Abstract

Application of light-emitting diodes (LEDs) based visible light communication (VLC) in underwater wireless communication has become a hot topic. However, on the one hand, the performance of underwater VLC (UVLC) system is limited due to power attenuation in water medium. On the other hand, increasing the driving power will induce nonlinearity from the imperfect optoelectronic components. Particularly at high signal amplitude, nonlinearity will become the dominant bottleneck. In this paper, we focus on nonlinearity mitigation method which preprocesses signal at transmitter-side. Multi-bit delta-sigma modulation combined carrier-less amplitude and phase modulation (DSM-CAP) is proposed to obtain quantized signal with lower peak-to-average power ratio (PAPR). Furthermore, as assuming the quantization noise being additive white noise is not appropriate in nonlinearity, modulus pruned weighted look-up table (MP-WLUT) is employed to modify the signal before DSM quantization to mitigate pattern dependent nonlinear distortion. Experimental results indicate that the DSM-CAP has better nonlinearity mitigating performance than normal CAP. At the data rate of about 1.69Gbp/s, utilizing MP-WLUT pre-distorted DSM-CAP an improvement of 1.44 dB Q-factor is realized compared with normal CAP without WLUT, and the size of MP-WLUT can be reduced to 62.5% of the full-size WLUT.

Highlights

  • In recent years, with the rapid development of ocean exploration, the demand for high-speed underwater data transmission is increasing

  • At the data rate of about 1.69Gbp/s, utilizing modulus pruned weighted look-up table (MP-WLUT) pre-distorted Delta-sigma modulation (DSM)-Carrier-less amplitude and phase (CAP) an improvement of 1.44 dB Q-factor is realized compared with normal CAP without WLUT, and the size of MP-WLUT can be reduced to 62.5% of the full-size WLUT

  • For normal CAP and DSM-CAP, the weight corresponding to the lowest bit error rate (BER) decreases as average power of transmitted signal is reduced

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Summary

Introduction

With the rapid development of ocean exploration, the demand for high-speed underwater data transmission is increasing. Existing underwater wireless communication methods such as acoustic communication and radio frequency (RF) communication have their own limitations due to low bandwidth and high attenuation, respectively. It is reported that visible light has a low attenuation window at the blue-green spectra region in water, providing gigabit-per-second order of magnitude transmission speed [1]. The impact of nonlinearity becomes severe for signal with high amplitude. Signal with higher PAPR is more susceptible to nonlinear distortion, which is a non-trivial problem in UVLC system

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