WO_NA02_E1_1 UMTS Cell Selection and Reselection-54

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

Setting Up a Cell and Public Channels

RNC Node B UE

Process for setting up a cell

Process for setting up public transmission

channels (PRACH and SCCPCH)

Process for broadcasting system messages

UE Registers upon Switch-on


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







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; and

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/N0 (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)

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 > 0

Squal ＝ Qqualmeas － Qqualmin

Srelev ＝ 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

Qmeas,s：Quality measurement result of serving cell.

Qmeas,n：Quality measurement result of neighbor cell.

Qhyst1s ：Hysteresis value when measurement value is CPICH RSCP.

Qhyst2s ：Hysteresis value when measurement value is CPICH Ec/No.

Qoffset1s,n ：Offset of two cells when measurement value is CPICH

RSCP.

Qoffset2s,n ：Offset of two cells 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 ＝ Qmeas,s + Qhysts

Rn ＝ Qmeas,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 CellUMTS

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

GSM→UMTS Cell Reselection Procedure

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/No

2：CPICH RSCP

Default Value 1：CPICH Ec/No

Configuration

Path

View->Configuration Management->RNC NE->RNC Radio

Resource Management->UltranCell->UltranCellXXX-> Cell

Selection and Reselection -> Advanced Parameter Manager->

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


Resource Management->UtranCell->UtranCellXX->Cell

Selection and Reselection-> Cell Selection and ReselectionX-

> Modify Advanced Parameter-> Minimum Required Quality

Level in the Cell (Qqualmin)

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




> Modify Advanced Parameter-> 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


Resource Management->UtranCell->UtranCellXX-> Modify

Advanced Parameter->PRACH-> Maximum Allowed UL TX

Power of RACH(dBm)

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 the 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 0: Not configured to UE.

1: Configured to UE.

Default Value 1: Configured to UE.

Configuration

Path




> Modify Advanced Parameter-> S-intrasearch 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 Sintrasearch, UE may choose to

not 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->UtranCell->UtranCellXX->Cell Selection and

Reselection-> Cell Selection and ReselectionX-> Modify Advanced

Parameter-> 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 the inter-frequency

measurement. If the value is True, Sintersearch is configured to

UE, and UE judges whether to perform the inter-frequency

measurement.




Configuration

Path




> Modify Advanced Parameter-> S-intersearch 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 Sintersearch, UE may choose to

not 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


UE to trigger inter-frequency measurement.


Default Value 10dB




Parameter-> 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 the

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.




Configuration

Path




> Modify Advanced Parameter-> 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


UE to trigger inter-RAT measurement.


Default Value 6dB




Parameter-> 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




> Modify Advanced Parameter-> 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




> Modify Advanced Parameter-> Qhyst2s (dB)

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］dB

RNC：D=P+50，［0，100］

Default Value 0dB


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］dB

RNC：D=P+50，［0，100］

Default Value 0dB


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


Resource Management->UltranCell-> UtranCellXX->Cell


>Advanced Parameter Manager -> 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: Barred

2: Not Barred

Default Value 2: Not Barred

Configuration

Path


Resource Management->UltranCell->UltranCellXXX->Cell

Selection and Reselection -> Cell Selection and ReselectionX-

> Advanced Parameter Manager-> 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: Allowed

1: Not Allowed

Default Value 0: Allowed

Configuration

Path


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 cell broadcast in

either SIB11 or SIB11bis, the default parameter is broadcast in

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: SIB11

1: SIB11bis

Default Value 0: SIB11

Configuration

Path


Resource Management->UTRAN Cell -> UTRAN Cell xxx ->

Neighbouring Cell ->Neighbouring Cell xxx -> Modify ->

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 highest priority is 0, the lowest priority is

2.

Range and Step ［0，2］

Default Value 0

Configuration

Path


Resource Management->UTRAN Cell -> UTRAN Cell xxx -

>Neighbouring Cell -> Measurement Priority of Neighboring

Cell

Content







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







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







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 BEARER

RECONFIGURATION COMPLETE

Documents

WO_NA02_E1_1 UMTS Cell Selection and Reselection-54