Telstra engineers suspect a "vast" undercurrent of illegal repeaters are causing issues for the carrier's Next G mobile network across Australia.
General manager of radio network development within Telstra's engineering division, Stephen Howell, told iTnews that although technicians had identified "tens of cases" of illegal repeater use in Australia each year, many more devices were likely in use without the telco's knowledge.
"We're fairly sure that there's a background of these devices that are causing some impact that we can't see in our network statistics, but they are still causing some loss of coverage," Howell said.
"There's probably a vast number out there that just don't show up in our network stats but still have some impact on the network."
Repeaters — active devices used to strengthen weak mobile phone signals — are not prohibited in Australia, but generally cannot be activated without permission from the spectrum owner and device registration by the Australian Communications and Media Authority.
Fines of up to $165,000 and/or imprisonment are possible penalties for illegal use.
The devices are regulated to prevent them interfering with the services of other users in the cell.
At worst, an illegal repeater can knock coverage out to an entire area.
"We had one case probably a couple of years ago now where [mobile coverage to] the south-east corner of Shepparton was completely wiped out," Howell said.
"We had people coming into our Telstra shop in Shepparton complaining that the coverage had just disappeared from that corner of Shepparton.
"It turned out to be a repeater around the Kialla area. When we shut that repeater down, the coverage came back."
More commonly, illegal repeaters cause a degradation — rather than catastrophic failure — of coverage in a cell site.
"Most people in the cell won't notice it but what happens is those on the edge of the cell will find that they don't have any coverage where they would normally get coverage," Howell said.
Spikes in uplink noise in cellular sites are the most common indicators of the potential presence of an illegal repeater.
The spikes show up in Telstra's network monitoring statistics, but only when the interference is at a "medium-to-high level".
"We can't see the very subtle interference that happens sometimes, and yet we can get customer impacts and complaints," Howell said, noting it was why engineers suspected more widespread use of illegal repeaters than those the statistics caught.
Of course, once a Telstra technician was sent out to locate the source of interference, there was no guarantee it was an illegal repeater.
"When TV masthead amplifiers go faulty, they can cause a similar impact. So when our [technicians] go out searching for the source of the interference we don't know what [is causing it]," Howell said.
In any event, identifying the source of interference "is a massive job", according to Howell.
"Sometimes it takes [the technicians] two days to find it," he said. "It's no small thing."
New meaning to mobility?
Telstra is not alone in experiencing illegal repeater use.
In May, Globe Telecom highlighted rampant use of illegal repeaters in the Philippines as a reason for weak signals and dropped calls experienced by users in cell sites.
One of Globe's problems was locating the devices. According to a news report, they were often hidden in "trees, building windows, toilet areas, rooftop areas and building spaces".
Telstra has also had some challenging finds.
"We've had [cases] where the interference goes up at a particular time of the day. There was one [where at] exactly the same hour every day the interference went up," Howell said.
"It turned out to be a boat coming back to harbour. [Technicians] had to chase the boat to try and work out where [the repeater] was.
"That's about the strangest [location]."
The most recent cases recorded by Telstra were in the mid-west of Western Australia, where six illegal repeaters were found over a two-month period to July 2012.
Telstra has recently endorsed and started selling the first legal repeater device for its network.
The Telstra Mobile Smart Antenna is a second-generation Nextivity Cel-Fi device that is now being sold by Telstra after completing a series of trials.
According to Howell, Telstra had been looking for appropriate repeater technology "since the CDMA days", when illegal booster devices caused interference problems for the carrier.
"We'd been searching for a long time for a repeater that doesn't cause an issue in our network," he said.
"Finally, a year or so ago, we found one. The initial device we were given from [Nextivity] didn't quite meet what we needed in the network, [but] this second variant does".
The Telstra version of the Nextivity device contains features developed exclusively for the telco that prevent it being used to "illegally repeat a signal which Telstra doesn't own".
Unlike some of the illegal repeaters, the Nextivity device also has the 'smarts' to ensure it doesn't swamp the base station it is repeating signal from.
"Instead of just being a simple RF amplifier, which is what 'dumb' repeaters are, this one will do things like read the control messages coming off the base station, and then it can determine things like how much power to transmit back on," Howell said.
"It doesn't just amplify the signal by a set amount, which is what these dumb repeaters do.
"This one will actually physically know how far away it is from the base station and be able to modify its power in the uplink so it doesn't swamp the base station."
Currently, the device is available from Telstra directly, partially so that the carrier can ensure it will work for the customer requesting it.
"The device is designed to be a coverage enhancement solution where the coverage is limited by low signal strength," he said.
"We would like to make sure that the person's not requesting a device because of an interference issue problem which this won't fix.
"So we don't want to sell these to anyone who asks because we may be selling them something which just won't work for them."