UE power saving with RRC semi-connected state in LTE

This paper provides an approach where the MTC device may change to a power saving state for longer periods while the device and the network keep all related user plane security contexts and bearers. The device can return to a communication state without necessarily requiring RRC connection setup procedures. It is expected that with such an approach the sporadic higher level control plane signaling could be avoided when there are large amount of MTC devices which initiate packet transmissions periodically. Further it is expected that UE power consumption would be reduced. Simulation was done in a 3GPP Case 1 scenario. A simple intermittent traffic, 6 UEs per cell and a fixed long DRX parameter were in use in the evaluation. Different RRC release timer values were assumed to simulate different RRC connection states. The results show that with this approach both signaling load and energy consumption can be improved as it can avoid frequent transition in RRC-CONNECTED and RRC-IDLE states in device. For example, at a RRC release timer of 5 seconds, geometrically distribution of mean inter-burst arrival time of 30 seconds, the relative signaling load is 5.6 times less and the energy consumption in UE is about 3 times better with than without a RRC-SEMICONNECTED state.