AT&T describes 'critical' need for 600 MHz field testing

Testing hardware and software in field trials has been routine for wireless operators, especially when new spectrum bands are introduced, but in the case of 600 MHz, which would involve both the introduction of a new spectrum band, and "perhaps new 5G technology," the need for thorough testing "would be even more critical," AT&T (NYSE: T) told the FCC in a filing earlier this week.

The filing describes a meeting via teleconference between AT&T representatives and FCC staff that focused on AT&T's First Field Application (FFA) testing practices in connection with CTIA's proposal to permit 600 MHz licensees to engage in market testing. CTIA has been talking with the FCC about a proposal that would define "commence operations" in such a way that 600 MHz licensees will be allowed to initiate critically important market testing in limited markets and geographic areas, with unlicensed white space device users and low-power television (LPTV) remaining in the band for a time.

"The new 600 MHz bands will be used to provide mobile broadband to consumers, so will be cleared of secondary users," said Scott Bergmann, vice president, regulatory affairs at CTIA, in a statement to FierceWirelessTech. "The 'commence operations' definition triggers the clearing of this spectrum so that it can be used for mobile broadband but also allows secondary users to stay in the spectrum until the last possible moment. By clarifying that mobile providers may conduct market trials as usual, the proposal simply allows new licensees to clear spectrum in a limited number of areas to test equipment that will be used to build out these new mobile broadband networks."

The proposal revolves around the two-part incentive auction that FCC Chairman Tom Wheeler says he is confident will start at the end of March 2016. He's also referred to it as a Rubik's cube because it has so many moving parts. An auction of this size and scope hasn't been done before in the U.S. Last month, the FCC laid out a road map for how the process will work. 

Testing in various bands is routine for wireless operators, but in the 600 MHz band, it's particularly important as there has never been deployment in this spectrum anywhere in the world to understand how equipment will work in the field, according to CTIA. AT&T says its FFA process typically follows lab testing by its vendors, then testing in AT&T's own labs, but testing in a live network is essential. Field testing of hardware and software will often uncover issues that weren't apparent in lab testing.

By way of example, AT&T said it uses two core network equipment vendors, along with other vendors that provide antennae and other hardware and software components. In its network, there are at least five major baseband configurations and at least nine major radio head configurations. All possible combinations of the configurations are included in the testing. Initial hardware tests might require a cluster of only 20 to 50 sites, but device testing, to incorporate multiple morphologies, typically requires a cluster of 50 to 150 sites. Software testing usually requires the largest testing areas, as many as 200 to 300 sites, to cover as many combinations as possible.

The FCC plans to allow the use of unlicensed TV white space devices and wireless microphones in the duplex gap and guard band and may assign full power TV broadcasters to the spectrum in the 600 MHz band itself. "The necessity of field tests to evaluate the operation of hardware, software and devices in the presence such of co- and adjacent channel impairments will add to the variables that must be evaluated prior to any commercial deployments," AT&T said.

Equipment vendors have said they expect to deliver equipment for the 600 MHz band relatively quickly; the time-consuming part will be clearing of the spectrum.

For more:
- see this filing

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