Inter Frequency Handover 3a44e

Inter Frequency Handover UMTS on 2nd Carrier

Inter-Frequency Handover

• Inter-frequency handover (IFHO) allows the UTRAN to switch the serving frequency of the UE during dedicated channel state. • Like the inter-RAT handover, the inter-frequency handover procedure consists of two steps: – The inter-frequency measurements – The inter-frequency handover

• Since IFHO is a hard handover, it employs compressed mode to facilitate inter-frequency measurements.

Enabling IFHO RNC Parameter

Level

at&t Default

fddIfHoSupp

RNC

FALSE *

defaultHoType

RNC

1*

Level

at&t Default

Comment Indicates if the RNC s Inter-Frequency Handover. * Should be set to TRUE to enable IFHO. For performing IFHO or IRAT HO for UEs that have drifted to another RNC, the SRNC needs to know the handover type for cells in the DRNC. This information is set in defaultHoType in the WcdmaCarrier MO and is defined for each carrier that serves as a DRNC. IFHO_PREFERRED = 0, GSM_PREFERRED = 1 NONE = 2 *Should be set to 0 to allow IFHO in the drift RNC.

Cell Parameter

hoType

Cell

1*

Comment This parameter indicates per cell if GSM HO, IFHO or none shall be attempted: IFHO_PREFERRED = 0, GSM_PREFERRED = 1 NONE = 2 * Should be set to 0 to enable IFHO.

UeRc Parameter

Level

at&t Default

Comment

C_IfHoAllowed

UeRc

0*

Indicates per UeRc state if Inter-Frequency HO is allowed; 0 = Not Allowed, 1 = Allowed * Should be set to 1 to enable IFHO

C_gsmHoAllowed

UeRc

1

Indicates per UeRc state if Inter-RAT HO is allowed; 0 = Not Allowed, 1 = Allowed

IFHO Block Diagram 1 2 This part is common to IF and IRAT

Call Start: DCH ESTABLISHED AND UE CAPABILITIES CHECK

CONNECTION QUALITY MONITORING START

3

BAD QUALITY DETECTED (event 2d or 6d) no yes

4

 IF neighbours exist AND  hoType condition fullfilled AND  IFHO allowed for current UeRc IF EVALUATION STOP

IF EVALUATION START (Compressed Mode)

4a 4b AS or RAB state change

 IF neighbours not available OR  IFHO not allowed for current UeRc

5 6

GOOD QUALITY DETECTED (event 2f or 6b)

yes

IFHO CONDITIONS FULLFILLED (event 2b)

IFHO EXECUTION

UE moves to new carrier

2

Connection Quality Monitoring

Connection Quality Monitoring consists of measurements based on: •DL P-ICH Ec/No and DL P-ICH RS measurements running in parallel; •UL UE Tx power measurements.

uplink

Ue Tx Power downlink

 quality = good if all measurement items are good

ICH RS ICH Ec/No

 quality = bad if at least one measurement is bad CONNECTION QUALITY MONITORING

Configurable thresholds for DL based event triggering

RS

Ec/No

bad

good

bad

UeTxPwr

good

good

bad

Max UE Tx pwr for UL based event triggering

Bad Quality Detected 3

UE

BAD QUALITY DETECTED (event 2d or 6d)

RNC RRC Connection Request

MEASUREMENT REPORT Reporting event type • Event 2d with indication if it is referring to Ec/No or RS measurements • Event 6d (UETX pwr)

RRC Connection Setup RRC Connection Setup Complete RRC Measurement Control RRC Measurement Report

Connection Quality Status Update e2d Ec/No E

E e2f Ec/No

OR

e2d RS

R

R

OR

Ec/No

RS

UeTx

e6d

T

T

e2f RS e6b Event 2d: If the WCDMA quality on the current used frequency goes below usedFreqThresh2d threshold minus the corresponding hysteresis, and the condition is maintained during timeToTrigger2d. (can be EcNo or Rs)

Event 6d: If the UE Tx Power reaches the maximum and the condition is maintained during a time period timeToTrigger6d Event 2f: If the WCDMA RAN quality on the current used frequency goes above usedFreqRelThresh2f+usedFreqThresh2d threshold plus the corresponding hysteresis, and the condition is maintained during timeToTrigger2f. (can be EcNo or Rs) Event 6b: If the UE Tx Power goes below ueTxPowerThresh6b threshold, and the condition is maintained during a time period timeToTrigg6b

