Estimation and Compensation of Doppler in 5G NR Based Non-Terrestrial Networks

With the increasing demand for global internet coverage, the Third-Generation Partnership Project (3GPP) has progressed in integrating the 5G New Radio technology with aerial or satellite access. 3GPP coined the term non-terrestrial networks (NTN) to refer to the aerial or satellite access activity. This integration of 5G with NTN has brought about new opportunities along with challenges to be addressed. The challenges arise due to the large propagation distance, different scattering environment, and the mobility of NTN terminals (satellites or high-altitude platform systems). The mobility of an NTN terminal causes a time-varying Doppler shift that must be accounted for. This Doppler shift significantly impacts the orthogonality of the 5G orthogonal frequency division multiplexing (OFDM) signals. In this paper, the throughput performance of 5G physical downlink shared channel (PDSCH) link is studied in NTN narrowband and NTN tapped delay line (TDL) channels for different satellite orbits. The analysis is carried out in two Doppler compensation scenarios. Firstly, the time-domain 5G OFDM signal is pre-compensated for the Doppler at transmitter before passing through the channel. Secondly, the received signal is compensated for the Doppler, then, passed through the general 5G terrestrial receiver. The paper outlines the estimation of overall Doppler offset at the receiver using a novel metric by using the repetitive portion of OFDM signal and the demodulation reference signal (DM-RS) of PDSCH. The results show that the Doppler compensation at the receiver provides almost similar performance as Doppler precompensation at the transmitter.