T-Mobile USA is ready to deploy a new LTE technology over the same 5GHz frequencies used by Wi-Fi following US government approval of the first "LTE-U" devices.

The Federal Communications Commission today authorized the first LTE-U (LTE for unlicensed spectrum) devices after a controversial process designed to ensure that cellular network use of the 5GHz band won't interfere with Wi-Fi networks.

"With LTE-U, starting this spring, T-Mobile customers will be able to tap into the first 20MHz of underutilized unlicensed spectrum on the 5GHz band and use it for additional LTE capacity," T-Mobile said immediately after the FCC decision. T-Mobile is deploying LTE-U technology from Ericsson and Nokia, who had their equipment certified by the FCC today.

LTE-U will help T-Mobile achieve its goal of offering gigabit LTE speeds, the carrier said.

Verizon Wireless is also planning to use LTE-U. The company said in September that it is "eager to deploy" the technology and developed an equipment testing plan, but it's not clear when a Verizon deployment will happen.

Cellular carriers in the US generally hold exclusive licenses to spectrum, while Wi-Fi operates in unlicensed frequencies. Anyone can operate in unlicensed spectrum without an FCC license as long as they use certified radio equipment and comply with power limits and other technical requirements.

“LTE-U allows wireless providers to deliver mobile data traffic using unlicensed spectrum while sharing the road, so to speak, with Wi-Fi," FCC Chairman Ajit Pai said in a statement today.

The plan to bring LTE to unlicensed Wi-Fi spectrum set off an industry fight. LTE-U deployment plans drew opposition in 2015 from cable companies and the Wi-Fi Alliance, an industry group that certifies equipment to make sure it doesn't interfere with other Wi-Fi equipment. Industry groups worked together to develop a "Coexistence Test Plan" to prevent interference, and the Wi-Fi Alliance said it's satisfied with the result even though the new testing is voluntary rather than required by the FCC.

Pai said that FCC staff "certified that the LTE-U devices being approved today are in compliance with FCC rules. And voluntary industry testing has demonstrated that both these devices and Wi-Fi operations can co-exist in the 5GHz band. This heralds a technical breakthrough in the many shared uses of this spectrum."

T-Mobile has been discussing its LTE over 5GHz plans since late 2014, and it likely would have deployed LTE-U earlier if not for the controversy over potential interference.

"LTE-U devices and equipment intelligently tap into and share underutilized unlicensed spectrum without affecting other users on the same band, including those using conventional Wi-Fi," T-Mobile said today. "LTE-U constantly seeks the least utilized channels to maximize efficiency and performance for everyone. As demand on the Wi-Fi network increases, LTE-U backs off, and as Wi-Fi demand wanes, customers can tap into that unused capacity for LTE."

Some observers still raise questions about how well the sharing plan will work in practice. "Whether LTE-U proves to be helpful or harmful to consumers remains to be seen," said Michael Calabrese of New America's Open Technology Institute. "Risking a tragedy of the unlicensed commons so that carriers can reduce their costs—and potentially begin charging subscribers for using unlicensed spectrum—may well turn out to be a big setback for ubiquitous and more affordable wireless connectivity.”