Annie Picart

Performance of block turbo coded 16-QAM and 64-QAM modulations

We present the results of our investigation concerning the performance of block turbo codes associated with high spectral efficiency QAM modulations. By using a pragmatic approach, simulation results show that all the block turbo coded QAM modulations we have tested are at 2.9/spl plusmn/0.2 dB of their Shannons limit. The block turbo coded QAM modulations also outperform TCM schemes by at least 1 dB at a BER (bit error rate) of 10/sup -5/. Concerning convolutional turbo coded QAM modulations, the block turbo coded QAM modulations exhibit slightly better performance for spectral efficiencies greater than 4 bits/s/Hz.

Turbo-detection: a new approach to combat channel frequency selectivity

In this paper, a receiver is proposed to combat intersymbol interference (ISI) generated over a frequency selective channel. The receiver is based on a symbol detector and a channel decoder separated by a deinterleaver. Through an iterative detecting-decoding process, using turbo-codes principle, the so-called turbo-detector manages to overcome frequency selectivity, especially over a Gaussian channel. Simulation results show the turbo-detector efficiency over both Gaussian and GSM channels.

Adapted iterative decoding of product codes

This paper deals with iterative decoding of product codes for high spectral efficiency transmissions. A solution is proposed to adapt the decoding algorithm to the characteristics of the encoder, the modulation and the number of decoding steps. A coding gain of up to 2 dB is then obtained for short codes. For long codes, the number of decoding steps to achieve a specified bit error rate (BER) can be reduced by 1 or 2, which is interesting in terms of decoding latency and power consumption.

Performance of turbo-decoded product codes used in multilevel coding

A powerful coding scheme based on multilevel coding and using a product code on the first partitioning level is proposed. The multistage decoder takes advantage of the iterative decoding of the product code to achieve a high coding gain. This coding scheme is compared to the one using the product code in a pragmatic approach with a Gray mapping. Results show that in the range of high bit error rates (BER greater than 10/sup -7/, a product code having a high code rate (R>0.8) associated with a Gray mapping is the best solution. For high transmission rate applications, in which the required BER is lower than 10/sup -7/, multilevel coding with a turbo-decoded product code is the recommended solution.

Potential applications of low complexity non-binary high code rate block turbo codes

High code rate block turbo codes (BTC) using Bose-Chaudhuri-Hocquenghem (BCH) codes have already demonstrated near Shannon performances for quadrature phase-shift keying (QPSK) over additive white Gaussian noise (AWGN) channel. We show here that very low complexity Reed-Solomon (RS) BTC can also achieve reliable transmission at less than 1 dB from Shannon limit with the same transmission conditions. Performances of this RS-BTC over binary symmetric channel (BSC) and binary erasure channel (BEC) are also investigated in this paper. Potential applications for this study are high speed optical transmission and data storage.

TurboWm: enhanced robustness in image watermarking using turbo codes

In this paper, we investigate the improvement achieved by turbo coding for robustness in still image watermarking. We use an error correcting scheme based on the concatenation of a BCH product code and a repetition code. The product code is iteratively decoded using the Chase-Pyndiah algorithm (turbo decoded). For this study, we set the watermarking distortion to around 38 dB and we consider different payloads that can correspond to different applications and services. We compare different coding strategies (i.e. repetition code only and a concatenation of product and repetition codes) in terms of robustness to different photometric attacks, in particular additive noise or lossy compression. Typically, for a payload of 121 bits, the robustness gain for a given message error probability is significant: first error appears at a JPEG quality factor of about 25% with the new coding scheme instead of about 50% when using only repetition codes.

Small block Reed-Solomon BTC for reliable transmission

The performance of nonbinary BTC with QPSK modulation over AWGN channel is studied. The most widely used nonbinary code is Reed-Solomon (RS) code, which has the maximum distance separable (MDS) property. A single error-correcting RS component code to construct RS product codes is proposed. The so constructed RS product codes can achieve reliable transmission from Shannon limit using QPSK modulation over AWGN channel with block size almost three times smaller than that of BCH-BTC of similar code rate. The turbo decoder decodes the resulting code.