Orthogonal Time Frequency Space Modulation (OTFS) for Positioning Using LEO Satellites

Abstract

This paper analyses the achievable delay and Doppler estimation accuracies and the Multipath Error Envelopes (MEE) of Low Earth Orbit (LEO) Position-Navigation-Timing (PNT) systems, using the novel Orthogonal Time Frequency Space (OTFS) modulation. In this paper we investigate the advantages the OTFS modulation, which has originally been designed for communication purposes, may bring to the positioning field in LEO-PNT systems, in particular in the presence of doubly-selective wireless fading channels exhibiting both delay and Doppler spreads. We show how a LEO air-to-ground channel fits this description due to its fast dynamics, and we present the improvements of using OTFS with respect to the standard spread-spectrum single-carrier Binary Phase Shift Keying (BPSK) modulation in terms of delay-Doppler estimation accuracy, in addition to a comparison of their performance in LEO multipath scenarios through their respective MEEs.