2 drive test analysis ver1

Internal
Drive Test Analysis
HUAWEI TECHNOLOGIES CO., LTD. All rights reserved
www.huawei.com
Version1.0

Upon completion of this course, you will be
able to:
Understand the common procedure
Of drive test data analysis
Identify the basic problems and cause
of the problems
Propose the solutions to solve the
network problems
HUAWEI TECHNOLOGIES CO., LTD. All rights reserved Page 2

Chapter 1 Common procedure of drive test data
analysis
Chapter 2 Case study for drive test analysis
Chapter 3 Practice on drive test analysis

Common procedure of DT data analyze
1. Check if the Drive test KPIs meet the requirement. If not, identify the problematic log
files. 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 points
that miss the KPI requirement?
3. (If new site or cluster) Check the distribution of each BCCH (CGI), pay attention to
the crossed feeder.
4. Analyze the points that miss the KPIs point by . point. (
To make the analysis more
comprehensive , get more information from engineering parameters, BSC data
configuration, 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 change
request
4. Re- Drive Test to verify the problem after implemented the solutions

Chapter 1 Common procedure of drive test data
analysis
Chapter 2 Case study for drive test analysis
Chapter 3 Practice on drive test analysis

Coverage
• Downlink RxLevel
• Coverage of single cell
• Coverage of whole network

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
Good coverage (overshooting)
In urban area, Lower Antenna Height (=25m), Greater downtilt (=6 degree),
and Lower EIRP (=41 dBm) are used to control overshooting interference.

Coverage(one cell)
The following example shows the
downlink RxLevel(Dedicated Mode)
decreases when MS is driving away
from BTS.
The RxLevel decrease faster when
Antenna Downtilt increase.
Downtilt: 0 drgree
Downtilt: 8 drgree
Variation
due to
shadowing
Global
means
RxLevel
Variation
s due to
Rayleigh
fading

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

Coverage Issues
• Coverage hole
• Sudden Decrease on Signal Level
• Line of Sight Lost
• Lack of Dominant Server
• Coverage Overlapping
• Overshooting

Coverage Hole
Legend
RxLevel
RxQuality
Poor Coverage
Areas
Bad
RxQuality
Call
Drop
RxLevel(Serving Cell) is about (or less than) -95 dBm
RxLevel(Neighbours) are about (or less than) -95 dBm

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
Page 12

Line of Sight Lost
Signal Strength of Serving cell make fast up and down due
to far away server being blocked by obstacles from the
terrain. The other way, signal from the server lose line of
sight(LOS) to the mobile because of a hill of something.
RxQuality goes
worse when the
level drops down
fast

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
located on the cell
borders and there is no
any best server to keep
the call.
Lack of Dominant Server
Causes too many
handovers

Coverage Overlapping
Signal Level of 3–4
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.
Page 15

Overshooting
Serving
BTS
cell
Other cell B
BSIC 1
Freq. 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 assigned TCH
Coverage spot
(island effect)
Neighbour cell A
BSIC 1
Freq. A
for the handover is not
used
Cell A will have unused
TCH (handover)
The call might be
dropped because it
cannot make the
handover or bad quality

Propose solutions for Coverage Issue
Solution of low coverage
Solution of no dominant cell ,overshooting and overlapping

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 Proposal
Most effective solution,
but the cost is highest
Using prediction tool(U-net) to identify the best
locations to put new sites
Sector Addition
Effective solution
but only for Omni-Site
Using prediction tool(U-net) to identify the
recommended azimuth of new sectors
Antenna
Height Difficult, high cost
recommended height, type, azimuth or down tilt of
sector.
Type Difficult, high cost
Azimuth Easy to operate
Downtilt Easy to operate
Hardware
Feeders Only for troubleshooting
Referring to hardware checking guide
Connectors Only for troubleshooting
Jumpers Only for troubleshooting

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
recommmended height, type, azimuth or
Type Difficult, high cost
Azimuth Easy to operate
downtilt of sector.
Downtilt Easy to operate
Parameter Output Power related
Easy to operate, but with
risk of coverage reduction
Referring to Data Configuration Reference
Help

Cross Feeder
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 new
cell site that has three sectors, A, B, and C:

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
and lists of adjacent sectors would be
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:

There are 3 types of crossed feeder:
Crossed transmit feeders
Crossed receive feeders
Crossed transmit and receive feeders

The problems raised by crossed feeder
issue
Crossed Normal Situation Feeder Situation

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

How to detect crossed feeder issue by DT
Crossed transmit feeders will result in the swap of 2 or more sectors
BCCH frequency and TCH’s. As the sectors are pointing in the
incorrect 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.

