The present invention relates to a first network node. The first network node is configured to operate in a first Radio Access Technique, and the first network node comprises: a processor configured to receive a radio resource request for a reference signal to be transmitted by a user device, determine that the user device is served by a second network node configured to operate in a second RAT allocate a radio resource for the reference signal; a transceiver configured to transmit a first control signal to the user device, the first control signal indicating the allocated radio resource, receive a reference signal via the allocated radio resource from the user device; wherein the processor is further configured to measure the reference signal.