07 RN33027EN40GLA0 Intrafrequency HO Signaling

1 Nokia Siemens Networks RN33027EN40GLA0

Radio Access Network Signaling Intra-frequency Handover Signaling


Nokia Siemens Networks Academy

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Intra-frequency Handover Mechanism

Arises when inter-RNC SHO is not possible:

Iur interface (between neighbouring RNCs)

not implemented, or congested, or not

supporting user plane, or due to whatever

reason inhibiting inter-RNC SHO

Soft/er handover Hard handover

Intra-frequency handover

Mobile Evaluated Handover

UE simultaneously connected to many cells

(maximum 3):

Cells belonging to same site (intra-BTS), SOFTER HANDOVER

Cells belonging to different sites (inter-BTS), SOFT HANDOVER

The group of serving cells is called ACTIVE SET


There are two types of handovers, namely soft handover (SHO) and hard handover (HHO) handled by RAN.

Soft Handover

Soft handover operates using Mobile Evaluated Handover (MEHO) principle. This means that UE measures, compares handover thresholds given by RNC and sends measurement report to RNC when the results crosses the intended thresholds. However, the main decision algorithm of SHO is at RNC.

The objectives of soft handover are:

1. Optimum fast power control, i.e., UE is always connected to strongest cells in an area.

2. Seamless handover without disconnection of the user. Macrodiversity combining of UL from multiple cells is also advantage from SHO when UE is at cell boundary with insufficient reception from a single cell.

There are three soft handover types:

1. Softer handover between cells within a BS.

2. Soft handover between BS's within a RNC.

3. Soft handover between BS's controlled by different RNC's.

Hard Handover

In interfrequency hard handover, the decision algorithm considers configuration of radio network, i.e., frequency allocation and neighbour cell definition. In an example scenario, a UE is at a location with possible/needed intefrequency handover. The RNC informs the UE to start periodic reporting of interfrequency measurements. Based on the measurement report sent by UE and control parameters, RNC takes decision. Thus hard hardover is based on Network Evaluated Handover (NEHO).


Soft Handover

Cell 1 Cell 2

UE enters the SHO area,

where coverage area of

cell 1 and 2 overlap

1

1

Cell 2 has available resources,

so its added to the AS. UE is connected both to cell 1 and 2.

2

2

UE exits SHO

area. Theres no reason for

remaining

connected to cell 1.

3

3


Intra-frequency Handover Process

SHO need detection (internal in UE)

(based on RNP parameters)

1

Measurement reporting (from UE to RNC)

(based on RNP parameters)

2

Active Set update

(commanded from RNC to UE)

3


Intra-frequency Handover Event

EVENT 1C REPLACEMENT

EVENT 1B DELETION

EVENT 1A ADDITION

Intra-frequency handover is said to be mobile evaluated, because its up to the mobile

to recognise the need to perform a soft-handover SHO events

The following SHO events are currently implemented:

A monitored CPICH is good enough to be added in the active set

A serving CPICH is no more good enough to stay in the active set

AS is full, a monitored CPICH becomes better than a serving one


Intra-frequency Handover Measurements

The handover measurement is based on CPICH Ec/No.

RSSI

RSCPNoEc /

CPICH Ec/No is the received energy per chip divided by the power density in the WCDMA carrier band:

The accuracy of pilot Ec/No measurements is important for handover performance.

Measurement accuracy depends on the filtering length and mobile speed.

When a UE moves slowly or is stationary, filtering length (in ms) has to be long just enough to avoid fast fades leading to errors and causing unnecessary handovers within a short period. On the other hand long filtering length will cause handover delays to fast moving UEs.

received signal code power

received signal strenght indicator


Events 1A and 1B

What is meant by good enough?

A monitored adjacent cell is ADDED to the Active Set when its good enough to bring a gain.

A serving cell is DELETED from the Active Set when its no longer good enough.


