Precoding And Detection For Orthogonal Time Frequency Space Signal Under High-mobility Scenarios

With the rapid development of transportation,such as vehicles,high-speed trains,and airplanes,the demand for mobile communication services will continue to grow.One of the technically challenge of the next generation communication system is to be suitable for highmobility scenarios,while millimeter waves suffers from Doppler effect at high speed.Orthogonal Time Frequency Space(OTFS)is a novel modulation scheme with significant benefits for anti-Doppler effect since it provides a stationary channel between the transmitter and the receiver,thus the waveform of OTFS is suitable for high-mobility.This thesis fucus on the signal detection algorithm and the precoding schemes of the OTFS system.Firstly,this thesis studies the characteristics of rapidly time-varying channels and the basic schemes of OTFS modulation,and analyzes the sparsity of delay-Doppler domain channels.Based above,the bit error rate(BER)of OTFS system and orthogonal frequency division multiplexing(OFDM)system under rapid time-varying channel are simulated.It is concluded that OTFS system has great anti-Doppler performance.Secondly,an pilot-aided channel estimation method is studied and the pilot overhead is analyzed.The simulation results show that the proposed channel estimation scheme is accurate under different conditions.Thirdly,in order to reduce the complexity of the equalizer,considering the sparsity of delay-Doppler domain channels,this thesis studies the message passing(MP)detection algorithm based on the factor graph of probability model.It proposes a linear low-complexity iterative maximal ratial comining(MRC)detector for the MIMO-OTFS system,based on one used for the SISO-OTFS system.The main idea is to extract and combine the symbols in the delay-Doppler grid and maximize the signal-to-noise ratio(SNR).The simulation results shows that the presented detector has better BER performance under high SNR and lower computation complexity comparing to the MP detector.Finally,according to the reconstructed signal input-output relationship,the transmitted delay-Doppler resource blocks are extracted along the delay domain,which gives the equivalently multipath channel between transmitted vector and received vector.Considering above,this thesis studies the precoding schames for MIMO-OTFS system based on codebook and singular value decomposition(SVD),and then modifies the MRC detector.The simulation results shows that both presented precoding schemes has great BER performance,and the SVD based precoding sheme has excellent BER performance.