Interoperability Between UMTS and LTE(RAN16.0_Draft a)

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Interoperability Between UMTS and

LTE Feature Parameter Description

Issue Draft A

Date 2014-01-20

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Huawei Technologies Co., Ltd.

Address: Huawei Industrial Base

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People's Republic of China Website: http://www.huawei.com

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1 About This Document...1

1.1 Scope...1 1.2 Intended Audience...1 1.3 Change History...1

2 Overview...8

2.1 Background...8 2.2 Function Classification...8 2.3 Application Scenarios...10

2.3.1 Scenario 1: Only Data Cards, Only Data Services, LTE Coverage Still Incomplete...10

2.3.2 Scenario 2: Not Only Data Cards, Only Data Services, CSFB Supported, LTE Coverage Still Incomplete...11

2.3.3 Scenario 3: Data and VoIP Services Supported, LTE Coverage Still Incomplete...12

3 Cell Reselection Between UMTS and LTE...14

3.1 Overview...14

3.2 LTE-to-UMTS Cell Reselection...14

3.3 UMTS-to-LTE Cell Reselection...15

3.3.1 Overview...15

3.3.2 Criteria for Starting Measurements...15

3.3.3 Criteria for Triggering Cell Reselection...16

3.4 UMTS-to-LTE Quick Cell Reselection...19

3.5 UMTS-to-LTE Fast Return...20

3.5.1 Overview...20

3.5.2 UMTS-to-LTE Fast Return...22

3.5.3 Enhanced UMTS-to-LTE Fast Return...22

3.5.4 Selecting Frequencies to Be Carried in the RRC CONNECTION RELEASE Message...23

4 PS Redirections and Handovers Between UMTS and LTE...25

4.1 Overview...25

4.2 LTE-to-UMTS PS Redirections and Handovers...25

4.3 UMTS-to-LTE PS Redirections and Handovers...26

4.3.1 Overview...26

4.3.2 Coverage-based UMTS-to-LTE PS Redirections and Handovers...28

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4.3.2.2 Triggering...29

4.3.2.3 UE Redirections or Handovers to LTE...29

4.3.2.4 Measurements...30

4.3.2.5 Decision and Execution...33

4.3.3 Service-based UMTS-to-LTE PS Redirections and Handovers...37

4.3.3.1 Overview...37

4.3.3.4 Measurements on LTE Signal Quality...39

4.3.3.6 Anti-ping-pong Measures...46

4.3.4 Load-based UMTS-to-LTE PS Redirections and Handovers...47

4.3.4.1 Overview...47

4.3.4.4 UE Selection for LDR...49

4.3.4.5 Measurements...50

4.3.4.7 Suggestions for LDR Action Configurations...53

4.4 Measures to Prevent Frequent Retries After a UMTS-to-LTE PS Handover Failure...54

4.5 Measures to Prevent Ping-Pong Blind Redirections Between UMTS and LTE...55

4.6 Data Forwarding During UMTS-to-LTE Handovers...55

4.6.1 Overview...55

4.6.2 How The Data Forwarding Procedure Flows...55

5 CSFB...57

5.1 Overview...57

5.2 CS Fallback Guarantee for LTE Emergency Calls...58

5.2.1 Overview...58

5.2.2 Policy...58

5.3 CS Fallback Guarantee for LTE Common Calls...59

5.3.1 Overview...59

5.3.2 Policy...59

5.4 CSFB Delay Reduction...60

5.5 Ultra-Flash CSFB...61

6 SRVCC from LTE to UMTS with PS Handover...65

6.1 Overview...66

6.2 Handover Execution...66

7 RIM Based UMTS Target Cell Selection for LTE...69

7.1 Overview...70

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7.2.1 RIM Procedure...70

7.2.2 Reporting of UMTS Cell Load Status...72

8 Related Features...74

8.1 WRFD-140226 Fast Return from UMTS to LTE...74

8.1.1 Required Features...74

8.1.2 Mutually Exclusive Features...74

8.1.3 Impacted Features...74

8.2 WRFD-020129 Service-Based PS Service Redirection from UMTS to LTE...74

8.3 WRFD-140218 Service-Based PS Handover from UMTS to LTE...75

8.4 WRFD-150219 Coverage Based PS Redirection from UMTS to LTE...75

8.5 WRFD-150220 Coverage Based PS Handover from UMTS to LTE...75

8.6 WRFD-150216 Load Based PS Redirection from UMTS to LTE...76

8.7 WRFD-150217 Load Based PS Handover from UMTS to LTE...76

8.8 WRFD-150215 SRVCC from LTE to UMTS with PS Handover...76

8.9 WRFD-150231 RIM Based UMTS Target Cell Selection for LTE...77

8.10 WRFD-160271 Ultra-Flash CSFB...77

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9.1.1 System Capacity...78

9.1.2 Network Performance...78

9.8 WRFD-140102 CS Fallback Guarantee for LTE Emergency Calls...81

9.11 WRFD-160271 Ultra-Flash CSFB...82

10 Engineering Guidelines...83

10.1 WRFD-020126 Mobility Between UMTS and LTE Phase 1...83

10.1.1 When to Use Mobility Between UMTS and LTE Phase 1...83

10.1.2 Feature Deployment...83

10.2.1 When to Use Fast Return from UMTS to LTE...88

10.2.2 Required Information...89

10.2.3 Planning...89

10.2.4 Deployment...89

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10.2.6 Parameter Optimization...95

10.2.7 Troubleshooting...95

10.3.1 When to Use Service-Based PS Service Redirection from UMTS to LTE...96

10.3.2 Required Information...97 10.3.3 Planning...97 10.3.4 Deployment...97 10.3.5 Performance Monitoring...117 10.3.6 Parameter Optimization...118 10.3.7 Troubleshooting...118

10.4.1 When to Use Service-Based PS Handover from UMTS to LTE...118

10.5.1 When to Use Coverage Based PS Redirection from UMTS to LTE...142

10.6.1 When to Use Coverage Based PS Handover from UMTS to LTE...157

10.7.1 When to Use Load Based PS Redirection from UMTS to LTE...169

10.7.2 Required Information...169

10.7.3 Planning...169

10.7.5 Performance Monitoring...195

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10.7.7 Troubleshooting...196

10.8.1 When to Use Load Based PS Handover from UMTS to LTE...196

10.9 WRFD-140102 CS Fallback Guarantee for LTE Emergency Calls...222

10.9.1 When to Use CS Fallback Guarantee for LTE Emergency Calls...222

10.9.3 Performance Monitoring...225

10.10.1 When to Use SRVCC from LTE to UMTS with PS Handover...226

10.11.1 When to Use RIM Based UMTS Target Cell Selection for LTE...232

10.11.2 Required Information...232 10.11.3 Planning...233 10.11.4 Deployment...233 10.11.5 Performance Monitoring...239 10.11.6 Parameter Optimization...239 10.11.7 Troubleshooting...239 10.12 WRFD-160271 Ultra-Flash CSFB...239

10.12.1 When to Use Ultra-Flash CSFB...239

10.12.2 Required Information...239 10.12.3 Planning...240 10.12.4 Deployment...240 10.12.4.1 Requirements...240 10.12.4.2 Data Preparation...240 10.12.4.3 Precautions...240 10.12.4.4 Activation...241 10.12.4.4.1 Using MML Commands...241 10.12.4.4.2 MML Command Examples...241

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10.12.4.5 Activation Observation...242