Event 1A : Addition

Event 1A reporting range [dB] (RNP parameter, default 4dB )

Ec/No

Time

Initial cell=CPICH 1

Monitored cell=CPICH 2

Reporting Period

(RNP parameter, default 0.5s )

CPICH 2 is good enough!


Event 1B : Deletion

CPICH 1

CPICH 2

Event 1B reporting range [dB] (RNP parameter, default 6dB )

Reference cell

CPICH 1 is no longer good enough!

Ec/No

Time


Event 1C : Replacement

Ec/No

Time

CPICH 1

CPICH 3

Monitored cell= CPICH 4

Event 1C margin [dB] (RNP parameter, default 4dB )

CPICH 2

Active set is FULL


Soft Handover: Radio Link Addition (1/3)

UE Node B (SRNC)

Node B (DRNC)

1. Measurement Report

RRC RRC

SRNC DRNC

2. Radio Link Setup Request

RNSAP RNSAP

3. Radio Link Setup Request

C-NBAP C-NBAP

4. Radio Link Setup Response

C-NBAP C-NBAP

RNSAP RNSAP

5. Radio Link Setup Response

AAL2SIG

6. Establish Request

AAL2SIG

Not in

IP-based

Iur


1. Measurement Report: event triggered, e.g. a cell entered the reporting range

2. The S-RNC requests the setup of a radio link via a new cell, which is controlled by another RNC. Parameters: Cell-id, Transport Format Set per DCH, Transport Format Combination Set,Frequency,

Uplink Scrambling Code

3. On availability of resources asked for in section 1., the D-RNC requests resources from the Node B.

Parameters: Cell-id, Transport Format Set per DCH, Transport Format Combination Set, Frequency, Uplink Scrambling Code

4. Successful resource allocation by the Node B.Parameters: Signaling link termination, AAL2 address, AAL2 Binding Identities for Transport bearers

5. Feedback from DRNC to SRNC.

Parameters: AAL2 address, AAL2 Binding Identities for Transport bearers, Neighbouring cell information

6.-9. AAL2 based transport bearer resources are set up on Iur and Iub.

The Connection Element Identifiers and the AAL2 Binding ID are transferred to tie transport bearer and DCH together.

10-11. The Node B notifies uplink the Drift-RNC of the establishment of uplink synchronization.

The D-RNC passes the notification on to the Serving RNC by using the RNSAP-Layer.

12-13. By exchanging DCH-Frame protocol frames for sending these messages Node B and

D-RNC establish uplink and downlink synchronisation for the data transport bearer(s).



UE Node B (SRNC)

Node B (DRNC)

SRNC DRNC

7. Establish Confirm

8. Establish Request

9. Establish Confirm

AAL2SIG AAL2SIG

AAL2SIG

AAL2SIG

AAL2SIG

AAL2SIG

10. Radio Link Restore Indication

D-NBAP D-NBAP

11. Radio Link Restore Indication

RNSAP RNSAP

DCH- FP 12. Downlink Synchronisation

13. Uplink Synchronisation

DCH- FP

DCH- FP

DCH- FP

Not in

IP-based

Iur

Not in

IP-based

Iub



UE Node B (SRNC)

Node B (DRNC)

SRNC DRNC

14. Active Set Update

RRC RRC

15. Active Set Update Complete

RRC RRC


Soft Handover: Radio Link Deletion (1/2)

UE Node B (SRNC)

Node B (DRNC)

SRNC DRNC

1. Active Set Update

RRC RRC

2. Active Set Update Complete

RRC RRC 3. Radio Link

Deletion Request

RNSAP RNSAP

4. Radio Link Deletion Request

D-NBAP D-NBAP

5. Radio Link Deletion Response

D-NBAP D-NBAP 6. Radio Link

Deletion Response

RNSAP RNSAP


Soft Handover: Radio Link Deletion (2/2)

UE Node B (SRNC)

Node B (DRNC)

