Research And Design Of Underwater Acoustic Communication System Based On Fountain Codes

Because of the complexity and variety of underwater acoustic channels,underwater acoustic communication has the characteristics of small available bandwidth,large transmission delay,serious noise interference and serious selectivity in both time and frequency domains.Transmission errors caused by transmitting information in underwater acoustic channels are unavoidable,therefore we require a good performance error control scheme to improve the quality of underwater acoustic communications.ARQ is not feasible due to the long propagation delay in underwater acoustic communication,and FEC is a more feasible channel error correction scheme.Fountain code is a new technology of low density and low SER channel coding scheme,and the sender does not need to know the channel state,because it can automatically achieve link rate matching.The coding and decoding algorithm have linear complexity and significant error correction.Fountain code has drawn wide attention of scholars at home and abroad.Considering that OFDM can overcome the frequency-selective fading,so it is the focus of underwater acoustic communication.Therefore,fountain code is applied to underwater acoustic communication system in this paper.In this paper,we analyze the physical characteristics of the underwater acoustic channel and modulation techniques,which provide the theoretical basis for the underwater acoustic simulation.Then we introduce the coding and decoding theory of the three fountain codes in detail,and briefly introduce the basic principles,and analyze the performance of OFDM-LDPC code,OFDM-LT code and OFDM-Raptor code in the underwater acoustic simulation model.The simulation results show that the fountain code is feasible as channel coding in underwater acoustic communication.Although its SER is slightly inferior to LDPC code,fountain code can use error-rate-free characteristics to automatically adjust bitrate and ensures reliable data transmission in low SNR.At the end of the paper,a hardware system that can be used for underwater acoustic communication is constructed and tested.The experimental results show that fountain code can ensure the reliability of underwater acoustic system.