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

WCDMA RAN

Interoperability Between UMTS andLTE Feature Parameter Description

Issue Draft ADate 2014-01-20

HUAWEI TECHNOLOGIES CO., LTD.

Copyright Huawei Technologies Co., Ltd. 2014. All rights reserved.No part of this document may be reproduced or transmitted in any form or by any means without prior writtenconsent of Huawei Technologies Co., Ltd. Trademarks and Permissions

and other Huawei trademarks are trademarks of Huawei Technologies Co., Ltd.All other trademarks and trade names mentioned in this document are the property of their respective holders. NoticeThe purchased products, services and features are stipulated by the contract made between Huawei and thecustomer. All or part of the products, services and features described in this document may not be within thepurchase scope or the usage scope. Unless otherwise specified in the contract, all statements, information,and recommendations in this document are provided "AS IS" without warranties, guarantees or representationsof any kind, either express or implied.

The information in this document is subject to change without notice. Every effort has been made in thepreparation of this document to ensure accuracy of the contents, but all statements, information, andrecommendations in this document do not constitute a warranty of any kind, express or implied. Huawei Technologies Co., Ltd.Address: Huawei Industrial Base

Bantian, LonggangShenzhen 518129People's Republic of China

Website: http://www.huawei.comEmail: [email protected]

Issue Draft A (2014-01-20) Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.

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Contents

1 About This Document..................................................................................................................11.1 Scope..............................................................................................................................................................................11.2 Intended Audience..........................................................................................................................................................11.3 Change History...............................................................................................................................................................12 Overview.........................................................................................................................................82.1 Background.....................................................................................................................................................................82.2 Function Classification...................................................................................................................................................82.3 Application Scenarios...................................................................................................................................................102.3.1 Scenario 1: Only Data Cards, Only Data Services, LTE Coverage Still Incomplete................................................102.3.2 Scenario 2: Not Only Data Cards, Only Data Services, CSFB Supported, LTE Coverage Still Incomplete............112.3.3 Scenario 3: Data and VoIP Services Supported, LTE Coverage Still Incomplete....................................................123 Cell Reselection Between UMTS and LTE.............................................................................143.1 Overview......................................................................................................................................................................143.2 LTE-to-UMTS Cell Reselection...................................................................................................................................143.3 UMTS-to-LTE Cell Reselection...................................................................................................................................153.3.1 Overview...................................................................................................................................................................153.3.2 Criteria for Starting Measurements...........................................................................................................................153.3.3 Criteria for Triggering Cell Reselection....................................................................................................................163.4 UMTS-to-LTE Quick Cell Reselection........................................................................................................................193.5 UMTS-to-LTE Fast Return..........................................................................................................................................203.5.1 Overview...................................................................................................................................................................203.5.2 UMTS-to-LTE Fast Return.......................................................................................................................................223.5.3 Enhanced UMTS-to-LTE Fast Return.......................................................................................................................223.5.4 Selecting Frequencies to Be Carried in the RRC CONNECTION RELEASE Message..........................................234 PS Redirections and Handovers Between UMTS and LTE.................................................254.1 Overview......................................................................................................................................................................254.2 LTE-to-UMTS PS Redirections and Handovers..........................................................................................................254.3 UMTS-to-LTE PS Redirections and Handovers..........................................................................................................264.3.1 Overview...................................................................................................................................................................264.3.2 Coverage-based UMTS-to-LTE PS Redirections and Handovers.............................................................................284.3.2.1 Overview................................................................................................................................................................28

WCDMA RANInteroperability Between UMTS and LTE Feature ParameterDescription Contents


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4.3.2.2 Triggering...............................................................................................................................................................294.3.2.3 UE Redirections or Handovers to LTE...................................................................................................................294.3.2.4 Measurements.........................................................................................................................................................304.3.2.5 Decision and Execution..........................................................................................................................................334.3.3 Service-based UMTS-to-LTE PS Redirections and Handovers................................................................................374.3.3.1 Overview................................................................................................................................................................374.3.3.2 Triggering...............................................................................................................................................................384.3.3.3 UE Redirections or Handovers to LTE...................................................................................................................384.3.3.4 Measurements on LTE Signal Quality...................................................................................................................394.3.3.5 Decision and Execution..........................................................................................................................................424.3.3.6 Anti-ping-pong Measures.......................................................................................................................................464.3.4 Load-based UMTS-to-LTE PS Redirections and Handovers....................................................................................474.3.4.1 Overview................................................................................................................................................................474.3.4.2 Triggering...............................................................................................................................................................494.3.4.3 UE Redirections or Handovers to LTE...................................................................................................................494.3.4.4 UE Selection for LDR............................................................................................................................................494.3.4.5 Measurements.........................................................................................................................................................504.3.4.6 Decision and Execution..........................................................................................................................................514.3.4.7 Suggestions for LDR Action Configurations.........................................................................................................534.4 Measures to Prevent Frequent Retries After a UMTS-to-LTE PS Handover Failure..................................................544.5 Measures to Prevent Ping-Pong Blind Redirections Between UMTS and LTE..........................................................554.6 Data Forwarding During UMTS-to-LTE Handovers...................................................................................................554.6.1 Overview...................................................................................................................................................................554.6.2 How The Data Forwarding Procedure Flows............................................................................................................555 CSFB...............................................................................................................................................575.1 Overview......................................................................................................................................................................575.2 CS Fallback Guarantee for LTE Emergency Calls.......................................................................................................585.2.1 Overview...................................................................................................................................................................585.2.2 Policy.........................................................................................................................................................................585.3 CS Fallback Guarantee for LTE Common Calls..........................................................................................................595.3.1 Overview...................................................................................................................................................................595.3.2 Policy.........................................................................................................................................................................595.4 CSFB Delay Reduction................................................................................................................................................605.5 Ultra-Flash CSFB.........................................................................................................................................................616 SRVCC from LTE to UMTS with PS Handover....................................................................656.1 Overview......................................................................................................................................................................666.2 Handover Execution.....................................................................................................................................................667 RIM Based UMTS Target Cell Selection for LTE.................................................................697.1 Overview......................................................................................................................................................................707.2 RIM-based Reporting of UMTS Cell Load Status.......................................................................................................70



