WCDMA RF optimization

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Copyright © 2007 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Radio
Frequency Optimization

Foreword
 RF (Radio Frequency) optimization is the most important
step to ensure the quality of the network.
 RF optimization will solve network problems related to
neighbor cell list, coverage and interference.

Objectives
 Upon completion of this course, you will be able to:

Know the steps of RF optimization

Know how to solve the RF problems caused by neighbor cell
list, poor coverage and interference

Contents
 RF Optimization Workflow
 Typical Problems Analysis in RF optimization

RF Optimization Workflow
Start
Preparation:
 Set the optimization target
 Divide the optimization cluster
 Draw out the test route line
 Prepare the DT tools
Data Collection:
 DT test
 Indoor DT test
 RNC configuration data
The DT result is satisfied
with optimization target?
RF optimization
finished
Y
Problem Analysis
 neighbor cell list
 poor coverage
 pilot pollution
 handover
 interference
N
Adjustment:
 Engineering parameters adjust
 Neighbor cell list adjust

Target Item
Reference
Value
Remark
Coverage Probability ≥95%
CPICH Ec/Io ≥ -12dB & RSCP ≥
-95dBm
CPICH Ec/Io ≥ -12dB ≥95% Scanner result
CPICH RSCP ≥
-95dBm
≥95% Scanner result
SHO Percentage 30%-40%
Pilot pollution
Percentage
≤5%
 Set RF optimization target, for example:

 RF optimization clusters division

Cluster is the area for one time drive test

One cluster should contains 15 to 25 sites

Cluster division should consider the following factor, such
as:

Terrain

Traffic

Routeline

 Preparation for DT (drive test)

Hardware

Testphone

Scanner

GPS

Software

Drivetestsoftware, forexample, GENEXProbe

Drivetestpostprocesssoftware, forexample, GENEX
Assistant

Contents
 Preparation of RF Optimization

Contents

RF case related to neighborcell list

RF case related to bad coverage

RF case related to interference

Case 1
 Description

In DT, call drop happened

Check the signaling trace at UE side
Call Drop
After call drop, begin
to read
system information

 Data analysis

Check cell information from UE active set and cell information
from scanner at call drop points.
From ScannerFrom UE
No SC
170 cell!!
Why?
Case 1

 Data analysis

Checking monitor set

Missing neighbor cell

Delayed handover
Check monitor set for
the scramble measured
by scanner
SC 170 is not in monitor set
Case 1

 Data analysis

Check the latest measurement controlmeasurement control
Search for the latest intra-
frequency measurement control
Call drop
point
Case 1

Measurement ID is 1. It is Intra-
frequency measurement control
Check the list of intra-frequency
neighbor cell in measurement
control and no SC 170
The primary scramble
of the cell is 6
Case 1

 Solution

Add neighbor cells in neighbor cell list
 Summary

In the beginning stage of network, it is very common that
missing neighbor cell cased cause call drop.

Analysis with signaling procedure is the common way to find
and solve the problem

Some problems can be avoided if the Combined Neighbor Cell
Algorithm is switched on.
Case 1

 Phenomenon description

In DT, call drop
happened at cell A
Case 2
Cell B (PSC277)
Cell A
(PSC58)

 Phenomenon description

In Cell A, UE keeps reporting PSC 277 1A event.

RNC received this event and send Active Set Update to UE
according to the signaling trace record

UE send Active Set Update complete to RNC

Then, RNC send Active Set Update to delete PSC 277 from
active set

Finally call drop happened due to RL failure
Case 2

 Problem Analysis

From the signaling trace of DT, it looks like the handover is
complete successfully.

But, according to the signaling trace from CDT, the handover
failed actually.
Case 2


Signaling trace from CDT shows:
Case 2
UE NodeB RNC
Measurement control (1A Event for PSC 227)
Radio Link Setup
Radio Link Setup Response
Active set update
Active set update complete
Radio Link Failure

Cell B (PSC277)
Cell A (PSC58)
Cell C (PSC277)

After checking the
neighbor cell list, the
following problem is
found

Cell C has the same
PSC as Cell B
Case 2

Cell ID PSC
A 58
B 277
C 277
Cell ID NCell ID
A C
C A
Cell B
(PSC277)
Missing
configuring
NCell
Mistake for
configuring
NCell
Case 2

The neighbor cell list shows
Cell C
(PSC277)
Cell A
(PSC58)


Based on the analysis above, the new NodeB is not the one of
cell B, but the one of cell C

Even the cell C prepared resource for UE according to the RNC
command of “Radio Link Setup”, it can not find the UE uplink
signal.

