FCC's Next Moves on Receivers Still Unclear, Experts Say

Several experts we asked Wednesday said it’s not clear what the FCC will do next. A technologist involved in the proceeding said there were hints last fall the FCC would act, but little since. The FCC didn't comment.

“The receiver performance NOI docket has been pretty quiet, largely because there doesn't seem to be a strong consensus as to what the commission can or should do, except that prescriptive regulatory standards are disfavored,” said Joe Kane, Information Technology and Innovation Foundation director-broadband and spectrum policy.

Kane said the issue won’t go away. “The need to find more spectrum will increasingly include consideration of whether subpar receivers are precluding productive use of neighboring bands,” he said: “The commission should make this a consideration on a band-by-band basis, even if it doesn't go forward with rulemaking on the topic in general.”

“The FCC's proceeding on receiver interference immunity could result in a Statement of Principles that sets forth a generalized set of factors or circumstances in which the commission would identify out-of-band signal interference with receiver devices operating within a specific band to be harmful,” emailed Free State Foundation Director-Policy Studies Seth Cooper. That kind of “mild approach to receiver interference immunity might be viable because it rightly would avoid new mandates on spectrum users or receiver device manufacturers,” he said: It could also “provide some guidance to incumbent users of spectrum regarding when and how they can safely and confidently increase or expand usage of their licensed spectrum without the raising specter of government intervention.”

C-Band Issues

During the FCBA webinar, Hank Hultquist, AT&T vice president-federal regulatory, said his main focus on receivers has been on radio altimeters in the C band (see 2201210001). “One of the things I found most interesting about the altimeter receiver performance is the incredible variance in their relative immunity from transmission in what’s now the C band,” he said. “There’s a huge variance among models of altimeters that up until all this blew up a little over a year ago were all in the market, were all being sold, were competing with each other, and they had just wildly different relative performance,” he said.

The C-band fight shows some altimeter makers didn’t pay as much attention to potential interference from operations several hundred megahertz away, Hultquist said: “That’s a public policy problem that we should care about.” There has been a lot of collaboration to address C-band/radio altimeter issues, Hultquist said. That should be seen as a “success story, but it’s a success story of cleaning up a mess, not a success story of avoiding a mess,” he said.

There’s “a huge focus” on front-ends and filtering, but the NOI’s focus was on receivers more generally “and receivers are more than just RF front-ends,” said former FCC Chief Technology Officer Monisha Ghosh, now an engineering professor at Notre Dame. “A receiver has a performance metric and that metric varies depending on what that receiver is trying to do,” she said: “For an altimeter it would be how precise is the altitude reading and it’s not going to be how much did the RF input to this altimeter change, because there’s so much more that goes on.”

“To truly understand” the impact of out-of-band interference “you need a really good model for the probabilistic nature of this interference,” Ghosh said. “You need a good end-to-end model, not just RF-level interference” of how the transmitter and receiver “behave in terms of their respective metrics,” she said. Receiver manufacturers need to be transparent about how their systems treat interference “and not just raise a red flag,” she said.

Addressing receivers is “really a problem of balancing equities,” said Pierre de Vries, Silicon Flatirons Center director emeritus. “Spectrum is mostly fully allocated so if you want to change your use in one band, it affects the services in the other bands,” he said.

There are two ways to approach receivers -- focusing on the RF environment or on the equipment, de Vries said. “You need to make sure that your signal-to-noise ratio is appropriate,” he said. “You can do that by reducing the power of the noise, i.e., the transmitter in the next-over band. You can do it by improving the design signals. … You can improve filtering.” Focusing on equipment is much easier for transmitters than for receivers, he warned.

There’s a misconception that all receivers are poorly designed, said John Gifft, John Deere senior attorney-hardware, software and connectivity,, who noted the company has been designing receivers since 1999. When Deere works on improving the performance of receivers, it also focuses on making them more accurate, he said.

Deere supports voluntary, industry-based standards and opposes mandatory standards, Gifft said. The FCC likely has less legal authority to regulate receivers than it does transmitters, he said: “We feel that would preclude them from establishing general standards.” Mandatory rules would also “stifle innovation,” he said. The FCC also doesn’t have the staff or expertise to create technical standards, he said.

Receivers have evolved and are improving, said Kumar Balachandran, principal researcher at Ericsson. “The general rule I have learned is that when you want really good filters they tend to be large,” he said: “When you have very small filters, then their performance tends to be relatively lower in comparison.”