Dn03298108 1 en Global PDF Paper a4 GSM WCDMA Plan

GSM-WCDMA inter-systemhandover feature planning andsystem impact for GSM/EDGEBSS

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© Nokia CorporationNokia Proprietary and Confidential

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2002545Nokia GSM/EDGE BSS10.5 SystemDocumentation Set

2 (62) © Nokia CorporationNokia Proprietary and Confidential


GSM-WCDMA inter-system handover feature planning and system impact for GSM/EDGE BSS

Contents

Contents 3

1 Overview of GSM-WCDMA inter-system handover 51.1 GSM-WCDMA cell re-selection and inter-system handover 61.2 WCDMA�GSM cell re-selection and inter-system handover 7

2 System impact for GSM-WCDMA inter-system handover 92.1 Introduction 92.2 Requirements 92.2.1 Hardware 92.2.2 Software 102.2.3 Frequency band support for GSM-WCDMA inter-system handover 102.2.4 Requirements forGSM-WCDMA inter-systemhandover related features 112.3 BSS Performance 112.3.1 OMU signalling 112.3.2 TRX signalling 112.3.3 MCMU 112.3.4 OMU 122.3.5 BCSU 122.3.6 PCU 122.3.7 TCSM 132.4 User Interface 132.4.1 ISHO parameters 132.5 Inter-system handover impact on NSS 142.5.1 Inter-system handover and UMTS changes in MSC 142.6 Impact on Interfaces 152.6.1 Impact on A interface 152.6.2 Impact on Abis interface 162.6.3 Impact on Gb interface 172.6.4 Impact on Iu interface 172.7 Feature Interoperability 172.7.1 GSM-WCDMA inter-system handover interaction with other features and

functionalities 172.7.2 Capacity and restrictions of GSM-WCDMA inter-system handover 182.8 Related Topics 19

3 Inter-system handover from GSM to WCDMA 213.1 GSM-WCDMA cell re-selection in idle state 213.1.1 Cell re-selection with non-GPRS capable mobiles 233.1.2 Cell re-selection with GPRS capable mobiles 253.2 GSM-WCDMA handover process 283.3 WCDMA RAN cell measurements for GSM-WCDMA inter-system

handover 31

4 Inter-system handover from WCDMA to GSM 354.1 WCDMA-GSM cell selection and re-selection 354.2 WCDMA-GSM handover process 374.2.1 Downlink DPCH power 40



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Contents

4.2.2 Uplink DCH quality 414.2.3 UE Tx power 424.2.4 Low measured absolute CPICH RSCP 434.2.5 Low measured absolute CPICH Ec/No 444.3 GSM cell measurements for WCDMA-GSM inter-system handover 454.3.1 Inter-system handover decision algorithm 464.3.2 Interaction with inter-frequency handover 484.4 WCDMA compressed mode 494.4.1 Compressed mode functionality 524.4.2 Selection of downlink compressed mode method 544.4.3 Operator controllable compressed mode parameters 564.4.4 Effect of compressed mode on WCDMA coverage and capacity 57




1 Overview of GSM-WCDMA inter-systemhandover

The inter-system handover is a handover (HO) between GSM and WCDMAnetworks. The change of GSM and WCDMA network can also happen in idlemode when there is cell re-selection. The cell re-selection is also done for packetdata even if the mobile is not in idle mode.

The inter-system handover from GSM to WCDMA is initiated by the GSM radionetwork, and the inter-system handover from WCDMA to GSM is initiated bythe WCDMA radio network (that is, UTRAN).

In order for an operator to be able to provide seamless coverage in areas whereWCDMA is not available, for example in rural areas, inter-system handoversprovide a method of extending the radio network coverage area by making ahandover between the WCDMA network and GSM network.

Additionally, in situations where the WCDMA network and GSM networkoverlap, an inter-system handover can be made in order to balance or control thetraffic load between the systems. An example of this is where the speechconnection is handed over to the GSM network to allow data connections to behandled by the WCDMA network.

The inter-system handovers are hard handovers and therefore cause a temporarydisconnection of the real time (RT) radio access bearer.

The inter-system handovers are also network-evaluated handovers (NEHO).However, the user equipment (UE) must be capable of supporting inter-systemhandovers completely before this feature can be used.



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Overview of GSM-WCDMA inter-system handover

1.1 GSM-WCDMA cell re-selection and inter-systemhandover

For a dual mode GSM/WCDMA mobile, the GSM-WCDMA inter-systemhandover feature enables the measurements and cell re-selection of neighbourWCDMA RAN cells while the MS has been camped on a GSM cell in the idlestate.

The GSM-WCDMA inter-system handover deals with handovers that occurbetween the GSM and the WCDMA RAN. The handovers can take place fromthe GSM BSS to WCDMA RAN and vice versa when the dual mode GSM/WCDMA MS is in a dedicated state.

The dual mode GSM/WCDMA mobiles are divided into two categories: GPRSand non-GPRS capable mobiles. There are both common and category-specificoperator parameters for the adjustment of mobile functionality in the idle state,packet idle mode, dedicated state and packet transfer mode.

In the first Nokia inter-system handover implementation (RAN1.5 & BSS10.5),the handovers are based on the load and coverage situation in the serving cell, seefigure Load and coverage reason handovers. Later in RAN2 and BSS11 releases,there will be traffic and service based handover features implemented in the RANand BSS.

Benefits of the inter-system handover

" When the networks overlap, handovers from GSM BSS to WCDMA RANcan be made in order to reduce traffic load in the GSM.

" Handovers from WCDMA RAN to GSM BSS can be made in order toenable the operator to provide a seamless coverage in areas whereWCDMA RAN is not available. The handover extends the radio networkcoverage.

" Due to the inter-system handover, seamless continuity of speechconnections and certain data services between WCDMA RAN and GSMnetworks are available for all dual mode subscribers. Dual mode mobilessupport both GSM and WCDMA RAN. In addition to this, dual modemobiles may also support GPRS.




Figure 1. Load and coverage reason handovers

1.2 WCDMA�GSM cell re-selection and inter-systemhandover

The handover control of the RAN supports inter-system handovers, both fromWCDMA to GSM and from GSM to WCDMA. Inter-system handover isrequired so that the coverage areas of GSM and WCDMA can complement eachother. When the coverage areas of WCDMA and GSM are overlapping eachother, an inter-system handover can be used to control the load and/or servicesbetween the systems. The inter-system handover is a hard handover, which meansthat an inter-system handover causes a short disconnection of a real-time radioaccess bearer.

GSM highloaded

WCDMA lowloaded

Mobile moving

Load and Coverage Reason HandoverCircuit Switched traffic

Load reasonhandover for speech

and for HSCSD

GSM

GSM

GSM GSM GSM

WCDMA WCDMA

WCDMA GSM

GSM can be used to extendWCDMA coverage area

WCDMA can be usedto relieve GSM overload

Load reasonhandover

Coverage reasonhandover



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The handover control within the Nokia RAN supports also cell re-selection. Bothcircuit-switched (CS) and packet-switched (PS) services can also be maintainedbetween GSM/GPRS and WCDMA networks.

The inter-system handover of packet-switched services between WCDMA andGPRS is based on the cell re-selection procedure. The Handover Control of theRAN supports the network initiated cell re-selection from WCDMA to GPRS inCELL_DCH state of connected mode. In the CELL_PCH and URA_PCH statesof connected mode, the cell re-selection from WCDMA to GPRS is initiated bythe mobile station.

The network initiated cell re-selection (for packet data) from WCDMA to GPRSand inter-system handover (for circuit-switched data) from WCDMA to GSM arenetwork-evaluated handovers (NEHO). The decision algorithm of the inter-system handover and network initiated cell re-selection is located in the RadioNetwork Controller (RNC). The RNC makes the decision on the basis ofperiodical inter-system measurement reports received from the mobile station andrelevant control parameters. The RNC orders the mobile station to start theperiodical reporting of inter-system measurement results only when an inter-system handover or cell re-selection is needed. The measurement objectinformation (cells and frequencies) for the inter-system measurement isdetermined by the RNC.

Unless the mobile station is equipped with dual receivers it can only be tuned toone frequency at a time. Therefore, compressed mode must be used at thephysical layer of the radio interface to allow the MS to make the required inter-system (GSM) measurements while maintaining its existing connection.

Related topics

GSM-WCDMA cell re-selection in idle state

GSM-WCDMA handover process

WCDMA RAN cell measurements for GSM-WCDMA inter-system handover

WCDMA-GSM cell selection and re-selection

WCDMA�GSM handover process

GSM cell measurements for WCDMA-GSM inter-system handover

WCDMA compressed mode

Planning GSM-WCDMA inter-system handover




System impact for GSM-WCDMA inter-system handover

2 System impact for GSM-WCDMA inter-system handover

2.1 Introduction

This chapter lists the system impact for GSM-WCDMA inter-system handover.