That does why the “Radio Link Failure” is sent by NodeB
Case 2

 Solution

Change the wrong neighbor cell list
Case 2

 Summary

Phenomenon for wrong neighbor cell list

FromDT, radiolinkbranchisaddedintoactiveset, then
deletedfromactivesetrepeatedly.

SHOsuccessrateislow

Radiolinkfailureislowinthewrongneighborcell, for
example, cellCincase2

Calldropishighinthecellwithwrongneighborcell, for
example, cellAincase2
Case 2

 Summary

About SHO event, UE will only report PSC to RNC in
Measurement Report

RNC will find the right cell according to the neighbor cell list
between cell ID and PSC

This problem is mainly happened in dense urban when is PSC
is reused a lot
Case 2

 Description
Case 3
14603 (Frequency A)
14602 (Frequency B) 14031 (Frequency B)
Inter-RAT handover based on coverage
14605 (Frequency C)
Inter-frequency handover based on capacity
Call drop rate high

 Description

UE is in Cell 14602 with frequency B

When 14602 is in high load level, UE will be handed over to
14603 with another frequency A

When 14603 is in high load level, UE will be handed over to
14605 with frequency C

Because frequency A and C are not used continuously at this
area, UE has to be handed over to Cell 14031 with frequency
B

14603 and 14605 can share the load level, but the call drop
rate in 14603 is very high.
Case 3

 Analysis

Because it’s difficult to do drive test for collecting signaling
trace, the IOS (Information of Subscriber) trace is used.

Based on the analysis for the call dropped UE, there is one
thing is common:

Beforecalldropin24603, allUEsinitiatedcompressmode,
andsendMeasurementReporttoRNCperiodically, but
handoverisnottriggered.
Case 3

 Analysis
Case 3
2D Event
Compress
mode
Inter-frequency
measurement
control
Inter-frequency
Measurement
report

 Analysis

Open “Inter-frequency Measurement Control”, the Cell 14605
with frequency C is put in the first place

And in the following measurement report, UE only report Cell
14605

But the cell 14605 cell signal level is lower than -90dBm, which
can not trigger handover, till call drop.
Case 3

 Analysis

Measurement Control
Case 3
Cell 14605 with
Frequency C
Cell 14031 with
Frequency B

 Analysis

Measurement Report
Case 3
Cell 14605 with
Frequency C
Cell 14605 CPICH
& Ec/Io

 Question

Why the handover can not be triggered?

Since the network give UE the information of cell 14605 and
cell 14031, Why UE only report cell 14605?

Did UE measure cell 14301, just not report it?

Or, UE never measure cell 14301, just 14605?
Case 3

 Analysis

UE report cell 14605 CPICH RSCP is 19, which is -96dBm.

After checking the RNC configuration file, this CPICH RSCP
level can not trigger inter-frequency handover

Actually, because cell 14605 and 14603 are in one sector, their
signal level should be same.
Case 3

 Analysis

If UE can report cell 14031, the handover may be triggered

After analyze the compress mode principle, it is found that UE
can only monitor 1 WCDMA frequency in the gap of compress
mode.
Case 3

 Analysis

Because UE can not measure cell 14301 with frequency B,
only monitor cell 14605 with frequency C, and meanwhile cell
14605 and 14603 signal level are same, the call dropped due
to the poor signal of 14605 and 14603

How to make UE monitor cell 14301 with frequency B instead
of 14605 with frequency C?
Case 3

 Solution

Delete the neighbor relation from 14603 with frequency A to

Add the neighbor relation from 14602 with frequency B to
Case 3

 Solution
Case 3
14603 (Frequency A)
14602 (Frequency B) 14031 (Frequency B)
14605 (Frequency C)
Inter-RAT handover based on coverage
Inter-frequency handover based on capacity

 Summary

Do not configure two different frequency neighbor cells in
WCDMA system
Case 3

Contents

RF case related to neighbor cell list

RF case related to bad coverage

RF case related to interference

 Description

In drive test for RF optimization, call drop happened in the
circle area
Case 1

 Analysis

After analyze the signal level of this area, the call drop is
caused by discontinuous coverage of the cell with PSC 442
Case 1
Problem Zone

 Analysis

After checking the RF
transmission
environment, the signal
is blocked by the glass
wall
Case 1
The Wall
Call drop
Antenna

 Solution

Solution 1: Decrease the downtilt to increase the signal level

Maybetheproblemareawillbecomebetter, butduetothe
wall, thisproblemmaystillexistnearby.

