UMTS RF Optimization-Cases

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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 cased by neighbor cell list,

poor coverage and interference


Contents

� RF Optimization Workflow

� Typical Problems Analysis in RF optimization


RF Optimization WorkflowStart

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


RF Optimization Workflow

≤5%Pilot pollution Percentage

30%-40%SHO Percentage

Scanner result≥95%CPICH RSCP ≥

-95dBm

Scanner result≥95%CPICH Ec/Io ≥ -12dB

CPICH Ec/Io ≥ -12dB & RSCP ≥ -95dBm

≥95%Coverage Probability

RemarkReference

ValueTarget Item

� 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

� Route line



� Preparation for DT (drive test)� Hardware

� Test phone

� Scanner

� GPS

� Software� Drive test software, for example, GENEX Probe

� Drive test post process software, for example, GENEX Assistant


Contents

� Preparation of RF Optimization



Contents


� RF case related to neighbor cell 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 DropAfter 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 Scanner From 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)� Problem Analysis

� After checking the

neighbor cell list, the

following problem is

found

� Cell C has the same

PSC as Cell B

Case 2


277C

277B

58A

PSCCell ID

CA

AC

NCell IDCell ID

Cell B (PSC277)

Missing configuring

NCellMistake for configuring

NCell

Case 2� Problem Analysis

� 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

� From DT, radio link branch is added into active set, then deleted

from active set repeatedly.

� SHO success rate is low

� Radio link failure is low in the wrong neighbor cell, for example, cell

C in case 2

� Call drop is high in the cell with wrong neighbor cell, for example,

cell A in case 2

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-frequency 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:

� Before call drop in 14603, all UEs initiated compress mode, and

send Measurement Report to RNC periodically, but handover is

not triggered.

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 14031, just not report it?

� Or, UE never measure cell 14031, 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 14031 with frequency B,

only monitor cell 14605 with frequency C, and meanwhile cell

14605 and 14603 signal level are the same, the call dropped

due to the poor signal of 14605 and 14603

� How to make UE monitor cell 14031 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-frequency 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






� 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

� Maybe the problem area will become better, but due to the wall,

this problem may still exist nearby.

� Solution 2:Increase the antenna height

� After checking the installation condition, it’s very hard to increase

the height

� Even increased the height, the problem may still exist due to the

wall.

Case 1


� Solution

� Solution 3:

� Move the antenna position if possible, and the main direction

antenna is parallel with the side of the wall

Case 1

Original Position

New Position

Wall� Move the antenna position to

right about 15 meters

considering the installation

condition


� Solution

� Solution 3:

� About the antenna downtilt, two strategies are designed.

� First, 10 degrees

Case 1

10 Degree


� Solution

� Solution 3:

� Second, 5 degrees

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

� PSC 184: sector 1 & sector 3

� PSC 185: sector 2 & sector 4

� PSC 186: sector 5

� After adjustment, 2 cells:

� PSC184: sector1 & sector3

� PSC185: sector4 & sector5

� Delete sector 2

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:

� Site 1 cell A

� Site 2 cell C

� Site 3 cell C

� Site 4 cell C

� Site 5 cell C

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

� Change the antenna downtilt from 10 to 7

� Increase CPICH Tx power 1.5 dB higher

� Decrease other cell signal – change the antenna downtilt

� From 7 to 10 for site 2 cell C

� From 5 to 8 for Site 3 cell C



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

� Find the reason caused pilot pollution

– Due to no strong signal

– Due to too much strong signal

� After the adjustment, the DT has to be done at this cluster to

confirm that no new problem appeared

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

� Increase the antenna height can solve this problem

� Solution 2

� Move the installation place near to the border

� Solution 3

� 3G and 2G use the same place

Case 4


Case 4

� Solution

� Solution 3 is adopted

Road

R

X

R

X

T

X

/

R

X

T

X

/

R

X

2G

BTS

3G

NodeB


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

� But only 1 cell in active set and 1 Cell in monitor set

� Consider the missing neighbor cell

� But the cell in monitor set has very good quality –

RSCP -65dBm and Ec/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

cell56 vs cell041

-30

-20

-10

0

time

EcNo cell56

cell041


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

Handoverarea

HandoverareaBefore 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)


Contents






-105.4-101.6-822006-5-16 17:00KwongYu3625031

-105.5-94.89-74.32006-5-16 17:00KwongYu2625021

-105.3-102.34-74.52005-5-16 17:00KwongYu1625011

VS.MinRTWPVS.MeanRTWPVS.MaxRTWPTime(As hour)CellNameCellIdRNCId

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-modulation caused by bad connectors

� Inter-modulation by GSM


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

-105.65-92.65-97.722005-11-15 2:00Pocitos_C11643201

-104.65-96-97.12005-11-15 20:00Palacio_C11461201

-105.65-91-96.742005-11-15 0:00Ciudad Vieja_C11623201

-97.65-93.65-96.622005-11-15 17:00Centro_C11932201

-105.66-87.65-95.862005-11-15 4:00Centenario_C11942201

-105.66-88.65-93.942005-11-15 4:00Aguada_C11912201

RTWP_MINRTWP_MAXRTWP_MEANTime(As hour)CellNameCellIdRNCId


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

� U Country UMTS frequency

– 1900MHz

� A country GSM frequency

– 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

� Related to the weather

– Rain day, no interference

– Cloudy day, less interference

– Sunny day, high interference

� Related to the seasons also

– 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

Thank youwww.huawei.com

UMTS RF Optimization-Cases

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