Study On Channel Estimation And Equalization Technology For UFMC System

As a candidate waveform of 5G,UFMC can reduce the out-of-band radiation by sub-band filtering to reduce the interference caused by time-frequency offset and achieve relaxed synchronization,it may more efficiently support internet of things(IoT)and machine type communication(MTC).Compared with the OFDM system,the UFMC system without cyclic prefix(CP)provides a “soft protection” against inter-symbol interference(ISI)through the slow-down produced by filtering in the time domain under multipath channel,but the “soft protection” effect on ISI is not significant when the multipath delay is large,and inter-carrier interference(ICI)is also generated due to the disruption of the orthogonality.As an important part of signal processing in UFMC systems,channel estimation and equalization technology will also be affected by interference.However,existing UFMC channel estimation and equalization algorithms do not take into account ISI/ICI.This thesis addresses interference issues under multipath channels,and some improvements have been made on the channel estimation and equalization algorithms for OFDM systems with insufficient CP.This thesis first analyzes the interference of UFMC receivers under multipath channels,and simulates the tolerance on multipath by comparing it with OFDM system.In the channel estimation,ISI is suppressed by feedback equalization according to the system interference expression under multipath channel.The ICI term is reduced by self-elimination algorithm based on analyzing the gradual property of ICI coefficients generated by subcarriers and redesign the pilot coefficient by considering the factors of the filter in the UFMC system.Finally,the estimated value is obtained according to the minimum mean square error criterion(MMSE).Simulation results demonstrate that the improved algorithm applied in UFMC can suppress the interference well and improve the accuracy of estimation.As in the OFDM system,the effect of the channel can be eliminated in the UFMC system with simple one-tap equalization.However,in the scenario where the multipath delay is extended and the channel fading seriously,the single-tap equalization is not enough.This thesis first analyzes the complexity of the equalization algorithm commonly used,and proposes a low-complexity frequency domain equalization algorithm based on existing parallel-interference-cancellation(PIC)algorithm.After zero-forcing equalization,this algorithm approximately reconstructs the inter-carrier and inter-symbol interference according to the residual interference expression about the data outside reliable range,and finally performs iterative interference cancellation for each carrier in parallel.The simulation results show that the complexity of the proposed algorithm is lower and the bit error rate can be reduced to a certain extent under the multipath channel.