Interworking Guideline LTE WCDMA GSM

Unique document identifier (ID) D436057350 Version number 7

LTE interworking with WCDMA and GSM RL60, RU50, RG30 Version 7 - May 2014

NPO Engineering Guideline

This material, including documentation and any related computer programs, is protected by copyright controlled by Nokia. All rights are reserved. Copying, including reproducing, storing, adapting or translating, any or all of this material requires the prior written consent of Nokia. This material also contains confidential information, which may not be disclosed to others without the prior written consent of Nokia.

NPO Global Author Guidelines 13th May 2014

©2014 Nokia. All rights reserved

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Change history

Version

Date

Author of the version

Status

Comments

1.0

25th June 2011

Gerson Man

Draft

Updates after review comments

6.0

6th May 2013

Raivo Tender

Approved

RG30 and RL40 RAN features added to section 2

7.0

19th May 2014

Tomas Novosad

Approved

Removal of redundant contents. New contents added for RL60, RU50 and RG30.

Reviewed by 13th May 2014

Lorena Serna, Kirsi Teravainen, Jarkko Itkonen, Guan Siong Phua

Approved by 19th May 2014

Lorena Serna

Organization

Name

NPO Global

Tomas Novosad

Owner

Document ID


Document Title

Location


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D436057350


LTE Interworking with WCDMA and GSM RL60, RU50, RG30

https://sharenetims.inside.nokiasiemens networks.com/Overview/ D436057350


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Table of contents 1 Purpose and Scope...............................................................5 2 Introduction............................................................................7 2.1 2.2 2.3 2.4 2.5

Inter-RAT Planning Process..........................................................................7 List of Features for LTE – WCDMA – GSM Interworking...............................7 Process for Inter-RAT Mobility Planning........................................................9 User Equipment Procedures in Idle Mode...................................................10 Preparing GSM and WCDMA Networks for LTE Introduction......................11

3 Inter-RAT Neighbor List Planning........................................13 3.1 Introduction.................................................................................................13 3.2 Maximum Number of Inter-RAT Neighbors.................................................14

4 Inter-RAT Idle Mode Mobility................................................16 4.1 LTE Idle Mode Mobility Procedures.............................................................16 4.2 System Information Broadcast....................................................................16 4.3 Cell Selection..............................................................................................17 4.3.1 Reselection Priorities Management..........................................................18 4.3.2 Cell Priority Planning................................................................................18 4.3.3 Triggering UE Measurements..................................................................20

5 ISHO Optimization...............................................................22 5.1 ISHO Performance Analysis Methods.........................................................22 5.2 Drive Tests..................................................................................................23 5.3 KPI and Counter Analysis...........................................................................24 5.3.1 Where to find Information on KPIs and Counters.....................................24 5.3.2 Tool Support.............................................................................................25 5.4 ISHO Message Flow Analysis.....................................................................26 5.4.1 Example 1: Message Flow Analysis, Air-Interface, Inter eNB HO.............26 5.4.2 Example 2: Message Flow Analysis, Re-Selection LTE-WCDMA.............28 5.4.3 Example 3: Message Flow Analysis, RRC Conn. Release with Redirection from LTE to WCDMA...........................................................................................29 5.4.4 Example 4: Message Flow Analysis at other Network Interfaces.............30 5.4.5 Example: Trouble Shooting, Intra LTE Handover.....................................35 5.5 ISHO Message Flow Charts........................................................................35 5.5.1 RL30: LTE56: Inter RAT handover from LTE to WCDMA.........................36 5.5.2 LTE442: RL30: eNACC to GSM...............................................................37 5.5.3 Intra eNodeB Handover...........................................................................38



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5.5.4 5.5.5 5.5.6 5.5.7 5.5.8 5.5.9 5.5.10 5.5.11 5.5.12

Inter eNodeB Handover...........................................................................39 Inter eNodeB S1 Based Handover...........................................................40 Cell Reselection from LTE to WCDMA or GERAN...................................41 Cell Reselection to LTE from WCDMA or GERAN...................................43 E-UTRAN TO UTRAN Iu mode Inter RAT Handover................................45 UTRAN Iu mode to E-UTRAN Inter RAT handover..................................47 E-UTRAN to GERAN A/Gb mode Inter RAT handover...........................49 GERAN A/Gb mode to E-UTRAN Inter RAT handover...........................51 CS Fallback to UTRAN or GSM via Redirect.........................................53

6 References..........................................................................57



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1 Purpose and Scope Subscriber mobility requires interworking between LTE and WCDMA/GSM. This guideline introduces the software solutions that make it possible and the necessary planning and optimization tasks related to the Inter RAT handover between LTE and GSM/WCDMA networks. Software solutions for the interworking of LTE and WCDMA / GSM can be structured into: 

Basic mobility mechanisms (Idle mode)



Data service continuity



Seamless Voice & Data service continuity



iSON features to handle mobility

Figures below show an overview of the features that enable the interworking towards WCDMA and GSM respectively

Figure 1: Mobility States and Features that enable mobility (LTE- WCDMA)



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Figure 2: Mobility States and Features that enable mobility (LTE- GSM)



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2 Introduction Mobile subscribers expect continuous network availability and full service continuity. Smooth transitions between different technologies are necessary.

2.1 Inter-RAT Planning Process There are 4 sequential tasks when planning Inter-RAT interworking: 

Agree the Inter-RAT strategy with customer



Decide, which features shall be used



Create the Inter-RAT neighbor list (in case of no SON support)



Activate and configure the features as described in this guideline

Note1: Idle Mode Mobility from LTE to WCDMA or GSM may not require the planning of an Inter-RAT neighbor list in all cases. It is however important to identify preference order of all layers involved and assign relevant priorities. Note2: CS fallback to UTRAN and GSM via redirect requires planning of an Inter-RAT neighboring via preference layers. Estimating the necessary work time: Necessary work time could be estimated, depending on project specific requirements, during a trial in a limited geographical area

2.2 List of Features for LTE – WCDMA – GSM Interworking The below features provide the mobility functionality between LTE and GSM/WCDMA. Note that features need to be supported by the User Equipment as well. Sources: Nokia Roadmap [16], status 1Q 2014, Nokia Focal Point [18], NPO feature reference Wiki [20], and Nokia NE LTE training materials [19].

