omf000403 gsm interference analysis issue1[1].0

7/23/2019 OMF000403 GSM Interference Analysis ISSUE1[1].0

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Huawei Confidential. All Rights Reserved

OMF000403

GSM Interferene Anal!sis

ISS"# $.0


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2 Internal Use

To introduce affection brought by

interference to the GSM system, fault

location method and troubleshooting

method, this course hereby lists out

the possible interference sources, and

offers description of cases to facilitate

fault location and troubleshooting.


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3 Internal Use

O%&etivesO%&etives

Upon completion this course, you will be

able to

Understand the cause of interference andmaster the method of locating the

interference source!

Master the method of o"ercoming

interference.


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# Internal Use

Chapter 1Ch

apter 1 OverviewOverview

Chapter 2 Location and Clearance of Interference

Chapter 3 Case Analysis


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$ Internal Use

Affetion of InterfereneAffetion of Interferene

%hen there is interference in the networ&, the subscribers usually encounter the

following phenomenon The subscriber cannot hear the "oice , and the bac&ground noise is too loud.

%hen fi'ed telephone subscriber calls MS subscriber, or MS subscriber calls fi'ed

telephone subscriber, call drop occurs after (du, du , du) is heard.

The con"ersation cannot be carried on smoothly, and call drop often happens.

%hen interference e'ists in the networ&, from the result of traffic statistic, there are

some characteristic as following.

There are *e"el #+*e"el $ interference band in T- measurement function , and

the measurement "alue is more than .

ongestion rate is comparati"ely high.

The call drop rate is higher than other cells.

The hando"er success rate is low.

Through /ri"e Test, it is found that

It is difficult to hando"er .

The 0' le"el is high, but the 1uality is bad.

Through tracing the bis interface signaling with signaling analyer

4M56725$8, it is found that the bit error rate is higher than other cells.


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9 Internal Use

Classifiation of Interferene SouresClassifiation of Interferene Soures

'atural 'oise

tmosphere noise

Gala'y noise

Solar noise 41uiet period8

Man()ade 'oise

Interference of ignition systems of "ehicles or other engines

Interference of electronic communication system

Interference of power line

Interference of scientific research, medical and household appliances


7/54: Internal Use

Main Interferene Soures Affeting Mo%ile Co))uniationMain Interferene Soures Affeting Mo%ile Co))uniation

Internal interference

T0; fault if the performance of T0; is reduced due to manufacture

cause or application, which will cause self


8/54? Internal Use


0epeater interference

s the installation of repeater is non standard, causing insufficient

isolation between the donor antenna and the subscriber antenna, so

self


9/54A Internal Use


B'ternal interference

Interference of other communication e1uipment with high power

0adar station @rom :5s+?5s of the 25th century, the fre1uency used by

the decimeter wa"e radar was similar to that of GSM, and its transmitting

power was "ery high, which generally reached tens and hundreds of

&ilowatts, so the out


10/545 Internal Use

Chapter 1 Overview

Chapter 2Chapter 2 Location and Clearance of InterferenceLocation and Clearance of Interference

Chapter 3 Case Analysis


11/54 Internal Use

*isovering Interferene via OMC +raffi Measure)ent*isovering Interferene via OMC +raffi Measure)ent

*isovering ,otential interferene via traffi statistis result

hec& the ("erage T- busy time 4second8) in T- measurement

function of each cell, the reason is that this inde' can show the T-

mean occupied time 4s)8, which is usually called (T- mean holding

time) in the =S of other manufacturer), within the measurement period.