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7.2.1 RIM Procedure..........................................................................................................................................................707.2.2 Reporting of UMTS Cell Load Status.......................................................................................................................728 Related Features...........................................................................................................................748.1 WRFD-140226 Fast Return from UMTS to LTE........................................................................................................748.1.1 Required Features......................................................................................................................................................748.1.2 Mutually Exclusive Features.....................................................................................................................................748.1.3 Impacted Features......................................................................................................................................................748.2 WRFD-020129 Service-Based PS Service Redirection from UMTS to LTE..............................................................748.2.1 Required Features......................................................................................................................................................748.2.2 Mutually Exclusive Features.....................................................................................................................................748.2.3 Impacted Features......................................................................................................................................................748.3 WRFD-140218 Service-Based PS Handover from UMTS to LTE..............................................................................758.3.1 Required Features......................................................................................................................................................758.3.2 Mutually Exclusive Features.....................................................................................................................................758.3.3 Impacted Features......................................................................................................................................................758.4 WRFD-150219 Coverage Based PS Redirection from UMTS to LTE........................................................................758.4.1 Required Features......................................................................................................................................................758.4.2 Mutually Exclusive Features.....................................................................................................................................758.4.3 Impacted Features......................................................................................................................................................758.5 WRFD-150220 Coverage Based PS Handover from UMTS to LTE...........................................................................758.5.1 Required Features......................................................................................................................................................758.5.2 Mutually Exclusive Features.....................................................................................................................................758.5.3 Impacted Features......................................................................................................................................................758.6 WRFD-150216 Load Based PS Redirection from UMTS to LTE...............................................................................768.6.1 Required Features......................................................................................................................................................768.6.2 Mutually Exclusive Features.....................................................................................................................................768.6.3 Impacted Features......................................................................................................................................................768.7 WRFD-150217 Load Based PS Handover from UMTS to LTE..................................................................................768.7.1 Required Features......................................................................................................................................................768.7.2 Mutually Exclusive Features.....................................................................................................................................768.7.3 Impacted Features......................................................................................................................................................768.8 WRFD-150215 SRVCC from LTE to UMTS with PS Handover................................................................................768.8.1 Required Features......................................................................................................................................................768.8.2 Mutually Exclusive Features.....................................................................................................................................768.8.3 Impacted Features......................................................................................................................................................778.9 WRFD-150231 RIM Based UMTS Target Cell Selection for LTE.............................................................................778.9.1 Required Features......................................................................................................................................................778.9.2 Mutually Exclusive Features.....................................................................................................................................778.9.3 Impacted Features......................................................................................................................................................778.10 WRFD-160271 Ultra-Flash CSFB.............................................................................................................................779 Impact on the Network...............................................................................................................78



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9.1 WRFD-140226 Fast Return from UMTS to LTE........................................................................................................789.1.1 System Capacity........................................................................................................................................................789.1.2 Network Performance................................................................................................................................................789.2 WRFD-020129 Service-Based PS Service Redirection from UMTS to LTE..............................................................789.2.1 System Capacity........................................................................................................................................................789.2.2 Network Performance................................................................................................................................................789.3 WRFD-140218 Service-Based PS Handover from UMTS to LTE..............................................................................799.3.1 System Capacity........................................................................................................................................................799.3.2 Network Performance................................................................................................................................................799.4 WRFD-150219 Coverage Based PS Redirection from UMTS to LTE........................................................................799.4.1 System Capacity........................................................................................................................................................799.4.2 Network Performance................................................................................................................................................799.5 WRFD-150220 Coverage Based PS Handover from UMTS to LTE...........................................................................809.5.1 System Capacity........................................................................................................................................................809.5.2 Network Performance................................................................................................................................................809.6 WRFD-150216 Load Based PS Redirection from UMTS to LTE...............................................................................809.6.1 System Capacity........................................................................................................................................................809.6.2 Network Performance................................................................................................................................................809.7 WRFD-150217 Load Based PS Handover from UMTS to LTE..................................................................................809.7.1 System Capacity........................................................................................................................................................809.7.2 Network Performance................................................................................................................................................819.8 WRFD-140102 CS Fallback Guarantee for LTE Emergency Calls.............................................................................819.8.1 System Capacity........................................................................................................................................................819.8.2 Network Performance................................................................................................................................................819.9 WRFD-150215 SRVCC from LTE to UMTS with PS Handover................................................................................819.9.1 System Capacity........................................................................................................................................................819.9.2 Network Performance................................................................................................................................................819.10 WRFD-150231 RIM Based UMTS Target Cell Selection for LTE...........................................................................829.10.1 System Capacity......................................................................................................................................................829.10.2 Network Performance..............................................................................................................................................829.11 WRFD-160271 Ultra-Flash CSFB.............................................................................................................................8210 Engineering Guidelines...........................................................................................................8310.1 WRFD-020126 Mobility Between UMTS and LTE Phase 1.....................................................................................8310.1.1 When to Use Mobility Between UMTS and LTE Phase 1......................................................................................8310.1.2 Feature Deployment................................................................................................................................................8310.2 WRFD-140226 Fast Return from UMTS to LTE......................................................................................................8810.2.1 When to Use Fast Return from UMTS to LTE.......................................................................................................8810.2.2 Required Information..............................................................................................................................................8910.2.3 Planning...................................................................................................................................................................8910.2.4 Deployment.............................................................................................................................................................8910.2.5 Performance Monitoring..........................................................................................................................................95



