ISHO and Cell Re-Selection StrategyProposal

Contents Introduction Parameters for Inter System Handover and Cell Reselection ISHO and Cell Reselection Strategies

Introduction Inter System Handover to GSM is possible for both Real Time

(RT) and Non Real Time (NRT) bearers Inter System Handover of NRT services between WCDMA and

GPRS/EDGE is based on the cell reselection procedure Handover to GSM mainly happens based on event triggered

coverage reason The RNC makes the decision on the basis of periodical inter

system (GSM) measurement report received from the UE and relevant control parameters

Neighbouring Cell in Nokia RNC 32 intra frequency neighbours 48 inter frequency neighbours 32 inter system neighbours (BSIC & frequency)

Introduction All together there are five different quality and/or coverage

based triggered events for ISHO :

GSM handover caused by CPICH Ec/No (event 1F) GSM handover caused by CPICH RSCP (event 1F) GSM handover caused by Ue Tx Power (event 6A) GSM handover caused by DL DPCH power (Node B radio

link measurement) GSM handover caused by UL DCH quality (UL outer

loop power control)General definitions: General definitions:

ISHO ISHO :: Only happen in Traffic modeOnly happen in Traffic mode

Cell ReCell Re--selectionselection : Only happen in IDLE mode: Only happen in IDLE mode

What needs to be considered when planning for ISHO? Parameter related:

Neighbour plan Cell reselection triggering parameters ISHO triggering parameters 2G/3G quality thresholds for ISHO

The parameter consideration depends on many factors: ISHO strategy according to operators requirements; KPI requirements: ISHO success rate, interruption time, impact to CSSR or CDR avoid pingpong under different scenarios: high/low mobility, indoor/outdoor, coverage/interference limiting case, etc.

The parameter consideration depends on many factors: ISHO strategy according to operators requirements; KPI requirements: ISHO success rate, interruption time, impact to CSSR or CDR avoid pingpong under different scenarios: high/low mobility, indoor/outdoor, coverage/interference limiting case, etc.

Network related:What is the co-siting plan for dual mode operator?NSS/MSC load balancing, e.g. between GSM900 and GSM1800How the network handles roaming users? E.g. 2G roamer using 3G handsets and handset having different setting on mode selection.Whether 3G operator has it own 2G network, or has roaming agreement with other 2G operators.

UE related:UE dependency on USIM setting, e.g. RAT priority for cell camping. However, UE may not comply with 3GPP. E.g. 7600 will always try to camp on the previous RAT after power on.UE measurement performance: 7600 seems to have different (worse?) measurement performance than 6650 as 7600 seems always to trigger HO earlier than 6650

WCDMA to GSM Handover ProcessHandover triggering threshold set in RNC

Event triggered coverage based on HO fulfilled in RNC

RNC commands UE to start ISHO measurement periodically

Measurement are done in Compressed Mode

RSSI measurement and verification for GSM cells

UE reports best GSM cells having strongest RSSI results back to RNC

RNC makes HO decision and command UE to selected target cell

ISHO ParametersParameter Default*HHoEcNoThreshold -12 dB*HHoEcNoCancel - 9 dB

CPICH EcNo *HHoEcNoCancelTime 1280 ms*HHoEcNoTimeHysteresis 100 msEcNoFilterCoefficient 600 ms*HHoRscpThreshold -105 dBm

CPICH RSCP *HHoRscpCancel -102 dBmHHoRscpFilterCoefficient 200 ms*HHoRscpTimeHysteresis 100 ms*HHoRscpCancelTime 1280 ms

UL Tx Pow er GsmUETxPwrThrAMR -3 dBGsmUETxPwrFilterCoeff 10 msGsmUETxPwrTimeHyst 320 ms

DL DCH GsmDLTxPwrThrAMR -3 dBUL Quality ULQualDetRepThreshold 0.5 s

Measurem ent GsmMeasRepInterval 0.5 sReporting GsmNcellSearchPeriod 0

Param eters GsmMaxMeasPeriod 6 meas. reportGsmMinMeasInterval 2 s

HO *AdjgRxLevMinHO -95 dBmDecision AdjgTxPwrMaxTCH 33 dBm

Algorithm GsmMeasAveWindow 6 meas. report

* Key Parameters

ISHO Coverage Triggered Events

HHoRscpCancel = -102 dBmHHoEcNoCancel = -9 dB

HHoRscpThreshold = -105 dBmHHoEcNoThreshold = -12 dB

Reporting starts here, 1F

No reporting after this, 1E

CPICH RSCP or EcNo

Serving WCDMA cell

HHoRscpTimeHysterisis = 100 msHHoEcNoTimeHysterisis = 100 ms

TimeHHoRscpCancelTime = 1280 msHHoEcNoCancelTime = 1280 ms

Inter System Handover Decision The 2G parameters required for the ISHO need to be fulfilled before the UE can handover from 3G to 2G

Cell Reselection Parameters

Cell reselection (3G) Default*Ssearch_RAT 4 dB*QqualMin -18 dB*Qhyst1 0 dBAdjgQoffset1 -10 dBAdjgTempOffset1 3 dBAdjgPenaltyTime 0 s*AdjgQrxlevMin - 101 dBm

* Key Parameters

Cell Reselection Triggering Event

CPICH Ec/No RxLev

CPICH Ec/No = - 14 dBAdjgQrxlevmin = -101 dBm

Reselect to 2G

Whilst camping on 3G, UE will measure 2G neighbours if :CPICH Ec/No < Qqualmin + SsearchRAT (= -14 dB)* Qqualmin = -18 dB* SsearchRAT = 4 dBUE will reselect to 2G if RxLev > CPICH RSCP + Qhyst1* Qhyst1 = 0 dB AND * RxLev > AdjgQrxlevMin = -101 dBm