If it is found that the "erage T- busy time 4second8 of certain cell is

comparati"ely short 4such as less than 5s8, then maybe there is strong

interference in the cell, causing that hando"er6call drop happens due to

bad 1uality after T- channel occupied to MS.

ertainly, if hardware fault occurs in certain T0; 4non


12/542 Internal Use

*isovering interferene via handover data*isovering interferene via handover data

%hen certain cell initiates hando"er, if the a"erage recei"ing 1uality 4uplin&8

is # 4this is true when there is no fre1uency hopping, if there is, it shouldbe $8, and the mean recei"ing le"el is 2$4


13/543 Internal Use

*isovering ,otential interferene via all dro, inde-*isovering ,otential interferene via all dro, inde-

If the call drop times of certain cell is rather higher the the other with same

traffic load, and the main cause of call drop is owning to connection fault,then it is possibly caused by interference.

If the a"erage recei"ing le"el during call drop is comparati"ely high 42$8,

while the a"erage recei"ing 1uality le"el is 9, then the cell should be listed

into the interference source.


14/54# Internal Use

*isovering ,otential interferene via interferene %and*isovering ,otential interferene via interferene %and

=TS will utilie an idle TS in a frame to scan the uplin& fre1uencies of the

fre1uencies used by T0;, and then ma&e measurement to the le"el $interference band. The default setting of interference bands in =S of

-uawei is as follows 5, 5$, A?, A5, ?: and ?$ 4unit


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OMC Alar) and Su%sri%er Co),laintOMC Alar) and Su%sri%er Co),laint

Subscriber complaint is also important clew for finding the potential

interference. Information which should be collected from user complaintincludes MS number, MS model, called number and fault phenomenon of

calling side and fault phenomenon of called side and particular fault location,

etc. If the alarm information is more detailed, it will be more easily to find out

the networ& problems.

%hen there is interference in the networ&, the direct feelings of the

subscriber may be hea"y noise, both parties or either party cannot hear

each other clearly, call drops and call cannot be put through, etc. Thus, when

many subscribers within the same area complain the same problem, then

wor& should be done to chec& whether there is interference in the area.


16/549 Internal Use

*isovering Interferene via *rive +est*isovering Interferene via *rive +est

there are two /ri"e Test methods a"ailable idle mode test and dedicated

mode test. Under the idle mode, the test e1uipment can measure the signal le"el of

both ser"ing cell and ad>acent cell. In addition, the e1uipment can also

perform fre1uency scanning test to the specified fre1uency or fre1uency

band.

Under dedicated mode test, the test e1uipment can measure the signalle"els, recei"ing 1ualities, power control registrations and time ad"ance, etc.

of both the ser"ing cell and ad>acent cells. %hen high le"el 4358 and low

1uality 40'EFual98 remain in certain section, it can be concluded that

interference e'ists in the section. @urther, part test e1uipment can directly

display the frame elimination rate 4@B08. Generally when the @B0 2$D,

subscribers can feel the discontinuous "oice, that is to say, interferencee'ists in this section of highway.


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Reo))ended roedures for /oation andReo))ended roedures for /oation and

Clearane of InterfereneClearane of Interferene

/etermine Interference ell according to 7ey erformance Inde' 47I8

hec& larm of HM

@re1uency lanning hec&

hec& arameter Setting of ell

/ri"e Test

Interference learance


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rief introdution to S,etru) Anal!1errief introdution to S,etru) Anal!1er

Spectrum nalyer is a broadband signal recei"er with high performance

which can display the spectrum of the recei"ing signals. The recei"ing signal resolution bandwidth 40=%8 namely the minimum

signal bandwidth the Spectrum nalyer can recognie. The smaller theparameter is, the higher the recei"ing sensiti"ity of instrument.

Input fre1uency the fre1uency range the Spectrum nalyer can recei"e. Sensiti"ity generally the minimum recei"ing le"el with - signal bandwidth

is defined as recei"ing sensiti"ity of the Spectrum nalyer. The recei"ingsensiti"ity of -?$ series Spectrum nalyer can be below


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*iretional Antenna*iretional Antenna

/irectional antenna is used for searching interference sources. The stronger

the directionality of antenna is, the higher the antenna gain is. nd the abilityto search will become better. So the logarithm


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+he wa! to +est Internal Interferene+he wa! to +est Internal Interferene

Set the Spectrum nalyer to proper state

@or A55M =TS f5KA52M-,SJK35M-,TTK5,0=%K35&-,=%K35&-!