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10.2.6 Parameter Optimization...........................................................................................................................................9510.2.7 Troubleshooting.......................................................................................................................................................9510.3 WRFD-020129 Service-Based PS Service Redirection from UMTS to LTE............................................................9610.3.1 When to Use Service-Based PS Service Redirection from UMTS to LTE.............................................................9610.3.2 Required Information..............................................................................................................................................9710.3.3 Planning...................................................................................................................................................................9710.3.4 Deployment.............................................................................................................................................................9710.3.5 Performance Monitoring........................................................................................................................................11710.3.6 Parameter Optimization.........................................................................................................................................11810.3.7 Troubleshooting.....................................................................................................................................................11810.4 WRFD-140218 Service-Based PS Handover from UMTS to LTE..........................................................................11810.4.1 When to Use Service-Based PS Handover from UMTS to LTE...........................................................................11810.4.2 Required Information............................................................................................................................................11810.4.3 Planning.................................................................................................................................................................11810.4.4 Deployment...........................................................................................................................................................11810.4.5 Performance Monitoring........................................................................................................................................13710.4.6 Parameter Optimization.........................................................................................................................................14110.4.7 Troubleshooting.....................................................................................................................................................14110.5 WRFD-150219 Coverage Based PS Redirection from UMTS to LTE....................................................................14210.5.1 When to Use Coverage Based PS Redirection from UMTS to LTE.....................................................................14210.5.2 Required Information............................................................................................................................................14210.5.3 Planning.................................................................................................................................................................14210.5.4 Deployment...........................................................................................................................................................14310.5.5 Performance Monitoring........................................................................................................................................15610.5.6 Parameter Optimization.........................................................................................................................................15710.5.7 Troubleshooting.....................................................................................................................................................15710.6 WRFD-150220 Coverage Based PS Handover from UMTS to LTE.......................................................................15710.6.1 When to Use Coverage Based PS Handover from UMTS to LTE........................................................................15710.6.2 Required Information............................................................................................................................................15710.6.3 Planning.................................................................................................................................................................15710.6.4 Deployment...........................................................................................................................................................15710.6.5 Performance Monitoring........................................................................................................................................16710.6.6 Parameter Optimization.........................................................................................................................................16810.6.7 Troubleshooting.....................................................................................................................................................16810.7 WRFD-150216 Load Based PS Redirection from UMTS to LTE...........................................................................16910.7.1 When to Use Load Based PS Redirection from UMTS to LTE............................................................................16910.7.2 Required Information............................................................................................................................................16910.7.3 Planning.................................................................................................................................................................16910.7.4 Deployment...........................................................................................................................................................16910.7.5 Performance Monitoring........................................................................................................................................19510.7.6 Parameter Optimization.........................................................................................................................................196



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10.7.7 Troubleshooting.....................................................................................................................................................19610.8 WRFD-150217 Load Based PS Handover from UMTS to LTE..............................................................................19610.8.1 When to Use Load Based PS Handover from UMTS to LTE...............................................................................19610.8.2 Required Information............................................................................................................................................19710.8.3 Planning.................................................................................................................................................................19710.8.4 Deployment...........................................................................................................................................................19710.8.5 Performance Monitoring........................................................................................................................................22110.8.6 Parameter Optimization.........................................................................................................................................22210.8.7 Troubleshooting.....................................................................................................................................................22210.9 WRFD-140102 CS Fallback Guarantee for LTE Emergency Calls.........................................................................22210.9.1 When to Use CS Fallback Guarantee for LTE Emergency Calls..........................................................................22210.9.2 Deployment...........................................................................................................................................................22210.9.3 Performance Monitoring........................................................................................................................................22510.10 WRFD-150215 SRVCC from LTE to UMTS with PS Handover..........................................................................22610.10.1 When to Use SRVCC from LTE to UMTS with PS Handover...........................................................................22610.10.2 Required Information..........................................................................................................................................22610.10.3 Planning...............................................................................................................................................................22610.10.4 Deployment.........................................................................................................................................................22610.10.5 Performance Monitoring......................................................................................................................................23110.10.6 Parameter Optimization.......................................................................................................................................23210.10.7 Troubleshooting...................................................................................................................................................23210.11 WRFD-150231 RIM Based UMTS Target Cell Selection for LTE.......................................................................23210.11.1 When to Use RIM Based UMTS Target Cell Selection for LTE........................................................................23210.11.2 Required Information..........................................................................................................................................23210.11.3 Planning...............................................................................................................................................................23310.11.4 Deployment.........................................................................................................................................................23310.11.5 Performance Monitoring......................................................................................................................................23910.11.6 Parameter Optimization.......................................................................................................................................23910.11.7 Troubleshooting...................................................................................................................................................23910.12 WRFD-160271 Ultra-Flash CSFB.........................................................................................................................23910.12.1 When to Use Ultra-Flash CSFB..........................................................................................................................23910.12.2 Required Information..........................................................................................................................................23910.12.3 Planning...............................................................................................................................................................24010.12.4 Deployment.........................................................................................................................................................24010.12.4.1 Requirements....................................................................................................................................................24010.12.4.2 Data Preparation...............................................................................................................................................24010.12.4.3 Precautions........................................................................................................................................................24010.12.4.4 Activation.........................................................................................................................................................24110.12.4.4.1 Using MML Commands................................................................................................................................24110.12.4.4.2 MML Command Examples...........................................................................................................................24110.12.4.4.3 Using the CME..............................................................................................................................................241



