Inter-RAT Handover Description

Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd

RAN

Inter-RAT Handover Description Issue 02

Date 2008-07-30

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RAN Inter-RAT Handover Description Contents

Issue 02 (2008-07-30) Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd

i

Contents

1 Inter-RAT Handover Change History ................................................................................1-1

2 Inter-RAT Handover Introduction......................................................................................2-1

3 Inter-RAT Handover Algorithms........................................................................................3-1 3.1 UMTS-to-GSM Handover Types............................................................................................................. 3-1 3.2 UMTS-to-GSM Handover Procedure ...................................................................................................... 3-2

3.2.1 Coverage-based UMTS-to-GSM Handover Procedure.................................................................... 3-3 3.2.2 QoS-based UMTS-to-GSM Handover Procedure............................................................................ 3-4 3.2.3 Load-based UMTS-to-GSM Handover Procedure........................................................................... 3-5 3.2.4 Service-based UMTS-to-GSM Handover Procedure ....................................................................... 3-6

3.3 Preconditions for UMTS-to-GSM Handover ........................................................................................... 3-6 3.3.1 Service Handover Indicator............................................................................................................ 3-7 3.3.2 Capabilities of Deciding UMTS-to-GSM Handover...................................................................... 3-17 3.3.3 Rules for Enabling UMTS-to-GSM Handover .............................................................................. 3-17

3.4 UMTS-to-GSM Handover Measurement............................................................................................... 3-20 3.4.1 UMTS-to-GSM Handover Measurement Switches ....................................................................... 3-20 3.4.2 UMTS-to-GSM Handover Measurement Report Modes................................................................ 3-21 3.4.3 UMTS-to-GSM Handover Measurement Events........................................................................... 3-22 3.4.4 UMTS-to-GSM Handover Neighboring Cell Combination Algorithm........................................... 3-25 3.4.5 UMTS-to-GSM Handover Measurement Quantity........................................................................ 3-25 3.4.6 UMTS-to-GSM Handover L3 Filtering ........................................................................................ 3-25 3.4.7 UMTS-to-GSM Handover Compressed Mode .............................................................................. 3-25 3.4.8 BSIC Verification Requirements for GSM Cells ........................................................................... 3-25

3.5 UMTS-to-GSM Handover Decision and Execution ............................................................................... 3-25 3.5.1 Coverage-Based and QoS-Based UMTS-to-GSM Handover Decision and Execution .................... 3-25 3.5.2 Load-Based and Service-Based UMTS-to-GSM Handover Decision and Execution...................... 3-25 3.5.3 UMTS-to-GSM Handover Retry .................................................................................................. 3-25 3.5.4 UMTS-to-GSM Multimedia Fallback........................................................................................... 3-25 3.5.5 UMTS-to-GSM Handover in the PS Domain with NACC or PS Handover.................................... 3-25

3.6 Inter-RAT Handover of HSDPA ............................................................................................................ 3-25 3.7 Inter-RAT Handover of HSUPA ............................................................................................................ 3-25 3.8 GSM-to-UMTS Handover .................................................................................................................... 3-25 3.9 Interoperability Between Inter-RAT Handover and Inter-Frequency Handover ....................................... 3-25



Contents RAN

Inter-RAT Handover Description

ii Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd

Issue 02 (2008-07-30)

3.10 Signaling Procedures for Inter-RAT Handover..................................................................................... 3-25 3.10.1 UMTS-to-GSM Handover in CS Domain ................................................................................... 3-25 3.10.2 UMTS to GSM Handover in PS Domain .................................................................................... 3-25 3.10.3 UMTS-to-GSM Handover in Both CS Domain and PS Domain .................................................. 3-25 3.10.4 GSM-to-UMTS Handover in CS Domain ................................................................................... 3-25 3.10.5 GSM-to-UMTS Handover in PS Domain ................................................................................... 3-25

4 Inter-RAT Handover Parameters ......................................................................................4-25

5 Reference Documents.........................................................................................................5-25



RAN Inter-RAT Handover Description 1 Inter-RAT Handover Change History


1-1

1 Inter-RAT Handover Change History

Inter-RAT Handover Change History provides information on the changes between different document versions.

Document and Product Versions

Document Version RAN Version RNC Version NodeB Version

02 (2008-07-30) 10.0 V200R010C01B061 V100R010C01B050 V200R010C01B041

01 (2008-05-30) 10.0 V200R010C01B051 V100R010C01B049 V200R010C01B040

Draft (2008-03-20) 10.0 V200R010C01B050 V100R010C01B045

There are two types of changes, which are defined as follows:

l Feature change: refers to the change in the feature of a specific product version. l Editorial change: refers to the change in information that has already been included, or

the addition of information that was not provided in the previous version.

02 (2008-07-30) This is the document for the second commercial release of RAN10.0.

Compared with 01 (2008-05-30) of RAN10.0, issue 02 (2008-07-30) of RAN10.0 incorporates the changes described in the following table.



1 Inter-RAT Handover Change History RAN


1-2 Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd

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Change Type Change Description Parameter Change

Feature change None The parameters that are changed to be non-configurable are listed as follows: l Service Handover Indicator l Service parameter index l Required 2G Capability l Inter-RAT H handover decision

THD

Editorial change

A parameter list is added. See chapter 4 Inter-RAT Handover Parameters.

None

01 (2008-05-30) This is the document for the first commercial release of RAN10.0.

Compared with draft (2008-03-20) of RAN10.0, issue 01 (2008-05-30) of RAN10.0 incorporates the changes described in the following table.


Feature change None None

Editorial change

General documentation change: l The Inter-RAT Handover Parameters is

removed because of the creation of RAN10.0 parameter reference.

l The structure is optimized.

None

Draft (2008-03-20) This is a draft of the document for the first commercial release of RAN10.0.

Compared with issue 02 (2007-12-24) of RAN6.1, issue Draft (2008-03-20) of RAN10.0 incorporates the changes described in the following table.



RAN Inter-RAT Handover Description 1 Inter-RAT Handover Change History


1-3


The description of inter-RAT handover based on QoS is added, as listed below: l 3.1 UMTS-to-GSM

Handover Types l 3.2 UMTS-to-GSM

Handover Procedure l "Triggering of Event 3A"

in 3.4.3 UMTS-to-GSM Handover Measurement Events

l "Measurement Timer Length" in 3.4.7 UMTS-to-GSM Handover Compressed Mode

l 3.5.1 Coverage-Based and QoS-Based UMTS-to-GSM Handover Decision and Execution

Added parameters The following parameter is described in 3.4.3 UMTS-to-GSM Handover Measurement Events. l Down Link

RSCP Used-Freq THD Hyst

The following parameters are described in 3.4.7 UMTS-to-GSM Handover Compressed Mode. l Down Link QoS

Measure timer length

l Up Link Qos Measure timer length

Deleted parameter 2D2F Measure Quantity

The inter-RAT handover measurement quantities are changed, as described in 3.4.5 UMTS-to-GSM Handover Measurement Quantity.

Added parameter 3A Used-Freq Measure Quantity for Qos

Deleted parameter Cell offset The cell individual offset of a cell is used together with the neighboring cell oriented individual offset. For detailed information, see 3.4.3 UMTS-to-GSM Handover Measurement Events.

Added parameters l Cell oriented Cell Individual Offset

l Neigbhoring cell oriented CIO

Feature change

UMTS-to-GSM Handover Penalty algorithm is changed to UMTS-to-GSM Handover Retry algorithm, see 3.5.3 UMTS-to-GSM Handover Retry

Added parameters l 3A event retry period

l 3A event retry max times

l 3C event retry period

l 3C event retry max times



1 Inter-RAT Handover Change History RAN



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Interchanging Load Information in UMTS-to-GSM and GSM-to-UMTS Load/Service-Based Handover, see l 3.5.2 Load-Based and

Service-Based UMTS-to-GSM Handover Decision and Execution

l 3.8 GSM-to-UMTS Handover

Added parameters l Send Load Info to GSM Ind

l NCOV Reloc Ind based on GSM cell load

l CS domain Reloc GSM load THD

l PS domain Reloc GSM load THD

The description of inter-RAT handover of HSDPA is moved from the HSDPA feature document, see 3.6 Inter-RAT Handover of HSDPA.

None.

The description of inter-RAT handover of HSUPA is moved from the HSUPA feature document, see 3.7 Inter-RAT Handover of HSUPA.

None.

The default value of Service Parameter Index is changed.

l The default value of Service Parameter Index is changed from 49 to 99.

l The default value table of service handover indicators is changed.

The default value of 3C hysteresis is changed.

The default of 3C hysteresis is changed from 4 to 0.

Editorial change

General documentation change: Implementation information has been moved to a separate document.

None



RAN Inter-RAT Handover Description 2 Inter-RAT Handover Introduction


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2 Inter-RAT Handover Introduction

Inter-RAT handover provides coverage expansion, load sharing, and layered services. It saves cost by utilizing the existing GSM network resources.

Inter-RAT handover refers to the handover between UMTS and GSM. The reason for the handover can be coverage limitation, link stability control or load limitation of the 3G system. For detailed information on the relation to other handover types, see Intra-Frequency Handover Introduction.

Inter-RAT handover can be UMTS-to-GSM or GSM-to-UMTS handover. As shown in the following figure, for a UE in CELL_DCH state, the UMTS-to-GSM handover procedure is triggered when the UMTS Radio Access Network (RAN) initiates handover or cell reselection to the GSM.

Figure 2-1 Inter-RAT handover

In this handover, however, GSM and UMTS dual-mode mobile stations (MSs) are required, and both the GSM MSC and the GSM BSS must be upgraded.

Impact l Impact on System Performance

Inter-RAT handover measurement may be implemented in compressed mode; therefore, one of the impacts on the system is from the compressed mode. When too many UEs



2 Inter-RAT Handover Introduction RAN



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stay at the cell edge, the downlink capacity and uplink coverage of the system may decrease. Another impact is from the QoS requirement for the delay-sensitive services, because hard handover can introduce handover delay.

l Impact on Other Features This feature has no impact on other features.

l Miscellaneous A dual-mode UE is required to support inter-RAT handover. That is, the UE must support both GSM and UMTS, and its network selection mode must be set to auto.

Network Elements Involved

Table 2-1 NEs involved in inter-RAT handover

UE NodeB RNC MSC Server MGW SGSN GGSN HLR

√ √ √ √ √ √ – –

NOTE l – = NE not involved l √ = NE involved UE = User Equipment, RNC = Radio Network Controller, MSC Server = Mobile Service Switching Center Server, MGW = Media Gateway, SGSN = Serving GPRS Support Node, GGSN = Gateway GPRS Support Node, HLR = Home Location Register



RAN Inter-RAT Handover Description 3 Inter-RAT Handover Algorithms


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3 Inter-RAT Handover Algorithms

Inter-RAT Handover Algorithms covers the technical aspects of the feature：

l UMTS-to-GSM Handover Types l UMTS-to-GSM Handover Procedure l Preconditions for UMTS-to-GSM Handover l UMTS-to-GSM Handover Measurement l UMTS-to-GSM Handover Decision and Execution l Inter-RAT Handover of HSDPA l Inter-RAT Handover of HSUPA l GSM-to-UMTS Handover l Interoperability Between Inter-RAT Handover and Inter-Frequency Handover l Signaling Procedures for Inter-RAT Handover

3.1 UMTS-to-GSM Handover Types Based on the handover triggering causes, UMTS-to-GSM handover can be categorized into five types: coverage-based UMTS-to-GSM handover, QoS-based UMTS-to-GSM handover, load-based UMTS-to-GSM handover, service-based UMTS-to-GSM handover, and speed-based UMTS-to-GSM handover.

The following table lists the five types of UMTS-to-GSM handovers.

