Pulse Doppler multiple input multiple output (MIMO) radar allows to simultaneously detect targets' range, azimuth and velocity. Achieving high resolution requires a large number of transmit and receive antennas, as well as high sampling rates leading to a torrent of samples. Overcoming the rate bottleneck, sub-Nyquist sampling methods have been proposed that break the link between single antenna radar signal bandwidth and range resolution. In this work, we present a sub-Nyquist MIMO radar (SUMMeR) system that extends these methods to a multiple antenna setting. We apply the Xampling framework both in time and space, thus reducing both the number of deployed antennas and samples per receiver, without degrading time and spatial resolution, as illustrated in the simulations.

In previous work, we have shown that the noncoherent direction of arrival (DOA) estimation by an array of sensors is insensitive to sensor phase errors. Here, we analyze the effects of sensor location errors on noncoherent DOA estimation. In the presence of additive white Gaussian noise, we show that the distribution of magnitude-only measurements collected by a sensor array may be approximated by a Gaussian distribution. Further, if one of the sources is received with high signal-to-noise ratio, the mean of the Gaussian distribution is a function of location errors while the variance of the Gaussian distribution is invariant with location errors. We derive a closed-form analytical expression for the hybrid Cramer-Rao bound of the spatial frequency difference between two sources. Numerical results illustrate that, unlike phase errors that have no effect on noncoherent DOA estimation, both noncoherent and coherent DOA estimation are affected by location errors.

In a fast-fading environment, e.g., high-speed railway communications, channel estimation and tracking require the availability of a number of pilot symbols that is at least as large as the number of independent channel parameters. Aiming at reducing the number of necessary pilot symbols, this work proposes a novel technique for joint channel tracking and decoding, which is based on the following three ideas. 1) Sparsity: While the total number of channel parameters to be estimated is large, the actual number of independent multipath components is generally small; 2) Long-term versus short-term channel parameters: Each multipath component is typically characterized by long-term parameters that slowly change with respect to the duration of a transmission time slot, such as delays or average power values, and by fast-varying fading amplitudes; and 3) Code-aided methods: Decision-feedback techniques can optimally leverage past, and partially reliable, decisions on the data symbols to obtain “virtual” pilots via the expectation-maximization (EM) algorithm. Numerical results show that the proposed code-aided EM algorithm is effective in performing joint channel tracking and decoding even for velocities as high as 350 km/h, as in high-speed railway communications, and with as few as four pilots per orthogonal frequency-division multiplexing data symbol, as in the IEEE 802.11a/n/p standards, outperforming existing schemes at the cost of larger computational complexity.

This work presents a new array geometry, which is capable of providing O(M2N2) degrees of freedom (DOF) using only MN physical sensors via utilizing the second-order statistics of the received data. This new array is composed of multiple, identical minimum redundancy subarrays, whose positions follow a minimum redundancy configuration. Thus the new array is a minimum redundancy array (MRA) of MRA subarrays, and is termed as nested MRA. The sensor positions, aperture length, and the number of DOF of the new array can be predicted if these parameters of MRA subarrays are given. Numerical simulations demonstrate the superiorities of the proposed array geometry in resolving more sources than sensors and DOA estimation.

Cloud radio access network (C‐RAN) is a prominent architecture for fifth generation wireless cellular system that is based on the centralisation of baseband processing for multiple distributed radio units (RUs) at a control unit (CU). In this study, it is proposed to leverage the C‐RAN architecture to enable the implementation of direct localisation of the position of mobile devices from the received signals at distributed RUs. With ideal connections between the CU and the RUs, direct localisation is known to outperform traditional indirect localisation , whereby the location of a source is estimated from intermediary parameters estimated at the RUs. However, in a C‐RAN system with capacity limited fronthaul links, the advantage of direct localisation may be offset by the distortion caused by the quantisation of the received signal at the RUs. In this study, the performance of direct localisation is studied by accounting for the effect of fronthaul quantisation with or without dithering. An approximate maximum likelihood localisation is developed. Then, the Cramér–Rao bound on the squared position error of direct localisation with quantised observations is derived. Finally, the performance of indirect localisation and direct localisation with or without dithering is compared via numerical results.

A train backbone network consists of a sequence of nodes arranged in a linear topology. A key step that enables communication in such a network is that of topology discovery (TD), or train inauguration, whereby nodes learn in a distributed fashion the physical topology of the backbone network. While the current standard for train inauguration assumes wired links between adjacent backbone nodes, this work investigates the more challenging scenario in which the nodes communicate wirelessly. The key motivations for this desired switch from wired TD to wireless one are the flexibility and capability for expansion and upgrading of a wireless backbone. The implementation of TD over wireless channels is made difficult by the broadcast nature of the wireless medium, as well as by fading and interference. A novel TD protocol is proposed, which overcomes these issues and requires relatively minor changes to the wired standard. The protocol is shown via analysis and numerical results to be robust to the impairments caused by the wireless channel, including interference from other trains.

