Performance of belief propagation coded modulation with iterative decoding

We consider bit-interleaved coded modulation with iterative decoding for bandwidth-efficient transmission over Rayleigh fading channel. A serially concatenated iterative scheme (BPCM-ID) combining low-density parity-check codes (LDPC) with multilevel modulation is proposed. Differing from other serially concatenated iterative decoding schemes, the whole iterative process of BPCM-ID is divided into outer iteration and inner iteration to avoid too much error feedback to the demapper which may cause severe degradation of decoding performance. It helps to improve the robustness of the system. Another advantage, in contrast to using convolutional codes or turbo codes, is its low complexity while maintaining high BER performance because the check equations are used to terminate the both iterations. We also study the different mapping constellations for 16-QAM. Simulations show that BPCM-ID can achieve not only large coded gains but also diversity with robust convergence performance and low complexity.