IFHO Evaluation Start 4 Compress Mode

•

Compressed Mode Methodology is dependant on the Bearer type: – For conversational bearers, compressed mode is accomplished by accelerating the data transmission rate (by halving the spreading factor) for a brief period of time to allow a break in transmission for IFHO OR IRAT measurements – For non-conversational class bearers, data transmission is briefly suspended by higher layers (layer2) to allow for IFHO or IRAT measurements to be performed

•

•

Due to limitations in the Compressed Mode gap patterns used, measurements for Inter-Frequency Evaluation and Inter-RAT Evaluation are not performed simultaneously. A decision has to be made on whether evaluation should be made for Inter-Frequency handover or Inter-RAT handover or Inter-RAT CellChange. The type of handover to be attempted is set by the parameter hoType (IFHO_PREFERRED, GSM_PREFERRED, NONE) and per carrier frequency for external DRNC cells (defaultHoType).

IFHO Condition Fulfilled 5 IFHO CONDITIONS FULFILLED (event 2b)

UE

RRC Connection Request

RNC Ec/No or RS Used frequency

RRC Connection Setup

Ec/No / RS Non-used frequency

RRC Connection Setup Complete RRC Measurement Control

Execute handover (event 2b)

RRC Measurement Report

Start IF meas.

RRC Measurement Control RRC Measurement Report

Condition on used frequency: • Ec/No < UsedFreqThresh2dEcno + UsedFreqRelThresh4_2bEcno - Hyst4_2b / 2 • RS < UsedFreqThresh2dRs + UsedFreqRelThresh4_2bRs - Hyst4_2b / 2 • RS < UsedFreqThresh2dRs + UsedFreqRelThresh4_2bRs + utranRelThreshRs - Hyst4_2b / 2

AND •Depending on whether the IF measurements were started due to Ec/No or •RS or •UE Tx power time

Condition on non-used frequency: • Ec/No > NonUsedFreqThresh4_2bEcno + Hyst4_2b / 2 AND • RS > NonUsedFreqThresh4_2bRs + Hyst4_2b / 2

5

IFHO Condition Fulfilled

• If the Inter-Frequency Handover Evaluation receives an event 2b MEASUREMENT REPORT while it is already processing another MEASUREMENT REPORT, the new one is buffered. • There is one buffer for the only specified event 2 MEASUREMENT REPORT. The buffer holds only the last received report so a new received report overwrites a report already in the buffer. • If no event 2b report is buffered, then IFHO attempts shall be repeated. The number of

IFHO Execution 6 Flow Diagram

• The Execution part assesses the amount of resources in the target WCDMA RAN cell, according to the proposal received from the Inter-Frequency Handover Evaluation algorithm. It interacts with the Capacity Management functions. • If the attempt succeeds, the actions necessary to fulfill the handover proposal are executed.

• If execution fails, exception handling is performed to return to stable situation and keep the UE connection on the source WCDMA RAN frequency.

IFHO EXECUTION

IFHO – Parameters Parameter

usedFreqThresh2dEcNo

usedFreqThresh2dRS

timeToTrigger2dEcNo

Level

Cell

Cell

RNC

at&t Default

-12 (HHO) -15 (SHO)

Comment

Threshold for event 2d (the estimated quality of the currently used WCDMA RAN frequency is below a certain threshold). Used if measurement quantity is configured to be Ec/No.

-103 to -109 (HHO) -112 (SHO)

Threshold for event 2d (the estimated power level of the currently used WCDMA RAN frequency is below a certain threshold). Used if measurement quantity is configured to be Rs.

320

Time in milliseconds (ms) between detection of event 2d and sending of the measurement report, when the measurement quantity is ICH EC/NO. Time in milliseconds (ms) between detection of event 2d and sending of the measurement report, when the measurement quantity is ICH RS.

timeToTrigger2dRS

RNC

320

hysteresis2d

RNC

4

Hysteresis for event 2d (Unit: 0.5 dB).

usedFreqRelThresh2fEcno

RNC

2

Relative threshold for event 2f vs event 2d for the used frequency when the measurement quantity is Ec/No.

usedFreqRelThresh2fRs

RNC

6

Relative threshold for event 2f vs event 2d for the used frequency when the measurement quantity is RS.

timeToTrigger2fEcNo

RNC

640

Time in milliseconds (ms) between detection of event 2f and sending of the measurement report, when the measurement quantity is ICH EC/NO. Time in milliseconds (ms) between detection of event 2f and sending of the measurement report, when the measurement quantity is ICH RS.

timeToTrigger2fRS

RNC

640

hysteresis2f

RNC

2

Hysteresis for event2f (Unit: 05.dB).

