Optimization of Protograph-Based LDPC Coded BICM-ID for the Poisson PPM Channel

Protograph-based LDPC coded bit-interleaved coded modulation (BICM) schemes are able to achieve near Shannon-limit performance over the additive white Gaussian noise (AWGN) channel. However, the performance of protograph-based BICM and BICM with iterative decoding (BICM-ID) schemes over the Poisson pulse-position modulation (PPM) channel has not been adequately studied. In this work, we investigate and optimize the performance of protograph-based BICM-ID schemes for the Poisson PPM channel. We propose a modified protograph extrinsic information transfer (PEXIT) algorithm and construct an optimized protograph code for the BICM-ID schemes. Threshold analysis and simulation results demonstrate that, for the case of BICM-ID, our proposed code is superior to existing protograph codes, achieving a threshold within a gap of 0.6 dB to the capacity.