Joint Channel Estimation Iterative Equalization Algorithm For Doubly Selective Fading Channels

In wireless communication system,due to the influence of multipath and doppler frequency shift,the wireless channel will exhibit frequency selective fading in the frequency domain and time selective fading in the time domain.This kind of wireless channel is called doubly selective fading channel.Doppler frequency shift and multipath fading seriously affect the receiving effect of the signal,resulting in a significant decrease in the reliability and transmission efficiency of the communication system.Channel equalization can effectively eliminate or reduce Inter Symbol Interference(ISI)caused by multipath delay.It is one of the important means to improve the transmission performance of doubly selective fading channels.For the channel equalization problem of doubly selective fading channels,the specific research work of this thesis is as follows:Gaussian Message Passing(GMP)algorithm based on Nonlinear Data Directed Estimation(NDDE)preprocessing is designed.The joint iteration of equalizer and decoder is realized with low computational complexity.In order to improve the accuracy of channel estimation,a channel estimation strategy based on decoding feedback and channel interpolation is proposed.The decoding feedback strategy makes use of the error correction ability of the channel decoder.By expanding the length of the pilot sequence,it can effectively mitigate the impact of time-varying channel.Simulation results show that,compared with GMP algorithm,the convergence speed of GMP joint iterative algorithm based on NDDE preprocessing is faster,and the proposed two channel estimation strategies further improve the accuracy of channel estimation.The linear detector in the Orthogonal Approximate Message Passing(OAMP)algorithm needs to rely on accurate channel prior information.Due to the existence of channel estimation error,the OAMP based equalizer will be subject to various types of interference.In order to realize information matching between channel estimator and equalizer,OAMP iterative equalization algorithm based on error correction is designed.The algorithm uses the analysis results of channel estimation error to correct the input noise variance of OAMP algorithm and further improve the accuracy of data detection at the receiver.Simulation results show that compared with OAMP algorithm,OAMP iterative equalization algorithm based on error correction has better bit error rate performance.