Experimental Demonstration of 55-m / 2-Gbps Underwater Wireless Optical Communication Using SiPM Diversity Reception and Nonlinear Decision-Feedback Equalizer

Abstract

Underwater wireless optical communication (UWOC) is considered as an enabling technology with a mass of potential applications. The silicon photomultiplier (SiPM) exhibits a bright prospect for UWOC thanks to the traits of low-light detection capability, low-voltage operation, and superior operability. However, the performance of the SiPM-based UWOC system is severely degraded by the dead-time caused nonlinear response. In this paper, to mitigate the dead-time induced nonlinear distortion and explore the achievable capacity of the newly developed SiPM, we propose and experimentally demonstrate a 55-m / 2-Gbps UWOC system by virtue of SiPM diversity reception and nonlinear decision-feedback equalizer (NDFE). The performance of NDFE is superior to that of the conventional decision-feedback equalizer (DFE), and NDFE with a pruning factor of 5 declares similar performance as that without pruning strategy, while the number of the nonlinear equalizer can be reduced by ∼ 31.8%. Significant performance improvement is also obtained by the proposed scheme under different turbidity waters. The measured data rate is pushed from 1 Gbps to 2 Gbps with a receiver sensitivity as low as −41.96 dBm, which to the best of our knowledge is the largest data rate ever achieved using the off-the-shelf SiPM among the reported UWOC works. In accordance with the receiver sensitivity and the model of optical propagation in the water channel, the maximum attainable distance / data rate is predicted to be 147 m / 1 Gbps and 128 m / 2 Gbps with the proposed scheme. The research results are promising for long-reach and high-speed UWOC.INDEX TERMS Underwater wireless optical communication (UWOC), visible laser diode (LD), silicon photomultiplier (SiPM), diversity reception, nonlinear decision-feedback equalizer (NDFE).

Shannon–Hartley Channel Capacity for Underwater Wireless Optical Communications

“…Figure shows a plot of the channel capacity C max (eq ) in comparison to experimental results drawn from the literature. − These are for underwater optical communication channels as a function of distance, z . While there have been tremendous strides in the past few years in realizing high data rate underwater optical channels, the experimental conditions vary widely across data encoding schemes, optical powers, wavelengths, seawater types, distances, and transmit-receive beam configurations.…”

“…Solid lines are the maximum channel capacity C max (eq ) for various types of seawater. Circles show experimental data harvested from the literature. − The acoustic communications upper limit (dashed line) is an extrapolation of the upper bounds for Deep Sea State 0 developed from ref and shown for comparison.…”

“…Recently, there has been an upsurge in interest in underwater optical wireless communications. ,,− Here “wireless” is interpreted to mean there is no waveguiding of the light and that the communication channel is the water medium itself. Furthermore, in practical applications, the water medium is seawater.…”

“…Although there have been significant advances in demonstrating underwater wireless communications using various data encoding schemes over several distances, − there seems to be no agreed approach to understanding the informational capacity for this mode of communication. In fact, to date, experimental results show little or no alignment with the existing limits on informational capacity.…”

Short-range medium-rate fleet communications using SPAD arrays

“…Another recent development in the field of underwater communication is the use of single-photon avalanche diode (SPAD) [8][9][10] and silicon photomultiplier (SiPM) [11][12][13][14] receivers. Being sensitive to the arrival of single photons, SPAD and SiPM have exceptional sensitivity and noise performance compared to standard avalanche photodiodes (APD) and are instrumental to achieving new range records in underwater optical communications.…”