Table 3-1 UMTS-to-GSM handover types

UMTS-to-GSM handover Types

Description

Coverage-based UMTS-to-GSM handover

The coverage of the UMTS is incontinuous at the initial stage of the 3G network. On the border of the coverage, the poor signal quality of UMTS triggers the UMTS-to-GSM measurement. If the signal quality of GSM is good enough and all the services of the UE are supported by the GSM, the coverage-based UMTS-to-GSM handover is triggered.



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UMTS-to-GSM handover Types

Description

QoS-based UMTS-to-GSM handover

According to the Link Stability Control Algorithm, the RNC needs to trigger the QoS-based UMTS-to-GSM handover to avoid call drops.

Load-based UMTS-to-GSM handover

If the load of the UMTS is heavy and all the RAB of the UE are supported by the GSM, the load-based UMTS-to-GSM handover is triggered.

Service-based UMTS-to-GSM handover

Based on layered services, the traffic of different classes is handed over to different systems. For example, when an Adaptive Multi Rate (AMR) speech service is requested, this service can be handed over to the GSM.

Speed-based UMTS-to-GSM handover

When the Hierarchical Cell Structure (HCS) is used, the cells are divided into different layers on the basis of coverage. Typically, a marco cell has large coverage and low priority, whereas a micro cell has small coverage and high priority. UMTS-to-GSM handover can be triggered by the UE speed estimation algorithm of the HCS. A UE moving at high speed is handed over to a cell with larger coverage to reduce the times of handover, whereas a UE moving at low speed is handed over to a cell with smaller coverage. For detailed information, see HCS Handover. NOTE: The principles of the UMTS-to-GSM handover based on HCS speed estimation are similar to those of inter-frequency handover, which will not be elaborated in this feature.

The coverage-based UMTS-to-GSM measurement and the QoS-based UMTS-to-GSM measurement can coexist.

3.2 UMTS-to-GSM Handover Procedure The UMTS-to-GSM handover procedure is divided into four phases: handover triggering, handover measurement, handover decision, and handover execution. The procedure varies with handover types.

l Coverage-based UMTS-to-GSM Handover Procedure l QoS-based UMTS-to-GSM Handover Procedure l Load-based UMTS-to-GSM Handover Procedure l Service-based UMTS-to-GSM Handover Procedure





3-3

3.2.1 Coverage-based UMTS-to-GSM Handover Procedure

Figure 3-1 Coverage-based UMTS-to-GSM handover procedure

l In the triggering phase The RNC sends a MEASUREEMNT CONTROL message to the UE, notifying the UE to measure the current carrier quality. This message defines the reporting rules and thresholds of events 2D and 2F. If the quality of the pilot signal in the current cell deteriorates, the CPICH Ec/No or CPICH RSCP of the UMTS cell that the UE accesses is lower than the corresponding threshold and the UE reports event 2D.

l In the measurement phase If the RNC receives a report of event 2D, the RNC may request the NodeB and UE to start the compressed mode to measure the qualities of GSM cells. Then, the RNC may send an inter-RAT measurement control message that defines the neighboring cell information, reporting period, and reporting rule.

In the measurement phase, either periodical measurement report mode or event-triggered measurement report mode can be used.

l In the decision phase






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After the UE reports event 3A, the RNC makes a handover decision. Or, after the UE periodically sends the measurement reports, the RNC evaluates the reports first and then makes a handover decision.

l In the execution phase The RNC initiates a handover procedure.

3.2.2 QoS-based UMTS-to-GSM Handover Procedure

Figure 3-2 QoS-based UMTS-to-GSM handover procedure

l In the triggering phase The Link Stability Control Algorithm makes a handover measurement decision.

l In the measurement phase The RNC requests the NodeB and the UE to start the compressed mode to measure the qualities of inter-RAT neighboring cells. Then, the RNC sends an inter-RAT measurement control message. This message defines neighboring cell information, reporting period, and reporting rule.

In the measurement phase, the method of periodical measurement report or event-triggered measurement report can be used.

l In the decision phase After the UE reports event 3A, the RNC performs the handover. Otherwise, the UE periodically generates measurement reports, and the RNC makes a decision after evaluation.





3-5

l In the execution phase The RNC executes the handover procedure.

3.2.3 Load-based UMTS-to-GSM Handover Procedure

Figure 3-3 Load-based UMTS-to-GSM handover procedure

l In the triggering phase When the load of the UMTS cell that the UE accesses is higher than the related threshold, the Load Reshuffling (LDR) algorithm makes a handover decision.

For detailed information of the LDR, see Load Reshuffling.

l In the measurement phase The RNC enables the compressed mode and starts the inter-RAT handover measurement.

l In the decision phase After the UE reports event 3C, the RNC makes a handover decision.







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3.2.4 Service-based UMTS-to-GSM Handover Procedure

Figure 3-4 Phases of UMTS-to-GSM handover based on service

l In the triggering phase When a service is established, the RNC requests the handover to the GSM based on the service type and service handover indicator assigned by the Core Network (CN).

l In the measurement phase The RNC enables the compressed mode and starts the inter-RAT handover measurement.

l In the decision phase After the UE reports event 3C, the RNC makes a handover decision.


3.3 Preconditions for UMTS-to-GSM Handover Before handover, the RNC checks whether the preconditions meet the triggering requirements of the UMTS-to-GSM handover. The preconditions include the service handover indicator, Capabilities of Deciding UMTS-to-GSM Handover, and Rules for Enabling UMTS-to-GSM Handover.

l Service Handover Indicator l Capabilities of Deciding UMTS-to-GSM Handover l Rules for Enabling UMTS-to-GSM Handover





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3.3.1 Service Handover Indicator The IE Service handover indicator indicates the CN policy for the service handover to the GSM. This IE is indicated in the Radio Access Bearer (RAB) assignment signaling assigned by the CN, or in Table 3-2 provided by the RNC side.

The algorithm switch SERVICE_HO_BASED_ON_RNC_SWITCH of Handover Algorithm Switch parameter decides whether the service attribute of inter-RAT handover is based on the RNC or the CN.

l If the switch is set to ON, the service attribute of inter-RAT handover is based on the parameter configured on the RNC side.

l If the switch is set to OFF, the service attribute of inter-RAT handover is first based on the CN when the indicator is contained in the RAB assignment signaling assigned by the CN. If the CN doesn't allocate service indicator, the service attribute of inter-RAT handover is based on the RNC side.

Values of Service Handover Indicator The service handover indicators are as follows:

l HO_TO_GSM_SHOULD_BE_PERFORM: means that the handover to the 2G network is performed when 2G signals are available.

l HO_TO_GSM_SHOULD_NOT_BE_PERFORM: means that the handover to the 2G network is performed when 3G signals are weak but 2G signals are strong.

l HO_TO_GSM_SHALL_NOT_BE_PERFORM: means that the handover to the 2G network is not performed even when 3G signals are weak but 2G signals are strong.

The following figure shows an example of rules for the indicator of the UMTS-to-GSM handover based on load and service.






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Figure 3-5 Example of rules for indicator of UMTS-to-GSM handover based on load and service

Principles of Setting Service Handover Indicator By default, the RNC does as follows:

l For a UE with a single signaling RAB, the RNC supports the handover to the GSM. But it is not recommended.

l For the UE accessing combined services (with CS services), the RNC sets the service handover indicator of the UE to that of the CS service, because the CS service has the highest QoS priority.

l For the UE accessing combined services (with only PS services), the RNC sets the service handover indicator of the UE to that of the PS service, which has the highest QoS priority.

Service Parameter Index If service handover indicators are not configured by the CN, each indictor can be set to Service parameter index of a service on the RNC.

Each Service parameter index is the index of one typical service RAB, which involves a set of service type, source description, CN domain ID, and Max rate (bit/s).

The following table describes the relationship between the set and the service handover indicators recommended by Huawei.





3-9

Table 3-2 Service handover indicators (default values)

Service Parameter Index

Traffic Class Source Description

CN Domain ID

Max Rate (bit/s)

Service Handover Indicator

Required 2G Capability

0 CONVERSATIONAL SPEECH CS_DOMAIN 12200 HO_TO_GSM_SHOULD_NOT_BE_PERFORM

GSM

1 CONVERSATIONAL UNKNOWN CS_DOMAIN 23850 HO_TO_GSM_SHOULD_NOT_BE_PERFORM

GSM

2 CONVERSATIONAL UNKNOWN CS_DOMAIN 28800 HO_TO_GSM_SHALL_NOT_BE_PERFORM

GSM


GSM


GSM

5 STREAMING UNKNOWN CS_DOMAIN 64000 HO_TO_GSM_SHALL_NOT_BE_PERFORM

GSM

6 STREAMING UNKNOWN PS_DOMAIN 57600 HO_TO_GSM_SHALL_NOT_BE_PERFORM

EDGE

7 N.A. N.A. N.A. N.A. N.A. EDGE


9 N.A. N.A. N.A. N.A. N.A. GSM


11 CONVERSATIONAL UNKNOWN PS_DOMAIN 8000 HO_TO_GSM_SHALL_NOT_BE_PERFORM

GSM


EDGE






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CN Domain ID

Max Rate (bit/s)




EDGE

14 N.A. N.A. N.A. N.A. N.A. GSM


EDGE


EDGE


EDGE


EDGE


EDGE

20 N.A. N.A. N.A. N.A. N.A. N.A.


GSM


GSM


GSM


GSM





3-11



CN Domain ID

Max Rate (bit/s)




GSM


GSM


EDGE


EDGE

29 N.A. N.A. N.A. N.A. N.A. GPRS


31 N.A. N.A. N.A. N.A. HO_TO_GSM_SHALL_NOT_BE_PERFORM

EDGE


EDGE


EDGE

34 N.A. N.A. N.A. N.A. HO_TO_GSM_SHOULD_NOT_BE_PERFORM

EDGE


EDGE


EDGE






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CN Domain ID

Max Rate (bit/s)






40 INTERACTIVE UNKNOWN PS_DOMAIN 0 HO_TO_GSM_SHOULD_NOT_BE_PERFORM

GPRS


GPRS


GPRS


GPRS


GPRS

45 INTERACTIVE SPEECH PS_DOMAIN 128000 HO_TO_GSM_SHOULD_NOT_BE_PERFORM

EDGE


EDGE


EDGE


EDGE





3-13



CN Domain ID

Max Rate (bit/s)



49 INTERACTIVE UNKNOWN PS_DOMAIN 608000 HO_TO_GSM_SHALL_NOT_BE_PERFORM

EDGE

50 INTERACTIVE UNKNOWN PS_DOMAIN 768000 HO_TO_GSM_SHALL_NOT_BE_PERFORM

EDGE

51 INTERACTIVE UNKNOWN PS_DOMAIN 1024000

HO_TO_GSM_SHALL_NOT_BE_PERFORM

EDGE



EDGE



EDGE



EDGE



EDGE



EDGE



EDGE



EDGE






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CN Domain ID

Max Rate (bit/s)





EDGE



EDGE



EDGE

62 N.A. N.A. N.A. N.A. N.A. N.A.

63 N.A. N.A. N.A. N.A. N.A. N.A.

64 N.A. N.A. N.A. N.A. N.A. N.A.

65 N.A. N.A. N.A. N.A. N.A. N.A.

66 N.A. N.A. N.A. N.A. N.A. N.A.

67 N.A. N.A. N.A. N.A. N.A. N.A.

68 N.A. N.A. N.A. N.A. N.A. N.A.

69 N.A. N.A. N.A. N.A. N.A. N.A.

70 BACKGROUND UNKNOWN PS_DOMAIN 0 HO_TO_GSM_SHOULD_NOT_BE_PERFORM

GPRS


GPRS


GPRS


GPRS





3-15



CN Domain ID

Max Rate (bit/s)




GPRS


EDGE


EDGE


EDGE


EDGE

79 BACKGROUND UNKNOWN PS_DOMAIN 608000 HO_TO_GSM_SHALL_NOT_BE_PERFORM

EDGE

80 BACKGROUND UNKNOWN PS_DOMAIN 768000 HO_TO_GSM_SHALL_NOT_BE_PERFORM

EDGE

81 BACKGROUND UNKNOWN PS_DOMAIN 1024000


EDGE



EDGE



EDGE






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CN Domain ID

Max Rate (bit/s)





EDGE



EDGE



EDGE



EDGE



EDGE



EDGE



EDGE



EDGE

92 N.A. N.A. N.A. N.A. N.A. N.A.

93 N.A. N.A. N.A. N.A. N.A. N.A.

94 N.A. N.A. N.A. N.A. N.A. N.A.

95 N.A. N.A. N.A. N.A. N.A. N.A.

96 N.A. N.A. N.A. N.A. N.A. N.A.

97 N.A. N.A. N.A. N.A. N.A. N.A.

98 N.A. N.A. N.A. N.A. N.A. N.A.





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CN Domain ID

Max Rate (bit/s)



99 N.A. N.A. N.A. N.A. N.A. N.A.

3.3.2 Capabilities of Deciding UMTS-to-GSM Handover Before deciding UMTS-to-GSM handover, the RNC considers GSM cell capability, service capability and UE capability.

