Doppler Shift Estimation Based Channel Estimation for Orthogonal Time Frequency Space System

Yixiao Li, Sen Wang, Jing Jin, Wei Xiang, Hang Long

Abstract: Orthogonal time frequency space (OTFS) is a multi-carrier technique where a time-varying channel can be converted into a time-invariant channel in the delay-Doppler (DD) domain through a two-dimensional transformation. In practical wireless systems, due to the non-biorthogonal waveforms, the inter-carrier interference (ICI) will bring up phase shifts related to Doppler shifts, so that the channel in the DD domain is no longer invariant. Moreover, the limited frame durations will lead to channel dispersion, which makes it more difficult to estimate Doppler shifts. However, existing channel estimation schemes for OTFS are unable to accurately estimate the Doppler shifts. In this paper, we propose a novel channel estimation scheme. Firstly, we estimate Doppler shifts by linear fitting based on the channel dispersion in the DD domain. Then we calculate the power of dispersion paths as combining coefficients to obtain channel fading. Simulation results show that the proposed scheme can significantly reduce the normalized mean square error compared with conventional schemes, especially if Doppler shifts are large.