10.12.4.6 Deactivation...242

10.12.4.6.1 Using MML Commands...242

10.12.4.6.2 MML Command Examples...242

10.12.4.6.3 Using the CME...242

10.12.5 Performance Monitoring...243 10.12.6 Parameter Optimization...244 10.12.7 Troubleshooting...244

11 Parameters...245

12 Counters...1489

13 Glossary...1524

14 Reference Documents...1525

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1

About This Document

1.1 Scope

This document describes Interoperability Between UMTS and LTE, including its technical principles, related features, network impact, and engineering guidelines. This document covers the following features:

l WRFD-020126 Mobility Between UMTS and LTE Phase 1 l WRFD-140226 Fast Return from UMTS to LTE

l WRFD-020129 Service-Based PS Service Redirection from UMTS to LTE l WRFD-140218 Service-Based PS Handover from UMTS to LTE

l WRFD-150219 Coverage Based PS Redirection from UMTS to LTE l WRFD-150220 Coverage Based PS Handover from UMTS to LTE l WRFD-150216 Load Based PS Redirection from UMTS to LTE l WRFD-150217 Load Based PS Handover from UMTS to LTE l WRFD-140102 CS Fallback Guarantee for LTE Emergency Calls l WRFD-150215 SRVCC from LTE to UMTS with PS Handover l WRFD-150231 RIM Based UMTS Target Cell Selection for LTE

1.2 Intended Audience

This document is intended for personnel who: l Need to understand the features described herein l Work with Huawei products

1.3 Change History

This section provides information about the changes in different document versions. There are two types of changes, which are defined as follows:

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l Feature change

Changes in features of a specific product version l Editorial change

Changes in wording or addition of information that was not described in the earlier version

Draft A (2014-01-20)

Compared with Issue 05 (2013-12-30) of RAN15.0, Draft A (2014-01-20) for RAN16.0 includes the following changes.

Change Type Change Description Parameter Change Feature change Added descriptions of

preventing frequent retries after a U2L PS handover failure. For details, see section 4.4 Measures to Prevent Frequent Retries After a UMTS-to-LTE PS Handover Failure. Added the U2LphyChFailNum (BSC6900,BSC6910) parameter

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Change Type Change Description Parameter Change Added descriptions of

load-based LTE cell selection during UMTS-to-LTE handovers and redirections, including function

descriptions, related features, network impacts, and engineering guidelines in the following sections: 4.3.3 Service-based UMTS-to-LTE PS Redirections and Handovers 4.3.4 Load-based UMTS-to-LTE PS Redirections and Handovers 8.2 WRFD-020129 Service-Based PS Service

Redirection from UMTS to LTE

8.3 WRFD-140218 Service-Based PS Handover from UMTS to LTE

8.6 WRFD-150216 Load Based PS Redirection from UMTS to LTE

8.7 WRFD-150217 Load Based PS Handover from UMTS to LTE

9.2 WRFD-020129 Service-Based PS Service

Redirection from UMTS to LTE

9.3 WRFD-140218 Service-Based PS Handover from UMTS to LTE

10.3 WRFD-020129 Service-Based PS Service Redirection from UMTS to LTE

Added the following parameters: l ProcessSwitch5 (BSC6900,BSC6910): INTERRAT_LOAD_R EPORT_FROM_LTE_ SWITCH l U2LLTELoadSwitch (BSC6900,BSC6910)

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Change Type Change Description Parameter Change

10.4 WRFD-140218 Service-Based PS

Handover from UMTS to LTE

Added descriptions of functions for guaranteeing and improving network performance during

handovers for SRVCC from LTE to UMTS, including function descriptions, network impacts, and engineering guidelines in the following chapter and sections:

6 SRVCC from LTE to UMTS with PS Handover 9.9 WRFD-150215 SRVCC from LTE to UMTS with PS Handover

10.10 WRFD-150215 SRVCC from LTE to UMTS with PS Handover

Added the following parameters: l U2LLTELoadSwitch (BSC6900,BSC6910) l L2USRVCCEmerCal-lARP (BSC6900,BSC6910) Added descriptions of counters measuring LTE to UMTS handovers of only PS services. For details, see section 4.2 LTE-to-UMTS PS Redirections and Handovers.

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Change Type Change Description Parameter Change Added and modified

descriptions of measures for reducing the CSFB delay. For details, see section 5.4 CSFB Delay Reduction.

Added the following switches to the ImprovementSwitch (BSC6900,BSC6910) parameter in the MML command SET URRCTRLSWITCH: l PSHO_CSFB_CAP_EN Q_DELAY_SWITCH l CSFB_UE_DELAY_R AU_SWITCH l CSFB_UE_CS_IMEI_ QUERY_DISABLE_S WITCH

Added the Ultra-Flash CSFB feature's principles, related features, network impacts, and engineering guidelines. For details, see the following sections: l 5.5 Ultra-Flash CSFB l 8.10 WRFD-160271 Ultra-Flash CSFB l 9.11 WRFD-160271 Ultra-Flash CSFB l 10.12 WRFD-160271 Ultra-Flash CSFB

Added the following parameters: l PROCESSSWITCH2 (BSC6900,BSC6910): ULTRA_FLASH_CSF B_SWITCH l UltraFlashCSFBSR-BRate (BSC6900,BSC6910)

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Change Type Change Description Parameter Change Added the principle and

engineering guidelines for exchanging RAN

information management (RIM) messages through the eCoordinator. For details, see the following sections: l 7.2.1 RIM Procedure

l 10.3 WRFD-020129

Service-Based PS Service Redirection from UMTS to LTE

l 10.4 WRFD-140218

Service-Based PS Handover from UMTS to LTE l 10.7 WRFD-150216 Load Based PS Redirection from UMTS to LTE l 10.8 WRFD-150217 Load Based PS

Handover from UMTS to LTE

l 10.11 WRFD-150231 RIM Based UMTS Target Cell Selection for LTE

Added the following parameter:

PROCESSSWITCH5 (BSC6900,BSC6910): RIM_ON_ECO_SWITCH

Changed the parameter for U2L Blind Redir Anti-Pingpong Timer.

Changed the switch from the RsvU32Para10 parameter of the SET UALGORSVPARA command to the U2LBlindRedirPingpong-Timer(BSC6900,BSC6910) parameter of the SET UHOCOMM command.

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Change Type Change Description Parameter Change Changed the parameter for

Penalty Time for Service-based U2L Meas Expiry.

Changed the switch from the RsvU32Para9 parameter of the SET UALGORSVPARA command to the U2lServMcTimeOutPu-nishTime (BSC6900,BSC6910) parameter of the SET UU2LTEHONCOV command.

Optimized the mechanism for accessing the network at a decreased rate during an LTE-to-UMTS PS handover. For details, see section 4.2 LTE-to-UMTS PS Redirections and Handovers. Added PERFENH_SYSHO_IN_F AIL_RETRY_SWITCH to the CellConnAlgoSwitch1 (BSC6900,BSC6910) parameter in the following command:

ADD

UCELLCONNALGOPAR

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2

Overview

2.1 Background

As wireless data services rapidly grow and conditions mature for LTE commercial use, telecom operators are beginning to execute plans to build LTE networks upon existing UMTS networks. These two types of networks will have to coexist for a long time, so interoperability between UMTS and LTE is important. This feature helps make the most of existing network equipment, provide diversified services, and achieve smooth network evolution. Huawei products support interoperability between UMTS and time division duplex (TDD) LTE and between UMTS and frequency division duplex (FDD) LTE.

2.2 Function Classification

Interoperability between UMTS and LTE functions are classified by UE status, as shown in

Table 2-1.

Table 2-1 Interoperability between UMTS and LTE functions classified by UE status

UE Status Interoperability Between

UMTS and LTE Functions

Idle mode UMTS-to-LTE cell

reselection

Idle mode LTE-to-UMTS cell

reselection. See LTE document Idle Mode Management Feature Parameter Description for details.

