Research On Polar Codes And PPM Coding Technology In Laser-Generated Acoustic Underwater Communication

With the increasing awareness of territorial protection in various countries and the increasing demand for the development of marine resources,marine communication technology is required to be gradually improved.Laser-induced acoustic communication as a new type of cross-air water medium communication has been widely concerned.It combines laser wireless communication with underwater acoustic communication,and can give full play to the advantages of aerial platform andunderwater platform.The laser-induced sound technology directly realizes communication with underwater targets through remote control of blue-green lasers,such as airborne,spaceborne,and shipborne which has high flexibility and concealment.Because the signal transmission in laser-acoustic communication mode depends on air optical channel and underwater acoustic channel,on the one hand,the optical signal will be affected by atmospheric turbulence effect and atmospheric attenuation effect,on the other hand,the acoustic signal will be affected by underwater multipath effect and Doppler effect,which will cause distortion and frequency shift.The above reasons reduce the reliability and stability of the entire system communication and limit the transmission rate.Therefore,it is very valuable to discuss the channel coding and modulation technology suitable for laser-induced acoustic communication for the development and application of new marine communication technologies.Considering that polar codes had the advantages of reaching Shannon limit,good performance in short and medium codes,low coding complexity and so on,as well as pulse position modulation(PPM)had obvious advantages such as high anti-interference ability and low time slot error rate,by combining the two technologies,an application scheme of joint coding based on polar codes and PPM modulation in laser-induced acoustic communication was proposes.Firstly,three mechanisms of laser-induced sound and the characteristics of laser-induced sound transmission were discussed in the paper.On the basis of analyzing the channel polarization phenomenon,this paper introduced the coding method and decoding algorithm of polar codes in detail,and the joint coding structure and simulation model were given.Secondly,the effects of polar codes length,code rate and decoding list width on system performance were simulated and analyzed.Finally,the FPGA hardware and software implementation of joint coding and decoding scheme was discussed,and a set of experimental system of laser-induced acoustic communication based on Nd:YAG solid-state laser and hydrophone was designed,and the transmission performance was tested by the upper computer.The simulation results showed that,compared with the traditional PPM modulation system without polarization code,the coding gain of 1?2d B can be obtained by using polar codes and PPM joint coding under the same bit error rate.And the transmission performance test of the experimental system verified the error correction performance and real-time performance of the joint coding scheme system.It showed that system had better transmission performance when the joint coding scheme was adopted,which also fully demonstrated the technical advantages of joint coding.The paper can provide a certain reference for the development of marine communication technology.