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10.12.4.5 Activation Observation.....................................................................................................................................24210.12.4.6 Deactivation......................................................................................................................................................24210.12.4.6.1 Using MML Commands................................................................................................................................24210.12.4.6.2 MML Command Examples...........................................................................................................................24210.12.4.6.3 Using the CME..............................................................................................................................................24210.12.5 Performance Monitoring......................................................................................................................................24310.12.6 Parameter Optimization.......................................................................................................................................24410.12.7 Troubleshooting...................................................................................................................................................24411 Parameters.................................................................................................................................24512 Counters..................................................................................................................................148913 Glossary...................................................................................................................................152414 Reference Documents...........................................................................................................1525



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1 About This Document1.1 Scope

This document describes Interoperability Between UMTS and LTE, including its technicalprinciples, related features, network impact, and engineering guidelines. This document coversthe following features:l WRFD-020126 Mobility Between UMTS and LTE Phase 1l WRFD-140226 Fast Return from UMTS to LTEl WRFD-020129 Service-Based PS Service Redirection from UMTS to LTEl WRFD-140218 Service-Based PS Handover from UMTS to LTEl WRFD-150219 Coverage Based PS Redirection from UMTS to LTEl WRFD-150220 Coverage Based PS Handover from UMTS to LTEl WRFD-150216 Load Based PS Redirection from UMTS to LTEl WRFD-150217 Load Based PS Handover from UMTS to LTEl WRFD-140102 CS Fallback Guarantee for LTE Emergency Callsl WRFD-150215 SRVCC from LTE to UMTS with PS Handoverl WRFD-150231 RIM Based UMTS Target Cell Selection for LTE

1.2 Intended AudienceThis document is intended for personnel who:l Need to understand the features described hereinl Work with Huawei products

1.3 Change HistoryThis section provides information about the changes in different document versions. There aretwo types of changes, which are defined as follows:

WCDMA RANInteroperability Between UMTS and LTE Feature ParameterDescription 1 About This Document


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l Feature changeChanges in features of a specific product version

l Editorial changeChanges 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 includesthe following changes.

Change Type Change Description Parameter ChangeFeature change Added descriptions of

preventing frequent retriesafter a U2L PS handoverfailure. For details, seesection 4.4 Measures toPrevent Frequent RetriesAfter a UMTS-to-LTE PSHandover Failure.

Added theU2LphyChFailNum(BSC6900,BSC6910)parameter



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Change Type Change Description Parameter ChangeAdded descriptions of load-based LTE cell selectionduring UMTS-to-LTEhandovers and redirections,including functiondescriptions, related features,network impacts, andengineering guidelines in thefollowing sections:4.3.3 Service-based UMTS-to-LTE PS Redirectionsand Handovers4.3.4 Load-based UMTS-to-LTE PS Redirectionsand Handovers8.2 WRFD-020129 Service-Based PS ServiceRedirection from UMTS toLTE8.3 WRFD-140218 Service-Based PS Handover fromUMTS to LTE8.6 WRFD-150216 LoadBased PS Redirection fromUMTS to LTE8.7 WRFD-150217 LoadBased PS Handover fromUMTS to LTE9.2 WRFD-020129 Service-Based PS ServiceRedirection from UMTS toLTE9.3 WRFD-140218 Service-Based PS Handover fromUMTS to LTE9.6 WRFD-150216 LoadBased PS Redirection fromUMTS to LTE9.7 WRFD-150217 LoadBased PS Handover fromUMTS to LTE10.3 WRFD-020129Service-Based PS ServiceRedirection from UMTS toLTE

Added the followingparameters:l ProcessSwitch5

(BSC6900,BSC6910):INTERRAT_LOAD_REPORT_FROM_LTE_SWITCH

l U2LLTELoadSwitch(BSC6900,BSC6910)



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Change Type Change Description Parameter Change10.4 WRFD-140218Service-Based PSHandover from UMTS toLTE10.7 WRFD-150216 LoadBased PS Redirection fromUMTS to LTE10.8 WRFD-150217 LoadBased PS Handover fromUMTS to LTE

Added descriptions offunctions for guaranteeingand improving networkperformance duringhandovers for SRVCC fromLTE to UMTS, includingfunction descriptions,network impacts, andengineering guidelines in thefollowing chapter andsections:6 SRVCC from LTE toUMTS with PS Handover9.9 WRFD-150215 SRVCCfrom LTE to UMTS withPS Handover10.10 WRFD-150215SRVCC from LTE toUMTS with PS Handover

Added the followingparameters:l U2LLTELoadSwitch

(BSC6900,BSC6910)l L2USRVCCEmerCal-

lARP(BSC6900,BSC6910)

Added descriptions ofcounters measuring LTE toUMTS handovers of only PSservices. For details, seesection 4.2 LTE-to-UMTSPS Redirections andHandovers.

None



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Change Type Change Description Parameter ChangeAdded and modifieddescriptions of measures forreducing the CSFB delay. Fordetails, see section 5.4 CSFBDelay Reduction.

Added the followingswitches to theImprovementSwitch(BSC6900,BSC6910)parameter in the MMLcommand SETURRCTRLSWITCH:l PSHO_CSFB_CAP_EN

Q_DELAY_SWITCHl CSFB_UE_DELAY_R

AU_SWITCHl CSFB_UE_CS_IMEI_

QUERY_DISABLE_SWITCH

Added the Ultra-Flash CSFBfeature's principles, relatedfeatures, network impacts,and engineering guidelines.For details, see the followingsections:l 5.5 Ultra-Flash CSFBl 8.10 WRFD-160271

Ultra-Flash CSFBl 9.11 WRFD-160271

Ultra-Flash CSFBl 10.12 WRFD-160271

Ultra-Flash CSFB

Added the followingparameters:l PROCESSSWITCH2

(BSC6900,BSC6910):ULTRA_FLASH_CSFB_SWITCH

l UltraFlashCSFBSR-BRate(BSC6900,BSC6910)



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Change Type Change Description Parameter ChangeAdded the principle andengineering guidelines forexchanging RANinformation management(RIM) messages through theeCoordinator. For details, seethe following sections:l 7.2.1 RIM Procedurel 10.3 WRFD-020129

Service-Based PSService Redirectionfrom UMTS to LTE

l 10.4 WRFD-140218Service-Based PSHandover from UMTSto LTE

l 10.7 WRFD-150216Load Based PSRedirection fromUMTS to LTE

l 10.8 WRFD-150217Load Based PSHandover from UMTSto LTE

l 10.11 WRFD-150231RIM Based UMTSTarget Cell Selection forLTE

Added the followingparameter:PROCESSSWITCH5(BSC6900,BSC6910):RIM_ON_ECO_SWITCH

Changed the parameter forU2L Blind Redir Anti-Pingpong Timer.