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UE Status Interoperability Between UMTS and LTE

Functions Connected mode Data services LTE-to-UMTS PS

redirections or handovers. See LTE document Mobility Management in Connected Mode Feature Parameter Description for details. LTE-to-UMTS handovers based on the UMTS cell load UMTS-to-LTE quick cell reselection

Service-based UMTS-to-LTE PS redirections and handovers Coverage-based UMTS-to-LTE PS redirections or handovers Load-based UMTS-to-LTE PS redirections or handovers Voice services LTE-to-UMTS

circuit-switched fallback (CSFB) specified by 3GPP Release 8. See LTE document CS Fallback Feature Parameter Description for details. LTE-to-UMTS CSFB based on the UMTS cell load UMTS-to-LTE fast return CSFB guarantee for emergency calls originated on the LTE network

CSFB guarantee for common calls originated on the LTE network

LTE-to-UMTS SRVCC with PS handovers

Currently, LTE does not support voice services. Therefore, interoperability between UMTS and LTE does not address UMTS-to-LTE handovers of CS services or CS/PS combined services.

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2.3 Application Scenarios

2.3.1 Scenario 1: Only Data Cards, Only Data Services, LTE

Coverage Still Incomplete

Description

l UMTS/LTE multi-mode UEs only support PS services and PS handovers.

UMTS/LTE multi-mode UEs can initiate services in both the UMTS and LTE networks. l No IP Multimedia Subsystem (IMS) has been deployed on the LTE network and therefore

VoIP services are not supported. l LTE coverage is still incomplete.

UE Camping Policy

In scenario 1, the UE camping policy is as follows: An LTE-first policy is recommended for UE camping, because commercial UMTS/LTE multi-mode UEs are all in data-card mode.

To adopt an LTE-first policy for UE camping, set high priorities for LTE frequencies so that the LTE network is preferred during cell reselection.

Cell reselection is performed to shift UEs in idle mode or the CELL_PCH/URA_PCH state between UMTS and LTE. For details, see chapter 3 Cell Reselection Between UMTS and LTE.

CS Service Policy

CS services are not supported, because commercial UMTS/LTE multi-mode UEs are all in data-card mode.

PS Service Policy

In scenario 1, the PS service policy is as follows:

l Since LTE coverage is still incomplete, when a UE processing a PS service on the LTE network moves out of the LTE coverage area, a PS handover or redirection to the UMTS network is performed for the UE and the PS service. For details, see section 4.2 LTE-to-UMTS PS Redirections and Handovers.

l When a UE processing a PS service on the UMTS network moves to an LTE coverage area, a PS handover or redirection to the LTE network is not performed.

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2.3.2 Scenario 2: Not Only Data Cards, Only Data Services, CSFB

Supported, LTE Coverage Still Incomplete

Description

l Commercial UMTS/LTE multi-mode UEs in data-card mode and non-data-card mode are in use.

l No IMS has been deployed on the LTE network and therefore VoIP services are not supported.

l The networks and UEs support CSFB. l LTE coverage is still incomplete.

UE Camping Policy

In scenario 2, the UE camping policy is as follows:

Huawei products support either the LTE network or the UMTS network as the preferred choice for UE camping. An LTE-first policy is recommended for this phase. To adopt a UMTS-first policy for UE camping, set low priorities for LTE frequencies so that the UMTS network is preferred during cell reselection.

CS Service Policy

In scenario 2, the CS service policy is as follows:

l When a UE initiates a voice service on the LTE network, both the UE and the voice service will fall back to the UMTS network.

The CSFB policy is as follows:

– The eNodeB preferentially selects a non-overloaded UMTS target cell for CSFB to reduce the CSFB delay and improve user experience. For details, see chapter 8 "RIM Based UMTS Target Cell Selection for LTE."

– Emergency calls initiated on the LTE network are ensured a high CSFB success rate. For details, see chapter 5.2 CS Fallback Guarantee for LTE Emergency Calls. l A UE processing a CS service or CS/PS combined service on the UMTS network remains

on the UMTS network to ensure CS service continuity.

PS Service Policy

l Since LTE coverage is still incomplete in this phase, when a UE processing a PS service on the LTE network moves out of LTE coverage, a PS handover or redirection to the UMTS network will be performed. For details, see section 4.2 LTE-to-UMTS PS Redirections and Handovers. When a UE processing a PS service on the UMTS network moves to an LTE coverage area, the UE can remain on the UMTS network.

l A UMTS-first policy can be adopted for UE camping. Under this policy, when a UE initiates a PS service in a UMTS/LTE overlapping coverage area, a service-based UMTS-to-LTE PS handover or redirection is performed to shift the UE and the PS service to the LTE

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network. This mechanism makes efficient use of the LTE network. For details, see section

4.3.3 Service-based UMTS-to-LTE PS Redirections and Handovers.

l When a UE processing a PS service initiates a CS service, CSFB is performed and a PS handover or redirection is used to shift the PS service to the UMTS network. If the PS service is still in progress when the CS service is complete and the LTE signal quality meets specific conditions, a service-based UMTS-to-LTE PS handover or redirection is

performed to shift the UE and the PS service back to the LTE network. For details, see section 4.3.3 Service-based UMTS-to-LTE PS Redirections and Handovers.

l If a load-based LTE-to-UMTS handover is triggered when the LTE cell is congested, the UE is preferentially handed over to a non-congested or non-overloaded UMTS cell. This avoids inter-RAT ping-pong handovers, improves the handover preparation success rate, and reduces loads on the LTE network. For details, see chapter 7 RIM Based UMTS Target Cell Selection for LTE.

2.3.3 Scenario 3: Data and VoIP Services Supported, LTE Coverage

Still Incomplete

Description

l An IMS has been deployed on the LTE network. Therefore, both PS data services and VoIP services are supported.

l LTE coverage is still incomplete.

UE Camping Policy

An LTE-first policy is recommended. If the delay caused by CSFB is too long to ensure service quality, adopt a UMTS-first policy.

CS Service Policy

In scenario 3, the CS service policy is as follows:

l When a UE processing a VoIP service on the LTE network moves out of the LTE coverage area, the Single Radio Voice Call Continuity (SRVCC) feature converts the VoIP service to a CS service on the UMTS network. This mechanism ensures voice service continuity. For details, see chapter 7 "SRVCC from LTE to UMTS with PS Handover."

l A UE processing a CS service or CS/PS combined service remains on the UMTS network to ensure CS service continuity.

PS Service Policy

l Since LTE coverage is still incomplete, when a UE processing a PS service on the LTE network moves out of the LTE coverage area, a PS handover or redirection to the UMTS network is performed. For details, see section 4.1 "LTE-to-UMTS PS Redirections and Handovers." When a UE processing a PS service on the UMTS network moves to an LTE coverage area, the UE can remain on the UMTS network.

l A UMTS-first policy can be adopted for UE camping. Under this policy, when a UE initiates a PS service in a UMTS/LTE overlapping coverage area, a service-based UMTS-to-LTE

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PS handover or redirection is performed to shift the UE and the PS service to the LTE network. This mechanism makes efficient use of the LTE network. For details, see section

Service-based UMTS-to-LTE PS Redirections and Handovers.

l When a UE processing a PS service initiates a CS service, CSFB is performed and a PS handover or redirection is used to shift the PS service to the UMTS network. If the PS service is still in progress when the CS service is complete and the LTE signal quality meets specific conditions, a service-based UMTS-to-LTE PS handover or redirection is

performed to shift the UE and the PS service back to the LTE network. For details, see section Service-based UMTS-to-LTE PS Redirections and Handovers.

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3

Cell Reselection Between UMTS and LTE

3.1 Overview

Cell reselection between UMTS and LTE includes UMTS-to-LTE cell reselection, LTE-to-UMTS cell reselection, LTE-to-UMTS-to-LTE fast return, and LTE-to-UMTS-to-LTE quick cell reselection. When camping on the UMTS network, a UMTS/LTE multi-mode UE receives system information from the UMTS cell. System information block 19 (SIB19) carries the absolute priorities of the serving UMTS cell and LTE frequencies. If the absolute priorities of one or more LTE frequencies are higher than the absolute priority of the serving UMTS cell, the corresponding LTE cell or cells are the preferred target cells for cell reselection. If the absolute priorities of all LTE frequencies are lower than the absolute priority of the serving UMTS cell, UMTS cells are the preferred target cells for cell reselection.

