WCDMA RF Optimization

7/21/2019 WCDMA RF Optimization

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Copyright 2007 Huawei Technologies Co., Ltd. All rights reserved.

WCDMA RadioFrequency Optimization

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Page2Copyright 2007 Huawei Technologies Co., Ltd. All rights reserved.

Forewordl RF (Radio Frequency) optimization is the most important step to

ensure the quality of the network.

l RF optimization will solve network problems related to

neighbor cell list, coverage and interference.






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Objectivesl Upon completion of this course, you will be able to:

p Know the steps of RF optimization

p Know how to solve the RF problems cased by neighbor cell list,

poor coverage and interference






4


Contents

l RF Optimization Workflow

l Typical Problems Analysis in RF optimization






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RF Optimization WorkflowStart

Preparation:

l Set the optimization target

l Divide the optimization cluster

l Draw out the test route line

l Prepare the DT tools

Data Collection:

l DT test

l Indoor DT test

l RNC configuration data

The DT result is satisfied

with optimization target?

RF optimization

finished

Y

Problem Analysis

l neighbor cell list

l poor coverage

l pilot pollution

l handover

l interference

N

Adjustment:

l Engineering parameters adjust

l Neighbor cell list adjust






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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

Value Target Item

l Set RF optimization target, for example:






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RF Optimization Workflowl Preparation for DT (drive test)

p Hardware

n Test phone

n Scanner

n GPS

p Software

n Drive test software, for example, GENEX Probe

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






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Contentsl Preparation of RF Optimization







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Contents


p RF case related to neighbor cell list

p RF case related to bad coverage

p RF case related to interference






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Case 1

l Description

p In DT, call drop happened

p Check the signaling trace at UE side

Call Drop After call drop, begin

to read

system information

From the tracing result we can see that after UE send measurement

report it doesnt receive response from network and starts to read

system information. It means UE loses connection with network andgoes back to idle mode. It is a call drop.






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l Data analysis

p Checking monitor set

p Missing neighbor cell

p Handover failure

Check monitor set for

the scramble measured

by UE

SC 170 is not in monitor set

Case 1

We check the monitor set of the UE, still can not find the cell with

SC170.






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l Data analysis

p Check the latestmeasurement contro l measurement contro l

Search for the latest intra-

frequency measurement control

Call droppoint

Case 1

In order to confirm the guess for missing neighboring cell we check the

measurement control signaling from network because we can find the

configured neighboring cells in the signaling.






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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

The result shows that there is no cell with SC170 in measurement

control signaling. So the case is confirmed and it is because of missing

neighboring cell.






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l Solution

p Add neighbor cells in neighbor cell list

l Summary

p In the beginning stage of network, it is very common that missing

neighbor cell cased cause call drop.

p Analysis with signaling procedure is the common way to find and

solve the problem

p Some problems can be avoided if the Combined Neighbor Cell

Algorithm is switched on.

Case 1






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l Phenomenon description

p In DT, call drop

happens at cell A

Case 2

Cell B (PSC277)

Cell A

(PSC58)

Call drop happens at cell A when UE is moving from cell A to cell B.

The primary code is 58 in cell A and it is 277 in cell B.






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l Phenomenon description

p In Cell A, UE keeps reporting PSC 277 1A event.

p RNC receives this event and send Active Set Update to UE according

to the signaling trace record

p UE sends Active Set Update complete to RNC

p Then, RNC sends Active Set Update to delete PSC 277 from activeset

p Finally call drop happens due to RL failure

Case 2

UE detected that the signal of SC277 is good and report 1A event to

network. Network receives 1A event and decides to trigger soft

handover, so it send active set update to UE and then UE send activeset update complete to network. From these phenomenon It seems that

the soft handover procedure is complete.

But after that network sends active set update again to UE and the

content in active set update is to delete SC277. It is abnormal. Finally

call drop happens.






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l Problem Analysis

p From the signaling trace of DT, it looks like the handover is complete

successfully.

p But, according to the signaling trace from CDT (call detailed tracing),

the handover fails actually.

Case 2

Drive test just shows the signaling in the Uu interface. In this case it

looks like normal for active set update and active set update complete.

But if we trace all corresponding signaling from CDT we can find thehandover is not successful.






