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Unsupervised time domain nonlinear post-equalization for ACO-OFDM visible light communication systems

LED nonlinearity is an important issue limiting the performance of Visible Light Communication (VLC) systems. This form of distortion is particularly problematic when the system employs Optical-OFDM because of the high Peak-to-Average Power Ratio (PAPR) of its time domain symbol. This paper proposes using ancillary statistical properties of the O-OFDM signal in order to mitigate LED nonlinearities in an unsupervised fashion. By exploring the Gaussianity of the time domain OFDM signal and the idea of distribution equalization, we propose a semi-parametric approach to blind nonlinear post-equalization for asymmetrically clipped O-OFDM (ACO-OFDM) VLC systems. In addition to not requiring training data, the equalizer is robust to different LED types and it is adaptive to time-varying nonlinearities. Simulations with a realistic LED model show that the developed tool is capable of substantially mitigating the effects of nonlinear distortion on system performance.