UMTS Cell Selection and Reselection

ZTE University

Content

Strategy of PLMN Selection Strategy of Cell Selection and Reselection Strategy of LA and RA Update Strategy of URA Update Strategy of CELL Update

UE Registers upon Switch-on

Strategy of PLMN Selection

The USIM maintains a list of allowed PLMN types. During PLMN selection and reselection, based on the list of allowed PLMN types and a list of PLMN identities in priority order, the particular PLMN may be selected either automatically or manually. The UE will select a PLMN when it registers at power-on or re-registers after leaving connected mode. In addition, the UE can make periodic PLMN selection.

Support for PLMN Selection

The UE scans all RF channels according to its capabilities to find available PLMNs. On each carrier, the UE shall search for the strongest cell and read its system information. The allowed PLMN information in USIM determines which PLMN will be selected finally.

Whenever a UE is switched on or re-registers after leaving connected mode, it attempts to camp on the last registered PLMN. If there is no registered PLMN stored in the USIM, the UE selects and attempts registration on other PLMNs using either the automatic mode or the manual mode.

Once the UE has selected a PLMN, the cell selection procedure will be performed in order to select a suitable cell of that PLMN to camp on.

PLMN Selection-Automatic Mode

Manual PLMN Selection Mode

The UE displays all PLMNs that it finds by scanning all frequency carriers. The UE displays those PLMNs that are allowed as well as those that are not allowed. The user makes a manual selection, according to the available access technology for the chosen PLMN, and the UE attempts registration on this PLMN.

If the user selects an available PLMN in the forbidden PLMN list, the UE attempts to register and may receive a positive acknowledgement from the CN. In this case, the PLMN is removed from the forbidden list.

Roaming

Roaming is a service through which a UE is able to obtain services from another PLMN than the HPLMN. The behavior that the UE must follow is specified by agreements among the network operators. A UE in automatic mode, having selected and registered on a VPLMN, periodically attempts to return to its HPLMN. The time interval between consecutive attempts is stored in the USIM. The timer may have a value of between 6 minutes and 8 hours, with a step size of 6 minutes. In the absence of a fixed value, a default value of 30 minutes is used by the UE.

Content

Strategy of PLMN Selection Strategy of Cell Selection and Reselection Strategy of LA and RA Update Strategy of URA Update Strategy of CELL Update

Strategy of Cell Selection and Reselection

For normal service, the UE has to camp on a suitable cell, tune to that cell's control channel(s) so that the UE can:

Receive system information from the PLMN; Receive registration area information from the PLMN, e.g., location

area and routing area; Identify to which service area as specified by NAS that the serving

cell belongs. Receive other AS and NAS Information; Receive paging and notification messages from the PLMN; Initiate call setup for outgoing calls or other actions from the UE.

Cell Selection and Reselection (A)

To B

Cell Selection and Reselection (B)From A

Cell selection criteria-Rule S

Qqualmeas ： Measured cell quality value. The quality of the received signal expressed in CPICH Ec/No (dB).

Qrxlevmeas ： Measured cell RX level value. The quality of the received signal expressed in CPICH RSCP (dBm).

Qqualmin ： Minimum required quality level in the cell (dB). Qrxlevmin ： Minimum required RX level in the cell (dBm). Pcompensation ： max(UE_TXPWR_MAX_RACH － P_MAX, 0) (dB) UE_TXPWR_MAX_RACH ： Maximum TX power level on RACH (dBm) P_MAX ： Maximum RF output power of the UE (dBm)

Srxlev > 0 AND Squal > 0Squal ＝ Qqualmeas － QqualminSrxlev ＝ Qrxlevmeas － Qrxlevmin －Pcompensation

Camped Normally State

Select and monitor the indicated PICH and PCH of the cell according to information sent in system information.

Monitor relevant system information. Perform necessary measurements for the cell reselection

evaluation procedure. Execute the cell reselection evaluation process.

Measurement rules for cell re-selection

If Sx > SIntraSearch, UE does not measure intra-frequency cells. If Sx <= Sintrasearch, UE measure intra-frequency cells. If Sintrasearch is not broadcast, UE measure intra-frequency cells.

Whether to broadcast Sintrasearch or not is controlled by SintrasearchPre. If Sx > Sintersearch, UE does not measure inter-frequency cells.

If Sx <= Sintersearch, UE measure inter-frequency cells. If Sintersearch is not broadcast, UE measure inter-frequency cells.

Whether to broadcast Sintersearch or not is controlled by SintersearchPre. If Sx > SSearchRat, UE does not measure inter-RAT cells.

