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IEEE Vehicular Technology Conference

An improved quasi-cyclic low-density parity-check code for memory channels

M. Jayabalan, Hyuck Moo Kwon

Published Apr 12, 2005• 5 citations
Publisher

Abstract

This paper presents an improved construction of circulant sub-matrices based quasi-cyclic low density parity check codes (QC-LDPC) under fading channels. The proposed construction yields a performance gain of about 2 to 5 dB at a 10/sup -4/ bit error rate (BER). This paper also proposes a decoding method to reduce the implementation complexity in the belief propagation algorithm. Furthermore, this paper studies the performance of circulant sub-matrices based QC-LDPC codes at higher rates under AWGN and fading channels.

DOI
10.1109/vetecf.2004.1400515

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In this paper, we construct nonbinary quasi-cyclic low-density parity-check (QC-LDPC) codes whose parity check matrices consist of an array of square sub-matrices which are either zero matrices or circulant permutation matrices. We propose a novel method to design the shift offset values of the circulant permutation sub-matrices, so that the code length can vary while maintaining a large girth. Extensive Monte Carlo simulations demonstrate that the obtained codes of a wide range of rates (from 1/2 to 8/9) with length from 1000 to 10000 bits have very good performance over both AWGN and Rayleigh fading channels. Furthermore, the proposed method is extended to design multiple nonbinary QC-LDPC codes simultaneously where each individual code can achieve large girth with variable lengths. The proposed codes are appealing to practical adaptive systems where the block length and code rate need to be adaptively adjusted depending on traffic characteristics and channel conditions.