Research On Pre-equalization Technology Of OFDM System In Multipath Fading Channel

In time division duplex OFDM communication system,pre-equalization technology is a transmitter equalization technology which simplifies the design of receiver.It can effectively solve the contradiction between complex signal processing and simple design structure of user terminal in mobile communication.However,in multipath fading channels,when the maximum delay of transmission channel is longer than the length of cyclic prefix,the traditional pre-equalized OFDM system has a large equalization error,and the received signal still has inter-symbol interference.Because too long CP will seriously reduce the bandwidth utilization of pre-equalization system,it is particularly important to find a short CP pre-equalization scheme in wireless communication with scarce spectrum resources.Based on the idea of channel shortening,the pre-equalization technology of OFDM system in multipath fading channels is studied from the perspective of time-domain equalization technology of OFDM.The whole research work is carried out in the following two parts:1.Time domain equalization algorithm for OFDM system is studied.Firstly,the process and equalization performance of the zero elimination algorithm are analyzed in depth,and an adaptive maximum output SINR zero elimination algorithm is proposed for the noise gain introduced by the zero elimination algorithm.Secondly,in order to simplify the implementation of time-domain linear filtering of the zero elimination algorithm,a linear filtering algorithm based on polynomial zero elimination is proposed,and the feasibility of the algorithm is proved.A sub-optimal solution of tap coefficients is given.Finally,the equalization performance of the two algorithms is simulated and analyzed.The research shows that the optimized zero elimination algorithm can further improve the performance of the zero elimination algorithm,and the time-domain tap implementation method can achieve ideal equalization performance when the number of taps is low.2.Based on the design principle of OFDM pre-equalization system,a joint pre-equalization algorithm in time-frequency domain for OFDM is proposed.Firstly,the solution process of subcarrier pre-equalization factor and normalization factor is analyzed and deduced;secondly,aiming at the equalization error of zero-point elimination algorithm under different tap variables,the relationship between the tap variables of linear filter and BER is analyzed and deduced;finally,the PAPR performance and BER performance of this algorithm and traditional algorithm under the condition of insufficient CP are compared by simulation.The research shows that the proposed algorithm will not affect the PAPR performance of the system,and can effectively improve the BER performance of the OFDM pre-equalization system in multipath channels.At last,the thesis summarizes the work completed and the research results achieved in the subject,analyses the imperfections of the design scheme and the future improvement direction,and looks forward to the future research direction of the subject.