The Joint Demodulation and Decoding for BICM-ID System with BEC Approximation and Optimized Bit Mapping

To improve the performance further for the bit- interleaved coded modulation with iterative decoding (BICM-ID) system, a modified extrinsic information transfer (EXIT) model is presented, in which the decoding and the demodulation are modeled as two iterative processing units. By using the binary erasure channel (BEC) approximation for the a priori AWGN channel, the analytical formulation of mutual information for sub-channels in M-QAM are obtained. Besides, the grid depth-first searching algorithm (GDFSA) is modified for designing the optimal bit mapping distribution with minimum convergence rate. Using the DVB-S2 rate-0.5 64800-bit low-density parity-check (LDPC) code as demonstration, the simulations show that the BER performances achieve 0.225/0.650dB gains at 10^-5 for 16-QAM/32-QAM under AWGN channel, compared to the consecutive bit mapping.