Changed the switch from theRsvU32Para10 parameter ofthe SETUALGORSVPARAcommand to theU2LBlindRedirPingpong-Timer(BSC6900,BSC6910)parameter of the SETUHOCOMM command.



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Change Type Change Description Parameter ChangeChanged the parameter forPenalty Time for Service-based U2L Meas Expiry.

Changed the switch from theRsvU32Para9 parameter ofthe SETUALGORSVPARAcommand to theU2lServMcTimeOutPu-nishTime(BSC6900,BSC6910)parameter of the SETUU2LTEHONCOVcommand.

Optimized the mechanismfor accessing the network at adecreased rate during anLTE-to-UMTS PS handover.For details, see section 4.2LTE-to-UMTS PSRedirections andHandovers.

AddedPERFENH_SYSHO_IN_FAIL_RETRY_SWITCH tothe CellConnAlgoSwitch1(BSC6900,BSC6910)parameter in the followingcommand:ADDUCELLCONNALGOPAR

Editorial change None None



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2 Overview2.1 Background

As wireless data services rapidly grow and conditions mature for LTE commercial use, telecomoperators 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 betweenUMTS and LTE is important. This feature helps make the most of existing network equipment,provide diversified services, and achieve smooth network evolution. Huawei products supportinteroperability between UMTS and time division duplex (TDD) LTE and between UMTS andfrequency division duplex (FDD) LTE.

2.2 Function ClassificationInteroperability between UMTS and LTE functions are classified by UE status, as shown inTable 2-1.

Table 2-1 Interoperability between UMTS and LTE functions classified by UE statusUE Status Interoperability Between

UMTS and LTEFunctions

Idle mode UMTS-to-LTE cellreselection

Idle mode LTE-to-UMTS cellreselection. See LTEdocument Idle ModeManagement FeatureParameter Description fordetails.

WCDMA RANInteroperability Between UMTS and LTE Feature ParameterDescription 2 Overview


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UE Status Interoperability BetweenUMTS and LTEFunctions

Connected mode Data services LTE-to-UMTS PSredirections or handovers.See LTE document MobilityManagement in ConnectedMode Feature ParameterDescription for details.LTE-to-UMTS handoversbased on the UMTS cell loadUMTS-to-LTE quick cellreselectionService-based UMTS-to-LTE PS redirections andhandoversCoverage-based UMTS-to-LTE PS redirections orhandoversLoad-based UMTS-to-LTEPS redirections or handovers

Voice services LTE-to-UMTS circuit-switched fallback (CSFB)specified by 3GPP Release 8.See LTE document CSFallback Feature ParameterDescription for details.LTE-to-UMTS CSFB basedon the UMTS cell loadUMTS-to-LTE fast returnCSFB guarantee foremergency calls originatedon the LTE networkCSFB guarantee for commoncalls originated on the LTEnetworkLTE-to-UMTS SRVCC withPS handovers

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



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2.3 Application Scenarios2.3.1 Scenario 1: Only Data Cards, Only Data Services, LTECoverage Still IncompleteDescription

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 thereforeVoIP services are not supported.

l LTE coverage is still incomplete.

UE Camping PolicyIn scenario 1, the UE camping policy is as follows: An LTE-first policy is recommended for UEcamping, 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 theLTE network is preferred during cell reselection.Cell reselection is performed to shift UEs in idle mode or the CELL_PCH/URA_PCH statebetween UMTS and LTE. For details, see chapter 3 Cell Reselection Between UMTS andLTE.

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

PS Service PolicyIn 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 UMTSnetwork 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, CSFBSupported, LTE Coverage Still IncompleteDescription

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

l No IMS has been deployed on the LTE network and therefore VoIP services are notsupported.

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

UE Camping PolicyIn scenario 2, the UE camping policy is as follows:Huawei products support either the LTE network or the UMTS network as the preferred choicefor UE camping. An LTE-first policy is recommended for this phase. To adopt a UMTS-firstpolicy for UE camping, set low priorities for LTE frequencies so that the UMTS network ispreferred during cell reselection.

CS Service PolicyIn 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 "RIMBased 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 PolicyIn scenario 2, the PS service policy is as follows: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 UMTSnetwork will be performed. For details, see section 4.2 LTE-to-UMTS PS Redirectionsand Handovers. When a UE processing a PS service on the UMTS network moves to anLTE 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 initiatesa PS service in a UMTS/LTE overlapping coverage area, a service-based UMTS-to-LTEPS 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 section4.3.3 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 PShandover or redirection is used to shift the PS service to the UMTS network. If the PSservice is still in progress when the CS service is complete and the LTE signal quality meetsspecific conditions, a service-based UMTS-to-LTE PS handover or redirection isperformed to shift the UE and the PS service back to the LTE network. For details, seesection 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, theUE is preferentially handed over to a non-congested or non-overloaded UMTS cell. Thisavoids 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 UMTSTarget Cell Selection for LTE.

2.3.3 Scenario 3: Data and VoIP Services Supported, LTE CoverageStill IncompleteDescription

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

l LTE coverage is still incomplete.

