Research On LDPC Code And Polar Concatenated Code For Underwater Acoustic Communication

Hydroacoustic communication is one of the keys to the development of China’s marine information technology.The underwater environment is complex and variable,with narrow bandwidth,serious multipath effect,Doppler expansion,noise interference and other characteristics,which is a great challenge to the development of the reliability and effectiveness of hydroacoustic communication.Channel coding technology has an important impact on the reliability and effectiveness of hydroacoustic communication.Based on this,this thesis investigates the coding scheme of polarized code and LDPC code in hydroacoustic channel,and proposes the coding scheme of polarized code and LDPC code cascade in hydroacoustic communication system to explore their performance and advantages.This thesis focuses on the application of polarization code and LDPC code cascade in hydroacoustic communication system,and the main contents of the study are as follows:1)By analyzing the characteristics of the hydroacoustic channel and its underwater environment,two hydroacoustic channel models,the time-varying hydroacoustic channel model and the time-invariant hydroacoustic channel model,are established,and the two channel models are simulated using the BELLHOP tool.（2）In this thesis,the system models of polarization code and LDPC code in hydroacoustic channel are constructed,and the coding and decoding algorithms of polarization code and LDPC code are simulated and analyzed.For polarized codes,SC decoding algorithm,SCL decoding algorithm and BP decoding algorithm are studied,and different code lengths and multipath numbers of polarized codes are simulated under time-varying channels.For LDPC codes,the LLR BP decoding algorithm of LDPC codes is studied and simulated in terms of different code lengths and number of iterations for LDPC codes in time-varying and time-invariant channels.The results show that the simulation performance of the time-invariant channel is better than that of the time-varying channel under the same conditions,and the BER performance of LDPC codes improves to a certain extent with the increase of the number of iterations and code lengths.（3）In this paper,we propose the cascading of polarization codes and LDPC codes in a hydroacoustic OFDM system model,and simulate the cascading codes in time-varying channels and time-invariant channels.The performance analysis of the cascaded codes in terms of code length and multipath number is carried out in both channel models.The results show that the cascaded codes are better than the uncascaded LDPC codes and polarization codes in the hydroacoustic channel,and the cascaded codes can achieve the BER of10^-4～10^-3required for hydroacoustic communication in the hydroacoustic channel,so the cascaded codes of LDPC codes and polarization codes can be used as the candidate code words for the hydroacoustic channel.（4）For the case that the cascade code has consecutive errors in the hydroacoustic channel,this thesis proposes to add an interleaver to the cascade code.The experimental results show that the performance of cascade codes with interleaver is better than that without interleaver in hydroacoustic communication,and the BER performance of cascade codes with group interleaver is better than that with random interleaver.