Cell Selection in 5G-NR
1. Initial cell selection does not rely upon any stored information. The UE scans all RF channels within its supported frequency bands and scanning is based upon the synchronization raster.
2. UE is permitted to use stored information to support the cell selection procedure. This can include:
a. Carrier frequencies which it has previously camped on.
b. Can include cell parameters from previously received measurement control info.
c. Also in RRC release msg, gNB can direct towards specific carrier.
3. A ‘suitable’ cell is defined as a cell which:
a. Is not barred.
b. Belongs to the PLMN selected by the NAS layer.
c. Belongs to at least one Tracking Area which is not forbidden.
d. Satisfies the cell selection criteria.
4. 3GPP TS 38.304 specifics the cell selection criteria when below 2 conditions are met:
Srxlev > 0 AND Squal > 0
where; Srxlev = Qrxlevmeas – (Qrxlevmin + Qrxlevminoffset) – Pcompensation- Qoffsettemp
Squal = Qqualmeas – (Qqualmin + Qqualminoffset) – Qoffsettemp
where:
a. Qrxlevmeas:It is the SS-RSRP measured by the UE.
b. Qrxlevmin: It defines the minimum RSRP threshold for the cell.
c. Pcompensation: It is used to adjust the value of Qrxlevmin according to the UE transmit power capability.
d. Qoffsettemp: It is defined by the value of connEstFailOffset within the SIB 1. This temporary offset is applied if T300 timer is expiring.
e. Qqualmeas: It is the SS-RSRQ measured by the UE.
f. Qqualmin: It defines the minimum RSRQ threshold for the cell.