AT&T Wireless has partially disabled service at 16 cellphone towers in Oakland after the California city said they were interfering with its emergency communications system.
Police and firefighters had complained of poor coverage in some areas of the city as well as inside buildings, problems receiving and transmitting, unclear and varying audio levels, and problems with speaker mics. A report on the year-old system compiled for the city found it didn't meet the "performance level of a typical urban or metropolitan Public Safety radio system."
An investigation by the city of Oakland, later joined by the Federal Communications Commission and AT&T Wireless, traced the problem to GSM 850MHz service at AT&T Wireless base stations, according to the city.
The Oakland police radio system is based on a digital technology called P25 and operates on frequencies between 851MHz and 854MHz, while the cellular service in question operates in two bands, between 824MHz and 849MHz and between 869MHz and 894MHz.
Both technologies are in use across the U.S. and their frequencies, while close, should be sufficiently separated to avoid any interference.
But something is wrong in Oakland.
"Together, the city's and AT&T Wireless' engineering teams conducted joint testing and validation of the RF conditions taking place at one of their tower locations on East Ninth Street," the city said in a statement. "Both teams concluded that the AT&T 850MHz GSM cell site was causing significant interference to the City of Oakland's P25 System."
"The City of Oakland further advised the AT&T personnel that it had data proving many of their cell sites were exhibiting the same problem and advised them of the FCC rules giving absolute priority to public safety users and requesting they take immediate action to resolve this situation," the statement said.
AT&T confirmed it had partially disabled GSM service.
"AT&T is working closely with the City of Oakland to understand if the issues they've raised are connected in any way to AT&T's network," AT&T Wireless said in a brief statement. "In the interest of public safety and as a cautionary measure while we're looking into the matter, we have temporarily taken some 2G frequencies out of service at some cell sites in Oakland. We continue to operate on other 2G frequencies and our 3G and 4G service throughout the area is unaffected."
GSM is a second-generation cellular technology not capable of the fast data speeds that modern smartphones need. But while it is older technology, it supports customers using older and more basic handsets and helps fill in the gaps between high-speed coverage areas.
Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is firstname.lastname@example.org