Doppler Shift Estimation in 5G New Radio Non-Terrestrial Networks

TL;DR

This paper proposes a method for estimating Doppler shifts in 5G non-terrestrial networks without relying on GNSS signals by using reference signals within the OFDM carrier, enhancing robustness and reducing dependency on GNSS.

Contribution

It introduces a novel Doppler shift estimation technique using OFDM reference signals, enabling NTN devices to operate without GNSS support.

Findings

The proposed method effectively estimates Doppler shifts without GNSS.

Simulation results show comparable performance to GNSS-based methods.

Reduces reliance on weak and interference-prone GNSS signals.

Abstract

Evolving 5G New Radio (NR) to support non-terrestrial networks (NTNs), particularly satellite communication networks, is under exploration in 3GPP. The movement of the spaceborne platforms in NTNs may result in large timing varying Doppler shift that differs for devices in different locations. Using orthogonal frequency-division multiple access (OFDMA) in the uplink, each device will need to apply a different frequency adjustment value to compensate for the Doppler shift. To this end, the 3GPP Release-17 work on NTNs assumes that an NTN device is equipped with a global navigation satellite system (GNSS) chipset and thereby can determine its position and calculate the needed frequency adjustment value using its position information and satellite ephemeris data. This makes GNSS support essential for the NTN operation. However, GNSS signals are weak, not ubiquitous, and susceptible to interference and spoofing. We show that devices without access to GNSS signals can utilize reference signals in more than one frequency position in an OFDM carrier to estimate the Doppler shift and thereby determine the needed frequency adjustment value for pre-compensating the Doppler shift in the uplink. We analyze the performance, elaborate on how to utilize the NR reference signals, and present simulation results. The solution can reduce the dependency of NTN operation on GNSS with reasonable complexity and performance trade-off.