Time-Domain Hybrid Coded QAM Mitigating the Nonlinearity in Underwater VLC Systems.

We proposed a time-domain coded probabilistic shaping (TDHCQ) method to replace traditional time-domain hybrid QAM (TDHQ) in underwater VLC systems. Similar to TDHQ, it introduces shaping gain to approach the Shannon limit and enables a 16QAM system to operate at flexible communication rates without modifying the hardware. Simultaneously it enhances the system performance under strong amplitude nonlinearity by degenerating QAM constellation in non-equidistance PSK ones. These characteristics help the proposed coding scheme outperform TDHQ in the simulated underwater channel, expanding the operating distance by 22 % and increasing the quality factor by at most 0.32dB.