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Why perform a Drive test?

Every alive Network needs to be under continues

control to maintain/improve the performance.Optimization is basically the only way to keep track ofthe network by looking deep into statistics andcollecting/analyzing drive test data.

Drive test helps operation and maintenance fortroubleshooting purposes.

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GSM Parameters

RxLevel

RxQualityFrame Erasure Rate ( FER )Bit Error Rate ( BER )Carrier to Interferer ( C/I )Speech Quality Index ( SQI )

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RxLevelThe power level corresponding to the average receivedsignal level of the downlink as measured by the mobilestation.Normal Range is from -30 to – 70.Level lower than -70 shows low signal levels. Amplifiers, New site proposal, Hardware check could

alter the low signal level.

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RxQualityThe level corresponding to the mobile station'sperceived quality of the downlink signal.

Normal range is from 0 to 4.Quality higher than 4 can result in Call drops, Callblocks, Muted calls, Handover failures, Interference.Numerous alternatives could be used to make the

quality normal, which can include setting RFparameters from OMC.

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Frame Erasure Rate ( FER ) A speech quality degrade factor that indicates fadingand interference.

Normally should be less than 4%.FER greater than 4% that degrades RxLevel, RxQuality,BER, SQI and C/I indicates fading that leads to Calldrops, Call blocks, Muted calls and Handover failures.

FER plays a major role in troubleshooting ofInterference.

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Bit Error Rate ( BER )The number of received bits that have been altereddue to noise, interference and distortion, divided bythe total number of transferred bits during a studiedtime interval.For a perfect system, no bits are to be lost.Loss of bits can result in fading and interference that

leads to Call drops, Call blocks, Muted calls andHandover failures.

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Carrier to Interferer ( C/ I )Co–channel interference is the term used forinterference in a cell caused by carriers with the samefrequency present in other cells.Normal Range of C/I should be greater than 12 dB. Value lower than 12 dB indicates interference with acertain frequency that could be co-channel or adjacent

channel interference.Neighbor sites should be properly planned toovercome interference problems.

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Speech Quality Index ( SQI )SQI is an estimate of the perceived speech quality asexperienced by the mobile user, is based on handoverevents and on the bit error and frame erasuredistributions.SQI should be greater than 18.Low SQI indicates degraded speech quality and

interference.RF parameter tuning could level the SQI back to itsnormal value.

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CDMA Parameters

RxLevel

TxPowerCarrier Energy to Interference( Ec/Io )Carrier to Interferer ( C/I )Signal to Noise Ratio ( SNR )

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RxLevelThe power level corresponding to the average receivedsignal level of the downlink as measured by the mobilestation.Normal Range is from -30 to – 80.Level lower than -80 shows low signal levels.New site proposal, Hardware check could alter the low

signal level.

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TxPower

Tx Power Control determines how the transmit power

of the receiving base station will vary.TxPower should be upto -20. Value less than -20 will indicate Interference that canresult in Call drops, Call blocks, Voice breaks.

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Carrier Energy to Interference ( Ec/Io)

The ratio of received pilot energy, Ec, to total received

energy or the total power spectral density, Io.Ec/Io should be upto -13dB. Values less than -13dB could be due to bad terrain,interference or increased number of users.

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Carrier to Interferer ( C/ I )Co–channel interference is the term used forinterference in a cell caused by carriers with the samefrequency present in other cells.Normal Range of C/I should be less than 12dB. Value greater than 12 dB indicates interference with acertain frequency that results in a low throughput.

Neighbor sites should be properly planned toovercome interference problems.

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Signal to Noise Ratio ( SNR )

Signal to Noise ratio of the carrier.

SNR should be less than 6%. Values higher than that will result in low throughput, voice quality breaks

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