period (CTAP) is presented in this paper. The analytical framework is formulated for N devices, including the pico-net controller (PNC). The state transition diagram is modeled by a two-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the backoff stage and the second dimension is for the value of the backoff counter. The saturated throughput is approximated by the product of a weighted ratio of the throughput of the regular sub-CAP (RS-CAP) and the throughput of the RS-CAP minus the period necessary to transmit a packet before the end of the current RS-CAP, the probability of the number of devices in a beam sector, the number of beam sectors and the probability of false alarm. Numerical results of the saturated throughput corresponding to typical parameter values are presented. These results show the advantage of the cognitive IEEE 802.15.3c MAC in the D-CAP using the single carrier mode when the number of devices in the WPAN is large.

We introduce an iterative decoding algorithm for the decoding of coded interleaved frequency division multiple access (IFDMA) system in this paper. The iterative decoding algorithm incorporates a low complexity a posterior probability (APP) detector based on breadth-first tree search algorithm with a soft-input soft-out (SISO) error-correcting codes (ECC) decoder. The proposed detector combines the principles of the M-algorithm with QR decomposition (QRD-M) to generate soft decision statistics in place of the conventional APP detector which has a high computational cost. We show through simulations that the purposed iterative decoding algorithm is able to achieve significant performance gain using only very small number of iterations. Furthermore, the simulated bit error rate (BER) performance of a system using the proposed algorithm not only exhibits similar diversity order as the hypothetical matched filter bound but also approaches it at high signal-to-noise ratio (SNR).

In this paper, we investigate the use of block spread (BS) and frequency hopping (FH) techniques in coded interleaved frequency division multiple access (IFDMA) systems to achieve maximum channel diversity order. We derive the upper bound on the theoretical bit error rate (BER) that shows the maximum achievable diversity order under maximum likelihood sequence estimation (MLSE). Next, we establish the design criteria for the two different techniques to achieve the maximum diversity order. We also compare the two techniques in terms of their operational complexity and performance. Moreover, we show, through simulation, that the maximum diversity order can be achieved by using a low complexity detector in practical systems instead of the high complexity MLSE.

In this paper, two distributed transmission schemes, namely Distributed Transmitter Maximal Ratio Combining (D-TxMRC) and Distributed Space Time Block Coding (D-STBC) are analysed. The array and diversity gain inherent to the underlying Multiple Input Multiple Output (MIMO) technique are studied, both under independent and correlated fading scenario. It is shown that D-TxMRC is capable of achieving high array gain at the expense of complexity, while only limited array gain is attained using D-STBC scheme. As far as diversity gain is concerned, both schemes achieve full diversity in the order of total number of cooperating nodes under independent fading. The overall performance of the schemes under random network scenario is analysed using average outage probability as a performance metric. The averaging encompasses channel variation as well as network dependent parameters. Effects of different network parameters towards system performance are also analysed. Finally, the performance of cooperative schemes in a more practical network with regular node placements are also studied.

Zero-IF architecture is a competitive alternative to the conventional super-heterodyne architecture for RF-to-baseband conversion in OFDM systems. Despite its advantages of low cost and high integratability, it suffers from the I/Q imbalance that contributes amplitude and phase mismatches between in-phase and quadrature branches, resulting in signal distortion and performance degradation. In this paper, we revisit the problem in a theoretical viewpoint through a minimum distance analysis. In particular, we aim at proving that when the subcarriers are paired symmetrically to a center frequency and the maximum likelihood decoding is employed, the transmitter I/Q imbalance can provide an additional degree of diversity in frequency selective fading channels.

In this paper, a low complexity antenna selection scheme for multi-antenna broadcast systems is developed. Using sum-rate capacity maximisation as the selection criteria, the proposed scheme exploits the duality principle of broadcast and multiple access channel in order to reduce the computational complexity. The performance of the proposed scheme under i.i.d. Rayleigh fading channel is then evaluated via Monte Carlo simulation under different system parameters, and its performance is compared to the full complexity brute force scheme. It is demonstrated that the scheme is able to achieve most of the gain available in the system with a considerably lower complexity.

Network MIMO is a technology being developed towards lifting the interference limits on wireless network through collaborative transmissions from multiple base stations. However its great potential is shadowed by the stringent requirement of high speed/capacity backbones facilitating information exchange, including data, control signals, and channel state information amongst the base stations. In this paper, we propose a user-selective collaboration scheme to mitigate the backbone requirement by reducing the information exchange required. We define a certain threshold for users in each base station and only those users exceeding the threshold will be served by multiple base stations collaboratively. The other users will be served by a single base station as in a conventional non-collaborative transmission. The threshold is determined in such a way that the users with collaborative transmissions enjoy maximized sum rates whereas the others without collaborative transmissions sacrifice only marginal potential collaboration gain in terms of achievable maximized sum rates. As the amount of information to be exchanged will be a square function of the number of users served by the collaborative base stations, the user-selective scheme can reduce the backhaul overhead significantly.

In this paper, a low complexity a posterior probability (APP) detector based on breadth-first tree search algorithm is purposed for coded interleaved frequency division multiple access (IFDMA) system. The proposed detector combines the principles of the M-algorithm with QR decomposition (QRD-M) to generate soft decision statistics in place of the full APP detector which has a high computational cost. We first demonstrate that an IFDMA system can be viewed as a MIMO system at the receiver and then derive the proposed detector. Simulated results show that the bit error rate (BER) performance of a system using the proposed QRD-M detector performs better than a system using frequency domain equalizer, especially for channels with greater diversity. Moreover, the simulated BER performance exhibits similar diversity order as the maximum channel diversity order.

A novel algorithm called partial transmit sequence-active interference cancellation (PTS-AIC) is proposed to implement interference avoidance functionality in an ultra-wideband (UWB) OFDM device. It can be considered as another application of the PTS algorithm that has been applied to an OFDM transmission to reduce its peak-to-average power ratio. Specifically, PTS-AIC with adjacent subblock partitioning and interleaved subblock partitioning are proposed and compared. It is shown that the PTS-AIC can provide deep notch on the interference band. The x%-excess interference power is defined as a performance measure for PTS-AIC. Compared to existing approaches, PTS-AIC provides more flexibility in parametrizing the algorithm for trade-off between performance and complexity.

An emerging short range wireless personal area network (WPAN) is the IEEE 802.15.3c. It can transmit Gigabits per second. In this paper, an approximate analytical formulation of the saturated throughput of IEEE 802.15.3c MAC in the directional contention access period (D-CAP) in the presence of contention time allocation period (CTAP) is presented. The analytical framework is formulated for N devices, including the pico-net controller (PNC). The state transition diagram is modeled by a two-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the backoff stage and the second dimension is for the value of the backoff counter. The saturated throughput is approximated by the product of a weighted ratio of the throughput of the regular sub-CAP (RS-CAP) and the throughput of the RS-CAP minus the period necessary to transmit a packet before the end of the current RS-CAP, the probability of the number of devices in a beam sector and the number of beam sectors. Numerical results of the saturated throughput corresponding to typical parameter values are presented. These results show the advantage of IEEE 802.15.3c MAC in the D-CAP using the single carrier mode when the number of devices in the WPAN is large.