If Sx <= SSearchRat, UE measure inter-RAT cells. If SsearchRat is not broadcast, UE measure inter-RAT cells. Whether to

broadcast SsearchRat or not is controlled by OtherRATInfoPre. Where, Sx is Squal.

Cell reselection criteria-Rule R

Qmap,s ： Mapping value of serving cell quality measurement. Qmap,n ： Mapping value of neighbor cell quality measurement Qhyst1s ： Hysteresis value when measurement value is CPICH RSCP. Qhyst2s ： Hysteresis value when measurement value is CPICH Ec/No. Qoffset1s,n ： Cell reselection offset when measurement value is CPICH

RSCP. Qoffset2s,n ： Cell reselection offset when measurement value is CPICH

Ec/No. The new cell is better ranked than the serving cell during a time interval

Treselection according to the R criteria. More than 1 second has elapsed since the UE camped on the current

serving cell.

Rs ＝ Qmap,s + Qhyst,sRn ＝ Qmap,n －Qoffsets,n

Intra-Frequency Cell Re-Selection

Time

P-CPICH Ec/Io

Serving CellServing Cell

Neighboring Cell

Neighboring Cell

Neighboring cell criterion S

is fulfilled and is ranked

Neighboring cell better ranking

than Serving cell

UE perform cell reselection

Treselections

Qmeas,s + Qhyst2s

Qmeas,n - Qoffset2s,n

Qqualmin

UE perform intra-frequency measurements

Qqualmin + SIntraSearch

Inter-RAT Cell Re-Selection

Time

Quality/Rx Lev

GSM Serving Cell

UMTS Serving Cell

GSM Neighboring Cell UMTS

Neighboring Cell

Inter-RAT cell criterion S is

fulfilled and is ranked

Neighboring cell better ranking

than Serving cell

UE perform inter-RAT cell

reselection

Treselections

Qmeas,s + Qhyst1s

Qmean,n – Qoffset1s,n

QRxLevMin

UE perform inter-RAT

measurements

Qqualmin + SSearchRat

Inter-RAT Cell Re-Selection

Yes

Quality measure for Cell Selection and ReselectionParameter Name QualMeas

Description This parameter indicates the quality measure for cell selection and reselection.

Range and Step 1: CPICH Ec/No2: CPICH RSCP

Default Value 1

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter-> Cell Selection and Reselection -> Measurement Quality for Cell Selection and Reselection

Minimum Required Quality Level in the Cell

Parameter Name QQualMin

Description This parameter indicates the minimum required quality level of the cell which satisfies the condition of being selected or reselected by UE. When the quality measure is CPICH Ec/No, only the measured quality of the cell is over Qqualmin can the cell be selected. It’s -18dB by default.If value of the parameter is increased, it’s harder for the cell to satisfy the condition of being selected.If value of the parameter is decreased, it’s easier for the cell to satisfy the condition of being selected.

Range and Step ［ -24 ， 0 ］ dB step 1dB

Default Value -18dB

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UtranCell->UtranCellXX->Modify Advanced Parameter->Cell Selection and Reselection->Qqualmin-offset

Minimum Required Received Level in the Cell

Parameter Name QRxLevMin

Description This parameter indicates the minimum required received power level of the cell which satisfies the condition of being selected or reselected by UE. When the quality measure is CPICH RSCP, only the measured received power level of the cell is over Qrxlevmin can the cell be selected. If value of the parameter is increased, it’s harder for the cell to satisfy the condition of being selected. If value of the parameter is decreased, it’s easier for the cell to satisfy the condition of being selected.

Range and Step ［ -115 ， -25 ］ dBm step 2dBm

Default Value -115dBm

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UtranCell->UtranCellXX->Modify Advanced Parameter->Cell Selection and Reselection->Minimum Required Received Level in the Cell (Qrxlevmin)

Maximum Allowed UL TX Power of RACH

Parameter Name MaxRACHTxPwr

Description This parameter indicates the maximum allowed UL transmission power of RACH.If value of configuration is increased, the maximum allowed UL transmission power of RACH increases.If value of configuration is decreased, the maximum allowed UL transmission power of RACH decreases.

Range and Step ［ -50 ， 33 ］ dBm

Default Value 24dBm

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Prach->Maximum Allowed UL TX Power of RACH

Sintrasearch Configuration Tag

Parameter Name SIntraSearchPre

Description This parameter is a switch indicating whether Sintrasearch is configured or not. If the value is False, Sintrasearch is not configured to UE and UE performs periodical intra-frequency measurement. If the value is True, Sintrasearch is configured to UE, and UE judges whether to perform the intra-frequency measurement.