2.2 Requirements

2.2.1 Hardware

Table 1. Required additional hardwareor firmware

Networkelement

HW/FW required

BSC No requirements

BTS No requirements

TC No requirements

SGSN No requirements



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2.2.2 Software

Table 2. Network elements requiredsoftware

Networkelement

Software releaserequired

MSC M11

Nokia NetAct OSS3.1 ED2(EnhancementDelivery)

BSC S10.5

SGSN SG2

NetAct Planner Planner V

Nokia 2nd Gen. B13.1

Nokia Talk-family DF6

Nokia PrimeSite DF6

Nokia MetroSite CXM3.0

Nokia InSite I3

Nokia UltraSite CX3.0

RNC RN1.5.1

WBTS WN1.1

2.2.3 Frequency band support for GSM-WCDMA inter-system handover

The following frequency bands support GSM-WCDMA inter-system handover:

" GSM 800

" GSM 900

" GSM 1800

" GSM 1900




2.2.4 Requirements for GSM-WCDMA inter-system handover relatedfeatures

GSM-WCDMA inter-system handover requires dual mode (GSM-WCDMA) ortri-mode (GSM-GPRS-WCDMA) mobile station. GSM-WCDMA inter-systemhandover is an optional BSS feature.

2.3 BSS Performance

2.3.1 OMU signalling

Table 3. ISHO impact to OMU signalling

Network element Impact

BTS No impact.

BSC No impact.

2.3.2 TRX signalling

Table 4. ISHO impact to TRX signalling


BTS No impact.

BSC No impact.

2.3.3 MCMU

Table 5. ISHO impact to MCMU


BTS No impact.



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Table 5. ISHO impact to MCMU (cont.)


BSC No impact.

2.3.4 OMU

Table 6. ISHO impact to OMU


BTS No impact.

BSC No impact.

2.3.5 BCSU

Table 7. ISHO impact to BCSU


BTS No impact.

BSC No impact.

2.3.6 PCU

Table 8. ISHO impact to PCU


BTS No impact.

BSC No impact.




2.3.7 TCSM

Table 9. ISHO impact to TCSM


BTS No impact.

BSC No impact.

2.4 User Interface

2.4.1 ISHO parameters

HOC parameters

ISHO thresholds:

" threshold for multi-RAT MS (QSRC)

" minimum traffic load for a speech call (LTSC)

Reported WCDMA RAN cells:

" number of cells from the access technology FDD (FDMR)

ISHO penalty:

" minimum interval between unsuccessful ISHO attempts(UMIU)

Averaging parameters:

" all adjacent WCDMA RAN cells averaged (UAAC)

" adjacent WCDMA RAN cell averaging window size (UAWS)

" number of WCDMA RAN zero results (UNOZ)

For information on related MML commands, see Handover Control ParameterHandling (command group EH).



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BTS parameters

" GPRS threshold to search WCDMA RAN cells (QSRP)

" GPRS fdd cell reselect offset (GFDD)

" GPRS minimum fdd threshold (GFDM)

" threshold to search WCDMA RAN cells (QSRI)

" fdd cell reselect offset (FDD)

" minimum fdd threshold (FDM)

For information on related MML commands, see Base Transceiver StationHandling in BSC (command group EQ).

2.5 Inter-system handover impact on NSS

2.5.1 Inter-system handover and UMTS changes in MSC

This feature is a basic requirement for the operators who want to ensure asuccessful migration to 3G and want to be able to offer a wide range of highquality services for 2G and/or 3G subscribers. This feature enables a variety ofbusiness strategies for all types of operators, because roaming agreements arepossible between GSM and UMTS operators and the operator can also supportboth GSM and UMTS in his own network.

When this feature is activated, the following types of handovers are supported:

" InterSystem RNC < > BSC R99

" IntraSystem RNC < > RNC

" InterSystem RNC -> BSC R98

" BSC R98/R99 < > BSC R98/R99

The handovers mentioned above are possible in Inter MSC (Inter PLMN andIntra PLMN) and Intra MSC (Inter PLMN and Intra PLMN).

Handover BSC R98 -> UMTS is not possible.




Changed functionality in the MSC

To be able to connect UMTS radio network to the MSC and to be able to makeIntra-UMTS/Inter-system handovers, the following requirements were set to theMSC:

" Security Requirements due to Inter-system handover

" Key handling in basic and subsequent Inter-MSC handovers

" BSSMAP R99 implementation in A interface

" RANAP implementation in MAP E interface

" MAP phase 3 implementation in E interface

" Requirements coming from the support for Multiple RNCs per Multimediagateway

" Signalling requirements for Gs interface

" Charging and Statistics support

" Access and handover control

For detailed descriptions of the above mentioned requirements, see FEATURE1260 Inter-system handover and UMTS changes in MSCin MSC documentation.

2.6 Impact on Interfaces

2.6.1 Impact on A interface

Table 10. This table indicates the impacts on A interface


BSC New messages:

" Handover to UTRAN commandmessage (MSC -> BSS)

Messages that have changes ininformation elements:

" Handover Request message (MSC ->BSS)

" Handover Required message (BSS ->MSC)

" Handover Command (MSC -> BSS)



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Table 10. This table indicates the impacts on A interface (cont.)


MSC A interface support for 3GPP 24.008Mobile Radio Interface Layer 3specification (CC/MM), release 1999.

2.6.2 Impact on Abis interface

Table 11. This table indicates the impacts on Abis interface.


BTS No impact.

BSC New messages:

" UTRAN Classmark Change message(UE -> BSS)

" System Information Type 2quatermessage (BSS -> UE)

" Packet System Information Type3quater message (BSS -> UE)

" Measurement Information message(BSS -> UE)

" Inter System to UTRAN HandoverCommand message (BSS -> UE)

Messages that have changes ininformation elements:

" Packet System Information Type 2message (BSS -> UE)

" System Information Type 3 message(BSS -> UE)

" Channel Activation message (BSC ->BTS)

" SACCH Info Modify message (BSC ->BTS)

" Handover Failure message (UE ->BSS)




2.6.3 Impact on Gb interface


BTS No impact.

BSC No impact.

SGSN

2.6.4 Impact on Iu interface


BTS No impact.

BSC No impact.

MSC Iu interface support for 3GPP 25.413UTRAN Iu Interface RANAP Signalling,release 1999.

2.7 Feature Interoperability

2.7.1 GSM-WCDMA inter-system handover interaction with other featuresand functionalities

BSC Initiated Traffic Reason Handover (TRHO)

When deciding on an initiation of a BSC Initiated TRHO, both the completedBSC Initiated TRHOs and the load decrease of the serving cell due to an inter-system handover (ISHO) are taken into consideration. Correspondingly, whendeciding on an initiation of an ISHO, both the completed ISHOs and the loaddecrease of the serving cell due to a BSC Initiated TRHO are taken in toconsideration.

Both of the above conditions are valid, when a new BSC Initiated TRHO, orISHO are evaluated after either a previous TRHO or ISHO, but before a new loadinformation report has been received.

For more information, see RF Power Control and Handover Algorithm, sectionBSC Initiated Traffic Reason Handover in BSC documentation.



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GPRS

The GPRS feature affects the visibility of new ISHO parameters which aredefined only for GPRS capable mobiles.

GPRS related parameters are: GPRS threshold to search WCDMA RANcells (QSRP) , GPRS fdd cell reselect offset (GFDD), GPRSminimum fdd threshold (GFDM). They are visible only if the GPRS featureis activated. For more information, see BSS Radio Network ParameterDictionary, section BTS in BSC documentaion.

For more information on the GPRS feature, see GPRS in BSC in BSCdocumentation.

Support of PCCCH/PBCCH

Support of PCCCH /PBCCH feature is needed for sending new and modified PSImessages in the PBCCH.

For more information on the feature, see for example, GSM/EDGE FeatureDescription, section Support of PCCCH/PBCCH in BSC documentation.

Common BCCH Control for GSM 800/1900 & GSM 900/1800

Common BCCH Control for GSM 800/1900 & GSM 900/1800 feature decreasesthe maximum number of neighbour GSM cells and BA frequencies.

For more information on the feature, see Overview of GSM/EDGE CommonBCCH.

2.7.2 Capacity and restrictions of GSM-WCDMA inter-system handover

The Release '99 level 3GPP standard allows a GSM cell to send the informationof a maximum of 96 neighbour cells (includes cells of GSM, WCDMA RANusing FDD and WCDMA RAN using TDD) to a mobile.

According to the 3GPP standard, a dual mode GSM/WCDMA mobile is able tomonitor a maximum of 32 FDD type WCDMA RAN cells on up to threefrequencies.

Note

The dual mode GSM/WCDMA mobile's behaviour is not specified if the numberof the sent 3G frequencies or other cell information elements exceeds the mobile'smonitoring capabilities as defined in the 3GPP standard.




Radio network limitations

The maximum number of neighbour WCDMA RAN cells per serving cell islimited to 32.

If the GSM-WCDMA Inter-System Handover feature is in use, the maximumnumber of neighbour GSM cells (ADJC) per a serving cell (or segment) is:

" 31 without the Common BCCH feature

" 30 if there is also at least one of the Common BCCH features activated

The UARFCN (UTRAN absolute radio frequency channel number) + scramblingcode combinations of neighbour WCDMA RAN cells, which are defined for thesame segment, must be unambiguous. In other words, a segment cannot have twoor more neighbour WCDMA RAN cells with the same UARFCN and scramblingcode.

The identifications of neighbour WCDMA RAN cells which are defined for thesame serving GSM cell, must be unambiguous. In other words, a serving GSMcell cannot have two or more neighbour WCDMA RAN cells which use the sameMCC +MNC +RNC id+CI combination and/or WCDMA RAN cell index value.