When camping on the LTE network, a UMTS/LTE multi-mode UE receives system information from the LTE cell. SIB3 carries the absolute priority of the serving LTE cell, SIB5 carries the absolute priorities of the LTE frequencies, and SIB6 carries the absolute priorities of the UMTS frequencies. You can manipulate these priorities to favor UMTS or LTE cells as target cells for reselection.

When camping on the UMTS network, a UMTS/LTE multi-mode UE can initiate UMTS-to-LTE cell reselection only when it is in the CELL_PCH or idle state. To accelerate the reselection process, you need to enable fast state transition from CELL_DCH to CELL_PCH or from CELL_DCH to the idle state. With this function, the UMTS/LTE multi-mode UE can transit to the CELL_PCH or idle state within a short period of time after data transmission is complete, thereby initiating the UMTS-to-LTE cell reselection.

The SibCfgBitMap(BSC6900,BSC6910) parameter in the ADD/MOD UCELLSIBSWITCH command specifies whether to broadcast SIB19.

3.2 LTE-to-UMTS Cell Reselection

LTE-to-UMTS cell reselection is used when the LTE network is new and provides incomplete coverage, but the UMTS coverage is complete. LTE-to-UMTS cell reselection is based on absolute priorities and mainly involves the LTE network.

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3.3 UMTS-to-LTE Cell Reselection

3.3.1 Overview

This chapter describes the WRFD-020126 Mobility Between UMTS and LTE Phase 1 feature. When a UE in the UMTS network receives SIB19 and specific conditions are met, the UE starts measuring the LTE signal quality. Based on the measurement results, the UE camps on the best cell by performing reselection.

3.3.2 Criteria for Starting Measurements

SIB19 carries the absolute priority of the serving UMTS cell, the absolute priorities of the LTE frequencies, and the cell reselection thresholds. Different radio access technologies (RATs) must have different priorities. Upon receiving SIB19, the UE does the following:

l If Srxlev_ServingCell is less than or equal to S_{prioritysearch1} or Squal_ServingCell is less than or equal to S_{prioritysearch2}, the serving UMTS cell has poor signal quality. In this situation, the UE starts measuring the signal quality of the neighboring LTE cells that work on low- and high-priority frequencies.

l If Srxlev_ServingCell is greater than S_{prioritysearch1} and Squal_ServingCell is greater than S_{prioritysearch2}, the serving UMTS cell has good signal quality. In this situation, the UE measures the signal quality of the LTE frequencies that have higher absolute priorities than the serving cell at an interval of at least Thigher_priority_search.

Where,

l According to section 4.2.2 Requirements in 3GPP TS 25.133 V11.5.0, the value of Thigher_priority_search is the number of frequencies multiplied by 60, in the unit of second.

l The SPriority(BSC6900,BSC6910) parameter in the ADD UCELLSELRESEL or MOD UCELLSELRESEL command specifies the absolute priority of the serving UMTS cell. l The NPriority(BSC6900,BSC6910) parameter in the ADD UCELLNFREQPRIOINFO

or MOD UCELLNFREQPRIOINFO command specifies the absolute priorities of the LTE frequencies.

l The ThdPrioritySearch1(BSC6900,BSC6910) and ThdPrioritySearch2 (BSC6900,BSC6910) parameters in the ADD UCELLSELRESEL or MOD

UCELLSELRESEL command specify the values of Sprioritysearch1 and Sprioritysearch2, respectively.

– Sprioritysearch1 specifies the CPICH RSCP thresholds for measuring the low- and high-priority LTE frequencies. CPICH RSCP refers to the common pilot channel received signal code power.

– Sprioritysearch2 specifies the CPICH Ec/N0 thresholds for measuring the low- and high-priority LTE frequencies. CPICH Ec/N0 refers to the signal-to-noise ratio of the CPICH. The other variables are defined as follows:

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– Squal: cell quality value (dB), which applies only to FDD cells – Qrxlevmin(BSC6900,BSC6910): required minimum RX level – Qqualmin(BSC6900,BSC6910): required minimum quality level

– SrxlevServingCell: serving cell's RSCP measured by the UE minus Qrxlevmin (BSC6900,BSC6910).

– Squal_ServingCell: serving cell's Ec/N0 measured by the UE minus Qqualmin (BSC6900,BSC6910).

The UE should not perform cell reselection to a cell for which cell selection criterion S is not fulfilled. For details about criterion S, see UE Behaviors in Idle Mode Feature Parameter

Description.

3.3.3 Criteria for Triggering Cell Reselection

After measuring the UMTS serving cell and LTE frequencies, the UE shifts to the best cell by performing reselection.

SIB19 carries the absolute priority of the serving UMTS cell, the absolute priorities of the LTE frequencies, and the cell reselection thresholds. The UE performs cell reselection based on the absolute priorities.

Section 5.2.6.1.4a Absolute priority based criteria for inter-frequency and inter-RAT cell reselection in 3GPP TS 25.304 V11.3.0 specifies five sets of criteria for cell reselection based on the absolute priorities. However, criteria set 2 is used for inter-frequency scenarios, not for inter-RAT scenarios, and SIB19 does not carry the absolute priorities of UMTS inter-frequencies by Huawei products. Therefore, criteria set 2 is not supported by Huawei products.

Criteria sets 1, 3, 4, and 5 apply to UMTS-to-LTE reselection. Criteria sets 1 and 3 use the reference signal received power (RSRP) as the measurement quantity, while criteria sets 4 and 5 use the Reference Signal Received quality (RSRQ) as the measurement quantity. For a description of each criteria set, see Table 3-1.

The RSRQSwitch(BSC6900,BSC6910) parameter in the ADD UCELLNFREQPRIOINFO or MOD UCELLNFREQPRIOINFO command controls whether the UE performs cell

reselection based on the RSRQ of the LTE frequency. When RSRQSwitch

(BSC6900,BSC6910) is set to TRUE and the UE supports the RSRQ-based measurement, the UE performs cell reselection based on the RSRQ. Otherwise, the UE performs cell reselection based on the RSRP.

Table 3-1 Criteria sets 1, 3, 4, and 5 for triggering cell reselection

Criteria Set Description

Criteria set 1 l The absolute priority of an LTE frequency is higher than the absolute priority of the serving UMTS cell.

l The Srxlev value of the LTE frequency, Srxlev_{nonServingCell,}has remained above the threshold Thresh_high for a period of time longer than Treselection.

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Criteria Set Description

Criteria set 3 l The absolute priority of an LTE frequency is lower than the absolute priority of the serving UMTS cell.

l SrxlevnonServingCell has remained above Threshlow for a period of time longer than Treselection.

l SrxlevServingCell has remained below Threshserving,low for a period of time longer than Treselection, or

Squal_ServingCell has remained below 0 for a period of time longer than

Treselection.

Criteria set 4 l The absolute priority of an LTE frequency is higher than the absolute priority of the serving UMTS cell.

l The Squal value of the LTE frequency, Squal_{nonServingCell,}has remained above the threshold Thresh_high2 for a period of time longer than Treselection.

Criteria set 5 l The absolute priority of an LTE frequency is lower than the absolute priority of the serving UMTS cell.

l SqualnonServingCell has remained above Threshlow2 for a period of time longer than Treselection.

l SqualServingCell has remained below Threshserving,low2 for a period of time longer than Treselection.

