2 drivetest analysis ver1

7/30/2019 2 DriveTest Analysis Ver1

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Drive Test Analysis

HUAWEI TECHNOLOGIES CO., LTD. All rights reserved

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Upon completion of this course, you will be

able to:

HUAWEI TECHNOLOGIES CO., LTD. All rights reserved Page 2

Of drive test data analysis

Identify the basic problems and cause

of the problems

Propose the solutions to solve thenetwork problems


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Chapter 1Chapter 1 Common procedure of drive test dataCommon procedure of drive test data

analysisanalysis


Chapter 2Chapter 2 Case study for drive test analysisCase study for drive test analysis

Chapter 3 Practice on drive test analysisChapter 3 Practice on drive test analysis


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Common procedure of DT data analyze

1. Check if the Drive test KPIs meet the requirement. If not, identify the problematic logfiles. Capture the figure and events (e.g. locations, time, identify problematic cells)

2. Check the RxLevel and RxQual distribution, check if they are related to the pointsthat miss the KPI requirement?

3. (If new site or cluster) Check the distribution of each BCCH (CGI), pay attention tothe crossed feeder.


4. Analyze the points that miss the KPIs point by point. (To make the analysis morecomprehensive , get more information from engineering parameters, BSC dataconfiguration, traffic statistic and BTS alarms)

5. Identify the possible causes of each problem points ,discuss with customers

4. Propose solutions and get approval from customers before execute the changerequest

4. Re- Drive Test to verify the problem after implemented the solutions


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Chapter 1Chapter 1 Common procedure of drive test dataCommon procedure of drive test data

analysisanalysis


Chapter 2Chapter 2 Case study for drive test analysisCase study for drive test analysis

Chapter 3 Practice on drive test analysisChapter 3 Practice on drive test analysis


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Coverage

Downlink RxLevel

Coverage of single cell

Coverage of whole network



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Coverage

EIRP(dBm)

L(dB)

Network Coverage is evaluated by:

RxLev = EIRP(dBm) L(dB)

Where:

EIRP = Effective Isotropic Radiated Power

L = Propagation Losses


RxLev(dBm)

Unexpected coverage

(overshooting)Good coverage

In urban area, Lower Antenna Height (=6 degree),

and Lower EIRP (


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Coverage(Network)

The picture shows the coverage of a city, which contains good and bad

coverage areas.

The distribution of downlink RxLev concentrates from -80 to -95 dBm.

Good Coverage


Bad Coverage


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Coverage Issues Coverage hole

Sudden Decrease on Signal Level

Line of Sight Lost Lack of Dominant Server

Coverage Overlapping



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Coverage Hole

RxQuality

RxLevel

Legend

Poor CoverageAreas

BadRxQuality

CallDrop


RxLevel(Serving Cell) is about (or less than) -95 dBm

RxLevel(Neighbours) are about (or less than) -95 dBm


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Sudden Decrease on Signal Level

RxLev(Serving Cell and

Neighbors) decrease in a

short time.

Check if there is big change

of testing environment, e.g.

check if the test was

performed on a highway


and that particular area was

a tunnel or not.

Signal level on the chart will

make a curve rather than

unstable changes.

This usually cause Ping

Pong Handovers

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Line of Sight Lost


Signal Strength of Serving cell make fast up and down dueto far away server being blocked by obstacles from theterrain. The other way, signal from the server lose line ofsight(LOS) to the mobile because of a hill of something.

RxQuality goesworse when thelevel drops downfast


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Lack of Dominant Server

Signal Level of more

than one cell (Serving

Cell and Neighbors) are

not high enough.

This might happen

because the MS is


borders and there is no

any best server to keep

the call.

Lack of Dominant Server

Causes too many

handovers


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Coverage Overlapping Signal Level of 34

cells are too closed to

each other.

This might point

overlapping cells.

This will cause quality


problems because of

frequency reuse and

frequent HO

Immediate action to

optimize cell coverage

should be taken by

power reductions,

downtilt or other

configuration changes.

