PCP-M based OTFS Time Synchronization for LEO Systems

The high-speed relative motion between Low Earth Orbit (LEO) satellites and terrestrial users induces significant Doppler shifts, which disrupt the orthogonality of Orthogonal Frequency Division Multiplexing (OFDM) subcarriers, thereby introducing inter-carrier interference (ICI) and degrading system performance. By mapping signals to the delay-Doppler domain, Orthogonal Time Frequency Space (OTFS) modulation effectively addresses such high-Doppler environments, preserving signal orthogonality and mitigating ICI. Time synchronization remains a critical component in LEO satellite communications. Consequently, OTFS systems require high-precision time synchronization algorithms to counteract the severe Doppler shifts inherent in LEO satellite scenarios. To this end, this paper proposes a PCP-M-based OTFS time synchronization method, which innovatively combines the cyclic-prefix pilot (PCP) structure with M-sequences, leveraging the periodicity of the PCP and the superior autocorrelation and pseudo-random properties of Msequences to achieve two-stage, two-dimensional synchronization in the delay-time domain. Simulation results demonstrate that the proposed PCP-M pilot achieves high time synchronization accuracy at low power levels, outperforming conventional constantamplitude high-power pilots. Compared to existing PCP-based approaches, it significantly enhances estimation accuracy while effectively mitigating Doppler spread in LEO satellite scenarios.