SRNC DRNC

AAL2SIG

7. Release Request

AAL2SIG

8. Release Confirm

9. Release Request

10. Release Confirm

AAL2SIG AAL2SIG

AAL2SIG

AAL2SIG

AAL2SIG

AAL2SIG

Not in

IP-based

Iur

Not in

IP-based

Iub


Message Example: MEASUREMENT CONTROL (1/3)

MEASUREMENT CONTROL

DL-DCCH-Message

integrityCheckInfo

messageAuthenticationCode: '00000001 11010010

00111010 10110100'B

rrc-MessageSequenceNumber: 3

message

measurementControl

r3

measurementControl-r3

rrc-TransactionIdentifier: 0

measurementIdentity: 1

measurementCommand

setup

intraFrequencyMeasurement

intraFreqCellInfoList

removedIntraFreqCellList

removeAllIntraFreqCells: NULL

newIntraFreqCellList

NewIntraFreqCell

intraFreqCellID: 0

cellInfo

modeSpecificInfo

fdd

primaryCPICH-Info

primaryScramblingCode: 30

readSFN-Indicator: TRUE

tx-DiversityIndicator: FALSE

NewIntraFreqCell

intraFreqCellID: 1

cellInfo

modeSpecificInfo

fdd

primaryCPICH-Info


readSFN-Indicator: TRUE

tx-DiversityIndicator: FALSE

Cell with

PSC 30

Cell with

PSC 50



intraFreqMeasQuantity

filterCoefficient: fc3

modeSpecificInfo

fdd

intraFreqMeasQuantity-FDD: cpich-Ec-N0

intraFreqReportingQuantity

activeSetReportingQuantities

sfn-SFN-OTD-Type: noReport

cellIdentity-reportingIndicator: FALSE

cellSynchronisationInfoReportingIndicator: TRUE

modeSpecificInfo

fdd

cpich-Ec-N0-reportingIndicator: TRUE

cpich-RSCP-reportingIndicator: TRUE

pathloss-reportingIndicator: FALSE

monitoredSetReportingQuantities

sfn-SFN-OTD-Type: noReport

cellIdentity-reportingIndicator: FALSE

cellSynchronisationInfoReportingIndicator: TRUE

modeSpecificInfo

fdd

cpich-Ec-N0-reportingIndicator: TRUE

cpich-RSCP-reportingIndicator: TRUE

pathloss-reportingIndicator: FALSE

Use CPICH Ec/No for

interfrequency measurement

Active set reporting

Monitored set reporting



reportCriteria

intraFreqReportingCriteria

eventCriteriaList

IntraFreqEventCriteria

event

e1a

triggeringCondition: monitoredSetCellsOnly

reportingRange: 6

w: 0

reportDeactivationThreshold: t2

reportingAmount: ra-Infinity

reportingInterval: ri0-5

hysteresis: 0

timeToTrigger: ttt100

reportingCellStatus

allActiveplusMonitoredSet: viactCellsPlus2


event

e1b

triggeringCondition: activeSetCellsOnly

reportingRange: 8

w: 0

hysteresis: 0


reportingCellStatus

withinActiveSet: e3


event

e1c

replacementActivationThreshold: t3

reportingAmount: ra-Infinity

reportingInterval: ri0-5

hysteresis: 4


reportingCellStatus

allActiveplusMonitoredSet: viactCellsPlus2

measurementReportingMode

measurementReportTransferMode: acknowledgedModeRLC

periodicalOrEventTrigger: eventTrigger

1A

1C

1B


Message Example: MEASUREMENT REPORT (1/2)

