RLC SDU Loss and Arrival Delay in Multi-SIM UEs

The number of User Equipments (UEs) with multiple active subscriber identities (Multi-SIM) will increase throughout the coming years. The requirement in such UEs for each of the Subscriber Identity Modules (SIMs) to have parallel network access, invoke access conflicts on baseband/RF level. These conflicts ends up in one or more of the inserted SIMs being denied access for brief period of time, usually on the scale of tenths of milliseconds repeated every half to two minutes. These Multi-SIM conflicts are analysed using a combination of link level, and frame based simulation. The simulation clarifies the impact of Global System for Mobile (GSM)-like idle mode operations conflicting with an active Long Term Evolution (LTE) connection. The presented results show the effect Multi-SIM has on Radio Link Control (RLC) Unacknowledged Mode (UM) Service Data Unit (SDU) drop rate, and Acknowledge Mode (AM) SDU arrival time. It is shown that the impact of Multi-SIM on the drop rate and arrival time of the SDUs is based not only on the amount of conflicts between the SIMs, but also on the time alignment between the basestations retransmission timing strategy and the placement of the conflicts in time. The results may prove as base for discussions on some requirements to the basestations network configuration and performance.