Efficient Uplink Multi-Beam Initial Access Scheme for Inactive Users in mmWave Networks

Abstract

The interface between the Radio Access Network and Core Network is kept for Radio Resource Control (RRC) Inactive relative to RRC Idle, and the initial access should be conducted for inactive user equipments (UEs) to reduce the delay of link connection when inactive UEs switch to active. However, due to less interaction information between inactive UEs and transmission and reception points (TRPs), it is necessary to conduct initial access by beam sweeping rather than refined beam alignment. In this paper, an effective uplink multi-beam initial access scheme for inactive UEs in mmWave networks is proposed, where uplink beam sweeping and fast beam recovery is considered. Due to the application of digital beamforming technology and considering that TRP scanning beam number is more than that of UE scanning beams, the delay of uplink based beam sweeping is significantly reduced in the proposed initial access scheme, compared with the traditional downlink based beam sweeping. Furthermore, when the serving beam pair is blocked or not available, fast beam recovery would be conducted by using backup beam pair, where the cases that the backup beam pair and serving beam pair belonging to the same TRP or different TRPs are considered. Simulation results present the effect of density of TRPs, beam sweeping cycle and UE speed on outage probability and average rate after inactive UEs switching to active, and verify initial access performance gain of the proposed initial access scheme.