A multistatic radar set-up is considered in which distributed receive antennas are connected to a Fusion Center (FC) via limited-capacity backhaul links. Similar to cloud radio access networks in communications, the receive antennas quantize the received baseband signal before transmitting it to the FC. The problem of maximizing the detection performance at the FC jointly over the code vector used by the transmitting antenna and over the statistics of the noise introduced by backhaul quantization is investigated. Specifically, adopting the information-theoretic criterion of the Bhattacharyya distance to evaluate the detection performance at the FC and information-theoretic measures of the quantization rate, the problem at hand is addressed via a Block Coordinate Descent (BCD) method coupled with Majorization-Minimization (MM). Numerical results demonstrate the advantages of the proposed joint optimization approach over more conventional solutions that perform separate optimization.

We consider the classical Direction of arrival (DOA) estimation problem in the presence of random sensor phase errors are present at each sensor. To eliminate the effect of these phase errors, we propose a DOA recovery technique that relies only on magnitude measurements. This approach is inspired by phase retrieval for applications in other fields. Ambiguities typically associated with phase retrieval methods are resolved by introducing reference targets with known DOA. The DOA estimation problem is formulated as a nonlinear optimization in a sparse framework, and is solved by the recently proposed GESPAR algorithm modified to accommodate multiple snapshots. Numerical results demonstrate good DOA estimation performance. For example, the probability of error in locating a single target within 2 degrees is less than 0.1 for SNR ≥ 15 dB and one snapshot, and negligible for SNR ≥ 10 dB and five snapshots.

A novel Bayesian modulation classification scheme is proposed for a single-antenna system over frequency-selective fading channels. The method is based on Gibbs sampling as applied to a latent Dirichlet Bayesian network (BN). The use of the proposed latent Dirichlet BN provides a systematic solution to the convergence problem encountered by the conventional Gibbs sampling approach for modulation classification. The method generalizes, and is shown to improve upon, the state of the art.

We study compressive sensing in the spatial domain for target localization in terms of direction of arrival (DOA), using multiple-input multiple-output (MIMO) radar. A sparse localization framework is proposed for a MIMO array in which transmit/receive elements are placed at random. This allows to dramatically reduce the number of elements, while still attaining performance comparable to that of a filled (Nyquist) array. Leveraging properties of a (structured) random measurement matrix, we develop a novel bound on the coherence of the measurement matrix, and we obtain conditions under which the measurement matrix satisfies the so-called isotropy property. The coherence and isotropy concepts are used to establish respectively uniform and non-uniform recovery guarantees for target localization using spatial compressive sensing. In particular, nonuniform recovery is guaranteed if the number of degrees of freedom (the product of the number of transmit and receive elements MN) scales with K(log G)2, where K is the number of targets, and G is proportional to the array aperture and determines the angle resolution. The significance of the logarithmic dependence in G is that the proposed framework enables high resolution with a small number of MIMO radar elements. This is in contrast with a filled virtualMIMO array where the product MN scales linearly with G.

The problem addressed is source localization via time-difference-of-arrival estimation in a multipath channel. Solving this localization problem typically implies cross-correlating the noisy signals received at pairs of sensors deployed within reception range of the source. Correlation-based localization is severely degraded by the presence of multipath. The proposed method exploits the sparsity of the multipath channel for estimation of the line-of-sight component. The time-delay estimation problem is formulated as an ℓ1-regularization problem, where the ℓ1-norm is used as a channel sparsity constraint. The proposed method requires knowledge of the pulse shape of the transmitted signal, but it is blind in the sense that information on the specific transmitted symbols is not required at the sensors. Simulation results show that the proposed method delivers higher accuracy and robustness to noise compared to conventional or even super-resolution MUSIC time-difference-of-arrival source localization methods.

Utility (e.g., sum-rate) maximization for multiantenna broadcast and interference channels (with one antenna at the receivers) is known to be in general a non-convex problem, if one limits the scope to linear (beamforming) strategies at transmitter and receivers. In this paper, it is shown that, under some standard assumptions, most notably that the utility function is decreasing with the interference levels at the receivers, a global optimal solution can be found with reduced complexity via a suitably designed branch-and-bound method. Although infeasible for real-time implementation, this procedure enables a non-heuristic and systematic assessment of suboptimal techniques. In addition to the global optimal scheme, a real-time suboptimal algorithm, which generalizes the well-known distributed pricing techniques, is also proposed. Finally, numerical results are provided that compare global optimal solutions with suboptimal (pricing) techniques for sum-rate maximization problems, affording insight into issues such as the robustness against bad initializations in real-time suboptimal strategies.

In this paper, a single antenna downlink channel with K users is analyzed in the presence of Rayleigh flat fading. A limited channel state information (CSI) feedback scheme is considered, where only 1-bit feedback per user is available at the base station for each fading block. We study the outage performance of such channels. The two cases of short-term and long-term average power constraints are analyzed. Closed-form expressions for the outage probability of the 1-bit feedback scheme are presented. At high SNR, the diversity-multiplexing tradeoff (DMT) is explicitly derived. We show that for the short-term average power constraint case, with only 1-bit feedback, the scheme achieves not only a DMT that increases linearly with the number of users in the system, but also the same tradeoff as if perfect CSI feedback were available at the base station. For longterm average power constraint, it is concluded that power allocation based on the feedback bit is crucial in further improving the DMT. An additional factor of two in the DMT is achieved compared with the short-term average power constraint case.

