RRC State Handling for 5G

Standardization work for the 5th Generation of mobile communications (5G) is under way in the 3rd Generation Partnership Project (3GPP). The design of the user equipment (UE) state machine is one of the central questions related to the overall control plane design. In this article, we present a state machine for 5G that consists of a novel Radio Resource Control (RRC) Connected Inactive state in addition to the conventional RRC Idle and RRC Connected states. In RRC Connected Inactive, the UE Context is stored in the UE and in the network, and the connection between the Radio Access Network (RAN) and the Core Network (CN) is kept active to minimize control plane latency and UE power consumption during state transition. In addition, RRC Connected Inactive is configurable so that requirements of diverse 5G use cases can be fulfilled without increasing the overall number of RRC states. Performance analysis shows that RRC Connected Inactive can achieve up to 8x latency improvement, 5x power efficiency and 3.5x signaling overhead reduction, when compared to Long Term Evolution (LTE) RRC Idle.