What is cell selection? What is the criteria for cell selection?
After selecting a PLMN UE need to select a cell to obtain normal or emergency service. Cell selection procedure is divided into two types
- Initial cell selection : When UE does not have any prior knowledge about RF channels in UTRA band or
- Stored information cell selection: This procedure requires stored information of carrier frequencies and optionally also information on cell parameters, e.g. scrambling codes, from previously received measurement control information elements.
Cell Selection Criteria
Cell selection criteria S is fulfilled when
- for FDD cells: Srxlev > 0 AND Squal > 0
- for TDD cells: Srxlev > 0
How Squal and Srxlev calculated
Squal = Qqualmeas – (Qqualmin + QqualminOffset)
Srxlev = Qrxlevmeas – (Qrxlevmin + QrxlevminOffset) – Pcompensation
||Cell Selection quality value (dB). Applicable only for FDD cells.
||Cell Selection RX level value (dB)
||Measured cell quality value. The quality of the received signal expressed in CPICH Ec/N0 (dB) for FDD cells. CPICH Ec/N0 shall be averaged. Applicable onlyfor FDD cells.
||Measured cell RX level value. This is received signal, CPICH RSCP for FDD cells (dBm) and P-CCPCH RSCP for TDD cells (dBm).
||Minimum required quality level in the cell (dB). Applicable only for FDD cells.
||Offset to the signalled Qqualmin taken into account in the Squal evaluation as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN
||max(UE_TXPWR_MAX_RACH – P_MAX, 0) (dB)
||Maximum TX power level an UE may use when accessing the cell on RACH (read in system information) (dBm)
||Maximum RF output power of the UE (dBm)
What is a reserved cell? How to check if 3GPP cell is reserved?
A cell is reserved if it is indicated as reserved in RRC System Information Block type 3.
Following exceptions to these definitions are applicable for UEs:
- Camped on a cell that belongs to a LA that is forbidden for regional provision of service, and during emergency calls.
- As an outcome of the manual CSG selection procedure the UE is allowed to access an acceptable cell which fulfils the cell selection criteria and is not barred or reserved for operator use for UEs not belonging to AC 11 or 15 and inform NAS that access is possible (for location registration procedure).
How to know if cell is reserved?
Use 3GPP Decoder to decode System Information Block 3 (SIB 3).
- Check for Cell Access Restriction information element
- Cell Access Restriction can have one of these set
- Cell Reserved for operator use – Value can be reserved or not reserved
- Cell Reservation Extension – Value can be Reserved or Not Reserved
- Cell Reserved for CSG – Value can be Reserved or Not reserved
What is a suitable cell? What are the minimum criteria for 3G suitable cells?
A suitable cell in UTRAN system is a cell on which UE can camp on and obtain normal services like voice call and packet call. If UE can not get normal services from the particular cell after camping then it is not considered as a suitable cell.
- A suitable cell in 3G is part of either
- the selected PLMN or
- the registered PLMN or
- a PLMN of the equivalent PLMN list
- The cell is not barred as per latest system information
- The cell is not part of forbidden location area for roaming
- Cell selection criteria are fulfilled.
If the above criteria is not fulfilled then the cell may be a acceptable cell, barred cell or reserved cell.
What makes a cell acceptable in 3G UMTS system?
In acceptable cell UE can camp and make emergency call and receive ETWS notifications if it is supported. An acceptable cell should fulfill the following requirements to make emergency call and receive ETWS primary notifications with or without security support.
- An 3GPP acceptable cell should not be a barred cell
- All acceptable cells should fulfill cell reselection criteria
What is 3GPP? Why 3GPP Exists?
3GPP stands for 3rd generation partnership project. 3GPP combines six telecommunication standardardization groups (ARIB, ATIS, CCSA, ETSI, TTA, TTC) to produce specifications and reports for different 3GPP technologies like 3G (UMTS), HSPA, LTE, LTE Advanced, etc.
3GPP has for technical specification groups. Those are Radio Access Networks (RAN), Service & Systems Aspects (SA), Core Network & Terminals (CT) and GSM EDGE Radio Access Networks (GERAN).
All technical groups meets four to six times every year to discuss and approve new 3GPP features.
The last meeting of the cycle of Plenary meetings is TSG SA, which also has responsibility for the overall coordination of work and for the monitoring of its progress.