This work studies the throughput scaling laws of ad hoc wireless networks in the limit of a large number of nodes. A random connections model is assumed in which the channel connections between the nodes are drawn independently from a common distribution. Transmitting nodes are subject to an on-off strategy, and receiving nodes employ conventional single-user decoding. The following results are proven: 1) for a class of connection models with finite mean and variance, the throughput scaling is upper-bounded by O(n1/3) for single-hop schemes, and O(n1/2) for two-hop (and multihop) schemes; 2) the Θ(n1/2) throughput scaling is achievable for a specific connection model by a two-hop opportunistic relaying scheme, which employs full, but only local channel state information (CSI) at the receivers, and partial CSI at the transmitters; 3) by relaxing the constraints of finite mean and variance of the connection model, linear throughput scaling Θ(n) is achievable with Pareto-type fading models.

This paper presents an analysis of target localization accuracy, attainable by the use of multiple-input multiple-output (MIMO) radar systems, configured with multiple transmit and receive sensors, widely distributed over an area. The Cramer–Rao lower bound (CRLB) for target localization accuracy is developed for both coherent and noncoherent processing. Coherent processing requires a common phase reference for all transmit and receive sensors. The CRLB is shown to be inversely proportional to the signal effective bandwidth in the noncoherent case, but is approximately inversely proportional to the carrier frequency in the coherent case. We further prove that optimization over the sensors' positions lowers the CRLB by a factor equal to the product of the number of transmitting and receiving sensors. The best linear unbiased estimator (BLUE) is derived for the MIMO target localization problem. The BLUE's utility is in providing a closed-form localization estimate that facilitates the analysis of the relations between sensors locations, target location, and localization accuracy. Geometric dilution of precision (GDOP) contours are used to map the relative performance accuracy for a given layout of radars over a given geographic area.

In this paper, a practical solution to implement the distributed interference alignment (IA) algorithm of [1] in a cellular communication system is proposed. In the training period of the proposed strategy, the User Equipment (UE) and the Base Station (BS), without knowing a priori the interference covariance matrix, update directly the preceding and interference suppression matrices based on the received signals by a minor subspace tracking algorithm. At the end of the training phase, the preceding and interference suppression matrices are then used at the UE and BS, respectively, for the transmission period. A special spatial reuse method is also proposed for the training period to lower the system overhead. Numerical system performance results are provided, showing that the algorithm, referred to as Interference Subspace Tracking IA (IST-IA), yields a good tradeoff between throughput gains, on one side, and training overhead and computational complexity, on the other. It is also argued that IST-IA is a promising solution not only for training but also for the tracking phase, if applicable.

This paper studies the throughput scaling of wireless networks over channels with random connections, in which the channel connections are independent and identically distributed (i.i.d.) according to a common distribution. The channel distribution is quite general, with the only limitations being that the mean and variance are finite. Previous works have shown that, when channel state information (CSI) of the entire network is known a priori to all the nodes, wireless networks are degrees-of- freedom limited rather than interference limited. In this work, we show that this is not the case with a less demanding CSI assumption. Specifically, we quantify the throughput scaling for different communication protocols under the assumption of perfect receiver CSI and partial transmitter CSI (via feedback). It is shown that the throughput of single-hop and two-hop schemes are upper-bounded by respectively, O(n1/3) and O(n1/2), where n is the total number of source-to-destination pairs. In addition, multihop schemes cannot do better than the two-hop relaying scheme. Furthermore, the achievability of the Theta(n1/2) scaling for the two-hop scheme is demonstrated by a constructive example.

Relay networks having n source-to-destination pairs and m half-duplex relays, all operating in the same frequency band and in the presence of block fading, are analyzed. This setup has attracted significant attention, and several relaying protocols have been reported in the literature. However, most of the proposed solutions require either centrally coordinated scheduling or detailed channel state information (CSI) at the transmitter side. Here, an opportunistic relaying scheme is proposed that alleviates these limitations, without sacrificing the system throughput scaling in the regime of large n. The scheme entails a two-hop communication protocol, in which sources communicate with destinations only through half-duplex relays. All nodes operate in a completely distributed fashion, with no cooperation. The key idea is to schedule at each hop only a subset of nodes that can benefit from multiuser diversity. To select the source and destination nodes for each hop, CSI is required at receivers (relays for the first hop, and destination nodes for the second hop), and an index-valued CSI feedback at the transmitters. For the case when n is large and m is fixed, it is shown that the proposed scheme achieves a system throughput of m/2 bits/s/Hz. In contrast, the information-theoretic upper bound of (m/2) log log n bits/s/Hz is achievable only with more demanding CSI assumptions and cooperation between the relays. Furthermore, it is shown that, under the condition that the product of block duration and system bandwidth scales faster than log n log log n, the achievable throughput of the proposed scheme scales as Theta (log n). Notably, this is proven to be the optimal throughput scaling even if centralized scheduling is allowed, thus proving the optimality of the proposed scheme in the scaling law sense. Simulation results indicate a rather fast convergence to the asymptotic limits with the system's size, demonstrating the practical importance of the scaling results.

