Abstract In this paper, we extend the geometrical one‐ring multiple‐input multiple‐output (MIMO) channel model with respect to frequency selectivity. Our approach enables the design of efficient and accurate simulation models for wideband space‐time MIMO channels under isotropic scattering conditions. Two methods will be provided to compute the parameters of the simulation model. Especially, the temporal, frequency and spatial correlation properties of the proposed wideband space‐time MIMO channel simulator are studied analytically. It is shown that any given specified or measured discrete power delay profile (PDP) can be incorporated into the simulation model. The high accuracy of the simulation model is demonstrated by comparing its statistical properties with those of the underlying reference model with specified correlation properties in the time, frequency and spatial domain. As an application example of the new MIMO frequency‐selective fading channel model, we study the influence of various channel model parameters on the system performance of a space‐time coded orthogonal frequency division multiplexing (OFDM) system. For example, we investigate the influence of the antenna element spacings of the base station (BS) antenna as well as the mobile station (MS) antenna. It turns out that an increasing of the antenna element spacing at the BS side results in a higher diversity gain than an increasing of the antenna element spacing at the MS side. Furthermore, the diversity gain brought in by space‐time block coding schemes is investigated by simulation. Our results show that transmitter diversity can significantly reduce the symbol error rate (SER) of multiple antenna systems. Finally, the influence of the Doppler effect and the impact of imperfect channel state information (CSI) on the system performance is also investigated. Copyright © 2009 John Wiley & Sons, Ltd.

This paper investigates the effects of channel estimation errors on the symbol-error-rate (SER) performance of a cooperative communication system operating in an amplify-and- forward (AF) mode. A pilot symbol assisted modulation scheme with linear minimum mean square estimation (LMMSE) is used for the channel estimation. An accurate and easy-to-evaluate SER expression is presented for uncoded cooperative communication systems with quadrature amplitude modulation (QAM) and phase-shift keying (PSK) constellations. Numerical simulations are conducted to verify the correctness of the proposed analytical formulation. It is shown that the performance loss caused by channel estimation errors increases mainly with the normalized maximum Doppler frequency.

Cooperative diversity is a promising technology for future wireless networks. In this paper, we consider a cooperative communication system operating in an amplify-and-forward (AF) mode with an imperfectly-known relay fading channel. It is assumed that a pilot symbol assisted modulation (PSAM) scheme with linear minimum mean square estimator (LMMSE) is used for the channel estimation. A simple and easy-to-evaluate asymptotical upper bound (AUB) of the symbol-error-rate (SER) is derived for uncoded AF cooperative systems with quadrature amplitude modulation (QAM) constellations. Based on the AUB, we propose a criterion for the choice of parameters in the PSAM scheme, i.e., the pilot spacing and the Wiener filter length. We also formulate an optimum power allocation problem for the considered system. The optimum power allocation can be found by means of a gradient search over a continuous range. Numerical simulations are presented to verify the correctness of the theoretical results and the benefits of the parameter optimization.

Unitary space-time constellation design is considered for noncoherent multiple-antenna communications, where neither the transmitter nor the receiver knows the fading coefficients of the channel. By employing the Clarke's subdifferential theorem of the sum of the kappa largest singular values of a unitary matrix, we present a numerical optimization procedure for finding unitary space-time signal constellations of any dimension. The Chernoff bound of the pairwise error probability is used directly as a design criterion. The constellations are found by performing gradient descent search on a family ldquosurrogaterdquo functions that converge to the maximum pairwise error probability. The complexity of the search procedure increases with the dimension and the size of the constellation, but it can be considered to be acceptable for an off-line design procedure. Since the designed constellations are unstructured, and, thus, require an exhaustive search over all codewords in decoding, their main practical value is to serve as constellation design performance benchmarks. We compare the performance of the new constellations to that of some other well-known constellations. Computer simulation results illustrate typically about 0.4-3.5 dB performance gains.

