In order to effectively improve the transmission rate of Visible Light Communication (VLC) system and reduce the Bit Error Rate (BER) of the communication system, a multilevel Protograph Low-density Parity-check Codes (PLDPC) and iterative decoding design scheme is proposed.

First, the multilevel PLDPC code and modulation constellation structure in the VLC system based on Color Shift Keying (CSK) are thoroughly investigated, and a multilevel PLDPC-CSK transmission scheme is designed. Secondly, based on the perceived color constraints, the method of transmitting consecutive symbol sequences is introduced, and the CSK mapping scheme that minimizes the number of symbol sequences at the minimum Euclidean distance is proposed. Finally, a multi-level iterative soft decoding scheme is designed based on the multi-level PLDPC-CSK transmission system.

The simulation results show that at the data rates of R=2 and 3 bits/symbol, the multilevel PLDPC-CSK design scheme for symbol sequences proposed in this paper has a performance gain of about 1.8 and 4.5 dB, respectively, compared with the standard and other same-rate CSK constellation structures.

In summary, the BER performance of the design scheme of the paper is significantly better than that of the comparison scheme, which improves the reliability of data transmission and optimizes the system performance of VLC.