In this work, a multicell cooperative zero-forcing beamforming (ZFBF) scheme combined with a simple user selection procedure is considered for the Wyner cellular downlink channel. The approach is to transmit to the user with the ldquobestrdquo local channel in each cell. The performance of this suboptimal scheme is investigated in terms of the conventional sum-rate scaling law and the sum-rate offset for an increasing number of users per cell. We term this characterization of the sum-rate for large number of users ashigh-loadregimecharacterization, and point out the similarity of this approach to the standard affine approximation used in the high-signal-to-noise ratio (SNR) regime. It is shown that, under an overall power constraint, the suboptimal cooperative multicell ZFBF scheme achieves the same sum-rate growth rate and slightly degraded offset law, when compared to an optimal scheme deploying joint multicell dirty-paper coding (DPC), asymptotically with the number of users per cell. Moreover, the overall power constraint is shown to ensure in probability, equal per-cell power constraints when the number of users per-cell increases.

This work studies the throughput scaling in the limit of large networks for a previously published two-hop opportunistic relaying protocol for more general fading conditions. In the Rayleigh fading environment, the throughput scaling was obtained directly from the closed-form throughput expression of the finite network. For other fading channels, unfortunately, the exact closed-form throughput analysis turns out to be intractable. Inspired by the multiuser diversity interpretation of the throughput scaling in the Rayleigh case, we introduce the conjecture that for general fading channels, the throughput scaling of the opportunistic scheme is of the same order as the multiuser diversity of the underlying fading model. While the rigorous proof of the conjecture is still ongoing, in this paper, we make two observations that shed additional light on the throughput of wireless networks.

A network consisting of n source-destination pairs and m relays with no direct link between source and destination nodes, is considered. Focusing on the large system limit (large n), the throughput scaling laws of two-hop relaying protocols are studied for Rayleigh fading channels. It is shown that, under the practical constraints of single-user encoding-decoding scheme, and partial channel state information (CSI) at the transmitters (via integer-value feedback from the receivers), the maximal throughput scales as log n even if joint scheduling among relays is allowed. Furthermore, a novel opportunistic relaying scheme with receiver CSI, partial transmitter CSI, and decentralized relay scheduling, is shown to achieve the optimal throughput scaling law of log n.

This paper investigates achievable rates for a wireless communication system when neither the transmitter nor the receiver has a priori knowledge of the channel state information (CSI). The dynamics of the flat fading channel are characterized by a known Doppler spectrum. Quantitative results are provided for independent and identically distributed (i.i.d.) Gaussian signals and long data blocks. Expressions for the achievable rates include a lower bound on mutual information, and the achievable rates of pilot-aided systems with optimized resource allocation. A simple, low-duty-cycle signaling scheme is proposed to improve the information rates in the low signal-to-noise ratio (SNR) regime, and the optimal duty cycle is expressed as a function of the fading rate and SNR. It is demonstrated that the resource allocation and duty cycle developed for Gaussian signals can also be applied to systems using other signaling formats.

Turbo space-time codes with symbols precoded by randomly chosen unitary time variant linear transformations (TVLT) are investigated in this paper. It is shown that turbo codes with TVLT achieve full diversity gain and do not require exhaustive tests of the rank criterion. We prove that the coding gain performance of turbo space-time codes with TVLT improves with the Hamming distance between codewords (number of different columns). As an additional benefit of the application of TVLT, with the removal of the constant modulation condition, we prove that throughput rates achieved by these codes are significantly higher than those for conventional space-time codes. Numerical results are provided to demonstrate diversity gains, coding gains and rates of turbo space-time codes with TVLT

We study power allocation for the decode-and-forward cooperative diversity protocol in a wireless network under the assumption that only mean channel gains are available at the transmitters. In a Rayleigh fading channel with uniformly distributed node locations, we aim to find the power allocation that minimizes the outage probability under a short-term power constraint, wherein the total power for all nodes is less than a prescribed value during each two-stage transmission. Due to the computational and implementation complexity of the optimal solution, we derived a simple near-optimal solution. In this near-optimal scheme, a fixed fraction of the total power is allocated to the source node in stage I. In stage II, the remaining power is split equally among a set of selected nodes if the selected set is not empty, and otherwise is allocated to the source node. A node is selected if it can decode the message from the source and its mean channel gain to the destination is above a threshold. In this scheme, each node only needs to know its own mean channel gain to the destination and the number of selected nodes. Simulation results show that the proposed scheme achieves an outage probability close to that for the optimal scheme obtained by numerical search, and achieves significant performance gain over other schemes in the literature

For a multiple-input single-output (MISO) downlink channel with M transmit antennas, it has been recently proved that zero-forcing beamforming (ZFBF) to a subset of (at most) M "semi-orthogonal" users is optimal in terms of the sum-rate, asymptotically with the number of users. However, determining the subset of users for transmission is a complex optimization problem. Adopting the ZFBF scheme in a cooperative multi-cell scenario renders the selection process even more difficult since more users are involved. In this paper, we consider a multi-cell cooperative ZFBF scheme combined with a simple sub-optimal users selection procedure for the Wyner downlink channel setup. According to this sub-optimal procedure, the user with the "best" local channel is selected for transmission in each cell. It is shown that under an overall power constraint, a distributed multi-cell ZFBF to this sub-optimal subset of users achieves the same sum-rate growth rate as an optimal scheme deploying joint multi-cell dirty-paper coding (DPC) techniques, asymptotically with the number of users per cell. Moreover, the overall power constraint is shown to ensure in probability, equal per-cell power constraints when the number of users per-cell increases.

