A simplifed joint demapping and decoding for LDPC coded BICM systems

To make full use of the characteristics of LDPC decoding, Stephan ten Brink had proposed a joint iterative demapping and decoding algorithm for LDPC coded BICM systems. Based on Brink proposed algorithm, we propose a modified joint iterative scheme to further reduce the computation complex. Different from the algorithm presented by Brink, in the process of iterative demapping and decoding, the proposed method simplifies the update calculation of the LDPC parity check nodes by adopting the UMP-BP. More importantly, to compensate for the performance degradation brought by UMP-BP, LLRs optimization based on certain optimality criterion is employed for the proposed method. Numerical analysis shows that the complexity of the proposed method is less than traditional joint iterative algorithm. Simulation results also show that by LLRs optimization the proposed method achieves noticeable performance improvement compared with the BICM-ID and the joint iterative algorithm.