Idle Mode Mobility:



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

RL10 / RL15TD: LTE762, Idle mode mobility from LTE to WCDMA, GSM or other LTE



RL10:

LTE870, Idle Mode Mobility from LTE to CDMA/eHRPD



RL30:

LTE807, Idle Mode Mobility from LTE to CDMA/1xRTT



RL30:

LTE426, System Time Broadcast for SIB8



RL50 / RL35TD LTE1036, RSRQ Based Reselection



RL50 / RL45TD: LTE 1442 CSG Idle Mode Mobility. Only works for Open Access eNB



RU20

RAN2067, RAN2067 LTE Interworking



RU50

RAN3069, RAN3069 RSRQ based LTE Reselection



RU50

RAN2881, RAN2881 WCDMA and GSM Layer Priorities



RG20:

BSS21353, LTE System Information

Data Service Continuity: 

RL10 / RL15TD: LTE423, LTE RRC Connection Release with Redirect



RL30 / RL25TD: LTE56, Inter RAT Handover from LTE to WCDMA



RL40 / RL35TD: LTE898, Inter RAT Handover from LTE to TD-SCDMA



RL30 / RL25TD: LTE442, eNACC from LTE to GSM



RL30 / RL25TD: LTE490, MOCN with Full IRAT Mobility (Subscriber profile ID selective neighbor cell list),



RL40 / RL35TD: LTE1387, Load Based Handover – Load Balancing



RL40:



RL50 / RL35TD: LTE1407, RSRQ Based Redirection



RL50 / RL35TD: LTE1060, TDD-FDD Handover,


LTE984, Redirect from LTE to GSM with SIB (Also for CSFB)


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

RL50 / RL35TD: LTE486, PLMN ID selected mobility profiles,



RL50 / RL45TD: LTE1170, LTE Inter-Frequency Load Balancing,



RL60 / RL45TD: LTE498, RIM for Network Assisted Cell Change from LTE to GSM (RAN Information Management for GSM)



RL35TD:



RL60 / RL45TD: LTE57, Handover WCDMA -> LTE



RL60 / RL45TD: LTE1198, RSRQ Based Mobility (Thresholds for Measurements),



RL60 / RL45TD: LTE60, Inter RAT handover to eHRPD_3GPP2,



RL60:

LTE498, Automatic retrieval of system information from BSC,



RU20:

RAN2176, RAN2176 LTE PS Handover



RU40:

RAN2127, RAN2127 Smart LTE layering



RU50:

RAN2264, RAN2264 Smart LTE Handover



RU50:

RAN2980, RAN2980 Measurement based LTE layering



RU50:

RAN1688, RAN1688 HSUPA CM for LTE and Inter-frequency Handover



RG20:

BSS21355, Intersystem NACC for LTE,



RG20EP2:

RG301736 , Intersystem NACC from GSM to TD-SCDMA,



RG30:

RG301737, Inter System NCCR for LTE,

LTE898, TD-LTE to TD-SCDMA

Seamless Voice & Data Service Continuity: 

RL20 / RL25TD: LTE562, CSFB from LTE to UTRAN and GSM via redirect



RL20:

LTE22, Emergency Calls via CSFB, part of slideset for LTE562



RL40:

LTE736, CSFB from LTE to UTRAN and GSM based on PS HO



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

RL40 / RL45TD: LTE872, SRVCC from LTE to WCDMA (Also I-HSPA5)



RL40 / RL45TD: LTE873, SRVCC from LTE to GSM



RL60

LTE874, LTE1441, CSFB to CDMA/1xRTT for dual RX UEs



RU30 faster CSFB

RAN2746, RAN2746 Fast HSPA Mobility includes DMCR feature for



RU40:

RAN2435, SRVCC from LTE to WCDMA ,



RU40:

RAN2435 SRVCC from LTE and CSFB with HO



RG30

RG301854, Fast Return to LTE

O&M SON Feature with Relation to Handover: 

RL30:

LTE782, ANR fully UE Based – Intra LTE, Intra Frequency



RL30:

LTE783, ANR InterRAT UTRAN



RL30:

LTE784, ANR InterRAT GERAN



RL30:

LTE510, Synchronization of InterRAT Neighbors



RL30:

LTE771, Mobility Robustness Optimization intra LTE intra Frequency,



RL40: LTE1222, Mobility Robustness Optimization – scheduling of Inter-RAT SON features



RL40:

LTE953, Trace Support for Minimization of Drive Tests, Intra-LTE only



RL50

LTE507, Inter RAT Neighbor Relation Optimization



RL60

LTE556, Inter frequency ANR fully UE based



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2.3 Process for Inter-RAT Mobility Planning The below information is needed to plan the parameter settings: 1.Available System Release: The first step in parameter planning is to identify, what system releases are to be used: 

System Release LTE (e,g.RL50, RL 60)



System Release GSM (e.g. RG20, RG30)



System Release WCDMA (e.g. RU40, RU50)

2. Available ISHO Features and Strategy: Based on the system release the available ISHO features have to be identified and it can be defined, what set of features shall be considered for the network. The feature selection shall however follow certain strategy which reflects the customer situation, assumptions, and expectations. There is not such “one and correct” default strategy, but it is something to be agreed with customer. 3. Parameter Planning Once the a) system release and b) feature set are identified, the parameters can be planned. An excel sheet about such mobility related parameter is available at [24] (excerpt from the parameter dictionary). It contains: 

parameters name



ranges



default values (If applicable)

The latest updates on all parameter default settings are available online, inside the Nokia intranet – see the PDDB and PKDB as part of MINT tool [4]

4. Inter-RAT Neighbor list Planning and the Role of Self Optimizing Network (SON) Features Release RL60 solves inter frequency LTE neighbors (fully UE based) as per 3GPP. Inter-RAT neighbors can be created and optimized via set of NetAct based SON features. NetAct Optimizer and NetAct Configurator are required.