An analytical formulation of the mean detection time and the distribution of the detection time of a wireless microphone (primary user) in an IEEE 802.22 wireless regional area network (WRAN) is presented. The IEEE 802.22 WRAN has a number of customer-premises equipments (CPEs) in the coverage area of its base station. Out of this number of CPEs, a number of them are within the coverage area of the microphone. All of the CPEs can be inactive or active. This is modeled by a discrete time Markov chain. If the microphone turns on or becomes active, the WRAN must be able to detect the microphone and vacates the channel within a time threshold. It is assumed that as long as one of the active CPEs, within the coverage area of the microphone, detects the microphone as active, the microphone is detected. The mean and the distribution of the detection time of the microphone are derived by modeling the detection time by an absorbing discrete time Markov chain. Numerical results corresponding to typical parameter values are presented. The tradeoffs among the number of CPEs, coverage range of the wireless microphone (primary user) and probability of detection are investigated.

In this paper, antenna selection algorithm for multiuser downlink systems where each terminal is equipped with multiple antennas is proposed. As opposed to point to point systems, the broadcast nature of the transmission complicates the selection process as the selection criteria must take into consideration performances of all users collectively. Moreover, computational complexity required needs to be kept as low as possible for practical reason. Exploiting duality between broadcast and multiple access channel, the proposed scheme provides a heuristic approach to selection process in order to maximise the sum-rate capacity of the system, and it is shown that a close to optimal performance can be attained at a considerably lower complexity.

The performance of fast frequency hopping OFDM (FFH-OFDM) is evaluated under UWB channels with several types of receivers. It is shown that FFH-OFDM has a significant improvement over a conventional OFDM system. The receiver algorithms for the FFH-OFDM considered in this paper are zero-forcing (ZF), minimum mean square error (MMSE), QR- MMSE and sorted QR-MMSE (SQR-MMSE). Soft-output metric computation is proposed for the coded case that yields further gain over hard-output decision. The simulation results show the advantage of QR-MMSE and sorted QR-MMSE receivers in the uncoded case while MMSE has better performance for the coded case with a convolutional coding scheme. The insight on the performance advantage of MMSE over QR-based receivers for the coded case is also provided.

In this paper, we propose to exploit the richly scattered multi-path nature of a frequency selective channel to provide additional degrees of freedom for designing effective precoding schemes for multi-user communications. We design the precoding matrix for multi-user communications based on the generalized multi-unitary decomposition (GMUD), where the channel matrix H is transformed into PiRrQiH. An advantage of GMUD is that multiple pairs of unitary matrices Piand Qican be obtained with one single Rr, Since the column of Qican be used as the transmission beam of a particular user, multiple solutions of Qiprovide a large selection of transmission beams, which can be exploited to achieve high degrees of orthogonality between the multipaths, as well as between the interfering users. Hence the proposed precoding technique based on GMUD achieves better performance than precoding based on singular value decomposition.

A block-spreading code division multiple access (BS-CDMA) system is proposed for broadband uplink transmission, giving rise to a significantly improved multiuser performance without using complex multiuser detection techniques. This is because the code orthogonality is easily maintained when channel variation across the consecutive blocks, in a block-by-block high-speed transmission, is negligible. The proposed system uses frequency domain equalisation at the receiver to combat multipath interference efficiently over frequency selective fading channels. We propose despreading before equalisation, which reduces the frequency domain process to symbol-wise operation. A cell-specific scrambling code is employed to suppress other-cell interference for uplink transmission in a multicell system. Our analytical and simulation studies show that the proposed BS-CDMA system has superior multiuser performance over the conventional direct sequence CDMA and cyclic prefix CDMA systems for uplink transmission.

In this paper, an energy efficient structure for beacon signal transmission is proposed for incumbent wireless microphone protection in a cognitive radio system. The proposed structure consists of two consecutive parts: synchronization with index and synchronization with payload, transmitted as in-phase and quadrature components respectively. As opposed to the current beacon design, it can achieve more reliable and balanced error protection for the beacon components, while keeping the system complexity low.

In this paper, we propose a decomposition method called Generalized Multi-Unitary Decomposition (GMUD) which is useful in multi-user MIMO precoding. This decomposition transforms a complex matrix H ∈ Cm×ninto H = PiRQiH, where R is a special matrix whose first row contains only a non-zero user defined value at the left-most position, Piand Qiare a pair of unitary matrices. The major attraction of our proposed GMUD is we can obtain multiple solutions of Piand Qi. With GMUD, we propose a precoding method for a MIMO multi-user system that does not require full channel state information (CSI) at the transmitter. The proposed precoding method uses the multiple unitary matrices property to compensate the inaccurate feedback information as the transmitter can steer the transmission beams of individual users such that the inter-user interference is kept minimum.

In this paper, we investigate the advantages of applying random network coding in sensor networks for security purpose. In particular, the problem of constructing a secure multi-path in wireless sensor networks is considered. However, unlike previous wiretapping scenarios, where the threat is posed by external wiretappers, we approach the security from an internal angle: all nodes comply with the communication protocols yet are potential eavesdroppers. By exploiting the advantages provided by random network coding, dense deployment of sensor nodes, and directed diffusion, a novel secure multi-path construction protocol is proposed. Mathematical analysis and computer simulations show that the proposed protocol can attain the maximum achievable transmission rate, at the same time, it prevents intermediate nodes from acquiring any information transmitted from the source to destination.

In this paper, we consider the detection of OFDM signals used for cognitive radios. Based on the special feature - cyclic prefix embedded in OFDM signals, we propose an optimal Neyman-Pearson likelihood test for the signal detection. We have derived rigorously the probability distribution function of the corresponding decision statistics under frequency selective fading channels and obtained the closed forms of the probability of signal detection and the false alarm rate. The optimal threshold is also derived with respect to a given false alarm rate. Finally, simulations have been conducted to illustrate the promising performance of the proposed detection for OFDM signals under multipath fading environments.

An analytical formulation of the dynamic spectrum allocation problem for handling multiclass services in two cellular radio systems using a complete sharing (CS) scheme is presented. A CS scheme with multiple guard channels for giving prioritization of radio system 1psilas new and handoff call connection over those of radio system 2 and giving prioritization of handoff connections over new connections in each radio system is used for the resource sharing policy at the connection level. The CS model is solved using a K-dimensional Markov chain. Numerical results are illustrated to show the performance of this scheme. The performance metrics include new and handoff connection blocking probabilities and system utilization.

This paper analyses the effect of relay node and the importance of power allocation scheme in cooperative relay networks. It is shown that adding relay node alone is not sufficient to improve system performance. Under a simplest scenario where relay node adopts decode and forward relaying, direct transmission may perform better under certain cases with equal total power constraints. Furthermore, in practical scenario when source node has to transmit its message to relay node before cooperatively transmitting it to destination, the existence of relay node may even degrade system performance. By adopting the right relaying technique and proper power allocation scheme, it is shown that cooperative relay transmission can be made strictly better than direct transmission.

A CDMA scheme employing block processing (BS-CDMA) had been proposed earlier as an effective multiple access scheme that is robust against multiuser interference (MUI) during uplink transmission where conventional CDMA schemes fail due to orthogonality destruction. However, residual MUI arises in BS-CDMA and its degradation impact becomes severe when high mobility users are present. Two interference cancellation techniques are proposed in this paper that utilizes the users' mobility condition to determine the detection ordering sequence. Based on extensive simulation studies, results show that the proposed techniques perform well in the presence of high number of users with high mobility.

When an ultrawideband (UWB) transmitter is operating, it must not cause interference to existing primary users. Three new techniques are proposed in this paper in order to enhance the active interference cancellation (AIC), which is a technique to avoid causing the interference, for multiband-OFDM UWB transmitters. The first technique applies cyclic shifting while the second technique applies phase shifting to the frequency-domain data symbols. The third technique is a combination of these two techniques and is shown to improve the performance by about three orders of magnitudes. It is shown by simulation that the proposed techniques are able to enhance the performance of AIC significantly albeit higher complexity and a need for sending feed-forward bits.

