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Radio InterferenceOptimization

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What is Interference

Electronic 'noise' caused by radio waveswhen they interfere with the transmissionof other waves of same wavelength

passing through the same path One major challenge when optimizing GSM

network is the detection of cells sufferingfrom interference as interference is

limiting the capacity and

harming the quality of the network

This problem occurred due to

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Types of Interference

There are two categories ofinterference source that are:- Internal Interference: Co-channel or

Adjacent channel interferencecausing internal interference.- External Interference: Exists when

there is another transmitter orsomething else acting as atransmitter outside the network suchas TV transmission, Railway Stationfrequency, and microwave links.

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InterferenceIdentification

1. using Radio Network Statistic

Radio network statistic (RNS) can be

used to analyze if specific cells sufferfrom interference and whichfrequency channels are involved.

A cell in GSM can suffer frominterference either in the uplink ordownlink or in both directions.

As the interference is related to thefre uenc or a set of fre uencies in

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There are several indicators fromRadio Network Statistics that

can be used to identify theinterference in the network

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. e corre a onbetween RxLevel to

RxQual An indication for interference will bethat the receive level is good but atthe same time the receive quality is

poor

This can be analyzed for bothdirections (uplink and downlink)

separately

It is better to have this figure forBCCH TRX and hopping TRX so we

can identify whether interference

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. e corre a onbetween RxLevel to

RxQual

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2. Drop Call Performance

Usually when the cell hasinterference problem, the drop callwill be higher than usual, but it

depends on severity of interferencelevel

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3. HandoverPerformance

Intra Cell Handover indicates that cellsuffers from bad quality at good level

The HO performance to neighborrelation that has interference willlook bad

The other indicator is a lot ofreversion to old channel activity dueto target frequency might beinterfered

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4.Scanning frequency atidle mode

Another ways to identify internalinterference in GSM network is byscanning frequency at idle mode.

At this case, GSM recommendationintroduces reference value ofinterference level (GSM

Recommendation. 05.05).The actual interference ratio shall be

less than a specified limit, called the

reference interference ratio.

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The following figure shows sample of result of scanningfrequency using Tems Investigation

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C/Ia calculation shows that carrier tointerference level of first adjacent(200KHz spacing) and second

adjacent (400 KHz spacing) exceedsminimum value of interference level(-9 dB for first adjacent and -41 dB

for second adjacent). So, we canconclude that there is no interferenceto channel 512.

Distribution C/I from drive test with

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External Interference

External interference cant bedetected using drive test tool. Asinstead, scanning frequency using

spectrum analyzer is used to observethe source of external frequency.

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ow o o veInterference Problem in

GSM NetworkThe solution for interference problemdepends on the following factors1. Whether interferer comes from

internal or external source2. What is the cause of internalinterference, whether it were caused

by bad frequency planning, sitelocation, coverage problem orimplementation problem.

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The following flow chart shows howto overcome interference problem inthe network

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The potential interferer can beidentified by displaying the cellsusing the same or adjacent

frequency (frequencies)geographically.

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The other solution to reduceinterference level in the network isactivation radio network features.

The following radio features areproposed to be activated to reduceinterference level in the network:

1. Discontinuous Transmission (DTX)2. BTS and MS Power Control3. Frequency Hopping4. Multiband Cell can be analternative for operator who has

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Thank

You