@or ?55M =TS f5K:$M-,SJK5M-,TTK5,0=%K35&-,=%K35&-. Screw out the connector of output port of /U di"ider, then connect the output signal

of the di"ider to the Spectrum nalyer to carry out a test. If the fractional fre1uency

spectrum le"el is less than L?5d=m, it shows that there is no internal interference! if

more than L?5d=m, it shows that /U or T0; inside =ase Station are under

interference or self


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+he wa! to +est #-ternal Interferene+he wa! to +est #-ternal Interferene

%hen we are sure that interference is caused by the e'ternal cause, first we

should confirm the location of interference source and the spectrum

distribution state. @irst, set the Spectrum nalyer to proper state.

hoose output port of di"ider of cell under interference.

Screw out the selected connector, then use oa'ial able to import the

output signal of di"ider to the Spectrum nalyer!

iew the spectrum distribution state of the Spectrum nalyer, and findout the abnormal interference signal. The way to calculate the le"el of

interference signal is as follows

ntenna port interference le"el K interference le"el tested by the

Spectrum nalyer L $d= Tower Top mplifier Gain 3d= cable

loss L :d= di"ider gain.

The ma'imum interference le"el at antenna port without influence on

system K



+he wa! to Searh #-ternal Interferene Soures+he wa! to Searh #-ternal Interferene Soures

In the cell under interference, select a test point without building obstruction.

Set the Spectrum nalyer, and connect the directional antenna.

If there is rotatable platform, the antenna can be placed on it, and ma&e the

wa"e beam of the antenna point to the front, and the antenna with "ertical

polariation should be placed "ertically! if there is no interferent signal, one

can raise the antenna o"er head with hands. 0otate the antenna slowly, and

at the same time "iew the change of signal of the Spectrum nalyer. Hncethere e'ists abnormal signal, fi' the orientation of the antenna immediately

and change uptilt of the antenna to ma&e the recei"ing signal to the

strongest.

nalye the signal spectrum distribution carefully, and confirm that it is

interference signal, record the signal strength and record the aimuth and

downtilt of antenna wa"e beam. @ind new test point along with the direction of antenna wa"e beam, then

return to step 2 to carry out a test till interference source is found.



Chapter 1 Overview

Chapter 2 Location and Clearance of Interference

Chapter 3 Case AnalysisChapter 3 Case Analysis


24/542# Internal Use

Antenna erfor)ane *egradationAntenna erfor)ane *egradation

Fault desri,tion2 There are $ =TSs for a certain networ& in a county

configured as S#6#6# and 96969, the =TS type includes =TS25 and =TS35.The interference band $ in T- measurement function of some cells is o"er

$, and there is no alarm information in HM


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Fault loation ,roess

0egister the statistics tas& of interference band of 2# hours for the cellwith problems, it is found that interference band $ mainly occurs in

daylight, and in the small hours near middle night, the interference band

"alue is almost 5.

fter opening the idle =U0ST of all =TSs and transmitting it in the early

morning, it is found that the interference band occurs. It disappears aftertransmitting is stopped. It can be >udged from this phenomenon that the

interference comes from internal networ& and has nothing to do with

other e1uipment.

Jo fre1uency in the networ& and data are modified before the

interference occurs, accordingly, the interference is irrele"ant with the

fre1uency planning. It can be seen from the abo"e second and third points that the problem

is rele"ant with the =TS e1uipment.

Hbser"e the 0;M test interface of /U with the spectrum analyer in

pea& hour in the daylight, it can be seen that unstable strong broadband

interference and rise of bac& noise occur.





