go_na25_e1_1 2g-3g cell reselection & handover-37

7/28/2019 GO_NA25_E1_1 2G-3G Cell Reselection & Handover-37

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2G-3G Cell Reselection & Handover

ZTE university



Objectives

To know interworking between 2G-3G networksTo master strategies of reselection & handover between 2G-3G networks

To know algorithms of cell reselection & handover between 2G-3G networks



Contents

Condi t ions fo r 2G-3G in terwork in g 2G-3G reselection & handover strategies2G-3G reselection algorithms2G-3G handover algorithms2G-3G load-balance handover algorithms



Conditions for 2G-3G interworkingDefinition of UTRAN

adjacent cellsDefine cells out of BSCDefine adjacent cell for

cell reselection/ handover

2Quater system

messageMS reads system

messageMeasurement of UTRAN

systems

Setting of 2G-3Ginterworking parameters

Handover & reselectionparameters

2G coveredarea

3G coveredarea

Makemeasurement of 3G network atthe its edge area

MS moves to2G networkafter originatinga call in 3Gnetwork



Conditions for 2G-3G interworking

2quater messageThe precondition for system to send message is that dataconfiguration must meet one of the following criteria:The cell is configured with 3G adjacent cells;The cell supports NC2 function (network controls cellreselection);

2quater contentDescription of FDD(TDD) at UTRAN sideDescription of 3G measurement parametersDescription of GPRS 3G measurement parametersNetwork control measurement parametersInformation of cells adjacent to UTRAN FDD(TDD)



Conditions for 2G-3G interworking (extendedfunctions of inter-working)

IUR-G interfaceTo realize wireless integration of 2G and 3G networksTo reach inter-system balance based on information of GSMcell capacity and loadTo select handover target cell based on information of GSMcell capacity and loadTo select target cell of RAB redirection based on information of GSM cell capacity and load



Contents

Conditions for 2G-3G interworking2G-3G reselect io n & hand ov er s t ra tegies

2G-3G reselection algorithms2G-3G handover algorithms2G-3G load-balance handover algorithms



2G-3G interworking strategies

ReselectionPLMN selection/cell reselection2G-3G interworking occurs when UE is in idle mode

Handover CS handover/PS handover

When subscriber originates service, 2G-3G interworking occursduring the service connection between UE and mobilenetworks. The service falls into two types:

– CS handover CS – PS handover PS



2G-3G interworking strategies

2G-3G interworking strategies:Only when UE leaves 3G-covered area , will it perform3G-2G cell reselection; once it returns to 3G-coveredarea, it will start 2G-3G cell reselection.

In order to ensure the continuity of speech, 3G-2Ghandover should be supported.CS service which is being performed in 2G networkdoesn t need handover to 3G network, so as to reduce

call drops due to UTRAN handover (hard handover).In order to guarantee PS subscribers satisfaction, bi -directional handover of PS service is recommended.



2G-3G Reselection algorithms-PLMNselection/reselection

UE can select and roam between 2G and 3G networks throughselecting PLMN MCC+MNC , and there is no need to upgrade 2Gnetwork.Whether 3G and 2G adopt the same PLMN-ID, the strategy of „preferably selecting 3G network can be realized.

Set 3G network to be homenetwork HPLMN ,UE

searches and makesreselection periodically after it switches to 2G networkVPLMN .

3G and 2G adopt differentPLMN-ID

Set 3G network with the

preferred radio access technology

Access Technology , then UE

will preferably adopt 3G to make

radio access when it selects

PLMN.

3G and 2G adopt thesame PLMN-ID



2G-3G Reselection algorithms-PLMNselection/reselection

PLMN selection& reselection

3G and 2G networksare configured withdifferent IDs duringnetwork planning;

HPLMN (home network)of USIM is set to be 3Gwhen an account isopened;

Set USIM PLMNreselection interval whenan account is opened;note there is an“hysteresis of 6mins”.