UE Camping PolicyAn LTE-first policy is recommended. If the delay caused by CSFB is too long to ensure servicequality, adopt a UMTS-first policy.

CS Service PolicyIn 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 serviceto 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 networkto ensure CS service continuity.

PS Service PolicyIn scenario 3, 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 UMTSnetwork is performed. For details, see section 4.1 "LTE-to-UMTS PS Redirections andHandovers." When a UE processing a PS service on the UMTS network moves to an LTEcoverage 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 initiatesa 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 LTEnetwork. This mechanism makes efficient use of the LTE network. For details, see sectionService-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 PShandover or redirection is used to shift the PS service to the UMTS network. If the PSservice is still in progress when the CS service is complete and the LTE signal quality meetsspecific conditions, a service-based UMTS-to-LTE PS handover or redirection isperformed to shift the UE and the PS service back to the LTE network. For details, seesection Service-based UMTS-to-LTE PS Redirections and Handovers.



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3 Cell Reselection Between UMTS and LTE3.1 Overview

Cell reselection between UMTS and LTE includes UMTS-to-LTE cell reselection, LTE-to-UMTS cell reselection, UMTS-to-LTE fast return, and UMTS-to-LTE quick cell reselection.When camping on the UMTS network, a UMTS/LTE multi-mode UE receives systeminformation from the UMTS cell. System information block 19 (SIB19) carries the absolutepriorities of the serving UMTS cell and LTE frequencies. If the absolute priorities of one ormore LTE frequencies are higher than the absolute priority of the serving UMTS cell, thecorresponding LTE cell or cells are the preferred target cells for cell reselection. If the absolutepriorities 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 informationfrom the LTE cell. SIB3 carries the absolute priority of the serving LTE cell, SIB5 carries theabsolute priorities of the LTE frequencies, and SIB6 carries the absolute priorities of the UMTSfrequencies. You can manipulate these priorities to favor UMTS or LTE cells as target cells forreselection.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 reselectionprocess, you need to enable fast state transition from CELL_DCH to CELL_PCH or fromCELL_DCH to the idle state. With this function, the UMTS/LTE multi-mode UE can transit tothe 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/MODUCELLSIBSWITCH command specifies whether to broadcast SIB19.

3.2 LTE-to-UMTS Cell ReselectionLTE-to-UMTS cell reselection is used when the LTE network is new and provides incompletecoverage, but the UMTS coverage is complete. LTE-to-UMTS cell reselection is based onabsolute priorities and mainly involves the LTE network.For details, see LTE document Idle Mode Management Feature Parameter Description.

WCDMA RANInteroperability Between UMTS and LTE Feature ParameterDescription 3 Cell Reselection Between UMTS and LTE


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3.3 UMTS-to-LTE Cell Reselection3.3.1 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 startsmeasuring the LTE signal quality. Based on the measurement results, the UE camps on the bestcell by performing reselection.

3.3.2 Criteria for Starting MeasurementsSIB19 carries the absolute priority of the serving UMTS cell, the absolute priorities of the LTEfrequencies, and the cell reselection thresholds. Different radio access technologies (RATs) musthave different priorities. Upon receiving SIB19, the UE does the following:l If SrxlevServingCell is less than or equal to Sprioritysearch1 or SqualServingCell is less than or

equal to Sprioritysearch2, the serving UMTS cell has poor signal quality. In this situation, theUE starts measuring the signal quality of the neighboring LTE cells that work on low- andhigh-priority frequencies.

l If SrxlevServingCell is greater than Sprioritysearch1 and SqualServingCell is greater thanSprioritysearch2, the serving UMTS cell has good signal quality. In this situation, the UEmeasures the signal quality of the LTE frequencies that have higher absolute priorities thanthe 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 ofsecond.

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

l The NPriority(BSC6900,BSC6910) parameter in the ADD UCELLNFREQPRIOINFOor MOD UCELLNFREQPRIOINFO command specifies the absolute priorities of theLTE frequencies.

l The ThdPrioritySearch1(BSC6900,BSC6910) and ThdPrioritySearch2(BSC6900,BSC6910) parameters in the ADD UCELLSELRESEL or MODUCELLSELRESEL 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 receivedsignal 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: Srxlev: cell RX level value (dB)



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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). SqualServingCell: 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 notfulfilled. For details about criterion S, see UE Behaviors in Idle Mode Feature ParameterDescription.

3.3.3 Criteria for Triggering Cell ReselectionAfter measuring the UMTS serving cell and LTE frequencies, the UE shifts to the best cell byperforming reselection.SIB19 carries the absolute priority of the serving UMTS cell, the absolute priorities of the LTEfrequencies, and the cell reselection thresholds. The UE performs cell reselection based on theabsolute priorities.Section 5.2.6.1.4a Absolute priority based criteria for inter-frequency and inter-RAT cellreselection in 3GPP TS 25.304 V11.3.0 specifies five sets of criteria for cell reselection basedon the absolute priorities. However, criteria set 2 is used for inter-frequency scenarios, not forinter-RAT scenarios, and SIB19 does not carry the absolute priorities of UMTS inter-frequenciesby 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 thereference signal received power (RSRP) as the measurement quantity, while criteria sets 4 and5 use the Reference Signal Received quality (RSRQ) as the measurement quantity. For adescription of each criteria set, see Table 3-1.The RSRQSwitch(BSC6900,BSC6910) parameter in the ADD UCELLNFREQPRIOINFO orMOD UCELLNFREQPRIOINFO command controls whether the UE performs cellreselection based on the RSRQ of the LTE frequency. When RSRQSwitch(BSC6900,BSC6910) is set to TRUE and the UE supports the RSRQ-based measurement, theUE performs cell reselection based on the RSRQ. Otherwise, the UE performs cell reselectionbased on the RSRP.

