Leszek Szczecinski

Spatial modulation: optimal detection and performance analysis

In this letter, we derive the optimal detector for the so-called spatial modulation (SM) system introduced by Mesleh et al. in (Mesleh, 2006). The new detector performs significantly better than the original (~ 4 dB gain), and we support our results by deriving a closed form expression for the average bit error probability. As well, we show that SM with the optimal detector achieves performance gains (~ 1.5 - 3 dB) over popular multiple antenna systems, making it an excellent candidate for future wireless communication standards.

Space shift keying modulation for MIMO channels

In this paper, we present space shift keying (SSK) as a new modulation scheme, which is based on spatial modulation (SM) concepts. Fading is exploited for multiple-input multiple-output(MIMO) channels to provide better performance over conventional amplitude/phase modulation (APM) techniques. In SSK, it is the antenna index used during transmission that relays information, rather than the transmitted symbols themselves. This absence of symbol information eliminates the transceiver elements necessary for APM transmission and detection (such as coherent detectors). As well, the simplicity involved in modulation reduces the detection complexity compared to that of SM, while achieving almost identical performance gains. Throughout the paper, we illustrate SSKs strength by studying its interaction with the fading channel. We obtain tight upper bounds on bit error probability, and discuss SSKs performance under some non-ideal channel conditions (estimation error and spatial correlation). Analytical and simulation results show performance gains over APM systems (3 dB at a bit error rate of 10-5), making SSK an interesting candidate for future wireless applications. We then extend SSK concepts to incorporate channel coding, where in particular, we consider a bit interleaved coded modulation (BICM) system using iterative decoding for both convolutional and turbo codes. Capacity results are derived, and improvements over APM are illustrated (up to 1 bits/s/Hz), with performance gains of up to 5 dB.

Generalized space shift keying modulation for MIMO channels

A fundamental component of spatial modulation (SM), termed generalized space shift keying (GSSK), is presented. GSSK modulation inherently exploits fading in wireless communication to provide better performance over conventional amplitude/phase modulation (APM) techniques. In GSSK, only the antenna indices, and not the symbols themselves (as in the case of SM and APM), relay information. We exploit GSSKpsilas degrees of freedom to achieve better performance, which is done by formulating its constellation in an optimal manner. To support our results, we also derive upper bounds on GSSKpsilas bit error probability, where the source of GSSKpsilas strength is made clear. Analytical and simulation results show performance gains (1.5-3 dB) over popular multiple antenna APM systems (including Bell Laboratories layered space time (BLAST) and maximum ratio combining (MRC) schemes), making GSSK an excellent candidate for future wireless applications.

Rate Allocation and Adaptation for Incremental Redundancy Truncated HARQ

This paper considers incremental redundancy hybrid ARQ (HARQ) transmission over independent block-fading channels. The transmitter, having no knowledge of the instantaneous channel state information (CSI) can or - allocate the transmission rate knowing the statistics of the channel, or - adapt the transmissions rates using the outdated CSI, i.e., the one experienced by the receiver in the past transmissions that resulted in a packet decoding failure. Aiming at throughput maximization problems under constraint on the outage probability, we show how to optimize the rate-adaptation and rate-allocation policies using dynamic programming framework. Numerical examples obtained in a Rayleigh-fading channel show that rate adaptation provides notable gains over a rate allocation and non-adaptive HARQ, and, for high SNR, only a few transmissions are necessary to approach closely the ergodic capacity.

Distribution of L-values in gray-mapped M 2 -QAM: closed-form approximations and applications

In this paper we develop closed form approximations for the probability density function (PDF) of the reliability metrics (L-values) in bit-interleaved coded modulation (BICM). The expressions are valid for M2-ary quadrature amplitude modulations (M2-QAM) with binary reflected Gray mapping when the metrics are calculated using the so-called max-log approximation. Based on the developed expressions, we also propose two simple Gaussian mixture approximations that are analytically tractable. We apply our developments to efficiently calculate the BICM capacity, and to develop bounds on the coded bit-error rate when a convolutional code is used. The coded performance of a hybrid automatic repeat request (HARQ) based on constellation rearrangement is also evaluated.

A simple detect-and-forward scheme in fading channels

In this letter, we introduce and analyze a detect-and-forward scheme for cooperative communications over fading channels based on the transmission of partial source-relay channel state information. The proposed scheme is simple to implement and its efficiency is demonstrated through constrained capacity calculation and throughput evaluation based on practical coding schemes.

Exploiting UEP in QAM-based BICM: interleaver and code design

In this paper we formally analyze the interleaver and code design for QAM-based BICM transmissions using the binary reflected Gray code. We develop analytical bounds on the bit error rate and we use them to predict the performance of BICM when unequal error protection (UEP) is introduced by the constellation labeling. Based on these bounds the optimum design of interleaver and code is found, and numerical results for representative configurations are presented. When the new design is used, the improvements may reach 2 dB, and they are obtained without any increase on the transceivers complexity. We also introduce the concept of generalized optimum distance spectrum convolutional codes, which are the optimum codes for QAM-based BICM transmissions.

Probability Density Functions of Logarithmic Likelihood Ratios in Rectangular QAM

Closed-form expressions for the probability density function (PDF) of logarithmic likelihood ratios (LLR) in rectangular quadrature amplitude modulations are derived. Taking advantage of assumed Gray mapping, the problem is solved in one dimension corresponding to the real or imaginary part of the symbol. The results show that sought PDFs are linear combinations of truncated Gaussian functions. This simple result stands in contrast with often assumed Gaussian distribution for the LLRs. Histograms of LLRs obtained via simulations confirm our analysis

Modulation doping for iterative demapping of bit-interleaved coded modulation

In this letter, the problem of the transmitter design for bit-interleaved coded modulation (BICM) with the receiver employing iterative demapping, is addressed. Conventionally, the design is focused on the appropriate choice of the constellation mapping so that the iterative process converges to small values of bit- or block- error rates. Here, instead of a difficult design of a new mapping, we propose to use symbols modulated using two different mappings. Through numerical simulation, our simple design is shown to outperform the conventional approach without increase in the receivers complexity.

Performance evaluation of linear turbo receivers using analytical extrinsic information transfer functions

Turbo-receivers reduce the effect of the interference-limited propagation channels through the iterative exchange of information between the front-end receiver and the channel decoder. Such an iterative (turbo) process is difficult to describe in a closed form so the performance evaluation is often done by means of extensive numerical simulations. Analytical methods for performance evaluation have also been proposed in the literature, based on Gaussian approximation of the output of the linear signal combiner. In this paper, we propose to use mutual information to parameterize the logarithmic-likelihood ratios (LLRs) at the input/output of the decoder, casting our approach into the framework of extrinsic information transfer (EXIT) analysis. We find the EXIT functions of the front-end (FE) receiver analytically, that is, using solely the information about the channel state. This is done, decomposing the FE receiver into elementary blocks described independently. Our method gives an insight into the principle of functioning of the linear turbo-receivers, allows for an accurate calculation of the expected bit error rate in each iteration, and is more flexible than the one previously used in the literature, allowing us to analyze the performance for various FE structures. We compare the proposed analytical method with the results of simulated data transmission in case of multiple antennas transceivers.