Timing advance and Doppler shift estimation in 5G NTN satellite networks

Описание: 10th LINCS Scientific Highlights by Ashutosh Balakrishnan (Télécom Paris) 

Abstract

Accurate timing advance (TA) computation is critical in 5G non-terrestrial networks (NTN). It is necessary to compute it accurately to avoid inter user interference in the uplink at the satellite (BS) level. Estimating TA in low earth orbit (LEO) satellite networks is more challenging than in classical terrestrial deployments due to the larger path loss and high-speed movement of non-stationary LEO satellites. Capturing the doppler shift also becomes very pertinent in such scenarios. The problem becomes more challenging in the event of the UE being mobile itself. In this talk, we first showcase an extended Kalman filter (EKF) based recursive Bayesian framework to accurately estimate the TA and Doppler shift in the presence of LEO satellite-UE joint motion dynamics. The framework first accurately models the joint motion dynamics and then constructs a Jacobian to linearize the inherent non-linearities present in the motion process. Probabilistic insights are also provided. The proposed framework is also useful when the satellite and UE clocks are not in sync, with the corresponding clock drift a function of the measured time difference of arrivals. Our results showcase the efficacy and robustness of the proposed EKF framework to estimate the TA and Doppler shift, even at very high UE speeds. The work is expected to be extremely useful in realizing LEO satellite based non-terrestrial networks. Further, as a current work, we are working on statistical characterization of the Doppler shift experienced at the UE. We showcase the probability densities of the Doppler shift in a 2D isotropic scenario and the engineering insights through it.