Cell selection consists of the UE seeking stronger cell on all supported frequencies of each transport supported rat until it finds a suitable cell. The main requirement for cell selection is that it should not take too much time that becomes more difficult with the growing number of frequencies and rats to be searched. The CNS can accelerate the search process indicating the rats associated with selected PLMN. In addition, the UE can use the information stored in a previous access.
The criterion for selecting cell is known as the criterion and is met when the cell receives the level selection and quality levels are above a certain value:
Srxlev > 0 and Squal > 0,
Srxlev = Qrxlevmeas − (Qrxlevmin − Qrxlevminoffset)
Squal = Qqualmeas (Qqualmin + Qqualminoffset)
where Qrxlevmeas is the measured cell get the level, also known as Qrxlevmin, is a RSRP minimum receive level in the cell. Qqualmeas and Qqualmin are parameters that are appropriate for the level of quality, also known as RSRQ.
Qrxlevminoffset and Qqualminoffset are offsets that can be configured to prevent table tennis between PLMNs, which may otherwise arise due to fluctuating radio conditions. Offsets are taken into account only when you perform a search for higher priority PLMN while camped on a cell suitable for a visited PLMN.
Selection of parameters related cells are running in the SIB1 message.
In certain specific cases, additional conditions are defined:
- Departure from the connected mode, the UE must try normally to select the cell to which it was connected. However, the connection press the message may include information on the UE leadership to look for a cell on a particular frequency.
- When performing “any cell selection”, the UE is trying to find an acceptable any cell looking for all supported frequencies PLMN all rats. The UE can stop looking at finding a cell that meets the criterion “quality” for that rat.
Note that only checks the consistency of the cell more strongly on a certain frequency. In order to avoid the UE need to acquire from a candidate of cells that don’t match the criteria for the suitability of the information, is provided inter-RAT cells.