| In recent years,people have attached great importance to the development of marine resources,and underwater wireless optical communication technology has been comprehensively developed.With the deep exploration of marine resources,communication scenarios have become more complex.In many scenarios,the communication terminals not only need to meet the requirements of real-time communication,but also need to achieve ranging and navigation.The integration of underwater wireless optical communication and ranging can realize the dual functions of communication and ranging through a single hardware platform,greatly reducing the system volume and cost,which is an important research direction in the field of underwater detection.Although some researchers have proposed the integration technology of space wireless optical communication and ranging,the detectors they use mostly work in analog mode,and the low sensitivity of such detectors makes it difficult to directly apply the system to the underwater weak link environment.The underwater single photon communication system built by our team uses ultra-high sensitivity single photon detector to receive optical signals,which can realize underwater photon counting communication with Symbol Error Rate（SER）of1.8×10-3.Based on the existing underwater single photon communication system,this paper conducts research on the integration of underwater photon counting communication and ranging,and the main work contents and achievements are as follows:（1）A long-term and high-precision ranging scheme based on Field Programmable Gate Array（FPGA）and TDC-GPX2 was achieved,and a TDC-GPX2time measurement module and FPGA control circuit were designed.The FPGA writes configuration data into the TDC-GPX2 through the Serial Peripheral Interface（SPI）,and when the ranging decision bit is received,it synchronously controls the TDC-GPX2 to perform photon flight fine time measurement and reads the measurement result through the SPI bus.By designing a test scheme,the influence of time interval and the difference in delay line length on the measurement performance of the TDC-GPX2 module was tested.The test results show that the time measurement accuracy of the TDC-GPX2 module was better than 0.0137 ns.（2）A time-sharing scheme of underwater photon counting communication and ranging was proposed and achieved.When ranging is required,the sending end controls the laser to aim at the target and emit the optical pulse,measure the time interval between emission and reception of optical pulses,and then control the laser to aim at the receiving end and send the time data to the receiving end;When communication is required,the laser only needs to be aimed at the receiving end for normal communication.In order to verify the feasibility of this scheme,an underwater photon counting communication and ranging time-sharing system was built.The experimental results showed that when ranging,the ranging accuracy was better than 0.846 cm;when communicating,the communication SER was 7.4×10-3 at a time slot frequency of 1 MHz.（3）An integrated scheme of underwater photon counting communication and ranging was proposed and achieved.To implement this scheme,a special data frame was designed.The communication data and the locally randomly generated ranging sequence were loaded onto the same data frame,and the photon flight time was obtained by comparing the ranging sequence in the echo,so as to realize the integration of communication and ranging.In order to verify the feasibility of this scheme,an integrated underwater photon counting communication and ranging system was built.The experimental results show that when the time slot frequency was 1 MHz and the number of photons in the time slot were only 7,the communication SER of the system is 3.2×10-3,and the ranging accuracy reaches centimeter level. |
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