Research On The Key Technology Of FRFT-OFDM System In Time Varying Channel

In the wireless mobile communication system,due to the Orthogonal Frequency Division Multiplexing(OFDM)system can effectively reduce the intersymbol interference caused by multipath.and it has a higher spectrum efficiency.therefore,it's very suitable for high-speed data transmission.However,the traditional OFDM systems,when the receiver and transmitter have relative motion,the orthogonality of the OFDM system is vulnerable to damage,resulting in a severe inter carrier interference,and bring down the system performance seriously.To solve this problem,this article based on the study of OFDM system and Fractional Fourier Transform(FRFT),then for the Fractional Fourier Transform of the key technology of OFDM(FRFT-OFDM)systems were studied.such as the cyclic prefix,the selection of the optimal order time and the channel estimation and equalization technology.This article main research contents as follows:1.The basic definition of Fractional Fourier Transform and properties are studied,focus on the sampling theorem and the discrete fractional Fourier algorithm of chirp periodic concept implied.2.The OFDM system and FRFT-OFDM system were analyzed.After analyzing the impact of FFT-OFDM system model and time-varying channel environment,then the FRFT-OFDM system is introduced.The structure,model of FRFT-OFDM system is analyzed.and the process of transmitting the signal through the FRFT-O FDM system is deduced.3.In the FRFT-OFDM system,the cyclic prefix is added and estimation of channel impu lse response is derived.Add the cyclic prefix based on discrete Fractional Fourier Transform of a periodic chirp.For the FRFT-OFDM systems in the case of the presence of doppler shift,by using pilot and linear interpolation method to estimate the channel impulse response,and through comparing with the OFDM system.4.In the FRFT-OFDM system,the optimal selection of order and equivalent is derived.For the FRFT-OFDM system optimal order selection,according to the equivalent channel impulse response information,select the Fractional Fourier Transform optimal order.In the Fourier transform domain,by using the minimum mean squared error criterion for equilibrium system,and through comparing with the OFDM system simulation.Simulation results show that the FRFT-OFDM system has better anti-interference ability than the OFDM system.