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l Problem Analysis

p Signaling trace from CDT shows:

Case 2

UE NodeB RNC

Measurement report (1A Event for PSC 227)

Radio Link Setup

Radio Link Setup Response

Active set update

Active set update complete

Radio Link Failure

The signaling tracing result from CDT shows that NodeB can not

synchronize radio link with UE so it reports radio link failure to RNC. So

handover fails and call drops. But why the previous signaling is normal?






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Cell B (PSC277)

Cell A (PSC58)

Cell C (PSC277)

l Problem Analysis

p After checking the

neighbor cell list, the

following problem is

found

p Cell C has the same

PSC as Cell B

Case 2

We check the neighboring cell list of cell A and find the problem. Cell C

which is far away from cell A has the same scrambling code 277 with

cell B.






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277C

277B

58 A

PSCCell ID

C A

AC

NCell IDCell ID

Cell B

(PSC277)

Missing

configuringNCell Mistake forconfiguring

NCell

Case 2l Problem Analysis

p The neighbor cell list shows

Cell C

(PSC277)

Cell A

(PSC58)

Cell B should be the neighboring cell of cell A but the actual

configuration is that cell C is the neighboring cell of cell A. It is obviously

wrong configuration and it causes handover failure and call drop.






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l Problem Analysis

p Based on the analysis above, the new NodeB is not the one of cell

B, but the one of cell C

p 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.

p That is why the Radio Link Failure! is sent by NodeB

Case 2

After RNC receives 1A event for SC277, it asks NodeB to prepare radio

resource. But this NodeB is not the one for cell B but for cell C. Cell C is

far away from cell A can the NodeB can not find the UE, so the NodeBsends radio link failure to RNC.






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l Solution

p Change the wrong neighbor cell list

Case 2






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l Summary

p Phenomenon for wrong neighbor cell list

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

active set repeatedly.

n SHO success rate is low

n Radio link failure is high in the wrong neighbor cell, for example, cell C in

case 2

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

in case 2

Case 2






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l Summary

p About SHO event, UE will only report PSC to RNC in Measurement

Report

p RNC will find the right cell according to the neighbor cell list

between cell ID and PSC

p This problem is mainly happened in dense urban when is PSC is

reused a lot

Case 2






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Contents










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l Description

p In drive test for RF optimization, call drop happened in the circle

area

Case 1






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l Analysis

p 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






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l Analysis

p After checking the RF

transmission

environment, the signal

is blocked by the glass

wall

Case 1

The Wall

Call drop

Antenna






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l Solution

p Solution 1: Decrease the downtilt to increase the signal level

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

problem may still exist nearby.

p Solution 2:Increase the antenna height

n After checking the installation condition, it"s very hard to increase the

height

n Even increased the height, the problem may still exist due to the wall.

Case 1






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l Solution

p Solution 3:

n 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

Walln Move the antenna position to right

about 15 meters considering the

installation condition






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l Solution

p Solution 3:

n About the antenna downtilt, two strategies are designed.

n First, 10 degrees

Case 1

10 Degree






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l Solution

p Solution 3:

n Second, 5 degrees

Case 1

5 Degree






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l Summary

p Before RF adjustment, site survey should be done.

p Find the problem and the reason, design several strategies for the

adjustment

p 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






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l Description

p In drive test for RF optimization, bad Ec/Io is found on the bridge

Case 2

Bad Ec/Io






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l Analysis

p Check the RSCP value of scanner, the result shows the RSCP value

is good.

Case 2

p Based on this, pilot pollution

need be considered in this area.

p Check the top N pilot RSCP and

Ec/Io in scanner result

From the drive test result of scanner we can see that there are five cells

with strong signal level.

All the RSCP values of the cells are around -80dBm. It means thesignal level is high enough. But all the Ec/Io values are less than -13dB,

it means the signal quality is not good.

In the area several strong pilots coexist and the signal quality is bad. It

is typical pilot pollution.






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l Analysis

p From the DT result, it shows the RSCP value is strong, but the

Ec/Io is bad.

p And the signal level of different cell are very similar.

p Find the cells which cover this area

Case 2

We want to find which cells can cover the area with pilot pollution and

try to make a dominant cell in this area.