Ultra-wideband indoor line-of-sight frequency-domain channel measurements have been performed in the 2-6 GHz frequency band using three different transmit/receive antenna combination pairs. The effects of antenna directivity on path loss and multipath propagation in the channel are analyzed extensively for various omnidirectional and directional antenna combinations. A statistical model of the path loss in the channel is presented, in which all path loss exponents result in better than free space loss. The shadow fading experienced in the channel is shown to highly agree with the normal probability assumption. There is a significant reduction in root mean square delay spread when directional antennas are used at the transmitter and receiver or solely at the receiver with respect to an omnidirectional/omnidirectional antenna pair. Finally, a distance-dependent statistical impulse response model of the channel is presented along with simulation results that significantly concur with the measured data.

Approximately 3 dB signal-to-noise ratio (SNR) loss is always paid with conventional differential space-time block codes (STBCs), compared with coherent STBCs. In this paper, a multiple-symbol differential detection (MSDD) technique is proposed for M-ary phase-shift keying (PSK) STBCs. The new scheme can greatly narrow the 3-dB performance gap by extending the observation interval for differential decoding. The technique uses maximum-likelihood sequence detection instead of traditional symbol-by-symbol detection, and is carried out on the slow, flat Rayleigh fading channel. A generalized decision metric is derived for an observation interval of arbitrary length. It is shown that for a moderate number of symbols, MSDD provides approximately 1.5 dB performance improvement over conventional differential detection. In addition, a closed-form pairwise error probability and approximate bit-error probability (BEP) are derived for multiple-symbol differential binary PSK STBC. Results show that the theoretical BEP matches simulation results well. The BEP is shown to converge asymptotically with the number of symbols in the observation interval to that of the differential scheme with coherent detection.

We study power allocation for the space-time-coded decode-and-forward cooperative diversity protocol in a wireless network under the assumption that only mean channel gains are available at the transmitters. In a Rayleigh fading channel with uniformly random node locations, a near-optimal power allocation that minimizes the outage probability is derived under a short-term power constraint, wherein the total power is fixed for each two-stage transmission. This near-optimal scheme allocates one half of the total power to the source node and splits the remaining half equally among selected relay nodes; a node is selected for relay if it is able to decode the signal from the source and its mean channel gain to the destination is above a threshold. Numerical results show that this scheme significantly outperforms the constant-power scheme, wherein all nodes use the same power at all times, and the best-select scheme, which employs one relay node with the largest mean relay-destination gain

In this paper we extend our previously proposed layered turbo coded multiple-input multiple-output (MIMO) scheme by introducing new techniques to improve the design of the transmitter and the receiver. These MIMO systems feature two antenna per layer with random antenna grouping, which reduces interference between layers. And multidimensional set partition is applied to encoder design to improve the coding gain. Based on these design techniques, the receiver only uses simple parallel interference cancellation (PIC) with spatial matched filtering (SMF) to separate the signals from different layers. It is shown that the performance of the proposed scheme is within 2 dB of outage capacity and is similar or better than other proposed MIMO schemes using more sophisticated interference suppression techniques.

In this paper, information rates of mobile radio channels without channel state information (CSI) at either the transmitter or the receiver are investigated. The channel is modeled as a time varying Rayleigh fading process whose dynamics are characterized by a Doppler spectrum with specified normalized fading rate. Results are presented in terms of the block length, the normalized fading rate, and the signal-to-noise ratio (SNR), for the Clarke's Doppler spectrum and uniform spectrum.

We present a semiblind iterative receiver for space-time coded data transmitted through unknown MIMO frequency selective quasistatic Rayleigh fading channels. The expectation maximization (EM) algorithm is used in the channel estimation process, while a BCJR algorithm for multiple antenna systems is used for both data detection, over the channel trellis, and decoding, over the space-time code trellis. Noise variance estimation is also performed by the receiver. Simulation results showing the diversity gain over MIMO flat fading channels are presented.

New expressions are derived for the exact symbol error probability and bit-error probability for optimum combining with multiple phase-shift keying. The expressions are for any numbers of equal-power cochannel interferers and receive branches. It is assumed that the aggregate interference and noise is Gaussian and that both the desired signal and interference are subject to flat Rayleigh fading. The new expressions have low computational complexity, as they contain only a single integral form with finite limits and finite integrand.

