Real-Time and High-Speed Underwater Photon-Counting Communication Based on SPAD and PPM Symbol Synchronization

Abstract

Photon-counting detectors can increase the range of underwater optical wireless communication (UWOC) by enhancing the detection sensitivity and have thus become an active research area in recent years. However, system performance still needs to be improved in the reported underwater photon-counting communication (UPCC) experiments. In this study, a real-time, high-speed UPCC system was designed and experimentally validated based on a single-photon avalanche diode (SPAD). A reliable symbol synchronization method based on pulse-position modulation (PPM) was developed. This method achieved slot synchronization by using a narrow-pulse-width laser and a simple matched filter and realizes frame synchronization through an improved synchronization sequence. In addition, channel errors were corrected by serially concatenated convolutionally coded PPM (SCPPM), and digital signals were processed in real time based on field-programmable gate arrays (FPGAs). Finally, desktop communication experiments were completed at a slot frequency of 25 MHz and a communication rate of 6.21 Mbps. The system exhibited a bit error rate (BER) of less than 10 -7 , a received optical power of only -84.3 dBm, and an efficiency of 1.35 photons per bit.

The research progress in underwater wireless optical communication technology

“…In 2021 [43] , Pengcheng Lab's SiPM-based receivers can support 11.6 attenuation lengths at 1Gbps. In the same year [44] , the Shanghai Institute of Technology and Physics achieved a communication sensitivity of 1.35 photos/bit using photon counting reception technology. In 2022 [45] , the Xi'an Institute of Optics and Mechanics analyzed and compared the communication performance of various intensity modulations based on photon counting communication systems.…”

50 m/187.5 Mbit/s real-time underwater wireless optical communication based on optical superimposition

“…The blue laser diode (LD), with high power, is gradually becoming the mainstream as the light source in the long-distance UWOC system [5][6][7][8][9][10] . Besides, many researchers employed high-sensitivity optical detectors such as a multi-pixel photon counter (MPPC), single-photon avalanche diode (SPAD), and photomultiplier tube (PMT) as receivers to detect weak optical signals [6][7][8][9][10][11] .…”

“…In 2021, a real-time UWOC system based on SPAD and pulseposition modulation (PPM) was conducted at a data rate of 6.21 Mbit/s when the received optical power was only −84.3 dBm [11] . However, due to the high implementation cost of real-time communication systems and the absence of detectors with high bandwidth and sensitivity, few real-time UWOC systems support a high data rate of hundreds of megabits per second with a transmission distance of dozens of meters, hindering the practical implementation of UWOC systems.…”

“…Spatial summing is effective in improving the performance, which has been widely used in the visible light communication (VLC) system to mitigate the nonlinear effect. [12] LD/APD 60 (tap water) / / 2.5 Gbit/s OOK AWG/OSC 2019 [5] LD/APD 56 (tap water) 0.0876 m −1 4.9056 3.31 Gbit/s QAM AWG/OSC 2020 [13] LD/MPPC 100 (pool water) 0.24 m −1 24 8.4 Mbit/s OOK AWG/OSC 2020 [6] LD/PMT 100 (pool water) 0.0585 m −1 5.85 200 Mbit/s OOK AWG/OSC 2021 [7] LD/PMT 150 (pool water) 0.053 m −1 8.775 500 Mbit/s PAM AWG/OSC 2021 [8] LD/PMT 200 (pool water) 0.0325 m −1 6.5 500 Mbit/s PAM AWG/OSC 2021 [9] LD/PMT 100.6 (tap water) 0.0658 m −1 6.6195 3 Gbit/s OOK AWG/OSC 2022 [10] LD/PMT 5 (turbid water) / / 10 Mbit/s PPM FPGA 2016 [14] LD/PIN 3 (artificial seawater) 0.481 m −1 1.443 50 Mbit/s QAM FPGA 2019 [15] LED/PIN 1.2 (tap water) / / 2.34 Gbit/s DMT FPGA 2020 [16] LED/APD 10 (tap water) 0.056 m −1 0.56 1 Mbit/s FSK FPGA 2020 [17] LD/APD 3.6 (tap water) / / 2.2 Gbit/s OFDM FPGA 2020 [18] LD/SPAD 2 (tap water) / / 6.21 Mbit/s PPM FPGA 2021 [11] LD/PMT 50 (pool water) 0.1307 m −1 In 2013, a VLC transmitter employing discrete power level stepping was proposed to address the nonlinearity, restricted dynamic range, and complex system designs of the conventional optical transmitters [22] . In 2017, a highly compact array of micro-LED pixels was proposed to generate a discrete optical signal, which achieved a data rate up to 200 Mbit/s [23] .…”

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.…”