Table 3-1 Criteria sets 1, 3, 4, and 5 for triggering cell reselectionCriteria Set DescriptionCriteria set 1 l The absolute priority of an LTE frequency

is higher than the absolute priority of theserving UMTS cell.

l The Srxlev value of the LTE frequency,SrxlevnonServingCell, has remained abovethe threshold Threshhigh for a period oftime longer than Treselection.



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Criteria Set DescriptionCriteria set 3 l The absolute priority of an LTE frequency

is lower than the absolute priority of theserving UMTS cell.

l SrxlevnonServingCell has remained aboveThreshlow for a period of time longer thanTreselection.

l SrxlevServingCell has remained belowThreshserving,low for a period of timelonger than Treselection, orSqualServingCell has remained below 0 fora period of time longer thanTreselection.

Criteria set 4 l The absolute priority of an LTE frequencyis higher than the absolute priority of theserving UMTS cell.

l The Squal value of the LTE frequency,SqualnonServingCell, has remained abovethe threshold Threshhigh2 for a period oftime longer than Treselection.

Criteria set 5 l The absolute priority of an LTE frequencyis lower than the absolute priority of theserving UMTS cell.

l SqualnonServingCell has remained aboveThreshlow2 for a period of time longerthan Treselection.

l SqualServingCell has remained belowThreshserving,low2 for a period of timelonger than Treselection.

The following are details about the parameters referenced in Table 3-1:l Threshhigh 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 theabsolute priority of the serving UMTS cell. The ThdToHigh(BSC6900,BSC6910)parameter specifies the value of Threshhigh. The greater the value of this parameter, theless likely reselection is to occur.

l Threshlow 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 theabsolute priority of the serving UMTS cell. The ThdToLow(BSC6900,BSC6910)parameter specifies the value of Threshlow. The greater the value of this parameter, the lesslikely reselection is to occur.



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

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

l Threshserving,low is the threshold for the serving cell's RSCP during reselection to an LTEcell working at an LTE frequency with a lower absolute priority. The ThdServingLow(BSC6900,BSC6910) parameter specifies the value of Threshserving,low. When the LTEfrequencies of lower absolute priorities are being measured, if the signal quality of theserving UMTS cell constantly remains below Threshserving,low and the signal quality of acell at theLTE frequency satisfies the formula SrxlevnonServingCell > Threshlow, the UEtriggers reselection to the cell. The greater the value of this parameter, the more likely cellreselection 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 theabsolute priority of the serving UMTS cell. The ThdToHighRSRQ(BSC6900,BSC6910)parameter specifies the value of Threshhigh2. The greater the value of this parameter, theless likely reselection is to occur.

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

l Threshlow2 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 theabsolute priority of the serving UMTS cell. The ThdToLowRSRQ(BSC6900,BSC6910)parameter specifies the value of Threshlow2. The greater the value of this parameter, theless likely reselection is to occur.

l Threshserving,low2 is the CPICH Ec/N0 threshold for the serving UMTS cell when the UEreselects a cell working on a lower-priority LTE frequency. The ThdServingLow2(BSC6900,BSC6910) parameter specifies the value of Threshserving,low2. After the cellreselection measurement starts, if the signal quality of the serving cell remains lower thanthis parameter value and the signal quality of the target cell using a lower-priority frequencyremains 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 greatestSrxlevnonServingCell value.

The following parameters are set by running the ADD UCELLNFREQPRIOINFO or MODUCELLNFREQPRIOINFO 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 MODUCELLSELRESEL command:l Treselections(BSC6900,BSC6910)l ThdServingLow(BSC6900,BSC6910)l ThdServingLow2(BSC6900,BSC6910)

3.4 UMTS-to-LTE Quick Cell ReselectionA UMTS/LTE multi-mode UE camping on the UMTS network can initiate UMTS-to-LTE cellreselection 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 triggeredonly when the UE does not transmit or receive service data during the time length of an inactivitytimer.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 enhancedfast dormancy and in the CELL_DCH state

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

To accelerate the UMTS-to-LTE cell reselection, you need to enable the UMTS-to-LTE quickcell reselection function by running the SET URRCTRLSWITCH command withFAST_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 transmitor 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) andtherefore the cell reselection process is faster.State transition from CELL_DCH to CELL_PCH or the idle state by running the SETURRCTRLSWITCH command withUL_DUAL_MODE_UE_D2P_OR_D2I_SWITCH set to an appropriate value underPROCESSSWITCH4(BSC6900,BSC6910). WhenUL_DUAL_MODE_UE_D2P_OR_D2I_SWITCH is cleared, the UE transits fromCELL_DCH to CELL_PCH. When UL_DUAL_MODE_UE_D2P_OR_D2I_SWITCHis 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. SelectUL_DUAL_MODE_UE_D2P_OR_D2I_SWITCH if some UEs in the network do notsupport 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 fromCELL_DCH to CELL_FACH when it does not transmit or receive service data duringthe time length specified by PsInactTmrForFstDrmDch(BSC6900,BSC6910) andthen transits from CELL_FACH to CELL_PCH or the idle state when it does nottransmit or receive service data during the time length specified byPsInactTmrForFstDrmFach(BSC6900,BSC6910). After UMTS-to-LTE quick cellreselection is enabled, the UE is able to transit from CELL_DCH directly to CELL_PCHor the idle state when it does not transmit or receive service data during the time lengthspecified by PsInactTmrForFstDrmDch(BSC6900,BSC6910) without the need towait until PsInactTmrForFstDrmFach(BSC6900,BSC6910) expires. This shortensthe 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 theUE does not transmit or receive service data during the time length specified byPsInactTmrForFstDrmDch(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 stateUMTS-to-LTE quick cell reselection does not provide gains for these UEs. State transitionfrom CELL_FACH to CELL_PCH or the idle state is triggered when the UE does nottransmit or receive service data during the time length specified byPsInactTmrForFstDrmFach(BSC6900,BSC6910) regardless of whether UMTS-to-LTEquick cell reselection is enabled.Changing the value of PsInactTmrForFstDrmDch(BSC6900,BSC6910) orPsInactTmrForFstDrmFach(BSC6900,BSC6910) affects this feature and the EnhancedFast Dormancy feature. For details about enhanced fast dormancy, see Enhanced FastDormancy Feature Parameter Description.