Neighbour Cell Definition Information required to define 2G cells adjacency to 3G cells :

GSM site information MNC MCC LAC CI BCCH BSIC RAC BSC

Additional information (optional) Longtitude Latitude

Strategy Objectives

Ensure service continuity Obtain maximum use of WCDMA

Better quality (AMR, PS bit rates) Investment efficiency

Avoid ping-pongs Analysis

WCDMA coverage does not just end at the edge of roll-out, it also stops in indoor before GSM

GSM

WCDMA

ISHO and Cell Reselection Strategies 1) Bordering strategy

The 3G to 2G border needs to be clearly identified Then define the 2G adjacency to the 3G sites which are at

the border. At least 2 or 3 tiers need to be defined as to overcome fast moving handover or cell reselection.

GSM 1800GSM GSM

GSM

GSM3G coverage area

GSM GSM

3G

ISHO and Cell Reselection Strategies 2) Within cluster strategy

Weak coverage or coverage hole can sometime occur within a cluster itself. Meaning that even though there is 3G coverage in the cluster but due to missing sites there will be some weak area. By utilizing the existing 2G sites we can solve the drop call problem in the area.

This is done by defining 2G neighbours in most 3G cells in the cluster (affected areas only). The amount of 2G neighbours needs not to be many, but co-sitting 2G cells need to be added in the neighbour at least.

The parameter package for 3G->2G will be set in such that once the threshold has been reached, ISHO or cell reselection will be done quickly and easily. These events will only happen in 3G coverage hole spots (e.g. indoor no 3G coverage)

GSM 1800GSM GSM

GSM

GSM3G coverage area

GSM GSM

hole

3G

Inter-system neighbor definition (1/7)Environment

Problems: Manage the different site densities : more sites in GSM than

in WCDMA macro-layer Therefore more than 32 neighbors could be required

Take into account the different site configuration GSM and WCDMA collocated/not collocated M900 and M1800 collocated/not collocated

Define simple and deployable processes Make use of the existing neighbouring definition rather than simulating

Avoid handovers to bad quality cells Rather drop the call in WCDMA than increase counters in GSM

Assumptions WCDMA and M1800 coverage are equivalent M900 coverage wider and deeper than WCDMA and M1800 Traffic is higher on GSM1800

Inter-system neighbor definition (2/7)Principles

When WCDMA and M900 are collocated Use the underlying M900 cell as the basis for neighbor definition Ignore the underlying M1800 cell if it exists

When WCDMA and M1800 are collocated Use the underlying M1800 cell as the basis for neighbor definitions

If the WCDMA site is standalone Use existing processes for neighbor definitions, define neighbors with

sorrounding/related WCDMA cells.

Use all M900 neighbors of the underlying neighbor M900 provides a continuous coverage

Use M1800 neighbors of the underlying neighbor only when standalone

Inter-system neighbouring definition (3/7)3G2G

Tri-band collocated site (WCDMA site collocated with dual band site M900/M1800)

900

M900

WCDMA

Collocated tri-band site

M900

M1800

Neighbour

Neighbour

M1800

Neighbour

IsolatedM1800 site

Inter-system neighbouring definition (4/7)3G2G

WCDMA site collocated with M900 site only

900

M900

WCDMA

Collocated tri-band site

M900

Neighbor

Neighbor

M1800

IsolatedM1800 site

Neighbor

Inter-system neighbouring definition (5/7)3G2G

WCDMA site collocated with M1800 site only

900

WCDMA

Collocated tri-band site

M900

M1800

Neighbor

Neighbor

M1800

Neighbor

IsolatedM1800 site

Inter-system neighbouring definition (6/7)3G2G

Isolated WCDMA site

Inter-system neighbouring definition (7/7)2G3G

Collocated 2G/3G site The WCDMA cell must be declared as neighbour cell of

The GSM collocated M900/M1800 All the GSM neighbours of all the collocated GSM cells

No ISHO for 2G->3G

Summary

UE (idle or traffic mode) in 3G network will be able handover or Re-

Selection to 2G network when 3G coverage degrades.

When there is a 3G coverage hole area, UE in that area will camp/HO

to 2G network. When a UE makes a AMR call outside 3G area, and moves into the 3G

area, there is NO ISHO to 3G network. Only when the UE terminates the AMR call in 2G (within 3G area), then the UE in idle mode will perform Cell Re-Selection to 3G network.

When a UE makes a PS call (GPRS) outside the area, and moves into the 3G trial area, the UE will perform a Cell Re-Selection to 3G Cell.

UE needs to be in dual mode.

ISHO and Cell Re-Selection StrategyContentsIntroductionIntroductionWhat needs to be considered when planning for ISHO?WCDMA to GSM Handover ProcessISHO ParametersISHO Coverage Triggered EventsInter System Handover DecisionCell Reselection ParametersCell Reselection Triggering EventNeighbour Cell DefinitionStrategyISHO and Cell Reselection StrategiesISHO and Cell Reselection StrategiesInter-system neighbor definition (1/7)EnvironmentInter-system neighbor definition (2/7)PrinciplesInter-system neighbouring definition (3/7)3G2GInter-system neighbouring definition (4/7)3G2GInter-system neighbouring definition (5/7)3G2GInter-system neighbouring definition (6/7)3G2GInter-system neighbouring definition (7/7)2G3GSummary