DD-Domain Pilot Design for OTFS-Based Integrated Sensing and Communication in LEO Non-Terrestrial Networks

Abstract

Low Earth Orbit (LEO) non-terrestrial networks (NTNs) suffer from severe Doppler shifts and rapidly time-varying channels, making orthogonal frequency-division multiplexing (OFDM)-based integrated sensing and communication (ISAC) vulnerable to intercarrier interference. Although orthogonal time frequency space (OTFS) and delay-Doppler (DD)-domain ISAC are promising for high-mobility links, pilot overhead and Doppler precompensation under LEO NTN channels remain insufficiently addressed. This paper proposes a DD-domain embedded pilot framework for OTFS-based ISAC. A single pilot pulse with a rectangular guard region supports data transmission, channel estimation, and navigation parameter extraction. Doppler precompensation assisted by ephemeris information confines the residual Doppler spread and reduces the pilot overhead to about 0.7%. A simplified three-bin fractional interpolator with pilot cancellation aware of fractional offsets is further used to mitigate Dirichlet kernel spreading. Simulations over the 3GPP NTN-TDL-C channel show that the OTFS-Pilot scheme retains much of the high-SNR gain of ideal OTFS over OFDM and OFDM with serial interference cancellation (OFDM-SIC) and exhibits a sensing accuracy trend approximately parallel to the reference Cramér-Rao bound (CRB) within the valid fixed guard regime under ephemeris errors.