Solution 2:Increase the antenna height

Aftercheckingtheinstallationcondition, it’sveryhardto
increasetheheight

Evenincreasedtheheight, theproblemmaystillexistdueto
thewall.
Case 1

 Solution

Solution 3:

Movetheantennapositionifpossible, andthemain
directionantennaisparallelwiththesideofthewall
Case 1
Original
Position
New
Position
Wall

Movetheantennapositiontorightabout15meters
consideringtheinstallationcondition

 Solution

Solution 3:

Abouttheantennadowntilt, twostrategiesaredesigned.

First, 10degrees
Case 1
10 Degree

 Solution

Solution 3:

Second, 5degrees
Case 1
5 Degree

 Summary

Before RF adjustment, site survey should be done.

Find the problem and the reason, design several strategies for
the adjustment

One time adjustment, and check the performance at the same
time. Adjustment and performance checking should be done at
the same to improve the work efficiency.
Case 1

 Description

In drive test for RF optimization, the area Ec/Io is bad
Case 2

 Analysis

Checking the cell distribution at this area
Case 2
PSC185
PSC184PSC186

 Analysis

One site with 3 cells, PSC184, 185 and 186 cover this area

Two cells, PSC 184 and 185, are separated to two sectors to
cover different direction
Case 2

 Analysis

The area is covered by different cell – PSC 184 and 185

No dominant cell – PSC 184 and 185 is the best cell crossly in
this area
Case 2

 Solution

Change the sector PSC, or combine some sector

Previously, 3 cells

PSC184: sector1&sector3


PSC186: sector5

After adjustment, 2 cells:



Deletesector2
Case 2

 After adjustment, the drive test for PSC 184 and 185
Case 2

 The comparison result for scanner Ec/Io
Case 2

 The comparison result for UE Ec/Io
Case 2

 Summary

In order to get better coverage performance at the place with
complicated transmission environment, splitter is used to
separate one cell into different sectors to cover different area.

In this case, the sector should be designed reasonably to
control the interference
Case 2

 Description

In drive test for RF optimization, bad Ec/Io is found on the
bridge
Case 3

 Analysis

Check the RSCP value of scanner, the result shows the RSCP
value is good.
Case 3

Based on this, pilot pollution need be considered in this area.

Check the top N pilot RSCP and Ec/Io in scanner result

 Analysis

From the DT result, it shows the RSCP value is strong, but the
Ec/Io is bad.

And the signal level of different cell are very similar.

Find the cells which cover this area
Case 3

 Analysis
Case 3
Site 1 Cell A
Site 5 Cell C
Site 2 Cell C Site 3 Cell C
Site 4 Cell C

 Analysis

On the bridge, the signal from different cell can cover this area
due to reflection of the river and no building.

From DT, following cell cover this area:

Site1cellA

Site2cellC

Site3cellC

Site4cellC

Site5cellC
Case 3

 Analysis

Need to find the
best cell

Check the map,
the site 6 is very
near to the
bridge.
Case 3
Site 1 Cell A
Site 5 Cell C
Site 4 Cell C
Site 6

 Analysis

After checking site 6 RF
environment, it is difficult to
increase the antenna height or
move site 6 position to avoid
the blocking caused by the
building
Case 3
The residence buildings
are much higher than
antenna, which block
the signal of site 6

 Analysis

Then, site 1 cell
A can be the
best cell to
cover this area
Case 3
Site 1 Cell A
Site 5 Cell C
Site 4 Cell C

 Analysis

Then, try to
increase the
signal of site 1
cell A, and
decrease other
cells

To confirm this,
DT for site 1 cell
A needs to be
done
Case 3
Site 1 Cell A
Site 5 Cell C
Site 4 Cell C

 Solution

Increase the signal of site 1 cell A

Changetheantennadowntiltfrom10to7

IncreaseCPICHTxpower1.5dBhigher

Decrease other cell signal – change the antenna downtilt

From7to10forsite2cellC

From5to8forSite3cellC


Case 3

 Confirmation

After the modification, the DT shows the pilot pollution area
as below
Case 3

 Confirmation

The Ec/Io comparison
Case 3
After
Before

 Summary

To solve the pilot pollution, the following issues has be
considered

Findthereasoncausedpilotpollution
– Due to no strong signal
– Due to too much strong signal

Aftertheadjustment, theDThastobedoneatthiscluster
toconfirmthatnonewproblemappeared
Case 3

 Description

In DT, video call quality is decreased at the problem
area. Also, the PS call drop happened several times
Case 4
Problem Area
3G Antenna
2G Antenna

 Analysis
 RSCP distribution in DT
Case 4
Problem
area

 Analysis

Ec/Io distribution in DT
Case 4
Problem
area
Problem
area

 Analysis

Checking the RF environment, the antenna is installed on 10-
meter platform

2G and 3G antenna are installed at one platform, but 3G
antenna is a little bit inner than 2G antenna.