Fast frequency hopping OFDM (FFH-OFDM) is a recently proposed concept to enhance conventional OFDM performance without using channel coding by fully exploiting frequency diversity available within one OFDM symbol. Previously, a linear receiver of FFH-OFDM requires zero-forcing (ZF) or minimum mean squared error (MMSE) detection algorithm. This paper introduces QR-based receivers for FFH-OFDM systems to further enhance the detection performance. By exploiting a special form of an effective channel matrix with the proposed scheme, a reduced complexity algorithm of QR decomposition is proposed. Simulation results indicate that the QR-based receivers outperform the MMSE and ZF receivers by about 4 dB and more than 5 dB at FER= 10-2, respectively, in an uncoded case. In a coded case, however, the MMSE receiver has similar performance to the proposed QR-based receivers.

An analytical formulation of the saturated throughput of Prioritized Contention Access (PCA) with Hard Distributed Reservation Protocols (DRPs), Quiet Period (QP) and Beacon Period (BP) in Cognitive WiMedia MAC is presented. The analytical framework is formulated for one Hard DRP class and N PCA classes. The state transition diagram for the ith priority PCA class is modeled by a tri-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the backoff stage, the second dimension is for the value of the backoff counter, while the third dimension is mainly for the delay due to DRP transmissions or QP and BP. A numerical result of the saturated throughput corresponding to typical parameter values is presented.

Analytical formulations of dynamic spectrum access (DSA) with complete partitioning (CP), complete sharing (CS) and virtual partitioning (VP) for two radio systems are presented. The DSA with CP and CS models are solved explicitly using two one-dimensional Markov chains and a two-dimensional Markov chain, respectively, while the DSA with virtual partitioning model is solved numerically using a two-dimensional Markov chain. Grades of service (GoSs) like system airtime, blocking probabilities and preemption probabilities are considered. The performance of these GoS measures and the effect of the size of the nominal number of frequency channels for DSA with VP are evaluated. Numerical results illustrate that the advantages of DSA with VP as compared with DSA with CP and DSA with CS.

This paper proposes an accurate UWB multiple-cell localization system which adopts an adaptive TDOA combination algorithm to reduce the localization uncertainty. The time difference of arrival (TDOA) is adaptively combined in such a way that only makes use of the best directional motion increments to reduce both the random channel noise and the geometric errors. Furthermore, maximum signal to noise ratio (SNR) TDOA combining and tracking error controlling are employed to reduce the localization uncertainty. Unlike the conventional TDOA equation solutions, the algorithm avoids using the nonlinear triangular calculation and the TDOA matrix inversions to improve the performance with minimizing dilution of precision (DOP). This method shows a very good competition compared to the existing methods in tracking/filtering process and even achieves a better Cramer-Rao bound (CRB). The hardware including the moving target (tag) and the receiver system had been designed with a very low cost, and long battery life. Finally, after giving the analysis of DOP, the real experimental system reveals that it outperforms the other methods in term of CRB evaluation and error (bias) mitigation.

In this paper, we propose a coverage optimization algorithm based on QoS requirements. The coverage optimization algorithm improves the network QoS performance by the joint-optimization of coverage, routing, energy efficiency and delay. The QoS metrics are created with the priorities of the routing consistence, network lifetime and the coverage model, etc. Also, a new method is developed to take advantages of the dense area to compensate the sparse area with the predictor plus interpolation method. With this method, relaying nodes from dense area are chosen to provide compensating coverage for the sparse area. Furthermore, this method can greatly improve the network lifetime by extending the contingent battery life of the nodes in the spare area. Finally, the simulation results perform the evaluation for our algorithm.

We investigate the impact on the overall throughput of ad-hoc networks using two node connectivity control schemes. We propose a varying power constant connectivity (VPCC) scheme, where each node in a network regulates its transmission power until the number of its neighbors (node connectivity) is maintained at some desired number, whose optimal value is a design parameter to be determined. The achievable throughput is compared with the commonly adopted constant power varying connectivity (CPVC) scheme, where each node transmits at a constant power and hence has fixed transmission coverage but the connectivity changes from node to node. We derive the theoretical probability mass function of the number of neighbors of a given node for the CPVC scheme, and the probability density function of the coverage radius for the VPCC scheme. Simulation results are made to study the achievable throughput of the two schemes under the Poisson packet arrival assumption and when carrier- sense multiple access with collision avoidance and exponential back-off timer are used. The results from the simulation show that even if VPCC may result in a higher average number of hops per transmission under the same traffic condition, it can still achieve a much higher throughput than CPVC scheme. To have a better insight, we postulate and verify via simulations that the overall system throughput depends only on a parameter, which is equal to the frequency reuse factor divided by the average number of hops regardless of the schemes and the nodal density. This relationship provides a useful guide to designers, in which the parameter can be computed to predict the throughput before the most suitable scheme is selected.

An analytical formulation of the saturated throughput of burst mode prioritized contention access (PCA) with hard distributed reservation protocols (DRPs) and beacon period (BP) in WiMedia MAC is presented. The analytical framework is formulated for one hard DRP class and N PCA classes. The state transition diagram for the ith priority PCA class is modeled by a tri-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the backoff stage, the second dimension is for the value of the backoff counter, while the third dimension is mainly for the delay due to DRP transmissions or BP. The probability of the number of consecutive DRP MASs and the number of consecutive PCA MASs are derived, taking into consideration of all possible combinations of the DRP locations in a superframe. These probabilities are essential for the modeling of the Markov chain.

Analytical formulations of dynamic spectrum access (DSA) with perfect sensing (PS) and imperfect sensing (IS) for two radio systems are presented. The DSA with PS model is solved explicitly using a two-dimensional Markov chain, respectively, while the DSA with IS model is solved numerically using a two-dimensional Markov chain. Grades of service (GoSs) like system airtime and blocking probabilities are considered. The performance of these GoS measures and the effect of the probability of false alarm and probability of misdetection for DSA with IS are evaluated. Numerical results illustrate that the effect of DSA with IS as compared with DSA with PS.

An analytical formulation of the saturated throughput of Prioritized Contention Access (PCA) with Hard Distributed Reservation Protocols (DRPs) and Beacon Period (BP) in the presence of bit error for WiMedia MAC is presented. The analytical framework is formulated for one Hard DRP class and N PCA classes. The state transition diagram for the ith priority PCA class is modeled by a tri-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the backoff stage, the second dimension is for the value of the backoff counter, while the third dimension is mainly for the delay due to DRP transmissions or BP. Numerical results of the saturated throughput corresponding to data rate of 1 Gbps are presented.

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems based on biphase shift keying (BPSK), orthogonal pulse position modulation (OPPM) and pulse shape modulation (BPSM). A set of M = 2ksymbols are constructed by using L = 22lorthogonal pulse positions and N = 22k-l-1biorthogonal pulses, where k and l are nonnegative integers such that 0 ≤ l ≤ k - 1. The selection of number of pulse positions and pulses depend on the system performance and the availability of orthogonal pulses with estimable auto-correlation properties. The proposed scheme achieves higher data rate by introducing more number of orthogonal pulses in the same pulse repetition interval. It also reduces the system complexity by half by introducing antipodal version of orthogonal pulses. The proposed transmission scheme is analyzed through computer simulations in the presence of multipath channel.

