Research On Underwater High Speed Laser Communication System Based On FPGA

Coming into the middle of the 21 st century,land resources are increasingly scarce,while Marine resources account for more than 70% of the earth’s resources.Therefore,many coastal countries in the world focus on the development of underwater technology,among which underwater wireless communication technology plays a crucial role in the exploration of Marine resources.At present,three main underwater wireless communication technologies are underwater acoustic communication,underwater electromagnetic communication and underwater optical communication.Compared with the other two methods,underwater optical communication has its unique advantages.First of all,underwater optical communication has the natural advantages of large bandwidth,low delay and good security,and the communication speed can reach the order of Gbps.Secondly,the underwater optical communication equipment has the advantages of low cost and small size.The main work is as follows:In this paper,an underwater laser communication system based on OOK modulation is designed and implemented.The FPGA chip of Xilinx platform is used to complete the modulation algorithm of transmitter and demodulation algorithm of receiver.In view of the weak anti-interference capability of OOK signal,the slide-window filter was designed to de-noise the sampled signal before demodulation,and a smoother signal to be demodulated was obtained.After entering the demodulation stage,in order to obtain the frame head of the signal to be demodulated,a peak detection module is designed before the decision,which ensures that the system demodulation can obtain the frame head position information within 5 sampling periods.At the same time,in order to make the system still have excellent demodulation performance in different underwater environments,the weight calculation of the adaptive threshold and the fixed threshold is used to obtain the joint threshold before the judgment.Simulation results show that the bit error rate of the joint threshold judgment is lower than that of the other two threshold judgment methods.Based on the above design,the underwater laser communication system is built in this paper,which includes transmitter,underwater channel and receiver.With the corresponding drive circuit,light source detector and FPGA communication board,the transmitter end and the receiver end are encapsulated,while the underwater channel chooses laboratory pool and outdoor pool as two underwater environments.Finally,the communication test was carried out on the constructed system.In different water quality environments,the communication rate of at least 108)and 25(7 was finally achieved,which verified the feasibility of the designed OOK underwater high-speed real-time laser communication system.