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Overshooting

BTS

Serving

cell Other cell BBSIC 1Freq. A

MS is covered by the

serving cell, but is

outside the cell

BSC thinks that it is

neighbor cell A and

makes a handover to

cell A

The MS is not near cell

A so the assi ned TCH


Coverage spot(island effect)

Neighbour cell ABSIC 1Freq. A

for the handover is notused

Cell A will have unused

TCH (handover)

The call might bedropped because it

cannot make the

handover or bad quality


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Propose solutions for Coverage Issue

Solution of low coverage

Solution of no dominant cell ,overshooting and overlapping



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Solutions of Low Coverage

Possible solution can be listed as below:

New Site Proposal

Sector Addition

Site Configuration Change (Antenna Type, height, azimuth, tilt changes)

Loss or Attenuation Check ( Feeders, Connectors, Jumpers, etc..)

Proposal Remark How to do

New Site ProposalMost effective solution,

but the cost is hi hest

Using prediction tool(U-net) to identify the best

locations to ut new sites


Sector Addition Effective solutionbut only for Omni-Site

Using prediction tool(U-net) to identify therecommended azimuth of new sectors

Antenna

Height Difficult, high cost

Using prediction tool(U-net) to identify the

recommended height, type, azimuth or down tilt of

sector.

Type Difficult, high cost

Azimuth Easy to operate

DowntiltEasy to operate

Hardware

Feeders Only for troubleshooting

Referring to hardware checking guide

Connectors Only for troubleshooting

Jumpers Only for troubleshooting


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Solutions of overshooting or overlapping

Possible solution can be listed as below: Site Configuration Change (Antenna Type, height, azimuth, tilt changes)

Cell Configuration Change (Carrier Power Type, Static TRX Power Class, Fine Tuning

of Static TRX Power)

Proposal Remark How to do

Antenna

Height Difficult, high cost

Using prediction tool(U-net) to identify the

recommmended hei ht t e azimuth or

Type Difficult, high cost

Azimuth Easy to operate


downtilt of sector.

Downtilt Easy to operate

Parameter Output Power relatedEasy to operate, but with

risk of coverage reduction

Referring to Data Configuration Reference

Help


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What is crossed feeder issue (1)

The term crossed feeder is used to describe the problem that

arises when the feeders for two or more sectors in a site are

inadvertently connected incorrectly. For Example, consider a newcell site that has three sectors, A, B, and C:

Cross Feeder



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The crossed feeder problem would arise

if the feeder for sector A is connected to

sector C and vice versa. When this

happens, the sectors typically continue

to provide good coverage. However, the

network parameters for the two sectors

are also reversed. For example, the

parameters storing the sectors' BCCH


an s s o a acen sec ors wou e

swapped.

For example, suppose we run a drive test

through the area served by the cell

whose feeders are crossed display the

ServBCCH attribute on the Map while

the cell sectors are colored by BCCH.

This is what we might see:


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There are 3 types of crossed feeder:

Crossed transmit feeders

Crossed receive feeders


Crossed transmit and receive feeders


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The problems raised by crossed feeder

issue


Crossed Feeder SituationNormal Situation


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The problems raised by crossed feeder issue

Crossed feeder will raise many problems, such as:

A greater degree of interference

A poor uplink signal strength


A poor performance of handover


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How to detect crossed feeder issue by DT


Crossed transmit feeders will result in the swap of 2 or more sectors

BCCH frequency and TCHs. As the sectors are pointing in theincorrect direction, performance will suffer as the frequency plan has

been changed and a greater degree of interference will be present.


In DT, we will find that the handset receives the signal which shouldn't

have been received in the current cell.


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In the example shown above, point A is in the area of coverage of Cell

D3, but the handset at point A receives the stronger signal of Cell D2. Itindicates that TX feeders were crossed between Cell D3 and Cell D2.


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It is not easy to detect this fault by DT, because the BCCH frequencies will

appear exactly as they were designed. However, the statistics for the cell


Uplink signal strength would be very poor

Link balance would be larger than expected

Handover success rate would be very low


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The MR measurement is very useful in detecting this type of feeder

cross.

Uplink-and-Downlink Balance Measurement per TRX and TCH

Receive Level Measurement per TRX are the most useful statistics .