The following are details about the parameters referenced in Table 3-1:

l Thresh_high is the relative threshold for the target cell's RX level to EQrxlevmin

(BSC6900,BSC6910) when the absolute priority of the target frequency is higher than the absolute priority of the serving UMTS cell. The ThdToHigh(BSC6900,BSC6910) parameter specifies the value of Thresh_high. The greater the value of this parameter, the less likely reselection is to occur.

l Thresh_low is the relative threshold for the target cell's RX level to EQrxlevmin

(BSC6900,BSC6910) when the absolute priority of the target frequency is lower than the absolute priority of the serving UMTS cell. The ThdToLow(BSC6900,BSC6910) parameter specifies the value of Thresh_low. The greater the value of this parameter, the less likely reselection is to occur.

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l EQrxlevmin(BSC6900,BSC6910) is the minimum required RX level of the cell on the target frequency.

l Treselection is the reselection delay. The Treselections(BSC6900,BSC6910) parameter specifies the value of Treselection.

l Threshserving,low is the threshold for the serving cell's RSCP during reselection to an LTE cell working at an LTE frequency with a lower absolute priority. The ThdServingLow (BSC6900,BSC6910) parameter specifies the value of Thresh_serving,low. When the LTE frequencies of lower absolute priorities are being measured, if the signal quality of the serving UMTS cell constantly remains below Thresh_serving,low and the signal quality of a cell at theLTE frequency satisfies the formula Srxlev_{nonServingCell}> Thresh_low,the UE triggers reselection to the cell. The greater the value of this parameter, the more likely cell reselection based on absolute priorities is to occur.

l Threshhigh2 is the relative threshold for the target cell's signal quality to EQrxlevmin (BSC6900,BSC6910) when the absolute priority of the target frequency is higher than the absolute priority of the serving UMTS cell. The ThdToHighRSRQ(BSC6900,BSC6910) parameter specifies the value of Threshhigh2. The greater the value of this parameter, the less likely reselection is to occur.

l EQrxlevmin(BSC6900,BSC6910) is the minimum signal quality of a cell using the target frequency.

l Thresh_low2 is the relative threshold for the target cell's signal quality to EQrxlevmin (BSC6900,BSC6910) when the absolute priority of the target frequency is lower than the absolute priority of the serving UMTS cell. The ThdToLowRSRQ(BSC6900,BSC6910) parameter specifies the value of Thresh_low2. The greater the value of this parameter, the less likely reselection is to occur.

l Thresh_serving,low2 is the CPICH Ec/N0 threshold for the serving UMTS cell when the UE reselects a cell working on a lower-priority LTE frequency. The ThdServingLow2 (BSC6900,BSC6910) parameter specifies the value of Thresh_serving,low2. After the cell reselection measurement starts, if the signal quality of the serving cell remains lower than this parameter value and the signal quality of the target cell using a lower-priority frequency remains high during the cell reselection delay time specified by Treselections

(BSC6900,BSC6910), the UE will perform cell reselection. To summarize:

l If the criteria in criteria set 1 or 4 are fulfilled, the UE performs reselection to a cell working at an LTE frequency with a higher absolute priority.

l If the criteria in criteria set 3 or 5 are fulfilled, the UE performs reselection to a cell working at an LTE frequency with a lower absolute priority.

l If the criteria in neither group are fulfilled, the UE remains on the UMTS network. If multiple cells fulfill a set of criteria, the UE performs reselection to the cell with the greatest SrxlevnonServingCell value.

The following parameters are set by running the ADD UCELLNFREQPRIOINFO or MOD UCELLNFREQPRIOINFO command:

l ThdToHigh(BSC6900,BSC6910) l ThdToLow(BSC6900,BSC6910)

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l EQrxlevmin(BSC6900,BSC6910) l ThdToHighRSRQ(BSC6900,BSC6910) l EQqualmin(BSC6900,BSC6910) l ThdToLowRSRQ(BSC6900,BSC6910)

The following parameters are set by running the ADD UCELLSELRESEL or MOD UCELLSELRESEL command:

l Treselections(BSC6900,BSC6910) l ThdServingLow(BSC6900,BSC6910) l ThdServingLow2(BSC6900,BSC6910)

3.4 UMTS-to-LTE Quick Cell Reselection

A UMTS/LTE multi-mode UE camping on the UMTS network can initiate UMTS-to-LTE cell reselection only when it is in the CELL_PCH or idle state. In RAN14.0 and earlier versions, state transition to the CELL_PCH or idle state is slow because the state transition is triggered only when the UE does not transmit or receive service data during the time length of an inactivity timer.

The inactivity timer can be:

l PsInactTmrForCon(BSC6900,BSC6910) (conversational services), PsInactTmrForStr (BSC6900,BSC6910) (streaming services), PsInactTmrForInt(BSC6900,BSC6910) (interactive services), or PsInactTmrForBac(BSC6900,BSC6910) (background services) for UEs that are not enabled with enhanced fast dormancy

l PsInactTmrForFstDrmDch(BSC6900,BSC6910) for UEs that are enabled with enhanced fast dormancy and in the CELL_DCH state

l PsInactTmrForFstDrmFach(BSC6900,BSC6910) for UEs that are enabled with enhanced fast dormancy and in the CELL_FACH state

To accelerate the UMTS-to-LTE cell reselection, you need to enable the UMTS-to-LTE quick cell reselection function by running the SET URRCTRLSWITCH command with

FAST_RETURN_LTE_BY_CELL_SELECT_SWITCH under PROCESSSWITCH4 (BSC6900,BSC6910) set to ON. The details of this function are as follows:

l For UEs that are not enabled with enhanced fast dormancy

State transition to the CELL_PCH or idle state is triggered when the UE does not transmit or receive service data during the time length specified by PsInactTmrForFstDrmDch (BSC6900,BSC6910), not the time length specified by PsInactTmrForCon

(BSC6900,BSC6910). The default value of PsInactTmrForFstDrmDch

(BSC6900,BSC6910) is less than that of PsInactTmrForCon(BSC6900,BSC6910) and therefore the cell reselection process is faster.

State transition from CELL_DCH to CELL_PCH or the idle state by running the SET URRCTRLSWITCH command with

UL_DUAL_MODE_UE_D2P_OR_D2I_SWITCH set to an appropriate value under PROCESSSWITCH4(BSC6900,BSC6910). When

UL_DUAL_MODE_UE_D2P_OR_D2I_SWITCH is cleared, the UE transits from CELL_DCH to CELL_PCH. When UL_DUAL_MODE_UE_D2P_OR_D2I_SWITCH is selected, the UE transits from CELL_DCH to the idle state.

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UL_DUAL_MODE_UE_D2P_OR_D2I_SWITCH under PROCESSSWITCH4 (BSC6900,BSC6910) is cleared by default. Select

UL_DUAL_MODE_UE_D2P_OR_D2I_SWITCH if some UEs in the network do not support state transition from CELL_DCH to CELL_PCH.

l For UEs that are enabled with enhanced fast dormancy and in the CELL_DCH state – When RNC_EFD_D2F_SWITCH under OptimizationSwitch(BSC6900,BSC6910) is

set to 1 by running the SET URRCTRLSWITCH command, the UE transits from CELL_DCH to CELL_FACH when it does not transmit or receive service data during the time length specified by PsInactTmrForFstDrmDch(BSC6900,BSC6910) and then transits from CELL_FACH to CELL_PCH or the idle state when it does not transmit or receive service data during the time length specified by

PsInactTmrForFstDrmFach(BSC6900,BSC6910). After UMTS-to-LTE quick cell reselection is enabled, the UE is able to transit from CELL_DCH directly to CELL_PCH or the idle state when it does not transmit or receive service data during the time length specified by PsInactTmrForFstDrmDch(BSC6900,BSC6910) without the need to wait until PsInactTmrForFstDrmFach(BSC6900,BSC6910) expires. This shortens the duration of the UMTS-to-LTE cell reselection.