2.8 Related Topics




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3 Inter-system handover from GSM toWCDMA

3.1 GSM-WCDMA cell re-selection in idle state

The main principle in the implementation of WCDMA RAN selection handling isto enable an operator to define the WCDMA RAN measurement offsets and cellre-selection thresholds by the RNC. They are sent to the mobile in the SystemInformation messages or/and in the Packet System Information messages.

A dual mode GSM/WCDMA mobile is able to perform a cell re-selection fromthe GSM network to the WCDMA RAN network in the idle state if the mobile isinformed about the WCDMA RAN cells. The cell re-selection is based onparameters sent by the BSC to the mobile.

The following must be taken into account when planning re-selection from GSMto WCDMA RAN in idle state:

" AWBTS must be defined as a neighbour WCDMA RAN cell for the BTSin the BSC. The following BTS parameters must have proper values beforemobile-originated cell re-selection to WCDMA RAN is possible for a non-GPRS capable mobile:

- threshold to search WCDMA RAN cells (QSRI)

- fdd cell reselect offset (FDD)

- minimum fdd threshold (FDM)

" The BTS parameter GPRS threshold to search WCDMA RAN cells(QSRP) must have a proper value before mobile-originated cell re-selection to WCDMA RAN is possible for a GPRS capable mobile whichuses parameters received from the BCCH.

" If the cell re-selection parameters are sent on the PBCCH for GPRScapable mobiles, the following BTS parameters must have proper valuesbefore mobile-originated cell re-selection to WCDMA RAN is possible fora GPRS capable mobile:



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Inter-system handover from GSM to WCDMA

- GPRS fdd cell reselect offset (GFDD)

- GPRS minimum fdd threshold (GFDM)

The dual mode GSM/WCDMA mobiles start and stop measuring the neighbourWCDMA RAN cells according to the parameter:


The tri-mode GSM/GPRS/WCDMA mobiles start and stop measuring theneighbour WCDMA RAN cells according to the parameter:


The WCDMA RAN cell re-selection parameters are sent in the messages:

1. System Information Type 2quater

To non-GPRS capable mobiles and GPRS capable mobiles, if PBCCH(Packet BCCH) is not allocated.

The content of this message is used only by non-GPRS capable mobiles, ifPBCCH is allocated.

2. Packet System Information Type 3quater

To GPRS capable mobiles, if PBCCH is allocated.

You can prevent the neighbour WCDMA RAN cell measurements, and therebyalso the cell re-selections from a GSM cell to WCDMA RAN by adjusting thevalues of the parameters which control the WCDMA RAN cell measurement inthe idle state. This is done by setting the value 15 for the following parameters inthe GSM cell:

" threshold to search WCDMA RAN cells (QSRI) and/or


If you want to get measurements about the neighbour WCDMA RAN cellscontinuously and try to prevent the WCDMA RAN cell re-selections from a GSMcell, you can do this by:

1. setting the value 7 for the following parameters in the GSM cell:








2. and by setting the value 15 for the following parameters:


" GPRS fdd cell reselect offset (GFDD)

3.1.1 Cell re-selection with non-GPRS capable mobiles

The System Information messages enabling the cell re-selection with non-GPRScapable mobiles are sent by the network to the mobiles. The inter-system cell re-selection requires the sending of a new System Information message: SI 2quater.The cell re-selection parameters that are sent on SI 2quater messages for non-GPRS capable mobiles are:




The set below is repeated for every neighbour WCDMA RAN cell:

" WCDMA downlink carrier frequency (FREQ)

" downlink transmission diversity (DIV)

" scrambling code (SCC)

Parameters from the SI 2quater messages allow the mobile to build lists which areused for measurement reporting.

Algorithm for cell re-selection

You can control the measurements for re-selection by the parameter thresholdto search WCDMA RAN cells. The parameter defines a threshold and alsoindicates whether these measurements are performed when RLA_C (a runningaverage of received signal level) of the serving GSM cell is below or above thethreshold.

If the broadcast neighbour cell list from the BSC to the mobile containsinformation on the WCDMA RAN cells, the mobile updates the value RLA_Cfor the serving cell and each of the minimum of six strongest non-serving GSMcells at least every five seconds.

The mobile reselects a suitable WCDMA RAN cell, if its measured RSCP valueexceeds the value of RLA_C for the serving cell and all of the suitable non-serving GSM cells. The mobile also selects all of the suitable non-serving GSMcells by the value fdd cell reselect offset for a period of five seconds.



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For FDD the mobile selects the WCDMA cells, whose measured Ec/No value isequal or greater than the value minimum fdd threshold. In case a cell re-selectionoccurs within the previous 15 seconds, fdd cell reselect offset isincreased by 5 dB, where:

" Ec/No and RSCP are the measured quantities

" minimum fdd threshold and fdd cell reselect offset arebroadcast on BCCH of the serving cell

If more than one WCDMA RAN cells fulfil the above criteria, the mobile selectsthe WCDMA RAN cell with the greatest RSCP value.

Note

The parameters that are required to determine whether the WCDMA cell issuitable are broadcast on BCCH of the WCDMA RAN cell. A mobile may startre-selection towards the WCDMA RAN cell before decoding the BCCH of theWCDMA RAN cell. If the WCDMA RAN cell is not suitable, this leads to ashort interruption of service.

After the mobile has re-selected a GSM cell from an WCDMA RAN cell there isa five-second pause to the cell re-selection to WCDMA RAN.




Figure 2. Cell re-selection process (Non-GPRS capable phone)

3.1.2 Cell re-selection with GPRS capable mobiles

If PBCCH is allocated, the idle state parameters are sent to the GPRS capablemobile in the Packet System Information (PSI) messages on the PBCCH.

The roles of the PSI messages are:

" PSI Type 1 informs about the content changes of PSI 3quater message onthe GSM cell.

" PSI Type 2 informs the sending status of PSI 3quater message on the GSMcell.

" PSI Type 3quater contains information about neighbour WCDMA RANcells of the GSM cell.

The cell re-selection parameters which are sent in PSI 3quater messages on thePBCCH for GPRS capable mobiles are:

Check levels fromserving GSM

Compareof all GSM cellsto WCDMAneighbour

Check qualityof

WCDMA cells, nopriorities between

WCDMAneighbour

RLA_C means runningsignal level which couldcompared to received

code power

MS will re-select WCDMA cell in casequality is

CPICH Ec/No > FDD_QmiThis shall be done within 30

GSM MS starts WCDMAmeasurements

in running average signal (RLA_C)level is below or certain

RLA_C # Qsearc_l(Non GPRS)

GSM MS can select WCDMA cell ifthe level the serving GSM and

non-serving GSM cells has exceededcertain offset for a period of

CPICH RSCP > RLA_C + FDD_Qoffset(Non GPRS)



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" GPRS fdd cell reselect offset (GFDD).




" scrambling code (SCC).

If PBCCH is not allocated on the serving GSM cell, the GPRS capable mobilesuse the idle state parameters that are sent in System Information messages (SI) onthe BCCH.

The cell re-selection parameters which are sent in SI 2quater messages on theBCCH for GPRS capable mobiles are:



" fdd cell reselect offset (FDD).




" scrambling code (SCC).

The cells with other radio access technologies may be included in the GPRS 3Gcell re-selection list. If the PBCCH is available, the GPRS 3G cell re-selection listis taken from the 3G neighbour cell list which is broadcast on PBCCH.Otherwise, the 3G cell re-selection list which is broadcast on BCCH is used.

Mobile controlled inter-system cell re-selection for PS connection

The GSM network does not send any of the PSI 13, PACKET MEASUREMENTORDER or PACKET CELL CHANGE ORDER messages on PCCCH andPACCH at the first phase implementation of GSM-WCDMA inter-systemhandover. Therefore a dual mode GSM/WCDMA mobile is also able to initiateand control inter-system cell re-selections from GPRS to WCDMA RAN for a PS




connection according to the WCDMA RAN related idle state parameters receivedfrom BCCH/CCCH or PBCCH/PCCCH when the mobile is in the packet transfermode. The mobile uses the same parameters and algorithm for inter-system cellre-selections than in the packet idle mode.

Algorithm for cell re-selection

The network controls the measurements for the re-selection of the cells by theparameter GPRS threshold to search WCDMA RAN cells which isbroadcast on the BCCH or/and the PBCCH. GPRS threshold to searchWCDMA RAN cells defines a threshold and indicates whether thesemeasurements are performed when RLA_P (the received level average) of theserving cell is below or above the threshold. If the re-selection list containsWCDMA RAN frequencies, the mobile updates the value RLA_P for the servingcell and each of the at least six strongest non-serving GSM cells at least everyfive seconds.

When a GPRS capable mobile uses the parameters that are sent on the BCCH, themobile selects a WCDMA cell, if:

" its measured RSCP (received signal code power) value exceeds the valueof RLA_P for the serving GSM cell and all of the suitable non-servingGSM cells by the value fdd cell reselect offset for a period offive seconds.

" The WCDMA RAN cell's measured Ec/Io value is equal or greater than thevalue minimum fdd threshold.

If more than one WCDMA RAN cell fulfils the above criteria, the mobile selectsthe WCDMA RAN cell with the greatest RSCP value.

