Telco M1 has been fined $25,000 for failing again to meet a new standard for outdoor 3G coverage.

An independent test conducted by the Infocomm Development Authority (IDA) in the second and third quarter of last year showed that the telco fell short of the 99 per cent outdoor mobile network coverage required during that period - except in August. The worst performance was in June when M1's network covered just 97.87 per cent of Singapore, but in other months, the telco fell short only marginally.

SingTel and StarHub, however, met the requirement, which was introduced in April 2012. Previously, telcos were required to ensure their networks covered 95 per cent of the outdoor areas islandwide.

In a statement on Friday, IDA said that M1's mitigation factor was its continued efforts to improve overall coverage. When it was first fined $10,000 for poor 3G service in late 2012, M1's network coverage was only at 94.6 per cent based on a test done in September that year. That year, SingTel and StarHub were also fined $10,000 each for failing to meet the mark in the same test.

An M1 spokesman said: "We note that M1's network delivered the best call quality, with the highest call success rate and the lowest call drop rate, during IDA's quality of service audit."

Separately, IDA also tested buildings for mobile signals after its new standard - requiring more than 85 per cent coverage on all floors in tall buildings - came into force in April last year. All three telcos did not met the requirement in some buildings here in the second and third quarter of last year.

But the regulator has given them six months to improve coverage in these buildings. It will test mobile signals in these buildings again in early and middle of this year before deciding on a penalty.

Meanwhile, all three telcos met the IDA's requirement for mobile coverage in new train and road tunnels to be at least 99 per cent, up from 95 per cent since April last year.

The regulator said it is currently studying the feasibility of forming service quality standards of mobile broadband. Operators that failed to meet these standards may be fined up to $50,000 for each standard breached per month.