Mitigating Nonlinearity Characteristics of Gray-Coding Square 8QAM in Underwater VLC system

Visible light communication(VLC) has become a state-of-art technology in wireless communication which take the advantages of unlimited bandwidth, green source with no pollution, combination communication with illumination. However, when we need to transmit for a long distance or at a high data rate, the underwater visible light communication (UVLC) system will suffer from severe nonlinearity. In this paper, we proposed a gray-coding square (GCS) 8QAM based underwater VLC system which performs better than normal rectangular QAM and circular (7,1) 8QAM. Different from circular (7,1) which own the maximum minimum Euclidean distance, the GCS 8QAM own the thoroughly gray-coding of every constellation point. The GCS-8QAM can achieve a higher data rate of 1.62Gb/s at 240mA bias current and 1.4Vpp than circular(7,1) and rectangle, and more operation range at bigger bias current and V
_pp
, which prove that GCS-8QAM is more suitable for nonlinear situations and higher data rate transmission in UVLC system.