Efficient Doppler Compensation for LEO Satellite Downlink OFDMA Systems

Low earth orbit (LEO) satellite-enabled orthogonal frequency division multiple access (OFDMA) systems will play a pivotal role in future integrated satellite-terrestrial networks to realize ubiquitous high-throughput communication. However, the high mobility of LEO satellites and the utilization of Ku-Ka and millimeter wave (mmWave) bands introduce wide-range Doppler shifts, which are especially detrimental to OFDMA-based systems. Existing Doppler shift compensation methods are limited by the requirement for prior user location information and/or high computational complexities associated with searching across broad Doppler shift ranges. In this work, we propose a multi-stage Doppler shift compensation method aimed at compensating for wide-range Doppler shifts in downlink LEO satellite OFDMA systems over Ku-Ka to mmWave bands. The proposed method consists of three stages: incorporating the phase-differential (PD) operation into the extended Kalman filter (EKF) to widen the estimation range, enhancing compensation using a repetition training sequence, and utilizing the cyclic prefix (CP) for fine estimation. Simulation results demonstrate the proposed method's effectiveness in handling Doppler shifts in LEO SatCom over different channels and frequency bands. Moreover, the proposed method attains the maximum estimation range and exhibits high accuracy with low complexity, irrespective of the Doppler shift range, making it an effective, practical, and easily implementable solution in LEO satellite communication.