T-Mobile USA is asking the FCC for permission to conduct tests on pre-commercial LTE-U equipment in outdoor and indoor environments at multiple locations across the country.

The proposed test period is June 28 to Dec. 28, 2017. T-Mobile said the experiments will operate in AWS-1 spectrum licensed to T-Mobile as well as in unlicensed 5 GHz spectrum (in a downlink-only mode).

“The testing will be in a highly controlled field environment that will help T-Mobile to allow the pre-commercial testing of new products outside of a lab environment but in a controlled and managed manner,” the “uncarrier” stated in its application.

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The 30 locations across the country include addresses in Dallas; Largo, Florida; Montebello, California; Long Beach, California; Lynnwood, Washington; Stone Mountain, Georgia; Alpharetta, Georgia; Dearborn, Michigan; Brooklyn, New York; Las Vegas and Los Angeles.

T-Mobile explained that the trials at the various locations will allow the company to test prototype equipment prior to equipment verification, and the trials will consist of up to 10 small cells and access points; the mobile units will be receive-only in the unlicensed 5 GHz band but will also include an LTE transmitter that will operate in the AWS-1 spectrum.

The operator expects to use as many as 20 mobile units at each location. The application doesn't identify specific vendors of the equipment.

RELATED: T-Mobile launching some LTE-U now, LAA on the horizon

T-Mobile and Verizon have been the two most vocal operators about their desire to roll out LTE-U. The industry went through a months-long process of developing a test plan with the blessing of the Wi-Fi Alliance after Wi-Fi proponents questioned LTE-U’s ability to play fair with Wi-Fi in unlicensed spectrum. But clearly concerns remain about LTE-U.

CableLabs vows vigilance on coexistence with Wi-Fi

In honor of World Wi-Fi Day, CableLabs VP of Technology Policy Rob Alderfer this week advocated that the Wi-Fi industry resolve to support the continued growth of Wi-Fi with two major initiatives, one of which is to enable reliable coexistence between Wi-Fi and other technologies.

CableLabs worked diligently to surface problems with LTE-U coexistence technology and led industry-wide efforts in the Wi-Fi Alliance to develop tests that can verify how well LTE-U equipment shares spectrum with Wi-Fi before it hits the street. “Industry collaboration is an effective means of addressing coexistence issues and mobile carriers have stated that they will stick with the results of that process. We have since seen LTE-U devices approved after going through the tests,” he wrote.

RELATED: Samsung Galaxy S8 supports LTE-U, which both Verizon and T-Mobile aim to deploy

The LTE-U story is, for the most part, a good example of how industries can come together. “However, the level of collaboration seen since then has, unfortunately, diminished significantly,” he said. “Specifically, there isn't visibility into how the industry-agreed coexistence tests are implemented and used. No LTE-U vendor has released the results of its coexistence tests, even though they are happy to tout that they have passed with flying colors. Transparency is important to validate coexistence performance and mobile carriers and vendors should be more forthcoming.”

While LTE-U was developed outside the usual standards bodies, LAA-LTE is the one developed at the 3GPP. Alderfer said there’s more reason for optimism around LAA coexistence because it uses listen-before-talk etiquette similar to Wi-Fi. But, “when it comes to validating that optimism through coexistence tests, the work at 3GPP has been sorely lacking,” he said, adding that it’s important to get coexistence right since new technologies like MulteFire, eLAA and 5G are coming down the pike, and they'll be using unlicensed spectrum alongside Wi-Fi.