– When RNC_EFD_D2F_SWITCH under OptimizationSwitch(BSC6900,BSC6910) is set to 0, UMTS-to-LTE quick cell reselection does not provide gains for these UEs. State transition from CELL_DCH to CELL_PCH or the idle state is triggered when the UE does not transmit or receive service data during the time length specified by PsInactTmrForFstDrmDch(BSC6900,BSC6910), regardless of whether UMTS-to-LTE quick cell reselection is enabled.

l For UEs that are enabled with enhanced fast dormancy and in the CELL_FACH state UMTS-to-LTE quick cell reselection does not provide gains for these UEs. State transition from CELL_FACH to CELL_PCH or the idle state is triggered when the UE does not transmit or receive service data during the time length specified by

PsInactTmrForFstDrmFach(BSC6900,BSC6910) regardless of whether UMTS-to-LTE quick cell reselection is enabled.

Changing the value of PsInactTmrForFstDrmDch(BSC6900,BSC6910) or

PsInactTmrForFstDrmFach(BSC6900,BSC6910) affects this feature and the Enhanced Fast Dormancy feature. For details about enhanced fast dormancy, see Enhanced Fast

Dormancy Feature Parameter Description.

3.5 UMTS-to-LTE Fast Return

3.5.1 Overview

This section describes the WRFD-140226 Fast Return from UMTS to LTE feature.

In an area jointly covered by UMTS and LTE networks, a UE accesses a UMTS cell due to CSFB. When the UE finishes all services in the UMTS cell, it releases the RRC connection. In versions earlier than RAN14.0, if the absolute priority of a neighboring LTE cell's frequency is higher than that of the UMTS cell's frequency, the RRC CONNECTION RELEASE message does not contain the frequency information about neighboring LTE cells. As a result, the UE camps on a UMTS cell.

If a neighboring LTE cell fulfills the cell reselection conditions, the UE reselects the neighboring LTE cell. Before the reselection, the UE must receive system information MIB, SIB1, SIB3,

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SIB5, SIB7, or SIB19 and determine which criteria set listed in Table 3-1 will be used. As a result, the time for the UE to return from the UMTS network to the LTE network is long. The Fast Return from UMTS to LTE feature is introduced to reduce the time and improve user experience.

This feature applies to the areas that are jointly covered by UMTS and LTE networks and where the LTE network signal quality is satisfactory.

If the LTE network signal quality is poor, for example, when an RRC CONNECTION RELEASE message contains information about n (a positive integer) LTE frequencies whose signal quality is poor:

l UEs complying with a version earlier than 3GPP Release 10 select a suitable LTE cell from the LTE cells using n LTE frequencies. The selection lasts for at most 10 seconds. If no suitable LTE cell is found, these UEs select a suitable LTE cell from the LTE cells using frequencies supported by these UEs. If a suitable LTE cell is still not found, these UEs randomly camp on a suitable cell. For details, see section 8.5.2 Actions when entering idle mode from connected mode in 3GPP TS 25.331 V10.8.0.

l UEs complying with 3GPP Release 10 or later select a suitable LTE cell from the LTE cells using n LTE frequencies. The selection lasts for at most n seconds. If no suitable LTE cell is found, these UEs select a suitable LTE cell from the LTE cells using frequencies supported by these UEs. The selection lasts for 4 seconds. If a suitable LTE cell is still not found, these UEs randomly camp on a suitable cell. For details, see section 8.5.2 Actions when entering idle mode from connected mode in 3GPP TS 25.331 V10.9.0.

Note that the UE cannot process CS or PS services or CS+PS combined services while searching for a suitable LTE cell.

A UMTS-to-LTE fast return may not be performed in the following scenario: A UE that has performed a CSFB process moves to another RNC and the target RNC becomes the SRNC. In this case, the target RNC does not know whether the UE has performed a CSFB process, because certain information cannot be transmitted between RNCs. Hence, the SRNC instructs the UE to perform a UMTS-to-LTE fast return only if an End Of CSFB indication is carried in the IU RELEASE COMMAND message sent by the MSC when the CS service is released. If the MSC is not able to carry an End Of CSFB indication in the IU RELEASE COMMAND message, a UMTS-to-LTE fast return will not be performed in this scenario.

The Fast Return from UMTS to LTE feature enables a UE that moves from an LTE cell to a UMTS cell through CSFB to quickly return to the LTE network after the CS service or all services are finished.

This feature incorporates the following functions: l UMTS-to-LTE Fast Return

l Enhanced UMTS-to-LTE Fast Return

Before enabling the Enhanced to-LTE Fast Return function, you must enable the UMTS-to-LTE Fast Return function. However, before enabling the UMTS-UMTS-to-LTE Fast Return function, you do not need to enable the Enhanced UMTS-to-LTE Fast Return function.

Using the UMTS-to-LTE Fast Return function, a UE can quickly return to the LTE network after the UE finishes all services. Note that the application scenarios for this function are limited. However, using the Enhanced UMTS-to-LTE Fast Return function, the UE can quickly return to the LTE network after the UE finishes the CS service. It is recommended that both functions

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be enabled. In this document, "feature deployment" refers to the deployment of the Enhanced UMTS-to-LTE Fast Return function.

3.5.2 UMTS-to-LTE Fast Return

At the cell level, this function is controlled by the

HO_UMTS_TO_LTE_FAST_RETURN_SWITCH under the FastReturnToLTESwitch (BSC6900,BSC6910) parameter in the MOD UCELLHOCOMM command.

At the RNC level, this function is controlled by the

HO_UMTS_TO_LTE_FAST_RETURN_SWITCH under the HoSwitch

(BSC6900,BSC6910) parameter in the SET UCORRMALGOSWITCH command. When this function is configured at both the RNC and cell levels, the cell-level configuration takes effect. This function works as follows:

1. The RNC first determines that a UMTS/LTE UE is a CSFB UE if the UE meets either of the following conditions:

l When the UE is moving from an LTE cell to a UMTS cell through a PS handover, the RELOCATION REQUEST message contains a "cause" information element (IE) whose value is "CS Fallback triggered (268)" or a "CSFB Information" IE whose value is "CSFB" or "CSFB High Priority."

l When the UE is moving from an LTE cell to a UMTS cell through a redirection, the RRC CONNECTION REQUEST message does not contain the "Pre-redirection info" IE. (For details, see section 8.1.3.3 "RRC CONNECTION REQUEST message contents to set" in 3GPP TS 25.331 V9.4.0.) The first service that the UE processes after accessing the UMTS cell is a CS service.

2. After the UE is identified as a CSFB UE and the UE finishes all services in the UMTS cell, the RNC triggers the RRC connection release procedure.

3. The RNC includes the information about the neighboring LTE cells whose frequencies have higher absolute priorities than the frequency of the UMTS cell in an RRC

CONNECTION RELEASE message. Upon receiving the message, the UE selects a target cell based on the information and attempts to camp on this cell. (For details about suitable LTE cell selection, see section 8.5.2 Actions when entering idle mode from connected mode in 3GPP TS 25.331 V9.4.0. For details about a suitable LTE cell, see section 4 Overall process structure in 3GPP TS 23.122 V11.4.0.)

3.5.3 Enhanced UMTS-to-LTE Fast Return

At the cell level, this function is controlled by the

PERFENH_PS_FAST_RETURN_LTE_SWITCH under the FastReturnToLTESwitch (BSC6900,BSC6910)parameter in the ADD UCELLHOCOMM command.

At the RNC level, this function is controlled by the

PERFENH_PS_FAST_RETURN_LTE_SWITCH under the PerfEnhanceSwitch3 (BSC6900,BSC6910) parameter in the SET UCORRMPARA command.

When this function is configured at both the RNC and cell levels, the cell-level configuration takes effect.

