Research On Key Technologies Of RAKE Receiver For Mobile Underwater Acoustic Spread Spectrum Communication

There are many difficulties in underwater long-distance communication,such as the Doppler effect caused by the movement of communication nodes,the multipath effect caused by reflections on the seabed,and the low signal-to-noise ratio of the received signal.It is necessary to study a method that can be overcome in an underwater complex channel environment.These problems are to ensure the reliable transmission of underwater acoustic communication technology.Spread spectrum technology has the advantages of strong anti-multipath capability,low signal-to-noise ratio communication,and difficult interception.It is an important technology for underwater long-distance,high-secure communication.The research of Doppler estimation compensation,multipath channel estimation,RAKE receiver and other technologies can guarantee the stable operation of mobile underwater acoustic spread spectrum communication.Aiming at the underwater communication environment and communication system,the thesis first established an underwater acoustic channel model to study the influence of the Doppler and multipath effects of the underwater acoustic communication signal on the transmission signal in the underwater acoustic channel,and then studied and analyzed the spread spectrum communication system.Including spread spectrum system structure,spread spectrum code acquisition,carrier synchronization,analysis of spread spectrum system low signal-to-noise ratio transmission and anti-multipath ability.Aiming at the Doppler effect caused by the movement of the underwater acoustic communication terminal,the Doppler estimation based on the matched filter method and the fuzzy function method are studied,and the estimation accuracy of the two algorithms under different conditions is analyzed and discussed.Under the premise of a certain amount of calculation,a joint Doppler estimation algorithm based on matched filter method and ambiguity function method is designed,which is suitable for the communication of fast-moving underwater acoustic targets and has high estimation accuracy.Aiming at the important underwater acoustic channel time delay estimation problem in the RAKE receiver system,the channel estimation algorithm based on compressed sensing(CS)is studied and compared with the commonly used LS channel estimation algorithm in the single carrier system.This channel estimation method The signal-to-noise ratio is required to be high.Aiming at the communication characteristics of spread spectrum system under low signal-to-noise ratio,the adaptive channel delay estimation algorithm based on wavelet transform is further studied,and compared with the traditional channel delay estimation method.Aiming at the anti-multipath capability of the spread spectrum system,the RAKE receiver technology under the spread spectrum system is studied,and the basic principle of the RAKE receiver is analyzed.The performance comparison of the RAKE receiver system under different path selection methods,including the ideal RAKE(ARAKE),Selective RAKE(SRAKE)and partial RAKE(PRAKE)systems,as well as the effects of different combining methods and different tap numbers on the performance of RAKE receivers;for the situation of different underwater multi-path attenuation,an adaptive partial hybrid RAKE is designed The receiver scheme,which can adaptively select the best receiver,has better performance in complex underwater environments than traditional receiver types without increasing the complexity of the design.