Research On Channel Estimation And Signal Detection Scheme For Orthogonal Time Frequency Space System

Orthogonal Time Frequency Space(OTFS),as an emerging two-dimensional modulation scheme,not only exloits the advantage of Code Division Multiple Access and Orthogonal Frequency Division Multiplexing,but also can be well adapted to scenarios with high Doppler.In OTFS system,channel estimation and signal detection are two crucial parts.As the foundation of signal detection,channel estimation is affected by fractional Doppler in time-varying multipath channel as well as synchronization errors at the receiver.Meanwhile,when it comes to signal detection,the reliability of detection and overall computational complexity should be taken into consideration at the same time.After theoretical analysis of OTFS system,firstly,we focus on channel estimation scheme.Then,research on signal detection scheme is carried out based on previous research on channel estimation scheme for OTFS system.The main contributions of this paper are as follows:(1)In the process of analyzing OTFS system model,two types of synchronization errors are under consideration.One of which is know as Carrier Frequency Offset and the other is known as Timing Offset.The effects of synchronization errors on baseband received signal is then thoroughly analysed.In the meantime,an equivalent system model in matrix representation is presented,which also reveals the input-output relationship of OTFS system in different transformation domains.The equivalent system model in matrix representation serves as a theoretical foundation for channel estimation scheme as well as signal detection scheme.(2)In view of the fractional Doppler interference in time-varying multipath channel,we firstly discuss delay-Doppler domain channel estimation scheme.Subsequently,a time-domain channel estimation method based on embedded pilot pulses is proposed,which can compensate for fractional Doppler resulting from time-varying multipath channel along with synchronization errors.The performance of DD domain channel estimation and time domain channel estimation are compared through simulation.It can be concluded that time-domain equivalent channel matrix obtained through time-domain channel estimation method is useful to low complexity design of signal detection scheme.(3)Based on the research of OTFS system channel estimation technology,further study on signal detection technology is carried out.We design linear receiver and nonlinear receiver respectively.Firstly,a low-complexity Linear Minimum Mean Square Error receiver is proposed,whose computational complexity is much lower than that of the classic linear receiver.Subsequently,a non-linear receiver design scheme based on maximum ratio combined detection is presented.This method uses time-domain equivalent channel matrix for signal detection.Compared with the existing non-linear receivers,it not only reduces the computational complexity,but also compensates for the effects of synchronization errors on the OTFS system.