@irst replace all boards 4T0;, /U, @U, -, and power board8 of this

=TS 4=TS25, with Tower Top mplifier8 one by one, at the same timeobser"e the spectrum signal of 0;M test interface, it can be seen that

interference e'ists all the time. This indicates that the interference is

rele"ant with the antenna feeder 4including di"ider, combiner, feeder,

antenna, lightning arrester, Tower Top mplifier, >umper and connector8

instead of the board.

Since the abo"e =TS under test has the Tower Mount mplifier, the

antenna and feeder chec& is incon"enient, replace another

=TS354S#6#6#8 4dualumper at the top of the cabinet8 of the cells which

are with and without interference in the =TS in the e"ening. Then send

idle =U0ST, it is found that the interference follows the antenna and

feeder. This step helps further locate the fault which should e'ist in

antenna and feeder system.


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The situation remains the same e"en after replacing lightning arrester of

antenna feeder and chec&ing all >umper connectors. Then it can be surethat fault e'ists in the feeder or antenna.

0eplace the >umper 4i.e., antenna8 at the top of the tower, it is found that

the interference follows the antenna, so the feeder fault can be e'cluded

while the antenna fault is 1uite possible. 4It should be noted that the

e'ternal interference at this step cannot be e'cluded because the actual

installation place of the antenna does not change, but the e'ternal

interference has already been e'cluded in the abo"e step. 8

@inally chec& the antenna. The strong interference disappears

immediately after the antenna is replaced on the tower by using the

dual


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2? Internal Use

Antenna Conneted Inversel!Antenna Conneted Inversel!

Fault desri,tion2 the interference bands # and $ often occur in the traffic

measurement after certain =TS is on ser"ice, the inter


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2A Internal Use



Since the interference bands # and $ occur along with low hando"ersuccess rate and congestion, it is doubted that the interference causes

the abo"e phenomena.

hec& the fre1uency planning first, no problem is found. The e'ternal

interference becomes the chief consideration after the fre1uency

planning problem is e'cluded. hange the original used fre1uency A intothe far


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The congestion analysis indicates that T- assignment failure is usuallycaused by uplin&. fter registering the traffic measurement of

uplin&6downlin& balance, it is found that the measurement item of

uplin&6downlin& balance for cell and cell 3 focus on le"el and . This

indicates that se"ere imbalance occurs between uplin& and downlin&.

The imbalance between uplin& and downlin&, in combination with muchhando"er failure in cell and 3 turn the doubt to the antenna and feeder

which may be connected in"ersely.

Hn


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Co(hannel InterfereneCo(hannel Interferene

Fault ,heno)enon2 The co


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The fre1uencies assigned for the =TS are 9#, and A2 49# is of =-fre1uency8.

In the optimiing test, the recei"ing 1uality 41uality le"el is less than 38 is

continuously good as the downlin& signal le"el is


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arry out continuous con"ersation test with one test MS and scan testfor 9#N fre1uency with another MS. The test carried out again in the

section from /u ity to -uanggang re"eals that the signal strength of

9#N fre1uency is already less than


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3# Internal Use



arry out continuous con"ersation test with one test MS and scan test

for 9#N fre1uency with another MS. The test carried out again in the

section from /u ity to -uanggang re"eals that the signal strength of

9#N fre1uency is already less than


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3$ Internal Use



The interference disappears after the application is made to the

customer to modify the fre1uency. t the same time, the customer

should ad>ust the ad>acent cell relation of peer e1uipment.

arry out test again at the place where the original co


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39 Internal Use

Ad&aent(hannel InterfereneAd&aent(hannel Interferene

Fault ,heno)enon2The call drop ratio is uni"ersally high and e"en up to

about $D in busy hour after se"eral =TSs are cut o"er. nd it is difficult forthe call to be set up during on


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3: Internal Use



ll =TSs are connected to the same =S, and call drop occurs aftercuto"er of new =TSs.

