Beam Centric Doppler Pre-Compensation for LEO-based 5G-NTN

Integration of Non-Terrestrial Networks (NTN) components with 5G Terrestrial Networks (TN) is getting significant traction from academia and industry, resulting in the standardization of 5G-NTN in 3GPP. Low Earth Orbit (LEO) based 5G-NTN, especially regenerative payload, are of particular interest as they can provide latency and throughput comparable to terrestrial 5G networks. Initial synchronization is the first step when a User Equipment (UE) attempts to establish a data link with the gNB. However, the excessive Doppler caused by the LEO satellite's fast movement must be exclusively compensated before the UE can successfully align time and frequency. This work presents an effective method to address this issue. In this method, a regenerative LEO satellite-based 5G gNodeB (gNB) pre-compensates the Doppler with respect to its Beam Center (BC) before any transmission. Further, a UE post-compensates the residual Doppler to achieve successful initial synchronization. With the proposed methodology, we expect the accuracy of initial synchronization to be comparable to 5G-TN without increasing the processing complexity at the UE. Furthermore, for the realistic scenario, our analysis includes the effect of the LEO satellite trajectory error sphere and pointing error.