FCC TAC Looks at New Models for Addressing Interference in Shared Spectrum World

The spectrum and receiver working group is looking at the use of statistical models and risk-based decision making, said Lynn Claudy of NAB, a chairman of the working group. “The opportunity here is to manage risk and/or to spread the risk appropriately, so that spectrum is not underutilized as it would be if you're overly conservative.” There appears to be an “ever rising” radio-frequency (RF) noise floor as more devices use the same spectrum, he said.

The working group cast a wide net in looking at models for controlling interference, including how the Nuclear Regulatory Commission manages risk at nuclear power plants, Claudy said.

New issues are expected to arise as spectrum sharing and dynamic spectrum management become the rule in some bands, Claudy said. The working group is developing a “straw man” proposal for enforcement in a shared spectrum world, he said. “One of the issues that has come up is how to make sure that what a … database manager says to do is actually being done by the transmitters it supposedly is controlling.” Under sharing, there would be no central control as there has been under traditional spectrum regulation, Claudy said. “What all that means is that there are practical considerations to applying what works really well in theory.”

With the advent of software-defined radio, “we have the potential for all kinds of devices to generate interference in bands, even without any kind of spectrum sharing,” said Milo Medlin of Google, a TAC member. “Enforcement needs to be focused not just in the context of a database-driven system, but in the reality of the technology that we all are living with now.”

"That you know that there is interference is one thing,” said TAC Chairman Dennis Roberson of the Illinois Institute of Technology. “The ability to cause that interference to go away is quite another.” The working group is looking at a key issue that the FCC has been dealing with for decades, he said.

The working group on advanced spectrum sharing is looking at an ancillary issue, how to suppress interference, said Brian Daly of AT&T, a working group co-chairman. That group is also considering numerous other issues, including candidate bands for spectrum sharing and ideas for FCC and NTIA’s proposed RF model city, he said.

Spatial filtering can be a powerful tool, Daly said. As small cells are deployed and heterogeneous networks (HetNets) evolve, “interference cancellation can be even more important because the cancellation allows the HetNet operator to get the greatest possible gains from the small cells,” Daly said.

Early tests by NTIA show that LTE small cells are “quite robust” versus other transmissions, even when interference is “very high,” Daly said. Using an appropriate spectrum access system and lower-power LTE, small cells should be able to coexist with radars with relatively small exclusion zones, he said.

The FCC Office of Engineering and Technology is going through model city comments that were filed, said OET Chief Julius Knapp. “We'll be working with the NTIA to figure out what the next steps are,” he said. “Stay tuned.” One of the big problems for model cities will be “the lack of scale to sell into,” said Kevin Kahn of Intel, a TAC member. “So much of our market is determined as a national market.” Companies might not be willing to invest in building equipment for a single city, he said. “Ideally, we would, it’s a learning opportunity,” he said. “On the other hand, there are real costs associated with trying to do that.”

One tough spectrum sharing problem is that when rules for sharing are built around the characteristics of the existing system “the concern for the incumbent is they're locked in forever and nobody wants to be in that situation,” Knapp said. A key question is how do you share “and still provide the freedom for the incumbent service to grow and make changes,” he said.

A TAC working group on the IP transition meanwhile is examining how to accelerate the transition and which issues are slowing it down, said Nomi Bergman of Bright House Networks, a co-chairwoman of the working group. The working group is looking at everything from legacy systems like elevator phones to providing services for the disabled as potential choke points, she said.

A new TAC working group (CD June 11 p2) looking at mobile phone theft is making progress and is on target to recommend technical solutions by the end of the year, said Daly, who heads that group. One big takeaway is the problem is growing, with an estimated 3.1 million mobile phones stolen in 2013, he said.

A second new working group is looking at revisions to FCC Form 477, used for local phone competition and broadband reporting. The goal is “to improve the accuracy and the ease of submission for 477 data,” said Steve Lanning of ViaSat, chairman of the working group. “We consider this to be an important task because it becomes a vital input to the National Broadband Map.” Most U.S. communications companies use the map, he said.

TAC is scheduled to hold its final meeting of the year Dec. 4 and many of the working groups are to finalize reports by then, Knapp said. The reports should offer a limited number of “actionable” recommendations, he said. “Try to put in the perspective of what we really can do. Change the world is not an actionable recommendation.” FCC Chairman Tom Wheeler chaired TAC until last year when he was appointed to the commission.