The transmission 1uality is good, and T0; test is carried out for the

abo"e =TS with call drop and this indicates that each T0; is all right. Jo

fault is found by chec&ing the data and carrying out the test for 32=IB

port corresponding to the =TSs. @rom the abo"e analysis, the T0; fault,

=S hardware fault, interface circuit fault and transmission fault can

be e'cluded.

nalysis of traffic measurement result re"eals that serious interference

occurs in each cell of the abo"e se"eral =TS. Most cells ha"e

measurement "alues in interference band # and $, and the number of

channels falling into interference band $ in se"eral cells is up to :. So itis sure that the interference in the abo"e se"eral cells is 1uite serious.

Ad& t h l I t fAd& t h l I t f


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3? Internal Use



It is found that there are many ad>acent channels and the fre1uencyplanning is irrational after chec&ing the fre1uency configuration of abo"e

=TSs and the ad>acent cells. Bspecially, the area where the abo"e =TSs

are located, is newly added, and interference e'ists among them. nd

they also ha"e interference in between them and the surrounding

running =TSs.

all drop disappears after ad>usting and loading the fre1uency

configuration of this area.

I t f C d % OI t f C d % O


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3A Internal Use

Interferene Caused %! Over(overageInterferene Caused %! Over(overage

Fault ,heno)enon2The hand o"er success rate of a certain GSM networ&

is low, the call drop rate is high and con"ersation 1uality is poor. The hando"er success rate is less than ?5D, and the call drop rate is more than 2D.

It is found that there are many times of downlin&6uplin& strength hand o"ers

through "iew and analysis of traffic measurement data. while there are many

times of bad downlin& 1uality, and uplin& strength among the times of

unsuccessful hando"er. The analysis of cause of call drop indicates that the

times of bad downlin& 1uality are more than those of bad uplin& 1uality .There is no alarm message in HM system

I t f C d % OI t f C d % O


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#5 Internal Use



@rom the result of traffic measurement, it can be >udged that downlin&

interference may e'ist in the system or the co"erage is not "ery good. The actual result of /ri"e Test shows that the strength of outdoor signal

can be up to


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# Internal Use



The cause for bad networ& indices lies in o"erusting the networ&

parameter. The following operations can be adopted lower the power

le"el of cell = and add the ad>acent cell of cell =, at the same time

increase the le"el threshold of candidate cell from 5 to $. The networ&

indices e'hibit ob"ious impro"ement after the abo"e chec& andmodification are performed for all cells in the downtown area, moreo"er,

the hand o"er success ratio rises up to ?$D, while call drop ratio drops

to .3D.

R t I t fRe,eater Interferene


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#2 Internal Use

Re,eater InterfereneRe,eater Interferene

Fault ,heno)enon2 subscribers of a certain networ& complain that they

cannot occupy channel in some area for con"ersation since some day, ornoise is hea"y after occupancy of channel though the signal of MS is strong

at this time. There are two directional =TSs in this area and both of them are

=TS35 with the "ersion 5$.5$2A. The aimuth of the first cell directs at north.

The =TS in this area wor&s normally and the networ& indices conform to

re1uirement before the complaint. =oth =S and MS are de"ices of

-uawei and two =TSs are connected in star mode. The traffic measurementindices show that traffic of both =TSs decreases ob"iously after occurrence

of this problem, especially in the first and third cells. lthough the signal of

channel is "ery strong, the 1uality of "oice is poor. Then it can be seen from

traffic measurement that the interference band of these four cells is in class

three, four, and fi"e, and A$D of channels are under interference. In

addition, interference of different classes also e'ists in other cells. Sosubscribers complained strongly. nd there is no alarm message in HM

system

R t I t fRe,eater Interferene


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#3 Internal Use



The feedbac& of subscribers shows the possible causes as follows .roblem occurs in transmission and leads to error code! 2. roblem

occurs in antenna feeder! 3. @ault e'ists in TMU! #. Internal or e'ternal

interference may e'ist.

The traffic measurement console shows the possible reasons as follows

. There may e'ist strong uplin& interference signal in the north lean to

west in this area. This leads to interference of different le"els in the first,

second and third cells, especially in the first and third cells!

