Pro Wireless Users Look Askance at Proposed White-Space Rules
Spurred by Microsoft initiative, FCC updates target improved broadband in rural areas
If the last two rounds of spectrum reallocation were the world wars of the RF landscape, the aftermath has been a series of localized skirmishes that illustrate the ongoing conflict between spectrum’s longtime professional-broadcast users and the tech giants that are furiously gobbling it up for consumer applications.
Most recently, the FCC has proposed updates to TV White Space (TVWS) rules putatively in the pursuit of improved broadband for rural areas of the country, a move spurred by Microsoft and its Airband Initiative, which seeks to bring broadband connectivity to 3 million Americans in rural areas by July 2022.
However laudable that intent, it could create additional challenges and burdens for professional wireless users. For example, some collegiate football stadiums located in rural areas face a greater potential of having their broadcasts interfered with by high-powered white-space devices that are either fixed with increased antenna height or mobile on vehicles. This is especially true if FCC Part 74 licensed wireless-microphone operators continue to have problems registering for interference protection in the White Space database system intended to prevent TVWS operation on channels reserved by the licensee.
In a previous clash in late April, the FCC announced adoption of rules that make 1,200 MHz of spectrum in the 6 GHz band (5.925–7.125 GHz) available for unlicensed use, intended as a foundation for next-generation Wi-Fi 6, which will play a major role in the growth of Internet-of Things (IoT). But the move didn’t sit well with many professional wireless users.
“Despite opening portions of the 6785-7125 GHz spectrum for Part 74 licensed wireless microphones, the FCC is now chipping away at wireless microphones’ ability to operate by adding Wi-Fi to this spectrum,” says Jackie Green, director, Nexonic Design, an RF consultancy.
Currently, the FCC’s Notice of Proposed Rulemaking (NPRM) sought comment through June 2 on a proposal to permit higher transmit power and antenna height above average terrain for fixed white-space devices in less congested geographic areas. Joe Ciaudelli, director, spectrum and innovation, Sennheiser, and a private-sector advisor in the U.S. delegation to the ITU, agrees that some elements of Microsoft’s petition can be made to work with broadcasters’ needs but contends that others could create problems.
For instance, for fixed white-space devices in rural areas, Microsoft has proposed higher power limits, to 16 W from 10 W (a value that was 4 W when TVWS devices were first permitted), and higher antenna height above average terrain limits, from 250 meters to 500 meters.
“We don’t object, provided there is a commensurate increase in separation distances from licensed wireless mic that are registered for interference protection in the database system,” says Ciaudelli. “The FCC proposed an increase from 1 meter to 1.3 km. This is inadequate. I worked with Henry Cohen [senior RF systems design engineer/frequency coordinator, CP Communications] to calculate and propose increased separation distances proportional to the original TVWS rules.”
FCC defines “less congested” areas — a critical term in delineating rural sections of the country — as meaning that at least half the channels allocated for TV broadcast are not being used (i.e., vacant, white-space channels). Other stakeholders in the petition endorse a benchmark based on population density.
Ciaudelli contends that neither measure is adequate: “We oppose this because it is more appropriate to define less congested areas in terms of the spectrum resources rather than population density. Population density is ephemeral, particularly in areas that have seasonal fluctuations. Furthermore, there are areas such as just outside major cities that are sparsely populated [but] the TV-band spectrum is densely packed. For example, portions of Bergen County, NJ, located just outside Manhattan are rural in terms of population but receive all the New York City over-the-air television stations.”
Regarding higher-power mobile operation within “geo-fenced” areas, white-space devices are categorized as fixed or (lower-powered) personal/portable, and Microsoft is petitioning for high-powered TVWS devices fixed on a moving platform in rural areas. The initial justification was that such a configuration is benign when used on a slow-moving tractor operating on a large farm. Subsequently, a use case was also made for a school bus to allow students to have internet access during the ride to and from school. However, as Ciaudelli points out, this effectively blurs the distinction between fixed and personal/portable TVWS devices.
“Theoretically, the TVWS devices would transmit only within a defined geo-fenced area,” he said. “Our concern is that it will cross the boundary before [it] refreshes its channel-availability information from the database.”
On the matter of narrow-band IoT operations, Microsoft proposed a new class of TVWS device that uses less bandwidth for IoT applications and provided a test example and three topologies related only to agriculture in rural America. However, Ciaudelli counters, the proposed rule-change language doesn’t limit the use of narrowband TVWS devices to less congested areas.
“Our concern lies in the fact that Microsoft’s desired rule is not limited to less-congested areas like the other provisions found in its petition,” he says. “If it’s truly the intention to confine the use of these devices to rural areas, then their deployment should be limited to less-congested areas by rule.”
Regarding the application of higher power on adjacent channels, current FCC rules dictate that white-space devices must operate at lower power if there are not three continuous vacant channels available, which is rare even in some rural areas. It’s a restriction that Microsoft wants relaxed. NAB opposes this stipulation especially because of potential unknowns related to NextGen TV (ATSC 3.0).
The Bottom Line
Given the loss of so much critical RF spectrum in recent years, as well as assertedly less-than-stellar implementation and enforcement of regulations intended to protect what’s left of it for professional wireless-microphone users, some wonder if the remaining areas of operation are being slowly but surely nibbled away. Ciaudelli says he understands that assessment but doesn’t completely vilify Big Tech’s actions.
“A kinder, gentler way of looking at it is that they are trying to fulfill the FCC goal of maximizing spectrum resources to provide benefits to society,” he explains. “Providing internet access to underserved rural areas of America is a noble objective that should be pursued with vigor, especially since the mandate exists to protect incumbent, licensed services, including wireless microphones.”
However, he adds, not all of the provisions in the NPRM are focused on that goal. For instance, the proposal to introduce narrowband WSD for IoT applications is “out of place in this proceeding because it is not intended to provide broadband to citizens residing in rural America like the other provisions under consideration.
“There is plenty of alternative spectrum outside the TV band that is available and suitable for non-rural IoT applications,” Ciaudelli continues. “This coat-tailed element within the NPRM is an overreach by those who either don’t realize or appreciate the overwhelming contribution [of] live sports, news, and entertainment [in fueling] the U.S. economy.”