An Improved Two-Stage Time Synchronization Scheme for OTFS Systems

This paper presents a time synchronization scheme for orthogonal time frequency space (OTFS) systems by utilizing an embedded impulse pilot structure within each OTFS block in the delay-Doppler domain. The time synchronization process is equivalent to a two-stage timing offset (TO) estimation process that operates in the delay-time domain according to two modified timing metrics. The first stage identifies TO in the delay dimension, while the second stage determines TO in the time dimension. As compared with a previous related method, the proposed one achieves better performance, in terms of the probability of perfect time synchronization and the TO estimation error, with only a slight increase in complexity. This improvement enables itself to work at lower pilot power and thus to relieve the peak-to-average power ratio issue associated with OTFS systems.