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.