Google urges FCC to consider SAS model for 24 GHz band

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Google isn’t interested in seeing a three-tiered Spectrum Access System (SAS) in the 70/80 GHz bands, but it’s urging the FCC to seriously consider applying such a framework to the 24 GHz band.

In comments related to the FCC’s proceeding on spectrum bands above 24 GHz, Google said the 24 GHz band’s propagation characteristics make it a good candidate for an SAS-managed framework. Google is one of the entities working on providing SAS services as part of a three-pronged model for the 3.5 GHz band, also known as the Citizens Broadband Radio Service (CBRS) spectrum.

Not everyone is crazy about seeing the SAS model applied to other bands. U.S. wireless operators generally oppose it, saying the SAS for the 3.5 GHz band is still being worked out and remains unproven. In its comments, CTIA argued that developing and implementing an SAS regime in the millimeter wave bands will delay 5G deployment and noted that the SAS regime has yet to be deployed in any real-world environment.

But Google said that under SAS control, the 24 GHz band could provide extremely dense deployments of high-bandwidth, gigabit-class connectivity. Like it has done in the 3.5 GHz band, the commission could authorize three tiers of users: Incumbent, priority access and general authorized access.

“The nature of incumbent operations in the 24 GHz band makes this an especially attractive opportunity to extend the CBRS rules,” Google told the commission. “The FSS [fixed satellite services] uses in the band are few: Across the U.S. there are only six 24 GHz earth stations, clustered at just three sites. The handful of earth stations operate only in the uplink (Earth-to-space) mode in this band, and receive in a different band (typically 17 GHz). Therefore, potential coexistence issues among users of the band can be readily resolved with SAS-managed sharing.”

The propagation characteristics of the 24 GHz band, moreover, would facilitate sharing. That's because the zone surrounding an earth station – in which underlay services could be impacted by the earth station’s signal – would be very small due to high path losses, the company added. And a 24 GHz SAS could protect legacy fixed licensees within their licensed Economic Areas in a manner similar to how protections are provided for grandfathered Part 90 Subpart Z operations between 3.65 and 3.7 GHz.

Google and other prospective CBRS SAS operators are developing and plan to deploy clutter-aware propagation modeling technology that can increase efficiency by more accurately predicting coverage and interference. Including in-building propagation losses, the technology would offer the capability to, in effect, license spectrum in three dimensions, such that operators could operate over the same geography but at different heights, Google explained, referencing a typical situation encompassing different floors of a building. Such SAS-applied, clutter-aware modeling could be highly valuable in the 24 GHz band given the clutter loss and building loss for signals in these frequencies, Google asserted.

As for the 70/80 GHz bands, Google said the FCC should retain the existing light licensing approach that is adaptable and working well today. Google and Google Fiber pointed out that they have first-hand experience with the 70/80 GHz bands, having registered links for purposes ranging from the retail wireless broadband service of Webpass to developing Project Loon’s balloon-powered internet access technology.

For more:
- read this Google filing (PDF)

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