Study On Hfm Spread Spectrum In Under Water Acoustic Channel

With the gradual deepening of human exploration of the oceans,people's demand for reliable underwater communication is increasingly urgent.Acoustic wave is the most suitable carrier for underwater long-distance information transmission.Therefore,more and more researchers have begun to do research on underwater acoustic communication.However,the underwater acoustic channel has a narrow bandwidth,multipath and Doppler effect,and is one of the most difficult channels.Spread spectrum communication has good anti-jamming and anti-multipath capabilities and is widely used in wireless communications.Spread-spectrum communications can also perform well in severely time-varying and fading underwater channels.The traditional underwater acoustic spread spectrum communication methods have relatively low utilization ratios and are increasingly unable to meet the needs of underwater communication.Based on the previous research,this paper has conducted a certain research on underwater acoustic hyperbolic frequency modulated spread spectrum communication.Its main work is as follows:1.The physical characteristics of the underwater acoustic channel are analyzed,and a broadband multi-scale multi-lag underwater acoustic channel model is established.Some traditional underwater acoustic spread spectrum communication methods are introduced,the S2 C spread spectrum communication scheme is emphasized,and the shortcomings of existing spread spectrum communication schemes are analyzed.2.This paper analyzed and compared the characteristics of two kinds of FM signal LFM signals and HFM signals commonly used in underwater acoustic spread spectrum communication.A new HFM spread spectrum modulation scheme is proposed based on the multi-band transmission and sub-band selection activation strategy.The simulation analysis of the proposed scheme from the perspective of the number of subbands and the spread spectrum period.And we compared the proposed shceme with other existing underwater acoustic spread spectrum communication schemes.The proposed has better performance under the same frequency band utilization ratio.performance.3.The underwater acoustic multi-sequence spread spectrum communication is studied,and a cyclic shift-based underwater acoustic multi-sequence spread spectrum communication method is introduced.Based on the multi-sequence spread spectrum communication three further expansion schemes are proposed.By using quasi-orthogonal sequences for spreading modulation in adjacent cycles,the effect of the channel delay is reduced.The resulting interference between adjacent spreading symbols guarantees better bit error rate performance even when the maximum channel delay exceeds the spreading period.Through simulation analysis,the effectiveness of the scheme was verified.