3.5 UMTS-to-LTE Fast Return3.5.1 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 toCSFB. When the UE finishes all services in the UMTS cell, it releases the RRC connection. Inversions earlier than RAN14.0, if the absolute priority of a neighboring LTE cell's frequency ishigher than that of the UMTS cell's frequency, the RRC CONNECTION RELEASE messagedoes not contain the frequency information about neighboring LTE cells. As a result, the UEcamps on a UMTS cell.If a neighboring LTE cell fulfills the cell reselection conditions, the UE reselects the neighboringLTE 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 aresult, 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 userexperience.This feature applies to the areas that are jointly covered by UMTS and LTE networks and wherethe LTE network signal quality is satisfactory.If the LTE network signal quality is poor, for example, when an RRC CONNECTIONRELEASE message contains information about n (a positive integer) LTE frequencies whosesignal 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 nosuitable LTE cell is found, these UEs select a suitable LTE cell from the LTE cells usingfrequencies supported by these UEs. If a suitable LTE cell is still not found, these UEsrandomly camp on a suitable cell. For details, see section 8.5.2 Actions when entering idlemode 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 cellsusing n LTE frequencies. The selection lasts for at most n seconds. If no suitable LTE cellis found, these UEs select a suitable LTE cell from the LTE cells using frequenciessupported by these UEs. The selection lasts for 4 seconds. If a suitable LTE cell is still notfound, these UEs randomly camp on a suitable cell. For details, see section 8.5.2 Actionswhen 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 searchingfor a suitable LTE cell.A UMTS-to-LTE fast return may not be performed in the following scenario: A UE that hasperformed a CSFB process moves to another RNC and the target RNC becomes the SRNC. Inthis case, the target RNC does not know whether the UE has performed a CSFB process, becausecertain information cannot be transmitted between RNCs. Hence, the SRNC instructs the UE toperform a UMTS-to-LTE fast return only if an End Of CSFB indication is carried in the IURELEASE COMMAND message sent by the MSC when the CS service is released. If the MSCis not able to carry an End Of CSFB indication in the IU RELEASE COMMAND message, aUMTS-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 aUMTS cell through CSFB to quickly return to the LTE network after the CS service or all servicesare finished.This feature incorporates the following functions:l UMTS-to-LTE Fast Returnl Enhanced UMTS-to-LTE Fast ReturnBefore enabling the Enhanced UMTS-to-LTE Fast Return function, you must enable the UMTS-to-LTE Fast Return function. However, before enabling the 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 networkafter 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 returnto 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 EnhancedUMTS-to-LTE Fast Return function.

3.5.2 UMTS-to-LTE Fast ReturnAt the cell level, this function is controlled by theHO_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 theHO_UMTS_TO_LTE_FAST_RETURN_SWITCH under the HoSwitch(BSC6900,BSC6910) parameter in the SET UCORRMALGOSWITCH command. When thisfunction 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 valueis "CSFB" or "CSFB High Priority."

l When the UE is moving from an LTE cell to a UMTS cell through a redirection, theRRC CONNECTION REQUEST message does not contain the "Pre-redirection info"IE. (For details, see section 8.1.3.3 "RRC CONNECTION REQUEST message contentsto set" in 3GPP TS 25.331 V9.4.0.) The first service that the UE processes afteraccessing 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 frequencieshave higher absolute priorities than the frequency of the UMTS cell in an RRCCONNECTION RELEASE message. Upon receiving the message, the UE selects a targetcell based on the information and attempts to camp on this cell. (For details about suitableLTE cell selection, see section 8.5.2 Actions when entering idle mode from connected modein 3GPP TS 25.331 V9.4.0. For details about a suitable LTE cell, see section 4 Overallprocess structure in 3GPP TS 23.122 V11.4.0.)

3.5.3 Enhanced UMTS-to-LTE Fast ReturnAt the cell level, this function is controlled by thePERFENH_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 thePERFENH_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 configurationtakes 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, theRELOCATION REQUEST message contains a "cause" IE whose value is "CS Fallbacktriggered (268)" or a "CSFB Information" IE whose value is "CSFB" or "CSFB HighPriority."

l When the UE is moving from an LTE cell to a UMTS cell through a redirection, theRRC CONNECTION REQUEST message does not contain a "Pre-redirection info" IE.(For details, see section 8.1.3.3 "RRC CONNECTION REQUEST message contents toset" in 3GPP TS 25.331 V9.4.0.) After the RNC receives an RRC Connection SetupComplete 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, theRRC CONNECTION REQUEST message contains a "CSFB Indication" IE. (Fordetails, 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 COMMANDmessage from the CN to the RNC contains an "End Of CSFB" IE. (For details, seesection 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 UMTScell, the RNC triggers the RRC connection release procedure.

3. The RNC includes the information about the neighboring LTE cells whose frequencieshave higher absolute priorities than the frequency of the UMTS cell in an RRCCONNECTION RELEASE message. Upon receiving the message, the UE selects a suitableLTE cell based on the information and attempts to camp on this cell. (For details aboutsuitable LTE cell selection, see section 8.5.2 Actions when entering idle mode fromconnected mode in 3GPP TS25.331 V9.4.0. For details about a suitable LTE cell, seesection 4 Overall process structure in 3GPP TS 23.122 V11.4.0.)

3.5.4 Selecting Frequencies to Be Carried in the RRCCONNECTION RELEASE