020 wcdma interference problem analysis

7/29/2019 020 WCDMA Interference Problem Analysis

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HUAWEI TECHNOLOGIES CO., LTD. All rights reserved

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Internal

Interference ProblemAnalysis

ISSUE 1.0

HUAWEI TECHNOLOGIES CO., LTD. Page 1All rights reserved

The interference of WCDMA system

includes to parts, one part is self-

interference of system, the other part is

some abnormal interference. Usually,

abnormal interference can not be

predicted, in some cases, it will cause

some problems. In this slide, we willlearn how to locate the resource of

abnormal interference, and how to solve

abnormal interference problem


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

Locate the resource of interference

Learn how to solve abnormal interference

problem


Chapter 1 Abnormal interference typesChapter 1 Abnormal interference types

Chapter 2 Interference analysisChapter 2 Interference analysis

Chapter 3 Interference locationChapter 3 Interference location

Chapter 4 Typical cases analysisChapter 4 Typical cases analysis


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Abnormal interference types

Uplink abnormal interference

When uplink interference exist, the RTWP (Received

Total Wideband Power ) NodeB received will be higher,

then the output of UE will be increased, and interfere

adjacent cells

If RTWP is too high, it will cause the quality of uplink

badly, the call maybe dropped

According to interfered objectsAccording to interfered objects



Downlink abnormal interference

When downlink interference exist, the background

noise of UE will rises, BLER also rises, SIR will be

decreased, so the output of NodeB will be increased

If the output of NodeB has been up to maximum, but

Qos is still bad, the call maybe dropped

According to interfered objectsAccording to interfered objects


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Spurious emission interference come from other system

The frequency band of some system (GSM1800, PHS,

TD-SCDMA, etc.) is close to WCDMA frequency band,

can cause some spurious emission

Spurious emission can cause uplink interference or

downlink interference. Usually uplink spurious emission is

larger

According to interference resourceAccording to interference resource



Spurious emission interference of GSM1800 system to WCDMA


6771768392Inter-system isolation

(dB)

-105dBm/3.84MHz

(Noise)-96-100-105-112-121

Allowed interference of

interfered system

(dBm/3.84MHz)


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Spurious emission interference of GSM1800 system to WCDMA


4347525968Inter-system isolation

(dB)

-105dBm/3.84MHz

(Noise)-96-100-105-112-121

Allowed interference

of interfered system

(dBm/3.84MHz)


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Block

When interference is too high, and out of the

work range of WCDMA receiver, the receiver can

not demodulate the signal normally




Other interference

Microwave transmitter, lightening, etc. maybe cause some

interference in WCDMA frequency band. Some interference

is instantaneous, unabiding, have no more effect to

WCDMA system; some others are long-playing, continuous,

will affect WCDMA system heavily, so we need to eliminate

them or depress their effect



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2.1 External interference analysis2.1 External interference analysis

2.2 Internal interference analysis2.2 Internal interference analysis

2.3 Interaction interference analysis2.3 Interaction interference analysis


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External interference analysis

First type: these interference come from antenna interaction

Especially, when the antennas belong to different system had

been installed face to face, because isolation is smaller, so

spurious emission will affect the site

When environment is complex, and there are so many metal,

so there are so many interactive result

Second type: these interference come from some microwave

equipment

Some interference is periodical, just appears in special time

Some interference just appears in narrow band

External interference typeExternal interference type


External interference analysis

Adjust antenna: change the position, the direction of antenna, make

main beam of antenna fall away from interference resource

Use some method to decrease interference, e.g. we can check 2G

antenna has been added filter or not, antenna and feeder system is

OK or not. We also can modify the frequencies

If the interference come from microwave equipment, we should find

the transmitter

We can use Yagi antenna, and observe in which direction the

signal is strongest, then we can find the transmitter

External interference solutionExternal interference solution


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Internal interference analysis