Cognitive radio (CR) is seen as one of the revolutionary techniques for future spectrum utilization. The first and probably the most challenging task for CR is to detect/sense the white space of the spectrum for its usage. In this paper, detection of DVB-T signals is studied since TV band has been considered by Federal Communications Commission (FCC) to be pioneered for CR usage. Cyclostationary feature of DVB signals is explored so that the robust single-cycle detector (SCD) can be employed to handle the problem of noise uncertainty, to which the widely used energy detector (ED) is susceptible. Due to complexity concerns for real-time implementation, a blind twin peak (BTP) detector is proposed to approximate the performance of SCD while keep the complexity as low as ED.

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems using on-off keying (OOK) and pulse shape modulation (PSM). For this scheme, a set of orthogonal pulses is used to represent bits in a symbol. These orthogonal pulses are transmitted simultaneously in the same time slot resulting in a composite pulse. By assigning different subset of orthogonal pulses for each user, multi-user interference can be reduced considerably. The proposed transmission scheme can achieve higher data rate by using fewer pulses and can use fewer number of receiver correlators than those used in PSM. Due to the presence of OOK, the proposed scheme requires minimum energy and is applicable for energy constrained UWB systems. The bit-error-rate (BER) performance of the proposed transmission scheme is analyzed both mathematically and through computer simulations in additive white Gaussian noise (AWGN) channel and modified IEEE 802.15.3a S-V UWB multipath channel model. The present paper also compares the proposed scheme with existing PSM and its combined modulation schemes.

We detail a code mapping scheme designed especially for devices in the enhanced wireless personal area networks operating in both the 868 MHz and 915 MHz bands for the emerging IEEE 802.15.4b standard. This carefully designed coding scheme, called cyclic odd bit inversion length 16 (COBI-16), meets all the following three essential criteria: (a) no spikes in the frequency spectrum, (b) low complexity correlation operations and (c) simple frequency offset and DC compensation operations. The scheme is tested in both AWGN and Rayleigh fading (flat and frequency selective) channels. Both coherent and non-coherent demodulations are investigated. Also investigated are the synchronous false alarm rate and synchronous miss rate in the AWGN channel. The results show that the scheme conforms to all the stringent requirements defined by the IEEE 802.15.4b protocol. The scheme has been accepted by the IEEE 802.15.4b task group as the standard for data transmission.

This paper introduces a new cooperative localization method for wireless sensor network called symmetric multi-way ranging (SMWR). By performing multiway ranging symmetrically in two phases, this method is able to eliminate the error caused by crystal timing drift and is energy efficient as well. Simulation results show that the proposed SMWR method significantly outperforms prior work under random crystal timing drift assumption.

A cognitive radio network (CRN) is often described as a secondary communication network operating in a frequency band originally allocated to a primary network consisting of one or multiple primary users (PUs). In this paper, we consider a wireless ad hoc network as a CRN, which coexists with multiple geographically distributed PUs. A novel approach based on network coding is proposed for wireless multicast in CRNs to improve the throughput of the secondary network with minimum energy-per-bit, while protecting the PUs. Under interference power constraints for PUs, and signal-to-interference- plus-noise ratio (SINR) constraint for each transmission, we formulate the minimum-energy multicast in CRNs problem as a linear optimization, which is much easier to solve compared to the NP-hard problem associated with the routing solution. Computer simulations are presented to evaluate the performance gains achieved by the proposed technique in terms of network throughput as well as energy efficiency.

This paper evaluates the performance of distributed space time coding in generic ad-hoc network scenario. The condition where multiple nodes (confined within a certain geographical area) wanting to exchange information to one another is considered. Effect of different system parameters such as total number of nodes, path loss exponent, node density, and error threshold, toward overall system performance are analysed.

The present paper proposes a new relaying scheme called successive dirty paper coding. Theoretical achievable rate of the scheme is derived and its performance is compared to other existing relaying schemes in terms of their outage probability. It is shown via numerical studies and supported by simulation analysis that the proposed scheme is able to achieve higher bandwidth efficiency by reusing relay slots to transmit new messages. An improvement of up to M-fold, where M is the average number of relay stages in every transmission, compared to traditional non-cooperative relaying is observed.

Peak to average power ratio (PAPR) is one of the key parameters for efficient power amplification in multicarrier systems. Practical implementation difficulties and the performance constraints are two major limiting factors for many of the methods suggested for PAPR reduction. It is in this context, this paper suggests a simplified approach for PAPR reduction of multicarrier CDMA systems based on efficient coding of optimal binary phase sequences. Using this method, the side information related to phase values for PAPR reduction are spread using dedicated spread code and add with other user data before transmitting through channel. The overheads required for the proposed method is very minimal and the system performance is robust against channel estimation errors.

10.1109/PIMRC.2007.4394856

IEEE 802.15.4b is an enhanced standard to the IEEE 802.15.4, addressing the needs for high-data rate transmission using 868 or 915 MHz band in the wireless personal area networks. This paper details a modulation and code mapping scheme designed specifically for the standard's high rate transmission schemes operating in the 868 MHz and 915 MHz bands; which leads to efficient transmission and low implementation complexity. The code mapping scheme is called Quadrature Cyclic Odd Bit Inversion length 16 or Quad COBI-16. Among the scheme's desirable properties is that the total phase rotation in the I/Q plane accumulates to 0 degree over the complete symbol. The scheme is tested in both AWGN and Rayleigh frequency selective fading channels. The results show that it conforms to all the stringent requirements defined by the standard.

An analytical formulation of the saturated throughput enhancement of IEEE 802.11e using double increment plus one/ minus one half decrement (DIPO/MOHD) backoff mechanism for multiclass traffic is presented The analytical framework is formulated for N classes. The state transition diagram for the ith priority class is modeled by a two-dimensional discrete-time Markov chain One dimension of the Markov chain is for the backoff stage, and the second dimension is for the value of the backoff counter. The backoff stage moves to its previous backoff stage after a successful packet transmission and not back to the backoff stage 0 as in IEEE 802. lie. The advantages of this backoff mechanism are that it is easy to be implemented and can enhance the saturated throughputs. Numerical results of the saturated throughput corresponding to typical parameter values are presented The results show that the total saturated throughput using DIPO/MOHD can be better than that of IEEE 802. lie by up to 19%.

An analytical formulation of the saturated delay of Prioritized Contention Access (PCA) in the presence of Hard Distributed Reservation Protocols (DRPs) and Beacon Period (BP) in WiMedia MAC is presented. The analytical framework is formulated for one Hard DRP class and N PCA classes. The state transition diagram for the ith priority PCA class is modeled by a tri-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the backoff stage, the second dimension is for the value of the backoff counter, while the third dimension is mainly for the delay due to DRP transmissions or BP. A numerical result of the saturated delay corresponding to typical parameter values is presented.

The sum-rate of the broadcast channel in a multi-antenna multi-user communication system can be achieved by using precoding and adding a regular perturbation to the data vector. The perturbation can be removed by the modulus function, thus transparent to the receiver, but the information of the precoding matrix is needed to decode the symbols. This paper proposes a new technique to improve the multi-antenna multi-user system, by adding a continuous perturbation to the data vector without the need of information on the precoding matrix to be known at the receiver. The perturbation vector will be treated as interference at the receiver, thus it will be transparent to the receiver. The derivation of the continuous vector perturbation is provided by maximizing the signal-to-interference plus noise ratio or minimizing the minimum mean square error of the received signal.

This paper presents sub optimal method to perform antenna selection in MIMO-OFDM systems. This method allows reduction in the complexity by exploiting inter-subcarrier correlation or through disjoint selection of transmit and receive antennas. Their performances and complexities are then analysed and contrasted with respect to conventional brute force method.

