The survey analysed three mobile network quality indicators that are considered fundamental from the user viewpoint:
a) Coverage: Verification of signal levels.
The test equipment allowed us to measure the strength of the signal received by the mobile terminal. Measurements were made on the BCCH1 control channel and were thus not affected by the frequency hopping and downlink power control algorithms.
All measurements were geo-referenced to enable them to be represented later on a chart. This facilitates visualisation of the coverage levels of each operator on the assessed routes.
Table 1 - Signal strength on the control channel
|Signal Strength (dBm)|
|> -110 L <= -100
||Absence of Coverage|
b) Accessibility: Consists of verifying a mobile network's capacity to make calls.
The capacity to successfully make voice communication calls between two terminals - one in a mobile network and one in a fixed network.
In cases where it is not possible to establish communication or same was interrupted during the conversation phase, the test system identifies the cause of interruption or failure.
c) Audio quality: Consists of verifying conversation perception during a successful call and over a pre-set period of time.
To measure this indicator, a telephone conversation between two users is simulated.
The assessment method for audio quality as perceived by users is based on the "E-model" recommended by international agencies such as ETSI2 (ETR 250) and the ITU3 (ITU-T Recommendation G.107). The MOS (Mean Opinion Score) index is calculated based on this model.
(Click on the image to see the graphic in a new window)
Figure 5 - Methodology used for assessing audio quality
The MOS scale quantifies the effort needed to perceive a conversation. When perception is non-existent the MOS value is 0, it is 5 when communication is perfect.
Table 2 - MOS Scale
1) Broadcast control channel - Transports information to all mobile stations (MSs) served by a given BTS (Base Transceiver Station). Transmission occurs in downlink mode and carries various parameters, such as: CI (Cell Identity), LAC (Local Area Code), MCC (Mobile Country Code), MNC (Mobile Network Code), FH Algorithm.
2) European Telecommunications Standards Institute.
3) International Telecommunications Union.