For example, if the uplink-and-downlink balance is always in level 10

or level 11, we can consider that there is something wrong in the

receive path of the site, crossed receive feeder is a possible problem.


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Downlink RxQual Issue

What is RxQual Issue

The problems raised by RxQual issue

How to detect quality issue by DT

Poor Quality Issue


a ua ty ue to gna trengt s a

Bad Quality due to Signal Strength FER is OK

Bad Quality due to C/A Interference

Bad Quality due to Time Dispersion

The solution to RxQual issue


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The problems raised by RxQual Issue

Bad RxQual may raise many problems, such as:

Difficulty in accessing the network

Dro ed calls due to bad ualit


Poor handover success rate

Low MOS value (poor speech quality)


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Bad Quality due to Signal Strength FER is Bad

As the signal strength dropsdown, the quality of the callbecomes worse being effectedby interference and/ or fading.Consequently the system

becomes weaker to handle theinterference.

Drop calls and ping ponghandovers usuall ha en in


such environments.

RxLev (Serving Cell andNeighbors) is not high enough(about less than -95dbm).

Maybe there areinterferences in this region forbad FER.

Bad RxLev

Bad RxQual

Bad FER


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Bad Quality due to Signal Strength FER is OK

This case is similar withthe previous except forFER. Signal strength isalso bad in this, but FER is

still fine.

FER is ok, it means thatthere is no obvious


n er erence n e area.

The coverage is usuallythe problem in thissituation.

Bad RxLev

Bad RxQual

Fine FER


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Site


Time dispersion is caused by the reflections. The MS uses all or most of thereceived power, instead of only the direct signal, there is a larger probability to

decode the information. So the RxQual will be very bad perhaps.

MS

Reflecting object


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The MS is near thecell, it is less than 1mile far away.

The RxQual is verybad for the bad C/R,

in which, R stands forreflected signal and C

stands for ori inal


signal. The TA is too high.It is because that TAstands for thereflected signal but

the original signal.


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The solution to RxQual issue (2)

RxQual Issue Solution

Bad Quality due to C/A

Interference

Avoided adjacent frequencies in the same cell

and preferably in neighboring cells as well.


Bad Quality due to Time

Dispersion

Move the site to be placed near the reflecting

object to prevent time dispersion. Another

efficient solution is to modify the antenna

arrangement, either in azimuth (horizontally) or

by tilt (vertically).


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Interference Issue Hardware Problem

TRX Problem

Feeder & Arrester Problem

Intra-Interference


Adjacent channel & Co-channel

Inter-modulation Interference

Inter-Interference

Other Equipment


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Co-Channel & Adjacent Channel Interference

As beside Figure show Station A~D,

Supposing the frequency N have

already allocated to cell A-3.so

fre uenc N can not be allocate to


A1A2B1B2B3C1C2C3D1D2D3; and frequency

N1 can not be allocated to cell A1

A2A3B1C2D1D2

(No ,hoping)


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C/I Problem

C/I Definition

C/I: Carrier signal /Interference signal

Optimize C/I method

Im rove Covera e


Decrease Interference


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The solution to Interference, C/I,BER issue (1)

Interference Issue Solution

Serious interference due to Co-channel orAdjacent channel

Adjust cell frequency or adjustcoverage

Serious interference due to feeder or Arrester Check whether the Feeder and


an enna g en ng, or rec

replacement its.


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The solution to Interference,C/I,BER issue (1)

BER Issue Solution

Worst BER due to poor coverageImprove coverage by adjustingantenna azimuth and downtilt oradd new sites

Ensure the interference source


and solution as interference

solution.Worst BER due to Transmission Checking transmission alarm in

M2000

Worst BER to TRX At first check equipment alarm inM2000,ensure which TRX is

problem


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Handover signaling on Um(TEMS Message)


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Handover signaling on Um(TEMS Message)

BCCH of Neighbors

to be measuredServing Cell:DL DTX is ONRxLev(sub) is -109+ 62 =--49dBmRxQual sub is 0

Tell MS how to access toTarget TCH Channel

Target cell Description

Target channel DescriptionChannel Type, Timeslot

TSCRF hoppingMAIO, HSN


The RxLev ofNeighbors

Inter cell SynchronousHandover

Speech version: EFR

Handover Complete Handover Success!!!

