Incumbent Informing Capability (IIC) is actually the new kid on the block as far as spectrum-sharing mechanisms in the United States go. According to experts, the idea is for it to take over for the actual incumbent in this scenario, Environmental Sensing Capability (ESC), once it’s fully developed as a solution.

IIC Incomplete at this Time

In fact, the National Telecommunications and Information Administration (NTIA) just announced IIC will be used for 5G spectrum. Sheryl Genco, Director of the Institute of Telecommunication Sciences (ITS) at the NTIA, told 6GWorld that it’s still a work in progress. She couldn’t speak to specifics, but there are several phases in the capability’s development going beyond 2027.

“Right now, it’s what we call Phase Zero. Phase One is 2021-23 and that’s where we’re going to be talking about transitional [Citizens Broadband Radio Service; CBRS] portals, scheduler capabilities for at least some of the test ranges, things like that. Then, from 2021-23 on to the future, adding more and more development and capability,” she said.

There’s a relatively pressing need for the technology, with Genco having brought up the topic of IIC at the 6G Symposium, a virtual event co-hosted by InterDigital and the Institute for the Wireless Internet of Things (at Northeastern University) back in October. She had spoken of the potential for real-time spectrum management and how IIC was a “pre-decisional” idea in discussion between the Department of Defense (DoD), the Defense Spectrum Organization, and NTIA.

“The design to share gives us frequency-agile systems where that agility may happen one frame to the next […] It may blur the lines with regard to licensed and unlicensed bands and all of that comes down to real-time spectrum management,” she had said, mentioning how, through IIC, commercial users would be granted access to spectrum based on usage data provided by federal users (or incumbents).

“Commercial operations could then be controlled by commercially-operated [Spectrum Access Systems; SASes] to prevent interference to an incumbent. So, [IIC] could be really exciting, could eventually make use of all kinds of data. It’s important to the U.S. global leadership and next ‘G’s and it provides the NTIA the ability to control the usage of spectrum,” she had added.

IIC vs. ESC

In her recent interview with 6GWorld, she elaborated on how IIC would work. There would be a portal in which commercial entities would be notified of an incoming federal user.

“This way, for sure, from the DoD’s perspective, the radar would be detected and be able to operate,” she said. “The data would then grant access to commercial users that are in this nearby geographic area when it’s safe and appropriate for them to transmit and the commercial systems would be controlled through their SASes to prevent interference to the incumbent and abide by these rules.”

Andrew Clegg, Spectrum Engineering Lead at Google, also spoke to 6GWorld. Google is one such SAS, whose primary responsibility is to protect incumbents from harmful interference. Google accomplishes the task by authorising devices in the CBRS band to transmit based on their location and data from their Environmental Sensing Capability (ESC), a series of sensors along the coasts listening for radar.

However, in Google’s view ESC has limitations. As a result IIC is the favorable option between the two, according to a filing to the Federal Communications Commission that Clegg had co-written, specifically on the matter of “Facilitating Shared Use in the 3100-3550 MHz Band.” Clegg explained to 6GWorld how “quiet zones” have to be set up in consideration of CBRS devices up to 80 km away so that the ESC sensors themselves don’t get interfered with.

“So, depending on the geometry, the local geography, and things like that […] you can create kind of dead zones for CBRS in the vicinity of a sensor where you just can’t deploy CBRS. Because the sensors have to be on the coastline and the majority of the U.S. population is located along the coastlines, there are a lot of areas where it has a big population impact,” he said, explaining that devices up to 80 km away can still theoretically transmit, but interference from them has to be taken into consideration.

While the CBRS corresponds to the 3.5GHz (3.55-3.70GHz) band, the DoD has agreed to clear 100 MHz between 3.45 and 3.55 GHz for commercial use. It’s also been reported that ESC won’t even work in that latter band.

“The main reason is our sensors are designed to detect only certain radars,” said Clegg. “So, in CBRS, ITS, DoD working with ITS, told us which radar waveforms we needed to detect and our ESC sensors were built to detect those waveforms,” said Clegg. “In the 3450 band, there’s a different set of radars […] and it’s not necessarily a defined set of waveforms we’d have to detect. There could be advanced waveforms that they don’t want to reveal. There could be experimental waveforms that, even if they wanted to, they couldn’t tell us day to day what they might look like, and there might be passive systems that operate in the band.”

The Case to Protect and Share Spectrum

Additionally, Clegg pointed to another potential ESC shortcoming from the DoD’s perspective. With ESC, the SAS knows when an incumbent is operating, because the activity is detected. It’s less than ideal for security purposes. With IIC in contrast, an incumbent could use misdirection to its advantage by requesting protection when none is needed. There’s another IIC benefit to commercial parties at the opposite end of the figurative spectrum, too.

“Let’s say [the Navy is] just testing the radar when the ship’s in port […] they could say, ‘Well, we’re just not going to inform about that operation, because it doesn’t need protection,’ but right now we would detect that and we would shut down CBRS devices for a minimum of two hours, based upon a detection for some event that doesn’t necessarily need protection,” Clegg said.

Genco concurred. She explained how, if the DoD were to inform of its needs in a particular band, with IIC theoretically projected to operate throughout the spectrum, commercial users would benefit. They would maximise their use of the spectrum, reducing their dependency on ESCs all the while.

However, AT&T, T-Mobile, and Verizon have sought out more of a structured approach to spectrum sharing in the 3.45-3.55GHz band once it is allocated, following an auction currently slated for late 2021. The three providers had reportedly been seeking a dynamic in which the military pre-emptively sets aside locations and times at which they intend to use the spectrum, for greater predictability. Asked of the NTIA’s position in response, Genco said the goal is to facilitate spectrum sharing, but not necessarily on any terms.

“We should share, but if commercial users are going to take a hard stance one could imagine that we’d have to protect the use of those federal bands. So, who’s to say what would come of it, but I could imagine at NTIA our job is to protect and we’d have to figure that out,” she said.

She added that the Presidential mandate is to share and in her view doing so is critically important both to the roll-out of 5G and development of technology in general. She emphasised that everything on which her laboratory works supports 5G and/ or supports spectrum sharing. Clegg agreed about how much of a necessity it is.

“To the extent that we want to deploy, anybody wants to deploy 5G in mid-band or low-band spectrum, clearing is getting increasingly difficult. It’s going to always be a sharing situation. So finding ways to share limited resources is pretty much the way of the future for 5G,” he said.

Feature image courtesy of Yeexin Richelle (via Shutterstock).