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2.4 User Equipment Procedures in Idle Mode The UE performs PLMN selection, cell selection and cell reselection based on own measurements and information transmitted by the network. The network can transmit necessary information to the UE, if the associated features are enabled in the network and the parameters are set appropriately. The references [1] and [21] contain detailed descriptions for the basic procedures: 

PLMN Selection Procedure



Cell Selection



Cell Re-Selection LTE Intra-Frequency



Cell Re-Selection LTE Inter-Frequency

If a radio cell broadcasts information about Inter-RAT neighbors, the UE can conduct measurements for the Inter-RAT neighbors and may decide to conduct in idle mode an InterRAT cell reselection: 

LTE <-> WCDMA



LTE <-> GSM



LTE <-> CDMA2000

LTE -> UMTS neighbors: It is not necessary to specify individual neighbors for inter-system cell re-selection from LTE to UMTS. It is only necessary to specify the target RF carriers via using of multiple instances of the dlCarFrqUtra parameter within the UFFIM object LTE -> GSM neighbors: It is necessary to define GSM neighbors in terms of their RF carrier. This can be planned on a cell-by-cell basis, or all BCCH carriers can be listed in all LTE cells. The BCCH listing approach avoids the requirement for neighbor planning is practical as long as the number of BCCH carriers is not too high. GSM carriers are specified using multiple instances of the gerArfcnVal parameter within the GNFL object. Each GNFL object can accommodate 32 GSM RF carriers, which is more than the typical number of BCCH frequencies used. Intra LTE neighbors are solved as per 3GPP specification (fully UE based) since RL30 for intrafrequency (feature LTE 782) and from RL60 for interfrequency (feature LTE 556).



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Information about Inter-RAT neighbors/carriers can be stored in the LTE, WCDMA, GSM, CDMA2000 parameter database and will be send in the radio cell, in downlink direction, within the System Information Blocks (SIB).

2.5 Preparing GSM and WCDMA Networks for LTE Introduction Prior to the roll out of an LTE network it is necessary to re-work the handover parameters of existing WCDMA and GSM networks. Multi-RAT User Equipment (UE) will be able to operate on the LTE, WCDMA, GSM 900 or GSM1800 layer of a network, depending on its capabilities and on the network settings. The network operator must decide, under which conditions the different types of UE should operate on different network layers and in which ways the transitions are made. Earlier implemented concepts for WCDMA and GSM networks, as for instance Hierarchical Cell Structure, Load Depended Handover, Service Based Handover, Speed Sensitive Handover and other may need to be reviewed. To simplify network management, 3GPP has introduced the concept “Absolute Cell Priority” (ACP). One example could be to assign: 

High priority for High Capacity cells with limited coverage area, such as LTE 2600 MHz



Low priority for Low Capacity cells with large coverage area, such as GSM 900 MHz

If the concept Absolute Cell Priority (ACP) will be used, existing GSM and WCDMA networks can be prepared prior to the integration of the new LTE network layer. ACP parameters are available in system releases from RG20, RU20, RL20. ACP implementation could be done for GSM-WCDMA networks prior to a large scale rollout of LTE networks. Once ACP is working for the GSM-WCDMA layer in the planned way, the LTE layer can be added. 

Absolute priorities can be allocated to RF carriers belonging to both LTE and other RATs



Absolute priorities are broadcasted within the BCCH



Range of absolute priorities 0..7 (0 = lowest priority) Remark: In Nokia’s implementation value 8 means: not used)



Allocation of equal priorities to different RATs is not supported (3GPP)



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

UE performs only cell reselection evaluation for inter LTE frequency and InterRAT carriers within the SYS-Info and for which the UE has a priority



UE is camped on a cell which defines priorities for other network layers but not for the own, the UE assumes that the current layer has the lowest priority (lower than all 8 possible values)



Absolute priorities can also be signaled directly to individual UEs within an RRC Connection Release message, which will overwrite the absolute priorities in the SYSInfo.



Absolute priorities contained in the RRC Connection Release massage will expire when T320 expires or when the UE is entering RRC connected mode or performing PLMN selection.



Definition of priorities for priority based idle mode cell re-selection is opposite to the definition of the priorities for “Redirect” kind of features.



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3 Inter-RAT Neighbor List Planning 3.1 Introduction Neighbour planning traditionally involves identifying adjacencies for each cell within the network. These adjacencies are added to the databuild and are subsequently used to inform the UE of which cells to search for when completing handovers and cell re-selections. In general, UE are limited to the mobility routes defined by the neighbour list and missing neighbours can cause connections to drop. LTE does not require neighbour planning, and the UE is given the responsibility of identifying specific adjacencies prior to completing a handover or cell re-selection. Usually the neighbor list consists of radio cells that are located in close geographical proximity to a radio cell. SON (Self Optimizing Network) features support automatic creation of the Inter RAT neighbor list (LTE 783/784) since RL30. NetAct Optimizer and NetAct Configurator are needed. Nokia Recommendations: 

Exhaustive neighbour planning is not required for LTE



Consideration should be given to allocating measurement offsets to make specific neighbours appear either more or less attractive



Consideration should be given to allocating priorities to make specific RF carriers appear either more or less attractive

Intra LTE neighbors are solved as per 3GPP specification (fully UE based) since RL30 for intrafrequency (feature LTE 782) and from RL60 for inter frequency (feature LTE 556). 3G -> LTE neighbors: In terms of neighbor planning it is required to add LTE frequencies in the neighbor list so UE knows it has to measure it/them. The smart LTE handover feature (RAN2264 in RU50) brings need to deliver data for ADJE & ADJL objects. This is supported by Optimizer 8 EP1 (basic manual creation). An automation is planned to be in WCDMA AAO release 2.0 which provides support for scheduling adjacency creation/deletion – based on distance or KPIs. 2G -> LTE neighbors: There is support for idle mode cell reselection (2G-LTE) based on that MS is able to execute autonomous cell reselections from GSM cells to LTE cells. For dedicated mode, Nokia supports CS fall back, SRVCC to 2G, ECH (LTE-2G). In practice there are no network deployments of LTE-2G in connected mode yet, except the redirection (RG30 RG301854,Fast return to LTE feature). In terms of neighbor planning it means LTE Neighboring frequencies are defined in ADJL MOCs.