Usually, internal interference is because of unreasonable system

design

When WCDMA and 2G system use the same antenna and feeder

system, if rejection filters are not installed, the spurious emission

or intermodulation maybe interfere WCDMA

When we install antenna and feeder system, if the connecter is

loose, or feeder curvature is too large, it will cause some

interference

Of course, if antenna or feeder is damaged, it also cause

interference

Internal interference typeInternal interference type


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If isolation requirement is not very high (50dB), we can design antenna and

feeder system like this:

Example: WCDMA and GSM CoExample: WCDMA and GSM Co--SitingSiting

TMA

WCDMA

Filter WCDMA

GSM 1800

GSM 1800

TMA is optional

Dup-Filter

Dup-Filter


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Check antenna and feeder system

Add rejection filter

Modify frequencies

Internal interference solutionInternal interference solution







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Interaction interference analysis

When the antennas belong to different operator are

installed in the same platform, they will affect each other,

so intermodulation interference is very easy to happen

When environment is complex, or there are some high

building around the platform, intermodulation interference

maybe happen

Interaction interference typeInteraction interference type


Interaction interference analysis

Modifying frequencies to prevent third order

intermodulation from affecting WCDMA site

Adjust antenna to increase isolation between antennas

Adjust the direction, tilt angle of antenna

If intermodulation interference is caused by some metal

objects, we can try to move these objects; if the objects

can not be moved, we can try to move the antenna

Interaction interference solutionInteraction interference solution


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3.1 Interference location ways3.1 Interference location ways

3.2 RTWP test steps3.2 RTWP test steps

3.3 Uplink interference location steps3.3 Uplink interference location steps


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Interference location ways

We can check RTWP (Received Total Wideband Power ) to

look for interference.

When there is no subscriber, no amplifier, no interference,

RTWP should be about -105dBm; if TMA has been used, it

should be about -106dBm

If RTWP is just higher than normal value about 1~2 dB, it is

because of background noise, and it is no more effect

If RTMP is larger and change very fast, it means abnormal

interference happened

Uplink interferenceUplink interference


Interference location ways

According to drive test data analysis, if the pilot signal

of Best Server is very good, but Ec/Io is very bad, we

can confirm that downlink interference happened

Downlink interference can cause capacity decrease

If downlink interference is higher, call drop is easy to

happen

Downlink interferenceDownlink interference


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RTWP test steps

Step 1: find the cell we want to testStep 1: find the cell we want to test


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RTWP test steps

Step 2: check cell stateStep 2: check cell state


RTWP test steps

Step 3: start RTWP test taskStep 3: start RTWP test task


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RTWP test steps

Step 3: start RTWP test taskStep 3: start RTWP test task


RTWP test steps

Step 4: RTWP test data processingStep 4: RTWP test data processing


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RTWP test steps

Step 5: RTWP test data analysisStep 5: RTWP test data analysis







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Uplink interference location steps

Get the information about antenna and feeder system

Type, position, direction, tilt angle of antenna

Feeder type, coupler, jumper etc.

Check the antennas which belong to other operators near

our antennas: position, direction, frequency configuration

(if possible)

Check around our antenna there are some larger metal

objects or not

Step 1: get FNE (Fixed Network Element) informationStep 1: get FNE (Fixed Network Element) information



Prepare test antenna, feeder, connector (male or

female), match head

Get RTWP through NodeB

If need more test, we can use YBT250 or HP 8595E

frequency spectrum analyze

If need to test a small interference, YBT250 should

be connected to LNA (Low Noise Amplifier)

Step 2: test preparationStep 2: test preparation


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Put test antenna to the position of every antenna

