On the Clipping Noise in an ACO-OFDM Optical Wireless Communication System

In this paper, the clipping noise in an asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) wireless communication system is derived semi-analytically. Clipping noise in ACO-OFDM is introduced either because of insufficient forward biasing of the emitter, or a low power sensitivity of the detector. Following the Bussgang theorem, the non-linear distortion caused by the clipping of the time domain signal attenuates the frequency domain subcarriers at the receiver and adds zero-mean Gaussian noise. The attenuation factor and the clipping noise variance are determined and verified through simulation. Finally, bit-error ratio (BER) and goodput simulations compare the performance of ACO-OFDM with a direct-current-biased optical OFDM (DCO-OFDM) system for different clipping levels and multilevel quadrature amplitude modulation (M-QAM) schemes.