Drive Test Engineering Parameters in GSM Network
GSM Parameters :
1-RxLevel 2-RxQuality 3-Frame Erasure Rate ( FER )4-Bit Error Rate ( BER )5-Carrier to Interferes ( C/I )6-Speech Quality Index ( SQI )
1-RX Level
-The power level corresponding to the average received
signal level of the downlink as measured by the mobile station.
-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.
2-RX Quality
-The level corresponding to the mobile station's perceived
quality of the downlink signal.
Normal range is from 0 to 4.
-Quality higher than 4 can result in Call drops, Call blocks,
Muted calls, Handover failures, Interference.
-Numerous alternatives could be used to make the quality normal,
which can include setting RF parameters from OMC.
3-Frame Erasure Rate ( FER )
-A speech quality degrade factor that indicates fading
and 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 Call drops, Call blocks, Muted calls and
Handover failures.
-FER plays a major role in troubleshooting of
Interference.
4-Bit Error Rate ( BIR )
-The number of received bits that have been altered due
to noise, interference and distortion, divided by the total number of
transferred bits during a studied time 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 and Handover failures.
5-Carrier to Interferer ( C/ I )
-Co–channel interference is the term used for interference in a cell caused by carriers with the same frequency present in other cells.
-Normal Range of C/I should be greater than 12 dB.
-Value lower than 12 dB indicates interference with a certain frequency that could be co-channel or adjacent channel interference.
-Neighbor sites should be properly planned to overcome interference problems.
6- Speech Quality index (SQI)
-SQI is an estimate of the perceived speech quality as experienced by the mobile user, is based on handover events and on the bit error and frame erasure distributions.
-SQI should be greater than 18.
-Low SQI indicates degraded speech quality and interference.
-RF parameter tuning could level the SQI back to its normal value.