We demonstrate a super-quasi-orthogonal space- time (ST) trellis code for four transmit antennas with rectangular signal constellations for wireless communications with a spectral efficiency of 5bits/s/Hz, thus larger than only 4 bits/s/Hz as shown in our previous conference paper. Considering a mobile wireless communications system with four transmit antennas, we form an 8D signal constellation as Cartesian product of four 2D rectangular signal sets, an 8D point being transmitted by the first antenna as four concatenated 2D points in four consecutive channel uses. The 2D symbols transmitted by the other three antennas are not independent, but so chosen as to form, together with the symbols transmitted by the first antenna, the entries of a 4times4 quasi-orthogonal matrix. The union of two sets of quasi-orthogonal matrices forms a super-quasi-orthogonal signal set. With 4x4 quasi-orthogonal matrices, we then label the state transitions of a trellis diagram describing the operation of the encoder. The frame error rate (FER) and the bit error rate (BER) performance results show an excellent behavior of our proposed super-quasi-orthogonal ST trellis codes.

We demonstrate a super-quasi-orthogonal space- time (ST) trellis code for four transmit antennas with rectangular signal constellations for wireless communications with a spectral efficiency of 4 bits/s/Hz. Considering a mobile wireless communications system with four transmit antennas, we form an 8D signal constellation as Cartesian product of four 2D rectangular signal sets, an 8D point being transmitted by the first antenna as four concatenated 2D points in four consecutive channel uses. The 2D symbols transmitted by the other three antennas are not independent, but so chosen as to form, together with the symbols transmitted by the first antenna, the entries of a 4 times 4 quasi- orthogonal matrix. The union of two sets of quasi-orthogonal matrices forms a super-quasi-orthogonal signal set. With 4times4 quasi-orthogonal matrices, we then label the state transitions of a trellis diagram describing the operation of the encoder. The frame error rate (FER) and the bit error rate (BER) performance results show an excellent behavior of our proposed super-quasi- orthogonal ST trellis codes.

We suggest applying constellation shaping to reduce the peak and average power of orthogonal frequency division multiplexing (OFDM) signals using quadrature amplitude modulation (QAM) in all subcarriers without clipping or reducing the data rate. Adopting the successful shell mapping algorithm for high data rate transmission over telephone channels, as described in the V.34 Recommendation of ITU-T, we build a shell mapping algorithm for multidimensional constellation in the frequency domain for OFDM communication systems with N subcarriers. We give closed-form expressions of the functions needed to apply the constellation shaping algorithm for any N being a power of two. No side information needs to be transmitted and the data rate remains the same as for the basic OFDM system. Our simulation results show that we are able to reduce the peak and mean power by about 1 dB for OFDM signals with N = 16. For a higher number of subcarriers, we expect that we obtain more freedom in power minimization and the resulting gain will be higher. The only price to be paid is the enhanced complexity of the system by an amount that is rather acceptable.

In this paper, a narrowband multiple-channel transmission scheme with multiple transmit antennas is proposed and analyzed. The channelization is based on space-time signature matrices, which do not expand bandwidth, unlike conventional schemes such as code-division or time-division multiplexing. The channels can be used by multiple independent users in an uplink or downlink scenario (multiple access or broadcast channels, respectively), or by one user in a multiplexing scenario. The data transmitted on each channel is convolutionally encoded, interleaved, and then space-time block encoded before space-time channelization. Each channel has a unique interleaver and space-time signature, but the convolutional encoder and space-time block code encoder can be identical across channels. It is shown that asymptotic single-user-like performance can be achieved with optimal detection and decoding in a Rayleigh fading channel. Practical receiver algorithms are developed based on the iterative (turbo) detection technique. The simulation results demonstrate that these suboptimal receivers achieve single-user performance at moderate signal-to-noise ratios, and moderate user loads. In the single-user multiplexing case, a significant performance gain over single-channel transmission with the same data rate is obtained.

We consider the problem of creating signal constellations for trellis-coded unitary space–time communication links, where neither the transmitter nor the receiver knows the fading gains of the channel. Our study includes design techniques for trellis-coded schemes with and without parallel paths, which allows us to find a tradeoff between low complexity and high performance. We present a new formulation of the constellation design problem for trellis-coded unitary space–time modulation schemes. The two key differences in our approach against those of other authors are that we not only combine the constellation design and mapping by set partitioning into one step, but we also use directly the Chernoff bound of the pairwise error probability as a design metric. By novelly employing a theorem for the Clarke subdifferential of the sum of the$k$largest singular values of the unitary matrix, we also present a numerical optimization procedure for finding signal constellations resulting in high-performance communications systems. To demonstrate the advantages of our new design method, we report the best constellations found for trellis-coded unitary space–time modulation systems. Simulation results show that these constellations achieve 1 dB coding gain against the usually used constellations.