MEASUREMENT REPORT

UL-DCCH-Message

integrityCheckInfo


10011001 01101100'B


message

measurementReport

measurementIdentity: 1

measuredResults

intraFreqMeasuredResultsList

CellMeasuredResults

cellSynchronisationInfo

modeSpecificInfo

fdd

countC-SFN-Frame-difference

countC-SFN-High: 5

off: 6

tm: 12288

modeSpecificInfo

fdd

primaryCPICH-Info


cpich-Ec-N0: 40

cpich-RSCP: 47

CellMeasuredResults

cellSynchronisationInfo

modeSpecificInfo

fdd

countC-SFN-Frame-difference

countC-SFN-High: 9

off: 10

tm: 31041

modeSpecificInfo

fdd

primaryCPICH-Info


cpich-Ec-N0: 35

cpich-RSCP: 44

Cell with

PSC 30

Cell with

PSC 50


Message Example: MEASUREMENT REPORT (2/2)

eventResults

intraFreqEventResults

eventID: e1a

cellMeasurementEventResults

fdd

PrimaryCPICH-Info


Event 1A triggered for cell with

PSC 50


Message Example: ACTIVE SET UPDATE/ACTIVE SET UPDATE COMPLETE - Addition

ACTIVE SET UPDATE

DL-DCCH-Message

integrityCheckInfo

messageAuthenticationCode: '11100110 01000010 10011110 01100100'B


message

activeSetUpdate

r3

activeSetUpdate-r3


maxAllowedUL-TX-Power: 24

rl-AdditionInformationList

RL-AdditionInformation

primaryCPICH-Info


dl-DPCH-InfoPerRL

fdd

pCPICH-UsageForChannelEst: mayBeUsed

dpch-FrameOffset: 121

dl-ChannelisationCodeList

DL-ChannelisationCode

sf-AndCodeNumber

sf128: 5

tpc-CombinationIndex: 1

tfci-CombiningIndicator: FALSE

Add cell

with PSC 50

ACTIVE SET UPDATE COMPLETE

UL-DCCH-Message

integrityCheckInfo


11110001 01110000'B


message

activeSetUpdateComplete



Message Example: ACTIVE SET UPDATE/ACTIVE SET UPDATE COMPLETE - Deletion

ACTIVE SET UPDATE

DL-DCCH-Message

integrityCheckInfo


10100101 00111111'B


message

activeSetUpdate

r3

activeSetUpdate-r3


maxAllowedUL-TX-Power: 24

rl-RemovalInformationList

PrimaryCPICH-Info


Delete cell

with PSC 50

ACTIVE SET UPDATE COMPLETE

UL-DCCH-Message

integrityCheckInfo

messageAuthenticationCode:

'00111110 11001010 01001011

00000011'B


message

activeSetUpdateComplete



Review Questions

1. What is the correct sequence of events (1A/1B/1C) when a UE moves from cell 1 to cell 2 with soft handover region in the middle?

2. Which RRC message is used to inform UE to do soft handover?

Cell 1 Cell 2


Use the Iub trace to fill in the tables below

Exercise 10

BTS ID : 1 Cell ID : 1 Primary SC= 30

1-33 : CNBAP 1-34 : DNBAP

1-35 : AAL2SIG 1-36 : AAL2UP (HSDPA)

1-37 : AAL2UP (DCH)

BTS ID : 3 Cell ID : 3 Primary SC= 50

1-33 : CNBAP 1-34 : DNBAP

1-35 : AAL2SIG 1-36 : AAL2UP (HSDPA)

1-37 : AAL2UP (DCH)


Use the Iub trace to fill in the tables below Exercise 10

Message ID Message Name Information

313 RRC Connection Request Establishment cause=

444 Primary scrambling code=

Measurement Report Event 1A, Primary scrambling code=

Radio Link Setup Request Cell ID=

567 Establish Request BTS ID= , CID=

581 Establish Request BTS ID= , CID=

Active Set Update Add primary scrambling code= DL channelisation code: SF= , code number=

Measurement Report Event 1B, Primary scrambling code=

Active Set Update Remove Primary scrambling code= Cell ID=

1571 Cell ID=

1588 Release Request BTS ID= , CID=

1596 Release Request BTS ID= , CID=

07 RN33027EN40GLA0 Intrafrequency HO Signaling

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