Protograph-Based EXIT Analysis and Optimization of LDPC Coded DCO-OFDM in VLC Systems

The direct current (DC)-biased optical orthogonal frequency division multiplexing (DCO-OFDM) with low-density parity-check coding is a popular scheme for visible light communication systems. Under the optical power constraint for dimming control, the protograph-based extrinsic information transfer (PEXIT) analysis is utilized to optimize the DC bias and signal power jointly by searching the lowest optical threshold. To reduce the search space, an approximate method is proposed to simplify the PEXIT procedure of the optimal solution. Both the optimal configuration and simplified method are in good agreement with the simulation results.