Adaptive symbol-by-symbol decision feedback threshold detection receiver to suppress oceanic turbulence scintillation effect

Abstract

In this paper, an adaptive symbol-by-symbol decision feedback (DFB) threshold detection receiver is proposed that can suppress the scintillation effect of oceanic turbulence in underwater wireless optical communication (UWOC) system. The DFB receiver has a simple structure and can estimate the instantaneous channel state information (CSI) through the previously detected signal after adding pilot-symbols to the transmission data header. It thereby adaptively adjusts the decision threshold of the UWOC system receiver. The DFB receiver is independent of perfect CSI (PCSI). The channel model and transmitted signal power information are not essential for it. Moreover, the channel bandwidth can accommodate the inserted pilot-symbols. Using the gamma–gamma oceanic turbulence model, the performance of the DFB receiver under intensity fluctuation scintillation index σI2=0.15 and σI2=1.60 with different signal-to-noise ratios (SNRs) γ and different pilot-symbol lengths L was simulated. The results showed that the performance of the proposed DFB receiver was highly similar to the performance of the ideal receiver with PCSI known in advance. When σI2=1.60, γ=33dB, L=10, the bit error rate performance of the decision threshold TDFB of the DFB receiver was the same as that of the decision threshold TPCSI of the PCSI receiver, and the SNR gain loss was 0 dB. Furthermore, a wavelet denoising method was designed to improve the DFB receiver performance. When the sampling frequency of the DFB receiver was 25 MHz, σI2=1.60, γ=24dB, L=10, the proposed wavelet denoising preprocessing could obtain a SNR gain of 2.1 dB. These findings suggest that the proposed DFB receiver can promote the development of real-time applications of UWOC system.