Research On OFDM Underwater Acoustic Communication System Based On Virtual Time Reversal Mirror

Underwater acoustic communication is the core means of underwater information transmission,which plays an important role in supporting military activities and marine environment monitoring.However,the stability of underwater acoustic communication is challenged due to the serious impact of multipath effect and Doppler effect.Orthogonal frequency division multiplexing(OFDM)technology has strong anti multipath fading ability,and virtual time reversal mirror(VTRM)technology has good channel focusing performance.It is very suitable for underwater acoustic communication.Therefore,in order to improve the system communication performance,this thesis combines OFDM technology with VTRM technology and presents the contents as below.Firstly,this thesis explains the research background and application value of underwater acoustic communication.It analyses the research status of underwater acoustic communication and time reversal mirror technology.In addition,it introduces the main characteristics of underwater acoustic channel and the principle of three kinds of time reversal mirror in detail,which provides a theoretical basis for the following related research.Secondly,aiming at the influence of the side lobe of the main peak of the time reversal channel,this thesis adds the cyclic suffix to the OFDM symbol.Its purpose is to improve the channel equalization effect of VTRM technology in OFDM underwater acoustic communication system.Additionally,it estimates the channel by using the fractional Fourier transform algorithm and the orthogonal matching pursuit algorithm.The simulation results show that the combination of the technologies can improve the performance of the system effectively.Thirdly,In OFDM underwater acoustic communication system based on VTRM,M-ary differential amplitude phase shift keying technology is added for modulation and demodulation.Besides,this thesis adopts two-step method to estimate and compensate the wideband Doppler shift and narrowband Doppler shift.Finally,the reliability of the system is verified by simulation experiments.Finally,to solve the problem of high PAPR in OFDM underwater acoustic communication system,this thesis discusses selective mapping method,partial transmission sequence method and clipping method.It proposes an algorithm called DLPS-CF,which combines the double-layer optimized partial transmission sequence method with clipping filtering method.Simulation results show that DLPS-CF algorithm has better PAPR suppression effect than three traditional algorithms.