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3.2 Maximum Number of Inter-RAT Neighbors The number of Inter-RAT neighbor cells that can be planned is limited. LTE User Equipment (UE) can identify neighbors autonomously, but the network can send information on neighbor cells or frequencies that shall be monitored by the UE. The information on the neighbor cells or frequencies is transmitted in downlink direction with help of the System Information Blocks (SIBs) on the broadcast channels. Since the channel capacity is limited, only information about a limited number of neighbors can be transmitted. Therefore the number of neighbors must be limited. Alignment between different 3GPP specifications is necessary, with respect to max. size of RCC message versus max. size of SIB messages. If the operator configures SIB according to max. allowed size, the system will not work (i.e. cell setup is not successful), as the related SI messages (Containing the SIBs) are too big to be transmitted. As a consequence, the related cells can’t be taken into service. Maximum RRC message size for broadcast messages, assuming the exclusive usage of format 1C, is 1736 Bit / 217 Byte. The SI messages containing SIB5 or SIB8 can be much bigger, if the maximum allowed list sizes according to 3GPP definitions are used. Sub-Problem: Depending on system bandwidth and maximum code rate for SIB, the maximum RRC message size cannot be reached. The solution is to limit the SIB configurations. RL30 introduced the first consistency check in eNB & NetAct. The following restrictions currently apply for EUTRA, UTRA, GERAN and CDMA neighbors (since RL40): EUTRA Neighbor Restrictions SYSTEM INFORMATION BLOCK TYPE 5 contains information about other EUTRA frequencies and inter-frequency neighboring cells relevant for cell re-selection (including cell re-selection parameters common for a frequency as well as cell specific re-selection parameters). RL 60 - SIB 5 – Object IRFIM There are various limitations applied on the SIB5 which are connected with the LTE channel bandwidth, coding rate used for the SIB5 transmission. The rules are implemented as checks in parameter management system and are connected with the following parameters: IRFIM indentifier (irfimId) Reduced maximum number of LTE neighbor frequencies: The max. number of IRFIM instances shall be restricted to 5, instead of 8 for LTE bandwidth 1.4 and 3MHz.



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Inter-Frequency neighboring cell list (intFrNCList) Reduced maximum number of neighbor cells via complex rule. Inter-frequency blacklisted cell list (intFrBCList). There is again a complex rule on the max number of items. LTE – WCDMA Neighbor Restrictions SYSTEM INFORMATION BLOCK TYPE 6: contains information about UTRA frequencies and UTRA neighboring cells relevant for cell re-selection (including cell re-selection parameters common for a frequency as well as cell specific re-selection parameters); RL 60 - SIB 6 – Object UFFIM. There are not specific restrictions on the number of instances of the Object UFFIM except those 3GPP, i.e. 16 instances. The system has ability to adapt coding rate used for the SIB to accommodate required number of bits.

LTE – GSM Neighbor Restrictions SYSTEM INFORMATION BLOCK TYPE 7: contains information about GERAN frequencies relevant for cell re-selection (including cell re-selection parameters for each frequency). RL 60 - SIB 7 – Object GNFL. The restrictions are connected with the GERAN neighbour frequency configuration identifier (gnflId). The checking rule is connected with the coding rate of SIB7 and the LTE bandwidth used. Maximum number of GNFL instances is typically less than 16. LTE – CDMA 2000 Neighbor Restrictions: SYSTEM INFORMATION BLOCK TYPE 8: contains information about CDMA2000 frequencies and CDMA2000 neighboring cells relevant for cell re-selection (including cell reselection parameters common for a frequency as well as cell specific re-selection parameters). The following restrictions: RL 60 - SIB 8 – Object CDFIM There are restrictions on the number of items in CDMA2000 HRPD Neighbor Cell List (hrpdNCList). The maximum number of items is less than theoretical 32. Another restriction is connected with CDMA2000 1xRTT neighbour cell list (rttNCList) There is limitation on the maximum numbers of items instead of theoretical 40.



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4 Inter-RAT Idle Mode Mobility 4.1 LTE Idle Mode Mobility Procedures The LTE Idle Mode Mobility Procedures, including the Inter-RAT procedures, are defined in 3GPP 36.304. The procedures are mapped to Nokia Software Sales Features, such as: 

LTE39: System Information Broadcast



LTE51: Cell Selection and Re-Selection



LTE762: Idle Mode Mobility from LTE to other LTE bands, WCDMA and GSM



LTE870: Idle Mode Mobility from LTE to CDMA/eHRPD



LTE807: Idle Mode Mobility from LTE to CDMA/1xRTT



LTE426: System Time Broadcast for SIB8

4.2 System Information Broadcast The feature “LTE39: System Information Broadcast” is available since RL09 [4]. The eNodeB transmits in each cell physical synchronization signals and broadcast information supporting initial cell selection and cell re-selection. The synchronization signals are the basis for the UE to perform the initial cell search. The NAS (non-access stratum) can control the RAT(s) (radio access technologies) in which cell selection is performed, for example, by maintaining a list of forbidden registration areas and a list of equivalent PLMNs. The system information consists of several system information blocks (SIBs). The system information master (SI-M) contains information for the cell identification. The Si-M is carried on the BCH with a periodicity of 40ms. The system information 1 (SI-1) contains the SIB and scheduling information of other SIBs. The SI-1 is carried on DL-SCH with a periodicity of 80 ms. All others SIBs are carried as well on DL-SCH. The others SIBs are scheduled dynamically. The following information is contained in each of the supported SIB: 

SIB 1: The SIB1 contains information relevant when evaluating if a UE is allowed to access a cell and defines the scheduling of other system information blocks.



SIB 2: The SIB2 contains common and shared channel information.



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

SIB 3: The SIB3 contains cell re-selection information, mainly related to the serving cell.



SIB 4: The SIB4 contains information about the serving neighboring frequencies and intra-frequency neighboring cells relevant for cell re-selection.