Only after SABM & UAin Layer2 Message,handover success!

The purpose of Handover Analysis


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The purpose of handover analysis in DT is

understand 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 nei hbor audit work is needed in this network.

The purpose of Handover Analysis


To make optimization of HSR, the most effective way is based on traffic

analysis, combining DT events, neighbor audit, and data configuration

audit together.

Page 53


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Handover Types

Different handover types by network topology

Different handover types by algorithm

PBGT handover

Qualit handover


Edge Handover

Intracell Handover

Other types of handover


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Handover Types(Algorithm)


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Handover Types(Algorithm)

In DT, the most common handover

types happens in following order of

priority

TA

OM Forced HO

Directed Retry

TA Emergency HO

Bad Qualit HO

Edge HO

La er HO


RxLevel

PBGT

OL&ULHO

Rapid Level Drop HO

Load HO

Interference HO

PBGT HO

Fast Moving MS HO

Overlay/Underly HO


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Quality Handover


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Quality Handover Exp:

When:

DL RxQuality >= DL Quality HO

Threshold

handover caused by DLRxQuality takes place.

When:

Quality Handover


x ua ty >= ua ty

Threshold

handover caused by ULRxQuality takes place.

DL&UL Quality HOThresholds are generally

set to 6.

UL Quality HO cant bemonitored in DT.

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

EDGE Handover


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Edge Handover Exp:

When:

DL RxLevel < Edge HO DL

RX_LEV Thresholdhandover caused by DLRxLevel takes place.


UL RxLevel < Edge HO UL

RX_LEV Threshold

handover caused by ULRxQuality takes place.

UL EDGE handover cant be

monitored in DT.

Handover was performed to the cell withhigher downlink Rxlev.


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Other types of handover


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Other types of handover are not easy to judge or not easy to encounter

in DT test, for example :

TA handover

Directed Retry

Load handover

yp


Fast Moving MS HO

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For analysis of different types of handover or handover caused byuplink, it is recommended by traffic analysis or single-user signaling

tracing.


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Handover Issues

What is

Dragged Handover

Power Control Effect


ng ong an over

Missing Neighbor Relation

Fake Neighbor

Handover Failure

Dragged Handover


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

First thing to check will be handovermargins between the neighbors. Ifmargins for level, quality or powerbudget handovers are not setcorrectly, If margins are too much,handover will happen late, vice


versa. A Quality handover

should happen earlier

Dragged handover events oftenoccur after a GSM serving cell losesdominance for a significant timeperiod.

Dragged Handover often cause CallDrop or Handover Failure.

Power Control Effect


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Power Control Effect sometimesmay 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 power

Power control


as much as possible until a

quality 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 than

neighbors broadcasting level.

Ping-pong Handover


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Ping-pong handovers occur when the MS is handed over from one cell toanother but is quickly handed back to the original cell.

The shot shows two ping-pong handovers displayed on

the map along with theServering CI attribute. Thefirst ping-pong handover isfrom cell 12424 to cell 12368


Ping-pong HO

from cell 12424 to cell 12366

and back. Changes in thevalue of the CI is shown belowthe route. It can be clearlyvisualized by lines to cellsdisplay.

For most cases, Ping-pong Handover is caused by no dominant cell. There wasa handover back to cell 12366 after the second ping-pong handover, but this wasoutside of the defined window. The change in dominance after the handover was9dB, which represents a much healthier handover.


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Handover Failure


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Handover Failure: Handover attempt was failed and the call returned back to its

all channel.

Target Cell is BCCH is 13

BSIC is 65


Handover Failure

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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

Dragged Handover

PingPong Handover

Missing Neighbor Relation


Solutions of Handover Issues


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Issue Proposal

Dragged Handover

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

handover 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 is high or has congestion at measuring time.

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.


Ping-pong Handover 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 NeighborAudit. 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 and

Layer3 Message.

Check if the HSR between source and target cell is low. If it is, find the root cause of

handover failure reasons by traffic statistic analysis.


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Thank You

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