M. Debbah

Bio: M. Debbah is an academic researcher from Motorola. The author has contributed to research in topics: Spread spectrum & Probability distribution. The author has an hindex of 6, co-authored 8 publications receiving 255 citations.

MMSE analysis of certain large isometric random precoded systems

Abstract: Linear precoding consists in multiplying by an N/spl times/K matrix a K-dimensional vector obtained by serial-to-parallel conversion of a symbol sequence to be transmitted. In this paper, new tools, borrowed from the so-called free probability theory, are introduced for the purpose of analyzing the performance of minimum mean-square error (MMSE) receivers for certain large random isometric precoded systems on fading channels. The isometric condition represents the case of precoding matrices with orthonormal columns. It is shown in this contribution that the signal-to-interference-plus-noise ratio (SINR) at the equalizer output converges almost surely to a deterministic value depending on the probability distribution of the channel coefficients when N/spl rarr/+/spl infin/ and K/N/spl rarr//spl alpha//spl les/1. These asymptotic results are used to analyze the impact of orthogonal spreading as well as to optimally balance the redundancy introduced between linear precoding versus classical convolutional coding, while preserving a simple MMSE equalization scheme at the receiver.

A MMSE successive interference cancellation scheme for a new adjustable hybrid spread OFDM system

Abstract: The effects of uniform spreading in OFDM-CDMA systems is the harmonization at the reception of the signal to noise ratio between the sub-bands which prevents the good performance of successive decoding algorithms. This paper proposes a new hybrid spread OFDM (SOFDM) transmission scheme in which the spreading of the information is adjustable and not uniform along the carrier (frequency selective). Moreover a MMSE version of the V-BLAST successive interference cancellation algorithm suited for this hybrid modulator is derived. The performance of the combination of SHOFDM and MMSE V-BLAST is shown to both outperform COFDM and conventional and classical iterative detection algorithms for SOFDM in the realistic scenario of the 5 GHz HiperLAN/2 system.

Spread OFDM performance with MMSE equalization

Abstract: Upper-bounds on the bit error probability of an OFDM/CDMA system in a single user context are derived for a linear minimum mean-square-error (MMSE) receiver structure. All the calculus are performed in presence of a frequency-selective Rayleigh fading channel both in a coded (convolutive forward error correcting scheme) and uncoded scenario. Surprisingly, we show that coded SOFDM outperforms COFDM if the signal to noise ratio is greater than a given threshold which only depends on the code rate and not on the code structure. These theoretical results provide tools to optimally combine coding and spreading for increasing the spectral efficiency of OFDM/CDMA schemes.

Reception of multicarrier spread-spectrum signals

Abstract: A system (100), receiver (160-190) and method of operation for spread OFDM wireless communication (single user OFDM-CDMA with cyclic-prefix) by: equalizing the received spread OFDM signal (y) and splitting it into first and second portions (s1,s2); making a decision on the second portion and subtracting the second portion from the received signal to produce a first difference signal; processing the first difference signal to recover the first portion of the received signal in which symbol interfering terms of the second portion are substantially reduced; making a decision on the first portion and subtracting the first portion from the received signal to produce a second difference signal; and processing the second difference signal to recover the second portion of the received signal in which symbol interfering terms of the first portion are substantially reduced. The process may be iterated extensively at this stage. In a second stage, the recovered received signal is split into a greater number of portions (e.g. 4) and processed similarly to further reduce interference.

Channel estimation using the guard interval of a multicarrier signal

Abstract: A method of communication using Orthogonal Frequency Division Multiplexing (“OFDM”) comprises generating bit streams (bn∈(0,1),n=0,1, . . . ,K−1) and the corresponding sets of frequency domain carrier amplitudes (XO(k) to XN(k)), where k is the OFDM symbol number, modulated as OFDM symbols to be transmitted from a transmitter. Prefixes are inserted as guard intervals in the sample streams and the OFDM symbols are transmitted from the transmitter to a receiver. The receiver uses information from the prefixes to estimate the Channel Impulse Response (H(F) D) of the transmission channels and uses the estimated Channel Impulse Response (Ĥ(F) D) to demodulate the bit streams in the signals received. The prefixes (αk.co to αk.cD−1) are deterministic and are known to the receiver as well as to the transmitter. Preferably, the prefixes (αk.co to αk.cD−1) comprise a vector (PD) that is common to said symbols multiplied by at least one weighting factor (αk). The weighting factor (αk) preferably differs from one symbol to another but the elements of a given vector (PD) are multiplied by the same weighting factor. Preferably, the weighting factor (αk) has a complex pseudo-random value.

Random Matrix Theory and Wireless Communications

Abstract: Random matrix theory has found many applications in physics, statistics and engineering since its inception. Although early developments were motivated by practical experimental problems, random matrices are now used in fields as diverse as Riemann hypothesis, stochastic differential equations, condensed matter physics, statistical physics, chaotic systems, numerical linear algebra, neural networks, multivariate statistics, information theory, signal processing and small-world networks. This article provides a tutorial on random matrices which provides an overview of the theory and brings together in one source the most significant results recently obtained. Furthermore, the application of random matrix theory to the fundamental limits of wireless communication channels is described in depth.

