Karine Amis

New Iterative Detector of MIMO Transmission Using Sparse Decomposition

This paper addresses the problem of decoding in large-scale multiple-input–multiple-output (MIMO) systems. In this case, the optimal maximum-likelihood (ML) detector becomes impractical due to an exponential increase in the complexity with the signal and the constellation dimensions. This paper introduces an iterative decoding strategy with a tolerable complexity order. We consider a MIMO system with finite constellation and model it as a system with sparse signal sources. We propose an ML relaxed detector that minimizes the Euclidean distance with the received signal while preserving a constant

Multiple source cooperative coding using turbo product codes with a noisy relay

\ell_{1}

Space-time error correcting codes

-norm of the decoded signal. We also show that the detection problem is equivalent to a convex optimization problem, which is solvable in polynomial time. Two applications are proposed, and simulation results illustrate the efficiency of the proposed detector.

Achievable Throughput Optimization in OFDM Systems in the Presence of Interference and its Application to Power Line Networks

In this paper, we consider the case where data from a relatively large number of sources are to be transmitted to a single destination. We suppose that there is no communication between the sources and thus each source encodes its data independently using the same systematic linear block code. The codewords transmitted from the sources to the destination are eavesdropped by a relay. A product code is built at the relay, with rows being the possibly erroneous source codewords, using a second systematic linear block code as column encoder. The resulting additional redundancy is then transmitted to the destination. The product code matrix is pieced together from source codewords and relay redundancy received by the destination. Significant additional coding gain is achieved on the additive white Gaussian noise (AWGN) channel. Performance on the correlated flat Rayleigh fading channel is also given for different correlation coefficients yielding large diversity orders.

An improved iterative decoding algorithm for block turbo codes

A new space-time block code family for two transmitters, called the space-time error correcting codes (STECCs), is presented. As it is built from any linear forward error correcting code (FEC), a STECC is able to correct errors while achieving high spectral efficiencies. The key principle is the FEC linearity which is exploited to transmit linear combinations of FEC codewords to create a space-time redundancy. The proposed code exhibits interesting performance on an ISI-free block fading channel. This result is all the more true as the number of FEC codewords considered in the combination is high.

Interference alignment for a multi-user SISO interference channel

The aim of this paper is to study the bit-loading and power allocation problem in the presence of interference (Inter-carrier Interference (ICI) and Inter-Symbol Interference (ISI)) in Orthogonal Frequency Division Multiplexing (OFDM) systems. ISI and ICI significantly degrade the performance of OFDM systems and make the resource management optimized without the assumption of interference less efficient. To solve this problem, an initial solution based on the greedy approach is proposed in this paper. Then, several reduced complexity approaches, which yield a little degradation compared to the initial solution, have been developed. Simulation results presented in the context of Power Line Communication (PLC) show that the performance of proposed algorithms is tight with their upper bound. Moreover, these algorithms efficiently improve the system performance as compared to the constant power water-filling allocation algorithm as well as maximum power allocation algorithm.

Reduced complexity near-optimal iterative receiver for Wimax full-rate space-time code

Since the introduction of the block turbo code (BTC) except, several soft-input/soft-output (SISO) algorithms have been used in order to softly decode product codes. The classical Chase-Pyndiah algorithm seems to be one with the best trade-off between complexity and performance, especially for low error correction capability t (typically 1 or 2) where it is nearly optimal. However, as an algebraic decoding-based algorithm, the lack of codeword diversity is one of its weakness for BTCs with higher error correction capability and/or non binary BTCs. In this paper, we propose an improved iterative decoding algorithm for BTCs. We present a simple sliding encoding-window (SEW) based decoding algorithm which exploits the cyclic and systematic properties of RS and BCH codes. By adding the SEW algorithm to a classical algebraic decoding method, the proposed decoder can easily generate a list of codewords that are close to the decoded codeword. With the codeword diversity, we can compute more reliable soft output necessary in the turbo decoding process, Monte-Carlo simulations of binary and non-binary BTCs are carried out on Gaussian channels. The results show that the algorithm can improve the error performance up to 1.5 dB relative to the conventional Chase-Pyndiah decoder, while the increase in complexity due to the encoding is minor since it is a low-cost process compared to that of algebraic decoding. Compared to the other encoder-based decoding algorithms in the literature, the proposed algorithm has the advantage that there is no requirement to recompute the generator of parity-check matrix by using Gaussian elimination operations, thus a lower computational complexity

Robust Detection of Binary CPMs With Unknown Modulation Index

Our work addresses the single-input single-output interference channel. The goal is to show that although interference alignment is suboptimal in the finite power region, it is able to achieve a significant overall throughput. We investigate the interference alignment scheme proposed by Choi et al. (IEEE Commun. Lett. 13(11): 847-849, 2009), which achieves a higher multiplexing gain at any given signal dimension than the scheme proposed by Cadambe and Jafar (IEEE Trans. Inform. Theory 54(8), 2008). Then, we try to modify the IA design in order to achieve enhanced sum-rate performance in the practical signal-to-noise ratio (SNR) region. Firstly, we introduce a way to optimize the precoding subspaces at all transmitters, exploiting the fact that channel matrices in the interference model of a single-input single-output channel are diagonal. Secondly, we propose to optimize jointly the set of precoder bases within their associated precoding subspaces. To this end, we combine each precoder with a new combination precoder, and this latter seeks the optimal basis that maximizes the network sum rate. We also introduce an improved closed-form interference alignment scheme that performs close to the other proposed schemes.

On the use of Reed-Solomon codes in Space-Time Coding

IEEE802.16e standard proposes a full-rate space-time block code (STBC) achieving the optimum compromise between diversity and multiplexing gains (scheme C). When applied on modulated and FEC encoded data, under the constraint of practical feasibility, we prove the necessity for an iterative turbo-like receiver to outperform the spatial multiplexing structure (scheme B). Exploiting the particular definition of the code, we derive a reduced-complexity minimum mean square error (MMSE) turbo-equalizer and simulations show its efficiency.

A Computationally Efficient Discrete Bit-Loading Algorithm for OFDM Systems Subject to Spectral-Compatibility Limits

We consider soft-output detection of a binary continuous phase modulation (CPM) generated through a low-cost transmitter, thus characterized by a significant modulation index uncertainty, and sent over a channel affected by phase noise. The proposed detector is designed by adopting a simplified representation of a binary CPM signal with the principal component of its Laurent decomposition and is obtained by using the framework based on factor graphs and the sum-product algorithm. It does not require an explicit estimation of the modulation index nor of the channel phase and is very robust to large uncertainties of the nominal value of the modulation index. Being soft-output in nature, this detector can be employed for iterative detection/decoding of practical coded schemes based on a serial concatenation, possibly through a pseudo-random interleaver, of an outer encoder and a CPM modulation format.