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l Analysis

Case 2

Site 1 Cell A

Site 5 Cell C

Site 2 Cell C Site 3 Cell C

Site 4 Cell C

We find that signals from five cells can be detected in the area.






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l Analysis

p On the bridge, the signal from different cell can cover this area due

to reflection of the river and no building.

p From DT, following cell cover this area:

n Site 1 cell A

n Site 2 cell C

n Site 3 cell C

n Site 4 cell C

n Site 5 cell C

Case 2






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l Analysis

p Need to find the

best cell

p Check the map,

the site 6 is very

near to the

bridge.

Case 2

Site 1 Cell A

Site 5 Cell C


Site 4 Cell C

Site 6

To solve pilot pollution, a dominant cell need to be found. From the map

we can see that site 6 is very near to the area and we can try to use this

site to make a dominant cell.






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l Analysis

p 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 2

The residence buildings

are much higher than

antenna, which blockthe signal of site 6

But the signal of site 6 is blocked by high buildings, so it can not be

used.






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l Analysis

p Then, site 1 cell

A can be the best

cell to cover this

area

Case 2

Site 1 Cell A

Site 5 Cell C


Site 4 Cell C

We try site 1 again because it is also very near to the area.






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l Analysis

p Then, try to

increase the

signal of site 1

cell A, and

decrease other

cells

p To confirm this,

DT for site 1 cell

A needs to be

done

Case 2

Site 1 Cell A

Site 5 Cell C


Site 4 Cell C

The solution is to strengthen the signal of site 1 while weaken the signal

from other sites.






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l Solution

p Increase the signal of site 1 cell A

n Change the antenna downtilt from 10 to 7

n Increase CPICH Txpower 1.5 dB higher

p Decrease other cell signal # change the antenna downtilt

n From 7 to 10 for site 2 cell C

n From 5 to 8 for Site 3 cell C



Case 2






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l Confirmation

p After the modification, the DT shows the pilot pollution area as

below

Case 2

No pilot pollution

After the modification we perform drive test again. The result shows the

pilot pollution is cleared.






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l Summary

p To solve the pilot pollution, the following issues has be considered

n Increase one of the pilots and decrease the others in the same time

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

that no new problem appeared

Case 2






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l Analysis

p RSCP distribution in DT

Case 3

Bad RSCP






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l Analysis

p Ec/Io distribution in DT

Case 3

Problem

area

Problem

areaBad Ec/Io






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l Analysis

p Checking the RF environment, the antenna is installed on 10-

meter platform

p 2G and 3G antenna are installed at one platform, but 3G antenna

is a little bit inner than 2G antenna.

p After finishing DT in 2G, signal level is very stable

Case 3






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l Analysis

p If 3G and 2G antenna are installed at the same place, the problem

may be solved.

Case 3

Problem Area

3G Antenna

2G Antenna

p The short wall of this

platform may block the

signal of 3G

p Since 2G antenna isnear to the border, the

wall influence 2G little

Wall






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l Solution

p Solution 1

n Increase the antenna height can solve this problem

p Solution 2

n Move the installation place near to the border

p Solution 3

n 3G and 2G use the same place

Case 3






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Case 3

l Solution

p Solution 3 is adopted






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Case 3

l Summary

p Sharing the same installation place for 3G and 2G is very

common, and several strategies can solve the problem

p In this situation, 3G and 2G can share the feeder system, or

can only share the installation platform.

p Considering the factors of the installation and related

resource, a easiest and simplest method should be adopted






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Case 4l Description

p In DT, call drop happensa lot in the area

Call drops in

this corner






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Case 4

l Description

p Check the DT information, SC304 is in active set with the signal

level RSCP -76dBm and Ec/Io -18dB

l Analysis

p Consider the pilot pollution

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

p Consider the missing neighbor cell

n But the cell in monitor set has very good quality RSCP -65dBm and

Ec/Io -6dB

The drive test result shows that there is one cell in active set. RSCP is -

76dBm and Ec/Io is -18dB. It means the signal level is high but the

quality is bad.Pilot pollution can result in high signal level but bad signal quality but

there is only one cell in active set. So it is not pilot pollution.

In monitor set we can find a cell with good RSCP and Ec/Io. So it is not

neither because of missing neighboring cell.






