OTFS Signal Design And Channel Estimation Research

With the evolution of the sixth generation(6G)communication system,high-speed mobile scene communication has become one of the main research interests.In the high-speed mobile scenario,the orthogonality of the orthogonal frequency division multiplexing(OFDM)technology used in the fifth generation(5G)communication system will suffer serious interference in the time-varying and frequency-selective channel.Orthogonal time frequency space(OTFS)technology is a new modulation technology.In the OTFS technology,the signal generated in the delay-Doppler domain,and transformed into the time-frequency domain via the inverse symplectic finite Fourier transform(ISFFT)to solve the challenge of OFDM technology.In this thesis,we propose an OTFS signal design and a channel estimation algorithm.Firstly,the signal design and channel estimation in OTFS multiple-accessing scenario are proposed.The multiple-accessing problem in the OTFS system is modeled,and the performance of the existing single-impulse pilot signal scheme is analyzed.Based on the different characteristics of the delay-Doppler domain and the timefrequency domain,the uplink and downlink multiple-accessing signals are designed and the basic performance of the signal design scheme are evaluated.The simulation results show that the proposed channel estimation method has obvious advantages over the existing least square method,and the multiple access scheme meets the design requirements of no user interference and low complexity reception,and the performance is close to the ideal estimation.Then,we propose the adaptive orthogonal basis scheme.We analyze the Doppler dispersion problem of the existing OTFS technology,and propose an adaptive orthogonal basis modulation scheme to improve the Doppler dispersion problem.This scheme uses feedback parameters to design one or more sets of adaptive reference signal sequences.By comparing bit error rate(BER)and block error rate(BLER)performance curves under ideal channel estimation,the feasibility of the designed adaptive orthogonal basis scheme is proved.By comparing BER/BLER performance curves under three kinds of Doppler errors,it is considered that BER/BLER performance loss is within an acceptable range,so the designed adaptive orthogonal basis scheme has certain ability to cope with Doppler errors.Finally,we propose the OTFS signal design for the scenario of joint communication and radar sensing.In this scenario,the ambiguity function analysis of comparison scheme linear frequency modulation signal is carried out.Next,the ambiguity function of OTFS time-domain signal is derived,and the feasibility of OTFS signal for target detection and parameter estimation is analyzed.Compare and analyze the existing reference signal ambiguity function,analyze the target detection performance and design the frame structure that is conducive to radar perception.The simulation results show that OTFS radar has the basic ability of radar sensing signal.Compared with the two-dimensional matched filter estimation under the linear frequency modulation signal,the OTFS signal drops faster in the direction of Doppler domain,so that the two-dimensional matched filter estimation performance has advantages.