Prepared by: Radio Monitoring Team (Resource Management)

Background

This is the IDA "Cellular Mobile Telephone Network Performance" publication which will be made available on an annual basis. Currently, mobile service providers are required to submit their respective Quality of Service (QoS) reports to IDA. In addition, as part of IDA's continual effort in keeping with consumers better informed, IDA has since launched its own Cellular Network Performance Measurement System (CNPMS) in July 2000.

What is Measured?

IDA's CNPMS surveys the service quality of our three mobile service providers namely, SingTel Mobile, M1 and StarHub Mobile and it covers the GSM900 and GSM1800 mobile networks. The QoS parameters used in the survey include:

1. Call Success Rate;
2. Service Coverage (Street-level);
3. Voice Quality; and
4. Call Drop-out.

IDA may include additional parameters as and when available.

Definition of QoS Parameters

Methodology

IDA's CNPMS survey covers 47 routes including expressways, major and secondary roads/streets, and 20 HDB estates. The performance results of each mobile network are collected by means of drive tests along selected routes and HDB estates between 10 am and 8 pm on weekdays. To ensure the credibility of the performance results, mobile service providers are not informed of the routes and HDB estates that are randomly selected by IDA prior to the drive tests.

The car used in the drive tests is equipped with the CNPMS that automatically generates calls on the mobile telephone networks. The holding period of each test call is 100 seconds. A test call is generated 40 seconds after the previous test call is completed.

Interpretation of Results

In interpreting the results, it should be noted that:

• The drive test results represent a snapshot of the mobile service provider's network performance based on the specified routes/HDB estates during the time of day when the measurements were carried out and using a particular type of handset. The reported level of service quality may therefore not be exactly comparable with the consumer's own experience;
• Consumers should not treat the drive test results as recommended best buys. Factors such as price plans, value added services, customer care and support are not captured in this report; and
• External spectrum interference, where exists, may affect the network performance results.

Survey Results

Call Success Rate

A call is successful when a network connection is established. The call success rate shown below is based on an average of 896 call attempts per network:

Service Coverage (Street-Level)

The definition of service coverage in this case is based on signal strength. The availability of service coverage is therefore the ability of a network in achieving a minimum signal strength of -100dBm.

Of the successful calls established by the mobile networks along the 47 routes and in the 20 HDB estates, an average of 215,794 samples of signal strength were obtained for each network. Samples of signal strength were taken at approximately 0.5-second intervals.

The performances of SingTel Mobile, M1 and StarHub Mobile are as shown:

Voice Quality

As mobile phone users often equate quality of service with voice quality, IDA's voice quality indicator is developed to complement the service coverage indicator which is based on signal strength. This is to take into account the fact that both voice quality and signal strength are equally important in determining the quality of transmission.

To measure voice quality, the CNPMS injects a phonetically balanced speech sample into the network and compares a digital copy of the original with a copy received after passing through the network. The CNPMS then rates the latter according to its level of distortion using the Mean Opinion Score (MOS) method. MOS is a generally accepted and commonly used subjective quality rating scheme with the following ratings:

Based on the definition that an acceptable level of voice quality is one with an opinion score of at least "2", the percentage of samples with opinion scores greater than "2" for each mobile network is as shown:

Call Drop-out

A call is "dropped" when it is disconnected prematurely during the 100-second holding period. Call drop-outs may occur due to congestion, interference, weak signal strength, etc. The call drop-out statistics for each mobile network are shown below: