Efficient design of sum product decoding in log domain for LDPC codes in wireless network

Abstract

A coding and modulation technique is studied where the coded bits of an irregular low-density parity-check (LDPC)code are passed directly to a modulator .At the receiver, the variable nodes of the LDPC decoder graph are connected to detector nodes, and iterative decoding is accomplished by viewing the variable and detector nodes as one decoder. The code is optimized by performing a curve fitting on extrinsic information transfer charts. Low Density Parity Check Codes (LDPC) gives groundbreaking performance which is known to approach Shannon‟s limits for sufficiently large block length. Historically and recently, LDPC have been known to give superior performance than concatenated coding. In this paper we propose a very simple but powerful method for the Sum Product decoding of LDPC codes. A simple, yet effective decoding algorithm is proposed for low-densitya parity-check (LDPC) codes, which significantly simplifies the check node update computation of the optimal sum-product algorithm. It achieves essentially optimal performance by applying scaling in the decoder‟s extrinsic information. If no such scaling is applied, then the proposed algorithm has small performance degradation. Our method improves the performance of the existing log-domain sum product coding. This is done by introduction of a difference to sum ratio factor, in the check to bit node updating process. In this paper we compare the two methods and show that our proposed algorithm is better than the existing one. Our proposed algorithm gives us better signal to noise ratio for a reasonable complexity. Simulation results demonstrate that the proposed algorithms are effective in imparting a better performance in terms of a lower bit error rate (BER) at medium to high signal to noise ratio (SNR) when compared to the traditional sum product algorithm while adding fair amount of complexity