IFHO – Parameters Parameter

Level

at&t Default

ueTxPowerThresh6b

RNC

21

Comment Threshold for event 6b. Time between detection of event 6b and sending of the measurement report.

timeTrigg6b

timeTotrigger6d

usedFreqRelThresh4_2bEcNo

RNC

1280

RNC

N/A 320 *

RNC

Time between detection of event 6d and sending of the measurement report * Default value by Ericsson – has replaced timeTrigg6a

-1

Relative threshold for event 2b vs event 2d, when the 2d measurement with measurement quantity ICH EC/NO was started. This parameter is used to compute the absolute 2b Ec/No used frequency threshold, by adding it to the current 2d Ec/No threshold (absolute 2b Ec/No used frequency threshold = usedFreqThresh2dEcno + usedFreqRelThresh4_2bEcno).

usedFreqRelThresh4_2bRS

RNC

-3

Relative threshold for event 2b vs event 2d when the 2d measurement with measurement quantity ICH RS was started. This parameter is used to compute the absolute 2b Rs threshold, by adding it to the current 2d Rs threshold (absolute 2b Rs used frequency threshold = usedFreqThresh2dRs + usedFreqRelThresh4_2bRs).

nonUsedFreqThresh4_2bEcNo

RNC

-13

Threshold for measurement 4 event 2b for the non-used frequencies when the measurement quantity is Ec/No.

nonUsedFreqThresh4_2bRS

RNC

-105

Threshold for measurement 4 event 2b for the non-used frequencies when the measurement quantity is RS.

IFHO – Parameters Parameter

utranRelThreshRS

timeTrigg4_2b

Level

RNC

RNC

at&t Default

Comment

5

Relative threshold used during bad connection quality, when the measurement quantity is ICH RS. The absolute 2b used frequency threshold will be calculated as: absolute 2b Rs used frequency threshold = usedFreqThresh2dRs + usedFreqRelThresh4_2bRs + utranRelThreshRs.

100

Time between detection of event 2b and sending of the measurement report, for measurement 4. Unit: 1 ms

Hyst4_2b

RNC

10

Hysteresis for measurement 4 event 2b. Unit: 0.1dB

IfhoAmountPropRepeat

RNC

4

Maximum number of repeated proposals of non-used frequency cell(s) for handover based on the same measurement report

5

Minimum time interval between proposals of the same non-used frequency cell for handover based on the same measurement report. Unit: 0.2 seconds

IfHoPropRepeatInterval

RNC

IFHO 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.



Call continuity to for mobile units leaving and entering the multi-carrier area while in Cell_DCH stateis usually provided through IFHO

UMTS F2

UMTS F1

IFHO Scenario – Overlay Cell Reselection

IRAT

IFLS

IFHO

IRAT

IFHO

IFHO

IFHO

IRAT

IRAT

IRAT

F2

IRAT

GSM

B

B

B B

UMTS F2

B

B B B UMTS F1

B



F1 – IRAT and F2 - IFHO



Border setting for 2d thresholds for EDGE f2 cells. usedFreqThresh2dEcNo, usedFreqThresh2dRS.



Ensure quality on non used freq before event 2b. nonUsedFreqThresh4_2bEcNo, nonUsedFreqThresh4_2bRS These thresholds should always be higher than 2d triggers so ping-pong hard handovers don’t occuer.

F1

IFHO 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 F2 UMTS F1

IFHO Scenario – Infill sites Cell Reselection

IFHO

IRAT

IFHO IRAT

IFHO

F2

IFHO

IRAT



F1 – IRAT/IFHO and F2 IFHO



2d thresholds for F2 are set to border settings for quicker IFHO 2d thresholds for F1 are set to interior settings for slower IFHO.

F1



GSM Small road Drop Call!

UMTS F2 UMTS F1

Due to limitations in the Compressed Mode gap patterns used, measurements for Inter-Frequency Evaluation and InterRAT Evaluation are not performed simultaneously. A decision has to be made on whether evaluation should be made for Inter-Frequency handover or Inter-RAT handover or Inter-RAT CellChange.

Highway