A Simplified Soft-demapping Scheme for Probabilistic Constellation Shaping

Probabilistic constellation shaping (PCS) improves the spectral efficiency by adjusting the probability distribution of the transmitted symbols to match the channel characteristics. The conventional log-Maximum A Posteriori (log-MAP) algorithm can work for demodulation of PCS system by taking into account the probability of each constellation point. However, the conventional max-log-MAP algorithm cannot be applied directly. In this paper, a simplified soft-demapping scheme is proposed based on the max-log-MAP algorithm for the PCS system. The proposed scheme has a lower complexity than the log-MAP algorithm with acceptable performance loss. In addition, the distribution mismatch between transmitter and receiver is evaluated. The results show that four distributions are adequate for PCS-64 and PCS-256 to cover a wide range of signal-to-noise ratios.