Enhanced RACH Occasion in LEO-based Non-Terrestrial Networks

With the latest development of the low earth orbit (LEO) constellation, satellite communication is considered in 3GPP as a promising NR-based non-terrestrial network (NTN) solution for extending 5G service to underserved areas. Due to the inherent characteristics of NTN, such as long propagation delay and high speed movement, some NR functions need to be redesigned or amended. This paper focuses on the random access procedure where the UEs may or may not have GNSS capability. To reuse legacy RACH Occasion (RO) scheme, a UE is assumed to have its location information for tracking the ephemeris of LEO satellite and compensating the propagation delay of slang range; otherwise, the new design of RO scheme is inevitable. This paper considers the mixed environment where a portion of UEs have GNSS-capability. Three different RO schemes, which are backward compatible with legacy RO scheme, are proposed to resolve the potential issues. Simulation results show that the proposed RO schemes outperform the legacy RO scheme in terms of the average delay and probability of successful preamble transmission regardless of the UE with or without GNSS capability.