Research On Channel Coding Technology For Underwater Acoustic Spread Spectrum Communication Based On Short Code

Due to the effects of multipath and Doppler,the study of underwater acoustic communication is more complex than that of wireless communication.To achieve reliable communication performance,spread spectrum communication schemes combined with error correction coding techniques are commonly used.However,the direct spread spectrum communication system has low bandwidth utilization,and classical channel coding algorithms have limited coding gain.Modern coding algorithms that can achieve larger coding gain are generally applicable to long code block data,making them difficult to fit the communication delay requirements in low rate scenarios.This paper investigates the construction of short code length Low-density Parity-check(LDPC)codes,the decoding algorithm of LDPC codes,and the performance differences of direct spread spectrum,M-ary spread spectrum,and CSK spread spectrum communication schemes.Based on this,a spread spectrum coding system combined with short code length LDPC codes is proposed,and the system performance is verified through simulations and pool experiments.To address the problem that modern coding algorithms that can achieve larger coding gain are generally applicable to long code block data,which is difficult to fit the communication delay requirements in low rate scenarios,the construction of short code length LDPC codes is investigated.This includes three 1/2 rate,short code length LDPC codes and type I EG codes based on Euclidean Geometry proposed in the Consultative Committee for Space Data Systems(CCSDS)Orange Book CCSDS 231.1-O-1.The performance of these channel coding methods is verified through theoretical simulations.The research results show that several short LDPC codes can achieve good coding gain under Gaussian channels.To address the problem of high complexity of the Sum-Product Algorithm(SPA)decoding algorithm,the improved LDPC decoding algorithm is studied,and the performances of the Log-Likelihood domain and Sum-Product Algorithm(LLR-SPA),Min-Sum Algorithm(MSA),and Normalized Min-Sum Algorithm(NMSA)are verified through theoretical simulations.The research results show that compared with SPA,LLR-SPA reduces the algorithm complexity without reducing the error performance.MSA further reduces the algorithm complexity,but the error performance simultaneously declines.NMSA achieves performance close to SPA by selecting attenuation factors,with complexity similar to MSA.To address the problem of low bandwidth utilization in direct spread spectrum communication,direct spread spectrum,M-ary spread spectrum,and CSK spread spectrum coding systems are studied.A spread spectrum communication system combined with short code length LDPC codes is proposed,and the system performance is verified through simulations and pool experiments.The research results show that both the direct spread spectrum system and the general M-ary spread spectrum system can achieve significant coding gain,and the direct spread spectrum system can achieve optimal coding gain,which is related to the soft and hard decision inputs of the decoder.