If possible, during test, we had better shut off WCDMA

site if GSM and WCDMA use same antenna and feeder,

shut off GSM site also

In this condition, if there is some interference, it must

be external interference

Step 3: interference type judgmentStep 3: interference type judgment



If there is no interference, it maybe internal interference

or interaction interference

if GSM and WCDMA use same antenna and feeder,

open WCDMA site, confirm GSM site is off

If interference appears, it must be internal

interference

If there is no interference yet, it must be

interaction interference

Step 3: interference type judgmentStep 3: interference type judgment


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External interference usually come from other site of this

operator or other operators

Check in the same platform or nearby platform, there are

some other antennas or not, the distance between these

antennas is too close or not, the direction of these

antennas is straight to test antenna or not

Step 4: external interference locationStep 4: external interference location



Change the direction of test antenna, then observe RTWP result

If RTWP result has a large difference, the interference

probably come from this antenna

We can change the position or direction of this antenna to

try to solve problem; if the problem cannot be solved,

maybe we need to negotiate with other operator about

antenna and feeder system

Some external interference maybe come from some

microwave equipment. We can use Yagi antenna to locate

the direction of interference

Step 4: external interference locationStep 4: external interference location


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Check rejection filter has been added or not, if not, add it

So many internal interference is because of feeder,

jumper, or connector. The common problems are:

Connector loose

Connector badly

Jumper badly

Step 5: internal interference locationStep 5: internal interference location



Check the frequencies of WCDMA and GSM configured, the

probable reason is intermodulation

Modifying frequencies can solve the problem

Step 6: interaction interference locationStep 6: interaction interference location


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4.1 External interference case4.1 External interference case

4.2 Internal interference case4.2 Internal interference case

4.3 Interaction interference case4.3 Interaction interference case


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Section 1 External interference case

RTWPRTWPof Site 7of Site 701070A01070A,,cellcell00



FNE of Site 7FNE of Site 701070A01070A


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The antenna position of Site 7The antenna position of Site 701070A01070A

3

Car Park Platform

Sundays 3G DivAntenna/ 2G MainAntenna

Sundays 3G MainAntenna/ 2G Div

Antenna

Omni PagerAntenna

1

2

4

5



The photo of platformThe photo of platform


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The antenna positionThe antenna positionafter adjustmentafter adjustment

3

Car Park Platform

Sundays 2G Main/Div

Antenna

Sundays 3G Main/Div

Antenna

Hutchisons GSMRepeater Antenna

Hutchisons GSMRepeater Antenna

Omni Pager

Antenna

1

2

4

5







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Internal interference case

RTWP of Site 701180RTWP of Site 701180,,cell 0cell 0



RTWP of Site 701180RTWP of Site 701180,,cellcell11


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FNE of Site 70FNE of Site 7011801180


Internal interference caseThe position of interferenceThe position of interference


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SolutionSolution

Remove jumper, use a adapter

connect X20 to X5

The jumper between X5 and X20 (load)

badly5

Change jumperThe jumper between X4 and X12 badly4

Change jumperThe jumper between X4 and feeder badly3

Change connectorThe connector of jumper in X8 badly2

Fasten connectorThe connector of jumper between X2 and

feeder loose1


Internal interference caseRTWP of Site 701180RTWP of Site 701180,,cell 0cell 0, after adjustment, after adjustment


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RTWP of Site 701180RTWP of Site 701180,,cellcell1, after adjustment1, after adjustment







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Interaction interference case

RTWP of Site 701RTWP of Site 701310310, cell, cell00



FNE of Site 70FNE of Site 7013101310


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Near SUNDAYs antennas, there are two antennas belong to CSL (another

operator) straight to SUNDAYs antennas. The distance is about 2m

Photo of this sitePhoto of this site



There are three frequencies used in GSM site:

BCCH: 1871.6MHz (844)

TCH_1(HF): 1865.2~1870.4MHz (812~838)

TCH_2(HF): 1865.2~1870.4MHz (812~838)

Frequency distributionFrequency distribution


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We can modify the frequencies of GSM site to prevent third

order intermodulation from affecting WCDMA site:

BCCH: 1811.4MHz (543)

TCH_1(HF): 1810.8~1811.4MHz (540~543)

TCH_2(HF): 1810.8~1811.4MHz (540~543)

SolutionSolution



RTWP of Site 701310, cell 0, after adjustmentRTWP of Site 701310, cell 0, after adjustment


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Summary


Interference analysis and location

SummarySummary

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020 wcdma interference problem analysis

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