Range and Step False: Not configured to UE.True: Configured to UE.

Default Value True: Configured to UE.

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Cell Selection and Reselection-> Sintrasearch Configuration Tag

Intra-Frequency Measurement Trigger Threshold for Cell ReselectionParameter Name Sintrasearch

Description This parameter indicates the intra-frequency measurement triggering threshold for cell reselection (Sintrasearch) used by UE to judge whether intra-frequency measurement should be performed. When HCS is not used, if the quality of serving cell exceeds S intrasearch, UE doesn’t perform intra-frequency measurement. If the quality of serving cell is not larger than Sintrasearch or if Sintrasearch is not configured, UE performs intra-frequency measurement. Sintrasearch is delivered to the UE, if its value is increased, it’s easier for the UE to trigger intra-frequency measurement. If value of the parameter is decreased, it’s harder for the UE to trigger intra-frequency measurement.

Range and Step ［ 0 ， 20 ］ dB Step 2dB

Default Value 14dB

Configuration Path View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Cell Selection and Reselection->Intra-Frequency Measurement Trigger Threshold for Cell Reselection (Sintrasearch)

Sintersearch Configuration Tag

Parameter Name SInterSearchPre

Description This parameter is a switch which indicates whether Sintersearch is configured or not. If the value is False, Sintersearch is not configured to UE and UE performs periodical inter-frequency measurement. If the value is True, Sintersearch is configured to UE, and UE judges whether to perform the inter-frequency measurement.

Range and Step False: Not configured to UE.True: Configured to UE.

Default Value True: Configured to UE.

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Cell Selection and Reselection->Sintersearch Configuration Tag

Inter-Frequency Measurement Trigger Threshold for Cell ReselectionParameter Name Sintersearch

Description This parameter indicates the inter-frequency measurement triggering threshold for cell reselection (Sintersearch) used by UE to judge whether inter-frequency measurement should be performed. When HCS is not used, if the quality of serving cell exceeds S intersearch, UE doesn’t perform inter-frequency measurement. If the quality of serving cell is not larger than Sintersearch or if Sintersearch is not configured, UE performs inter-frequency measurement. When Sintersearch is delivered to the UE, if its value is increased, it’s easier for the UE to trigger inter-frequency measurement. If value of the parameter is decreased, it’s harder for the UE to trigger inter-frequency measurement.

Range and Step ［ 0 ， 20 ］ dB Step 2dB

Default Value 10dB

Configuration Path View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Cell Selection and Reselection->Inter-Frequency Measurement Trigger Threshold for Cell Reselection (Sintersearch)

Inter-system Information Configuration Tag

Parameter Name OtherRATInfoPre

Description This parameter is a switch indicating whether inter-RAT information parameters used for cell reselection are configured or not. If the value is False, inter-RAT information parameters are not configured to UE and UE performs periodical inter-RAT measurement. If the value is True, inter-RAT information parameters are configured to UE, and UE judges whether to perform the inter-RAT measurement.

Range and Step False: Not configured to UE.True: Configured to UE.

Default Value True: Configured to UE.

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Cell Selection and Reselection->Inter-System Information Configuration Tag

Inter-System Measurement Trigger Threshold for Cell ReselectionParameter Name Ssearch,RAT

Description This parameter indicates the inter-RAT measurement triggering threshold for cell reselection (Ssearch,RAT) used by UE to judge whether inter-RAT measurement should be performed. When HCS is not used, if the quality of serving cell exceeds Ssearch,RAT, UE may choose to not perform inter-RAT measurement. If the quality of serving cell is not larger than Ssearch,RAT or if Ssearch,RAT is not configured, UE performs inter-RAT measurement. When Ssearch,RAT is delivered to the UE, if its value is increased, it’s easier for the UE to trigger inter-RAT measurement. If value of the parameter is decreased, it’s harder for the UE to trigger inter-RAT measurement.

Range and Step ［ 0 ， 20 ］ dB Step 2dB

Default Value 6dB

Configuration Path View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Cell Selection and Reselection->Inter-System Measurement Trigger Threshold for Cell Reselection (Ssearch,RAT)

Reselection Hysteresis 1 of Serving Cell

Parameter Name Qhyst1s

Description This parameter indicates the hysteresis value for FDD cells in case the quality measure for cell selection and reselection is set to CPICH RSCP. In cell-ranking criterion R of cell reselection, the R value of serving cell equals to the measured value plus the hysteresis value. If value of the parameter is increased, it’s harder to trigger cell reselection as the R value of the serving cell will increase. If value of the parameter is decreased, it’s easier to trigger cell reselection as the R value of the serving cell will decrease.