When a GPRS capable mobile uses the parameters that are sent on PBCCH, themobile selects a WCDMA RAN cell, if:

" its measured RSCP value exceeds the value of RLA_P for the servingGSM cell and all of the suitable non-serving GSM cells by the value GPRSfdd cell reselect offset for a period of five seconds.

" The WCDMA RAN cell's measured Ec/Io value is equal or greater than thevalue GPRS minimum fdd threshold.

If more than one WCDMA RAN cell fulfils the above criteria, the mobile selectsthe WCDMA RAN cell with the greatest RSCP value.

Related topics




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3.2 GSM-WCDMA handover process

The Nokia GSM-WCDMA inter-system handover includes handovers forcoverage and load reasons. The measurement parameters of the WCDMA RANneighbour cells are sent to the dual mode GSM/WCDMA mobiles in theMeasurement Information messages.

The BSC performs the evaluation of a handover from GSM to WCDMA RANafter the evaluation of a downlink level handover.

The following prerequisites must be fulfilled in order to enable an inter-systemhandover from GSM to WCDMA RAN:

" The target cell candidates (WBTSs) are defined as neighbour WCDMARAN cells for the serving GSM cell in the BSC.

" The mobiles (which are in the dedicated state) are allowed to measure theneighbour WCDMA RAN cells of the serving GSM cell.

Define the measuring threshold by the parameter threshold formulti-RAT MS (QSRC).

" The mobile has sent the neighbour WCDMA RAN cell measurements tothe BSC.

" Early classmark sending is allowed for mobiles in the serving GSM cell.

You can control the early classmark sending by the parameter earlysending indication (ESI).

For more information, see Base Transceiver Station Handling in BSC(command group EQ) and BSS Radio Network Parameter Dictionary inBSC documentation.

" The mobile has sent the UTRAN CLASSMARK CHANGE message to theBSC.

A dual mode GSM/WCDMA mobile sends a UTRAN CLASSMARKCHANGE message to the BSC if the early classmark sending is allowed inthe serving GSM cell. The content of the message is required by an RNCwhich controls the target WCDMA RAN cell of the inter-system handoverattempt.

" The connection-specific penalty timer for inter-system handover attemptshas been expired.

The BSC initiates an inter-system handover attempt to the WCDMA RAN if:




" A neighbour WCDMA RAN cell is available (coverage).

The cell-specific penalty timer does not exist in the BSC for the WCDMARAN cell.

Ec/No measured by the mobile has to exceed the handover thresholdminimum CPICH Ec/Io level (MET).

" Traffic load of the serving GSM cell exceeds the threshold (load).

The load threshold are defined by the following parameter:

- minimum traffic load for a speech call (LTSC)

The handover algorithm uses one of these load thresholds according to theconnection type.

The procedure of the traffic load checking is similar compared to the BSCinitiated Traffic Reason Handover. The BSC initiates only as many inter-system handovers as the number of ongoing calls in the serving GSM cellis over the traffic load threshold. This means that the serving GSM cell isnot emptied into the WCDMA RAN.

Figure 3. GSM-WCDMA inter-system handover process

Handover Triggering Thresholds set in BSC

Inter-RAT measurements start ifthe RXLEV of the serving cell is above orbelow the given threshold Qsearch_C

Handover Decision is done ifLoad of the serving cell > Load_treshold

and CPICH Ec/No Threshold

MS selects the target UTRAN cell basedon the measurement result

Handover command is sent to MSC

In S10.5 the MS measuresthe UTRAN cells continuously.If they are defined asneighbours, measurementsare done during idle periods.



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Connection-specific penalty after inter-system handover to GSM

An inter-system handover from the WCDMA RAN to the GSM indicates highload in the WCDMA RAN. If a handover from the WCDMA RAN to the GSM isdetected, the handover algorithm is not allowed to initiate a handover back to theWCDMA RAN for the same connection during the 30-second penalty time.

Inter-system handover for speech connection

The BSC initiates an inter-system handover attempt for a speech connection if theWCDMA RAN cell signal quality and serving GSM cell traffic load thresholdsare exceeded.

Example 1.

The parameter minimum traffic load for a speech call (parameterLOAD_THRESHOLD_FOR_SC_IS_HO) has the value 60 (60%) and theparameter minimum CPICH Ec/Io level (parameter QSEARCH_C) has thevalue 18 (-15 dB).

In addition to above, the BSC has received and averaged measurement results forthe neighbour WCDMA RAN cell and calculated the traffic load of the servingGSM cell:

1. The traffic load of the serving GSM cell is 45% and the averaged Ec/No ofthe WCDMA RAN cell has the value 18 (the averaged Ec/Io level issmaller than -15.5 dB).

In this case the inter-system handover attempt is not possible due to toolow traffic load and low signal quality.

2. The traffic load of the serving GSM cell is 45% and the averaged Ec/No ofthe WCDMA RAN cell has the value 19 (the averaged Ec/Io is equal orgreater than -15 dB).

In this case the inter-system handover attempt is not possible due to toolow traffic load.

3. The traffic load of the serving GSM cell is 65% and the averaged Ec/No ofthe WCDMA RAN cell has the value 19 (the averaged Ec/Io is equal orgreater than -15 dB).

In this case, the inter-system handover attempt is possible.




Unsuccessful inter-system handover attempt

If the BSC has started the inter-system handover attempt towards a WCDMARAN cell and it fails, the BSC sets penalty timer for the target WCDMA RANcell. The BSC gets the duration of the WCDMA RAN cell penalty timer from thehandover parameter minimum interval between unsuccessful ISHOattempts (MIN_INTERVAL_BETWEEN_UNSUCC_ISHO_ATTEMPT).

The BSC controls the connection related inter-system handovers and inter-systemhandover attempts by using timers the durations of which are from the followinghandover parameters:

" min int between HO req

" min int between unsucc HO attempt.

Related topics


3.3 WCDMA RAN cell measurements for GSM-WCDMAinter-system handover

WCDMA RAN cell measurement and reporting

The dual-mode GSM/WCDMA mobile is able to measure the signal levels of theneighbour WCDMA RAN cells when it is in idle state and camped on a GSMcell. The information of the cells is sent to the mobile in System Information type2 quater (SI 2quater) messages or/and in Packet System information type 3 quater(PSI 3quater) messages.

The SI 2quater messages are sent to the mobile only if the serving GSM cell hasWCDMA RAN neighbour cells. The message is sent on the BCCH and it maycontain more than one instance.

The PSI 3quater messages are sent to the mobile only if the serving GSM cell hasWCDMA RAN neighbour cells. The message is sent on the PBCCH and it maycontain more than one instance.

The non-GPRS capable dual mode GSM/WCDMA mobiles are allowed and alsoforced to measure the WCDMA RAN neighbours in idle state, if the RXLEV ofthe serving GSM cell is below or above the threshold threshold to searchWCDMA RAN cells.



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The GPRS capable dual mode GSM/WCDMA mobiles are allowed and alsoforced to measure the WCDMA RAN neighbours in idle state if the RXLEV ofthe serving GSM cell is below or above the threshold GPRS threshold tosearch WCDMA RAN cells.

Measurement parameters of the WCDMA RAN neighbours are sent to a dualmode GSM/WCDMA mobile in Measurement Information (MI) message. Themobile is allowed and also forced to measure and report the WCDMA RANneighbours in dedicated state if the RXLEVof the serving GSM cell is below orabove the threshold threshold for multi-RAT MS. This means that in theimplementation of the first phase (S10.5) the mobile measures the neighbourWCDMA cells even though the traffic load of the serving cell is far below theinter-system handover triggering threshold.

The network sends the MI message to the mobile on the SACCH. If not allinformation fits into one message, the remaining information is sent in otherinstances of this message. The neighbour cell list is based on the SI 2quater orPSI 3quater message and built by the mobile. It is used for reporting when themobile enters the dedicated state, until the mobile has received all instances ofMeasurement Information messages that contain "3G Neighbour CellDescription" information element.

Information about WCDMA RAN cells is included in SI 2quater, PSI 3quater andMI messages only if the cells are defined as neighbour WCDMA RAN cells forthe serving GSM cell. The dual mode GSM/WCDMA mobiles are able to findand identify a WCDMA RAN cell by the following information:


" scrambling code (SCC)


You can define the maximum number of the neighbour WCDMA RAN cells(parameter FDD_MULTIRAT_REP) that are included by the mobile in the list ofthe strongest cells in a measurement report which is sent to the radio network.The name of the parameter is number of cells from the accesstechnology FDD. The mobiles are ordered to report to the BSC by using Ec/Ioas the measurement quantity.

The number of the WCDMA RAN cells from which the mobile is able to performneighbour cell measurements depends on the number of frequencies used.




According to the 3GPP standard the allowed reporting time is increased by fiveseconds for each additional WCDMA RAN frequency in the neighbour cell list.However, multiple WCDMA RAN cells on the same frequency in the neighbourcell list do not increase the allowed reporting time. This means that if there areWCDMA RAN neighbours in more than one WCDMA RAN frequency, there aregoing to be delays in the neighbour cell reporting.

Bookkeeping and averaging of the CPICH Ec/No of the neighbour WCDMARAN cell

The BSC averages the signal level of the neighbour WCDMA RAN cells(ECNO_NCELL(n)) only at the time when the averaged results are needed for thedecision procedure. The averaging procedure is able to take into account themaximum of 32 most recent measurement samples per neighbour WCDMA RANcell and maintain the last 32 measurement samples of up to 32 neighbourWCDMA RAN cells per a serving GSM cell.

