Optimal Transmission of VLC System in the Presence of LED Nonlinearity and APD Module Saturation

We address the optimal transmission of LED-based visible light communication (VLC) system using direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) modulation and avalanche photodiode (APD) receiver. The peak-to-average-power ratio (PAPR) characteristic of O-OFDM signal is studied, which reveals that the careful setting of transmission parameters is necessary for O-OFDM signal with high PAPR to avoid the severe nonlinear distortion. We further experimentally investigate the nonlinear distortion caused by the LED clipping and APD module saturation, and define a modified term called signal-to-noise and distortion ratio (SNDR) to measure the influence of nonlinear distortion on system performance. The derived explicit expression of SNDR shows that the performance depends on the transmission parameters of both direct current bias Vdc and peak-to-peak voltage Vpp. Meanwhile the sequential quadratic programming algorithm is applied to maximize SNDR and obtain the optimal transmission parameters. The optimal transmission of the nonlinear LED-VLC system is achieved via both simulations and experiments.