PLMN selection

RPLMN

HPLMN

“ Operator Controlled PLMN Selector with Access Technology” in USIM

PLMN with good signal quality (in randomorder)

Other PLMN [in order of signal quality (high-low)]

PLMN selection after UE is powered

Change of PLMN ie.reselection,

which occursduring cell

reselection

+“ User Controlled PLMN Selector

with Access Technology” in USIM

Histeresis of 6mins after UE resides in GSM network, it has to wait for at least

6mins before it can return to 3G network.



Cell selection: select the cell with the best signal in current network;Cell reselection: as signals of the serving cell (in which UE resides)and its adjacent cells change/deteriorate, UE needs to select a newcell with better signal to reside.

Reside inoriginal cell

Reside in cell at randomcall barring

Cell is non-HPLMN

Confirm primaryscrambling code of

cell

S principle not satisfied, keepsearching cells

Search cell S principleRead broadcastchannel

Normalresidence

Keepsearching

cells

PLMA selectionY

N

N

2G-3G Reselection algorithms-cellselection/reselection



2G-3G Reselection algorithms-cellselection/reselection-S principle

Formula:Squal = Qqualmeas – Qqualmin

Srxlev = Qrxlevmeas – Qrxlevmin – Compansation

If For FDD: Squal > 0 & Srxlev > 0

For TDD: Srxlev > 0then UE will take the cell as a suitable one and reside in it.

S- principle is used to judge whether a cell s signal RxLev

and RxQual are suitable for UE to redside in the cell.



2G-3G Reselection algorithms-cell selection/reselection-reselection parameter 1

Cell reselection flow in idle mode & key parameters:

Parameter Meaning Valuerange

Qsearch_I Search for 3G cells if signal level is below (0-7) or above(8-15) threshold0 = - 98 dBm, 1 = - 94 dBm, … ,6 = - 74 dBm, 7 = (always)8 = - 78 dBm, 9 = - 74 dBm, … ,14 = - 54 dBm, 15 = (never).Default value = (never).

0-15

Location: 3G adjacent cell list and cell reselection parameters are described in systembroadcast message SI2quater and SI2ter which is sent on BCCH or extendedBCCH.

Function: to control the adjacent cell measurement and reselection process under UEidle mode.



2G-3G Reselection algorithms-cellselection/reselection-reselection parameter 2

Cell reselection flow in idle mode & keyparameters:

Parameter Meaning Valuerange

FDD_Qoffset

Applies an offset to RLA_C for cell re-selection to accesstechnology/mode XXX (one or more) 0 = - (always select acell if acceptable), 1 = -28 dB, 2 = - 24 dB, … , 15 = 28 dB.Defaultvalue = 0 dB.

0-15

FDD_Qmin A minimum threshold for Ec/No for UTRAN FDD cell re-selection,0= -20dB,1=-6dB, 2= -18dB, 3= -8dB, 4= -16dB, 5= -

10dB, 6= -14dB, 7= -12dB.Defaultvalue= -12dB.

0-7



2G-3G Reselection algorithms-cell selection/reselection-reselection parameter 2

Application of FDD_Qoffset and FDD_Qmin

These two parameters control inter-system cell reselection process. Whena UE satisfies all the following conditions, it can make reselection toUTRAN adjacent cells.

RSCP >= FDD_Qoffset + RLA_C

RSCP >= FDD_Qoffset + RLA_n

Ec/No >= FDD_Qmin-FDD_Qmin_Offset

RSCP>= FDD_RSCP_threshold

Notes:

2G-3G cell reselection is not allowed within 5s after 3G-2G reselection; if more than one 3G cell satisfies the conditions, UE shall select the cell withthe largest RSCP value.



2G-3G Reselection algorithms-suggestions

Principle of field strengthOnly when the field strength of 3G network is guaranteed, willreselection to 3G occur. Normally, in 3G covered areas with weakfield strength and the marginal areas overlapped by 3G and GSMnetworks,this principle shall be considered first.

Principle of time efficiencyOn condition that the principle of field strength is satisfied, selectionto WCDMA should be as soon as possible, so as to providesubscribers with high-end services. In areas continuouly coveredby WCDMA network, this principle shall be considered first.

