A Two-Stage Channel Estimation Algorithm for OTFS in Fractional Doppler Channels
Xiaolin He, Pingzhi Fan, Qianli Wang
Abstract
Orthogonal time-frequency space (OTFS) modulation is a promising modulation technology, which can provide superior performance under high-mobility radio scenarios. However, fractional Doppler shift brings inter-Doppler interference (IDI), leading to performance deterioration of channel estimation. This letter proposes a two-stage algorithm for estimating the fractional Doppler channels. In the first stage, a rough position of each nonzero Doppler shift is estimated through the correlation of the basis function in the delay-Doppler (DD) domain. In the second stage, a quasi-Newton method is employed to iteratively re-estimate the fractional Doppler channel based on the prior estimation, thus resulting in significantly reduced estimation error caused by the IDI. Simulation results demonstrate that the proposed algorithm for channel estimation can achieve a much lower normalized mean square error (NMSE) than the baseline algorithms. Moreover, the achieved bit error rate (BER) is very close to that of perfect channel estimation.