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. It
indicates that TX feeders were crossed between Cell D3 and Cell D2.

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
would help us to detect the fault:
Uplink signal strength would be very poor
Link balance would be larger than expected
Handover success rate would be very low

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.

Crossed transmit and receive feeder
The symptom is similar with the fault “crossed transmit feeder”, and we can
detect the fault by DT easily .

Poor Quality Issue
Downlink RxQual Issue
What is RxQual Issue
The problems raised by RxQual issue
How to detect quality issue by DT
Bad Quality due to Signal Strength – FER is Bad
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

What is RxQuality Issue
Bad RxQual is one of the biggest problems in a Network. The RxQual
that a network operator can offer to customers mostly depends on the
RxLevel and the interference of the network.
There are two types of RxQual problems, uplink RxQual and downlink
RxQuality. We can only detect downlink RxQual problem by DT,
however, if the downlink RxQual is bad in one cell, there is a risk that
there would be problems on the uplink as well.

What is RxQual Issue
Bad
RxQua
lity
Good
RxQua
lity
RxQual is divided into eight levels which are from 0 to 7, the level 0 is the
best and the level 7 is the worst.

The problems raised by RxQual Issue
Bad RxQual may raise many problems, such as:
Difficulty in accessing the network
Dropped calls due to bad quality
Poor handover success rate
Low MOS value (poor speech quality)

Bad Quality due to Signal Strength – FER is Bad
As the signal strength drops
down, the quality of the call
becomes worse being effected
by interference and/ or fading.
Consequently the system
becomes weaker to handle the
interference.
Drop calls and ping pong
handovers usually happen in
such environments.
RxLev (Serving Cell and
Neighbors) is not high enough
(about less than -95dbm).
Maybe there are
interferences in this region for
bad FER.
Bad RxLev
Bad RxQual
Bad FER

Bad Quality due to Signal Strength – FER is OK
This case is similar with
the previous except for
FER. Signal strength is
also bad in this, but FER is
still fine.
FER is ok, it means that
there is no obvious
interference in the area.
The coverage is usually
the problem in this
situation.
Bad RxLev
Bad RxQual
Fine FER

Bad Quality due to C/A Interference
There is adjacent channel
interference in this case and
the RxQual is not good.
Bad Quality due to Adjacent
Interference.
Adjacent BCCH between
best server and best neighbor.

Site
MS
Time dispersion is caused by the reflections. The MS uses all or most of the
received power, instead of only the direct signal, there is a larger probability to
decode the information. So the RxQual will be very bad perhaps.
Reflecting object

The MS is near the
cell, it is less than 1
mile far away.
The RxQual is very
bad for the bad C/R,
in which, R stands for
reflected signal and C
stands for original
signal.
The TA is too high.
It is because that TA
stands for the
reflected signal but
the original signal.

The solution to RxQual issue (1)
RxQual Issue Solution
Bad Quality due to Signal Strength – FER is
Bad
Find out the interference source
(e.g. frequency planning) or /and
adjust the azimuth or down tilt of
the antenna or /and adjust the
power of the transmitter(s) to
improve coverage
Bad Quality due to Signal Strength – FER is
OK
There is no obvious interference in
this situation. Adjust the azimuth or
down tilt of the antenna or /and
adjust the power of the
transmitter(s) to improve coverage

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).

Interference Issue
Hardware Problem
TRX Problem
Feeder Arrester Problem
Intra-Interference
Adjacent channel Co-channel
Inter-modulation Interference
Inter-Interference
Other Equipment

Co-Channel Adjacent Channel Interference
As beside Figure show Station A~D,
Supposing the frequency N have
already allocated to cell A-3.so
frequency N can not be allocate to
A1、A2、B1、B2、B3、C1、C2、
C3、D1、D2、D3; and frequency
N±1 can not be allocated to cell A1、
A2、A3、B1、C2、D1、D2
(No ,hoping)

Co-Channel Adjacent Channel Interference
As below, From the neighbor
list ,BCCH 73 interfered
BCCH 72,it is adjacent
interference. When the co
channel or adjacent channel
happen
It will bring the strong
interference. The typical
phenomena:
High Rxlev
Worst Rxqual

C/I Problem
C/I Definition
C/I: Carrier signal /Interference signal
Optimize C/I method
Improve Coverage
Decrease Interference

C/I Problem due to poor coverage
RxLevel(Serving Cell) is about (or less than) -95 dBm;
RxLevel(Neighbours Cell) is about (or less than) -95 dBm;
Result: Worst C/I due to poor coverage.

