The Study Of The Key Technologies For Underwater Acoustic Communication Based On MIMO-OFDM

Strong multi-path interferences?high noise background in the marine environment and rapid channel structure varying make underwater acoustic channel the most difficult wireless communication channel.Besides,the limited bandwidth resources limit the capacity of the underwater acoustic channel,it is hardly to enhance the channel's capacity by increasing the transmitting power.Multi-input multi-output(MIMO)technology can improve the capacity of the channels significantly and essentially without extra energy consumption.Therefore,Orthogonal frequency division multiplexing(OFDM)which has high spectrum efficiency and good performance in anti-multipath and impulse noise combined with MIMO technology becomes one of the research priorities and hotspots in underwater acoustic communication.In this thesis,key technologies and applications of MIMO-OFDM are researched mainly for the neritic acoustic communication.The works are done as follows:1.Diversity in MIMO-OFDM underwater acoustic communication.Three kinds of diversity combining methods used in receive diversity are studied.And the application of time space code in shallow sea acoustic communication is also analyzed.Through the comparison of simulation and experiment results,the principles of selecting diversity methods are also given.2.MIMO-OFDM Channels estimation and compensation.Comparison of the different kinds of channel estimation and compensation techniques is given,the way of choosing compensation methods are also pointed out.The performance are compared with different pilot pattern?different guard intervals?and different interpolation methods are also analyzed.To overcome the disadvantage of error propagation,two improved decision feedback channel estimation algorithm technology are proposed,and experiment results performed with numerical simulation and tank-trial data are provided,demonstrating that the proposed algorithm can effectively reduce the occupancy of pilots,abate the burst noise effect,offer confined error propagation and significantly increase the quality of the system.3.MIMO-OFDM PAPR(Peak to Average Power Ratio)reduction.Comparisons of the different types of PAPR reduction methods are provide.To overcome the disadvantage of side information transmission,an improved selected mapping algorithm taking advantage of neritic channel's sparse character is proposed.Four different algorithms are listed,Experiment results performed with numerical simulation and tank are also provided,demonstrating that the proposed algorithm can differentiate between scrambling patterns without performance reduction,abate the burst noise effect,and significantly increase the quality of the system.