In photon-counting underwater optical wireless communication (UOWC), the recovery of the time slot synchronous clock is extremely important, and it is the basis of symbol synchronization and frame synchronization. We have previously proposed a time slot synchronous clock extraction method based on single photon pulse counting, but the accuracy needs to be further improved. Deep learning is very effective for feature extraction; synchronous information is already implicit in the discrete single photon pulse signal output by single photon avalanche diode (SPAD), which is used as a communication receiver. Aiming at this characteristic, a method of time slot synchronous clock recovery for photon-counting UOWC based on deep learning is proposed in this paper. Based on the establishment of the underwater channel model and SPAD receiver model, the Monte Carlo method is used to generate discrete single photon pulse sequences carrying synchronous information, which are used as training data. Two neural network models based on regression problem and classification problem are designed to predict the phase value of the time slot synchronous clock. Experimental results show that when the average number of photons per time slot is eight, photon-counting UOWC with a data rate of 1Mbps and a bit error rate (BER) of 5.35 × 10−4 can be achieved.

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As a new type of technology, the integrated system of underwater wireless optical communication and radar will play a huge role in realizing flexible and high-speed communication links between underwater vehicles, underwater monitoring points, and marine vessels. It plays an important role in wireless sensor networks, ocean exploration and detection. This paper proposes an integrated system of underwater wireless optical communication and radar, which integrates the functions of communication and radar in the same system. A time-slot synchronous clock recovery method is proposed to recover communication signals and achieve high-reliability communication; a high-precision target imaging algorithm based on the first photon is proposed to achieve high-precision radar imaging. The communication performance is verified by simulation, and the influence of radar imaging quality is verified by experiment. The results show that the system can not only achieve the function of single-photon wireless optical communication, but also achieve the highquality target imaging of single-photon level.

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