GSM Cell Capability GSM cell capability is configured through the parameter Inter-RAT cell type. This parameter indicates whether the cell supports the GSM, GPRS, EDGE.

Service Capability The Required 2G Capability specifies the capability of 2G cells required by inter-RAT handover. This indicates whether the service is supported by the GSM, GPRS, or EDGE.The default value provided by RNC see Table 3-2.

UE Capability Upon the reception of the UE capability information message, the RNC decides whether to start the inter-RAT measurement. The information indicates whether the UE supports the GSM, GPRS, or EDGE.

3.3.3 Rules for Enabling UMTS-to-GSM Handover The rules for enabling UMTS-to-GSM handover are based on the Service Handover Indicator and the three types of capability (GSM cell capability, service capability, and UE capability). The rules vary with different types of inter-RAT handover.

Rules for Enabling Coverage and QoS-based UMTS-to-GSM Handover The RNC initiates the coverage-based and QoS-based UMTS-to-GSM handover only when Service Handover Indicator is set as follows:

l HO_TO_GSM_SHOULD_BE_PERFORM l HO_TO_GSM_SHOULD_NOT_BE_PERFORM

In addition, the RNC initiates inter-RAT handover based on the following capabilities:

l GSM cell capability l Service capability (required by 2G) l UE capability

The following tables describe the capability of the coverage-based and QoS-based UMTS-to-GSM handover in the combination of the three "capabilities" listed above.






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Table 3-3 GSM neighboring cell with EDGE capability

Service capability (required by 2G) UE Capability

EDGE GPRS GSM

EDGE Allowed Allowed Allowed

GPRS Allowed Allowed Allowed

GSM Not allowed Not allowed Allowed

Not supported by 2G Not allowed Not allowed Not allowed

Table 3-4 GSM neighboring cell with GPRS capability


EDGE GPRS GSM


GPRS Allowed Allowed Allowed



Table 3-5 GSM neighboring cell with GSM capability


EDGE GPRS GSM

EDGE Not allowed Not allowed Allowed

GPRS Not allowed Not allowed Allowed



If the capability of all the GSM neighboring cells is "No capability", the inter-RAT measurement cannot be started.

Rules for Enabling Load and Service-based UMTS-to-GSM Handover The RNC initiates the load-based UMTS-to-GSM handover only when Service Handover Indicator is set as follows:

l HO_TO_GSM_SHOULD_BE_PERFORM l HO_TO_GSM_SHOULD_NOT_BE_PERFORM





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The RNC initiates the service-based UMTS-to-GSM handover only when Service Handover Indicator is set as follows:

l HO_TO_GSM_SHOULD_BE_PERFORM In addition, the RNC initiates UMTS-to-GSM handover based on the following capabilities:

l GSM cell capability l Service capability (required by 2G) l UE capability

The following tables describe the capability of the load and service-based UMTS-to-GSM handover in the combination of the three "capabilities" listed above.

Table 3-6 GSM neighboring cell with EDGE capability


EDGE GPRS GSM


GPRS Not allowed Allowed Allowed



Table 3-7 GSM neighboring cell with GPRS capability


EDGE GPRS GSM

EDGE Not allowed Allowed Allowed

GPRS Not allowed Allowed Allowed



Table 3-8 GSM neighboring cell with GSM capability


EDGE GPRS GSM

EDGE Not allowed Not allowed Allowed

GPRS Not allowed Not allowed Allowed








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If the capability of all the GSM neighboring cells is "No capability", the inter-RAT measurement cannot be started.

If the "Required 2G Capability" is "GPRS", "GSM", or "EDGE", the RNC does not consider whether the UE supports the EDGE. Only when the "Required 2G Capability" is "EDGE", the RNC checks the UE capability.

Switches for Service-Based UMTS-to-GSM Handover To perform the UMTS-to-GSM service-based handover, the RNC must turn on the related switches for services in the CS and PS domains.

l When a single CS service is initially set up by the UE, the RNC allows the UMTS-to-GSM service-based handover if Inter-RAT CS handover switch is set to ON.

l When a single PS service is initially set up by the UE, the RNC allows the UMTS-to-GSM service-based handover if Inter-RAT PS handover switch is set to ON.

l For the CS and PS combined services, no service-based handover is triggered.

3.4 UMTS-to-GSM Handover Measurement UMTS-to-GSM handover covers relevant switches, measurement report modes, measurement quantity, L3 filtering, measurement events, measurement range, compressed mode, and BSIC verification requirements for GSM cells.

l UMTS-to-GSM Handover Measurement Switches l UMTS-to-GSM Handover Measurement Report Modes l UMTS-to-GSM Handover Measurement Events l UMTS-to-GSM Handover Neighboring Cell Combination Algorithm l UMTS-to-GSM Handover Measurement Quantity l UMTS-to-GSM Handover L3 Filtering l UMTS-to-GSM Handover Compressed Mode l BSIC Verification Requirements for GSM Cells

3.4.1 UMTS-to-GSM Handover Measurement Switches Some switches are important for UMTS-to-GSM handover, because they decide whether the handover can be performed successfully.

These switches are the parameter values of Handover algorithm switch in the command SET CORRMALGOSWITCH, as described in the following table.





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Table 3-9 Switches of UMTS-to-GSM Handover Measurement

Switch Description Default Value

SIGNAL_HO_SWITCH The switch decides when the RNC performs the inter-frequency/inter-RAT coverage-based handover measurement. If the switch is set to ON, the RNC checks whether the inter-frequency or inter-RAT coverage-based handover measurement can be triggered after the RRC connection setup is completed (before the RB setup). If the switch is set to OFF, the RNC checks whether the inter-frequency or inter-RAT coverage-based handover measurement can be triggered after the RB setup is completed.

OFF

ACT_SET_QUAL_SWITCH The switch decides whether the RNC enables the active set quality measurement. If the switch is set to ON, the RNC enables the signal quality measurement to all the cells in active set after the RRC setup is completed (if the SIGNAL_HO_SWITCH is set to ON), or after the RB connection setup is completed (if the SIGNAL_HO_SWITCH is set to OFF). If the switch is set to OFF, the RNC does not initiate the active set quality measurement.

ON

INTER_RAT_PS_OUT_SWITCH The switch decides whether the RNC will initiate inter-RAT measurement to trigger inter-RAT handover of the PS domain from the UTRAN.

ON

INTER_RAT_CS_OUT_SWITCH The switch decides whether the RNC will initiate inter-RAT measurement to trigger inter-RAT handover of the CS domain from the UTRAN.

ON

3.4.2 UMTS-to-GSM Handover Measurement Report Modes For coverage or QoS based UMTS-to-GSM handover, there are two measurement report modes: event-triggered measurement report mode and periodical measurement report mode.






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For load or service based UMTS-to-GSM handover, the measurement report is event-triggered only.

The measurement report mode is configured through the parameter Inter-RAT report mode.

In periodical measurement report mode, the report interval also needs to be configured through the parameter Inter-RAT period report interval. The UE sends measurement reports periodically to the RNC according to the values of the report interval.

3.4.3 UMTS-to-GSM Handover Measurement Events When the measurement thresholds are reached, the UE reports the events to the RNC to trigger the related handover procedures.

Table 3-10 Events in inter-RAT handover

Event Description

Event 2D The estimated quality of the currently used frequency is below a certain threshold.

Event 2F The estimated quality of the currently used frequency is above a certain threshold.

Event 3A The estimated quality of the currently used UTRAN frequency is below a certain threshold and the estimated quality of the other system is above a certain threshold.

Event 3C The estimated quality of other system is above a certain threshold.

UMTS-to-GSM Handover Frequency Quality Estimation In UMTS-to-GSM handover, the report criteria of event 3A are based on the quality estimation of the frequency. The parameter Weight for used frequency is the frequency weighting factor used to calculate the quality of the current frequency. This parameter is used for event 3A only.

For detailed information about the quality estimation formula, see section "Frequency Quality Estimate" in 3GPP TS 25.331.

Triggering of Event 2D Event 2D is triggered on the basis of the following formula:

QUsed <= TUsed2d - H2d/2

where

l QUsed is the measurement value of the cell at the currently used frequency. l TUsed2d is the absolute quality threshold of the cell at the currently used frequency. Based

on the service type (CS , PS domain R99 service, or PS domain HSPA service) and measurement quantity (CPICH Ec/No or RSCP), this threshold can be configured through the following parameters: − Inter-RAT CS measure start Ec/No THD





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− Inter-RAT R99 PS measure start Ec/No THD − Inter-RAT H measure start Ec/No THD − Inter-RAT CS measure start RSCP THD − Inter-RAT R99 PS measure start RSCP THD − Inter-RAT H measure start RSCP THD

l H2d is 2D hysteresis, the hysteresis value of event 2D. l For the PS and CS combined services, the threshold(s) for CS services is (are) used.

When the conditions for event 2D are met and maintained in time-to-trigger specified by the parameter 2D event trigger delay time, the UE sends the measurement report of event 2D.

Triggering of Event 2F Event 2F is triggered on the basis of the following formula:

QUsed >= TUsed2f + H2f/2

where

l QUsed is the measurement value of the cell at the currently used frequency. l TUsed2f is the absolute quality threshold of the cell at the currently used frequency. Based

on the service type (CS , PS domain R99 service, or PS domain HSPA service) and measurement quantity (CPICH Ec/No or RSCP), this threshold can be configured through the following parameters: − Inter-RAT CS measure stop Ec/No THD − Inter-RAT R99 PS measure stop Ec/No THD − Inter-RAT H measure stop Ec/No THD − Inter-RAT CS measure stop RSCP THD − Inter-RAT R99 PS measure stop RSCP THD − Inter-RAT H measure stop RSCP THD

l H2f is 2F hysteresis, the hysteresis value of event 2F. l For the PS and CS combined services, the threshold(s) for CS services is (are) used.

When the conditions for event 2F are met and maintained in time-to-trigger specified by 2F event trigger delay time, the UE sends the measurement report of event 2F.

Triggering of Event 3A Event 3A is triggered on the basis of the following formula:

QUsed <= TUsed - H3a/2 and MOtherRAT + CIOOtherRAT >= TOtherRAT + H3a/2

where

l QUsed is the measurement value of the cell at the currently used frequency. l TUsed is the absolute quality threshold of the cell that uses the current frequency.

