Research On Anti-doppler Technology In Underwater Acoustic Communication Based On Orthogonal Multi-carrier Modulation

Orthogonal Frequency Division Multiplexing (OFDM) is an effective technologyfighting against signal distortion in a frequency selective fading channel，and it has a higherbandwidth efficiency．As the bandwidth resources of underwater acoustic channel areextremely limited，in order to improve communication speed and bandwidth efficiency，theapplication of OFDM technology，which has a higher communication speed and bandwidthefficiency，in underwater acoustic communication has practical significance．But its inherentshortcomings (eg large peak to average power ratio (PAPR)，phase noise and inter-carrierinterference (ICI)，susceptible to Doppler shift and easily influenced by time-varying channel)make the performance drops to an unacceptable degree when the underwater acoustic channelwas rapidly fading with Doppler effects and multi-path effects．Therefore seeking a new andbetter underwater acoustic communication system is important．Firstly，this article summarizes the characteristics of underwater acoustic channel andchannel modeling，and then analyzes the basic principles and key technologies of traditionalOFDM system based on Fourier transform，summed up the advantages and disadvantages ofthis system．As the orthogonal subcarriers are easily damaged，resulting in the problem ofinter-carrier interference，this article cites a new OFDM system based on fractional Fouriertransform，the system employs a set of LFM signals with overlapping spectrum instead of theoriginal sinusoidal signals as subcarriers to modulate information and use fractional Fouriertransform for modulation and demodulation method to transmit information．Besides， inorder to suppress multipath and Doppler effects in underwater acoustic channel，we also applychannel estimation and equalization，using a multiplicative filtering equalizer in fractionalFourier domain to equalize the output signal，in the OFDM system based on fractional Fouriertransform．Simulation results reveal：in underwater acoustic communication, the performanceof the new OFDM system based on fractional Fourier transform is superior to the traditionalOFDM system based on Fourier transform．...