Cell Selection Reselection

1 © NOKIA topic: cell selection & reselection/ July 2003 /Markus Wimmer

Cell Selection and Reselection


Cell Selection and Reselection: Motivation

CM requestsNAS control radiomeasurements

PLMNselected

PLMNavailable

registrationarea changes

locationregistration

response

indicationto usermanual mode

locationregistratio

n

cell selectionand reselection

PLMN selectionand reselection

automatic mode

RRC tasks:• PLMN selection

and reselection;• Cell selection and

reselection; • Location

registration.

if the UE is in the RRC idle

mode

if the UE is in the RRC connected modestates:• CELL_FACH,• CELL_PCH, and• URA_PCH


Operator controlled PLMN list

User controlled PLMN list

Last registered

PLMN

Home PLMN

Other PLMN‘s with RAT‘s the

UE is capable of

Switch on in automatic PLMN selection operation mode

PLMN Selection

HPLMN Search Period Timer6 .. 480 minutesDefault: 60 minutes


Cell Reservations and Cell Restrictions

Cell- acceptable- suitable- barred- reserved

Access Class barred:(UE access classes 0..9 and

11..15)

BCCH: Cell Access Restriction


Cell Reservations and Cell Restrictions

Cell Barred Cell reservedfor operator

Cell reservedfor future extension

Case

1

2

3

4

not barred

not barred

not barred

barred

not reserved not reserved

not reserved reserved

reserved ---

--- ---

suitable for selection and

reselection

suitable for AC 11 or 15 in HPLMN otherwise „barred“

Cell „barred“

Not suitable – not even for emergency call


Cell Reservations and Cell Restrictions: Access Class

UE RRC idle

I ignore all Access Class related cell

access restrictions

when selecting a cell to camp

on

UE RRC connected

Access Class only relevant

for access

Access Class irrelevantfor access suitable cell

suitable cell


Nokia Parameters for Cell Reservations and Restrictions• WCEL: CellBarred

Defines whether the cell is barred or not. A barred cell is a cell where a UE is not allowed to camp on. This parameter is part of SIB 3.0 (Barred), 1 (Not barred); default: 1.

• WCEL: TBarredWhen the cell is barred, UE regards the cell barred condition valid for a number of seconds defined by the value of 'Cell barred period'. This parameter is part of SIB 3.[10, 20, 40, 80, 160, 320, 640, and 1280] seconds; default: 40 seconds.

• WCEL: Cell_ReservedDefines whether the cell is reserved for operator use. This parameter is part of SIB 3.0 (Reserved), 1 (Not reserved); default: 1.

• WCEL: IntraFreq_Cell_Reselect_IndDefines whether intra-frequency cell re-selection is allowed when the cell is barred.This parameter is part of SIB 3/4.0 (Allowed), 1 (Not allowed); default: 0.


States and State Transition in the RRC Idle Mode

Cell Selection Process

NAS controls

AS controlscorrespondentprocedures

NAS:

PLMNselection

• RAT(s) associated with the selected PLMN• forbidden registration areas• list of equivalent PLMNs

UE CN

AS:attempts to find suitable cells



1

InitialCell Selection

Campednormally

CellReselectionEvaluationProcess

no cell informationstored for the PLMN

cell informationstored for the PLMN

go here whenevera new PLMNis selected

no suitable cell found

suitable cell found suitable cell found

ConnectedMode

suitablecell found

no suitablecell found

nosuitable

cellfound

StoredInformation

Cell Selection

trigger

suitablecell selected

no suitablecell found

Cell Selectionwhen leaving

connectedmode

leaveidle mode

return toidle mode

NASregistration

rejected

(adopted from TS 25.305 V3.11.0 chap. 5.5.2)



Camped onAny Cell

Any CellSelection

ConnectedMode

(Emergencycalls only)

return toidle mode

go here when no USIM in the UE

USIM inserted1

leaveidle mode

no acceptable cell found

an acceptable cell found

Cell Selectionwhen leaving

connectedmode

acceptablecell found

suitablecell found

1

CellReselectionEvaluationProcess

trigger

acceptable

cell selected

no acceptablecell found

(adopted from TS 25.305 V3.11.0 chap. 5.5.2)


Cell Selection Criterion S (in the FDD mode)

Qqualmeas (dB)(CPICH Ec/N0)

Qrxlevmeas (dBm)CPICH RSCP

Qqualmin(–24...0)

Qrxlevmin(–115...–25)

Srxlev > 0

Pcompensation

Squal > 0 S-Criterionfulfiled

Squal >0 ANDSrxlev > 0

suitable

cell?