Based on the service type (CS , PS domain R99 service, or PS domain HSPA service) and measurement quantity (CPICH Ec/No or RSCP) in the coverage-based handover, TUsed can be configured through the following parameters (These parameters are shared by the inter-freq and inter-RAT handover.): − Inter-RAT CS Used frequency trigger Ec/No THD






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− Inter-RAT R99 PS Used frequency trigger Ec/No THD − Inter-RAT H Used frequency trigger Ec/No THD − Inter-RAT CS Used frequency trigger RSCP THD − Inter-RAT R99 PS Used frequency trigger RSCP THD − Inter-RAT H Used frequency trigger RSCP THD In the uplink QoS-based handover, based on the measurement quantity (CPICH Ec/No or RSCP), TUsed is configured as the maximum value according to 3GPP specifications, as described below: − If the measurement quantity is CPICH Ec/No, TUsed is configured as the maximum

value 0 dB. − If the measurement quantity is CPICH RSCP, TUsed is configured as the maximum

value -25 dBm. In the downlink QoS-based handover: − If the measurement quantity is CPICH Ec/No, TUsed is configured as the maximum

value 0 dB. − If the measurement quantity is CPICH RSCP, based on the service type (CS, PS

domain R99 service, or PS domain HSPA service), TUsed can be configured as one of the following sums: − Inter-RAT CS Used frequency trigger RSCP THD and Down Link RSCP

Used-Freq THD Hyst − Inter-RAT R99 PS Used frequency trigger RSCP THD and Down Link RSCP

Used-Freq THD Hyst − Inter-RAT H Used frequency trigger RSCP THD and Down Link RSCP

Used-Freq THD Hyst − MOtherRAT is the measurement value of the cell (in another RAT) in the reporting

range. − CIOOtherRAT is the cell individual offset value of the cell (in another RAT) in the

reporting range which is equal to the sum of Cell oriented Cell Individual Offset and Neighboring cell oriented CIO.

− TOtherRAT is the absolute inter-RAT handover threshold. Based on the service type (CS , PS domain R99 service, or PS domain HSPA service), this threshold can be configured through the following parameters: − Inter-RAT CS handover decision THD − Inter-RAT R99 PS handover decision THD − Inter-RAT H handover decision THD

l H3a is 3A hysteresis, the hysteresis value of event 3A. l For the PS and CS combined services, the threshold(s) for CS services is (are) used.

When the conditions for event 3A are met and maintained in time-to-trigger specified by 3A event trigger delay time the UE sends the measurement report of event 3A.

Triggering of Event 3C Event 3C is triggered on the basis of the following formula:

MOtherRAT + CIOOtherRAT >= TOtherRAT + H3c/2

where





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l MOtherRAT is the measurement value of the cell (in another RAT) in the reporting range. l CIOOtherRAT is the cell individual offset value of the cell (in another RAT) in the reporting

range, which is equal to the sum of Cell oriented Cell Individual Offset and Neighboring cell oriented CIO.

l TOtherRAT is the absolute inter-RAT handover threshold. Based on the service type (CS , PS domain R99 service, or PS domain HSPA service), this threshold can be configured through the following parameters: − Inter-RAT CS handover decision THD − Inter-RAT PS handover decision THD

l H3c is 3C hysteresis, the hysteresis value of event 3C. l For the PS and CS combined services, the threshold(s) for CS services is (are) used.

When the conditions for event 3C are met and the delay requirement specified by the 3C event trigger delay time parameter can be satisfied, the UE sends the measurement report of event 3C.

3.4.4 UMTS-to-GSM Handover Neighboring Cell Combination Algorithm

The measurement range in the measurement control message sent to the UE is determined by the range of neighboring cells. After the active set is updated, the RNC updates the neighboring cell list by using the neighboring cell combination algorithm according to the status of the active set. This list includes the new intra-frequency, inter-frequency and inter-RAT neighboring cells.

Neighboring Cell Combination Switch The NCELL_COMBINE_SWITCH parameter of Handover Algorithm Switch decides the measurement range of neighboring cells.

l If the switch is set to ON, measurement objects are chosen from the neighboring cells of all the cells in the active set.

l If the switch is set to OFF, measurement objects are chosen from the neighboring cells of the best cell.

l The maximum number of neighboring cells is 32, no matter whether the measurement range is the

neighboring cells of the active set or those of the monitored set. l In default, the NCELL_COMBINE_SWITCH is set to ON.

Triggering of the Neighboring Cell Combination Algorithm After the active set update is complete, the RNC updates the neighboring cell list by using the neighboring cell combination algorithm:

l When receiving an event 1A or 1C report, the RNC uses this algorithm to update the neighboring cell list. If the Radio Links (RLs) from the DRNC are added to the active set, the SRNC buffers the intra-frequency, inter-frequency, and inter-RAT neighboring cells list from the DRNC until the RLs from DRNC are removed from the active set.

l When receiving an event 1B or 1D report or an RL OUT-OF-SYNCHRONIZATION message from the NodeB, the RNC uses this algorithm to update the neighboring cell list.






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Description of the Neighboring Cell Combination Algorithm After obtaining the inter-RAT neighboring cells of each cell in the active set, the RNC calculates the union neighboring cell set (referred to as Sall) of the active set by using the following method:

Step 1 The intra-frequency, inter-frequency and inter-RAT neighboring cells of each cell in the current active set are obtained.

Step 2 The RNC sequences the cells in the active set in descending order of CPICH Ec/No according to the latest measurement report (event 1A, 1B, 1C, or 1D) from the UE. The best cell is based on event 1D, whereas other cells are based on the latest measurement report.

Step 3 The cells in the active set are added to Sall.

Step 4 The neighboring cells of the best cell in the active set are added to Sall. The flag of the priority and The priority of neighbor cell, which are set for each neighboring cell, are used to change the order of adding the neighboring cells to Sall.

Step 5 The neighboring cells of other cells in the active set are added to Sall in descending order by CPICH Ec/No values of these cells in the active set. The neighboring cells of the same cell in the active set are added according to The priority of neighbor cell.

Step 6 If there are more than 32 neighboring cells in Sall, the top 32 neighboring cells are grouped into the final Sall.

l When The flag of the priority is switched to FALSE from TRUE, The priority of neighbor

cell is cleared. l When The flag of the priority is switched to TRUE from FALSE, the Priority of neighbor

cell is set simultaneously.

----End

3.4.5 UMTS-to-GSM Handover Measurement Quantity There is a choice of multiple measurement quantities used to measure the CPICH quality.

l In coverage-based UMTS-to-GSM handover, − Event 2D/2F or periodical measurement takes both CPICH Ec/No and RSCP as

measurement quantities. − Event 3A takes CPICH Ec/No, CPICH RSCP, and Auto as measurement quantities.

l In QoS-based UMTS-to-GSM handover, event 3A takes CPICH Ec/No and CPICH RSCP as measurement quantities.

The related parameter is 3A Measure Quantity and 3A Used-Freq Measure Quantity for Qos.

3.4.6 UMTS-to-GSM Handover L3 Filtering The UE performs the layer 3 (L3) filtering for the measurement value before it judges the measurement event and sends the measurement report.

The inter-RAT measurement model is similar to the intra-frequency measurement model. For detailed information, see L3 Filtering for Intra-Frequency Handover.





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The smoothed filter coefficient for layer 3 inter-RAT measurement is Inter-RAT filter coeff, and the smoothed filter coefficient for events 2D and 2F is 2D2F filter coeff.

3.4.7 UMTS-to-GSM Handover Compressed Mode Compressed mode is defined as the mechanism whereby certain idle periods are created in radio frames so that the UE can perform measurements during these periods.

Compressed Mode Concept Compressed Mode control is a mechanism whereby certain idle periods are created in radio frames during which the UE can perform measurements on other frequencies. The UE can carry out measurements in the neighbouring cell, such as GSM cell and FDD cell on other frequency. If the UE needs to measure the pilot signal strength of an inter-frequency WCDMA or GSM cell and has one frequency receiver only, the UE must use the compressed mode.

Each physical frame can provide 3 to 7 timeslots for the inter-frequency or inter-RAT cell measurement, which enhances the transmit capability of physical channels but reduces the volume of data traffic.

Therefore, the compressed mode is usually used in inter-frequency or inter-RAT handover. When the corresponding handover algorithm decides a measurement in compressed mode based on the UE capability, the RNC performs the following procedures:

Step 1 Sends parameters for the compressed mode to the NodeB and the UE.

Step 2 Sets parameters for inter-frequency or inter-RAT cell measurement control.

Step 3 Activates the compressed mode.

Step 4 Updates the measurement control information to the UE when required.

----End

Compressed Mode Types The compressed mode is of the following two types:

l Spreading factor reduction (SF/2) l High layer scheduling

Which type of the compressed mode to use is automatically decided by the RNC on the basis of the spreading factor used in the uplink or the downlink.

l When the downlink spreading factor is greater than or equal to the parameter DL SF threshold, the SF/2 approach is preferred. Otherwise, the high layer scheduling is used.

l When the uplink spreading factor is greater than or equal to the parameter UL SF threshold, the SF/2 approach is preferred. Otherwise, the high layer scheduling is used.

To initiate the high layer scheduling, set the following two switches:

l If the algorithm switch CMCF_DL_HLS_SWITCH of CMCF Algorithm Switch parameter is set to ON, the DL high-layer scheduling for the compressed mode is allowed.

l If the algorithm switch CMCF_UL_HLS_SWITCH of CMCF Algorithm Switch parameter is set to ON, the UL high-layer scheduling for the compressed mode is allowed.






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Compressed Mode Switches The parameter Dl SF limit CM ind decides whether to start the DL compressed mode according to the parameter Dl SF threshold to limit CM.

In addition, there are two switches, CMCF_UL_PRECFG_TOLERANCE_SWITCH and CMCF_WITHOUT_UE_CAP_REPORT_SWITCH, involved in starting the compressed mode. Both of them are values of the parameter CMCF algorithm switch that is configured through the command SET CORRMALGOSWITCH.


CMCF_UL_PRECFG_TOLERANCE_SWITCH

When the uplink SF is 4 (UL SF = 4), the compressed mode of reducing the SF by half (SF/2) fails to be initiated because the SF cannot be 2. This switch is used to decide whether the UL SF = 4 RB(s) is (are) allowed to be set up when the RNC is in the preconfigured state of the SF/2 compressed mode. If the switch is set to ON, the UL SF = 4 RB(s) is (are) allowed to be set up when the RNC is in the preconfigured state of the SF/2 compressed mode. However, if the compressed mode is triggered by event 2D, the compressed mode cannot be activated, that is, it cannot be initiated to start the inter-frequency or inter-RAT measurement. If the switch is set to OFF, the UL SF = 4 RB(s) is (are) not allowed to be set up when the RNC is in the preconfigured state of the SF/2 compressed mode.

OFF





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CMCF_WITHOUT_UE_CAP_REPORT_SWITCH

The UE can start the compressed mode on some frequency ranges that are not in the reported measurement range. Whether to start the compressed mode to take measurements on the frequencies within the frequency range depends on the switch. This switch is used to decide whether the UE need initiate the compressed mode to start the inter-frequency measurement for such frequencies. If the switch is set to ON for such frequencies, the UE must initiate the compressed mode to start the inter-frequency measurement. If the switch is set to OFF for such frequencies, the compressed mode need not be initiated before the inter-frequency measurement. Thus, the UE need not initiate the compressed mode to start the inter-frequency measurement.

OFF

Generally, it is recommended that the previously mentioned two switches are set to OFF.

