Energy efficiency enhancement with RRC connection control for 5G new RAT

To avoid the latency from RRC state transition procedure, legacy network maintains UE as RRC connected state for pre-defined time duration even without any traffic arrival. However, it consumes UE battery rapidly because UE should monitor PDCCH, and send CQI feedback periodically. In this paper, we design the RRC connection control to enhance energy efficiency with moderate control signaling overhead. In RRC INACTIVE state, the newly introduced in NR, both network and UE save UE context including bearer configuration and security even after UE released from network. Owing to the saved UE context, the RRC state transition from RRC INACTIVE to RRC CONNECTED requires fewer number of CN signalling. And thus network can release UE to RRC INACTIVE more aggressively with shorter timer. Furthermore, we propose the connectionless data transmission in RRC INACTIVE without RRC state transition to RRC CONNECTED. In our performance analysis, UE energy consumption can be improved by 50% for the modem only and 18% reduction for the total device including display. Furthermore, when the small data or background (keep-alive) traffic is transferred in RRC INACTIVE, the energy efficiency is increased up to double.