A joint detection-estimation scheme is proposed for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The transmitter employs a layered turbo space-time code. The iterative scheme proposed for the receiver integrates in one scheme turbo decoding, co-antenna interference suppression and channel estimation. A main observation is that the high coding gain of the turbo space-time code can compensate for the application of a simple co-antenna interference suppression scheme and can also facilitate good channel estimates. The performance of the MIMO-OFDM system is validated by simulations under various channel conditions, including high Doppler. Numerical results show that for a 4 transmit 4 receive antenna (4T4R) system, with a data rate of 4 Mb/s over a 1.25 MHz bandwidth, a packet error rate (PER) of 10/sup -2/ is achieved at a signal-to-noise ratio (SNR) of 16 dB for a typical urban channel with Doppler frequencies as high as 200 Hz. For a 4T6R system, the same performance can be achieved for only 6 dB SNR.

This paper develops an analytical model for evaluating the quality of service (QoS) in wireless ad-hoc networks. In doing so it extends the trunking theory concepts to encompass the effect of co-channel interference. Chosen as the QoS figure of merit, the transmission blocking probability is derived as a function of the number of nodes, the network density and parameters of a Markov chain model for the multiple user channel access protocol. This expression is validated by computer simulations.

Clipping is an efficient and simple method to reduce the peak-to-average power ratio (PAPR) of OFDM signals. However, clipping causes distortion and out-of-band radiation. In this paper, a novel iterative receiver is proposed to estimate and cancel the distortion caused by clipping noise. The proposed method is applied to clipped and filtered OFDM signals. It is shown by simulation that for an 802.11a system, the PAPR can be reduced to as low as 4 dB while the system performance can be restored to within 1 dB of the non-clipped case with only moderate complexity increase and with no bandwidth expansion.

Decision directed channel estimation is investigated in this paper. For systems with multiple transmit antennas, high computation complexity of the inversion of a data-dependent matrix hinders the application of optimal channel estimation. An iterative method is introduced to avoid the matrix inversion. Performance of the proposed method is demonstrated by simulation results.

UWB systems based on impulse radio have the potential to provide very high data rates over short distances. In this paper, a new pulse shape is presented that satisfies the FCC spectral mask. Using this pulse, the link budget is calculated to quantify the relationship between data rate and distance. It is shown that UWB can be a good candidate for reliably transmitting 100 Mbps over distances at about 10 meters.

A multiple-symbol differential detector is formulated for M-ary differential phase-shift keying modulation where the channel state information is unknown to the receiver. The maximum-likelihood decision statistic is derived for the detector, and its performance is demonstrated by analysis and simulation. Under the Gaussian assumption for the aggregate interference plus noise, an exact expression for the symbol pairwise error probability is developed for M-ary differential phase-shift keying modulation over a diversity, slow-fading Rayleigh channel in the presence of an interference source. A simpler expression of the pairwise error probability is developed for the asymptotic case of large signal-to-noise ratio and small signal-to-interference ratio. It is shown that with an increasing observation interval, the performance of the differential detector over an unknown channel approaches that of optimum combining with known channel.

A new closed-form expression is derived for the exact bit-error probability (BEP) for optimum combining with binary phase-shift keying. The exact BEP expression is for multiple, equal power, cochannel interferers and multiple reception branches. It is assumed that the aggregate interference and noise is Gaussian and that both the desired signal and interference are subject to Rayleigh fading. The derivation starts by expressing the optimum combining decision statistic as a sum of quadratic forms of Gaussian random variables and it proceeds to average over the fading interference. The new BEP expression has low complexity as it contains only finite sums and products.

We consider the design of a space-time coded modulation transmit-receive system employing symbol interleaving. An iterative receiver is derived based on the expectation-maximization algorithm with soft output symbol decoding and estimation of noise variance. The proposed system demonstrates very good performance over fast fading unknown channels in the presence of unknown additive white Gaussian noise.

A differential detection scheme for a multiple-input multiple-output (MIMO) DS/CDMA link is presented, where neither the transmitters nor the receivers know the channel state information (CSI). The transmission provides for full spatial diversity gain by a simple detection scheme, which is the natural extension of differential detection combined with an orthogonal transmit diversity (OTD) approach. Moreover, a capacity analysis for this scheme is illustrated. The capacity analysis and simulation results show that 3 dB loss is paid for differential detection compared to coherent detection.

The performance of multiple symbol differential detection (MSDD) over Rayleigh diversity channels and in the presence of cochannel interference is compared with that of optimum combining (OC). For this purpose, we derive the asymptotic expressions for the approximate upper bound of the bit error probability of MSDD for multiple phase shift keying modulation. Similar asymptotic expressions are derived for OC. These relatively simple expressions provide a clear insight into the performance of MSDD and OC. Through analysis and simulation results, we show that as the observation interval increases, the performance of MSDD approaches that of OC (with differential encoding).

In this paper we compute the channel capacity of M-ary pulse position modulation ultra-wideband (UWB) communications over multiple-access channels. Under certain assumptions, the multiple-access noise component at the receiver can be modeled as Gaussian. An expression for the signal-to-noise ratio is developed for UWB utilizing rectangular pulses. The information theoretic capacity of the UWB system is expressed as a function of number of users. Utilizing the expressions developed, other trade-offs can be determined between the system parameters and capacity.

