5 CSG Identification

25.3673GPPMobility procedures for Home Node B (HNB)Overall descriptionRelease 17Stage 2TS

One or more Closed Subscriber Group (CSG) cells are identified by a unique numeric identifier called CSG Identity or CSG ID. A UE belonging to a CSG has the corresponding CSG ID and associated PLMN ID in its CSG whitelist. The CSG whitelist is maintained and provided by NAS. The CSG ID is broadcast in system information by the CSG cell or hybrid cell, and used by the UE for cell (re)selection and handover purposes.

A cell may optionally broadcast the CSG Indicator, whose presence and value of TRUE indicates the cell is a CSG cell. The absence of the CSG indicator in a cell which broadcasts a CSG identity indicates that it is a hybrid cell.

A CSG cell or hybrid cell may broadcast the HNB Name, a textual identifier, in system information. The HNB Name can be used to aid the human user in manual selection of a CSG ID.

At the physical layer, a CSG cell is identified by its carrier frequency (UARFCN) and Primary Scrambling Code (PSC). A set of PSCs could be reserved for CSG deployment and this reserved PSC range may be signalled in system information. The PSC of a CSG cell belongs to the reserved PSC range if broadcast.

On the mixed carrier frequency shared by both non-CSG cells (UMTS macro cells) and CSG cells, CSG cells broadcast in system information the PSC range reserved by the network for CSG cells. The non-CSG cells may also broadcast the reserved PSC range. The reserved PSC range is only applicable to the UARFCN within the PLMN where the UE received this information. The UE considers the last received reserved PSC range to be valid within the entire PLMN for the duration of 24 hours. The UE may use the reserved PSC information for CSG cell search and (re)selection purposes, according to UE’s implementation.

NOTE: In shared network scenario, aligned PSC ranges are beneficial in the shared carrier frequency across the involved PLMNs. Furthermore, in deployments where cells broadcast different primary PLMN (with or without multiple PLMN IDs), it is beneficial that CSG and non-CSG cells will broadcast same PSC ranges. Moreover, it is beneficial if a CSG cell, if listed in system information and associated with a PLMN, is associated with the primary PLMN of the serving cell.

Non-CSG cells and CSG cells may broadcast indications of one or more carrier frequencies used for dedicated CSG deployment. This information may be used by a UE to avoid unnecessary measurements on that frequency even when cell measurement rules would require measurements of this carrier frequency. Indications of which carrier frequencies are dedicated to CSG-only deployment may be signalled in system information and are applicable only in the cell where this information is broadcast.