TEMS Investigation GSM

     TEMS Investigation is an air interface test tool for real-time diagnostics. It lets you monitor voice channels as well as data transfer over GPRS, circuit-switched (CSD) or high-speed circuit-switched (HSCSD) connections. Data sessions can be conducted from within TEMS Investigation. TEMS Investigation is equipped with advanced testing and inspection functions as well as powerful analysis and post-processing features useful to the experienced RF engineer. Data is presented in real time throughout. This makes TEMS Investigation ideal for advanced drive testing sessions of troubleshooting, performance tuning, etc. All data can also be saved in logfiles for purposes of post-processing

Measurements in Drive Testing

* C/I---This is the carrier signal to interference (plus noise) ratio.  It determines the quality and performance of the connection. The necessary threshold for good performance depends on the modulation type, the receiver design, and the service quality requirements (such as BER requirement)


* Rxlev---This is the received signal level, and is usually measured in dBm units. The Rxlev is measured on either
- The BCCH channel in idle mode
- Or on both the BCCH and the traffic channel, TCH

* BCCH : Broadcast Control Channel (provides general information about the network)

* TCH : Traffic Channel
Speech Quality---Speech quality can be evaluated by the following:
Subjective listening test
- A Personal opinion (okay, good enough, excellent, poor)
- MOS (mean opinion score (GSM standard procedure)
0: bad
1: poor
2: fair
3: good
4: excellen

* RxQual---This is a GSM standard metric, and is expressed in the range of 0 to 7 (0 meaning best quality).  For descent speech quality, Rxlev should not exceed a value of 4 more than 5% of the time for non-hopping networks.  For hopping networks, this is relaxed, and usually a threshold of 5 or 5.5 for the RxQual is used.

* SQI (Speech Quality Index)---This is not a GSM standard metric, and is only specific to the TEMS test equipments.  It is expressed in the range of 0 to 30 dB (30 meaning best quality).

Limitations of drive testing

1. Drive testing can only test the network performance on the streets and roads where vehicles can go

2. It can not be used to assess network performance such as drop rates, and quality statistics for calls made from nearby houses, alleys (where cars can not go), and from nearby office buildings, and shopping plazas, and etc

3. For testing and collecting measurements in areas and places where the vehicles can not go, walk-in tests are required (indoor test).

TEMS Investigation GSM can be run in two different modes: 

1. Drive testing mode. Information is read from one or several mobile stations, and optionally from a scanner and a GPS unit. 

2. Analysis mode. Information is read from a logfile