SIB 5:The block supports intra-LTE cell reselection



SIB 6:The block supports LTE-UTRAN cell reselection



SIB 7:The block supports LTE-GERAN cell reselection



SIB 8: The block supports LTE – CDMA (3GPP2) cell reselection

4.3 Cell Selection The feature “LTE51: Cell Selection and Re-Selection” is available since the intial LTE release. When a UE is switched on and a PLMN has been selected according to [1], the UE searches in idle mode for the strongest cell on all supported carrier frequencies of each supported RAT until a suitable cell is found. To speed up the procedure, the UE can use stored information from a previous access or otherwise conduct an Initial cell selection. As a result of successful cell selection, the UE camps on a certain cell. A cell is suitable for cell selection if the S- (selection) criterion is fulfilled: Srxlev > 0 with: Eq. 4.3.1-1 Srxlev = Qrxlevmeas – (Qrxlevmin – Qrxlevminoffset) – Pcompensation

Eq. 4.3.1-2

Pcompensation = max(Pemax – Pumax , 0)

Eq. 4.3.1-3

Pcompensation provides a contribution only if the UE has less TX power capabilities than allowed in the radio cell. Assuming that the power class of an UE is high enough and neglecting higher priority PLMNs, a cell is suitable if the measured RX level is higher than a minimum receive level which can be configured. The cell selection parameters are broadcasted in SIB1. Note that RSRQ based cell reselection is available with 3GPP Release 9. Nokia implementation can be seen from [17]. Main idea applies the rules below for cell selection/reselection based on RSRQ metrics:



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Squal = Qqualmeas – (Qqualmin + Qqualminoffset), where Squal = RSRQ – (qQualMinR9 + qQualMinOffsetR9) Once a suitable cell is found, the UE enters into the Normally Camped state and can obtain normal service. If no suitable cell is found, the UE enters into the Any Cell Selection mode. If LTE radio coverage is not available, capable Multi-RAT UE could select a WCDMA radio cell according to 3GPP 25.304 or a GSM radio cell according to 3GPP 43.022 or a CDMA2000 cell according to 3GPP2 C.S0024-A / C.S0005-A.

4.3.1 Reselection Priorities Management Absolute priorities of different E-UTRAN frequencies or inter-RAT frequencies may be provided to the UE in the system information, in the RRCConnectionRelease message, or by inheriting from another RAT at inter-RAT cell (re)selection. If priorities are provided in dedicated signaling, the UE shall ignore all the priorities provided in system information. If UE is in camped on any cell state, UE shall only apply the priorities provided by system information from current cell, and the UE preserves priorities provided by dedicated signaling unless specified otherwise. The UE shall delete priorities provided by dedicated signaling when: 

The UE enters RRC_CONNECTED state; or



The optional validity time of dedicated priorities (T320) expires; or



A PLMN selection is performed on request by NAS .

NOTE: Equal priorities between RATs are not supported. The UE shall only perform cell reselection evaluation for E-UTRAN frequencies and interRAT frequencies that are given in system information and for which the UE has a priority provided. The UE shall not consider any black listed cells as candidate for cell reselection. The UE shall inherit the priorities provided by dedicated signaling and the remaining validity time (i.e., T320 in E-UTRA, T322 in UTRA and T3230 in GERAN), if configured, at inter-RAT cell (re)selection. NOTE: The network may assign dedicated cell reselection priorities for frequencies not configured by system information.



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4.3.2 Cell Priority Planning The 3GPP-R8 concept Absolute Cell Priority allows to plan, towards which radio network layer a Multi-RAT capable UE shall preferably conduct Cell Re-Selection and Handover. Possible planning objectives and planning considerations could be (from top to bottom):     

UE shall re-select, according to its capabilities, to the layer with the highest capacity UE with WCDMA_GSM capabilities shall setup PS data calls on the WCDMA layer The low capacity GSM layer shall be reserved for UE with GSM capabilities only In GSM_1800 more frequencies are available compared to GSM_900; therefore the capacity can be higher in GSM_1800 Keep the GSM_900 layer free as long as possible, since GSM_900 cells have larger coverage area than GSM_1800 cells, but often lower capacity. GSM_900 can still provide radio coverage where GSM_1800 cannot provide coverage any more. Use GSM_900 as last resort, to keep up the service as long as possible.

Earlier implemented concepts for WCDMA and GSM networks, such as Hierarchical Cell Structure, Load Depended Handover, Service Based Handover and other may need to be reviewed. There is a strong relation to Capacity Management. Inappropriate feature configuration can lead to overload of network elements and poor user experience. The network operator may want the UE to conduct Cell Re-Selection preferably towards the following network layer, according to the UE Multi-RAT capabilities: UE Capabilities LTE + WCDMA + GSM _900_1800 WCDMA + GSM _900_1800 GSM_900_1800

Preferred Layer for UE Camping LTE WCDMA GSM_1800

Table 4.3.2-1 Example: Preferred layer for UE Camping

Then, the allocation of Absolute Cell Priorities could be: Absolute Cell Priority 7 6


Cell Priority

RAT

Frequency Band [MHz]

Cell Type

Cell coverage

Cell traffic capacity

LTE LTE

2600 900

Macro Macro

medium large

large


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5 4 3 2 1 0

lowest

UTRAN UTRAN UTRAN GSM GSM GSM

2100 / 900 2100 900 1800 / 900 1800 900

Micro Macro Macro Micro Macro Macro

small medium large small medium large

small

Table 4.3.2-2 Example: Absolute Cell Priority Allocation

Depending on the planning concept, the allocation of Absolute Cell Priorities may vary.

