Research On Anti-interference Technology Of Frequency Domain Equalization System In Time-selective Channel

In recent years,mobile communication technology and multimedia business got great progress and had caused wide public concern.Mobile intelligent terminal and hardware technology had penetrated into all aspects of people's daily life,so the application of high speed data transmission rate demand in the complex environment is also increasing.Under the condition of bad data transmission environments,there exists a multipath time delay,Doppler frequency shift and many other adverse factors.The intersymbol interference(ISI)and the intercarrier interference(ICI)will cause the serious deterioration on bit error rate(BER)of the system.This paper studies the key problems of frequency domain equalization system under time-varying channel.Firstly,the signal-to-noise ratio(SNR)and Doppler shift significantly affect the vehicular communication.Therefore,this paper investigates biases of an iterative Doppler shift estimator by addressing the approximation of autocorrelation function(ACF),and then we explicitly see estimation errors at high vehicle speeds.Accordingly,a refined process by exploiting the interpolation operation is proposed to reduce the estimation bias at high moving speeds.Subsequently,a SNR estimator is presented by utilizing the bias variation at different iterations,where the estimates of the Doppler shift in the first and the final rounds of iterations are combined together to construct a bias ratio,and then this ratio is employed to derive a SNR estimator.Sufficient computer simulations show that our proposed algorithm achieves accurate estimates for both the SNR and Doppler shift in wide ranges of working SNR and mobile speed.A shortening impulse response filter(SIRF)based on maximum compression SNR(MSSNR)criterion is studied under the time-varying multipath channel.In view of the traditional SIRF designed in quasi static channel,this article analysis mismatch problem in the time-varying channel.At the meanwhile,this article compares the SIRF performance,designed by channel coefficients corresponding to different time,about compression loss ratio and compression SNR.According to the research,there is a middle time in the time-varying channel.The SIRF constructed at this time will obviously improve the BER.Finally,this article based on frequency domain equalization system,proposes a MSSNR-SIRF designed based on multipath time-varying channel,in order to compete the ISI due to the time-varying channel and the shortage of Cyclic Prefix(Cyclic Prefix,CP).Computer simulation results show that the proposed improved SIRF design also has good performance in the frequency domain equalization system.