We analyze the performance of ultra-wideband (UWB) communications in the presence of interference. Closed-form expressions are provided for the jam resistance of UWB with binary pulse position modulation utilizing rectangular pulses. A simple approximation is obtained for the special case of tone interference. The jam resistance analysis is extended to more practical UWB waveforms such as Gaussian and Rayleigh monocycles. A comparison between the interference suppression capabilities of UWB and direct-sequence spread-spectrum (DS-SS) is carried out under conditions similar to both systems. It is shown that in most cases, the jam suppression of UWB is superior to that of DS-SS.

Abstract A channel‐coding scheme is introduced that features parallel concatenated recursive systematic codes with multilevel modulation and multiple transmit/receive antennas. The proposed scheme is a type of turbo space–time codes and is referred to asturbo multiple antenna coded modulation(turbo‐MACM). Turbo‐MACM combines the advantages of powerful turbo codes with the transmit/receive diversity of multiple antenna coded modulation. The scheme utilizes recursive and systematic constituent codes and features full rate and, as demonstrated by simulations, full spatial diversity. An iterative symbol‐by‐symbolmaximum a posteriori(MAP) algorithm operating in the log domain is developed for decoding turbo‐MACM. Simulation results are provided for 4‐PSK and 8‐PSK schemes over the block‐fading channel. It is shown that the scheme provides an advantage of 3 to 5 dB over conventional space–time codes of comparable complexity. Copyright © 2002 John Wiley & Sons, Ltd.

We derive performance bounds for a turbo space-time coded modulation (turbo-STCM) scheme over Rayleigh block-fading channels with multiple transmit and multiple receive antennas. The performance bounds are based on the union bound. It is shown that a subset of dominant error paths provide a good approximation of the bound thereby alleviating the computational effort involved in computing the full union bound. The bound is expressed in terms of parameters of the individual space-time codes that make up the turbo-STCM code, interleaver length, number of transmit/receive antennas, the squared Euclidean distance spectra, and the statistical properties of the channel. The theoretical expressions are demonstrated by a close match with simulation results. This bound provides researchers with a useful analytical tool for the design and analysis of turbo space-time codes.

In this paper we analyze the performance of ultra-wideband (UWB) communications in the presence interference. The interference is modeled as a zero mean random process with constant power spectral density over a certain bandwidth. Closed-form expressions are developed for the processing gain of a pulse position modulation UWB utilizing rectangular pulses. Simple approximations are obtained for special cases (narrowband and wideband interference). We compare the interference suppression properties of UWB and direct-sequence spread spectrum (DS-SS) under certain assumptions. It is shown that in case of narrowband interference (with respect to the spread spectrum bandwidth), UWB provides more effective interference suppression than DS-SS.

A channel coding scheme is analyzed that features parallel concatenated systematic space-time codes with multilevel modulation and multiple transmit/receive antennas. The scheme is referred to as turbo space-time coded modulation (turbo-STCM). It combines the advantages of turbo codes with the diversity of space-time codes. The scheme features full diversity and full rate. We also extend turbo-STCM to the case of large numbers of antennas (>2). Simulation results are provided over the block-fading channel. It is shown that this turbo scheme provides an advantage of 1.1 dB over conventional space-time codes of similar decoding complexity. The analytical union bound of the bit error probability is derived for turbo-STCM over the Rayleigh block-fading channel. The bound makes it possible to express the performance analysis of turbo-STCM in terms of the properties of the constituent space-time codes. The union bound is demonstrated for 8-PSK turbo-STCM with two transmit antennas and one or two receive antennas.

We compute the channel capacity of M-ary pulse position modulation (PPM) ultra-wideband (UWB) communications over the additive white Gaussian noise channel. The computation extends the known capacity of PPM orthogonal signals to incorporate UWB-specific constraints. The constraints are the power spectrum density limitation under FCC Part 15 rules and a specified spreading ratio. The UWB capacity is expressed as a function of range demonstrating a fundamental trade-off in UWB system design. UWB capacity is also compared to the capacity of M-ary phase shift keying (PSK) direct sequence spread spectrum (DS-SS). It is shown that for the same power constraint,. both systems have similar capacity at high signal to noise ratio (SNR). At low SNR, UWB has a significant advantage for multilevel modulations with M>4, while for M=2,4, DS-SS has a slight advantage.

In this paper we introduce a new scheme for parallel concatenated turbo space-time coding. We refer to turbo space-time coded modulation (turbo-STCM). Turbo-STCM use systematic space-time codes as constituent codes. Puncturing is used to obtain full rate codes. The new codes combine the high coding gain of turbo-codes with the spatial diversity advantage of space-time processing and the bandwidth efficiency of coded modulation under a single framework. Using simple STCM component encoders, performance is studied by simulations for a 4-PSK turbo-STCM code with two transmit and two receive antennas over a block fading channel. Significant gains are shown over conventional space-time coding. We also derive the union bound for 2 bps/Hz, 4-PSK turbo-STCM with two transmit and one receive antenna over the AWGN channel. The analysis provides a practical tool to analyze the performance of turbo codes with multiple antennas.

