Joint channel estimation with an enhanced companding PAPR reduction transform for ACO-OFDM system

Optical orthogonal frequency division multiplexing (OFDM) is one of the prominent schemes of visible light communications. It offers many advantages, such as high data rate, robust against fading, and better security. However, the asymmetrically clipped optical (ACO)-OFDM suffers from high peak to average power ratio (PAPR) due to the non-linear characteristics of the light-emitting diodes and the power amplifiers. In this article, an enhanced exponential companding (EEC) scheme, which improves the PAPR performance of the ACO-OFDM system with an unchanged average power, is proposed. The proposed EEC scheme offers more freedom and flexibility due to the use of two companding parameters and one threshold value. Moreover, a pilot-based channel estimation (CE), which is necessary to realize the channel state information at the receiver, is proposed. Therefore, the combined EEC transform and pilot-based CE improves the efficiency of the ACO-OFDM system. Simulation results show that the proposed combined EEC transform with CE provides the enhanced PAPR and bit error rate characteristics. The proposed EEC algorithm offers better PAPR reduction of 7.5 dB and net-gain of 6.3 dB than other non-linear companding methods.