Measurement Timer Length When the UE takes a long time to perform the inter-RAT measurement in compressed mode, the radio network will be affected. To avoid the influence, the system stops the inter-RAT measurement and disables the compressed mode if no inter-RAT handover occurs upon expiry of the inter-RAT measurement timer.

l The timer is specified by Inter-RAT measure timer length in inter-RAT handover based on coverage, load or service.

l The timer is specified by Down Link Qos Measure timer length/Up Link Qos Measure timer length in inter-RAT handover based on downlink/uplink QoS.

3.4.8 BSIC Verification Requirements for GSM Cells During inter-RAT measurement, it is recommended that the UE reports the GSM cell after the Base Transceiver Station Identity Code (BSIC) of the GSM cell is verified. This greatly enhances the reliability of handover.

The related parameter is BSIC verify switch.






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3.5 UMTS-to-GSM Handover Decision and Execution The UMTS-to-GSM handover decision and execution vary with different types of inter-RAT handover.

l Coverage-Based and QoS-Based UMTS-to-GSM Handover Decision and Execution l Load-Based and Service-Based UMTS-to-GSM Handover Decision and Execution l UMTS-to-GSM Handover Retry l UMTS-to-GSM Multimedia Fallback l UMTS-to-GSM Handover in the PS Domain with NACC or PS Handover

3.5.1 Coverage-Based and QoS-Based UMTS-to-GSM Handover Decision and Execution

The coverage-based and QoS-based UMTS-to-GSM handover is categorized into two types according to the following two measurement report modes: periodical measurement report mode and event-triggered measurement report mode. Each mode corresponds to a different decision and execution procedure.

Coverage-Based and QoS-Based UMTS-to-GSM Handover in Periodical Measurement Report Mode

After receiving the periodical measurement report of GSM cells, the RNC performs the following decision and execution procedures:

Step 1 Decide whether the quality of GSM cells meets the conditions of inter-RAT handover.

The evaluation formula is listed below:

Mother_RAT + CIOother_RAT ≥ Tother_RAT + H/2

where

l Mother_RAT is the measurement result of inter-RAT handover received by the RNC. l CIOother_RAT is the cell individual offset value of the target cell. It is equal to the sum of

Cell oriented Cell Individual Offset and Neighboring cell oriented CIO. Neigbhoring cell oriented CIO indicates the offset of the measurement cell relative to the best cell.

l Tother_RAT is the decision threshold of inter-RAT hard handover. Based on the service type (CS or PS service) and measurement quantity (CPICH Ec/No or RSCP), this threshold can be configured through the following parameters: − Inter-RAT CS handover decision THD − Inter-RAT R99 PS handover decision THD − Inter-RAT H handover decision THD

These thresholds are the same as the quality threshold of event 3A. For detailed information, see 3.4.3 UMTS-to-GSM Handover Measurement Events.

− H is the inter-frequency hard handover hysteresis value Inter-RAT hysteresis. − For the PS and CS combined services, one or more handover thresholds for CS

services are used.





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Step 2 Start the evaluation of the cells that meet the quality requirement and start the time-to-trigger timer. If the measurement report meet the following formula and time-to-trigger timer doesn't expire, stop the time-to-trigger timer.

Mother_RAT + CIOother_RAT < Tother_RAT - H/2

Where the parameters are the same as those previously described.

Step 3 Select the cells in sequence, that is, from high quality cells to low quality ones, to initiate UMTS-to-GSM handover in the cells where the handover time-to-trigger timer expires.

The length of the time-to-trigger timer is configured through the parameter Time to trigger for verified GSM cell (with BSIC acknowledged) or the parameter Time to trigger for non-verified GSM cell (with BSIC unacknowledged).

----End

Coverage-Based and QoS-Based UMTS-to-GSM Handover in Event-Triggered Measurement Report Mode

After receiving the event 3A measurement report of GSM cells, the RNC performs the following decision and execution procedures:

Step 1 Put all the GSM cells that trigger event 3A into a cell set and arrange the cells according to the measurement quality in descending order.

Step 2 Select the cells in sequence from the cell set to perform inter-RAT handover.

----End

3.5.2 Load-Based and Service-Based UMTS-to-GSM Handover Decision and Execution

The load status between the source cell and the target cell can be acquired by interchanging load information between a UMTS cell and a GSM cell during the load-based and service-based UMTS-to-GSM handover. Thus, whether to further conduct the handover can be determined to avoid the 2G cell overload and possible handover to the congested cell.

Decision and Execution Procedure of Load or Service-Based UMTS-to-GSM Handover

After receiving the event 3C measurement report of GSM cells, the RNC performs the following handover decision and execution procedure:

Step 1 Put all the GSM cells that trigger event 3C into a cell set and arrange the cells according to the measurement quality in descending order.

Step 2 Select the cells in sequence from the cell set.

To avoid the impact of the UE (in long-term measurement of compressed mode) on the radio network, the parameter Inter-RAT handover max attempt times is set to restrict the maximum attempts of the UMTS-to-GSM load-based or service-based handover. The parameter indicates the handover attempts made to the same cell or different cells. If the number of attempts exceeds the parameter value, the RNC does not initiate the handover.

----End






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Interchanging Load Information in Load or Service-Based UMTS-to-GSM Handover

The procedure of load information interchanging between the 3G source cell and 2G target cell is described as follows:

Step 1 When the RNC sends a RELOCATION REQUIRED message to the 3G CN,

l If the switch Send Load Info to GSM Ind is set to ON, the RELOCATION REQUIRED message includes the Information Element, Old BSS To New BSS Information that includes the load information of the 3G source cell.

l If the switch Send Load Info to GSM Ind is set to OFF, then the RELOCATION REQUIRED message does not include the Information Element, Old BSS To New BSS Information.

Step 2 When the RNC receives the RELOCATION COMMAND message from the 2G CN,

l If the switch NCOV Reloc Ind based on GSM cell load is set to ON, the RNC obtains the load information of the 2G target cell by reading the Information Element, Inter-System Information Transparent Container, which is included in the RELOCATION COMMAND message. − If the 2G load is lower than CS domain Reloc GSM load THD (for CS service), or

if the 2G load is lower than PS domain Reloc GSM load THD (for PS service), the RNC continues the inter-RAT handover procedure; otherwise, the RNC returns the Relocation Cancel message to the CN to cancel this inter-RAT handover and makes another handover attempt to the next candidate cell generated in the cell list based on inter-RAT measurement.

− If the Information Element, Inter-System Information Transparent Container, is not included in the RELOCATION COMMAND message, the load information of the 2G target cell is not considered and this inter-RAT handover is continued.

l If the switch NCOV Reloc Ind based on GSM cell load is set to OFF, the RNC continues the inter-RAT handover procedure without considering the thresholds.

----End

3.5.3 UMTS-to-GSM Handover Retry In case of inter-RAT handover failure, if the cause of the failure is not a configuration failure and the retry timer expires, the UE makes handover attempts to the cell again until the retry number exceeds the maximum retry number.

The inter-RAT handover retry algorithm works in the following two signaling procedures:

Signaling Procedure for Iu Relocation Step 1 The RELOCATION REQUIRED message is initiated on the Iu interface.

Step 2 If the RNC receives the RELOCATION PREPARATION FAILURE message, the inter-RAT handover fails.

If the cause of the failure is one of the following configuration failure, the RNC does not make a handover retry to the cell.

l Relocation Failure in Target CN/RNC or Target System, or l Relocation not supported in Target RNC or Target System, or





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l Relocation Target not allowed

Otherwise, the related retry timer for the cell is started. After the retry timer expires, the UE makes handover attempts to the cell again until the retry number exceeds the maximum retry number.

Step 3 If the RNC receives the RELOCATION COMMAND message, the handover on the Uu interface continues.

Step 4 If the handover succeeds or the new event 3A or 3C report is received, the periodical retry is stopped.

----End

Signaling Procedure for Service-Based Handover on the Uu Interface l For CS services or CS and PS combined services, the HANDOVER FROM UTRAN

signaling procedure on the Uu interface is performed only when the handover based on CS services is made.

l For a PS service or combined PS services, the CELL CHANGE ORDER FROM UTRAN or HANDOVER FROM UTRAN signaling procedure on the Uu interface is performed.

l If the HANDOVER FROM UTRAN FAILURE or CELL CHANGE ORDER FROM UTRAN FAILURE message is received, the handover on the Uu interface fails.

If the "Inter-RAT handover failure cause" in HANDOVER FROM UTRAN FAILURE message is "Configuration unacceptable", or if the "Inter-RAT change failure cause" in CELL CHANGE ORDER FROM UTRAN FAILURE message is "Configuration unacceptable", the RNC does not make a handover retry to the cell.

Otherwise, the related retry timer for the cell is started. After the retry timer expires, the UE makes a handover attempt to the cell again until the retry number exceeds the maximum number.

If the handover succeeds or the new event 3A or 3C report is received, the periodical retry is stopped.

The retry timer and maximum retry number for coverage-based and QoS-based inter-RAT handover are:

l 3A event retry period l 3A event retry max times

The retry timer and maximum retry number for load-based and service-based inter-RAT handover are:

l 3C event retry period l 3C event retry max times

3.5.4 UMTS-to-GSM Multimedia Fallback Before the RNC performs handover for the UE that subscribes to the video phone (VP) service, the RNC initiates multimedia fallback to change the VP service to the Adaptive Multi Rate (AMR) speech service, that is, to perform the UMTS-to-GSM handover based on the CS AMR speech service.






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Overview of Fallback Service Compared with the traditional speech service of the GSM, the VP service of the UMTS can transmit not only speech services between the calling party and the called party, but also the images and videos captured by both parties. Since the actual implementation is limited by terminals and networks, the VP service sometimes carries only speech and may fail to transmit images or videos. In this scenario, the Service Change and Unrestricted Digital Information Fallback (SCUDIF) provides the fallback mechanism that changes a video call to a common speech call.

As specified in 3GPP TS 23.172, the fallback service of the VP is categorized into the following two types:

l Fallback: the process of changing multimedia services back to speech services during call setup. The RNC doesn't take part in the process. Therefore the detailed description of Fall back process is not given hereinafter.

l Service change: the process of changing multimedia services back to speech services during the call.

The two types are both referred to as multimedia fallback in this feature.

Triggering of Fallback Service Currently, the network-initiated multimedia fallback is performed only for the UMTS-to-GSM handover. RAN 6.1 and later releases do not support service changes caused by the UEs.

Fallback is initiated on the following occasions:

l The RNC decides to send an inter-RAT handover request after receiving periodical measurement reports of event 1F, 3A, or 3C.

l The service is combined with a VP, and the "Alternative RAB Para" in the RAB ASSIGNMENT message is a valid AMR speech format.

Procedure of Fallback Service The following figure shows the service change procedure of UMTS-to-GSM handover. The network initiates the service change, that is, the RNC initiates the change from the VP service to the speech service during the call.





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Figure 3-6 UMTS-to-GSM handover in the CS domain

The procedure for the fallback service is described as follows:

Step 1 The CN sends the SRNC a RANAP RAB ASSIGNMENT REQUIREMENT message to set up the VP service. The message includes the "Alternative RAB Para" that has QoS parameters required for setting up the speech service.

Step 2 During UMTS-to-GSM handover, the SRNC sends a RANAP MODIFY REQUEST message to change the VP service to the AMR speech service. In the 3GPP R6 protocol, the Alternative RAB Configuration is also added to the RAB MODIFY REQUEST message, which enables the RNC to request the CN to change the VP service to the AMR speech service.

Step 3 The MSC initiates the Bearer Capability (BC) negotiation with the UE.

Step 4 After the negotiation is modified, the RNC is informed of performing service change. The multimedia fallback ends when the service change is completed.

When the multimedia fallback ends, the RNC decides whether to perform the UMTS-to-GSM handover according to the current measurements reported by the UE.