C/I Problem due to Interference (frequency)
RxLevel (Serving Cell) is about -70dBm; (strong)
RxLevel (Neighbors Cell) is about -65 to -80 dBm
Result: Worst C/I due to interference ( no dominant cell)

The solution to Interference, C/I,BER issue (1)
Interference Issue Solution
Serious interference due to Co-channel or
Adjacent channel
Adjust cell frequency or adjust
coverage
Serious interference due to feeder or Arrester
Problem
Check whether the Feeder and
antenna tightening, or direct
replacement its.

The solution to Interference,C/I,BER issue (1)
C/I Issue Solution
Worst C/I due to poor coverage
Improve coverage by adjusting
antenna azimuth and downtilt or
add new sites
Worst C/I to interference Ensure the interference source
and solution as interference
solution.

The solution to Interference,C/I,BER issue (1)
BER Issue Solution
Worst BER due to poor coverage
Improve coverage by adjusting
antenna azimuth and downtilt or
add new sites
Worst BER due to interference 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 in
M2000,ensure which TRX is
problem

Handover Issues
What is…
Handover procedure in network?
Handover Um signaling flow?
Purpose of Handover Analysis in DT?

Handover Procedure
Neighbor Cell_1
Serving Cell
Uplink MR (Measured by BTS)
•RXLEV Uplink
•RXQUAL Uplink
•TA
•Current BTS TX power
MS in dedicated mode
will continuously perform
Neighbor Cell2
Neighbor Cell2
Page 51
Downlink MR (Measured by MS)
•Downlink RXLEV(Sever)
•Downlink RXQUAL(Sever)
•RXLEV_NCELL(n) on the 6 best
neighboring cells (+BSIC)
BSC
measurements on serving
and neighbor cells.
Measurement Reports
are sent to BSC and used
in the handover algorithm.
Serving BSC decides
whether a handover is
necessary and send HO
command
Serving Cell

Handover signaling on Um(TEMS Message)
Tell MS how to access to
Target TCH Channel
Target cell Description
Target channel Description
Channel Type, Timeslot
TSC
RF hopping
MAIO, HSN
BCCH of Neighbors
to beS merevainsugr Cedell:
DL DTX is ON
RxLev(sub) is -109+ 62 =--49dBm
RxQual (sub) is 0
Handover Complete Handover Success!!!
The RxLev of
Neighbors
Inter cell Synchronous
Handover
Speech version: EFR
Only after SABM UA
in Layer2 Message,
handover success!

The purpose of Handover Analysis
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 neighbor audit work is needed in this network.
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

Handover Types
Different handover types by network topology
Different handover types by algorithm
PBGT handover
Quality handover
Edge Handover
Intracell Handover
Other types of handover

Handover Types(Network Topology)
Operator
MSC MSC
BSC BSC BSC BSC
BTS BTS BTS BTS BTS BTS
CELL CELL CELL CELL
Synchronous
Case 2
Case1 Intra cell HO
Case2 Synchronous Inter cell HO
Case3 Asynchronous Inter cell HO
Case4 Inter BSC HO
Case5 Inter MSC HO
Page 55
CELL CELL CELL CELL
Case 1
Asynchronous
Case 3
Case 4 Case 5

Handover Types(Algorithm)
In DT, the most common handover
types happens in following order of
priority
TA
RxQuality
OM Forced HO
Directed Retry
TA Emergency HO
Bad Quality HO
Edge HO
Layer HO
RxLevel
PBGT
OLUL
Interference HO
HO
Rapid Level Drop HO
Load HO
PBGT HO
Fast Moving MS HO
Overlay/Underly HO

PBGT Handover
PBGT HO Exp:
When:
RXLEV_NCELL(n) – (RXLEVEL+
PWR_DIFF) HO_MARGIN
MS is handed over to the
neighboring cell .
HO_MARGIN is usually set to 3 to
6 dB.
Serving
Cell
Target
Cell
HO_MARGIN 0
RXLEV_NCELL(n)
RX LEVEL + PWR_DIFF
PBGT HO Power-budget
HO_MARGIN could be increased
to reduce number of handovers.
HO_MARGIN should be
decreased if faster handover
decision is wanted.
PBGT Handover is considered as
most healthy handover in a
network.
Page 57
Distance
A typical PBGT HO