Range and Step ［ 0 ， 40 ］ dB step 2dB

Default Value 10dB

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Cell Selection and Reselection-> Reselection Hysteresis 1 of Serving Cell (QHyst1s)

Reselection Hysteresis 2 of Serving Cell

Parameter Name Qhyst2s

Description This parameter indicates the hysteresis value for FDD cells in case the quality measure for cell selection and reselection is set to CPICH Ec/No. In cell-ranking criterion R of cell reselection, the R value of serving cell equals to the measured value plus Qhyst2s. If value of the parameter is increased, it’s harder to trigger cell reselection as the R value of the serving cell will increase. If value of the parameter is decreased, it’s easier to trigger cell reselection as the R value of the serving cell will decrease.

Range and Step ［ 0 ， 40 ］ dB step 2dB

Default Value 2dB

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Cell Selection and Reselection-> Reselection Hysteresis 2 of Serving Cell (QHyst2s)

Quality Offset 1 Between Serving Cell and Neighbouring CellParameter Name Qoffset1s,n

Description This parameter indicates the quality offset of the serving cell and neighbor cell when the quality measure is CPICH RSCP. This parameter is required when queues cells in the cell reselection rule. This parameter is broadcast to UE in SIB11. R of neighbor cell = measured signal quality of neighbor cell - this offset. If value of the parameter is increased, it’s harder to trigger cell reselection as the R value of the neighbor cell will decrease. If value of the parameter is decreased, it’s easier to trigger cell reselection as the R value of neighbor cell will probably increase.

Range and Step OMCR ：［ -50 ， 50 ］ dBRNC ： D=P+50 ，［ 0 ， 100 ］

Default Value 0dB

Configuration Path View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Neighbouring Cell -> Advanced Parameter Manager-> Quality Offset 1(Qoffset1s,n ) Between Serving Cell and Neighbouring Cell Broadcasted in SIB11

Quality Offset 2 Between Serving Cell and Neighbouring Cell Parameter Name Qoffset2s,n

Description This parameter indicates the quality offset of the serving cell and neighbor cell when the quality measure is CPICH Ec/No. This parameter is required when queues cells in the cell reselection rule. This parameter is broadcast to UE in SIB11. R of neighbor cell = measured signal quality of neighbor cell - this offset. If value of the parameter is increased, it’s harder to trigger cell reselection as the R value of the neighbor cell will decrease. If value of the parameter is decreased, it’s easier to trigger cell reselection as the R value of neighbor cell will increase.

Range and Step OMCR ：［ -50 ， 50 ］ dBRNC ： D=P+50 ，［ 0 ， 100 ］

Default Value 0dB

Configuration Path View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX-> Neighbouring Cell -> Advanced Parameter Manager-> Quality Offset 2(Qoffset2s,n ) Between Serving Cell and Neighbouring Cell Broadcasted in SIB11

Cell Reselection Timer Value

Parameter Name Treselections

Description This parameter indicates the cell reselection timer value. UE will reselect the new cell if the new cell is best ranked according to the criterion R during a time interval indicated by Treselection and the new cell can be selected as new serving cell only after extension of the reselection timer. If value of the parameter is increased, it’s harder to trigger cell reselection. If value of the parameter is decreased, it’s easier to trigger cell reselection.

Range and Step ［ 0 ， 31 ］ s step 1s

Default Value 1s

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Cell Selection and Reselection->Cell Reselection Timer Value (Treselections)

Cell Barred Indicator

Parameter Name CellBarredInd

Description This parameter is cell barred indicator. If the cell barred indicator is set to “Barred”, UEs are not permitted to select/re-select this cell, even for emergency calls.

Range and Step 1: Barred2: Not Barred

Default Value 2: Not Barred

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX->Modify Advanced Parameter->Cell Selection and Reselection->Cell Barred Indicator

Intra-frequency Cell Reselection Indicator

Parameter Name InFreqReselInd

Description This parameter is intra-frequency cell reselection indicator. If cell is barred, if the value of this parameter is “Allowed”, UE is allowed to select other intra-frequency cell in case it satisfies the cell selection/relection condition. If it is set “Not Allowed”, when cell is barred, UE will not select another intra-frequency cell.

