Spectral and Energy Efficient Pilot-Assisted PAPR Reduction Technique for Underwater Wireless Optical Communication Systems

Pilot assisted (PA) technique is a promising method for reducing the peak-to-average power ratio (PAPR) in direct-current optical orthogonal frequency division multiplexing (DCO-OFDM). However, this technique still suffers from the deterioration of spectral efficiency (SE) due to the transmitted side information (SI), high required computational complexity (CC) and performance degradation in harsh environments like underwater wireless optical communications (UWOC) systems. To address these issues, this article presents a novel and efficient PA technique called efficient PA-DCO-OFDM (E-PA-DCO-OFDM). The proposed scheme overcomes the SE deterioration and high CC by transmitting only the index of the candidate pilot that provides the best PAPR reduction instead of transmitting the entire pilot data physically, and also decomposing the inverse fast Fourier transforms (IFFT) into two low-complexity matrices to avoid performing several IFFTs. Moreover, in challenging UWOC environments, the modulated data related to the index of the candidate pilot can be transmitted multiple times to guarantee the correct detection at the receiving end and enhance the overall performance without affecting the achieved SE. The proposed scheme is evaluated through simulation and experimental tests performed over a 2-meter UWOC system. For instant, E-PA-DCO-OFDM reduces the CC by up to 52.4% and significantly improves the SE compared to the conventional PA-DCO-OFDM with identical performance in terms of BER and PAPR. The proposed scheme's outperformance is also evaluated against existing benchmarks in terms of bit error rate (BER), achieved SE, PAPR, energy efficiency (EE), and CC.