Cell Selection Criterion S

Pcompensation= max(UE_TXPWR_MAX_RACH – P_MAX, 0)

Cell size defining parameters:• Qrxlevmin• Qqualmin

I am outside

I am inside,

but have not

enough power

-50 .. 33 dBm


(Initial) Cell Selection Process

Initial Cell Selection

(scan RF channel)

Stored Information Cell Selectionor

I have to find a

suitable cell

Squal = Qqualmeas – Qqualmin > 0Srxlev = Qrxlevmeas - Qrxlevmin – Pcompensation > 0

Once a suitable cell is found this cell is selected


Cell Selection When Leaving the RRC Connected Mode

• active set cells as candidates for cell selections; if not, then

• Stored information cell selection Squal > 0Srxlev > 0


Nokia Parameters for Cell Selection• WCEL: QrxlevMin

The minimum required RX level in the cell. This parameter is part of SIB 3.[-115 ... –25] dBm, step 2 dBm; default: -115 dBm.

• WCEL: QqualMin The minimum required quality level in the cell (Ec/No). This parameter is part of SIB 3.[-24 ... 0] dB, step 1 dB, default: -20 dB.

• WCEL: UEtxPowerMaxPRACHThis parameter defines the maximum transmission power level a UE can use on PRACH. The value of the parameter also effects the cell selection and reselection procedures. The value of the parameter is sent to UE in the Cell selection and re-selection of SIB 3 and 4 of the serving cell.[..]


Cell Reselection in the RRC Idle and RRC Connected Mode

S-Criterionfulfilled

cells with highest HCSPriorities &H > 0

measurementthresholds

cells with lower HCS

priority than in serving cell

If No Cellwith H>0accept allneighbors

HCS in use: HCS not in use:



H-Criterionfor fast

moving UEsfor slow

moving UEs

R-Criterioncell ranking




Cell Reselection: Measurement Rules with no HCS

SintrasearchSintersearchSsearchRAT m

No need to measure

neighbour cells

Intra- frequency

Sx=Squal (in FDD mode)

Intra-frequencyInter-frequency

serving cell

Example: Nokia Sintrasearch = 4dB, Sintersearch = 2dB,Ssearch_RAT = 0dB

Where to perform measurements

Intra-frequency

Inter-freqencyInter-RAT


Nokia Parameters for Cell Reselection (Part I)• WCEL: UseOfHCS

This parameter indicates whether the serving cell belongs to a Hierarchical Cell Structure (HCS). This parameter is part of SIB 11/12.0 (HCS not used), 1 (HCS in use); default: 0.

• WCEL: SintrasearchThe threshold for intra-frequency measurements, and for the HCS measurement rules. This parameter is part of SIB 3.[0 ... 20] dB, step 2 dB, default: 4 dB.

• WCEL: Sintersearch The threshold for inter-frequency measurements, and for the HCS measurement rules. This parameter is part of SIB 3.[0 ... 20] dB, step 2 dB, default: 2 dB.

• WCEL: Ssearch_RATThe RAT-specific threshold for inter-RAT measurement rules. This parameter is part of SIB 3.[0 ... 20] dB, step 2 dB, default: 0 dB.


Cell Reselection: Measurement Rules with HCS


Higher HCS priorityIntra-

frequencyInter-

frequency

SlimitsearchRAT m


Equal &higher HCS

priorityIntra-

frequency

Inter-frequenc

y


Srxlevs <= SsearchHCSif

if

Example: Nokia Sintrasearch = 4dB, Sintersearch = 2dB,Ssearch_RAT = 0dB,SsearchHCS = 1dB

Srxlevs > SsearchHCS


Cell Reselection: Measurement Rules with HCS


Higher HCS priorityIntra-

frequencyInter-

frequency

SlimitsearchRAT m


Intra-frequency

Inter-freqencyInter-RAT

Intra-frequenc

y,Inter-

frequency, &

Equal and higher HCS

priority inter RAT

Equal &higher HCS

priorityIntra-

frequency

Inter-frequenc

y


if Srxlevs <= SHCS,RATm measure on all Inter-RAT cells

ifSrxlevs > SHCS,RATm

Example: Nokia Sintrasearch = 4dB, Sintersearch = 2dB,Ssearch_RAT = 0dB, Slimit, searchRAT = 2dB SsearchHCS = -1dB, SHCS_RAT = 1dB


Nokia Parameters for Cell Reselection (Part II)• WCEL: SHCS_RAT

The RAT specific threshold for inter-RAT measurement rules. This parameter is part of SIB 3.[-1 ... 91] dB, step 2 dB, default: -1 dB (UE sets this value to 0).

• WCEL: Slimit_SearchRATThreshold for skipping inter-RAT measurement rules in HCS. Above this RAT specific threshold in the serving UTRA cell, the UE does not need to perform any inter-RATm measurements. This parameter is part of SIB 3.[0 ... 20] dB, step 2 dB, default: 2 dB.