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Case 4

l Analysis

p Check the signaling trace at UE side

Before call drop, UE

sends measurement

report to RNC with 1A

event for cell 298

From the signaling tracing result in UE side we can see that UE sends

measurement report with 1A event for SC298 to network, but it can not

receive active set update from network.






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Case 4

l Analysis

p Check the signaling trace at RNC side

RNC sent Active Set Update toUE, but no response. Then, RNC

send release RRC connection

Call Drop

The signaling tracing result in RNC side shows that RNC can receive

measurement report from UE and it sends active set update to UE, but

RNC can not receive response (active set update complete) from UE.So RNC release the connection.

From the signaling tracing result in both sides we can see that RNC

already sent active set update but UE can not receive it.






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Case 4

l Analysis

p Based on the DT and signaling trace, this call drop can be

considered as handover failure

p The following figure shows the signaling change at the corner.






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Case 4

l Analysis

p 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.

p After UE sent measurement report to RNC, cell 304 has become

very bad when RNC sent active set update.

At the corner Ec/Io of the cell 304 decreases while Ec/Io of the cell 298

increases. So the UE sends measurement report with 1A event to

network.But Ec/Io of the cell 304 decreases so fast. When RNC is sending

active set update, Ec/Io is so bad that UE can not receive the signaling

from cell 304. Finally handover fails and call drop happens.






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Case 4

l Adjustment

p Since cell 298 has better coverage at this area, handover can

happen earlier

n Decrease cell 304 coverage performance at this area

# Increase the downtilt from 5 to 9

# Adjust the direction from 0 to 310

n Increase cell 298 coverage performance at this area

# Decrease the downtilt from 5 to 4

# Adjust the direction from 300 to 270

This case shows a typical corner effect. Ec/Io of the source cell

increases too fast while Ec/Io of the target cell decreases too fast, So

UE can not receive active set update from network.The solution method is to move the handover area from the corner to

other place.






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Case 4

l Adjustment

p Result after adjustment

Handover

area

Handover

area

Before After

From the result we can see that the handover area is moved to other

place.






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Case 4

l Adjustment

p Comparison of Ec/Io of UE

Before After






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Case 4

l Summary

p Confirm the corner effect by analyzing signaling trace at UE

and RNC

p About corner effect, Taking the method make the handover

happen earlier, such as RF optimization

p Other method can also adopted

n Modify 1A event

n Modify CIO (Cell Individual Offset)






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Contents










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Case 1

l Analysis

p Connect to the problem NodeB, and monitor the RTWP

p Cell 62501 RTWP

Curve with red color shows RTWP in main diversity antenna.

Curve with blue color shows RTWP in secondary diversity antenna.






70


Case 1

l Analysis

p Cell 62502 RTWP

RTWP in main diversity is too high but secondary antenna is normal.






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Case 1

l Analysis

p Cell 62503 RTWP






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Case 1l Analysis

p The main diversity antenna is interfered seriously

p Can not find any relation between interference and time, and

the interference appears randomly

p Check the neighbor sites, no interference

l Deduction

p Inter-modulation cause the interference, could be

n Inter-modulation caused by bad connectors

n Inter-modulation by GSM

Only main diversity antenna has high RTWP and the interference

appears randomly, it means that the high RTWP is not caused by heavy

traffic.The neighbor sites have no interference, it means the high RTWP is not

caused by outside interference.

So maybe the high RTWP is caused by inter-modulation.






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Case 1

l Analysis

p Check the RF environment






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Case 1

l Analysis

p Check the RF environment

n No blocking or any reflection due to the glass wall

n The site RF condition is very good






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Case 1

l Analysis

p 2G and 3G share the feeder system

This site is a 2G&3G co-site. So maybe the high RTWP is caused by

2G&3G inter-modulation.






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Case 1

l Analysis

p Check 2G frequency planning

n Sector 1 # 538 with hopping frequency 821

# 538 # 1808.6MHz & 821 # 1867MHz


# 544 # 1811.6MHz & 821 # 1867MHz


# 858 # 1874.4MHz & 821 # 1867MHz






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Case 1

l Analysis

p Calculate the third order intermodulation

n Cell 1 # 1925.4MHz (2*1867-1808.6)

n Cell 2 # 1922.4MHz (2*1867-1811.6)

n Cell 3 # 1859.6MHz (2*1867-1874.4)

p The frequency used for WCDMA in this NodeBis 1922.4MHz

The third order inter-modulation is most popular in inter-modulation.