This paper presents a new ranging method called symmetric double side two way ranging with unequal reply time (SDS-TWR-URT). The proposed method is able to reduce the ranging error due to the clock crystal drift when there are significant variations in the reply time at the sensor nodes.

An analytical formulation of the saturated throughput of prioritized contention access (PCA) in the presence of soft distributed reservation protocols (DRPs) and beacon period (BP) in WiMedia MAC (formerly multi-band OFDM alliance (MBOA) MAC) is presented. The analytical framework is formulated for one soft DRP class and N PCA classes. The state transition diagram for the ith priority PCA class is modeled by a tri-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the backoff stage, the second dimension is for the value of the backoff counter, while the third dimension is mainly for the delay due to DRP transmissions or BP. Numerical results of the saturated throughput corresponding to typical parameter values are presented.

An analytical formulation of the saturated throughput of a Cooperative MAC in IEEE 802.11n for multiclass traffic is presented. A helper node is used to relay packets from the source node or access point (AP) to the destination node within a circular coverage. The analytical framework is formulated for N classes, K data rates and their corresponding K distances. The saturated throughput analysis for multiclass traffic is formulated using a two- dimensional discrete-time Markov chain rather than using an approximation. The critical probability that a helper node exists in a region to relay a packet is explicitly derived. Closed-form result for the saturated delay is also derived. Numerical results of the saturated throughput corresponding to typical parameter values are presented. The results show that the total saturated throughput using Cooperative MAC can be better than that of IEEE 802.11n using direct transmissions by up to 67% and the saturated delays using Cooperative MAC are also better than those of IEEE 802.11n.

The shadowing in ultra wideband (UWB) channels may degrade the system performance significantly. Although UWB multipath channels exhibit high resolution in space and time. The large scale shadow fading were moderately correlated based on UWB indoor channel measurement. In this paper, a new modelling method for correlated shadowing with log-normal distribution in UWB multiple-input multiple-output (MIMO) channels is proposed based on the Kronecker model and IEEE 802.15.3a channel model recommendation. Moreover, antenna selection technique with low hardware complexity is proposed for a UWB system with multiple receive or transmit antennas to mitigate its channel shadowing effect. The BER performance for orthogonal frequency division multiplexing (OFDM) UWB system with power based antenna selection is evaluated. Antenna selection technique is shown to be effective in mitigating the correlated shadow fading.

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems based on orthogonal pulse position modulation (OPPM) and bi-orthogonal pulse shape modulation (BPSM). A set of M=2ksymbols are constructed by using L = 2lorthogonal pulse positions and N = 2k-l-1biorthogonal pulses, where k > 1 and l are nonnegative integers such that 0 les l les k-1. The selection of the number of pulse positions and pulses depends on the system performance and the availability of orthogonal pulses with estimable auto-correlation properties. This scheme allows an increase in the number of bits per symbol and consequently, reduces the duration of the pulse repetition interval which is obtain by increasing the number of orthogonal pulses. The proposed scheme achieves higher data rate by using a large number of orthogonal pulses in the same pulse repetition interval. It also reduces the system complexity by half by introducing antipodal version of orthogonal pulses. The proposed transmission scheme is analyzed through computer simulations in a multipath channel using two sets of orthogonal pulses.

An analytical formulation of the saturated throughput of prioritized contention access (PCA) in the presence of hard distributed reservation protocols (DRPs) and beacon period (BP) in WiMedia MAC (formerly multi-band OFDM alliance (MBOA) MAC) is presented. The analytical framework is formulated for one hard DRP class and N PCA classes. The state transition diagram for the ith priority PCA class is modeled by a tri-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the backoff stage, the second dimension is for the value of the backoff counter, while the third dimension is mainly for the delay due to DRP transmissions or BP. Numerical results of the saturated throughput corresponding to typical parameter values are presented.

A joint transmit and receive antenna selection technique for MIMO-OFDM is presented. By appropriately ordering and tabulating the minimum channel sub-matrix's sub-stream signal to noise ratio in all subcarriers, an optimal antenna subset can be obtained. This procedure can be simplified further by analysing the inter-subcarrier correlation and by exploiting group selection methods. Complexity analyses on the proposed algorithm are presented, and performance improvements achievable are demonstrated through simulation studies.

The Cramer-Rao bounds (CRBs) of near field electromagnetic ranging (NFER) are derived for the cases of ranging and 2-D localization. From the derived CRBs, it is shown that the accuracies are dependent on the true location and frequency used, in addition to the signal-to-noise ratio. Ulitizing the derived bound for 2-D localization, the selection of frequency can be made to achieve the best average accuracy in different area sizes.

IEEE 802.15.4b is an enhanced standard to the IEEE 802.15.4, addressing the need for high-data rate transmissions in the 868 and 915 MHz band in the wireless personal area networks. This paper details a code mapping scheme designed specifically for the standard's 915 MHz band that leads to efficient transmission and low implementation complexity. The scheme is called quadrature cyclic odd bit inversion length 16 or Quad COBI-16 and one of its desirable properties is that the total phase rotation in the I/Q plane accumulates to 0 degree over the complete symbol. The scheme is tested in both AWGN and Rayleigh fading (flat and frequency selective) channels. Both coherent and non-coherent demodulations are investigated. Also investigated are the synchronous false alarm rate and synchronous miss rate in the AWGN channel. The results show that the scheme conforms to all the stringent requirements defined by the IEEE 802.15.4b protocol.

In this paper, we propose a near field wideband linear constraint minimum variance (LCMV) beamforming with entropy based artifacts removal for UWB imaging in breast cancer detection. We define an entropy function in antenna domain to measure the similarity of the different antenna signals and design a window function to eliminate the very similar artifacts at all antennas. This algorithm requires no prior knowledge about the breast and tumor, and brings no distortion to the tumor reflection. After removing the artifacts, we model the tumor as a near field region source. By applying the coherent signal subspace method, a wideband near field LCMV beamforming to the region source is developed. The output power of the beamforming forms the image of the breast with tumor embedded. Applied to 2D computed finite-difference time-domain (FDTD) data, the algorithm clearly identifies the 2mm-diameter tumor. Simulation results also demonstrate the efficiency and robustness of the proposed algorithm.

This paper presents the design of a (n,k) Reed-Solomon decoder for both errors and erasures. The key-equation solver is based on Sarwate's reformulated inversionless Berlekamp-Massey algorithm. The decoder has been implemented on FPGA and the maximum clock frequency can be 150 MHz for a (255, 239) code on a Xilinx Virtex-II device.

Near field electromagnetic ranging (NFER) can offer high localization accuracy from moderate precision measurements with inherent immunity against non-line-of-sight and multipath problems. This paper explores the factors affecting accuracy in ranging and 2-D localization using NFER by deriving the Cramer Rao bounds (CRBs). From the CRBs, it can be seen that besides the signal-noise ratio, the accuracy is dependent on the true location and the frequency used. Exploiting this property, ranging and maximum likelihood estimation (MEE) localization algorithms are developed for application of multiple frequencies to NFER to improve accuracy. Simulation results show that substantial improvement in accuracy is achieved for the algorithms over using a single frequency for NFER

This paper presents performance evaluation of antenna selection capability proposed in IEEE 802.16e (Amendment of IEEE 802.16-2004 standard for combined Fixed and Mobile Broadband Wireless Access operation in licensed band), under 2048 points orthogonal frequency division multiple access (OFDMA) mode of operation. It is shown that channel condition plays significant role on the amount of gain achievable by the scheme. Modification to the selection method is proposed and additional gain achieved is demonstrated. Measurements under different signal to noise ratio (SNR) values for different channel models are analysed. Results of the experimental studies are then summarised

