Square geometrical shaping 128QAM based time domain hybrid modulation in visible light communication system

We proposed two kinds of visible light communication(VLC) systems which respectively based on 64QAM/square geometrical shaping(SGS) 128QAM time domain hybrid modulation scheme (SGSHY) and 64QAM/128QAM time domain hybrid modulation scheme (REGHY). These two systems can operate around specific forward error correction (FEC) threshold and maximize the achievable information rate (AIR) of the system. The principles of SGSHY and REGHY are proposed in detail, which has very low computation complexity compared with probabilistic shaping. The SGSHY outperforms REGHY at high peak to peak voltage (Vpp). Experimental results show that at high Vpp like 1.4 V, which means the system is suffering from high nonlinear distortion, the AIR of SGSHY outperforms that of REGHY by 0.12Gb/s at the 2×10–2 FEC threshold. The AIR of the REGHY is at most 0.36Gb/s higher than that of 64QAM at 0.8V Vpp and 7% FEC threshold, while the (achievable information rate) AIR of SGSHY is at most 0.40Gb/s higher than that of 64QAM at 1.4 V Vpp and 20% FEC threshold.