4.3.3 Triggering UE Measurements When camping on a LTE cell, the UE regularly searches for a more suitable cell to camp on. According to information provided in SIB messages on the neighbor frequencies to monitor, the search space may include other LTE frequency bands and other RAT. The UE performs measurements when the following criteria are fulfilled 1. LTE Intra – Frequency: Srxlev <= Sintrasearch 2. LTE Inter - Frequency: cellReSelPrio (serving)

Srxlev <= Snonintrasearch OR cellReSelPrio(inter – f) >

3. From LTE to Inter - RAT: Srxlev <= Snonintrasearch OR cellReSelPrio (inter - RAT) > cellReSelPrio (serving) Note 1: The 3GPP parameter Snonintraserch is in Nokia terminology Snonintrsearch. It defines a threshold [Against qrxlevmin = minimum required RSRP level in the cell (dBm)] for inter-RAT and inter-frequency measurements. Note 2: Inter-Frequency and Inter–RAT Cell Reselection is supported since RL10, when feature LTE762 supports broadcasting SIB5, SIB6, SIB7 and LTE870 SIB8. Triggering UE Measurements for Inter-RAT Cell Re-Selection (LTE has higher priority) Srxlev

= Qrxlevmeas – (Qrxlevmin – Qrxlevminoffset) – Pcompensation

Srxlev

<= Snonintrasearch

Qrxleavmeas

<= Snonintrasearch +(Qrxlevmin – Qrxlevminoffset) – Pcompensation

In case Qrxxlevminoffset = Pcompensation = 0:



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Figure 4.3.3-3 Triggering UE Measurements for Inter-RAT Re-Selection (LTE has higher priority)



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5 ISHO Optimization ISHO performance optimization is specific to the implemented features. Only such functions can be tested that are supported by implemented features.

5.1 ISHO Performance Analysis Methods ISHO performance can be monitored with help of: 

Counter and KPI



Drive tests



System traces

Drive tests and traces allow a deep analysis for the handover functionality for a single UE, KPI and counter analysis can provide an overall picture for all UE that are operating in the network. Implemented counter and KPI are related to features. An example to some of implemented counter and KPI is provided below. More detailed list of implemented KPI and counters could be seen from training NEI material [22] or from the specification document [23]. The final goal could be to calculate the:

InterRAT _ Handover _ Success _ Rate % 

# _ Successfull _ InterRAT _ Handover *100 # _ Attempted _ InterRat _ Handover

Mutually for all neighbor relations as indicated in the below table: Original Cell ID

Destination Cell ID

# Attempted InterRAT Handover

# Successful InterRAT Handover

InterRAT handover Success Rate

201

301

100

99

99 %

201

302

100

5

5%

Table 4.3.3-3 Example InterRat Handover analysis

In the first row of the table a total of 100 InterRat Handover Attempts took place between cell 201 and cell 301. Out of these, 99 have been successful, which leads to an acceptable



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InterRat Handover Success Rate of 99%. Common sense to be applied to the number of samples should provide reasonable confidence….in this case a minimum of 500 samples with 5 failures are needed. In the second example, between cell 201 and cell 302 also 100 InterRAT Handover attempts took place. Unfortunately only 5 have been successful, which leads to a poor Inter RAT Handover Success Rate of only 5%. In such cases a deeper analysis of the below points must be conducted to improve the situation. In larger networks, a Top-20 list could be established and these cases could be followed up first.: 

Counter and sub-counter



parameter settings



setup of software and hardware



drive test files



trace analysis

5.2 Drive Tests Drive tests can be done to verify if enabled features work properly. If needed, corrective measures can be taken. Due to the fact that drive tests consume a considerable amount of time and resources it might be necessary to restrict the drive test activities to a limited geographical area when verifying the functionality of a new feature. A map can be printed to indicate at which geographical location the handover did not work or in which places unwanted handover take place (Ping-Pong handover). These cases can then be analyzed one by one. The most important question is to identify, from which cell to which cell the handover should have been conducted. An important question is, whether or not the two cells are already entered mutually in the eNB configuration files as neighbors. By analyzing the messages in the drive test file the possible reason for the dropped call or ping pong handover can be identified and corrections in the eNB configuration files can be done. It is also possible that handover performance is degraded by hardware issues, such as crossed antenna cables.



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5.3 KPI and Counter Analysis KPI and Counter analysis provides information how reliable the intersystem handover is working on network wide level. Note that drive tests allow only to analysis single UEs. The measured handover performance might also be influenced by UE specific capabilities

5.3.1 Where to find Information on KPIs and Counters

 Jump Portal - Information on KPI and counter is available, including the latest updates  Operating Documentation: Information on KPI and counter is also available from the operating documentation, which can be downloaded from the NOLS/PIC portal. The NED version contains a fast search engine. Also a PDF version can be downloaded for the LTE, WCDMA and GSM system releases. After downloading the ZIP file, click on: _startup.pdf to explore the available documentation.



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Figure 5.3.1-4 LTE RL60 Operating Documentation, online from NOLS.

5.3.2 Tool Support The Nokia solution for performance monitoring is NetAct Reporter. LTE RL60 is supported in Network Performance Manager (NPM) and in the Reporting Suites aligned with NetAct 8. NetAct is formed by different tools, some of them are basic functionality whereas others are optional. The basic idea of performance measurement as per reference [22] is on the following figure:



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Network Performance Manager (NPM)

Figure 5.3.2-5 NetAct KPI administration



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5.4 ISHO Message Flow Analysis Message flow analysis provides detailed information needed for troubleshooting. Either drive test log files or trace files may need to be analyzed. 

Standard Analysis: Drive test log file analysis



Deep Analysis:

Trace analysis

The messages should contain information as planned for the parameter settings in the eNB site configuration file and in the configuration files of other network elements. a) Standard Analysis (Drive Tests): Drive test log files can be analyzed. Prior to the cell reselection or handover, the UE should operate on the old Cell ID and afterwards on the new Cell ID. The Cell ID´s and the contents of transmitted SIB messages should be visible from the log file. If necessary, parameter settings in the eNB configuration files could be modified. Example tool: XCAL or NENO (Anite) b) Deep Analysis (Trace Analysis) Trace logs can be taken at the interface of two network elements. A protocol analyzer can display the data, specially the message flow in such way that it becomes readable for humans. Packets can be viewed or filtered according to specific contents. Statistics could be derived. Example tool: Wireshark

5.4.1 Example 1: Message Flow Analysis, Air-Interface, Inter eNB HO The following example refers to an intra-LTE, inter eNB handover. Once drive test equipment with Inter-RAT capabilities becomes available, the principles could be similar. An Inter eNodeB HO was conducted and the drive test log file was saved (XCal drive test tool). According to Figure 5.5.3-15 the following messages must be exchanged to conduct an Inter NodeB HO. For simplification, only the most important messages are mentioned:

Message Transfer 

UE UE U

eNB

RRC: MEASUREMENT REPORT



eNB

RRC: RRC CONNECTION RECONFIGURATION



eNB

RRC: RRC CONNECTION RECONFIGURATION

UE



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COMPLETE

Later the XCAL drive test log file was replayed and the following screen shots were taken. The following screen shot shows the situation shortly before the handover was executed. The UE is operating on the old Serving Cell with Cell ID = 203. In the centre the first message RRC: MEASUREMENT REPORT is highlighted. On the right hand site it is visible, that the proposed new LTE target cell has the Cell ID = 201.