Quality Handover
Quality Handover Exp:
When:
DL RxQuality = DL Quality HO
Threshold
handover caused by DL
RxQuality takes place.
When:
UL RxQuality = UL Quality HO
Threshold
handover caused by UL
DLUL Quality HO
Thresholds are generally
set to 6.
UL Quality HO can’t be
monitored in DT.
Handover was performed to a better quality
cell just after experiencing quality problems.
Page 58

EDGE Handover
Edge Handover Exp:
When:
DL RxLevel Edge HO DL
RX_LEV Threshold
handover caused by DL
RxLevel takes place.
When:
UL RxLevel Edge HO UL
RX_LEV Threshold
handover caused by UL
UL EDGE handover can’t be
monitored in DT.
Handover was performed to the cell with
higher downlink Rxlev.

Intracell Handover Based on Interference
The Intra–cell Handover
feature aims to maintain
good quality by performing
a handover to a new
channel within the same
cell when uplink or
downlink interference is
detected.
Interference is defined by
bad RxQual and high
enough RxLEV.
Intracell HO also can be
triggered by:
• Rate change between Full rate
and Half rate
• Handover between overlaid and
underlaid subcell. An example of intracell handover after
experiencing quality problems.

Other types of handover
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
Rapid Level Drop HO
Fast Moving MS HO
For analysis of different types of handover or handover caused by
uplink, it is recommended by traffic analysis or single-user signaling
tracing.
Page 61

Handover Issues
What is …
Dragged Handover
Power Control Effect
Ping–Pong Handover
Missing Neighbor Relation
Fake Neighbor
Handover Failure

Dragged Handover
There will be such cases that you will notice handover process taking
place a little late, which is called dragged handover.
First thing to check will be handover
margins between the neighbors. If
margins for level, quality or power
budget handovers are not set
correctly, If margins are too much,
handover will happen late, vice
A Quality handover
versa. should happen earlier
Dragged handover events often
occur after a GSM serving cell loses
dominance for a significant time
period.
Dragged Handover often cause Call
Drop or Handover Failure.

Power Control Effect
Power Control Effect sometimes
may mislead us, you might think
that handover is happening too
late between two neighbors.
When the call is continuing on a
timeslot that belongs to
TCHTRX, power control feature
will try to reduce output power
as much as possible until a
Power control
quality problem occurs. That’s
why you will see serving cell
signal level is less than
neighbor’s level. It looks less
but in reality, the signal level on
BCCH TRX is still higher than
neighbors broadcasting level.

Ping-pong Handover
Ping-pong handovers occur when the MS is handed over from one cell to
another but is quickly handed back to the original cell.
The shot shows two ping-pong
handovers displayed on
the map along with the
Servering CI attribute. The
first ping-pong handover is
from cell 12424 to cell 12368
and back and the second is
Ping-pong HO
from cell 12424 to cell 12366
and back. Changes in the
value of the CI is shown below
the route. It can be clearly
visualized by lines to cells
display.
For most cases, Ping-pong Handover is caused by no dominant cell. There was
a handover back to cell 12366 after the second ping-pong handover, but this was
outside of the defined window. The change in dominance after the handover was
9dB, which represents a much healthier handover.

If a handoff is not performed to a neighbor cell that seems to be best
server, 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 shows after
second handover in
the red box, a much
stronger Serving Cell
appears. ( suspect
there might be missing
neighbor in the 1st HO
attempt)
At this time Neighbor
audit should be
performed.

Fake Neighbor Relation
Sometimes you will see a good
handover candidate in the
neighbor list but handover will
not take place and call will drop.
Although that overshooting cell
with a very good signal level
appears in neighbor list, in reality
it is not. Just because the
serving cell has another
neighbor cell use same with the
same BCCHBSIC ,so the
measurement of the
overshooting cell appears in the
list.
Page 67

Handover Failure
Handover Failure: Handover attempt was failed and the call returned back to its
all channel.
Target Cell is
BCCH is 13
BSIC is 65
Target channel is
Handover Failure
Page 68
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 The 5.
handover has not
Channel mode is successfully AMR(SV3)
completed yet!
Handover Failure is
caused Another example: Excessive Nu bmy bTe20r 0o Ef xHpairneddover
Failure due to Hardware Problem

Proposal of Handover Issue
Dragged Handover
Ping–Pong Handover
Handover Failure

Solutions of Handover Issues
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.
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 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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