Random Access Preamble Design for 3GPP Non-terrestrial Networks

Satellite-based non-terrestrial networks (NTNs) can provide connectivity to geographical regions with inadequate cellular coverage. The 3rd Generation Partnership Project is developing specifications for NTNs based on 5G New Radio (NR). The NTN scenario entails large Doppler shifts and long propagation delays as compared to a terrestrial network. This necessitates revisiting the existing NR physical layer including the Physical Random Access Channel (PRACH), which was not designed to operate amid large carrier frequency offsets. In this paper, the design rationale is discussed for an NTN-specific PRACH preamble consisting of two concatenated preambles with different Zadoff-Chu root sequences. Simulation results validate that the proposed PRACH preamble meets the NTN performance requirements in terms of preamble detection, and timing and frequency offset estimation.