Tuesday, April 5, 2011


GSM BASICS which are indeed for a drive test engineer

Downlink and Uplink: The uplink (MS to BTS) frequencies are in the area 890 - 915 MHz and the downlink (BTS to MS) frequencies in the 935-960 MHz.

Downlink RF Characteristics: RxLevel, RxQual, FER, MS-TX-Power etc.

Particular frequency and Network Capacity: the more often you use a particular frequency within your network, the more capacity you can provide by your network. You will learn more about this topic by analyzing and implementing frequency plan (the shorter the distance, the tighter frequency planning allow more subscribers in the network)

Radio Network Capacity: depends on the number of cells on-air and the number of channels associated with each cell. The number of channel is increased in each sector, the erlong value would increase which allow more subscribers in the network

Transmission hop: a combination of sending and receiving ends.

Traffic: a load due to the calls generated by the subscribers.

Erlang: is the unit of traffic; one erlang means one busy subscriber/line

Tilting: is a way of mounting the cellular antenna, there are two type of rectification tasks could be done during your DT, up-tilting (the signal is transmitted at a positive angle) and down-tilting ( the signal is transmitted at a negative angle with the horizon)

Burst: time slots are arranged in a sequence 0-7, the repetitions of this sequence is called a TDMA frame, the information content carried in one time slot is called a burst.

Accessibility: SDCCH serviceability * TCH accessibility. Repeated short call set-ups must be exercised to measure accessibility performance of the network.

Retainibility: it takes all type of drops into consideration, for measuring retainibility and integrity of a network, long continuous calls must be performed by drive test

  • Make sure you have loaded correct cell file before proceeding to collect log file
  • Make sure one MS is in dedicated mode( long call) to measure quality and one MS is in Idle mode to scan all BCCH frequencies and another to make short call
  • Measure MPD from long call + short call, Integrity; SQI from long call, RxQual from long call, RXLevel from Idle mode, coverage area probability from idle mode, E2E call establishment success rate from short call
  • Compare the LAC ID, CI and BCCH according to your MDB and CRF of a new site
  • You can disable Cell File and start collecting log file when you face some sort of error in your cell file.
  • When you find RxLevel and RX Qual are poor (bellow the marks) just let your coordinator know the findings: it may be the effect of hardware installation error.
  • When you face some sort of HO problem, let your coordinator know the issue and try to find out whether all the neighbor relations are well defined or not; check site status: all the sites are on air. Prompt force HO and moving around 100 meter could be done to identify the real situation of your target cell.
  • Call termination problem due to overlay and underlay: check BCCH and let your coordinator know the issue
  • Always keep an eye on radio parameter, current channel, serving neighbor, C/I and C/A
  • If the RxLevel bad and RxQual is also bad then HO is due to RxQual
  • If RxLevel is bad and RxQual is good then HO is due to RxLevel
  • When BSIC and frequency are same; the SQI goes negative
  • There won’t be any significance difference between RXLevel sub and Rxlevel full when DTX is disabled
  • If you find call originating problem then click on presentation>signaling>layer3 Messages>properties>event to check message type|type6|type13|NCC|Message Type|LAC|NCC permitted|Band allocation|termination Failure
  • Range and threshold value of RxLevel sub ( -10dBm to -115dBm, higher is better, threshold value -95dBm) RxQual ( 0-7, lower is better, threshold value 5) SQI (-20 to 30, threshold value 18, higher value is better) C/I (-5 to 20, threshold value 12, higher value is better) FER full (lower value denotes the better network ) BER actual (the lower the value, the better the network ) RxLevel full ; a higher value represents better scenario.

  • Always Check and select proper comport configuration for RLC throughput
  • GPRS connected but connection is too slow; check RxLevel of your idle mode mobile and make a move to that specific SECTOR for the strongest RxLevel.
  • PDB activated and deactivated message; you will hear a confirmation message: GPRS and MMS have been activated…you may check command sequence for troubleshooting, if you are not clear about any configuration then contact your coordinator and describe the real scenario.

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