No benchmark for indoor 4G coverage has been set yet, as the authorities are still mulling over what the standards should be.
But such standards will likely take reference from current 3G requirements, which stipulate that at least 85 per cent of a building should be covered.
The Infocomm Development Authority (IDA) clarified last Friday that 3G coverage must generally be distributed within the building.
"It is not reasonable for an entire home or business unit to fall within the (allowed) 15 per cent with no coverage," an IDA spokesman said.
"However, recognising that there may be technical challenges in providing good service coverage in certain areas of a building due to structural designs of the building, coverage in storerooms, bomb shelters and toilets within an individual's premises is optional under the 3G framework," he added.
Many factors determine users' actual experience, including the type of handset, peak-hour traffic delays, content providers' system configuration and provisioned bandwidth capacity, and number of concurrent users at a site.
Mr Aaron Tan, 36, a freelance writer and M1 customer, said that until recently, he found it difficult to make calls on his mobile phone from his flat in Sengkang.
"Calls were often cut off. I had to stand next to the window to get voice and WhatsApp connections," he said. But all that suddenly ended last month.
Mr Tan has since been able to make and receive calls and connect to WhatsApp at home.
When The Straits Times conducted a 4G speed test in his home, we found that StarHub's download speeds were about 1Mbps or so. M1's hovered at around 13Mbps, and Singtel's at 80Mbps.
At night, when most users would be at home and online, a 150MB file from Dropbox could not be downloaded over StarHub's network; nor could a 140MB Terraria app from the Google Play store.
In comparison, it took just under two minutes to download the 150MB Dropbox file over M1's and Singtel's networks at night.
Many users have called for IDA to set benchmarks for mobile broadband speeds.
IDA said it is studying the feasibility of introducing a service quality framework for mobile broadband services, but many factors are at play to determine users' actual experience.
These factors include the type of handset used, peak-hour traffic delays, content providers' system configuration and provisioned bandwidth capacity, and the number of concurrent users at a location at the time of use.
"These are external factors that are beyond the control of the Internet service providers," IDA said.
As an interim measure, IDA has required telcos to measure and publish the typical download speeds for their mobile broadband plans.
"This allows end users to make informed choices about their broadband plan and the speeds they would likely experience," the authority said.