We detail a cyclic odd bit inversion length 16 (COBI-16) code mapping scheme designed especially for devices in the enhanced wireless personal area networks operating in the 915 MHz for the emerging IEEE 802.15.4b standard. This carefully designed coding scheme meets all the following three essential criteria: (a) no spikes in the frequency spectrum, (b) low complexity correlation operations and (c) simple frequency offset and DC compensation operations. The scheme is tested in both AWGN and Rayleigh flat and frequency selective fading channels. Both coherent and noncoherent demodulations are investigated. Also investigated are the synchronous false alarm rate and synchronous miss rate in the AWGN channel. The results show that the scheme conforms to all the stringent requirements defined by the IEEE 802.15.4b protocol. The scheme has been accepted by the IEEE 802.15.4b task group as the standard for data transmission

In this paper, a pulse UWB system based on 16-ary ternary orthogonal keying (TOK) is proposed for low power low data rate wireless personal area networks (WPAN). The novel ternary sequence based common signaling in the UWB system is proposed to support efficient implementation for both simple energy detectors and complex coherent detectors. Three variants on different pulse compression and clustering are also discussed and simulations have been conducted for both additive white Gaussian noise channels, UWB line-of-sight and non-line-of-sight fading channels. The results have demonstrated the superior performance of the proposed UWB system over other systems.

In this paper, diagonally loaded linear Minimum Mean Square Error (MMSE) equalization technique is proposed for Ultra Wideband (UWB) multipath channel in the presence of Inter Symbol Interference (ISI) and Multiple Access Interference (MAI). In the case of practical implementation under limited training sample support, the optimal solution for linear least squares problems is the Minimum Norm (MN) solution. But it suffers from performance degradation when the sample covariance matrices are ill-conditioned. Diagonal Loading (DL) technique is incorporated into MN solution and shown to achieve significant performance improvement when the amount of training symbols is comparable with the number of taps utilized by the equalizer. Moreover, a rank-reduced Multistage Wiener Filter (MWF) with DL is proposed for UWB multipath channel equalization which requires large number of taps. It is shown to converge to the MN solution with much reduced computational complexity.

Though the introduction of Code Division Multiple Access (CDMA) in Orthogonal Frequency Division Multiplexing (OFDM) technique, we propose a novel direct sequence spreading with chip interleaved scheme for a Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) system by re-ordering the chip sequences to achieve frequency diversity and randomization effect in frequency domain. MB-OFDM is a promising technique to implement high data rate Ultra-Wideband (UWB) transmission over short range in dense multipath environment with low-power consumption and low-cost characteristics. However, the original MB-OFDM proposal for 480Mbps mode could not achieve satisfactory performance due to the inability of the error correction code at high coding rate such as 3/4 to provide sufficient protection for OFDM to combat the deep fading in some of subcarriers. In this paper, a chip-interleaved MB-OFDM UWB system is introduced and discussed. The performance has been evaluated and simulation results show that the proposed chip interleaved scheme improves the performance for 480Mbps mode of about 1.5 dB at PER = 0.08. By using block spread chip interleaving structure, the interleaver structure for the proposed chip interleaved scheme is very simple to implement and has less delay latency.

In this paper, we introduce a novel sampling offset estimation scheme based on iterative two-dimensional estimation principle for Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) system. The proposed scheme estimates the sampling frequency offset through the phase distortion of pilot sub-carriers in each OFDM symbol and improves the accuracy by averaging the estimate from each pilot sub-carrier across both the sub-carrier dimension and the symbol dimension. Through analysis and simulation, we show that the proposed scheme is superior to existing schemes in minimizing the performance degradation due to sampling frequency offset in MB-OFDM system effectively, especially in long packet transmission.

In this paper, a new pulse-based UWB system is proposed with low power ranging. The ternary sequence based common signaling is proposed to support power efficient energy detectors, differential detectors, and coherent detectors simultaneously. The preamble for ranging is designed to have good autocorrelation properties. The on-off keying based power efficient modulation is combined with chip mapping/spreading to provide robust system performance even in a multipath fading channel. Furthermore, a low complexity energy detection receiver structure is elaborated for leading edge detection in a multipath rich channel. System simulations are performed to demonstrate the promising performance of the proposed system

We detail a cyclic odd bit inversion length 16 (COBI-16) code mapping and modulation scheme designed especially for devices in the enhanced wireless personal area networks (WPAN) operating in the 868 MHz for the emerging IEEE 802.15.4b standard. This COBI-16 scheme has been accepted and incorporated in the draft IEEE 802.15.4b standard. This carefully designed coding and modulation scheme meets all the following three essential criteria: (a) no spikes in the frequency spectrum, (b) low complexity correlation operations and (c) simple frequency offset and DC compensation operations. The transmitted signal meets all the IEEE standard's stringent PSD mask requirements. The system is tested in both AWGN and Rayleigh fading (flat and frequency selective) channels. Both coherent and non-coherent demodulations are investigated. Also investigated are the synchronous false alarm rate and synchronous miss rate in the AWGN channel

In this letter, we propose an entropy-based time window function for artifact removal in ultra-wideband (UWB) imaging of breast cancer detection. The artifact is due to the incident and skin-breast backscattered signal in such an imaging system. Observing that artifacts at different antennas are very similar, we define an entropy function in the antenna domain to measure the similarity of different antenna signals and design a rectangular window function to eliminate the artifacts. This window function is applied to the computed finite-difference time-domain (FDTD) data of the breast model with a tumor embedded. Compared with the Wiener filtering algorithm, this entropy-based algorithm is computationally simple. In addition, it requires no prior knowledge about the breast and the tumor and brings no distortion to the tumor reflection

This paper proposes an over-sampling multi-channel equalizer per sub-band for multi-band ultra-wideband (UWB) system and compares its performance with conventional RAKE receiver when operating in practical UWB channel models. Three transmission modes have been considered, and inter-symbol interference (ISI) is found to be inherent to certain transmission modes due to the large UWB channel delay spreads. Through detailed analytical and simulation studies, the proposed over-sampled minimum mean square error (MMSE) equalizer is shown to be able to handle ISI under any channel conditions or transmission modes, with an acceptable BER. In addition, the rich multipath diversity of the UWB channels is harnessed by the over-sampling scheme, for output SNR improvement. Over-sampling is done in the expense of an increase in system complexity

We present a statistical model for the characterization of ultra-wideband (UWB) channels for the outdoor office environment. The bandwidth is from 3-6 GHz and measurements are done for the line-of-sight (LOS) and non-line-of-sight (NLOS) cases. Small scale effects are modeled by the Saleh-Valenzuela (S-V) model with modifications on the ray arrival times and amplitude statistics to fit the empirical data. The ray arrival times are described by a mixture of Poisson processes while the amplitude statistics are follow a Nakagami distribution with the m parameter following a lognormal distribution. The parameters for the cluster and ray power-decay time constants, cluster and ray arrival times, mean excess delay and RMS excess delay are also extracted to define the channel model completely.

In this paper, a symbol relocated (SR) scheme has been proposed for variable spreading factor orthogonal frequency code division multiplexing (VSF-OFCDM) systems to achieve frequency diversity during retransmission. The performance has been evaluated for two combining schemes of hybrid auto repeat request (ARQ) namely chase combining and incremental redundancy. The results show that the proposed SR scheme achieves significant improvement in terms of system throughput over the conventional schemes. This effect is more significant for chase combining because the rotated mechanism is more effective when the same packet is transmitted during the retransmission. It is also found that SR scheme is not sensitive to Doppler frequency variation, which makes SR scheme an attractive candidate for fast fading channels. Further investigations also suggest the suitability of the SR scheme for smaller spreading factors (in frequency domain) and larger coding rates.