At the beginning of the service setup, the RNC saves the RAB Para and "Alternative RAB Para" in the RAB ASSIGNMENT or REQUEST RELOCATION REQUEST message. This makes preparations for notifying the CN of changing the VP service to the AMR speech service.

The CN initiates the RAB reconfiguration to inform the two calling parties of performing the multimedia fallback. The multimedia fallback of the calling party is consistent with that of the called party. The single VP service falls back to the single AMR speech service. The multi-RAB service combined with VP falls back to the multi-RAB service combined with AMR. If the multimedia fallback succeeds, that is, the video phone in the service falls back to speech successfully, the inter-RAT handover is initiated. Otherwise, the inter-RAT handover fails.

----End






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3.5.5 UMTS-to-GSM Handover in the PS Domain with NACC or PS Handover

The Network Assisted Cell Change (NACC) function can efficiently reduce the delay of UMTS-to-GSM handover. PS handover is similar to the inter-system handover in CS domains.

UMTS-to-GSM Handover in the PS Domain with NACC Some services have requirements for the delay. If the handover takes too long, TCP may start slowly or data transmission of the stream service may be interrupted due to the overflow of the UE buffer. The introduction of NACC enables the system information exchange between different BSSs, or between BSS and RAN. Thus the inter-system delay, especially inter-system delay in PS domains, can be reduced. With NACC, the RNC sends the cell change order to the UE, which contains the GSM EDGE Radio Access Network (GERAN) system information, when the UMTS-to-GSM handover in the PS domain is triggered.

Figure 3-7 NACC procedure

The procedure is as follows:

Step 1 After the SRNC receives a measurement report from the UE, the UE is reselected to the GERAN cell according to the decision.

Step 2 The SRNC sends a RAN INFORMATION REQUEST message to the SGSN.

Step 3 The SGSN forwards the message to the corresponding BSS.

Step 4 The BSS sends a GERAN SI/PSI message to the SRNC via the SGSN. RAN INFORMATION message can either be On-demand (single report) or On-modification (multiple reports).

Step 5 The SGSN forwards the report message to the SRNC through Iu interface.

Step 6 If there are several report messages, the SRNC terminates reporting by the TERMINATION/END message.

To enable the NACC function, do as follows:

l Run the SET CORRMALGOSWITCH command to set PS_3G2G_CELLCHG_NACC_SWITCH of Handover Algorithm switch to ON.





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l Run the ADD GSMCELL/MOD GSMCELL command to set Inter-RAT cell support RIM indicator to TRUE.

----End

UMTS-to-GSM Handover in the PS Domain with PS Handover To enable the PS HO function, do as follows:

l Run the SET CORRMALGOSWITCH command to set PS_3G2G_RELOCATION_SWITCH of Handover Algorithm switch parameter to ON.

l Run the ADD GSMCELL/MOD GSMCELL command to set Inter-RAT cell support PS HO indicator to TRUE.

3.6 Inter-RAT Handover of HSDPA The introduction of HSDPA does not affect the inter-RAT handover algorithms.

The switch CM permission ind on HSDPA decides whether the Compressed Mode (CM) can be used on HSDPA. For detailed information about the switch, see Inter-Frequency Handover of HSDPA.

When the UE is handed over to a cell supporting the F-DPCH from another system and a UL or DL event 4A is reported, the RNC decides whether to change the bearing mode of TRB and SRB.

If the TPC command is carried on the F-DPCH between the UE and the UTRAN, the SRB and the TRB are carried on the HS-DSCH. If a cell not supporting the F-DPCH is added to the active set, all the F-DPCHs are deleted. In addition, new DPCHs between the UE and all the cells in the active set are set up to carry the SRB and TPC commands. In this case, the TRB is still carried on the HS-DSCH.

3.7 Inter-RAT Handover of HSUPA The introduction of HSUPA does not affect the inter-RAT handover algorithms.

The switch CM permission ind on HSUPA decides whether the Compressed Mode (CM) can be used on HSUPA. For detailed information about the switch, see Inter-Frequency Handover of HSUPA.

3.8 GSM-to-UMTS Handover The GSM-to-UMTS handover is initiated by the GSM network, where the dual-mode (GSM and WCDMA) MSs are required. To support the GSM-to-UMTS handover, both the GSM MSC and the GSM BSS must be upgraded.






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GSM-to-UMTS Handover Penalty Algorithm For the GSM-to-UMTS handover, the measurement control message is delivered through a system information broadcast of 2G when the GSM cell has a WCDMA neighboring cell. The dual-mode MS performs the inter-RAT measurement in idle timeslots and reports the measurement results. Based on the reported measurement values, the BSC decides whether to perform the handover to the WCDMA network. If the decision is made, the BSC begins to perform the handover.

To avoid the ping-pong handover between GSM and UMTS, the GSM-to-UMTS handover penalty alogrithm is used.

When the UE is handed over from GSM to UMTS and if any CS domain service exists, the system increases the hysteresis of event 3A through the parameter Inter-RAT PingPong Hyst to prevent the UE from the ping-pong handover between GSM and UMTS in the period specified by the parameter Inter-RAT PingPong timer.

Interchanging Load Information in GSM-to-UMTS Load or Service-Based Handover

In GSM-to-UMTS handover based on load or service, RNC can make a decision about access admission considering the load information of the 3G target cell. This can avoid the worsening of the 3G system performance caused by GSM-to-UMTS handover based on load or service if the 3G system load is high.

The procedure is described as follows:

Step 1 When the RNC sends a Relocation Request Acknowledge message to the 3G CN,

l If the switch Send Load Info to GSM Ind is set to ON, the Relocation Request Acknowledge message includes the Information Element, New BSS To Old BSS Information, which includes the load information of the 3G target cell.

l If the switch Send Load Info to GSM Ind is set to OFF, the Relocation Request Acknowledge message does not include the Information Element, New BSS To Old BSS Information.

Depending on the network requirement, GSM decides whether to use the load information sent to 3G for judgement.

Step 2 When the RNC receives the RELOCATION REQUEST message from the 3G CN,

l If the 3G cell is not in the basic congestion state, the RNC continues the inter-RAT handover procedure.

l If the 3G cell is in the basic congestion state, the RNC returns RELOCATION FAILURE message to the CN to cancel the inter-RAT handover.

For the concept of "basic congestion", see Basic Congestion Triggering.

----End





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3.9 Interoperability Between Inter-RAT Handover and Inter-Frequency Handover

During the coverage-based and QoS-based UMTS-to-GSM handover, the measurements on both inter-frequency and inter-RAT neighboring cells can be made, which enables the cells to provide continuous coverage and high quality.

The preconditions for the measurements are as follows:

l Both inter-frequency and inter-RAT neighboring cells are available. l Inter-freq and Inter-RAT coexist switch is set to SIMINTERFREQRAT.

If Inter-freq and Inter-RAT coexist switch is set as follows:

l Inter-frequency measurement, which means that the RNC allows the UE to perform only this type of measurement.

l Inter-RAT measurement, which means that the RNC allows the UE to perform only this type of measurement.

l Concurrent inter-frequency and inter-RAT measurement, which means that the RNC allows the UE to perform both types of measurement in compressed mode at the same time.

During the concurrent inter-frequency and inter-RAT measurement, the values of the parameter InterFreq and InterRat coexist measure threshold choice for events 2D and 2F are chosen as follows:

l When the value COEXIST_MEAS_THD_CHOICE_INTERFREQ is chosen, the inter-frequency measurement threshold for event 2D is used.

l When the value COEXIST_MEAS_THD_CHOICE_INTERRAT is chosen, the inter-RAT measurement threshold for event 2D is used.

3.10 Signaling Procedures for Inter-RAT Handover There are five types of signaling procedures for inter-RAT handover.

l UMTS-to-GSM Handover in CS Domain l UMTS to GSM Handover in PS Domain l UMTS-to-GSM Handover in Both CS Domain and PS Domain l GSM-to-UMTS Handover in CS Domain l GSM-to-UMTS Handover in PS Domain

3.10.1 UMTS-to-GSM Handover in CS Domain This describes the UMTS-to-GSM handover in the CS domain.

The following figure shows the signaling procedures for the UMTS-to-GSM handover in the CS domain.






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Figure 3-8 UMTS-to-GSM handover in the CS domain

The signaling procedures are described as follows:

Step 1 The SRNC sends the 3G MSC a RANAP message RELOCATION REQUIRED if the condition of inter-RAT outgoing handover is met.

Step 2 As indicated in the received message, the 3G MSC forwards this request to the 2G MSC on the MAP/E interface through a MAP message PREPARE HANDOVER.

Step 3 The 2G MSC forwards the request to the BSC. The message shown in the figure is for reference only and is subject to the actual condition of the GSM.

Step 4 The BSC responds to this request. The message shown in the figure is for reference only and is subject to the actual condition of the GSM.

Step 5 Once the initial procedures are completed in the 2G MSC/BSS, the 2G MSC returns a MAP/E message PREPARE HANDOVER RESPONSE.

Step 6 The 3G MSC sends the SRNC a RANAP message RELOCATION COMMAND.





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Step 7 The SRNC sends the UE an RRC message HANDOVER FROM UTRAN through the existing RRC connection. This message may include information from one or several other systems.

Step 8 The BSC performs handover detection. The figure does not show such procedures as GSM BSS synchronization. The message shown in the figure is for reference only and is subject to the actual condition of the GSM.

Step 9 The UE sends the BSC a HANDOVER COMPLETE message.

Step 10 The BSC sends the MSC a HANDOVER COMPLETE message. The message shown in the figure is for reference only and is subject to the actual condition of the GSM.

Step 11 After detecting the UE in the coverage area of the GSM, the MSC sends the CN a MAP/E message SEND END SIGNAL REQUEST.

Step 12 The CN sends the former SRNC an IU RELEASE COMMAND message, requesting the former SRNC to release the allocated resource.

Step 13 After the bearer resource is released in the UMTS, the former SRNC sends the CN an IU RELEASE COMPLETE message.

Step 14 After the call ends, the CN sends the MSC a MAP/E message SEND END SIGNAL RESPONSE.

----End

3.10.2 UMTS to GSM Handover in PS Domain For a UE in idle mode or connected mode, if the SGSN changes with the shift of the system that the UE accesses from UMTS to GSM, the inter-SGSN handover will be performed.

Handover for the UE in Connected Mode The handover procedures are different in the following two cases:

l When the UE is in CELL_DCH state The UMTS-to-GSM handover in the PS domain is triggered after the UTRAN sends a CELL CHANGE ORDER FROM UTRAN message.

l When the UE is in CELL_FACH, CELL_PCH, or URA_PCH state The UMTS-to-GSM handover in the PS domain is triggered through the cell reselection.

The following figure shows an example of handover for the UE in CELL_FACH, CELL_PCH, or URA_PCH state.






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Figure 3-9 Example of the UMTS-to-GSM handover in the PS domain


Step 1 The UE in CELL_DCH state or the UTRAN (when the UE is in CELL_FACH state) decides to initiate an inter-RAT handover in the PS domain to hand over the UE to a new GSM cell and stop the data transmission between the UE and the network.

Step 2 The UE sends a ROUTING AREA UPDATE REQUEST message to the 2G SGSN. The Update Type in the message indicates RA update, combined RA/LA update, or combined





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RA/LA update with IMSI attach. The BSS adds the CGI including the RAC and LAC of the cell to the received message before forwarding the message to a new 2G SGSN.

Step 3 The new 2G SGSN sends an SGSN CONTEXT REQUEST message to the old 3G SGSN to obtain the MM and PDP contexts. The old 3G SGSN validates the old P-TMSI Signature. If the old P-TMSI Signature is valid, the old 3G SGSN starts a timer. Otherwise, the old 3G SGSN responds with an error cause.

