PLMN and Cell Selection

PLMN Selection

There are two modes for PLMN selection, automatic and manual.

The UE performs the registration on the PLMN if the UE is capable of services which require registration.

UE-NAS maintains a list of PLMNs in priority order. For each PLMN, associated RATs may be set. Selection of the PLMN is done by manual or automatic. This requests the AS to select a cell belonging to this PLMN.

UE scan all RF channels in the E-UTRA bands according to its capabilities to find the available PLMNs. On each carrier, the UE search for the strongest cell and read its system information, in order to find out which PLMNs the cell belongs to.

The search for PLMN is stopped or requested by NAS. The UE optimize PLMN search by using the stored information e.g. carrier frequencies and cell related parameters from previously received measurement control information.

If successful registration is achieved, the UE indicates the selected PLMN.

If the registration cannot be achieved because no PLMNs are available and allowable, the UE indicates “no service” to the user, waits until a new PLMN is available and allowable and then repeats the procedure.

Cell Selection

The UE uses one of the following two cell selection procedures:

Initial Cell Selection

This requires no prior knowledge of which RF channels are E-UTRA carries. The UE scans all RF channels in the E-UTRA band according to its capabilities find a suitable cell. On each carrier frequency, the UE need only search for the strongest cell. Once suitable cell is found this cell is selected.

Stored Information Cell Selection

This procedure requires stored information of carrier frequencies and optionally also information on cell parameters, from previously received measurement control information elements or from previously detected cells. Once the UE has found a suitable cell the UE selects it. If no suitable cell is found the Initial Cell Selection procedure should be started

The cell selection criteria S is fulfilled when:

Srxlev > 0 and Squal > 0

where:

Srxlev = Qrxlevmeas – (Qrxlevmin + Qrxlevminoffset) – Pcompensation Squal = Qqualmeas – (Qqualmin + Qqualminoffset)