Coarse Initial Time Synchronization for OTFS

In this paper, coarse initial time synchronization (CITS) is investigated for orthogonal time frequency space systems operating over the linear time-varying multipath channel exhibiting real-valued delay and Doppler shifts on the delay-Doppler grid. By acquiring a comb-type preamble frame waveform carrying the discrete-Fourier-transform sequence, a particular CITS system is developed to estimate the start time of a received preamble frame on the leading channel path. Based on the cross-ambiguity between the received signal and local discrete-frequency-shifted comb-type preamble signals for discrete time shifts, the CITS system can operate over a wide timing acquisition range and reach a coarse accuracy scale under the influence of data self-interference. When the channel exhibits a strong leading path and wide ranges of Doppler shifts, the comb-type CITS system is shown to outperform the conventional CITS systems acquiring a linear frequency modulated preamble waveform and a hybrid data/preamble frame waveform, significantly in estimation accuracy and robustness.