The measured value replaces RXLEV in the measurement reports.

Averaging procedure of the CPICH Ec/No of the neighbour WCDMA RAN cell

The averaging procedure is controlled by the following parameters:

1. adjacent WCDMA RAN cell averaging window size(ADJACENT_WCDMA_RAN_CELL_AVERAGING_WINDOW_SIZE)determines the averaging window size which is used for calculatingaveraged values from downlink (neighbour WCDMA RAN cell) signallevel measurements for handover threshold comparison and decision. Therange of the averaging window size is from 1 to 32 SACCH multiframeperiods, where the value 1 means that there is basically no averaging at all.

2. number of WCDMA RAN zero results(NUMBER_OF_WCDMA_RAN_ZERO_RESULTS) indicates themaximum number of zero results that can be omitted when themeasurement results of the neighbour WCDMA RAN cells are averaged.The range of the parameter is from 0 to 32 zero results.

3. all adjacent WCDMA RAN cells averaged(ALL_ADJACENT_WCDMA_RAN_CELLS_AVERAGED) indicateswhether the measurement results are averaged for every neighbourWCDMA RAN cell (value is 'yes') or only for the maximum of three cellswhich are the best according to the last measurement sample (value is 'no').

The averaging parameters are controlled on a cell-by-cell basis. The BSC mayaverage the signal level of the neighbour WCDMA RAN cells already after thefirst received measurement sample.



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Related topics





4 Inter-system handover from WCDMA toGSM

4.1 WCDMA-GSM cell selection and re-selection

After a UE has been switched on and a PLMN has been selected, the cellselection process takes place. This process allows the UE to select a suitable cellwhere it can camp in order to access available services. In 'Stored information cellselection', the UE uses stored information. In 'Initial cell selection', the UE doesnot use stored information. A suitable cell is selected when the cell selectioncriterion S is fulfilled:

" Srxlev > 0 AND Squal > 0

where:

" Squal = Qqualmeas � Qqualmin

" Srxlev = Qrxlevmeas � Qrxlevmin - Pcompensation

Squal Cell Selection quality value (dB).Applicable only for FDD cells.

Srxlev Cell Selection RX level value (dB)

Qqualmeas Measured cell quality value. The quality ofthe received signal expressed in CPICHEc/N0 (dB) for FDD cells. Applicable onlyfor FDD cells.

Qrxlevmeas Measured cell RX level value. This is areceived signal, CPICH RSCP for FDDcells (dBm) and P-CCPCH RSCP for TDDcells (dBm).

Qqualmin Minimum required quality level in the cell(dB). Applicable only for FDD cells.



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Inter-system handover from WCDMA to GSM

Qrxlevmin Minimum required RX level in the cell(dBm)

Pcompensation max(UE_TXPWR_MAX_RACH � P_MAX,0) (dB)

UE_TXPWR_MAX_RACH Maximum TX power level a UE may usewhen accessing the cell on RACH (read insystem information) (dBm)

P_MAX Maximum RF output power of the UE(dBm)

Cell re-selection

The following parameter are compared with Squal (CPICH Ec/No) for FDD cellsand Srxlev (P-CCPCH RSCP) for TDD cells in S-Criteria:

" Sintrasearch

" Sintersearch

" SsearchRAT

Then the cells are ranked according to the R-criteria. The UE selects the bestranked cell (the cell with the highest R value). The cell ranking criterion R isdefined by:

" Rs = Qmeas,s + Qhysts

" Rn = Qmeas,n - Qoffsets,n

where:

Qmeas is the quality value of the received signal based on CPICH Ec/No orCPICH RSCP for FDD cells, P-CCPCH RSCP for TDD cells and RxLev forGSM cells.

An example of the measurement rules of cell re-selection for FDD cells (Squal isused) is illustrated as follows:




Figure 4. Measurement rules of cell re-selection when HCS is not used

Region Condition Neighbour cells to bemeasured

1 Squal > Sintrasearch None

2 Sintersearch < Squal d Sintrasearch Intra-frequency cells

3 SsearchRAT < Squal d Sintersearch Intra- and inter-frequencycells

4 Squal d SsearchRAT Intra-, inter-frequency andinter-system cells

Related topics


4.2 WCDMA-GSM handover process

When a radio access bearer is handed over from one system to another, both thecore network and the target RNC (or BSC) are responsible for adapting the QoS(Quality of Service) parameters of the radio access bearer according to the target(GSM or WCDMA) system.

Sintrasearch Sintersearch SsearchRAT

4 3 2 1

WCDMACELL



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In the case of a network-initiated cell re-selection from WCDMA to GSM/GPRS,the RNC sends a cell change command to the MS which then is responsible foractually transferring the existing packet-switched connection to the target GSM/GPRS network.

Figure 5. WCDMA-GSM Handover Process

There is an option to restrict inter-system handovers for voice and data servicesby the use of the RNC parameters found in table below. However, for the launchnetwork there is no foreseen reason to restrict any particular service.

Parameter Setting Condition

GsmHandoverAMR 1 Yes

GsmHandoverCS 1 Yes

GsmHandoverNrtPS 1 Yes

Handover Triggering Thresholds set in RNC

Event Triggered Coverage/Capacitybased HO fulfilled in RNC

RNC Commands selected UE(s) to startIS measurements periodically

Measurements are done inCompressed Mode (CM)

RSSI measurements andverification for GSM cells

Coverage/capacity HO reasons

UE reports best GSM cells havingstrongest RSSI results back to RNC

RNC makes HO decision andcommands EU to target cell

Max 32 neighbours could bemeasured

Reporting cells are active setcells (max 3) + 6 GSMneighbours

Only one decision method forGSM HO





GsmHandoverRtPS 1 Yes

The alternative values of the parameters are as follows:

No Inter-system handover/Cell change to GSM is not allowed forthe particular service. The inter-system handover is alsoprohibited if the service is part of a multiservice.

Yes Inter-system handover/Cell change to GSM is allowed for aparticular service. In case of multiservice, an inter-systemhandover must be allowed for all CS and PS services whichparticipate in the multiservice before the inter-systemhandover is possible.

Priority Inter-system handover/Cell change to GSM is allowed for thatparticular service. The inter-system handover is also allowedif the service is part of a multiservice.

WCDMA-GSM inter-system handover triggers

For inter-system handovers, the RNC commands the UE to start compressedmode and make the measurements of the GSM network and report the resultsback to the RNC. Based on these measurement reports from the UE, the RNCmakes a handover decision and initiates resource reservation from the GSM BSC.

The main handover triggers for the uplink and downlink are:

" Inter-system handover (or cell re-selection) to GSM due to DownlinkDPCH power

" Inter-system handover (or cell re-selection) to GSM due to Uplink DCHquality

" Inter-system handover (or cell re-selection) to GSM due to UE Tx power

" Inter-system handover (or cell re-selection) to GSM due to CPICH RSCP

" Inter-system handover (or cell re-selection) to GSM due to CPICH Ec/No

For an overview, see Overview of GSM-WCDMA inter-system handover.



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4.2.1 Downlink DPCH power

The measurement reports from the base station are used to trigger inter-systemmeasurements when the downlink transmission power of the radio linkapproaches its maximum allowed power level.

The parameter GSMcauseTxPwrDL indicates whether an inter-system handovercaused by Downlink DPCH power is enabled.

Parameter Setting

GSMcauseTxPwrDL 0 (Not Used)

HhoMaxAllowedBitrateDL 64 kbit/s

In addition, the maximum allocated user bitrate on the downlink DPCH must belower than or equal to the bitrate threshold which is controlled with RNPparameter HHoMaxAllowedBitrateDL, before the RNC may start the inter-system measurement due to Downlink DPCH power.

When the inter-system handover is enabled, the RNC starts the inter-systemmeasurement procedure if the downlink transmission power of a single radio linkreaches a Measurement Threshold. The threshold is calculated in the followingway:

" Measurement Threshold >= CPICH_POWER +MAX_DL_DPCH_TXPWR + DL_DPCH_TXPWR_THRESHOLD

Where:

" CPICH_POWER is the downlink transmission power of the PrimaryCPICH of an active set cell.

" MAX_DL_DPCH_TXPWR indicates the maximum transmission powerlevel a base station can use on the DPCH, expressed as a relative value tothe CPICH.

DL_DPCH_TXPWR THRESHOLD (dB) is controlled with the following inter-system measurement control parameters, depending on the service type:

Parameter Setting

DL DPCH TxPwrThreshold RT PS -3 dB

DL DPCH TxPwrThreshold NRT PS -1 dB




Parameter Setting

DL DPCH TxPwrThreshold CS -3 dB

DL DPCH TxPwrThreshold AMR -1 dB

In case of multiservice, the RNC selects the greatest threshold value for thecalculation.

4.2.2 Uplink DCH quality

A handover to GSM can be triggered by bad uplink DCH quality. The handoveris enabled when the value of the parameter GSMcauseUplinkQuality is 'Inuse'. As with previous trigger mechanism the maximum allocated user bitrate onthe uplink DPCH must be lower than or equal to the bitrate threshold which iscontrolled with the parameter HhoMaxAllowedBitrateUL.

