Research On Time Reversal Mirror Spread Spectrum Underwater Acoustic Communication

Underwater acoustical web communication technology has become an impending task as mankind's pace of ocean development accelerating and underwater sensor net, surveillance system as well as prewarning web turn to be more and more urgent.However, with the characteristics of time-varying, space-varing, strong multipath interference, narrow available frequency band and high environment noise, underwater acoustical channel appears to be extremely severe, which slows down the development of underwater acoustical communication. Since spread spectrum communication is featured with strong anti-multipath, anti-interference, secret-keeping and communication web composing ability, spread spectrum communication can not be replaced by any other communication themes in underwater acoustical channel.The performance of several phase modulating approaches in Spread Spectrum (SS) UWA communication are comprehensively compared in this paper. The characteristics of low synchronization accuracy, strong anti-doppler ability and high reliability render SS communication based on difference coherent demodulation to be applied in high speed UWA communication. The low SS communication speed can be improved by M-ary and parallel combined spread spectrum approach. The high reliability of M-ary difference spread spectrum in complex UWA channel is testified by the experiment, as well as the inferior anti-multipath ability of parallel combined spread spectrum approach. The integration of M-ary spread spectrum technology and Pattern time delay coding theme can multiple communication speed rate.Time reversal mirror (TRM) is of great pragmatics since it will match the acoustic channel automatically without any priori knowledge and requires little channel estimation accuracy. In multi-user communication, the weak correlation between different communication knots determined by time-varying and space-varying characteristics of UWA channel is utilized to suppress the interference of non-expect-users. Synchronized by Gold series with Higher order after difference coding and channel estimated with carrier removing, higher requirement of equilibrium of Rake receriver can be met.The spread spectrum algorithm and simulation is achieved in this paper based on TMS320DM6446 platform in CCS environment. The high reliability of spread spectrum in UWA and strong interference-proof ability in multi-user communication of time reversal mirror are fully demonstrated by point-to-point and multi-user communication pool trial and lake experiment.Time reversal mirror (TRM) is takes advantage of the heterogeneity of the medium to match the acoustic channel automatically without any transcendental knowledge.