• WCEL: SsearchHCSThreshold for intra- and inter-frequency measurement rules in HCS. Below this limit in the serving cell, the UE initiates measurements of all intra and inter-frequency neighbouring cells of the serving cell. This parameter is part of SIB 3. [-1 ... 91] dB, step 2 dB, default: -1 dB (UE sets this value to 0).


Measurement Rules with HCS and fast moving UEs

NCR = cell reselection threshold (default: 8)TCRmax = time period

NCR/TCRmax

fast moving UE

time

TCrmaxHyst

measurement rule for fast moving UEs

measures neighbouring cells with equal or lower

HCS priority

priorizes cells with lower HCS priority for

re-selection

Example: Nokia TCRmax = 60s,NCR = 8,TCRmaxHyst = 0s

measurement rules forslow moving UEs

measurement rules forslow moving UEs


Nokia Parameters for Cell Reselection (Part III)• WCEL: NCr

This parameter defines the maximum number of cell reselections. If the number of cell reselections during the TCrmax time period exceeds the value of NCr, high mobility has been detected. Not used if TCrmax equals 'not used‚ This parameter is part of SIB 3.[1 ... 16], default: 8.

• WCEL: TCrmaxThe duration for evaluating the allowed amount of cell reselections. If the number of cell reselections during the time period defined by Tcrmax exceeds Ncr, high mobility has been detected. This parameter is part of SIB 3.[0 (= not used), 30, 60, 120, 180, 240] seconds, default: 60 seconds.

• WCEL: TCrmaxHystCell reselection hysteresis for reverting from UE high-mobility measurements. The additional time period before UE reverts to low-mobility measurements. This parameter is part of SIB 3. [0, 10, 20, 30, 40, 50, 60, 70] seconds, default: 0 seconds.


Cell Reselection: H-Criterion (slow moving UE)


only cells with

highest HCSpriorities &

H > 0


cells with lower HCS

priority than in serving cell

H-Criterionfor fast

moving UEsfor slow

moving UEs

R-Criterioncell ranking R-Criterion

cell ranking

Hs = Qmeas,s – Qhcss

Hn = Qmeas,n - Qhcsn – TOn * Ln

accept allneighbours

cells withH>0


no cells withH>0


Qmeas,n - Qhcsn

0time

TOn TOn

PENALTY_TIMEn PENALTY_TIMEn

TOn = 0 TOn = 0

StartTn

StartTn

StopTn

Hs = Qmeas,s – Qhcss

Hn = Qmeas,n - Qhcsn – TOn * Ln

Example:HCS_PRIOn <> HCS_PRIOs

=> Ln = 1 TOn = TEMP_OFFSETn * W(PENALTY_TIMEn – Tn)

Cell Reselection: H-Criterion (slow moving UE) and TOn


Nokia Parameters for Cell Reselection (Part IV)• WCEL: HCS_PRIO

This parameter defines the HCS priority level for a cell. Value 0 indicates the lowest HCS priority and value 7 indicates the highest HCS priority.[0 ... 7], default: 0.

• WCEL: QHCSQuality threshold level for applying prioritised hierarchical cell re-selection for a cell. Part of HCS Serving cell information (Qhcss). This parameter is part of SIB 3. [-24 ... 0] dB, step 0.5 dB, default: -24 dB.

• HOPS: AdjsHCSthresholdDefines the threshold level which must be exceeded by the CPICH Ec/No of the intra-frequency neighbouring cell before the hierarchical cell re-selection becomes possible (Qhcsn).[-24 ... 0] dB, step 0.5 dB, default: -24 dB. HOPI: AdjiHCSthreshold: [-24 ... 0] dB, step 0.5 dB, default: -24 dB. HOPG: AdjgHCSthreshold: [-110 ... -37] dBm, default: -110 dBm.


Nokia Parameters for Cell Reselection (Part IV)• HOPS: AdjsTempOffset1

This parameter is used in the cell ranking between cells when the intra-frequency neighbour cell has the same HCS priority level as the serving cell. [3, 6, 9, 12, 15, 18, 21, 100 (Infinity)] dB, default: 3 dB. HOPI: AdjiTempOffset1, HOPG: AdjgTempOffset1

• HOPS: AdjsTempOffset2This parameter is used in the cell ranking between WCDMA cells when the intra-frequency neighbour cell has the same HCS priority level as the serving cell. [2, 3, 4, 6, 8, 10, 12, 100 (Infinity)] dB, default: 2 dB. HOPI: AdjiTempOffset2

• HOPS: AdjsPenaltyTimeDefines the time period during which the Temporary Offset 1/2 is applied in the cell re-selection procedure for the intra-frequency neighbour cell in question.[0 ... 60] seconds, step 10 seconds, default: 0.HOPI: AdjiPenaltyTime, HOPG: AdjgPenaltyTime