After finishing DT in 2G, signal level is very stable
Case 4

 Analysis

If 3G and 2G antenna are installed at the same place, the
problem may be solved.
Case 4
Problem Area
3G Antenna
2G Antenna

The short wall of this platform may block the signal of 3G

Since 2G antenna is near to the border, the wall influence 2G little
Wall

 Solution

Solution 1

Increasetheantennaheightcansolvethisproblem

Solution 2

Movetheinstallationplaceneartotheborder

Solution 3

3Gand2Gusethesameplace
Case 4

Case 4
 Solution

Solution 3 is adopted

Case 4
 Question

Do you have other methods?

Case 4
 Summary

Sharing the same installation place for 3G and 2G is
very common, and several strategies can solve the
problem

In this situation, 3G and 2G can share the feeder
system, or can only share the installation platform.

Considering the factors of the installation and related
resource, a easiest and simplest method should be
adopted

Case 5
 Description

In DT, call drop happened a lot in the area

Case 5
 Description

Check the DT information, SC304 is in active set with
the signal level – RSCP -76dBm and Ec/Io -18
 Analysis

Consider the pilot pollution
 Butonly1cellinactivesetand1Cellinmonitor
set

Consider the missing neighbor cell

Butthecellinmonitorsethasverygoodquality–
RSCP-65dBmandEc/Io-6

Case 5
 Analysis

Check the signaling trace at UE side
Before call drop, UE
sends measurement
report to RNC with 1A
event for cell 298

Case 5
 Analysis

Check the signaling trace at RNC side
RNC sent Active Set Update to
UE, but no response. Then, RNC
send release RRC connection –
Call Drop

Case 5
 Analysis

Based on the DT and signaling trace, this call drop
can be take as handover failure

For example
cel l 56 vs cel l 041
- 30
- 20
- 10
0
t i me
EcNo
cel l 56
cel l 041

Case 5
 Analysis

Around the corner, the original cell 304 signal level
drop very quickly because of the building
shadowing, and the neighbor cell 298 increase
very quickly.

After UE sent measurement report to RNC, cell
304 has become very bad when RNC sent active
set update.

Case 5
 Adjustment

Since cell 298 has better coverage at this area,
handover can happen earlier

Decrease the coverage performance at this area
– Increase the downtilt from 5 to 9
– Adjust the direction from 0 to 310
 Increase the coverage performance at this area
– Decrease the downtilt from 5 to 4
– Adjust the direction from 300 to 270

Case 5
 Adjustment

Result after adjustment
Handover
area
Handover
areaBefore After

Case 5
 Adjustment

Comparison of Ec/Io of UE
Before After

Case 5
 Summary

Confirm the corner effect by analyzing signaling
trace at UE and RNC

About corner effect, Taking the method make the
handover happen earlier, such as RF optimization

Other method can also adopted

Modify 1A event

Modify CIO (Cell Individual Offset)

RNCI
d
CellId CellName Time(As hour)
VS.MaxRTW
P
VS.MeanRTW
P
VS.MinRTWP
1
6250
1
KwongYu1
2005-5-16
17:00
-74.5 -102.34 -105.3
1
6250
2
KwongYu2
2006-5-16
17:00
-74.3 -94.89 -105.5
1
6250
3
KwongYu3
2006-5-16
17:00
-82 -101.6 -105.4
Case 1
 Description
 From traffic statistic, the following RTWP problem is found

Case 1
 Analysis

Connect to the problem NodeB, and monitor the RTWP

Cell 62501 RTWP

Case 1
 Analysis

Cell 62502 RTWP

Case 1
 Analysis

Cell 62503 RTWP

Case 1
 Analysis

The main diversity antenna is interfered seriously

Can not find any relation between interference and time,
and the interference appears randomly

