Experimental Research On Underwater Wireless Optical Communication System Based On Multi-Pixel Photon Counter And Orthogonal Frequency Division Multiplexing

As human are facing the challenge of resources shortage on land,people have started turning their attention to the ocean.The ocean is the treasure house of the mankind and has occupied the core position of national strategies.By deploying underwater sensors and submersibles,and employing underwater communication technology as a guarantee for the interaction,people can acquire real-time marine information.Considering the large time delay,the low transmission speed of underwater acoustic communication and the large attenuation of radio frequency communication in the water,underwater wireless optical communication(UWOC)is gradually attracting widespread attention due to its advantages of high bandwidth,high speed and miniaturization.When light travels in seawater,it suffers from attenuation due to absorption and scattering,and thus the performance of communication system is deteriorated.The underwater wireless optical communication system has two important performance indicators,namely transmission rate and transmission distance.At present,underwater wireless optical communication is developing toward longer distance and higher speed.In this thesis,Monte Carlo method based on parrallel computing is utilized to simulate the propagation process of light in seawater channel,and various system parameters are comprehensively investigated.The underwater channel is studied by taking accout of various parameters on the light source,water type and detector.The simulation will guide and optimize our design of high-speed and long-distance underwater wireless optical communication system.In this thesis,an underwater wireless optical communication system with parallel transmission is studied.The avalanche photon diode(APD)with a high bandwidth and space division multiplexing(SDM)technology are emploied.Combined with orthogonal frequency division multiplexing(OFDM)and high-order quadrature amplitude modulation(QAM),the system achieves a net data rate of 4.12 Gbps.The system's transmission rate have reached a high level of several Gbps,but the transmission range is as short as a few meters,and the system requires strict link alignment.Therefore,we further propose to use a multi-pixel photon counter(MPPC)as a new type of high-sensitvity optical detector.Based on the high sensitivity and the array characteristics of the MPPC,the transmission distance of underwater wireless optical communication can be extended.A set of underwater wireless optical communication system based on MPPC and OFDM technology is constructed and its feasibility is theoretically analyzed and experimentally verificated.The system breaks through the limitation of the MPPC's bandwidth(approximately 4 MHz)by employing QAM-OFDM modulation,and successfully achieves a 21-m/312.03-Mbps underwater transmission.The paper theoratically analyzes and experimentally verifys the possible sources that induce the MPPC noise.