Parameter Setting

GSMcauseUplinkQuality 0 ( Not Used)

HhoMaxAllowedBitrateUL 32 kbit/s

The UL outer loop PC can be used to trigger inter-system (GSM) measurements,if the uplink quality stays constantly worse than a BER/BLER target and theuplink SIR target has reached the maximum value (the UE has reached either itsmaximum Tx power capability or the maximum Tx power level the UE can useon the DPCH).

The quality deterioration report from the UL OLPC can be enabled or disabledusing the parameter EnableULQualDetRep. If the uplink SIR target hasreached its maximum, and the uplink SIR Target modification commandsreceived by the outer loop PC control during ULQualDetRepThresholdseconds are all greater than zero, then the uplink outer loop PC controller sends aquality deterioration report.

Parameter Setting

EnableULQualDetRep 0 (no)

ULQualDetRepThreshold 5 s



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The UL outer loop PC repeats the quality deterioration reports until the uplinkSIR target decreases below the maximum value.

4.2.3 UE Tx power

The UE Tx power measurement report can be used to trigger inter-systemhandover measurements when the transmission power of the UE approacheseither its maximum RF output power capability or the maximum Tx power levelthe UE can use on the DPCH.

The parameter GSMcauseTxPwrUL controls whether an inter-system handoverto GSM caused by UE Tx power is enabled. In addition, the maximum allocateduser bitrate on the uplink DPCH must be lower than or equal to the bitratethreshold which is controlled with RNP parameterHHoMaxAllowedBitrateUL, before the RNC starts the inter-system (GSM)measurement due to UE Tx power.

Parameter Setting

GSMcauseTxPwrUL 0 (Not used)

HhoMaxAllowedBitrateUL 32 kbit/s

The measurement reporting for UE Tx power are based on the reporting events:

" 6A � The transmission power of the UE becomes greater than an absolutethreshold

" 6D � The UE transmission power reaches its maximum value.

Reporting event 6A: The UE Tx power measurement is used to trigger off inter-frequency or inter-system (GSM) measurements when the uplink transmissionpower of the mobile station approaches its maximum power capability. Thecontrol parameters used by the event 6A are:

Parameter Setting

GsmUETxPwrFilterCoef 8

GsmUETxPwrThrAMR -1 dB

GsmUETxPwrThrNrtPS -1 dB

GsmUETxPwrThrRtPS -3 dB




Parameter Setting

GsmUETxPwrThrCS -3 dB

GsmUETxPwrTimeHyst 1280 ms

The UE Tx power threshold defines the absolute threshold which is used by theUE to trigger the reporting event 6A. The threshold is calculated in the followingway:

" UE Tx power threshold = min( UE_TXPWR_MAX_DPCH, P_MAX) +UE_TXPWR_THRESHOLD

Where UE_TXPWR_MAX_DPCH indicates the maximum Tx power level(dBm) a UE can use on the DPCH. P_MAX indicates the maximum RF outputpower capability of the UE (dBm). UE_TXPWR_THRESHOLD (dB) iscontrolled with the threshold parameters found in the table above.

If the UE Tx power becomes greater than the reporting threshold (6A) or reachesits maximum value (6D), the UE sends the measurement report to the RNC.

Note

The RNC does not break off ongoing inter-system (GSM) measurement even ifthe UE Tx power decreases again below the reporting threshold and the mobilestation sends the corresponding measurement report (event 6B) to the RNC.

4.2.4 Low measured absolute CPICH RSCP

The parameter GSMcauseCPICHrscp indicates whether an inter-systemhandover to GSM caused by low measured absolute CPICH RSCP of the servingcell (or cells participating in soft handover) is enabled.

Parameter Setting

GSMcauseCPICHrscp 0 (Not used)

When the inter-system handover is enabled, the RNC sets up an intra-frequencymeasurements in order to monitor the absolute CPICHRSCP value.



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If the measured CPICH RSCP value of all active set cell becomes worse than theabsolute threshold/parameter HHoRscpThreshold, the UE sends the CPICHRSCP measurement report after the HHoRscpTimeHysteresis time period.

Parameter Setting

HHoRSCPThreshold -105 dBm

HhoRscpTimeHysteresis 640 ms

HhoRscpfilterCoefficient 0

HhoRscpCancel -100 dBm

HhoRscpCancelTime 1280 ms

HhoRscpCancel determines the absolute threshold which is used by the UE totrigger the reporting event 1E (a primary CPICH becomes better than an absolutethresold). HhoRscpCancelTime determines the period of time between thedetection of the event 1E and sending of the mesurement report.

Note

The RNC does not break off ongoing inter-system (GSM) measurement even ifthe measured CPICH RSCP of one or more active set cells increases again abovethe reporting threshold HHoRscpCancel and the UE sends the correspondingevent 1E triggered intra-frequency measurement report to the RNC.

4.2.5 Low measured absolute CPICH Ec/No

The parameter GSMcauseCPICHEcNo indicates whether an inter-systemhandover to GSM caused by low measured absolute CPICH Ec/No of the servingcell (or cells participating in soft handover) is enabled.

Parameter Setting

GSMcauseCPICHEcNo 0 (Not used)

When the inter-system handover is enabled, the RNC sets up the intra-frequencymeasurement reporting events 1E and 1F in order to monitor the absolute CPICHEc/No value.




If the measured CPICH Ec/No value of an active set cell becomes worse than theabsolute threshold/parameter HHoEcNoThreshold, the UE sends the event 1Ftriggered intra-frequency measurement report to the RNC. When the measuredCPICH Ec/No value of all active set cells has become worse than the reportingthreshold, the RNC starts the inter-system (GSM) measurement.

Parameter Setting

HhoEcNoThreshold -22 dB

HhoEcNoTimeHysteresis 640ms

HhoEcNoCancel -20 dB

HhoECNoCancelTime 1280 ms

HhoEcNoCancel determines the absolute threshold which is used by the UE totrigger the reporting event 1E (a primary CPICH becomes better than an absolutethresold). HhoEcNoCancelTime determines the period of time between thedetection of the event 1E and sending of the measurement report.

4.3 GSM cell measurements for WCDMA-GSM inter-system handover

The inter-system (GSM) measurement procedure is controlled with the followingparameters:

Parameter Setting

GsmMeasRepInterval 1

GsmNcellSearchPeriod 0 MeasReport

GsmMaxMeasPeriod 20 MeasReport

GsmMinMeasInterval 10 s

GsmMinHoInterval 10 s

GsmMeasRepInterval determines the measurement reporting interval forperiodical inter-system (GSM) measurements.



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GsmNcellSearchPeriod determines the number of periodical inter-system(GSM) measurement reports, starting from the first report after the measurementsetup, during which a handover to GSM is not possible. This period allows theUE to find and report all potential GSM neighbour cells before the handoverdecision.

GsmMaxMeasPeriod defines the maximum allowed duration of themeasurement by means of the maximum number of periodical inter-system(GSM) measurement reports during the measurement. If the RNC is not able toexecute the handover to GSM, it stops the GSM measurement after the UE hassent the predefined number of measurement reports to the RNC.

GsmMinMeasInterval determines the minimum interval between anunsuccessful inter-system (GSM) measurement or handover procedure and thefollowing GSM measurement procedure related to the same RRC connection.Repetitive GSM measurements are disabled when the value of the parameter iszero.

GsmMinHoInterval determines the minimum interval between a successfulinter-system handover from GSM to UTRAN and the following inter-systemhandover attempt back to GSM related to the same RRC connection. A returnhandover back to GSM is disabled when the value of the parameter is zero.

4.3.1 Inter-system handover decision algorithm

The measurement results of the GSM neighbour cell must satisfy the followingequation before the inter-system handover or cell change to GSM/GPRS ispossible:

" AVE_RXLEV_NCELL(n) > GSMncellRxLevMinHO (n) + max( 0,GSMncellTxPwrMaxTCH (n) � P_MAX )

Where AVE_RXLEV_NCELL(n) is the averaged GSM carrier RSSI value of theGSM neighbour cell (n). The RNC calculates the averaged value directly from themeasured dBm values, linear averaging is not used in this case. The slidingaveraging window is controlled with the parameter GsmMeasAveWindow.

Parameter Setting

GSMncellRxLevMinHo -95 dBm

GSMncellTxPwrMaxTCH 33 dBm

GsmMeasAveWindow 6 MeasReport




The parameter GSMncellRxLevMinHO(n) determines the minimum requiredRSSI (dBm) level which the averaged RSSI value of the GSM neighbour cell (n)must exceed before the inter-system handover is possible. The neighbour cellparameter GSMncellTxPwrMaxTCH(n) indicates the maximum Tx powerlevel (dBm) a UE may use in the GSM neighbour cell (n). P_MAX indicates themaximum RF output power capability of the UE (dBm).

The RNP parameter GsmNcellSearchPeriod determines the period startingfrom inter-system measurement setup during which an inter-system handover toGSM is not possible.

Parameter Setting

GsmNcellSearchPeriod 0 MeasReport

After the GSM neighbour cell search period has expired, the RNC evaluates theradio link properties of the best neighbour GSM cells after every inter-systemmeasurement report. The RNC performs the inter-system handover to the bestGSM neighbour (target) cell as soon as the best GSM neighbour cell meets therequired radio link properties.

