Chaos-Based Multicarrier VLC Modulator With Compensation of LED Nonlinearity

Abstract: The massive deployment of light-emitting diode (LED) lightning infrastructure has opened the opportunity to reuse it as visible light communication (VLC) to leverage the current RF spectrum crisis in indoor scenarios. One of the main problems in VLC is the limited dynamic range of LEDs and their nonlinear response, which may lead to a severe degradation in the communication, and more specifically in the bit error rate (BER). This is aggravated by the extensive usage of multicarrier multiplexing, based on optical orthogonal frequency division multiplexing (O-OFDM), characterized by a high peak-to-average power ratio. Here, we present a chaos-based coded modulation (CCM) setup specifically adapted to the LED nonlinearities. It replaces the usual modulation, while keeping the multicarrier O-OFDM structure unchanged. First, we obtain a semi-analytical bound for the bit error probability, taking into account the LED nonlinear response. The bound results particularly tight for the range of signal-to-noise ratio of interest. Then, we propose a method to design the modulator based on optimization techniques. The objective function is the semi-analytical bound, and the optimization is applied to a parameterization of the CCM conjugation function. This appropriately shapes the chaotic waveform and leads to BER improvements that outperform classical counterparts under ideal predistortion.