dt analysis - how to analyze handover in dt.ppt

8/10/2019 DT analysis - How to analyze Handover in DT.ppt

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HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

Security Level:

www.huawei.com

How to analyze HandoverIssues in DT


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Handover

What is Handover p rocedure in ne twork? Hando ver Um s igna l ing f low?

Purpos e o f Hando ver Ana lys i s in DT?


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Handover signaling on Um(TEMS Message)

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BCCH of Neighborsto be measured

Serving Cell:DL DTX is ON

RxLev(sub) is -109+ 62 =--49dBmRxQual (sub) is 0

The RxLev ofNeighbors

Tell MS how to access toTarget TCH Channel

Target cell Description

Target channel DescriptionChannel Type, TimeslotTSC

RF hoppingMAIO, HSN

Inter cell SynchronousHandover

Speech version: EFR

Handover Complete Handover Success!!!

Only after SABM & UAin Layer2 Message,handover success!


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The purpose of handover analysis in DT isunderstand the wireless handover performance of network.find out whether the handovers are healthy in this network.what is typical handover failure in this network.find out whether neighbor audit work is needed in this network.

To make optimization of HSR, the most effective way is based ontraffic analysis, combining DT events, neighbor audit, and dataconfiguration audit together.

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The purpose of Handover Analysis


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Handover Types

D i ffe ren t hando ver types by n e two rk topo logy D i fferen t handover types by a lgor i thm PBGT hando ver Qua l i ty hando ver Edge Hand ov er In t racel l Hand ov er O ther types o f hando ver


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Case1 Intra cell HO Case2 Synchronous Inter cell HO Case3 Asynchronous Inter cell HO Case4 Inter BSC HO Case5 Inter MSC HO

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Handover Types(Network Topology)

Operator

CELL CELL CELL CELL

Case 1

Synchronous

Case 2 Asynchronous

Case 3Case 4 Case 5

CELL CELL CELL CELL

MSC MSC

BSC BSC BSC BSC

BTS BTS BTS BTS BTS BTS


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HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 8

Handover Types(Algorithm)

In DT, the most commonhandover types happens infollowing order of priority

TA

RxQuali ty

RxLevel

PBGT

OL&UL

HO

OM Forced HO

Directed Retry

TA Emergency HO

Bad Quality HO

Rapid Level Drop HO

Load HO

Interference HO

Edge HO

Layer HO

PBGT HO

Fast Moving MS HO

Overlay/Underly HO


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PBGT HO Exp :

When:RXLEV_NCELL(n) (RXLEVEL+PWR_DIFF) > HO_MARGIN MS is handed over to theneighbor in g ce l l .

HO_MARGIN i s u sual ly se t to 3 to6 dB.

HO_MARGIN cou ld be increasedto reduce numb er of handovers .HO_MARGIN shou ld bedecreased i f fas ter handover

decis ion i s wanted .

PBGT Hando ver i s con s idered asmo st healthy hando ver in anetwork.

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PBGT Handover

Distance

ServingCell

TargetCell

RXLEV_NCELL(n)

RX LEVEL + PWR_DIFF

Power-budgetPBGT HO

HO_MARGIN > 0

A typical PBGT HO


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Qual ity Handov er Exp:

When:DL RxQuality >= DL Quality HOThresholdhandov er caused by DLRxQuali ty takes p lace.

When:UL RxQuality >= UL Quality HOThresholdhandov er caused by ULRxQuali ty takes p lace.

DL&UL Qual i ty HOThresholds are general lyset to 6.

UL Quality HO cant bem on itored in DT.

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Quality Handover

Handover was performed to a better qualitycell just after experiencing quality problems.


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EDGE Handover

Edge Handov er Exp:When:

DL RxLevel < Edge HO DLRX_LEV Thresholdhandov er caused by DLRxLevel takes p lace.

When:

UL RxLevel < Edge HO ULRX_LEV Thresholdhandov er caused by ULRxQuali ty takes p lace.

UL EDGE handover cant bem on itored in DT.

Handover was performed to the cell withhigher downlink Rxlev.