We consider the problem of creating signal constellations for trellis-coded unitary space-time communication links, where neither the transmitter nor the receiver knows the fading gains of the channel. Our study includes constellation-design techniques for trellis-coded schemes with and without parallel paths, which allows us to find a tradeoff between low complexity and high performance. We present a new formulation of the constellation design problem for trellis-coded unitary space-time modulation (TCUSTM) schemes. The two key differences in our approach against those of other authors are that we not only combine the constellation design and mapping by set partitioning into one step, but we also use directly the Chernoff bound of the pairwise error probability as a design metric. By novelly employing a theorem for the Clarke subdifferential of the sum of the k largest singular values of the unitary matrix, we also present a numerical optimization procedure for finding signal constellations resulting in high-performance communications systems. To demonstrate the advantages of our new design method, we report the best constellations found for TCUSTM systems. Simulation results show that these constellations achieve a 1-dB coding gain at a bit-error rate of 10-4against usually used constellations

In this paper, we present a new formulation of the problem of signal design for trellis-coded unitary space-time communication systems. Our approach differs from other methods in that we not only combine the constellation design and set partitioning process together, we also use directly the Chernoff bound of the pairwise probability of error as design metric, which is a better figure of merit than the previously used chordal distance, for unitary constellation design. By novelly employing a theorem regarding the Clarke subdifferential of the sum of the k largest singular values of the unitary matrix, we present a numerical optimization procedure for finding good constellations and report the best signal constellations found. Simulation results show that these constellations achieve 1 dB gain against the previously used constellations of unitary space-time signals.

In this paper, we propose a novel method for creating constellations of unitary space-time signals for non-coherent multiple-antenna communication link, where neither the transmitter nor the receiver knows the fading coefficients. By employing a theorem for the Clarke subdifferential of the sum of the k largest singular values of the unitary matrix, we present a numerical optimization procedure for finding good constellations of unitary space-time signals and report the best constellations found by this procedure. These constellations of unitary space-time signal improve the performance significantly upon previously best known constellations.

We give a new formulation of the problem of signal design based on the design criteria for trellis coded unitary space-time communication system. Two key differences in our approach from that of previous method are that we not only combine the constellation design and set partition process together, we also use directly the Chernoff bound of the pairwise probability of error as design metric, which is a better figure of merit than previously used chordal distance, for unitary constellation design. By novelly employing a theorem for the Clarke subdifferential of the sum of the k largest singular values of the unitary matrix, we present a numerical optimization procedure for finding good constellations and report the best signal constellations found. Simulation results show that these constellations improve significantly upon the previously used constellations of unitary space-time signals.

This paper proposes a novel bandwidth-efficient multiuser scheme with multiple antennas. By assigning each user a two-dimensional signature matrix and user-specific interleaver, K users can can occupy the same bandwidth as the single user. Both theoretical analysis and simulation results show that the single-user like performance can be achieved asymptotically.

In this letter, we study differentially modulated, iteratively decoded CDMA. The iterative multiuser receiver proposed consists of an additional soft-input soft-output (SISO) differential decoder, when compared to turbo multiuser detectors for absolutely modulated systems. Algorithms for iterative decoding with and without phase information at the receiver are developed. The resulting turbo receivers with differential modulation outperform coherent receivers with absolute modulation at moderate to high signal to noise ratios due to the interleaver gain associated with recursive inner encoders in serially concatenated encoding structures.

This paper explores the use of differential modulation as a rate-1 recursive code to improve performance in an iterative (or turbo) CDMA receiver in a convolutionally encoded system. We would expect an interleaver gain from the recursive nature of the differential encoder, and indeed such a gain over an absolutely encoded CDMA system is easily demonstrated through simulations. The iterative receiver proposed consists of an additional soft-input soft-output (SISO) differential decoder, when compared to turbo multiuser detectors for absolutely modulated systems. Algorithms for iterative decoding with and without phase information at the receiver are developed. The resulting coherent and non-coherent receivers with differential modulation both outperform coherent receivers with absolute modulation at moderate to high signal to noise ratios.