Wave-like Decoding of Tail-biting Spatially Coupled LDPC Codes Through Iterative Demapping

Spatially Coupled Low-Density Parity-Check (SCLDPC) codes show a universal behavior regardless of the specific channel front-end used, be it an equalizer, a QAM demapper or the like. It was shown that the required termination of SC-LDPC codes can be substituted by tail-biting codes with optimized mappings such that the rate-loss vanishes. However, the effect of threshold saturation must be triggered by additional knowledge, which, in turn, leads again to an effective rate-loss. In this paper, we show how this rate-loss can be mitigated by iterative demapping in combination with higher-order modulation, to further decrease the gap to capacity. We investigate the effect and potential of different labelings for such a set-up using new per-bit EXIT curves, and exemplify the method for a 16-QAM system, e.g., using set partitioning and other labelings.