A novel optimized constellation mapping scheme of the 16QAM for the BICM-ID in optical communication systems

Considering the limited performance of the traditional Gray mapping at medium-to-high signal noise ratio (SNR) region, a novel constellation mapping scheme of 16 quadrature amplitude modulation (QAM) is proposed by redistributing bit position in order to optimize performance at medium-to-high SNR region for Bit-interleaved coded modulation with iterative decoding (BICM-ID) system. The novel mapping scheme can raise the unequal degree of the protection. And then the experiments based on the criterion of the mutual information analysis are performed. The channel capacity in BICM-ID system is comparatively analyzed with several previous constellation mapping schemes, the simulation results show that the channel capacity of the novel mapping scheme is 1.58 bit/channel-use more than that of the Gray mapping scheme at medium-to-high SNR region. Furthermore, combined with the low-density parity-check (LDPC) code, the novel mapping scheme with the assistance of the extrinsic information transfer (EXIT) charts in optical communication systems also displays the promising performance.