Step 4 If the UE stays in connected mode before handover, the old 3G SGSN sends an SRNS CONTEXT REQUEST message. After receiving this message, the SRNS buffers the PDUs, stops sending the PDUs to the UE, and sends an SRNS CONTEXT RESPONSE message to the old 3G SGSN.

Step 5 The old 3G SGSN sends an SGSN CONTEXT RESPONSE message to the 2G SGSN, including the MM and PDP contexts.

Step 6 The security functions can be executed.

Step 7 The new 2G SGSN sends an SGSN CONTEXT ACKNOWLEDGE message to the old 3G SGSN. This informs the old 3G SGSN that the new 2G SGSN is ready to receive the PDUs belonging to the activated PDP contexts.

Step 8 The old 3G SGSN sends a DATA FORWARD COMMAND message to the SRNS. The SRNS starts a data-forwarding timer and sends the buffered PDUs to the old 3G SGSN.

Step 9 The old 3G SGSN tunnels the GTP PDUs to the new 2G SGSN. In the PDUs, the sequence numbers in the GTP header remain unchanged.

Step 10 The new 2G SGSN sends an UPDATE PDP CONTEXT REQUEST message to each related GGSN. Each GGSN sends an UPDATE PDP CONTEXT RESPONSE message after updating its PDP context fields.

Step 11 The new 2G SGSN sends an UPDATE GPRS LOCATION message, requesting the HLR to modify the SGSN number.

Step 12 The HLR sends a CANCEL LOCATION message to the old 3G SGSN. The old 3G SGSN responds with a CANCEL LOCATION ACK message. After the timer expires, the old 3G SGSN removes the MM and PDP contexts.

Step 13 The old 3G SGSN sends an IU RELEASE COMMAND message to the SRNS. After the data-forwarding timer expires, the SRNS responds with an IU RELEASE COMPLETE message.

Step 14 The HLR sends an INSERT SUBSCRIBER DATA message to the new 2G SGSN. The 2G SGSN constructs an MM context and PDP contexts for the UE and returns an INSERT SUBSCRIBER DATA ACK message to the HLR.

Step 15 The HLR sends an UPDATE GPRS LOCATION ACK message to the new 2G SGSN.

Step 16 If the association has to be established, the new 2G SGSN sends a LOCATION UPDATE REQUEST message to the VLR. The VLR stores the SGSN number for creating or updating the association.

Step 17 If the subscriber data in the VLR is marked as not confirmed by the HLR, the new VLR informs the HLR. The HLR cancels the old VLR and inserts subscriber data in the new VLR.

1. The new VLR sends an UPDATE LOCATION message to the HLR. 2. The HLR cancels the data in the old VLR by sending a CANCEL LOCATION message

to the old VLR.






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3. The old VLR acknowledges the message by responding with a CANCEL LOCATION ACK message.

4. The HLR sends an INSERT SUBSCRIBER DATA message to the new VLR. 5. The new VLR acknowledges the message by responding with an INSERT

SUBSCRIBER DATA ACK message. 6. The HLR responds with a UPDATE LOCATION ACK message to the new VLR.

Step 18 The new VLR allocates a new TMSI and responds with a LOCATION UPDATE ACCEPT message to the 2G SGSN.

Step 19 The new 2G SGSN checks the presence of the MS in the new RA. If all checks are successful, the new 2G SGSN constructs the MM and PDP contexts for the MS. A logical link is established between the new 2G SGSN and the UE. The 2G SGSN responds to the UE with a ROUTING AREA UPDATE ACCEPT message.

Step 20 The UE acknowledges the new P-TMSI by returning a ROUTING AREA UPDATE COMPLETE message, including all PDUs successfully sent to the UE before the routing area update procedure.

Step 21 The new 2G SGSN sends a TMSI REALLOCATION COMPLETE message to the new VLR if the UE confirms the VLR TMSI.

Step 22 The 2G SGSN and the BSS perform the BSS PACKET FLOW CONTEXT procedure.

----End

Handover for the UE in Idle Mode When the UE is in idle mode, the cell reselection procedure does not include the subprocedure marked with "UE CONNECTED".

3.10.3 UMTS-to-GSM Handover in Both CS Domain and PS Domain

UMTS-to-GSM Handover in Both CS Domain and PS Domain describes the UMTS-to-GSM handover in both CS domain and PS domain.

Inter-RAT Handover in Both CS Domain and PS Domain For a UE in CELL_DCH state using both CS and PS domain services, the inter-RAT handover procedure is based on the measurement reports from the UE but is initiated from the UTRAN.

The UE performs the inter-RAT handover from UTRA RRC Connected Mode to GSM Connected Mode first. After the UE sends a handover complete message to the GSM/BSS, the UE initiates a temporary block flow towards the GPRS to suspend the GPRS services. After the CS domain services are released on the GSM side, the inter-RAT handover in the PS domain resumes, which indicates that the handover is completed.

If the inter-RAT handover from UTRA RRC Connected Mode to GSM Connected Mode succeeds, the handover is regarded as successful, no matter whether the UE initiates a temporary block flow towards the GPRS.

In case of inter-RAT handover failure, the UE may go back to the UTRA RRC Connected Mode and re-establish the connection in the original state.





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Intra-SGSN Service Suspend and Resume

Figure 3-10 Intra-SGSN PS service suspend and resume


Step 1 The UE in connection with both CS and PS domains performs the UMTS-to-GSM handover, during which the CS service is handed over to the GSM.

Step 2 The UE sends a SUSPEND message to the BSS.

Step 3 The BSS forwards the SUSPEND message to the SGSN. The SGSN sends an SRNS CONTEXT REQUEST message to the SRNS, requesting the SRNS to stop sending downlink PDUs. After receiving the message, the SRNS buffers downlink PDUs and responds to the SGSN with an SRNS CONTEXT RESPONSE message. The SGSN returns a SUSPEND ACK message to the BSS.

Step 4 When the CS connection is terminated, the BSS may send a RESUME message to the SGSN. However, resume is impossible since the radio access system has changed. Therefore, the SGSN acknowledges the resume through a RESUME NACK message.

Step 5 The BSS sends an RR message CHANNEL RELEASE to the UE, indicating that the BSS fails to request the SGSN to resume the GPRS service for the UE.

Step 6 The UE sends a ROUTING AREA UPDATE REQUEST message to the SGSN to resume the GPRS service. The update mode depends on the network operation mode in use.

----End

Inter-SGSN Service Suspend and Resume The UE performs inter-RAT handover from UMTS to GSM during the CS connection, and the SGSN handling GSM cells is different from the SGSN handling UMTS cells, that is, the 2G and 3G SGSNs are separated.






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Figure 3-11 Inter-SGSN service suspend and resume


Step 1 The UE in connection with both CS and PS domains performs the UMTS-to-GSM handover, during which the CS service is handed over to the GSM.

Step 2 The UE sends a SUSPEND message to the BSS.

Step 3 The BSS forwards the SUSPEND message to the 2G SGSN. The 2G SGSN sends a SUSPEND ACK message to the BSS.

Step 4 After the CS connection is terminated, the BSS may send a RESUME message to the 2G SGSN. Since the resume is not required for the 3G SGSN, the 2G SGSN acknowledges the resume through a RESUME NACK message.

Step 5 The BSS sends an RR message CHANNEL RELEASE to the UE, indicating that the BSS fails to request the SGSN to resume the GPRS service for the UE.

Step 6 The UE sends a ROUTING AREA UPDATE REQUEST message to the SGSN to resume the GPRS service. The update mode depends on the network operation mode in use.

----End

3.10.4 GSM-to-UMTS Handover in CS Domain When a GSM cell has a neighboring UMTS cell, the measurement control information is contained in the system information. The dual-mode UE performs the inter-RAT measurement in idle timeslots and reports the measurement result. The BSC decides whether to start the inter-RAT handover according to the measurement result.

The GSM system uses time division multiple access technology, and the inter-RAT measurement is performed in idle timeslots. Therefore, the GSM need not support the compressed mode.





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Figure 3-12 GSM-to-UMTS handover in the CS domain


Step 1 The GSM decides to hand over the UE to the UMTS based on the measurement. The BSC sends a HANDOVER REQUIRED message to the 2G MSC, requesting the UMTS to prepare for handover.

Step 2 The 2G MSC forwards a MAP/E message PREPARE HANDOVER to the 3G MSC.

Step 3 The 3G MSC sends a RELOCATION REQUEST message to the RNC.

Step 4 After preparation, the RNC sends a RELOCATION REQUEST ACK message to 3G MSC.

Step 5 The 3G MSC sends a MAP/E message PREPARE HANDOVER RESPONSE to the 2G MSC.

Step 6 The 2G MSC sends a HANDOVER COMMAND message as a response to the initial request of the BSC.

Step 7 If the radio link exists, the BSC sends an INTER-SYSTEM TO UTRAN HANDOVER COMMAND message to the UE, instructing the GSM-to-UMTS handover.

Step 8 When detecting the UE, the RNC sends a RELOCATION DETECT message to the 3G MSC.

Step 9 After the handover, the UE sends a HANDOVER COMPLETE message to the RNC.

Step 10 The RNC sends a RELOCATION COMPLETE message to the 3G MSC.






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Step 11 When detecting that the UE is in the coverage area of the UMTS, the 3G MSC sends a SEND END SIGNAL REQUEST message to the 2G MSC, indicating that the handover is completed and the GSM resources occupied by the UE can be released.

Step 12 The 2G MSC sends a CLEAR COMMAND message to the BSC, requesting the BSC to release related resources.

Step 13 After the release, the GSM BSC sends a CLEAR COMPLETE message to the 2G MSC.

Step 14 The 2G MSC sends a SEND END SIGNAL RESPONSE message to the 3G MSC.

----End

3.10.5 GSM-to-UMTS Handover in PS Domain GSM-to-UMTS Handover in PS Domain describes the GSM-to-UMTS handover in the PS domain.





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Figure 3-13 GSM-to-UMTS handover in the PS domain


Step 1 The GSM decides to perform an inter-RAT handover in the PS domain and stops the data transmission between the UE and the network.

Step 2 The UE sends a ROUTING AREA UPDATE REQUEST message to the 3G SGSN. The Update Type parameter indicates RA update, combined RA/LA update, or combined RA/LA






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update with IMSI attach. The SRNC adds the RAC and LAC of the cell to the received message before forwarding the message to the new 3G SGSN.

Step 3 The 3G SGSN obtains the address of the old 2G SGSN, and then sends an SGSN CONTEXT REQUEST message to the old 2G SGSN to construct the MM and PDP contexts for the UE. The old 2G SGSN validates the P-TMSI signature of the UE.

If the signature is valid or is validated by the 3G SGSN, the 2G SGSN starts a timer.

Step 4 The old 2G SGSN responds with an SGSN CONTEXT RESPONSE message, including the MM and PDP contexts.

Step 5 The security functions can be executed.

Step 6 The 3G SGSN sends an SGSN CONTEXT ACKNOWLEDGE message to the 2G SGSN. The message informs the 2G SGSN that the 3G SGSN is ready to receive the PDUs belonging to the activated PDP contexts.

Step 7 The 2G SGSN copies and buffers N-PDUs, and then sends them to the 3G SGSN. Before the timer expires, if there are other N-PDUs from the GGSN, the 2G SGSN copies and sends them to the 3G SGSN. After the timer expires, the 2G SGSN does not send N-PDUs to the 3G SGSN any more.

Step 8 The 3G SGSN sends an UPDATE PDP CONTEXT REQUEST message to each related GGSN. Each GGSN updates its PDP context and responds with an UPDATE PDP CONTEXT RESPONSE message.

