From the UE perspective, it continues to be in activated state A until it receives a deactivation command from the eNB or the expiration of a deactivation timer configured by the eNB via higher layers (whichever occurs earlier) 720, after which the UE transitions 718 to the low power deactivated state.

As shown in the FIG. 7, for unlicensed carrier operation, the eNB may not have any transmissions in some subframes 736 (e.g., due to LBT procedure related delay) when the UE is in activated state. This is different from current LTE systems where activated UEs expect the eNB to transmit at least CRS in every subframe. The UEs need to receive frequent reference signal transmissions from the eNB (e.g., at least one transmission every X=10 or 20 ms) for AGC maintenance and fine time/frequency tracking.

For unlicensed carrier operation, the eNB may use any one of the following approaches to ensure that activated UEs have enough reference signals for AGC maintenance and fine time/frequency tracking. For example, in one embodiment for unlicensed carrier operation, the eNB may transmit discovery signals more frequently than what is considered standard. More particularly, the eNB may transmit discovery signals once every 10 ms to 20 ms. However, this embodiment's approach may most likely lead to increased interference on the unlicensed carrier frequency and increased eNB power consumption since the transmitted discovery signals are typically always transmitted by the eNB to facilitate cell detection.