Ultra-wideband (UWB) technology is one of the promising solutions for short-range indoor wireless communication applications. UWB systems spread the transmitted signal power over an extremely large frequency band, and the power spectral density of the signal is very low. Due to the wide bandwidth of the transmitted signal, UWB signal energy will spread over the frequency bands allocated to other radio systems. In order to evaluate the effects of UWB system to narrowband systems (such as IEEE802.11a wireless LAN) in its overlay band, it is important to understand and quantify the power spectral density (PSD) of UWB signal. In this paper, a detailed analysis on the PSD of direct sequence coded UWB (DS-UWB) signal is presented. The theoretical and simulation results reveal that the interfering DS-UWB power can be reduced by regulating UWB chip rate, pulse shape, pulse width and scrambling codes in the frequencies of victim narrowband systems.

In this paper, the architecture of a multi-antenna CDMA receiver that is realized with CORDIC processors is presented. With multiple antennas, the receiver has a good performance of BER (bit-error-rate) compared to RAKE receiver, and the hardware has nearly the same complexity as the RAKE receiver. The CORDIC structure using the shifting-addition operation instead of the complex multiplier is more feasible and flexible to realize WCDMA receiver with VLSI hardware architecture. For the WCDMA receiver, the FIR filter of the channel equalizer is also implemented with CORDIC so that the hardware complexity is reduced greatly. At last, the experiment results prove that the CDMA CORDIC receiver is good at both hardware efficiency and interference rejection.

In this letter, an improved square-root algorithm for Bell Labs Layered Space-Time (BLAST) system is proposed. It speeds up the original square-root algorithm by 36% in terms of the number of multiplications and additions. Compared with the recursive algorithm, it requires only a 13.6% higher number of multiplications and a 38.9% higher number of additions. Since it uses unitary transformations to avoid the computation of any matrix inversion or "squaring" operation, it maintains the advantages of the square-root based algorithms that are numerically stable, robust, and hardware friendly.

This paper presents an advanced architecture for residue number system (RNS)-based code-division multiple-access (CDMA) system for high-rate data transmission by combining RNS representation, phase shift keying/quadrature amplitude modulation (PSK/QAM) and orthogonal modulation. The residues obtained from a fixed number of bits are again divided into spread code index and data symbol for modulation. The modulated data symbol is spread using the indexed orthogonal codes and transmitted through a communication channel. The proposed system uses a lower number of orthogonal codes than conventional RNS-based CDMA and the performance is comparable. The computational complexity of the proposed system is compared against alternative schemes such as M-ary CDMA and conventional RNS-based CDMA. The modified system is simulated extensively for different channel conditions and the results are discussed.

This paper proposes a unified two-dimensional maximum-likelihood multipath channel estimator for both multicarrier and single-carrier CDMA systems with cyclic prefix. The conditions for the optimal training sequence and the lower bound for the performance of this estimator are obtained by solving an optimisation problem. Optimal and sub-optimal training sequences are designed from several classes of sequences with ideal autocorrelation and cross correlation properties. Furthermore, the complexity of this channel estimator is reduced considerably by applying the optimal training sequence. The simulation results demonstrate that this channel estimator combined with optimal or sub-optimal sequence can give near single-user channel estimation performance even for fully loaded systems.

Personal area networks (PANs) are expected to play an important role in future mobile ad-hoc wireless communications and information systems. This paper proposes an UWB-based alternate PHV layer for 802.15.4 low rate wireless personal area network (LR-WPAN) system with the intention to enhance such WPAN system with better location positioning capability. The proposed UWB transceiver operates in the first 500 MHz band, 3.1 - 3.6 GHz, within the FCC allocated UWB band. Original 802.15.4 code position modulation scheme is slightly modified to 2-PPM to cater UWB transmission. A simple peak detector based receiver is employed to sample and decode the transmitted symbol. Intensive simulation over IEEE 801.15.3a UWB channel models showed that the proposed UWB based alternate PHY layer can support 802.15.4 250 kbps 16-byte packet transmission over WPAN range of 5 m with 10% PER. It is also illustrated that, in general, PER increases over longer communication range and over longer channel delay spread.

One of the distinguishing features of impulse radio or ultra-wideband (UWB) systems is by their broad bandwidth. The resulting power spectral density of UWB systems can become very small due to the very large bandwidth. With such low radiated power, it is important to design a receiver that maximises the signal-to-noise ratio (SNR). Conventionally, this is achieved by a pulse matched filter. Due to the high data rate of UWB, pulse matching may not be feasible. Therefore, a template matching approach is employed instead. A local-oscillator (LO) based UWB receiver scheme is presented, derived from the conventional down-converter for narrowband systems. Instead of carrier modulation, the LO in the proposed receiver is for sub-optimal template matching with the received signals, matched in time but not in amplitude. This sub-optimal matched template is made possible by certain properties of the received UWB signals. The output is then low-pass filtered, and sampled. The selection of suitable low pass filters (LPF) and sampling rate for maximum energy collection with favourable correlation properties is investigated in this paper.

This paper proposes a multiband multicarrier CDMA system with a simplified receiver structure for downlink transmission. An adaptive algorithm is proposed for allocating multiple subbands for users based on their channel gain and usage. The band allocation algorithm together with adaptive modulation can considerably increase the system capacity. A simplified receiver structure intended to reduce the complexity of channel equalizer-despreader structure of conventional multicarrier CDMA system is also proposed. The combined system is extensively simulated for different channel parameters and the results are discussed.

This paper shows how a unified model can he used to describe the signal received in frequency domain over a multiple-antenna, frequency-selective, multipath fading channel for multicarrier CDMA and single carrier CDMA systems with cyclic prefix. This realization validates the abstraction of these CDMA problems into a mathematical model which can be used for practical problems such as channel estimation and data detection. Moreover, the optimal multiuser detection problem based on the maximal-likelihood criteria for this unified model is addressed as a combinatorial optimization problem. A sequential quadratic programming approach is proposed to approximate this problem, which corresponds to a near-optimal software-defined decision-feedback multiuser receiver for both single-carrier and multicarrier CDMA systems. An efficient gradient projection algorithm is applied for data detection in the proposed receiver. The simulation results show that this scheme can reach near single-user performance even for fully-loaded systems and outperform conventional soft-interference cancellation methods.

A dynamic subcarrier allocation algorithm is developed and studied in order to improve the capacity of a multi-user OFDM system in the downlink environment. The proposed algorithm uses a decentralized approach and considers the instantaneous channel response of each user in parallel. In order to reduce the complexity of the system, the available subcarriers are divided into a number of partitions and the algorithm attempts to allocate the partition with the highest average channel gain to each user. However, situations may arise whereby two or more users attempt to select the same partition. As such, an important aspect of the algorithm is to resolve such conflicts. Based on the above allocation plan, adaptive modulation is employed for each user on the allocated partitions. The results obtained show that the proposed dynamic allocation scheme outperforms a static allocation scheme in terms of a lower BER and a higher system capacity for the same SNR. In addition, it is possible to obtain performance improvements at the expense of an increase in the system complexity by dividing the subcarriers into a larger number of partitions.

A scheme for selecting two beams in a switched beam antenna system for providing downlink transmit diversity based on space-time block coding (STBC) technique is proposed. The scheme involves selecting a pair of beams based on the uplink reception of the switched beam antenna system, and determining from the pair of beams a corresponding pair of orthogonal beams. The scheme also involves providing the pair of orthogonal beams as pair of transmit beams, the switched beam antenna system achieves nearly the same system performance, in terms of bit error rate (BER), as much complex adaptive antenna system with STBC. Simulation results demonstrate the promising scheme.

