Serial Adaptive Clock Recovery Technology for Photon-Counting Wireless Optical Communication

In underwater photon counting wireless optical communication (UOWC), when the output of single photon detector (SPAD) is a discrete signal with Poisson distribution, how to recover the required time slot synchronization clock more accurately becomes a key step of the receiver's subsequent demodulation. We have previously proposed a method based on deep learning and multi-channel gated clock to recover the time-slot synchronization clock. After studying the single photon pulse interval, this paper adopts the pulse interval threshold to determine the adjustable slot synchronous clock with preset initial phase. After studying the number of multi-channel gated clocks, this paper proposes a serial adaptive clock recovery technology for photon counting wireless optical communication, and designs an algorithm based on this technology to continuously increase the accuracy. On the basis of the initial phase, the phase of the adjustable clock is moved by comparing the size of the counting single photon pulse to reduce resource consumption. The phase corresponding to the maximum photon count and reaching the preset peak value is the required time slot synchronization clock. The experimental results show that based on pulse-position modulation, when the slot frequency is 1MHz and there are only 7 photons in the slot, the system can realize the underwater photon counting wireless optical communication with SER of 2.2×10^-3. The performance index of 0.875 photons transmitting 1 bit data is achieved.