Algorithm Design And Simulation On Composite Sequence Based Underwater Spread Spectrum

Underwater acoustic spread spectrum is a major technique to fulfill safe,accurateunderwater acoustic communication.The design of proper spread spectrum sequence plays an important role in this technique.In this paper,spread spectrum sequence design techniques are investigated in detail to achieve a safer underwater acoustic spread spectrum communication.In this paper,a new composite spread spectrum sequence based on elementary cellular automata rule 30 and Quasi-Walsh is proposed.The auto-correlation and cross-correlation performance of this sequence is then evaluated by calculating and comparing with the correlation function of the traditional spread spectrum sequences such as m sequence,chaos sequence,PN sequence based on elementary cellular automata rule 30.In the end,an underwater direct sequence spread spectrum system is built using MATLAB to analyze the anti-jamming capability of the composite sequence.As an important assessment index for anti-jamming performance of a spread spectrum system,the bit error rates are calculated and analyzed for different spread spectrum sequences based on this system under several interference situations.The main results are as follows:(1)Compared with conventional spread spectrum sequence,the proposed sequence is more complicated and unpredictable,which means that it's a safer choice;(2)The proposed sequence has excellent performance in auto-correlation and cross-correlation;(3)The proposed sequence has good anti-Gaussian white noise interference ability and anti-Doppler shift ability;(4)Better performance on anti-single-tone interference and anti-multipath interference can be obtained in the system based on selected composite sequence compared with those based on other traditional sequences;(5)If other conditions are fixed,when the single-tone interference frequency is the same as the carrier frequency,the bit error rate of the system is the biggest.(6)In the effective working frequency range of the system,with the increase of Doppler frequency shift,the bit error rate of the system increases;(7)When the delay between multipath signal and main path signal exceeds the spreading code symbol width,the bit error rate of the system increases with the increasing multipath interference energy.