Research On Iterative Equalization Based On M-ary Spread Spectrum Code For UAC

Sound is the only information carrier that can travel long distances in the ocean.Therefore,underwater acoustic communication technology is significance to the development of marine resources,environmental investigations,and underwater wireless sensor networks.At present,improving the speed and robustness of underwater acoustic communication is mainly limited by the limited channel bandwidth and the varying underwater acoustic channel.Redundant information can be added to improve the system's error correction ability,but it will reduce the frequency band utilization;and a robust semi-blind channel update technique needs to be studied to update the channel impulse response with only a small number of pilot signals.the use of equalization technology can effectively improve the anti-interference ability of the underwater acoustic system.In addition,block coding can significantly reduce the complexity of equalization technology.However,if the coding length is too long,it is susceptible to channel changes and reduces the equalization performance.In addition,a robust semi-blind channel update technique needs to be studied to update the channel impulse response with only a small number of pilot signals.In view of the above problems,the thesis researches on a robust M-ary spread spectrum technology and low complexity iterative equalization technology,and a robust iterative equalization technique based on M-ary spread spectrum code for underwater acoustic communication is proposed.The main research content and innovative work of the paper are:(1)A robust underwater acoustic system based on M-ary spread spectrum coding is proposed.The system combines CQPSK and CMFSK based on CCK codes with LMS channel estimation technology and MMSE linear channel equalization technology to improve the UAC system's performance.This system can be applied to different channel environments.(2)A low-complexity soft information calculation method based on CCK codes is proposed.It is used in CCK codes to calculate soft information in channel update and iterative equalization technology.The calculation complexity is low and it is easy to implement in hardware.And this paper proposes a soft information channel update technology based on CCK code,which requires only a small number of pilot signals.It saves frequency band utilization and improves the robustness of the system.(3)A low-complexity iterative equalization system suitable for fast time-varying underwater acoustic environment is proposed.The system uses the CMSFK communication method,iterative equalization,and combined with the soft information channel update based on CCK codes.It can improve the anti-interference ability of the system.The performance comparison with linear equalization system and DFE equalization system verifies the performance of the system proposed in this paper is optimal.