If there are several neighbour GSM cells which meet the required radio linkproperties at the same time, the RNC ranks the potential target cells according tothe priority levels and select the highest ranked GSM neighbour cell to be thetarget cell. The priority order is controlled with the RNP parameterGSMncellPriorityCoverage which is defined for each GSM neighbourcell.

Parameter Setting

GSMncellPriorityCoverage 0

The crucial principle is that high priority cells are considered better than lowpriority cell: a cell is ranked higher than another cell if it has a higher prioritylevel even though its signal strength condition was worse. Signal strengthconditions have effect only between cells which have the same priority level.

BSIC verification

When an inter-system (GSM) measurement is initially started, the reportingquantity is GSM Carrier RSSI. The RNC selects the highest ranked GSMneighbour cell which meet the required radio link properties to be the target cellas descibed in Inter-system handover decision algorithm. After the target cellselection, the RNC repeats the inter-system measurement for the target GSM



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carrier. The RNC requests the BSIC verification before the execution of inter-system handover so that the mobile station can synchronise to the GSM cellbefore the handover execution, and also to verify the identification of the GSMneighbour cell if two or more neighbour GSM cells have the same BCCHFrequency.

Interactions between handover causes

The quality and coverage reason inter-system handovers have priority over theother inter-system handover causes. The RNC supports the following quality andcoverage reason inter-system handovers:

" Inter-system handover due to Uplink DCH quality

" Inter-system handover due to UE Tx power

" Inter-system handover due to Downlink DPCH power

" Inter-system handover due to CPICH RSCP

" Inter-system handover due to CPICH Ec/No.

If two or more of the above indicated quality and/or coverage causes are presentsimultaneously, the handover cause which has triggered first has the highestpriority.

4.3.2 Interaction with inter-frequency handover

If the serving cell (or cells participating in soft handover) has neighbour cells bothin another carrier frequency and in another radio access technology (GSM), andthe RNC receives the Service Handover IE from the CN, the RNC determines thepriorities between inter-frequency and inter-system handovers on the basis ofService Handover IE value:




" Should be handed over to GSM: Handover to GSM has priority over theinter-frequency handover. In this case the RNC does not start inter-frequency measurements until the inter-system (GSM) measurements arecompleted, that is, when no neighbour GSM cell is good enough for thequality and/or coverage reason handover.

" Should not be handed over to GSM: Inter-frequency handover has priorityover the handover to GSM. In this case the RNC does not start the GSMmeasurements until the inter-frequency measurements are completed, thatis, when no neighbour cell is good enough for the quality and/or coveragereason inter-frequency handover.

" Shall not be handed over to GSM: Inter-frequency handover has priorityover the handover to GSM. In this case the RNC does not initiate GSMmeasurements or handover to GSM even if no neighbour cell is goodenough for the quality and/or coverage reason inter-frequency handover.

If the RNC does not receive the Service Handover information element from theCN, the inter-frequency handover has priority over the handover to GSM as adefault value.

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4.4 WCDMA compressed mode

Compressed mode is a radio path feature that allows a single 3G user equipment(UE) to make measurements from either another FDD frequency or from theroaming partner's GSM network. The compressed mode functionality halts thetransmission and reception of the ongoing WCDMA call to performmeasurements on the other frequencies or system for a short period of time. Theintention is not to lose any user data but to compress the data transmission in thetime domain.

The compressed mode feature is obligatory if inter-frequency or inter-systemhandovers are needed. Compressed mode itself does not give any benefit for thenetwork operation. The advantage of it comes from inter-system and inter-frequency handovers.

Compressed mode is described in figure WCDMA compressed mode. Downlinkcompressed mode (DL CM) should be off when the GSM network is measured.Uplink compressed mode (UL CM) is needed to avoid interference, becauseduring WCDMA transmission, the signal leakage will also go to the GSMnetwork.



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Figure 6. WCDMA compressed mode.

The frame compression can be achieved with the following methods:

" Higher layer scheduling which means that DCH user data rate transmittedin the channel is reduced. Lower bit rate transport format combination setis constructed.

" Halving the spreading factor which doubles temporarily the physicalchannel data rate in the radio channel.

" Puncturing which means reducing the physical channel bit amount withspecial dynamic rate matching algorithm.

In practice, compressed mode takes place when inter-system handovermeasurement has to be performed. The RNC detects the possibility for ahandover based on neighbour cell definitions, channel allocations, cell layers andpossible other control parameters and orders the UE to measure certain frequency.The handover decision is based on measurement reports from the UE and controlparameters of the radio network.

GSM BTS WCDMA BTS

UL CM

transmissionpower

Measurement gap

Time

DL DL CM

Normal frameNormal frameCompressed

frame




Depending on the UE capabilities, the RNC commands the UE and the BTS toenter in compressed mode and provides downlink and/or uplink compressedmode parameters.

In RAN 1.5, the gap length (TGL) is always 7 slots. Single or double framepattern can be used according to the possibilities that the compressed modemethod allows. An example of the single and double frame pattern is shown inthe following figures:

Figure 7. Single frame gap. 7 slot gap. Variable number of normal framesbetween compressed frames. In the figure, there are 0 normalframes between compressed frames.

Figure 8. Double frame gap. 7 slot gap. Variable number of normal framesbetween compressed frames.

1 5 time slots

Normal Frame

CM Frame

8 time slots 7 time slots 8 time slots 7 time slots

CM Frame

Normal Frame

1 5 time slots

Normal Frame

CM Frame CM Frame

Normal Frame

11 time slots 7 time slots 12 time slots



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4.4.1 Compressed mode functionality

Puncturing

One method to create gaps in the transmission is to apply puncturing. This meansthat after coding, some bits are taken out. Puncturing up to about 20% could clear3 out of 15 slots.

In RAN 1.5 (R99 standards), puncturing is possible only with fixed startingpositions of the TrChs in the radio frame. In RAN 1.5, only downlink pure AMRservice uses fixed positions and only that service can be punctured. The NRT dataand CS data can not use puncturing. Puncturing can be used for all services whichuse fixed starting positions, as data rate and quality of channel by user's point ofview stays unmodified. The operator definable parameters MinDLAMRModeCMand LowerULAMRModeCM define the minimum allowed AMR mode and lowerAMR mode in compressed mode correspondingly in downlink and uplink.

Parameter Setting

MinDLAMRmodeCM 7.4 kbit/s

LowerULAMRmodeCM 7.4 kbit/s

The compressed mode by puncturing is possible only if the DCH has enough freepuncturing capacity; the total puncturing limit is set by the operator definableparameter DLPuncturingLimit.

Parameter Setting

DLPuncturingLimit 0.68

Splitting SF

The compressed mode by reducing the spreading factor (SF) by two can be usedin both downlink and uplink. It supports the single frame method and can also beused for all services, because the channel capacity is not decreased. Notehowever, that the new spreading code with the smaller spreading factor causes anincrease in transmitting power of about 3 dB.




There is a one-to-one mapping between the channelisation code used in thenormal mode and the one used in the compressed mode. That is why it is possibleto switch automatically, without signalling frame by frame, between two differentspreading factors and spreading codes. During the compressed mode, the originalspreading code is used in normal frames between gapped frames and the newspreading code, taken from one step higher in the OVSF tree which is used duringthe compressed frames.

It might be that a new required channelisation code is not free in downlinkdirection. In uplink this is not a problem. If the new required channelisation codeis not free in downlink direction, the higher layer can command the UE and theBTS to use an alternative scrambling code. The alternative scrambling codeallows the usage of channelisation codes of normal channelisation code tree andfrees hose channelisation codes.

The usage of alternative scrambling code is controlled with the RNP parameterAltScramblingCodeCM. The RNP parameter allows or denies the usage ofalternative scrambling code in cell level.

Table 12. Effect of CM to Coverage


AltScramblingCodeCM 0 Alternative ScramblingCode Used

If code splitting is used, the required power increases by 3 dB. All links for whichmeasurement results are available are checked by the system to ensure that thereis room for the power addition. The maximum power of the downlink radio linkwhich is derived by admission control has to be 3 dB higher than the biggestmeasurement result of all links in the active set. This is controlled by theparameter PowerMarginCMcodeHalving:

Parameter Setting

PowerMarginCMcodeHalving 3dB

If code splitting or puncturing is the last or the only option in the compressedmode strategy to realise compressed mode, no power level checkings are done,because it is better in poor conditions to offer the possibility to measure and try tofind a better connection in another cell than be limited within the serving cell.



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Higher layer scheduling

The higher layer scheduling (HLS) decreases the transport channel (TrCh)capacity and, thus, it can only be used for the NRT services. It cannot be used forcircuit switched data TrChs. Note that the compressed mode by HLS is not usedwith the fixed starting positions of the TrChs in the radio frame.

TrCh starting position HLS possible

Downlink AMR Fixed No

Uplink AMR Flexible Yes

Uplink NRT packetswitched data

Flexible Yes

Downlink NRT packetswitched data

Flexible Yes

With the parameter HLSModeSelection it is possible to control at the systemlevel whether compressed mode by ½ HLS is possible or is ¾ HLS used instead,if HLS is possible at all. Note that if ½ HLS is allowed but it is not possible toconstruct such TFCS, ¾ HLS is used if such TFCS is possible to construct:


HLSModeSelection 0 ½ HLS allowed

4.4.2 Selection of downlink compressed mode method

The compressed mode method used depends on the service and the mechanismthat triggered compressed mode.




