AT&T Mobility (NYSE: T) is working with several smaller carriers, likely including T-Mobile US (NYSE:TMUS) and U.S. Cellular (NYSE:USM), to prepare for interoperability between their different band classes in the 700 MHz band. In a filing with the FCC, AT&T revealed the progress it has made in following through on a commitment it made in September 2013 to support interoperability between Band Class 17 and Band Class 12 in the 700 MHz band.

In the filing, which was made last week, AT&T said that in the first half of this year it will bring devices to market that are fully capable of interoperating between Band 12 and Band 17.

The interoperability issue plagued the industry for years. Lower 700 MHz A Block licensees long argued that vendors like Apple (NASDAQ:AAPL) made equipment for AT&T's Band Class 17 and Verizon Wireless' (NYSE: VZ) Band Class 13, but not for those smaller companies such as C Spire Wireless and U.S. Cellular (NYSE:USM) that hold 700 MHz A Block spectrum in Band Class 12.

AT&T, which pushed for the creation of its own Band Class 17, previously argued it could not support Band Class 17 alongside Band Class 12 because it would be too expensive and would cause interference.

However, in September 2013, AT&T agreed to reverse its position and support both Band Class 17 alongside Band Class 12. Specifically, the company said it will develop, implement and deploy throughout its network multi-frequency band indicator (MFBI) capabilities that will let its network operate simultaneously in both Band 12 and Band 17 and support devices in both band classes.

In its progress report to the FCC, AT&T said it has completed lab testing of the MFBI feature with all of its Radio Access Network vendors. The carrier wrote it is "well into our field testing for all of our Macro-cellular vendors and progressing well with the exception of one vendor that has run into multiple software issues on their 3G (UMTS) cells, requiring software fixes that will need to be retested through the lab."

AT&T did not name the vendor and a spokeswoman declined to comment further.

"Although we have upwards of a four-week delay with this vendor, we are still highly confident we will meet our network deployment date," AT&T wrote. "In addition, for two of our three small cell vendors we have completed all of the field testing associated with the MFBI feature. As new small cells are deployed, the MFBI feature will be enabled. The last of small cell vendor projects was cancelled." AT&T agreed in 2013 to deploy the MFBI feature in its network by Sept. 30, 2015.

Without naming the operators, AT&T said it continues to have discussions with several Band 12 operators "to stay aligned technically to support LTE data roaming and when appropriate we will schedule Band 17/12 interoperability testing. It may be necessary for some operators to wait until Voice over LTE (VoLTE) roaming is available before operationalizing LTE data roaming."

The AT&T agreement has taken on new importance in the past year as T-Mobile has amassed a 700 MHz A Block spectrum portfolio that covers 190 million POPs. T-Mobile hopes to deploy all of that spectrum for LTE service this year. The agreement means that T-Mobile's 700 MHz devices will be able to roam onto AT&T's LTE network.

As part of the agreement it struck with the FCC in 2013, AT&T agreed that during first year of the device rollout period, which will start on Sept. 30 of this year, 50 percent of all new unique devices that AT&T launches that operate on the paired lower 700 MHz bands will be Band 12-capable devices.

"With recent 3GPP specification changes it is now possible to build Band 17 devices that are upgradeable to Band 12 MFBI using software," AT&T noted. "These devices require different filters/hardware than the legacy Band 17 devices. This requirement has been added to AT&Ts device requirements and RFP guidance."

AT&T said it is working with OEMs to launch "several device models" in the first half of this year that are upgradeable via software to support Band 12 MFBI software. "Assuming no issues are found with devices or networks, initial device verification will occur over the next 4 -6 months but the device launch is dependent on the Band 12 MFBI rollout across all AT&Ts network," AT&T wrote.

There are already devices on the market that support both Band 12 and Band 17, including the Samsung Galaxy Note 4 and Galaxy Note Edge. However, those devices do not include the MFBI feature. Additionally, AT&T noted there are several phones that will have Band 12 support after a software update, including the Samsung Galaxy Avant, ZTE ZMax, Sony Xperia Z3 and Motorola Nexus 6. The Samsung Galaxy Tab 4 8.0, Galaxy Tab S 10.5, along with the ZTE Z915 hotspot, also support Band 12.

For more:

- see this AT&T filing



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