Random Matrix Methods for Wireless Communications

Abstract: Blending theoretical results with practical applications, this book provides an introduction to random matrix theory and shows how it can be used to tackle a variety of problems in wireless communications The Stieltjes transform method, free probability theory, combinatoric approaches, deterministic equivalents and spectral analysis methods for statistical inference are all covered from a unique engineering perspective Detailed mathematical derivations are presented throughout, with thorough explanation of the key results and all fundamental lemmas required for the reader to derive similar calculus on their own These core theoretical concepts are then applied to a wide range of real-world problems in signal processing and wireless communications, including performance analysis of CDMA, MIMO and multi-cell networks, as well as signal detection and estimation in cognitive radio networks The rigorous yet intuitive style helps demonstrate to students and researchers alike how to choose the correct approach for obtaining mathematically accurate results

A Survey on the Successive Interference Cancellation Performance for Single-Antenna and Multiple-Antenna OFDM Systems

Abstract: Interference plays a crucial role for performance degradation in communication networks nowadays. An appealing approach to interference avoidance is the Interference Cancellation (IC) methodology. Particularly, the Successive IC (SIC) method represents the most effective IC-based reception technique in terms of Bit-Error-Rate (BER) performance and, thus, yielding to the overall system robustness. Moreover, SIC in conjunction with Orthogonal Frequency Division Multiplexing (OFDM), in the context of SIC-OFDM, is shown to approach the Shannon capacity when single-antenna infrastructures are applied while this capacity limit can be further extended with the aid of multiple antennas. Recently, SIC-based reception has studied for Orthogonal Frequency and Code Division Multiplexing or (spread-OFDM systems), namely OFCDM. Such systems provide extremely high error resilience and robustness, especially in multi-user environments. In this paper, we present a comprehensive survey on the performance of SIC for single- and multiple-antenna OFDM and spread OFDM (OFCDM) systems. Thereby, we focus on all the possible OFDM formats that have been developed so far. We study the performance of SIC by examining closely two major aspects, namely the BER performance and the computational complexity of the reception process, thus striving for the provision and optimization of SIC. Our main objective is to point out the state-of-the-art on research activity for SIC-OF(C)DM systems, applied on a variety of well-known network implementations, such as cellular, ad hoc and infrastructure-based platforms. Furthermore, we introduce a Performance-Complexity Tradeoff (PCT) in order to indicate the contribution of the approaches studied in this paper. Finally, we provide analytical performance comparison tables regarding to the surveyed techniques with respect to the PCT level.

Asymptotic Performance of Linear Receivers in MIMO Fading Channels

Abstract: Linear receivers are an attractive low-complexity alternative to optimal processing for multiple-antenna multiple-input multiple-output (MIMO) communications. In this paper, we characterize the information-theoretic performance of MIMO linear receivers in two different asymptotic regimes. For fixed number of antennas, we investigate the limit of error probability in the high-signal-to noise-ratio (SNR) regime in terms of the diversity-multiplexing tradeoff (DMT). Following this, we characterize the error probability for fixed SNR in the regime of large (but finite) number of antennas.As far as the DMT is concerned, we report a negative result: we show that both linear zero-forcing (ZF) and linear minimum mean- square error (MMSE) receivers achieve the same DMT, which is largely suboptimal even in the case where outer coding and deAcircnot coding is performed across the antennas. We also provide an apAcircnot proximate quantitative analysis of the markedly different behavior of the MMSE and ZF receivers at finite rate and nonasymptotic SNR, and show that while the ZF receiver achieves poor diversity at any finite rate, the MMSE receiver error curve slope flattens out progressively, as the coding rate increases. When SNR is fixed and the number of antennas becomes large, we show that the mutual information at the output of an MMSE or ZF linear receiver has fluctuations that converge in distribution to a Gaussian random variable, whose mean and variance can be characterized in closed form. This analysis extends to the linear reAcircnot ceiver case a well-known result previously obtained for the optimal receiver. Simulations reveal that the asymptotic analysis captures accurately the outage behavior of systems even with a moderate number of antennas.

MIMO channel modeling and the principle of maximum entropy

Abstract: We devise theoretical grounds for constructing channel models for multiple-input multiple-output (MIMO) systems based on information-theoretic tools. The paper provides a general method to derive a channel model which is consistent with one's state of knowledge. The framework we give here has already been fruitfully explored with success in the context of Bayesian spectrum analysis and parameter estimation. For each channel model, we conduct an asymptotic analysis (in the number of antennas) of the achievable transmission rate using tools from random matrix theory. A central limit theorem is provided on the asymptotic behavior of the mutual information and validated in the finite case by simulations. The results are useful both in terms of designing a system based on criteria such as quality of service and in optimizing transmissions in multiuser networks.