We study the application of the eigencanceler, a reduced-rank method based on the eigendecomposition of the estimated covariance matrix, to the wireless communication problem. Simple closed-form bounds are obtained for the bit-error rate of binary phase-shift keying modulation in the presence of cochannel interference in systems using sample matrix inversion (SMI) and the eigencanceler. The application of SMI and the eigencanceler to a flat fading time-division multiple-access system is studied in the context of the IS-54/IS-136 standard. It is shown that adaptive antennas in conjunction with reduced-rank processing can be used to increase capacity of such systems by reducing the frequency reuse factor from 7 to 1.

We derive expressions for the exact bit-error probability (BEP) for the detection of coherent binary phase-shift keying signals of the optimum combiner employing space diversity when both the desired signal and a Gaussian cochannel interferer are subject to flat Rayleigh fading. Two different methods are employed to reach two different, but numerically identical, expressions. With the direct method, the conditional BEP is averaged over the fading of both signal and interference, With the moment generating function based method, expressions are derived from an alternative representation of the Gaussian Q-function.

The performance of code-division multiple-access (CDMA) systems is affected by multiple factors such as large-scale fading, small-scale fading, and cochannel interference (CCI). Most of the published research on the performance analysis of CDMA systems usually accounts for subsets of these factors. In this work, it is attempted to provide a comprehensive analysis which joins several of the most important factors affecting the performance of CDMA systems. In particular, new analytical expressions are developed for the outage and bit-error probability of CDMA systems. These expressions account for adverse effects such as path loss, large-scale fading (shadowing), small-scale fading (Rayleigh fading), and CCI, as well as for correcting mechanisms such as power control (compensates for path loss and shadowing), spatial diversity (mitigates against Rayleigh fading), and voice activity gating (reduces CCI). The new expressions may be used as convenient analysis tools that complement computer simulations. Of particular interest are tradeoffs revealed among system parameters, such as maximum allowed power control error versus the number of antennas used for spatial diversity.

The capacity of wireless CDMA systems in the forward link is limited by both intra-cell and inter-cell cochannel interferences. In particular, when the mobile station is close to a cell boundary, the desired signal is disturbed by relatively strong interference from neighboring base stations. In this paper, a receiver architecture with smart antenna followed by a RAKE demodulator is suggested at a IS-95 CDMA mobile station for interference suppression and diversity combining. Such a structure can work well only when the channel vector of desired signal is correctly estimated. We use the identifying spreading codes (as in IS-95 for example) to provide and adaptively correct a channel vector estimate, suppress cochannel interference, hence improve the system capacity.

Optimum combining for space diversity reception is studied in digital cellular mobile radio communication systems with Rayleigh fading and multiple cochannel interferers. This paper considers binary phase-shift keying (BPSK) modulation in a flat Rayleigh-fading environment when the number of interferences L is no less than the number of antenna elements N(L/spl ges/N). The approach of this paper and its main contribution is to carry out the analysis in a multivariate framework. Using this approach and with the assumption of equal-power interferers, it is shown that the probability density function of the maximum signal-to-interference ratio (SIR) at the output of the optimum combiner has a Hotelling T/sup 2/ distribution. Closed form expressions using hypergeometric functions are derived for the outage probability and the average probability of bit error. Theoretical results are demonstrated by Monte Carlo simulations.

This paper describes the performance analysis of a direct-sequence (DS) code-division multiple-access (CDMA) personal communication system (PCS) sharing a common spectrum with narrowband microwave radio links. Spatial and temporal processing are combined to improve the performance of the DS-CDMA system subject to narrowband interference. Degrees of freedom (DOF) provided by space-time (ST) optimum combining schemes are exploited to combat both fading and interference. The performance of several space-time receiver architectures is evaluated in terms of average bit error rate (BER) and it is investigated how this performance is influenced by various parameters.

Spatial and temporal processing are combined to suppress narrowband interference in CDMA communications. Space-time (ST) processing provides degrees of freedom (DOF) for both interference cancellation and diversity combining. Two ST receiver architectures, cascade and joint, are studied. The main contributions of the paper are the development of new analytical expressions of (1) the asymptotic efficiency of each method, (2) the probability density function (PDF) of the signal-to-interference-plus-noise ratio (SINR) at the array output in a frequency selective Rayleigh fading environment, and (3) the average probability of bit error (BER) associated with each method.

This paper studies signal cancellation effects in adaptive radar. Using examples from Mountaintop data, it is shown that signal cancellation occurs when the target of interest is included in the weight vector training. The signal cancellation is due to calibration errors (mismatch between the target signal and presumed steering vector). An eigenanalysis-based adaptive beamformer is shown to have greater robustness to signal cancellation effects than the sample matrix inversion (SMI) method.

Adaptive antenna arrays are applied at the base station to improve performance of a mobile communication system operating in a flat slowly fading Rayleigh channel. Analytical expressions are derived for the average probability of error of the sample matrix inversion (SMI) and an eigenanalysis-based method for the case of a single co-channel interference. It is shown that the eigenanalysis-method is superior to the SMI method when the array covariance matrix is estimated from small data sets. The analysis is supported by numerical results obtained from simulations.