An FCC proceeding about how to handle the 3.45-3.55 GHz band is bringing up new questions about how spectrum gets managed in the 3.5 GHz Citizens Broadband Radio Access (CBRS) band.
If Google gets its way, it would mean transitioning away from the established Environmental Sensing Capability (ESC) system currently used to manage sharing in the CBRS band and adopting an Incumbent-Informing Capability (IIC) framework, which would put the federal government more in the driver’s seat.
Federated Wireless, which operates as a Spectrum Access System (SAS) administrator and built its own ESC network, says the ESC system works just fine and moving to another way of managing shared spectrum isn’t a good idea. Both Federated and Google are operating as SAS administrators; Google’s ESC system was built with CommScope.
The ESC network can detect when naval radar needs access to a portion of the 3.5 CBRS spectrum. Commercial users are then moved onto other channels, thereby protecting the incumbent government users, which are most often Navy ships. The ESC networks are built along the coastlines of the contiguous United States.
The disagreements about how to move forward are coming to light now in part because the FCC asked for comments in a Further Notice of Proposed Rulemaking (FNPRM) related to future commercial shared use of the 3.45-3.55 GHz band. Both Google and Federated have submitted comments to the FCC.
Federated Wireless advocates for combining the 3.45-3.55 GHz with CBRS and taking advantage of the ESC that’s already established. Google proposes that the ESC system be ditched in favor of the IIC-based system. The IIC idea is not new; it was brought up during initial conversations about how the CBRS should be managed, but the FCC and Department of Defense (DoD) decided to go with ESC, according to Kurt Schaubach, CTO of Federated Wireless.
In a recent blog post, he called out Google for raising the “disingenuous concern” that the ESC network is a failure and that regulatory bodies and the industry should consider the IIC approach. IICs may well become the best option for spectrum sharing in the future, but it’s going to take years of development, testing and operational training to do it right, he said.
The FCC’s FNPRM notes that the government is considering the development of an automated, real-time, IIC system that the National Telecommunications and Information Administration (NTIA) would operate in conjunction with the DoD to notify commercial entities when the latter would need to cease operations. That’s the kind of framework that Google supports because, it says in a November 20 filing (PDF), the IIC would help to overcome “major shortcomings” in the CBRS ESC framework.
Implications for PALs
Entities that bought licenses in the CBRS Priority Access License (PAL) auction this past summer surely are interested in any “shortcomings” associated with the CBRS framework. Bidders in the PAL auction spent more than $4.5 billion for their licenses and investments have been made in the General Authorized Access (GAA) portion of the band, which is for unlicensed users.
Federated Wireless takes a lot of pride in its ESC network. It built in redundancies, tweaked algorithms – everything they needed to meet five 9s reliability and withstand events like hurricanes. “We knew how vital it was going to be to have a network that performed well for customers once commercial service began,” Schaubach said, so they built in these geographic redundancies.
One example of the depths in which they’ve gone is tracking down interference emanating from a lobster shack in Maine. When the restaurant fired up its boilers to cook lobster, the generator used to run the boilers created interference with Federated's ESC and the company had to work with the lobster shack to mitigate the situation.
By contrast, Google and CommScope started their ESC network deployment later and use fewer sites, he said. “As we’ve clearly heard from customers who have converted from using Google as their service provider to us, they appear to have a number of performance issues,” he said. “They haven’t made the sort of investment that we’ve made in terms of optimization” and hardening.
For an end user, the lack of optimization could mean activations of dynamic protection areas (DPAs) that may be triggered by noise instead of real radar use, or it may be a failure of an ESC site due to loss of power that causes it to activate a DPA and reduce the amount of spectrum available for end users. “We’re able to provide a much more stable and reliable spectrum environment for customers because of the investment and work we did to optimize our ESC,” he said.
The problem they saw early on were false activations, much like if someone were to install a Ring doorbell and it goes off every time someone walks by with a dog. It takes a lot of fiddling to get it to work right and avoid those false triggers.
Google blames ‘whisper zones’
According to Andrew Clegg, Google’s spectrum engineering lead, the ESC framework was not Google’s first choice when decisions were made to go that route. The purpose of an ESC sensor is to detect government radar and alert the SAS so that it can reconfigure CBRS devices to avoid interference.
But there are “whisper zones” inherent in the design of ESC-based systems, and it doesn’t have anything to do with how Google’s network is designed or Federated’s network is designed. Whisper zones are areas near ESC sensors where CBRS operations are restricted so as not to cause interference to the sensors, which are listening for the radars in the same band.
Google and CommScope operate a joint ESC network and spent a lot of time engineering the sensors to minimize the whisper zones. They use an antenna design that attempts to minimize the response to potential interference. “We’ve gone to great lengths to carefully design our network,” Clegg said, adding that Google and others have asked Federated to reduce their impact because the more sensors that are deployed, or the more susceptible the sensor design is to interference from CBRS devices, the more impactful whisper zones become, which prevents people from being able to use the spectrum. But they’ve had no luck on that score.
It’s a timely issue because those who obtained licenses in the PAL auction are expected to deploy in earnest in the first quarter of 2021. But a whisper zone can block all 100 MHz of PAL spectrum (3550-3650 MHz) in areas near the ESC sensor, which is why Google worked hard to minimize its whisper zones, according to Clegg.
“We believe in the long run, the IIC will be less impactful to PALs,” and create a bigger playing field. “We feel it’s more secure,” and it gives the incumbent government users more control.
Once an IIC is built, it’s easy to apply to other spectrum bands, whereas if the industry sticks with ESC, it has to learn new waveforms and add more hardware, and that takes time. The IIC would be implemented through software.
Of course, they recognize that moving to IIC means deactivating the ESC network that Google and CommScope worked on for the past few years to design and deploy, but “we think in the long run, the CBRS users and the incumbents will benefit,” he said. By getting rid of the whisper zones, you get better access to the spectrum.
Jesse Caulfield, CEO of Key Bridge Wireless, which is also in the process (PDF) of getting an ESC network certified by the FCC, said the IIC system is “definitely more convenient” for a commercial operator, and he expressed his desire for IIC to the FCC and DoD back in 2011. But he’s since learned that it has a fatal flaw: It requires and presumes the government can and will create a legal, secure and reliable process to notify commercial operators.
“There have been studies, reviews and an endless sequence of meetings on this topic and while it may be technically possible, we’ve learned over the past half decade that there is no good reason the military can or should do this: the operational and information security risks are just too great,” he told Fierce via email, adding that ESC systems now seem to be operating as envisioned.
While the FCC and other stakeholders will have to decide which route makes the most sense, Clegg said Google and Federated are on the same side in that they want to continue to make CBRS a success – more than 100,000 CBRS radios have been deployed. But some tough decisions will need to be made, and relatively soon, as other spectrum bands get teed up.