HIDDEN NODE DETECTION IN LTE LICENSED ASSISTED ACCESS

The application relates to improved hidden node detection for Long Term Evolution LTE Licensed-Assisted Access LAA. Channel State Information CSI measurements can be seen as one existing solution that could be used for obtaining information about the existence of a hidden node. However, relying on CSI reporting alone is rather unreliable. One of the reasons for this is that the CSI measurements and reporting do not take into account the regulatory requirements such as LBT. A further possible way to detect hidden nodes is to perform LBT (clear channel assessment CCA) at the transmitter (e.g. eNB) and receiver (e.g. UE) at the same time. However, there is still the need for an improved solution for how to detect hidden nodes preventing LTE LAA uplink operation and complicating coexistence. These problems are solved by ensuring that interference from non-hidden nodes (such as WLAN node 1 in FIG. 1) is not measured. Therefore the serving eNB detects a free channel during LBT procedure, i.e. that non-hidden nodes are not transmitting, and informs the UE which performs the hidden node detection measurements, by downlink scheduling, whether the serving eNB is active in the current subframe. The UE then performs the measurements only in subframes of the channel occupied by the serving eNB. Thereby, the UE only captures interference coming from hidden nodes.