Nonlinearity mitigation in visible light communication

Abstract

A light emitting diode (LED) acts as a transmitter in visible light communication (VLC) system. However, the nonlinear characteristics of LED limits the performance of the VLC system by degrading the quality of transmitted signal. In recent years, several forms of predistorters have been proposed to mitigate the effects of LED nonlinearity, however none of them have been able to approach the performance of a linear VLC system. In this paper, we propose an adaptive-learning-architecture (ALA) based predistortion (PD) technique to estimate and compensate for LED nonlinearities in a VLC system. A DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) signal is considered. The performance with and without PD is analysed assuming optical line-of-sight (LOS) channel. It is shown that degradation due to LED nonlinearity can be compensated by using ALA-based PD, and the overall PD-LED system is able to approach near-linear performance. Further, the proposed PD architecture is also able to track the variations in LED nonlinearity and compensate them. Simulation results based on error vector magnitude (EVM), symbol error rate (SER), amplitude distortion (AM/AM) curves and constellation plots validate the performance of our proposed technique.