Iterative Decoding Of Low-density Parity-check Codes Research Articles

Construction and Iterative Decoding of LDPC Codes Over Rings for Phase-Noisy Channels

This paper presents the construction and iterative decoding of low-density parity-check (LDPC) codes for channels affected by phase noise. The LDPC code is based on integer rings and designed to converge under phase-noisy channels. We assume that phase variations are small over short blocks of adjacent symbols. A part of the constructed code is inherently built with this knowledge and hence able to withstand a phase rotation of 2π/M radians, where M is the number of phase symmetries in the signal set, that occur at different observation intervals. Another part of the code estimates the phase ambiguity present in every observation interval. The code makes use of simple blind or turbo phase estimators to provide phase estimates over every observation interval. We propose an iterative decoding schedule to apply the sum-product algorithm (SPA) on the factor graph of the code for its convergence. To illustrate the new method, we present the performance results of an LDPC code constructed over Z4 with quadrature phase shift keying (QPSK) modulated signals transmitted over a static channel, but affected by phase noise, which is modeled by the Wiener (random-walk) process. The results show that the code can withstand phase noise of 2° standard deviation per symbol with small loss.

Joint iterative decoding of LDPC codes for channels with memory and erasure noise

This paper investigates the joint iterative decoding of low-density parity-check (LDPC) codes and channels with memory. Sequences of irregular LDPC codes are presented that achieve, under joint iterative decoding, the symmetric information rate of a class of channels with memory and erasure noise. This gives proof, for the first time, that joint iterative decoding can be information rate lossless with respect to maximum-likelihood decoding. These results build on previous capacity-achieving code constructions for the binary erasure channel. A two state intersymbol-interference channel with erasure noise, known as the dicode erasure channel, is used as a concrete example throughout the paper.

Reliability-Based Iterative Decoding of LDPC Codes Using Likelihood Accumulation

In this work, we present an improvement on low complexity serial concatenation of belief propagation (BP) - order statistic decoding (OSD) algorithm for low-density parity-check (LDPC) codes. We introduce a more reliable method to reconstruct ordered information sequence in terms of the accumulated log-likelihood ratio (LLR) transitions of variable nodes. We give a general expression for both the existing BP-OSD algorithm and our proposed new method according to a structure similar to an infinite impulse response (IIR) filter. This improved algorithm achieves noticeable performance gains with only modest increase in computation complexity.

Performance of LDPC coded FMT systems over frequency selective fading channel

This paper proposes the Low Density Parity Check (LDPC) coded Filtered MultiTone (FMT) systems with high-order modulation for the high data rate reliable transmission over frequency selective fading channel. For the purpose of accomplishing soft input soft output iterative decoding of LDPC codes, a new soft decision metric generation method is proposed, which obviates the need of the noise variance estimation, for M-PSK/M-QAM-type high-order modulation over frequency selective fading channel. Computer simulation indicates that, there is no performance loss with our new metric, but the complexity of implementation is reduced, and that the LDPC codes are effective to improve the Bit Error Rate (BER) of FMT in frequency selective fading channel.