AT&T wants 3.5 GHz band divided into sub-bands to promote small cell deployment

AT&T Mobility (NYSE: T) is recommending that the FCC slice up the 3.5 GHz band into different sub-bands for various classes of users so that AT&T and other licensed spectrum holders can have more certainty in deploying technologies such as small cells in the band.

AT&T's proposal is one of many the FCC is likely to consider in the months ahead as it finalizes rules for the 3.5 GHz airwaves. In April the FCC issued updated proposals regarding a three-tiered access and spectrum-sharing model for the band, with a flexible approach now being proposed for the priority access tier that could include auctioned licenses under certain conditions.

The proposed band, the Citizens Broadband Radio Service, would use spectrum-sharing techniques to open up a total of 150 MHz in the 3.5 GHz band for general consumer use, carrier-grade small cell deployments, backhaul, fixed wireless broadband services and more. The proposed access and sharing model comprises federal and non-federal incumbents, priority access licensees (PALs) that will obtain licenses to the spectrum in geographic areas, and general authorized access (GAA) users, similar to unlicensed use.

As AT&T notes, in order to have all three groups coexist without interference, a database--or what the FCC calls a "Spectrum Access System" or "SAS"--will need to be developed and launched. The SAS will include a registry of all nodes and/or devices in the band, and will have access to their geo-operational status at all times, so that the FCC can maximize the band's use and prevent unintentional interference.

Since it is high-band spectrum, the thinking has been for a long time that 3.5 GHz spectrum could be used for small cells to boost network capacity. In a company blog post, Stacey Black, AT&T's assistant vice president of federal regulatory, noted that to do so, "new infrastructure will need to be developed and deployed and new devices will need to be developed and put in consumers hands.  This will require a significant investment and some degree of certainty is going to be required to justify that investment."

Black wrote that the approach of using a database to manage different users of the bands "has a high level of deployment risk--especially if attempted all at once. As history has recently shown with other complex systems, AT&T is concerned that if this PCAST model is rushed to market, it could have disastrous consequences and could actually set progress back."

AT&T is recommending a "transitional, phased-in, interim approach to deployment of PAL and GAA operations." AT&T wants to divide the band into PAL-only, shared use and GAA-only sub-bands. "This will allow PAL and GAA service providers to develop their products for initial deployment in a familiar environment, such as in our case, licensed geographic areas with a five-year license term and a renewal expectancy coupled to build-out requirements," Black wrote.

AT&T also thinks having separate PAL and GAA sub-bands "would provide immediate access for deployment without any fear of interference and 100% of the attention can be focused on preventing interference to/from the federal incumbent users." AT&T also wants to use the shared-use sub-band "as the development space" for the database that manages the band. That way, from AT&T's perspective, all of the users "collaborate, field test and ultimately deploy the three tier model without any concerns of interfering with the PAL or GAA-only sub-bands." Finally, when the database systems have been developed and fully tested and the transition period ends, AT&T thinks the three sub-bands can be eliminated, and allow all three user groups to share the entire band as originally intended.

For more:
- see this AT&T blog post

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