Figure 5.4.1-6 Serving Cell ID before handover

The transmitted parameters correspond with the parameters planned in the eNB site configuration file. The following screen shot shows the situation after the handover: The new serving cell is now Serving Cell ID = 201 and in the centre of the picture the last message in the sequence RRC: RRC CONNECTION RECONFIGURATION COMPLETE is highlighted.



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Figure 5.4.1-7 Serving Cell ID after handover

5.4.2 Example 2: Message Flow Analysis, Re-Selection LTE-WCDMA The message flow at the air interface can be analyzed for instance by recording and replaying the message flow with drive test tools such as XCal or other. The below XCAL screen shot is for feature: “LTE762: Idle mode mobility from LTE to WCDMA, GSM or other LTE bands”.



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Figure 5.4.2-8 XCal screenshot

The screen shot highlights the transmission of a SIB-6 message from the eNB to the UE, containing the information about the UTRA neighbor cell.

5.4.3 Example 3: Message Flow Analysis, RRC Conn. Release with Redirection from LTE to WCDMA The message flow at the air interface can be analyzed for instance by recording and replaying the message flow with drive test tools such as XCal or other.



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The below XCAL screen shot is for the feature: LTE 423: RRC Connection Release with Redirect from LTE to WCDMA” in a field customer project. The screen shot highlights the transmission of the WCDMA carrier info in the release message from the network to the user equipment.

Figure 5.4.3-9 XCal screenshot

If needed, a deep analysis can be conducted by verification of the message contents.

5.4.4 Example 4: Message Flow Analysis at other Network Interfaces A protocol analyzers as for instance Wireshark can record data at network interfaces. The data, specially the message flow, can be displayed in such way that it becomes readable for humans. Packets can be viewed or filtered according to specific contents. Statistics could be



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derived. In the following example the UE has conducted a Cell Re-Selection from LTE to HSPA and a Routing Area Update was conducted.

Figure 5.4.4-10 Cell Reselection from LTE to HSPA with Routing Area Update

During the Routing Area Update messages between network elements are exchanged as indicated in the message flow chart



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,



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. Analysis examples are provided: Gn Interface protocol analysis: The Gn interface is between the SGSN and the MME. During the “Routing Area Update Procedure” the SGSN will send first the message “SGSN Context Request” to the MME. The message is also visible in the below screenshot (Wireshark).

Iu Interface protocol analysis: The Iu Interface is between the NodeB and the SGSN.

the first message send from the UE to the SGSN is: “Routing Area Update Request”. The last message send from the UE to the SGSN is the message: “Routing Area Update Complete”. These messages are also visible in the below screenshot (Wireshark).



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5.4.5 Example: Trouble Shooting, Intra LTE Handover An example for trouble shooting related to Intra LTE handover can be downloaded from the LTE Optimization Training

5.5 ISHO Message Flow Charts The following are few examples for message flows. More can be found in the: 

Release dependent Nokia operating documentation LTE, WCDMA and GERAN



3GPPTS 23.401, 36.000

The following ISHO flow charts are directly related to Nokia feature descriptions:



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5.5.1 RL30: LTE56: Inter RAT handover from LTE to WCDMA

Figure 5.5.1-11 Message Flow for successful ISHO from LTE to WCDMA (Source: SFS)



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5.5.2 LTE442: RL30: eNACC to GSM

Figure 5.5.2-12 eNACC message sequence

Figure 5.5.2-13: Message Flow LTE562: RL20: CSFB to WCDMA or GSM via Redirect



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5.5.3 Intra eNodeB Handover

Figure 5.5.3-14: Intra eNodeB Handover

This message flow chart is not directly related to ISHO but displayed for completeness..



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5.5.4 Inter eNodeB Handover

Figure 5.5.3-15: Inter eNodeB X2 Based Handover Call Flow

This message flow chart is not directly related to ISHO but displayed for completeness



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5.5.5 Inter eNodeB S1 Based Handover UE

Source eNodeB

Target MME eNodeB Downlink User Plane data

Serving GW

PDN GW

HSS

Decision to trigger a relocation via S1 Handover Required

Handover Request Handover Request Acknowledge Create . Indirect Data Forwarding Tunnel Request Create Indirect Data Forwarding Tunnel Response

Handover Command Handover Command eNB Status Transfer eNB Status Transfer Only for Indirect forwarding of data

Detach from old cell and synchronize to new cell Handover Confirm Downlink data

Uplink User Plane data Handover Notify Modify Bearer Request

Modify Bearer Response Downlink User Plane data Tracking Area Update procedure Delete Session Request UE Context Release Command UE Context Release Complete Delete Session Response Delete Indirect Data Forwarding Tunnel Request Delete Indirect Data Forwarding Tunnel Response

Figur e 5.5.4-16: Inter eNodeB S1 Based Handover This message flow chart is not directly related to ISHO but displayed for completeness.



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5.5.6 Cell Reselection from LTE to WCDMA or GERAN Cell Re-Selection from LTE to WCDMA or GERAN in Idle Mode is controlled by the UE. The message flow for the Routing Area Update could be analyzed. The Routing Area Update without S GW change procedure takes place when a UE that is registered with an MME selects a UTRAN or GERAN cell and the S GW is not changed by the procedure.



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Figure 5.5.5-17 Routing Area Update with MME interaction and without S GW change



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The message flow with S GW Change is different and also available from 23.401.

