Improved Decoding for LDPC Coded Modulation Systems Using Averaged Log-Likelihood Ratios

In this paper, an improved iterative decoding algorithm based on averaged Log-Likelihood Ratio (LLR) is proposed for LDPC coded BICM systems. The extrinsic information delivered by every BP iteration is averaged and the averaged LLR values are used as a prior LLR fed back to the input of demodulator for the next iteration. This method can alleviate the LLR oscillation of certain variable nodes during BP iterations and thus make the extrinsic output of decoder is more credible. Simulation results show that, compared with the two conventional iterative decoding algorithms, this improved algorithm achieves noticeable error performance improvement with only modest increase in computation complexity.