Figure 9. Packet-switched NRT service downlink

However, when the compressed mode is triggered due to too high downlink RLTX power, the higher layer scheduling is the priority option.

Figure 10. CS data and packet-switched RT service downlink.

Yes

No

Use HLS

No

HLS possible

Link level powerlimit not reached

SF/2 code available

No

Yes

Yes

Use HLS

Use SF/2 with thesame scrambling code

Use SF/2 with anotherscrambling code

SF/2 code available

No

Yes





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The higher layer scheduling for packet-switched RT data is not possible and thatis why it is not checked whether there is room for power increase due to codesplitting.

Figure 11. Circuit-switched AMR

The above methodology is used when the triggering mechanism is too highdownlink RL TX Power. In other cases, the spreading factor is halved.

4.4.3 Operator controllable compressed mode parameters

The transmitted powers of the UE and the BTS increase during the gappedframes, which may affect cell capacity, coverage and quality. For this reason, thecompressed mode feature can be switched on or off at the system level by theRNC configuration parameter CMmasterSwitch.


CmmasterSwitch 0 Compressed Mode in Use

Yes

No


Yes

Yes


Use puncturing(for AMR speech)

Lower AMR rate(+puncturing)

No

SF/2 code available

AMR rate> MinDLAMRModeCM

Channel coding> DLPuncturingLimit

No

Puncturing possible onlywith fixed positions in3GPP Release 3= AMR speech




To further enhance the feature, you also have the possibility to limit the maximumnumber of UEs simultaneously in the compressed mode within one cell with theparameter MaxNumbUECMcoverHO:

Parameter Setting

MaxNumbUECMoverHO 16

Note also that the UE does not switch into the compressed mode withoutchecking the load within the cell and therefore ensuring the compressed modeaction does not detrimentally affect other cell users.

The decision whether the UE can be switched on compressed mode in downlinkis based on the following conditions:

" If PtxTotal is below PtxTarget and the number of UEs in the compressedmode is less than MaxNumbUECMcoverHO parameter indicates, the UEcan be switched on compressed mode.

" If PtxTotal is above PtxTarget + PtxOffset, no more UEs can be switchedon compressed mode.

" Whether the UE can be switched on compressed mode in uplink will bechecked analogously as in previous paragraphs. The measurement resultused now is PrxTotal and RNP parameters to set threshold points arePrxTarget and PrxOffset. MaxNumbUECMcoverHO parameter isused in both uplink and downlink.

4.4.4 Effect of compressed mode on WCDMA coverage and capacity

The effects of compressed mode can be characterised in two groups as shown infigure Compressed mode tuning and control mode, when analysing thecompressed mode characteristics the two splits should be studied independentlyand extensively for their performance effects.



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Figure 12. Compressed mode tuning and control model

It is important to have an analytical estimate of the possible degradation ofcapacity and coverage in an area where compressed mode is implemented. As theplanning tools do not explicitly analyse the effects of possible increase ofinterference and loading levels when the UEs are in CM. The effect of reducedcapacity or coverage are the by-products of the method applied for thecompressed mode.

Capacity reduction

The compressed mode decreases system capacity if higher Eb/No for users arerequired or power control efficiency is lower. The compressed mode may alsocause hard blocking if the spreading factor splitting is used. This is a directconsequence of the overall interference in the cell increasing, leading to a rise in

Compressed mode implementation

IS-IF handover

Coverage and qualityanalysis

Handover delay,interruption time

BER, BLERand FERcorrelation withpredictedquantities

Change in capacityand coverage

Power controlcharacteristicbehaviour in theareascompressedmode isimplemented

Controlindicator

Downlink/uplinkinterference levels

Location based effect

Controlindicator




the load and reducing capacity for the new users trying to access the cell. Theeffect is very small when considering a single UE in the compressed mode.However, it increases exponentially once a large number of UEs are continuouslyin the compressed mode.

When planning the compressed mode for the inter-system scenarios, it isimportant to estimate the probability factor which is derived from the averageload in the cell and the coverage probability that would lead to the ratio of UEs inthe connected state to trigger inter-system handovers. It is also important to notethat the effect is due to an increase in the requirement of the power per user in thecompressed mode but if the applied compressed mode method is HLS (dependingon services) which would maintain the power requirement the effect does notexist.

The table shows an average estimate of capacity reduction figures which arebased on the typical increase in the EbNo requirements when either puncturing orSF/2 is used. An exact increase in the Eb/N0 depends on the service, multipathdiversity, antenna diversity, mobile speed, uplink or downlink, measurement gaplength and compressed mode method (spreading factor or puncturing), and 1.5 dBrepresents a typical value.

Table 13. Capacity reduction

Assumption Effect to the capacity

Required Eb/NO is 1.5 dB higher duringcompressed frames

1.5 dB = 41% more interference

Every 3rd frame is compressed 41% /3 = 14% more interference

10% of the users are measuring at thesame time

14% /10 = 1.4% more interference

Capacity degradation < 2%

The parameterisation of the triggers initiating the compressed mode can be verychallenging as it depends on variable factors, one the most important ones beingthe type of service users are doing.

If the compressed mode parameters favour several UEs to perform handoversbetween carriers or systems, and if the implemented compressed modeparameters are the same in all areas, the effect discussed here will be highlyuncorrelated in the areas where there are mostly voice users to the areas wherethere are relatively large mix of services. This is due to different methods appliedfor the compressed mode in different scenarios.



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Coverage reduction

The compressed mode also has an adverse effect on the coverage for the cell, inparticular on the UL coverage. This is due to the fact that when the compressedmode is switched on, the power control must change its operation point. Thismeans that the transmitted power and outer-loop target is increased by the value:

Figure 13. Equation for coverage reduction

The equation can be used both with puncturing or code splitting. This increase ofthe power is needed because in the compressed mode, the same data amount istransmitted during a shorter time than in the normal mode. This would lead to adecrease in the coverage by the amount of the 10*log10((frame_length-gap_length)/frame_length).

The table presents a similar estimation for coverage reduction as the one for thecapacity. This implies that the coverage of a speech service would suffer by afactor of 2.1 dB since the UE requires roughly 4.2 dB of additional power toprocess the compressed mode. But this is strictly an estimation based onassumption of average increase in EbNo.

The NRT users can, however, reduce their bit rates so that the coverage reductionshould not affect the NRT bearers, whereas Speech service also has the possibilityto reduce to lower AMR which does not require as much increase in power as thatfor the SF/2.

Table 14. Coverage reduction

Assumption Effect to the coverage of real timeservices

Required Eb/N0 is 1.5 dB higher duringcompressed frames

1.5 dB reduced coverage

7-slot gap is used 10*log10(15/8) = 2.7 dB reducedcoverage

EbN0_CM SF_CM Slots_used_normal

EbN0_Normal SF_Normal Slots_used_CM




Table 14. Coverage reduction (cont.)

Assumption Effect to the coverage of real timeservices

Every 2nd frame is compressed with 20ms interleaving (speech)

4.2 dB / 2 = 2.1 dB reduced coverage

Handover delay

Before executing the handover, the RNC commands the UE to perform the GSMCarrier RSSI measurements. The UE using is also given the set of parametersdefining the compressed mode pattern specific to that service. In this section thedelay requirements are estimated.

Figure 14. Handover delay

+ +

Quantitativevalues

F1 GSM

Compressed mode duration

Time to measure BSIC decoding

Dependent factors:Number of cells todecode

Approx 50ms+10depending on the timerequired for the MS tomeasure the newDPCCH.

Interruption Time

New compressedmode pattern can besent to guide the UEinto BSICidentification process.



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As the figure above shows, the process carried during the compressed modeinvolves the measurement duration of the GSM carrier. Once the measurementsare performed, the RNC ranks the cells according to the received measurements(Highest RSSI having best priority) and sends a message to perform the BSICidentification.

BSIC Verification: The next step is identifying the BSIC. This measurement isbased on a transmission gap pattern sequence with the purpose "GSM InitialBSIC identification".

For the GSM cells that are requested with the verified BSIC, the UE attempts todecode the SCH on the BCCH carrier of the 8 strongest BCCH carriers of theGSM cells indicated in the measurement control information.

The worst case scenario for decoding a single BSIC are given in the table BSCIdecoding times in inter-system handover to GSM. The process is also guided bythe management parameter of GSMMaxMeasPeriod duration. It isimportant to note, however, that the RNC can terminate the measurementsimmediately when a suitable BSIC is found and reported. In RAN1.5, there isonly one BSIC to decode in time.

Table 15. BSCI decoding times in inter-system handover to GSM

#of BSIC Avg/s Worst/s

1 1.07 1.53

2 2.14 3.06

6 6.42 9.18

8 8.56 12.24

The parameter GSMMaxMeasPeriod tells the time that the RNC waits beforesending a command to execute the inter-system handover. The default value ofthe parameter is 20 measurement reports, which indicates a duration of 10seconds. Hence, during 10 seconds of measurement, if the UE does not report asuitable neighbour candidate to the RNC, the compressed mode is aborted. Onexpiration of this timer the HC entity of the RNC commands the UE to abort thecompressed mode.

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Dn03298108 1 en Global PDF Paper a4 GSM WCDMA Plan

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