From the result we can see that in cell 2 the result of the third order

inter-modulation is the frequency used by this NodeB. So the highRTWP is confirmed to be caused by inter-modulation.






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Case 1

l Analysis

p Conclusion

n The third inter-modulation of cell 2 is just in WCDMA uplink band

which is used by the NodeB. So RTWP in cell 2 is high while cell 1

and cell 3 are normal.






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Case 1

l Solution

p Change the hopping frequency of GSM

l Confirmation

p Check the RTWP again, the values are normal

We can change the frequency of inter-modulation by changing the

hopping frequency of GSM.






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Case 1

l Summary

p Characteristics of inner system interference

n The RTWP result are not same at the main and diversity antenna

n The amplitude of interference is big, and the difference is more than 10 dB

n High RTWP will appear in a duration, and will not change so frequently

n High RTWP will not show in a certain time each day, but randomly






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Case 2

l Description

p 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_MEAN Time(Ashour)CellNameCellIdRNCId

Several sites have high mean RTWP.






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Case 2

l Analysis

p Connect to the problem NodeB, and monitor the RTWP

p Take one site as example

Check one NodeB with high RTWP and find that sector C has problem

while other two sectors are normal.






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Case 2

l Analysis

p The main and diversity antenna have the same interference

trend

p The different between main and diversity is less than 10dB

Main diversity antenna and secondary antenna have similar RTWP. So

it is not caused by inter-modulation.






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Case 2

l Analysis

p Check the location of the sites with high RTWP

High

Medium

Low






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Case 2

l Analysis

p All the problem cells are in the third sector of the NodeB,

and the direction is to the northwest

p Many cells at this area show high interference, and the cells

with low RTWP are at low place

Only one sector in the NodeBs with problems has high RTWP. All the

sectors with high RTWP face the same direction (northwest).

All the sites with high RTWP are at high location. While the sites at lowlocation are normal.

From these phenomenon we can guess there are outside interference

from northwest.






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Case 2

l Analysis

p Analyze the RTWP in the nearly one month, the

interference shows randomly, but if appears, usually one

whole day, or several days

p The interference shows with high traffic, and also with low

traffic. No evidence shows it is related to the traffic

Continue to analyze the phenomenon. The interference is not related to

the traffic.






87


Case 2

l Analysis

p Maybe the interference comes from outside and the

northwest direction






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Case 2

l Analysis

p Use YBT250 to do the interference checking

Use frequency scanner to check outside interference.






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Case 2

l Analysis

p All the test results show the interference comes from the

same direction # to the country A

p But the distance to country A from the test place is around

50Km to 200Km






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Case 2

l Analysis

p Frequency analysis

n U Country UMTS frequency

# 1900MHz

n A country GSM frequency

# 1900MHz

U country UMTS and A country GSM use the same bind. So maybe A

country GSM system can cause interference to U country UMTS.






91


Case 2

l Analysis

p Maybe the interference comes from A country, but looks like

impossible because the distance (50 to 200Km) is beyond the

transmission

p To confirm this problem, use A country cell phone at the area

with high RTWP

p The result shows the phone does receive the A country GSM






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Case 2

l Conclusion

p The interference comes from A country GSM

p Even the distance is very far, the area between the border

is covered by a large water area

p Due to reflection the water, the signal can be transmitted

far away






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Case 2

l Conclusion

p After known the reason, the following character of this

kind of interference is found

n Related to the weather

# Rain day, no interference

# Cloudy day, less interference

# Sunny day, high interference

n Related to the seasons also

# Problems show at Summer more than Winter






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Case 2

l Summary

p Characteristics of external interference

n The RTWP result are same at the main and diversity antenna

n The amplitude of interference is small, and the difference is less than 10 dB

n The interference exists at large area, not just one cell, also including neighbor

cells

n The direction of external interference is obvious

n The cell with high antenna is easier to be interferenced






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Summaryl RF optimization

p Neighbor cell list optimization

p Coverage performance optimization

p Interference optimization






Thank youwww.huawei.com

WCDMA RF Optimization

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Transcript of WCDMA RF Optimization