This function works as follows:

1. The RNC first determines that a UMTS/LTE UE is a CSFB UE if the UE meets any of the following conditions:

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l When the UE is moving from an LTE cell to a UMTS cell through a PS handover, the RELOCATION REQUEST message contains a "cause" IE whose value is "CS Fallback triggered (268)" or a "CSFB Information" IE whose value is "CSFB" or "CSFB High Priority."

l When the UE is moving from an LTE cell to a UMTS cell through a redirection, the RRC CONNECTION REQUEST message does not contain a "Pre-redirection info" IE. (For details, see section 8.1.3.3 "RRC CONNECTION REQUEST message contents to set" in 3GPP TS 25.331 V9.4.0.) After the RNC receives an RRC Connection Setup Complete message, the UE successfully sets up a CS service within 10 seconds. l When the UE is moving from an LTE cell to a UMTS cell through a redirection, the

RRC CONNECTION REQUEST message contains a "CSFB Indication" IE. (For details, see section 8.1.3.3 "RRC CONNECTION REQUEST message contents to set" in 3GPP TS 25.331 V9.10.0.)

l After the UE finishes the CS service in a UMTS cell, an IU RELEASE COMMAND message from the CN to the RNC contains an "End Of CSFB" IE. (For details, see section 8.5.2 "Successful Operation" in 3GPP TS 25.413 V10.4.0.)

2. After the UE is identified as a CSFB UE and the UE finishes the CS service in the UMTS cell, the RNC triggers the RRC connection release procedure.

3. The RNC includes the information about the neighboring LTE cells whose frequencies have higher absolute priorities than the frequency of the UMTS cell in an RRC

CONNECTION RELEASE message. Upon receiving the message, the UE selects a suitable LTE cell based on the information and attempts to camp on this cell. (For details about suitable LTE cell selection, see section 8.5.2 Actions when entering idle mode from connected mode in 3GPP TS25.331 V9.4.0. For details about a suitable LTE cell, see section 4 Overall process structure in 3GPP TS 23.122 V11.4.0.)

3.5.4 Selecting Frequencies to Be Carried in the RRC

CONNECTION RELEASE Message

The method for selecting frequencies that are to be included in an RRC CONNECTION RELEASE message is as follows:

1. Select the initial frequency set.

Set A contains all LTE frequencies whose absolute priorities are higher than the absolute priority of the serving UMTS cell.

l The NPriority(BSC6900,BSC6910) parameter in the ADD

UCELLNFREQPRIOINFO or MOD UCELLNFREQPRIOINFO command specifies the absolute priorities of the LTE frequencies.

l The SPriority(BSC6900,BSC6910) parameter in the ADD UCELLSELRESEL or MOD UCELLSELRESEL command specifies the absolute priority of the serving UMTS cell.

2. Filter the initial frequency set.

Set B contains all LTE frequencies supported by the UE in set A.

When set B contains multiple LTE frequencies, select a maximum of four LTE FDD frequencies and a maximum of four LTE TDD frequencies based on absolute priorities. However, according to the 3GPP protocol, certain information cannot be transmitted between RNCs, including the EARFCNs for neighboring E-UTRAN cells. Therefore, the preceding frequency selection method does not apply to the following scenario: During an

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inter-RNC cell reselection, the source RNC still serves as the SRNC after the UE has moved from the source RNC to the target RNC.

To enable frequency selection in the preceding scenario, the following mechanism is introduced: When HO_UMTS_TO_LTE_FAST_RETURN_SWITCH under the HoSwitch(BSC6900,BSC6910) parameter in the SRNC MML command SET UCORRMALGOSWITCH is set to ON and

HO_IUR_U2L_FAST_RETURN_SWITCH under the HoSwitch1 parameter in the SRNC MML command SET UCORRMALGOSWITCH is set to 1, the RRC CONNECTION RELEASE message sent by the SRNC carries EARFCNs for all neighboring E-UTRAN cells of the UMTS cell under the target RNC. If

HO_UMTS_TO_LTE_FAST_RETURN_SWITCH is set to OFF or

RESERVED_SWITCH_4_BIT15 is set to 0, the RRC CONNECTION RELEASE message sent by the SRNC does not carry the EARFCNs.

The neighboring E-UTRAN cells and their EARFCNs need to be configured for the UMTS cell under the target RNC through the following operations:

l Configure EARFCNs for neighboring E-UTRAN cells by setting the LTEArfcn (BSC6900,BSC6910) parameter using the ADD ULTECELL command.

l Configure neighboring E-UTRAN cells using the ADD ULTENCELL command. The SRNC selects and delivers a maximum of four EAFCNs for FDD cells and a maximum of four EAFCNs for TDD cells from the EARFCNs of neighboring E-UTRAN cells for the UMTS cell under the target RNC.

If some LTE cells are configured as blacklisted cells using the ADD UCELLNFREQPRIOINFO command and

PERFENH_U2L_REDIR_WITH_BLACK_CELL_SWITCH under the

PerfEnhanceSwitch3(BSC6900,BSC6910) parameter in the SET UCORRMPARA command is set to ON, the RRC CONNECTION RELEASE message contains not only an LTE frequency but also those blacklisted cells working in the LTE frequency so that UEs cannot be handed over to the blacklisted cells based on fast return. If no LTE cells are configured as blacklisted cells or

PERFENH_U2L_REDIR_WITH_BLACK_CELL_SWITCH is set to OFF, the RRC CONNECTION RELEASE message does not contain blacklisted cells working in the LTE frequency.

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4

PS Redirections and Handovers Between

UMTS and LTE

4.1 Overview

This chapter describes PS directions and handovers from UMTS to LTE and from LTE to UMTS.

4.2 LTE-to-UMTS PS Redirections and Handovers

When a UE processing a PS service on the LTE network moves out of the LTE coverage area or the LTE signal quality falls below a specific threshold, a PS redirection or handover is performed to shift the UE to the UMTS network. The choice between a PS redirection and a PS handover depends on the UE capability.

LTE-to-UMTS PS handovers or redirections are performed mainly by the LTE network. For details, see LTE document Idle Mode Management Feature Parameter Description.

If certain UL/LTE multi-mode UEs do not support UMTS network measurements when in connected mode, the LTE network needs to support LTE-to-UMTS blind redirections or blind handovers.

NOTE

Most PS services involved in LTE-to-UMTS handovers are high-speed HSPA services. Currently, during handover preparations, if a PS service is not admitted to a UMTS cell, the PS service cannot use an R99 channel for an admission retry. When radio resources in the UMTS cell are congested, more handover preparations may fail.

To obtain the success rate of LTE-to-UMTS handovers, new UMTS counters are added for measuring LTE-to-UMTS PS handovers, as listed in the following table.

Counter Name Counter Description

VS.L2U.AttRelocPrepInPS Number of Preparation Attempts for Incoming PS Only L2U Handovers in Cell

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Counter Name Counter Description

VS.L2U.SuccRelocPrepInPS Number of Successful Preparations for Incoming PS Only L2U Handovers in Cell

VS.L2U.SuccRelocInPS Number of Successful Incoming PS Only L2U Handovers in Cell

The success rate of LTE-to-UMTS handover preparations and success rate of LTE-to-UMTS handovers are calculated using the following formulas:

l Success rate of LTE-to-UMTS handover preparations = VS.L2U.SuccRelocPrepInPS/ VS.L2U.AttRelocPrepInPS

l Success rate of LTE-to-UMTS handovers = VS.L2U.SuccRelocInPS/ VS.L2U.SuccRelocPrepInPS

As subscribed to PS services of high data rates, an LTE UE is prone to fail in admission after being handed over to UMTS, especially when the handover is performed based on coverage. In this case, call drops increase. A mechanism is introduced to decrease the PS service rate during inter-RAT PS handovers so that the success rate of PS handovers will be increased. The implementation is as follows:

When a PS service is handed over from an LTE cell to a UMTS cell:

l If a BE PS service fails to be admitted with the original rate, the UE re-attempts the admission after being switched from an HSPA channel to an R99 channel. If the UE still fails to be admitted, the UE re-attempts the admission by decreasing its data rate to the GBR. If the admission attempt fails, the UE continues to attempt admissions by further decreasing its data rate until it succeeds. The data rate can be decreased to 0 kbit/s. l If a streaming PS service fails to be admitted with the original rate, the UE re-attempts the

admission after being switched from the HSPA channel to the R99 channel. If the UE still fails to be admitted, the UE re-attempts the admission with its rate decreased to the GBR. This function can be enabled using the cell-level switch. The cell-level switch is set to on by selecting PERFENH_SYSHO_IN_FAIL_RETRY_SWITCH under the

CellConnAlgoSwitch1(BSC6900,BSC6910) parameter in the ADD UCELLCONNALGOPARA command.