Range and Step 0: Allowed1: Not Allowed

Default Value 0: Allowed

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->UltranCellXXX-> Cell Selection and Reselection -> Cell Selection and ReselectionX-> Advanced Parameter Manager-> Intra-frequency Cell Reselection Indicator

Broadcast in either SIB11 or SIB11bis

Parameter Name Sib11orSib11bis

Description This parameter indicates UTRAN neighbour cells are broadcast in either SIB11 or SIB11bis, the default parameter is SIB11. If there are so many neighbour cells, and the size of system message larger than 3552bit, select part of cells broadcast in SIB11bis

Range and Step 0: SIB111: SIB11bis

Default Value 0: SIB11

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->neighbouring cellXXX->Broadcast in either SIB11 or SIB11bis

Measurement Priority of Neighboring Cell

Parameter Name MeasPrio

Description This parameter indicates the measurement priority of the neighboring cell. The smaller value it is, the higher priority the cell has.

Range and Step ［ 0 ， 2 ］Default Value 0

Configuration Path

View->Configuration Management->RNC NE->RNC Radio Resource Management->UltranCell->neighbouring cellXXX->Measurement Priority of Neighboring Cell

Content

Strategy of PLMN Selection Strategy of Cell Selection and Reselection Strategy of LA and RA Update Strategy of URA Update Strategy of CELL Update

Strategy of LA and RA Update

If the LAI or RAI read from system information are different from those stored in USIM before the UE switches off, the UE will perform LA or RA update.

When the UE in IDLE mode moves to a new LA or RA or PLMN, it will perform update.

The process of LA or RA update is controlled by CN and is transparently transmitted as the RAN is concerned.

There are three types of update: normal update, periodic update and IMSI attach and detach.

LA and RA Structure

The LA is an area to which the CN sends a paging message for circuit switched service and the RA is an area to which the CN sends a paging message for packet switched services. Each area, LA or RA, may consist of several cells of one or more RNC, which are connected to the same core network. Each cell could belong to only one LA and one RA.

Normal LA and RA Updating

Normal update is performed when the UE moves in a cell belonging to a new LA or RA. The UE reads the LAI and the RAI in the system information and detects that one or both of the received area identities differ from the ones stored on the USIM. If the LAI or RAI received from the system information is not in the forbidden LAIs or RAIs list, an LA or RA update request is sent by the UE.

Periodic LA and RA Updating

Periodic LA and RA updating is used to notify the network of the UEs availability, and to avoid unnecessary paging attempts for a UE that has lost coverage and is not able to inform the CN that it is inactive. The periodic LA update procedure is controlled by a timer, called t3212, whose value is sent to UEs with broadcast message. The periodic RA update is controlled by a timer, called t3312, whose value is sent by the CN to the UE in the IMSI attach or in the routing area update message accept.

System Information

RRC Connection Setup

NAS Connection

RRC Connection Release

Location Update Flow

IMSI Attach/Detach

the UE sends an “attach” or “detach” message when it is powered on or off indicating whether the UE is active or inactive. The CN avoids performing paging attempts when IMSI detach is applied and the UE is switched off. When the UE is switched on, the UE performs a location registration request, indicating IMSI attach, if it is in the same LA or RA in which it was switched off. If the registration area is changed, a normal LA update is performed by the UE.

Content

Strategy of PLMN Selection Strategy of Cell Selection and Reselection Strategy of LA and RA Update Strategy of URA Update Strategy of CELL Update

Strategy of URA Update

If the new cell that the UE camps on is not in the same URA area as the former cell that the UE camps on, the URA Update is triggered.

The UE enters a cell that has no URAs defined. This will trigger a release of the RRC Connection and the UE enters Idle mode.

Process of URA Update

UE UTRAN

URA UPDATE

URA UPDATE CONFIRM

UE UTRAN

URA UPDATE

RRC CONNECTION RELEASE

Content

Strategy of PLMN Selection Strategy of Cell Selection and Reselection Strategy of LA and RA Update Strategy of URA Update Strategy of CELL Update

Strategy of CELL Update

Cell reselection in state CELL_FACH. Radio link failure in state CELL_DCH. T305 periodic cell update. The UE in state URA_PCH sends data in uplink. The UE in state CELL_FACH/CELL_DCH detects that an

RLC unrecoverable error of AM RLC entity.

Process of CELL Update

UE UTRAN

CELL UPDATE

CELL UPDATE CONFIRM

UE UTRAN

CELL UPDATE

CELL UPDATE CONFIRM

PHYSICAL CHANNEL RECONFIGURATION COMPLETE

UE UTRAN

CELL UPDATE

CELL UPDATE CONFIRM

RADIO BEARERRECONFIGURATION COMPLETE