Principle of electricity efficiencyDual-mode terminal consumes more power in performing inter-system signal measurement, so this principle shall be fullyconsidered when we deploy networks with overlapped coverageareas.



2G-3G Reselection algorithms-cell reselectionPS

PBCCH supported in BSSPSI3quarter sends parameters related to inter-system cell reselection (3Gadjacent cell information, measurement and control parameters of cellreselection) to MS.

PBCCH not supported in BSS / PBCCH not configuredPacket Cell Change Order or Packet Measurement Order sendparameters related to inter-system cell reselection (3G adjacent cellinformation, measurement and control parameters of cell reselection) toMS; these parameters will be used in PS cell reselection process.

parameter Meaning Value range

Qsearch_P Search for 3G cells if signal level below threshold (0-7): - 98,- 94, … , - 74 dBm, (always) or above threshold (8-15):-78, - 74, … , - 54 dBm, (never). Default value = (never).

0-15

FDD_ GPRS_ Qoffset

Applies an offset to RLA_P for cell re-selection to accesstechnology/mode XXX (one or more), 0 = - (always selecta cell if acceptable), 1 = -28 dB, 2 = - 24 dB, … , 15 = 28 dB.Default value = 0 dBm.

0-15



2G-3G Reselection algorithms -NCCR

Explanation of NC2/NCCR It supports different cell reselection parameters in PS service to realize cellreselection of “packet idle mode” and “packet transmission mode”.

Advantage: it makes full use of available network information to makereasonable judgment and realize optimized distribution of networkservices; it reduces the useless cell reselection performed by MS, and

improves TBF transmission efficiency.

Network_Control-Order

Meaning of value

MS operations

NC0 Controlled bynormal MS

MS executes autonomous cell reselection

NC1

Controlled byMS whichreports MRs

MS sends MRs to network; MS continues cell reselection.

NC2 Controlled bynetwork

MS sends MRs to network, and realizes cell reselection onlybased on the reselection order from network. Only when cellreselection is triggered by failure of sending downlink signalling or random access, will MS execute autonomous cell reselection.



2G-3G handover algorithms- 3G->GSM

For 3G-GSM CS handover, main requirements stay with3G network; for GSM network, attention should be paid tothe following:

BSSAP signaling Handover Request at A interface should at leastsupport R99 (version), which means it should adapt to the changes

of coding mode of Cell Identifier (Serving) which carries 3G servingcell ID;Ignore the RF value (6 , 7) in classmark2 which is carried inBSSAP signaling Handover Request;For the encrypted algorithm sent by GSM MSC, even theencryption function is not enabled in BSS, it can also ignore theencrypted algorithm and perform the following handover process.When BSS sends HANDOVER REQUEST ACK to GSM MSC,Chosen Encryption Algorithm IE must contain the specificencryption mode, whether encryption function is enabled or not.



2G-3G handover algorithms-- 3G->GSM

Signaling flow of 3G-GSM CS handover 2G MSC BSC3G MSCRNC

PREPARE HANDOVER

UE

RELOCATION REQUIRED

HANDOVER REQUEST

HANDOVER REQUESTACKPREPARE HANDOVER

RESPONSERELOCATION COMMAND

HANDOVER COMMANDHANDOVER DETECT

HANDOVER COMPLETE

HANDOVER COMPLETESEND END SIGNALREQUEST

RELEASE COMMAND

RELEASE COMPLETE SEND END SIGNALRESPONSE



2G-3G handover algorithms- GSM ->3G

GSM cell collects information of 3G adjacent cells and measurementparameters.

BSC broadcasts SI 2quater on BCCH or extended BCCH;MS may receive Measurement Information in downlink SACCH sent byBSC during a call.

