Research On Underwater Acoustic OFDM Channel Equalization Algorithm Based On MAP Criterion

Due to the characteristics of low channel capacity,strong multipath effect,strong underwater environmental noise and frequency and time selective fading,the performance of underwater acoustic communication system is affected.As an underwater high-speed transmission scheme,orthogonal frequency division multiplexing(OFDM)has the characteristics of anti frequency selective fading and high frequency band utilization.Aiming at the problem of channel estimation in underwater acoustic OFDM system,this paper designs a channel equalization method based on maximum a posteriori(map)criterion,and carries out simulation and experimental verification.The characteristics of underwater acoustic channel are studied,including channel noise,multipath effect and Doppler effect.Combined with underwater acoustic channel,an underwater OFDM communication system is designed,and the cyclic prefix,modulation mode and pilot setting of the system are studied.Aiming at the problem of underwater acoustic channel estimation,least square(LS)channel estimation,discrete Fourier transform(DFT)channel estimation,least mean square(LMS)adaptive equalization technology and threshold improved DFT channel estimation method are studied.In order to track the time-varying characteristics of the channel,a variable step frequency domain equalization algorithm based on the map criterion is designed.Combined with the variable step channel equalization algorithm,the algorithm can effectively improve the anti channel distortion performance and system stability of the communication system.Aiming at the problem of signal distortion caused by the Doppler effect,an underwater acoustic OFDM frequency offset estimation method based on the detection domain is studied,which effectively solves the inter-carrier interference(ICI)caused by Doppler,and carries out simulation and experimental verification.