CSG proximity detection enhancement using out-of-band radio of Home NodeB

3GPP Release 9 has introduced a proximity detection feature where the User Equipment (UE) when so configured is able to determine its proximity to a Closed Subscriber Group (CSG) or hybrid cell. The proximity is determined for CSG or hybrid cells whose CSG Identity (CSG ID) is in the UE's CSG whitelist. The UE sends an “entering” or “leaving” proximity indication to the Serving Radio Network Controller (SRNC) whenever it is entering or leaving respectively the proximity of one or more such cells. This helps the network to take the necessary actions for handover preparation viz. configure or take away handover measurements at the UE. The proximity detection feature is based on UE implementation and this paper proposes a macro cell based fingerprint method for proximity detection. This method offers reliable triggering of proximity indication but may not be very precise. Additionally an enhanced method is proposed using the out-of-band (OOB) radio integrated with the Home NodeB (HNB). In the enhanced method, OOB equipped UEs start searching for the HNB over the OOB link when the macro cell based fingerprint match occurs and “entering” proximity indication is sent only after the HNB is detected over the OOB link. The enhanced method offers higher precision and better network performance due to less measurement gaps being configured.