This function is recommended in heavily loaded cells to improve the success rate of inter-RAT incoming PS handovers.

4.3 UMTS-to-LTE PS Redirections and Handovers

4.3.1 Overview

UMTS-to-LTE PS interoperation involves UMTS-to-LTE PS redirections and UMTS-to-LTE PS handovers.

l During a UMTS-to-LTE PS redirection, the RNC sends the UE an RRC Connection Release message, which contains LTE frequencies.

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Redirections can be classified into non-neighboring-cell-based redirection and neighboring-cell-based redirection according to whether neighboring LTE cell

configuration are required. Redirections can also be classified into blind redirection and measurement-based redirection according to whether the UE supports the measurement of LTE cell signal quality. In the following sections, a UE measuring the signal quality of the LTE cell is referred to as the LTE measurement.

The differences between the non-based redirection and neighboring-cell-based redirection are as follows:

– Non-neighboring-cell-based redirection: The target redirection frequency is obtained from the LTE frequencies configured by the ADD

UCELLNFREQPRIOINFO command. NOTE

When HO_U2L_REDIR_BASED_ABSOLUTE_FREQ_SWITCH under the HoSwitch1 (BSC6900,BSC6910) parameter in the SET UCORRMALGOSWITCH command is selected, the UE performs a non-neighboring-cell-based redirection.

When no neighboring LTE cells are configured, you are advised to

select HO_U2L_REDIR_BASED_ABSOLUTE_FREQ_SWITCH. When this switch is turned on and neighboring LTE cells are configured, the non-neighboring-cell-based redirection is preferred.

l Neighboring-cell-based redirection: The target redirection frequency is obtained from the neighboring LTE cell frequencies as indicated by the LTEArfcn

(BSC6900,BSC6910) parameter configured by the ADD ULTENCELL or MOD ULTENCELL command.

l During a UMTS-to-LTE PS handover, the RNC sends a handover request to the LTE network through the core network (CN). When the LTE network finishes preparing resources, the UE and the PS service are handed over to the LTE network.

Compared with UMTS-to-LTE PS handover, UMTS-to-LTE PS redirection has the following advantages and disadvantages:

l Advantages: UMTS-to-LTE PS redirection has no special requirements for the CN and does not require the UE to support handovers. When the UE does not support LTE measurements and the blind redirection switch is turned on, the UE can redirect to an LTE network based on blind redirection.

NOTE

The blind redirection switch can be turned on only when LTE coverage is favorable. Otherwise, call drops may occur. To turn on the blind redirection switch, set the U2lBlindRedirSwitch

(BSC6900,BSC6910) parameter in the ADD UCELLHOCOMM or MOD

UCELLHOCOMM command to ON.

l Disadvantages: PS services are interrupted for a long time.

UMTS-to-LTE PS redirections and handovers are classified into the following types in terms of trigger causes:

l Service-based UMTS-to-LTE PS redirections and handovers. For details, see

section 4.3.3 Service-based UMTS-to-LTE PS Redirections and Handovers. l Coverage-based UMTS-to-LTE PS redirections and handovers. For details, see

section 4.3.2 Coverage-based UMTS-to-LTE PS Redirections and Handovers. l Load-based UMTS-to-LTE PS redirections and handovers. For details, see

section 4.3.4 Load-based UMTS-to-LTE PS Redirections and Handovers. The priorities of UMTS-to-LTE PS redirections and handovers triggered based on coverage, load, and service in descending order are as follows: coverage-based UMTS-to-LTE PS

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redirections and handovers, service-based UMTS-to-LTE PS redirections and handovers, and load-based UMTS-to-LTE PS redirections and handovers.

If the UMTS and LTE networks are deployed in Multi-Operator Core Network (MOCN) mode, operators must use the same PLMNs in their UMTS and LTE networks.

4.3.2 Coverage-based UMTS-to-LTE PS Redirections and

Handovers

This section describes the features WRFD-150219 Coverage Based PS Redirection from UMTS to LTE and WRFD-150220 Coverage Based PS Handover from UMTS to LTE.

4.3.2.1 Overview

Architecture

Figure 4-1 shows the architecture of coverage-based PS redirections or handovers from UMTS to LTE.

Figure 4-1 Architecture of coverage-based PS redirections or handovers from UMTS to LTE

Where,

l Trigger phase

Upon receiving the event 2D or 1F measurement report, the RNC determines the target network for redirections or handovers based on whether the UE supports the inter-frequency network, GSM network, or LTE network and based on the configurations of different networks, such as whether the handover or redirection switch is turned on or neighboring cells are configured. For details about redirections or handovers to an inter-frequency network and GSM network, see Handover Feature Parameter Description.

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This document describes the handover or redirection to the LTE network. For details about decisions on coverage-based UMTS-to-LTE PS redirections or handovers, see section

4.3.2.2 Triggering.

l Decision phase: determines whether to allow the UE to be redirected or handed over to LTE. For details, see section 4.3.2.3 UE Redirections or Handovers to LTE.

l Measurement phase: determines whether to start the LTE measurement, deliver the measurement control message, and process the measurement result. For details, see section

4.3.2.4 Measurements.

l Execution phase: determines which procedure to trigger measurement-based redirection, blind redirection, or handover. For details, see section 4.3.2.5 Decision and Execution.

Application Scenarios

In a UMTS+LTE network, this feature shifts UEs from UMTS to LTE through a redirection or handover if the LTE signal quality is better than the UMTS signal quality.

4.3.2.2 Triggering

Upon receiving an event 2D or 1F measurement report from a UE, the RNC determines whether to allow a coverage-based PS redirection or handover from UMTS to LTE.

4.3.2.3 UE Redirections or Handovers to LTE

The RNC allows a UE to be redirected or handed over to LTE when all the following conditions are met:

1. There are no CS RABs among the UE's RABs.

2. All PS RABs for the UE can be shifted to LTE through a handover or redirection. An RAB can be shifted to LTE through a handover or redirection only when the IE E-UTRAN Service Handover in the RAB Assignment Request message is not set to "Handover to E-UTRAN shall not be performed" and

HO_TO_EUTRAN_SHOULD_BE_PERFORM under the EUTRANSHIND (BSC6900,BSC6910) parameter in the ADD UTYPRABBASIC command is selected. 3. The UE supports both UMTS and LTE.

4. An LTE network is available.

The RNC uses the following methods to determine whether the LTE network is available: l If HO_U2L_REDIR_BASED_ABSOLUTE_FREQ_SWITCH under the

HoSwitch1(BSC6900,BSC6910) parameter in the SET UCORRMALGOSWITCH command is selected, the LTE network is available when an LTE frequency is configured.

l If HO_U2L_REDIR_BASED_ABSOLUTE_FREQ_SWITCH is not selected, the LTE network is available when a neighboring LTE cell is configured.

5. Switches related to coverage-based UMTS-to-LTE interoperability have been turned on. l The general switch for UMTS-to-LTE PS interoperability is turned on. This switch is

configured by HO_LTE_PS_OUT_SWITCH under the HoSwitch (BSC6900,BSC6910) parameter.

l Condition a (for based UMTS-to-LTE redirections) or condition b (for coverage-based UMTS-to-LTE handovers) is met.

Interoperability Between UMTS and LTE(RAN16.0_Draft a)