Design And Implementation Of Mobile Spread Spectrum Underwater Acoustic Communication Modem

Spread spectrum communication is one of the research hotspots in underwater acoustic communication.Since the underwater acoustic channel is a time-frequency dual-spread channel with limited bandwidth,improving the quality of underwater acoustic communication has always been a challenge.The underwater acoustic spread spectrum communication has strong anti-interference ability,long communication distance.It can work in a low signal-to-noise ratio environment.It can effectively reduce the problems caused by complex underwater acoustic channels.The underwater acoustic spread spectrum communication technology is used to design a set of underwater acoustic spread spectrum communication system for forwarding information between platforms in this article.Firstly this paper studies on the underwater acoustic c spread spectrum communication technology,1)We analyze the receiver algorithms of several different underwater acoustic direct spread spectrum communication systems,and conducts simulation research on its performance;2)Aiming at the Doppler phenomenon that may exist in the signal transmission and reception process,the Doppler coefficient estimation method in the DSSS system is used to estimate the Doppler frequency offset.Due to the need to realize the underwater acoustic spread spectrum communication under mobile conditions,the communication signal is susceptible to the Doppler effect,which reduces the processing gain.Therefore,it is necessary to estimate and compensate the Doppler frequency offset.Compared with the differential energy detector algorithm and the direct correlation algorithm,the improved differential energy detector algorithm can effectively suppress the interference of the carrier phase change.This feature can be used to solve the residual phase change interference.After Doppler compensation of the carrier under the condition of underwater acoustic mobile communication.Secondly,based on the theoretical research of underwater acoustic spread spectrum communication,an underwater acoustic spread spectrum communication modem was designed and realized.In order to be used on multiple platforms,this paper designs two sets of processing systems,both of which adopt the same design in acquisition system: One is a DSP-based communication processing system,with DSP as the processing core,and SPI communication bus for data acquisition with the acquisition system which can be used on unmanned submersible.Another one is a client processing system designed based on QT software,and UDP protocol and acquisition system are used for data transmission.This system can be used for ship platforms.Afterwards,on the basis of the hardware system,the software decoding program of the underwater acoustic spread spectrum communicator was realized.According to the demand of communication forwarding,the digital-to-analog conversion circuit required by the transmitting circuit is designed.And the software design of the digital-to-analog conversion circuit is realized.Finally,a number of tests and verifications were carried out for the underwater acoustic spread spectrum communication modem: Through the laboratory electric joint debugging test,the simulation conditioning circuit parameter index was tested.And the correctness of the communication signal generation and reception processing was verified;The pool test and tests in the sea area have verified that the various indicators of the communication modem designed in the paper can meet the design requirements.It is stable and reliable,and it has a low bit error rate.Then,it can be used with a certain relative speed.