In this paper we suggest a new single carrier cyclic prefix assisted multiple access scheme for the asynchronous broadband CDMA system in uplink. Frequency domain equalization is applied instead of conventional RAKE combining or time domain equalization. A new serial type multistage interference cancellation in frequency domain is proposed to cancel the multiple access interference while keeping low computational complexity. We also investigated the effects of interference rejection weight control for this multistage interference cancellation. Another hybrid system combining the successive interference cancellation and parallel interference cancellation is also proposed, which can reach the similar performance of the serial type while reducing the processing delay greatly.

A theoretical analysis has been made to compare the capacity performances of transmit diversity and beamforming in the downlink of direct-sequence code-division multiple-access (DS-CDMA) system. The performances of selection transmit diversity (STD), beamforming (BF), and beam selection transmit diversity (BSTD), which is a hybrid scheme of STD and BF, have been studied at system level with capacity as the performance index. Both fading and interference are jointly considered in multipath propagation environment. It was found that the comparison result strongly relates to the availability of path diversity. The system capacity is maximized by the BF in the presence of path diversity, otherwise it is the BSTD that achieves the best overall capacity performance.

This paper presents an advanced architecture for a residue number system (RNS) based CDMA system for high-rate data transmission by combining RNS representation, PSK/QAM modulation and orthogonal modulation. The proposed system uses a lesser spreading factor than RNS based CDMA and the performance is comparable. The modified system is simulated extensively for different channel conditions and found that it can be used for faster data transmission without affecting the system performance.

This paper is concerned with a new method to enhance the bandwidth efficiency of an MC-CDMA system by using a residue number based representation for information symbols. The residues are mapped into a set of orthogonal sequences and are transmitted in parallel. To increase the data rate further, a modified residue representation scheme is used with significantly lesser number of orthogonal sequences. A multicarrier modulation scheme is used for both transmission and reception of residue channels. The issues involved in the design of an enhanced RNS based MC-CDMA architecture is discussed and the performance of the system is evaluated in a frequency selective Rayleigh fading channel via extensive simulations.

Joint beamforming and power control is an efficient technique to increase the capacity of DS-CDMA systems. It is shown that the optimal solution of the uplink beamforming weights is independent of the combined path loss/shadowing effect. Based on this, a novel approach is proposed to implement adaptive beamforming and power control by converting the joint problem into a simple power control problem. It generates the optimal beamforming weights in each slot based on estimated channel responses. Computer simulations show that the new approach has much faster convergence for transmission power than the traditional LMS algorithm.

This paper presents a new method to improve bandwidth efficiency of RNS based CDMA system by combining RNS representation, PSK/QAM modulation and orthogonal modulation. Using the proposed method significantly reduces the computational complexity of the receiver unit and significantly increases the data transmission rate. The modified system is simulated extensively for different channel conditions and found that it can be used for faster data transmission without affecting the system performance.

This paper explores the use of redundant residue number systems to incorporate incremental redundancy in a communication system. By exploiting this property further, one can design an appropriate coding scheme for transmission at the currently experienced SNR level. A link adaptation procedure and an adaptive decoding method is presented for the efficient implementation of the system. The proposed system is extensively simulated with parameters suitable for wireless local area network (WLAN) standards and the results are discussed.

The downlink channel covariance matrix (DCCM) is of vital importance in determining downlink beamforming weights for base station (BS) antenna array systems. For the frequency-division-duplex (FDD) mode, DCCM is difficult to obtain due to a lack of direct measurement of downlink channel responses. In this paper, a novel technique is proposed for estimating DCCM using uplink channel responses only, which does not need direction-of-arrival (DOA) estimation and its association. The downlink beamforming scheme is then proposed for wireless DS-CDMA systems, using the obtained DCCM information together with the so-called virtual uplink beamforming and power control technique. Computer simulations show that using the BS antenna array together with this new beamforming technique can provide larger system capacity than traditional DOA-based approaches, which just direct the main beam toward the desired user.

Two suboptimal algorithms are proposed for downlink beamforming in FDD DS-CDMA mobile radio by using uplink beamforming weights. One is a null-constrained method, which maintains the same null positions for both uplink and downlink beam patterns; the other is a frequency-calibrated method which constrains the same main beam positions for both patterns. We also evaluate the multicell downlink capacity of DS-CDMA systems using a per-user-per-weight beamforming scheme. Outer cell interference is modeled as an AWGN process whose variance is proportional to the average intracell total transmitted power. Computer simulations are given to compare the single cell and multicell capacities using different downlink beamforming weight generation algorithms.

Downlink beamforming is a promising technique for direct-sequence code-division multiple-access (DS-CDMA) systems with multimedia services to effectively reduce strong interference induced by high data rate users. A new downlink beamforming technique is proposed that converts the downlink beamforming problem into a virtual uplink one and takes into account the data rate information of all users. Since the main complexity of this method is due to the existence of multidelay paths, two simplified algorithms are suggested using an equivalent one-path channel vector to replace multipath channel vectors. Computer simulation results are given to evaluate the downlink capacity of DS-CDMA systems using a base station antenna array and the new algorithms proposed.

Establishing synchronization with locally generated spread code is one of the most important tasks in DS-CDMA systems for effective and reliable communications. A three-step procedure is proposed in this paper for fast code synchronization and subsequent path delay estimation for a single base station based system in a multipath environment. The synchronization procedure starts from the slot synchronization and then frame synchronization with the help of long code masked symbol. The path delays are estimated from the power delay profile computed from the instantaneous signal power of pilot symbols. The average power delay profile is used as the threshold. This three-step procedure is extensively simulated for different power delay profiles and the results are discussed.

High data rates in wireless radio environments are becoming common. Current system designs are inadequate to meet the speed requirements that are anticipated in the newer services. The computational complexities in the subsystems increase in direct proportion. We propose alternative multiply accumulate units for the pulse shaping filters that use a new representation for their coefficients. Consequently, these new structures are fast, efficient and consume less power. The filters proposed take into account constraints, such as, intersymbol interference, response characteristics etc. in their design methodology.

A flexible experimental 12-element antenna array testbed was built for high data rate mobile communications and PCS applications. The supported simultaneous data sampling rate on 12 elements is about 3.5 MHz. An indoor field trial was conducted to demonstrate performance improvement in terms of BER and SNR using adaptive beamforming techniques like blind algorithms over the switched diversity method. Spatial division multiple access (SDMA) is also discussed to demonstrate the system capacity enhancement using an adaptive array for DECT. Experiments have been conducted to demonstrate multipath mitigation, interference suppression and capacity enhancement.

Adaptive antenna arrays can be employed to improve the transmission quality and thus to increase the capacity of wireless communication systems. We address the transmit antenna array techniques for base-to-mobile (downlink) transmission in frequency-division-duplex (FDD) based cellular CDMA systems. A new criterion for transmit weight estimation is developed, which is based upon maximizing the transmit signal-to-interference-plus-noise ratio (SINR) and using downlink channel responses estimated by a probing feedback approach. Computer simulations show that the new transmit antenna array technique is effective for improving the capacity of the wireless communication systems.

We present a new closed-form bit error probability formula for narrow-band FSK with limiter-discriminator-integrator detection in Rayleigh fading channels. This formula eliminates the tedious numerical integrations required in previous publications. The computed results are verified by experiment. We provide physical explanations, on how the system parameters such as fading, IF filter bandwidths and FM carrier frequency deviations affect the error performance, not previously available in the literature.>