What You Need to Know About the 3.5 GHz Band on Campus
This frequency could provide a cost-effective link between cellular and WiFi.
- By Dian Schaffhauser
- 04/05/18
Rare is the campus with total coverage of cellular service. Maybe the problem surfaces for your institution in its basement-level spaces, or that oldest building on campus with walls built to bomb-shelter standards, or the newest, LEED-certified facility that uses energy-efficient glass or other construction materials that block radio frequency. Whatever the site or cause, it's a big problem. Most mobile traffic originates inside buildings (ABI Research pegs it at more than 80 percent), so people get frustrated when they can't use their devices to make a phone call — particularly in an emergency.
"Cellular has never been easy, especially in higher ed," asserted Rod Perry, principal of Cellular Savvy Consulting. "You have to have infrastructure from four carriers; the carriers don't have the money to build everything out; and historically [they] were only interested in covering sports arenas and stadiums, with a particular focus on the 'big schools.'" Forget about that basement where nothing cellular penetrates. You just have to suffer with "cellular dead zones."
While some schools have purchased distributed antenna system equipment to improve cellular performance, DAS is an expensive option ($2-$4 per square foot for coverage of all major carriers), said Perry, and most institutions have decided it makes more sense to put that money into robust WiFi. And even where DAS has gone in, he noted, campuses still need cellular radios to power the system, and "carriers are not always willing to provide those at no cost."
Of course, there are WiFi and even wired connections that may exist in cellular dead zones, but use of those comes with its own complexities (like needing to log in) and still aren't widely used for voice applications.
What's needed is a service that's as simple to use as cellular but as pervasive and inexpensive as WiFi. 3.5 gigahertz Citizens Broadband Radio Service (CBRS) may be the answer.
The Basics of 3.5 GHz CBRS
This frequency exists halfway between the existing WiFi bands (2.4 GHz and 5 GHz) and is used right now by naval radar systems and for satellite ground communications. Importantly, it taps a 150-megahertz band of contiguous spectrum.
Under the previous administration, the Federal Communications Commission began studying the possibility of setting up new rules for making excess spectrum available to as wide a set of users as possible. The agency came up with a three-tier spectrum-sharing framework: "incumbent," "priority access license" (PAL) and "general authorized access" (GAA). A "spectrum access system" (SAS) would coordinate usage among those incumbent military and satellite users and the new "commercial" users.
As described by the trade association CBRS Alliance, the SAS is an "advanced, highly automated radio spectrum coordinator" within the CBRS band in charge of "protecting" the incumbent users from the new ones and "optimizing efficient use of the available spectrum in the band for all users." The 150 MHz of spectrum would be dynamically shared. According to the new FCC rules, at least 80 MHz of the spectrum would be made available for "general authorized access," but sometimes, where there are no incumbents or PAL users in an area, the entire 150 MHz would be opened up for use by GAA users.
Although the incumbents take priority over everything else in the spectrum, there's a "struggle afoot," said Perry, regarding the PALs. "Historically, the PALs were going to cover a fairly small area and be for a three-year duration. This means that non-traditional users like higher ed could economically purchase a PAL and reserve some spectrum for their specific users." Now, however, there's a big move by the mobile operators to pressure the FCC to structure PALs like their regular cellular spectrum leases — with big areas and 10-year-plus terms. "This move," he warned, "would essentially just turn the PALs over to the cell carriers and that spectrum would look like cellular spectrum today — proprietary and expensive."