20 Support for Multi-USIM devices

38.3003GPPNRNR and NG-RAN Overall descriptionRelease 17Stage 2TS

20.1 General

NG-RAN may support one or more of the following enhancements for MUSIM device operation:

– Paging Collision Avoidance, as described in clause 20.2;

– UE notification on Network Switching, as described in clause 20.3;

20.2 Paging Collision Avoidance

The purpose of paging collision avoidance is to address the overlap of paging occasions on both USIMs when a MUSIM device (e.g. dual USIM device) is in RRC_IDLE/RRC_INACTIVE state in both the networks (e.g. Network A and Network B) associated with respective USIMs. Network A is NR and Network B is E-UTRA or NR.

A MUSIM device may determine potential paging collision on two networks and may trigger actions to prevent potential paging collision on NR network as specified in TS 23.501 [3].

NOTE: It is left to UE implementation as to how it selects one of the two RATs/networks for paging collision avoidance.

20.3 UE notification on Network Switching

For MUSIM operation, a MUSIM device in RRC_CONNECTED state in Network A may have to switch from Network A to Network B. Network A is NR and Network B can either be E-UTRA or NR. Before switching from Network A, a MUSIM device should notify Network A to either leave RRC_CONNECTED state, or be kept in RRC_CONNECTED state in Network A while temporarily switching to Network B.

When configured to do so, a MUSIM device can signal to the Network A a preference to leave RRC_CONNECTED state by using RRC (see TS 38.331 [12]) or NAS signalling (see TS 23.501 [3]). After sending a preference to leave RRC_CONNECTED state by using RRC signalling, if the MUSIM device does not receive an RRCRelease message from the Network A within a certain time period (configured by the Network A, see TS 38.331 [12]), the MUSIM device can enter RRC_IDLE state in Network A.

When configured to do so, a MUSIM device can signal to the Network A a preference to be temporarily switching to Network B while remaining in RRC_CONNECTED state in Network. This is indicated by scheduling gaps preference.This preference can include information for setup or release of gap(s). The Network A can configure at most 4 gap patterns for MUSIM purpose: three periodic gaps and a single aperiodic gap. The Network A should always provide at least one of the requested gap pattern or no gaps. Network providing an alternative gap pattern instead of the one requested by the UE is not supported in this release.