Check the neighbor site, no interference
 Deduction

Inter-modulation cause the interference, could be

Inter-modulationcausedbybadconnectors

Inter-modulationbyGSM

Case 1
 Analysis

Check the RF environment

Case 1
 Analysis

Check the RF environment

No blocking or any reflection due to the glass wall

The site RF condition is very good

Case 1
 Analysis

2G and 3G share the feeder system

Case 1
 Analysis

Check 2G frequency planning

Sector 1 – 544 with hopping frequency 821
– 544 – 1811.6MHz & 821 – 1867MHz

– 538 – 1808.6MHz & 821 – 1867MHz

– 858 – 1874.4MHz & 821 – 1867MHz

Case 1
 Analysis

Calculate the third order intermodulation

Cell 1 – 1922.4MHz

Cell 2 – 1925.4MHz

Cell 3 – 1859.6MHz

Check cell 2 uplink interference

The interval of 2 interference is
821-544

Case 1
 Analysis

Conclusion

The third intermodulation of cell 1 and cell 2 is just in WCDMA
uplink band

Case 1
 Solution

Change the hopping frequency of DSC
 Confirmation

Check the RTWP again, the values are normal

Case 1
 Summary

Characteristics of inner system interference

The RTWP result are not same at the main and diversity antenna

The amplitude of interference is big, and the difference is more than 10
dB

High RTWP will appear in a duration, and will not change so frequently

High RTWP will not show in a certain time each day, but randomly

Case 2
 Description

In a commercial network of country U, the following RTWP
problem is found from traffic statistic
RNCI
d
CellId CellName Time(As hour)
RTWP_MEA
N
RTWP_MA
X
RTWP_MI
N
201 11912 Aguada_C 2005-11-15 4:00 -93.94 -88.65 -105.66
201 11942 Centenario_C 2005-11-15 4:00 -95.86 -87.65 -105.66
201 11932 Centro_C
2005-11-15
17:00
-96.62 -93.65 -97.65
201 11623 Ciudad Vieja_C 2005-11-15 0:00 -96.74 -91 -105.65
201 11461 Palacio_C
2005-11-15
20:00
-97.1 -96 -104.65
201 11643 Pocitos_C 2005-11-15 2:00 -97.72 -92.65 -105.65

Case 2
 Analysis

Connect to the problem NodeB, and monitor the RTWP

Take one site as example

Case 2
 Analysis

The main and diversity antenna have the same
interference trend

The different between main and diversity is less than
10dB

Case 2
 Analysis

Check the location of the sites with high RTWP
High
Medium
Low

Case 2
 Analysis

All the problem cells are in the third sector of the
NodeB, and the direction is to the northwest

Many cells at this area show high interference, and the
cells with low RTWP are at low place

Case 2
 Analysis

Analyze the RTWP in the nearly one month, the
interference shows randomly, but if appears, usually one
whole day, or several days

The interference shows with high traffic, and also with
low traffic. No evidence shows it is related to the traffic

Case 2
 Analysis

Maybe the interference comes from outside and the
northwest direction

Case 2
 Analysis

Use YBT250 to do the interference checking

Case 2
 Analysis

All the test results show the interference comes from the
same direction – to the country A

But the distance to country A from the test place is
around 50Km to 200Km

Case 2
 Analysis

Frequency analysis

UCountryUMTSfrequency
– 1900MHz

AcountryGSMfrequency
– 1900MHz

Case 2
 Analysis

Maybe the interference comes from A country, but looks
like impossible because the distance (50 to 200Km) is
beyond the transmission

To confirm this problem, use A country cell phone at the
area with high RTWP

The result shows the phone does receive the A country
DSC

Case 2
 Conclusion

The interference comes from A country GSM

Even the distance is very far, the area between the
border is covered by a large water area

Due to reflection the water, the signal can be transmitted
far away

Case 2
 Conclusion

After known the reason, the following character of this
kind of interference is found

Relatedtotheweather
– Rain day, no interference
– Cloudy day, less interference
– Sunny day, high interference

Relatedtotheseasonsalso
– Problems show at Summer more than Winter

Case 2
 Summary

Characteristics of external interference

The RTWP result are same at the main and diversity antenna

The amplitude of interference is small, and the difference is less than 10
dB

The interference exists at large area, not just one cell, also including
neighbor cells

The direction of external interference is obvious

The cell with high antenna is easier to be interferenced

Summary
 RF optimization

Neighbor cell list optimization

Coverage performance optimization

Interference optimization

WCDMA RF optimization

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Editor's Notes