3G initialstage

3G expansionstage

3G maturestage

HO due tocoverage

HO due tocoverage

HO due tocoverage

HO due to serviceHO due to service

Network resourceoptimization

Network resourceoptimization

Messages to be collectedby MSDescription of 3G

adjacent cell parametersConfiguration of 3G

adjacent cellsParameters of adjacent

cell measurementHandover parameters



2G-3G handover algorithms- GSM ->3G HOparameters

Parameter Meaning Value range

Qsearch_C Search for 3G cells if signal level below threshold (0-7):- 98, - 94, … , - 74 dBm, (always)or above threshold (8-15):- 78, - 74, … , - 54 dBm, (never)

0-15

Qsearch_C_Initial

Indicates the Qsearch value to be used in connected mode beforeQsearch_C is received,0 = use Qsearch_I, 1 = (always).Default value = use Qsearch_I.

0/1

3G_SEARCH_ PRIO

Indicates if 3G cells may be searched when BSIC decoding isrequired,0 = no, 1 = yesDefault value = yes

0/1

Besides the important parameters listed above, some other parameters are also sent to MS in the systemmessages, such as:

FDD_REP_QUANT measurement of quantity, RSCP or Ec/No

REPORT_TYPE type of MR, MR or EMR ;…



2G-3G handover algorithms- GSM ->3GHO parameters

Signaling flow of GSM-3G CS handover 2G MSC

HANDOVER COMMAND

HANDOVER REQUIRED

BSC MS

HANDOVER COMMAND

RELEASE COMPLETE

RELEASE

3G MSCRNC

PREPARE HANDOVERREQUEST

PREPARE HANDOVERRESPONSE

RELOCATION REQUEST

RELOCATIONRESPONSE ack.

IAM

ACM

PROCESS SIGNALLINGRELOCATION DETECT

ANM

SEND END SIGNALRELOCATION

COMPLETE



2G-3G handover algorithms-strategy of networkselection priority

The strategy is to decide which network shall be prioritized for handover.

To decide target cell through processing of MRs and the strategy of networkselection priority :

MSC controls strategy of network selection priority

HANDOVER REQUEST carries “Service Handover” field, which is used to indicatehandover strategy for BSC in the following handover process.

BSC controls the strategy of network selection priority

Based on the configuration principles set in OMCR, BSC decides which network shallbe prioritized for handover according to the strategy of network selection priority,which can be set in OMCR as well.

Both ways can be adopted:

Prioritize WCDMA cells

Prioritize GSM cells

What s more, if both W CDMA and TD-SCDMA adjacent cells are available atthe same time, the priority of WCDMA and TD-SCDMA can be decidedthrough parameter “ FDD/TDD handover” FDDTDDPrio at iBSC side.



Contents

Conditions for 2G-3G interworking2G-3G reselection & handover strategies2G-3G reselection algorithms2G-3G handover algorithms2G-3G load-balance hand ov er algo r i thm s



Load-balance handover algorithms- directed-retry handover process

UE UTRAN

Signaling connection establishment request

Signaling connection establishment reject

Signaling establishment fails due to lack of

resource in 3G network; 3G is redirected to be2G network; UE starts access again in 2G

network without target cell defined.

To support directed-retry, the switch DrInd shall be open at iBSC OMCR.



Load-balance handover algorithms- traffichandover process

For 3G-GSM CS handover requirements stay with WCDMA network.

CN UTRAN

Assignment request

Success response toassignment request

When RNC receives RAB assignment message, if CN

requires handover of corresponding services to 2G system,

UTRAN handover process will be started, which is 3G-2G

handover, thus 3G network performance will be optimized.

Handover request



Load-balance handover algorithms- handover due to serving cell load

CNUTRAN

Assignment request

Assignment failure

Service establishment fails due to lack of resource in 3G

network; if it s 2G -supported CS service or low-rate PS

service, 3G will appoint suitable 2G cell, and CN will start

handover to the appointed 2G cell.

iBSC sends LOAD INDICATION BSSAP to MSC periodically.



Load-balance handover algorithms-comparative analysis of handover algorithms

Methods Voicehysteresis

Successrate

Influence to 3Gnetwork Application scenario

Directed-retry Long Low Light Signalling establishment

failure

Servicehandover Short High Serious

CN requests handover of service to 2G network after

service establishmentsuccess.

Handover for load balance Short High Serious Cell with light congestion

go_na25_e1_1 2g-3g cell reselection & handover-37

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