Idle Mode Behavior

UMTS on 2nd Carrier

Idle Mode - Cell Selection • In the initial cell selection procedure

UE scans all WCDMA radio frequency channels to find a suitable cell. On each carrier, the UE searches for the cell with the highest signal level, according to the cell search procedure, and reads the system information on the BCCH.

UMTS F1

UMTS F2

In a dual carrier environment, UEs will tend to select onto f1 first an then move onto f2 via idle mode reselection.

Idle Mode - Cell Selection Background Information for Cell Selection • Cell Selection occurs if

Squal > 0 and Srxlev > 0

• With the att baseline parameters

Squal = Qqualmeas – qQualMin = Qqualmeas – (-19) Srxlev = Qrxlevmeas – qRxLevMin – Pcompensation = Qrxlevmeas – (-115) – max (maxTxPowerUl - P, 0) = Qrxlevmeas – (-115) – max(24 – 21, 0) = Qrxlevmeas + 115 – 3 P is the output power class of the UE

Thus, Cell Selection occurs when

Qqualmeas > -19 dB -> CPICH Ec/No measured by UE Qrxlevmeas > -112 dBm -> CPICH RSCP measured by UE

Idle Mode - Cell Reselection • The UE performs the cell reselection

procedure in the following cases:

– When the cell on which it is camping is no longer suitable

– When the UE, in "camped normally" state, has found a neighboring cell better than the cell on which it is camping

– When the UE is in "limited service" state on an acceptable cell

• The UE reselects the new cell if it is better ranked than the serving cell during a time interval treSelection.

Idle Mode - Cell Reselection Background Information for Cell Reselection Ranking for UMTS neighbors will only occur if:

Squal > 0 and Srxlev > 0

Ranking with qualMeasQuantity = 1 (RSCP)

R(serving) = Qmeas(serving) + qHyst1 = Qmeas(serving) + 2 R(neighbor) = Qmeas(neighbor) - qOffset1sn = Qmeas(neighbor) - 0

Ranking with qualMeasQuantity = 2 (Quality) R(serving) = Qmeas(serving) + qHyst2 = Qmeas(serving) + 2 R(neighbor) = Qmeas(neighbor) - qOffset2sn = Qmeas(neighbor) – 0

The parameters make the serving cell stronger and the neighboring cell weaker. This is done to prevent continuous cell reselections along the cell border.

-> used in AT&T

Idle Mode - Measurement • UE measures and evaluates the neighbour cells listed in system SIB11. • Intra-frequency:

– Squal > Sintrasearch (12dB), No measurement – Squal <= Sintrasearch, perform measurement (QualMeas <=-7) – Sintrasearch = 0, parameter is not sent and measurements are performed all the time.

• Inter-frequency: – Squal > Sintersearch(10dB), No measurement – Squal <= Sintersearch, perform measurement (QualMeas <=-9) – Sintersearch = 0, parameter is not sent and measurements are performed all the time.

Inter-RAT:

– Squal > SRatsearch(4dB) AND SRxlev > sHcsRat (-105 taken as 0 by the UE), No measurement

– Squal <= SRATsearch (QualMeas <=-15) OR SRxlev <= sHcsRAT (RxLevMeas<=-115), perform measurement

Idle Mode – Cell_Fach Measurements • The parameters fachMeasOccaCycLenCoeff and interFreqFddMeasIndicator

are used to control the UE measurement activities for inter-frequency and inter-RAT neighbors.

• fachMeasOccaCycLenCoeff > 0, perform inter-frequency and inter-RAT measurements.

• If fachMeasOccaCycLenCoeffis = 0 (at&t) the parameter is not sent in system information and the UE is not allowed to perform measurements on other frequencies and RATs.

• If interFreqFddMeasIndicator = TRUE, the UE will evaluate cell reselection criteria on inter-frequency cells in state CELL_FACH.

• If interFreqFddMeasIndicator = FALSE, the UE will neither perform measurements nor evaluate cell reselection criteria on inter-frequency cells in state CELL_FACH

Idle Mode – Parameters

Parameter Level at&t Default Comment

qQualMin Cell -19

Cell selection/reselection in idle mode. Minimum required (acceptable) quality level in

the cell (dB).

qRxLevMin Cell -115

Cell selection/reselection in idle mode. Minimum required (acceptable) quality level in

the cell (dBm).

sInterSearch Cell 22(10dB) Trigger measurements of F2. Higher the value, quicker it is.

qOffset1sn Nbr 0

Signal strength offset between source and target cell to be used for cell ranking based

on CPICH RSCP. The parameter is defined per WCDMA neighbor relation and per

GSM neighbor relation (dB). Lower the value, the quicker it is

qOffset2sn Nbr 0

Signal strength offset between source and target cell to be used for cell ranking based

on CPICH Ec/No (dB). The parameter is defined per WCDMA neighbor relation.

Lower the value, the quicker it is

treSelection Cell 1 Time to reselect.

interFreqFddMeas

Indicator Cell 1

Indicates if the UE is required to perform measurements and evaluate the cell

reselection criteria for Interfrequency neighbors in state CELL_FACH. The parameter is

defined per cell (CELL_FACH not used by AT&T currently).

fachMeasOccaCy

cLenCoeff Cell 0

Used by the UE to calculate the FACH measurement occasions

(CELL_FACH not used by AT&T currently).

Idle Mode Scenario – Overlay

Adding the second carrier where capacity increase is most needed.

As the traffic in the network increases, the second carrier coverage is then expanded gradually.

Service continuity for call

origination while in idle mode is

provided through inter-

frequency cell reselection.

UMTS F1

UMTS F2

UMTS F1

Idle Mode Scenario – Overlay

One-way neighbour cell relations are defined from the f2 cell to all surrounding f1 cells

UMTS F2

qRxLevMin is set to -107 for

border cells. Similar to f1 and

irat border. Sintersearch on f2 border

cells should be 0. So UEs

camped on these border

cells are always searching

for better f1 cells. Interior

F1/F2 cells can have the

sintersearch = 21 (8dB) so

UEs start searching when

EcIo is below -11.

Two-way neighbour relations

are defined only between the

underlaying f1 cell and

overlaying f2 cell.

F1 F1 F1 F1 F1

F2 F2 F2

qOffsetsn =0, all cells are treated equally in idle mode.

B

B

B

B B

B

B

B B

Idle Mode Scenario – Infill sites

A F2 cell is added where there is a coverage hole.

Scenario is only caused when F1 cell cannot be built in the area.

Requires the spectrum to be cleared for both band!

Long term plan should be to either

convert the F2 cell into F1 or dual

banding the infill site

UMTS F1

UMTS F2

Idle Mode Scenario – Infill sites qRxLevMin is set to -107 for

F2. qRXLevMin remains at -

115 for F1 cells but can be

set to -107 if the coverage

hole is large.

Sintersearch on F2 cell

should be 0. So UEs

camped on the cell are

always searching for better

f1 cells.

Two-way neighbour relations

are defined between the first

tier F1 and F2 cells

F1 F1 F1 F1

F2

qOffsetsn =0, all cells are treated equally in idle mode.

UMTS F1

UMTS F2

One way nbrs are defined to

second tier F1 cells.