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Intracell Handover Based on Interference

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The Intra cel l Handoverfeature a ims to mainta ingood q ua li ty by pe r fo rminga handover to a newchannel wi th in th e samecel l wh en upl ink ordow nl ink in ter ference i sdetected.

Interference is defined bybad RxQual and h ighenou gh Rx LEV.

Intracel l HO also c an be

t r iggered by: Rate change betw een Full rate

and Half rate Handover be tween over la id and

under la id su bcel l . An example of intracell handover afterexperiencing quality problems.


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Handover Issues

What is Dragged Hand ov erPow er Contro l Effec tPing Pong Hando verMiss ing Neighb or Relat ionFake Neighbo rHandov er Fai lure


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Dragged Handover

There will be such cases that you will notice handover process takingplace a little late, which is called dragged handover.

Firs t th ing to check w i l l be handov ermargins be tween the ne ighbors . Ifmargins for level, qual i ty or po werbud get handovers are not se tcorrec t ly, If margins are too m uch ,handov er wi l l h appen la te, v iceversa. A Quality handover

should happen earlier

Dragged handover events of tenocc ur af te r a GSM serving c e l l loses

dom inance for a s igni f icant t imeperiod.

Dragged Handover often cause CallDrop or Handover Failure.


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Power Control Effect

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Power Control Effect sometimes

may mislead us, you might thinkthat handover is happening toolate between two neighbors.

When the call is continuing on atimeslot that belongs toTCHTRX, power control featurewill try to reduce output poweras much as possible until aquality problem occurs. Thatswhy you will see serving cellsignal level is less thanneighbors level. It looks lessbut in reality, the signal level onBCCH TRX is still higher thanneighbors broadcasting level.

Power control


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Missing Neighbor RelationIf a handoff is not performed to a neighbor cell that seems to be bestserver, there is a possibility of a missing neighbor relation. This will

happen with sudden appearance of strong cell in the neighbor list just after a handover.

The shot show s af tersecond handover in

the red box , a muchst rong er Serving Cellappears.

At th is t ime Neighbo raudi t should beperformed.


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Sometimes you will see a

good handover candidate inthe neighbor list buthandover will not take placeand call will drop.

Although that neighboring

cell with a very good signallevel appears to be aneighbor, in reality it is not.Just because the serving cellhas another neighbor withthe same BCCH, this cellappears in the list.

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Fake Neighbor Relation


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Handover Failure

Handover Failure: Handover attempt was failed and the call returned backto its all channel.

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Handover Failure

Target Cell is BCCH is 13

BSIC is 65Target channel is 900M RF hopping Channel. Half Rate MA list is 1, 17, 18, 19, 20, 21, 22, 23, 24 MAIO is 4, HSN is 31, TSC is 5. Channel mode is AMR(SV3)

The handover has notsuccessfully completed yet!

Handover Failure iscaused by T200 ExpiredAnother example: Excessive Number of Handover

Failure due to Hardware Problem


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Proposal of Handover Issue

Dragg ed Hand ov erPing Pong Hando verMissin g Neigh bo r Rela t ionHand ov er Failure


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Solutions of Handover Issues

Issue Proposal

Dragged Handover

Check if the parameter of handover, such as: PBGT, Quality, Interference, Edgehandover threshold, and P/N Value is set too high.Check if there is no dominant coverage. Referring to the solution of Low

Coverage. Check if the traffic volume of target cell at measuring time.

Ping-pong Handover

Check if there is hardware problem. Referring to hardware checking guide Check if there is no dominant coverage. Referring to the solution of Low

Coverage. Check if the parameter of handover, such as: PBGT, Quality, Interference, Edge

handover threshold, and P/N Value is set too low . Check if there is overlapping coverage area, which may also cause ping-pong

handover.

Missing Neighbor

Neighbor Audit. Check if there is neighbor missing according to data

configuration in OMC.

Handover Failure

Find out the cause of Handover failure form Um signaling flow from Layer2 andLayer3 Message.

Check if the HSR between source and target cell is low. If it is, find the rootcause of handover failure reasons by traffic statistic analysis.


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dt analysis - how to analyze handover in dt.ppt

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