It is found that it is difficult to put through the call in the first and third

cells through onudged from this point that interference only e'ists in uplin&.8



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## Internal Use



arry out test on site with antenna feeder analyer. Jo problem of =TS

itself is found, and the situation remains the same after TMU is replaced.Therefore, we as& customers whether there are such newly constructed

e1uipment as microwa"e station, repeater, etc. surrounding the =TS.

They told that they didnCt set up them.

It is said that hina Mobile sets up a repeater in the area, which is

located about two &ilometers away in the north lean to the west of both

=TSs of -uawei, and when it is acti"ated, the problem will occur in-uawei =TS. Then customers negotiated with hina Mobile se"eral

times. @inally hina Mobile carried out on


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#$ Internal Use

Mirowave InterfereneMirowave Interferene

@ault phenomenon it is found that call drop rate in the second and third cell

of a certain =TS 4S262628 in traffic measurement increases abruptly. alldrop rate is up to about 25D at some time.



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#9 Internal Use



iew of =S traffic measurement shows that idle T- number ininterference band in this =TS begins to increase in interference band 3udged from the abo"e phenomenon

that interference e'ists.

Since this =TS operates well before, the problem of fre1uency planning

can be e'cluded.

erform power


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#: Internal Use



iew of all =S traffic measurement data shows that interference ofdifferent le"els e'ists in the cells of all =TSs nearby, which is facing the

same direction as the second and third cells in this =TS. nd

sometimes S/- channels in the cells with serious interference are

all occupied at the same time, while the occupancy ratio of S/- at

the same time is "ery little according to the amount of subscriber. So it

can be sure that e'ternal interference e'ists in uplin&, but theinterference may be rele"ant with direction instead of fre1uency.

To further locate, >umpers of the first and third cell are interchanged on

the rac& top. s a result, it is found that interference occurs in the first

cell, but interference disappears in the third cell, so this has pro"ed the

abo"e >udgement.

Since interference is not rele"ant with fre1uency, =TS interference may

be caused by high


48/54

#? Internal Use



Measurement on =TS di"ider output port with spectrum analyer showsthat high


49/54

#A Internal Use

False InterfereneFalse Interferene

Fault ,heno)enon2 the reconstruction of some office found that the

interference band of an S96969 =TS25 in a county is "ery high.Theinterference band of two cells in it changed from $ to :.



50/54

$5 Internal Use



/uring the past interference test ofthis office, some cells with highinterference band were located. This is because antenna

intermodulation resulted in the interference of normal signal in case of

large traffic and it made the interference band "ery high. So change the

antenna, but the interference band did not fall down ob"iously after that.

/uring the prior period, the fre1uency planning has been chec&ed

se"eral times, and the ad


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$ Internal Use



Trace the state of interference band of each channel "ia Maintenanceonsole and find that high interference band mainly focuses on the four

T0;s of the cell.

@irst set the fre1uency with less interference to the T0; with more

interference, and find that the interference band does not change. It

shows there is no relation to the fre1uency. %hether there is something

wrong with T0; board or not is un&nown. -owe"er, the situation is

unchanged after the T0;s were interchanged.

Then confirm the T0; numbers, and find that the four carriers come

from the same di"ider. @rom the abo"e process, the problem may be

the di"ider. =ut it is found that the interference band becomes high

when the =TS is e'panded from S#6#6# to S96969. %hile thecombiner6di"ider used to be normal. Maybe the de"ices brea& down

after some time. So we decided to change the combiber6di"ider to ha"e

a try.



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$2 Internal Use



The idea that four carriers with high interference band are connected tothe same second le"el di"ider before the di"ider is changed. The :


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$3 Internal Use

Su))ar!Su))ar!

H"er"iew

*ocation and learance of Interference ase nalysis

Su))ar!Su))ar!


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omf000403 gsm interference analysis issue1[1].0

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