Qmeas,n – Qoffsets,n

PENALTY_TIMEnPENALTY_TIMEn

TOn = 0 TOn=0Start

Tn Start

Tn StopTn

Rs = Qmeas,s + Qhysts

Rn = Qmeas,n - Qoffsets,n - TOn * (1 – Ls)

Example:HCS_PRIOn = HCS_PRIOs

=> Ln = 0 TOn = TEMP_OFFSETn * W(PENALTY_TIMEn – Tn)

Cell Reselection: R-Criterion and TOn

Qmeas,s

temp. offset only used with HCS

TOn

TOn


Rs = Qmeas,s + Qhysts

Rn = Qmeas,n - Qoffsets,n - TOn * (1 – Ls)

Cell Reselection: R-Criterion

Qmeas,n

Qmeas,s

Qm

eas

Rs

Rn

Qoffsets,n

Qhysts

Rn > Rs =>„cell reselection“

Example:HCS_PRIOn <> HCS_PRIOs

=> Ln = 1

Treselection


Nokia Parameters for Cell Reselection (Part V)• WCEL: Qhyst1 (Qhyst2)

Qhyst1 is used for TDD and GSM cells, and for FDD cells when cell selection and re-selection quality measure is set to CPICH RSCP (CPICH Ec/No) (Qhyst1s/ Qhyst2s). This parameter is part of SIB 3.[0 ... 40] dB, step 2 dB, default: 4 dB.

• HOPS: AdjsQoffset1 (AdjsQoffset2) This parameter is used in the cell re-selection and ranking between WCDMA cells. The value of this parameter is subtracted from the measured CPICH RSCP (CPICH Ec/No) of the intra-frequency neighbour cell before the UE compares the quality measure with the cell re-selection/ranking criteria.[-50 ... 50] dB, default: 0 dB. HOPS: AdjsQoffset1 (AdjsQoffset2), HOPG: AdjgQoffset1, (AdjgQoffset2)

• WCELL: TreselectionThe UE triggers the reselection of a new cell if the cell reselection criteria are fulfilled during the time interval Treselection. This parameter is part of SIB 3.[0 ... 31] seconds, default: 0 seconds.

The remaining parameters were already specified under Nokia Parameters for Cell Reselection (Part IV).


Cell Reselection: Measurement Requirements – Serving CellDRXcycle

Nserv

S

S

S S

start measurement on all neighbouring cells

12 seconds

if still no suitable cells

UE initiates cell selection procedures for the

selected PLMN

UE “out of service area”

At least one• CPICH Ec/Io

measurement• CPICH RSCP

measurement• S criterion

evaluation

DRX cycle

if UE RRC idle

if UE in CELL_FACH, CELL_PCH or URA_PCH


Cell Reselection: Measurement – Intra-frequency Cells


measurement, orCPICH RSCP measurement

TmeasureFDD cycle

3 dB

Serving cellIntra-frequency cell

time

UE is capable of evaluating that an intra-frequencycell has become better ranked (if Treselection = 0)

within TmeasureFDD


Cell Reselection: Measurement– Inter-frequency Cells


measurement orCPICH RSCP measurement

(Ncarrier-1) * TmeasureFDD cycle

3 dB for CPICH Ec/Io 5 dB for CPICH RSCP

Serving cellInter-frequency cell

time

UE is capable of evaluating that an inter-frequencycell has become better ranked (if Treselection = 0)

within (Ncarrier -1) * TmeasureFDD


Cell Reselection: Measurement Requirements + GSM Cells

DRX cyclelength [s]

Nserv [number ofDRX cycles]

TmeasureFDD [s](number ofDRX cycles)

TevaluateFDD [s](number ofDRX cycles)

TmeasureGSM [s](number ofDRX cycles)

0.08 4 0.64 (8 DRX cycles)2.56 (32 DRX cycl)2.56 (32 DRX cycl)

0.16 4 0.64 (4) 2.56 (16) 2.56 (16)

0.32 4 1.28 (4) 5.12 (16) 5.12 (16)

0.64 4 1.28 (2) 5.12 (8) 5.12 (8)

1.28 2 1.28 (1) 6.4 (5) 6.4 (5)

2.56 2 2.56 (1) 7.68 (3) 7.68 (3)

5.12 1 5.12 (1) 10.24 (2) 10.24 (2)

In idle mode, UE supports DRX cycles lengths 0.64, 1.28, 2.56 and 5.12 s

Each GSM neighbour

• GSM BCCH carrier RSSI

TmeasureGSM

BSIC at least every 30 seconds for each of the 4 strongest GSM BCCH carriers

30 seconds

+

(DRX cycle length table source: TS 25.133 V3.11.0 chap. 4.2.2.1)


Cell Reselection: Maximum Interruption in Paging Reception

50 ms

50 ms

50 ms

TSI

TBCCH

intra-frequency

inter-frequency

inter-RAT

Cell Selection Reselection

Documents

Transcript of Cell Selection Reselection