Cell Selection Criteria in 3G UMTS

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

Squal Cell Selection quality value (dB). Applicable only for FDD cells.
Srxlev Cell Selection RX level value (dB)
Qqualmeas 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.
Qrxlevmeas Measured cell RX level value. This is received signal, CPICH RSCP for FDD cells (dBm) and P-CCPCH RSCP for TDD cells (dBm).
Qqualmin Minimum required quality level in the cell (dB). Applicable only for FDD cells.
QqualminOffset 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
Pcompensation max(UE_TXPWR_MAX_RACH – P_MAX, 0) (dB)
UE_TXPWR_MAX_RACH Maximum TX power level an UE may use when accessing the cell on RACH (read in system information) (dBm)
P_MAX Maximum RF output power of the UE (dBm)

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