Step 9 The 3G SGSN sends an UPDATE GPRS LOCATION message to the HLR.

Step 10 The HLR sends a CANCEL LOCATION message to the 2G SGSN. After the timer expires, the 2G SGSN removes the MM and PDP contexts. The 2G SGSN responds with a CANCEL LOCATION ACK message.

Step 11 The HLR sends an INSERT SUBSCRIBER DATA message to the 3G SGSN. The 3G SGSN constructs an MM context and sends an INSERT SUBSCRIBER DATA ACK message to the HLR.

Step 12 The HLR sends an UPDATE GPRS LOCATION BY RETURNING AN UPDATE GPRS LOCATION ACK message to the 3G SGSN.

Step 13 If the association has to be established, that is, if the Update Type parameter indicates a combined RA/LA update with IMSI attach requested, or if the LA changed with the RA update, the 2G SGSN sends a LOCATION UPDATE REQUEST message to the VLR. The VLR stores the SGSN number for creating or updating the association.

Step 14 If the subscriber data in the VLR is marked as not confirmed by the HLR, the new VLR informs the HLR. The HLR cancels the old VLR and inserts subscriber data in the new VLR.

1. The new VLR sends an UPDATE LOCATION message to the HLR. 2. The HLR cancels the data in the old VLR by sending a CANCEL LOCATION message

to the old VLR. 3. The old VLR acknowledges the message by responding with a CANCEL LOCATION

ACK message. 4. The HLR sends an INSERT SUBSCRIBER DATA message to the new VLR. 5. The new VLR acknowledges the message by responding with an INSERT

SUBSCRIBER DATA ACK message. 6. The HLR responds with an UPDATE LOCATION ACK message to the new VLR.





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Step 15 The new VLR allocates a new TMSI and notifies the 3G SGSN by sending a LOCATION UPDATE ACCEPT message.

Step 16 The 3G SGSN checks the presence of the MS in the new RA. If all checks are successful, the 3G SGSN constructs MM and PDP contexts for the MS. The 3G SGSN sends a ROUTING AREA UPDATE ACCEPT message to the UE.

Step 17 The UE sends a ROUTING AREA UPDATE COMPLETE message to confirm the allocated P-TMSI.

Step 18 The 3G SGSN sends a TMSI REALLOCATION COMPLETE message to the new VLR.

Step 19 If the UE has uplink data or signaling to send, the UE sends a SERVICE REQUEST message to the SGSN. The service type indicates the required service (data or signaling).

Step 20 The 3G SGSN sends a RAB ASSIGNMENT REQUEST message to the SRNS. The SRNS sends a RADIO BEARER SETUP REQUEST message to the UE. The UE responds with a RADIO BEARER SETUP COMPLETE message. The SRNS sends a RAB ASSIGNMENT RESPONSE message to the SGSN. The SRNS sends N-PDUs to the UE.

----End





RAN Inter-RAT Handover Description 4 Inter-RAT Handover Parameters


4-1

4 Inter-RAT Handover Parameters

Inter-RAT Handover Parameters provides information on the effective level and configuration of the parameters related to the feature.

Table 4-1 Parameters related to Inter-RAT Handover

Parameter Name Parameter ID Effective Level Configurationon ...

2D event trigger delay time TrigTime2D

Cell(ADD CELLINTERRATHOCOV) RNC(SET INTERRATHOCOV) RNC

2D hysteresis HystFor2D


2D2F filter coeff FilterCoefOf2D2F


2F event trigger delay time TrigTime2F


2F hysteresis HystFor2F


3A event retry max times AmntOfRpt3A

Cell(ADD CELLINTERRATHOCOV) RNC



4 Inter-RAT Handover Parameters RAN



Issue 02 (2008-07-30)


RNC(SET INTERRATHOCOV)

3A event retry period PeriodFor3A


3A event trigger delay time TrigTime3A


3A hysteresis Hystfor3A


3A Measure Quantity MeasQuantityOf3A


3A Used-Freq Measure Quantity for Qos

UsedFreqMeasQuantityForQos3A

Cell(ADD CELLQOSHO) RNC(SET QOSHO) RNC

3C event retry max times AmntOfRpt3C

Cell(ADD CELLINTERRATHONCOV) RNC(SET INTERRATHONCOV) RNC

3C event retry period PeriodFor3C


3C event trigger delay time TrigTime3C


3C hysteresis Hystfor3C

Cell(ADD CELLINTERRATHONCOV) RNC





4-3


RNC(SET INTERRATHONCOV)

BSIC verify switch BSICVerify

Cell(ADD CELLINTERRATHONCOV) Cell(ADD CELLINTERRATHOCOV) RNC(SET INTERRATHONCOV) RNC(SET INTERRATHOCOV) RNC

Cell oriented Cell Individual Offset CIO

Cell(ADD CELLSETUP) RNC(ADD NRNCCELL) RNC

CM permission ind on HSDPA

HsdpaCMPermissionInd RNC(SET CMCF) RNC

CMCF Algorithm Switch CmcfSwitch

RNC(SET CORRMALGOSWITCH) RNC

CS domain Reloc GSM load THD CSHOOut2GloadThd


Dl SF limit CM ind DlSFLimitCMInd RNC(SET CMCF) RNC

DL SF threshold DlSFTurnPoint

Cell(ADD CELLCMCF) RNC(SET CMCF) RNC

Dl SF threshold to limit CM LimitCMDlSFThd RNC(SET CMCF) RNC

Down Link Qos Measure timer length DLQosMcTimerLen


Down Link RSCP Used-Freq THD Hyst DlRscpQosHyst


Handover Algorithm Switch HoSwitch

RNC(SET CORRMALGOSWITCH) RNC






Issue 02 (2008-07-30)


InterFreq and InterRat coexist measure threshold choice

CoexistMeasThdChoice

Cell(ADD CELLHOCOMM) RNC(SET HOCOMM) RNC

Inter-freq and Inter-RAT coexist switch InterFreqRATSwitch

Cell(ADD CELLHOCOMM) RNC

Inter-RAT CS Used frequency trigger Ec/No THD UsedFreqCSThdEcN0


Inter-RAT CS Used frequency trigger RSCP THD UsedFreqCSThdRSCP


Inter-RAT H Used frequency trigger Ec/No THD UsedFreqHThdEcN0


Inter-RAT H Used frequency trigger RSCP THD UsedFreqHThdRSCP


Inter-RAT R99 PS Used frequency trigger Ec/No THD

UsedFreqR99PsThdEcN0


Inter-RAT R99 PS Used frequency trigger RSCP THD

UsedFreqR99PsThdRSCP


Inter-RAT cell support PS HO indicator SuppPSHOFlag

Cell(ADD GSMCELL) RNC

Inter-RAT cell support RIM indicator SuppRIMFlag

Cell(ADD GSMCELL) RNC

Inter-RAT cell type RatCellType Cell(ADD GSMCELL) RNC





4-5


Inter-RAT CS handover decision THD TargetRatCsThd


Inter-RAT CS handover decision THD

InterRATNCovHOCSThd


Inter-RAT CS handover switch CSServiceHOSwitch


Inter-RAT CS measure start Ec/No THD

InterRATCSThd2DEcN0


Inter-RAT CS measure start RSCP THD

InterRATCSThd2DRSCP


Inter-RAT CS measure stop Ec/No THD

InterRATCSThd2FEcN0


Inter-RAT CS measure stop RSCP THD

InterRATCSThd2FRSCP


Inter-RAT filter coeff InterRATFilterCoef

Cell(ADD CELLINTERRATHOCOV) RNC(SET INTERRATHOCOV) Cell(ADD CELLINTERRATHONCOV) RNC(SET INTERRATHONCOV) RNC

Inter-RAT H handover decision TargetRatHThd

Cell(ADD CELLINTERRATHO RNC






Issue 02 (2008-07-30)


THD COV) RNC(SET INTERRATHOCOV)

Inter-RAT H measure start Ec/No THD

InterRATHThd2DEcN0


Inter-RAT H measure start RSCP THD

InterRATHThd2DRSCP


Inter-RAT H measure stop Ec/No THD

InterRATHThd2FEcN0


Inter-RAT H measure stop RSCP THD

InterRATHThd2FRSCP


Inter-RAT handover max attempt times InterRATHOAttempts


Inter-RAT hysteresis HystforInterRAT


Inter-RAT measure timer length InterRATMeasTime

Cell(ADD CELLINTERRATHOCOV) RNC(SET INTERRATHOCOV) Cell(ADD CELLINTERRATHONCOV) RNC(SET INTERRATHONCOV) RNC

Inter-RAT PingPong InterRATPingPongHysCell(ADD CELLINTERRATHO RNC





4-7


Hyst t COV) RNC(SET INTERRATHOCOV)

Inter-RAT PingPong timer

InterRATPingPongTimer


Inter-RAT PS handover decision THD

InterRATNCovHOPSThd


Inter-RAT PS handover switch PSServiceHOSwitch


Inter-RAT R99 PS handover decision THD TargetRatR99PsThd


Inter-RAT R99 PS measure start Ec/No THD

InterRATR99PsThd2DEcN0


Inter-RAT R99 PS measure start RSCP THD

InterRATR99PsThd2DRSCP


Inter-RAT R99 PS measure stop Ec/No THD

InterRATR99PsThd2FEcN0


Inter-RAT R99 PS measure stop RSCP THD

InterRATR99PsThd2FRSCP


Inter-RAT report mode InterRatReportMode

Cell(ADD CELLINTERRATHOCOV) RNC(SET RNC






Issue 02 (2008-07-30)


INTERRATHOCOV)

NCOV Reloc Ind based on GSM cell load NcovHoOn2GldInd

RNC(SET INTERRATHONCOV) RNC

Neighboring cell oriented CIO CIOOffset

Cell(ADD INTERFREQNCELL) Cell(ADD INTRAFREQNCELL) Cell(ADD GSMNCELL) RNC

PS domain Reloc GSM load THD PSHOOut2GloadThd


Send Load Info to GSM Ind SndLdInfo2GsmInd

RNC(SET INTERRATHONCOV) RNC

The flag of the priority NPrioFlag

Cell(ADD INTERFREQNCELL) Cell(ADD INTRAFREQNCELL) Cell(ADD GSMNCELL) RNC

The priority of neighbor cell NPrio

Cell(ADD INTRAFREQNCELL) RNC

Time to trigger for non-verified GSM cell

TimeToTrigForNonVerify

RNC(SET INTERRATHOCOV) Cell(ADD CELLINTERRATHOCOV) RNC

Time to trigger for verified GSM cell TimeToTrigForVerify


UL SF threshold UlSFTurnPoint

Cell(ADD CELLCMCF) RNC(SET CMCF) RNC





4-9


Up Link Qos Measure timer length ULQosMcTimerLen


Weight for Used frequency WeightForUsedFreq

Cell(ADD CELLINTERFREQHOCOV) RNC(SET INTERFREQHOCOV) Cell(ADD CELLINTERRATHOCOV) RNC(SET INTERRATHOCOV) RNC





RAN Inter-RAT Handover Description 5 Reference Documents


5-1

5 Reference Documents

Inter-RAT Handover Reference Documents lists the reference documents related to the feature.

l 3GPP TS 23.122: Non Access Stratum functions related to Mobile Station (MS) in idle mode

l 3GPP TS 24.008: Mobile radio interface layer 3 specification; Core Network Protocols - Stage 3

l 3GPP TS 25.304: UE Procedures in Idle Mode and Procedures for Cell Reselection in Connected Mode

l 3GPP TS 25.331: RRC Protocol Specification l 3GPP TS 23.060: General Packet Radio Service (GPRS); Service description l 3GPP TS 25.931: UTRAN Functions, Examples on Signalling Procedures