5.5.7 Cell Reselection to LTE from WCDMA or GERAN Cell Re-Selection to LTE from WCDMA or GERAN in Idle Mode is controlled by the UE. The Tracking Area Update could be monitored. According to 23.401 a standalone tracking area update (with or without S GW change) occurs when a GPRS-attached or E UTRAN-attached UE experiences any of the following conditions: 

UE detects it has entered a new TA that is not in the list of TAIs that the UE registered with the network;



the periodic TA update timer has expired;



UE was in UTRAN PMM_Connected state (e.g. URA_PCH) when it reselects to E UTRAN;



UE was in GPRS READY state when it reselects to E UTRAN;



the TIN indicates "P-TMSI" when the UE reselects to E-UTRAN (e.g. due to bearer configuration modifications performed on GERAN/UTRAN);



the RRC connection was released with release cause "load re-balancing TAU required";



the RRC layer in the UE informs the UE's NAS layer that an RRC connection failure (in either E-UTRAN or UTRAN) has occurred;



a change of the UE Network Capability and/or MS Network Capability and/or UE Specific DRX Parameters and/or TS 24.008 [47] MS Radio Access capability (e.g. due to GERAN radio capability change or CDMA 2000 Radio Access Technology Capability change) information of the UE.



for a SR-VCC capable UE, a change of MS Classmark 2 and/or MS Classmark 3 and/or Supported Codecs.



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Figure 5.5.6-18 E-UTRAN Tracking Area Update without S GW Change (3GPP TS23.401)

The message flow with S GW Change is different and also available from 23.401.



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5.5.8 E-UTRAN TO UTRAN Iu mode Inter RAT Handover Preparation Phase:

Execution phase:



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Figure 5.5.7-19 E-UTRAN to UTRAN Iu mode Inter RAT handover (3GPP TS23.401)



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5.5.9 UTRAN Iu mode to E-UTRAN Inter RAT handover Preparation Phase

Execution Phase:



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Figure 5.5.8-20 UTRAN Iu mode to E-UTRAN Inter RAT handover (3GPP TS23.401)



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5.5.10

E-UTRAN to GERAN A/Gb mode Inter RAT handover

The procedure is based on PS handover for GERAN A/Gb mode defined in TS 43.129. Preparation phase:

Execution phase:



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UE

Source eNodeB

Source Target Target SGSN Serving GW Serving GW

Target BSS Source MME

PDN GW

HSS

Uplink and Downlink User Plane PDUs 1. Handover Command 2. HO from E-UTRAN Command

4. GERAN A/Gb Access Procedures 5. XID Response Downlink User Plane PDUs Sending of uplink data possible

Only if ”Direct Forwarding” applies Only if ”Indirect Forwarding” applies

6. PS Handover Complete 7. XID Response 8. Forward Relocation Complete Notification 8a. Forward Relocation Complete Acknowledge 9. Modify Bearer Request For Serving GW relocation Steps 9, 10 and 11, and the following User Plane path, will be handled by Target Serving GW

(A)

10. Modify Bearer Request 10a. Modify Bearer Response

11. Modify Bearer Response 12. XID Negotiation for LLC ADM 12a. SABM UA exchange re-establishment and XID negotiation for LLC ABM) Uplink and Downlink User Plane PDUs 13. Routeing Area Update procedure 13a. PS Handover Complete Ack 14. Delete Session Request 14b. Release Resource

(B) 14a. Delete Session Response 15. Delete Indirect Data Forwarding Tunnel Request 15a. Delete Indirect Data Forwarding Tunnel Response 16. Delete Indirect Data Forwarding Tunnel Request 16a. Delete Indirect Data Forwarding Tunnel Response

Figure 5.5.9-21 E-UTRAN to GERAN A/Gb mode Inter RAT handover (3GPP TS23.401)



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5.5.11

GERAN A/Gb mode to E-UTRAN Inter RAT handover

The procedure is based on PS handover for GERAN A/Gb mode, defined in TS 43.129 Preparation phase:

Execution phase:



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Figure 5.5.10-22 GERAN A/Gb mode to E-UTRAN Inter RAT handover (23.401)



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5.5.12

CS Fallback to UTRAN or GSM via Redirect

CS Fallback to GSM via RRC connection release with redirection for MTC in ECM-IDLE



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UE in ECM-IDLE state (1)

UE in ECM-IDLE state (2),

UE in ECM-IDLE state (3), reference [44]:



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UE in ECM-IDLE state (4):

UE in ECM-CONNECTED state (1):



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6 References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24


3GPP 36.304: User Equipment (UE) procedures in idle mode 3GPP 23.401: General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network NEI Complex – Inter-RAT Mobility, LTE-Online Parameter Knowledge Dictionary Database – part of MINT Tool https://mint.emea.nsn-net.net Section: Idle Mode Mobility Jump portal, (counters, KPI): https://sharenetims.inside.nokiasiemensnetworks.com/Open/444546453 3GPP Specification 36.300 Novosad, T.: Radio Network Planning for Rollout, Training, Mobility part, 3GPP Specification 36.133 RL30 Training, NE, LTE807: Idle mode mobility from LTE to CDMA/1xRTT RL30 Training, NE, LTE56: InterRAT Handover to WCDMA RL30 Training, NE, LTE442: Network Assisted Cell Change to GSM RL30 Training, NE, LTE490: Subscriber profile ID selective neighbor cell list RL30 Training, NE, LTE562: CSFB to WCDMA or GSM via Redirect, LTE22: Emergency Call Handling RL30 Training, NE, ANR InterRAT with O and M.pdf (LTE783, 784, 510) 3GPP TS 36.331 NOKIA Radio Cluster Roadmaps, LTE1036 – RSRQ based reselection, RL50 NOKIA Focal Point (feature per release info, similar to roadmaps, but with less restrictive access policy), NOKIA NE LTE training materials, select relevant directory, NPO WiKi – RF features and reference page, Radio Network Planning for Roll-out NPO training set, LTE Performance Management NEI Kollar, M.: LTE RAN KPI Specification Document RL60/45, Teravainen,Kirsi: I-RAT Mobility Parameters – excel list: https://sharenetims.inside.nokiasiemensnetworks.com/Overview/D515511001


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Interworking Guideline LTE WCDMA GSM

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