• United States

FAQ: What in the wireless world is CBRS?

News Analysis
Jul 27, 20215 mins

Citizens Broadband Radio Service is shared wireless spectrum in the 3.5GHz band that could have big implications for building private LTE networks and for extending public 4G and 5G services.

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Credit: Thinkstock

First off, CBRS is an acronym for Citizens Broadband Radio Service, and the upshot for IT pros is that it’s enabling enterprises to build their own private 4G/5G networks and result in improved 4G/5G offerings from service providers. Here’s a primer on CBRS—because you are going to want to know about this.

CB, as in CB radio?

No, good buddy, this has nothing to do with the Citizens’ Band radio service used by truckers for two-way voice communications and that lives in the 27MHz band in the US. CBRS lives in the 3.5GHz band.

What is CBRS then?

CBRS is a band of radio-frequency spectrum from 3.5GHz to 3.7GHz that the Federal Communications Commission has designated for sharing among three tiers of users: incumbent users, priority licensees and generally authorized, which is lightly licensed.

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The incumbents are those who have historically held exclusive rights to the band, namely satellite ground stations and the US Navy. Priority licenses were auctioned off last year, allowing licensees to use the band in particular US counties so long as they don’t interfere with the incumbents and tolerate possible interference from the incumbents. (ISPs like Verizon and Comcast spent the lion’s share of the money paid out in the auction.) Generally authorized access gives users the right to use the band as long as they don’t interfere with the other two categories of users.

Who’s guarding against interference?

A network of sensors—the Environmental Sensing Capability (ESC)—detects use of CBRS. Devices that want to use the CBRS band first put in requests to a cloud-based Spectrum Access System (SAS) to reserve unused channels in a particular geographic area. If channels are free, SAS can grant the requests. When devices that have been granted permission to use channels are done with them, the channels are put back into the pool that the SAS can draw from to grant further requests.

How did the 3.5 GHz band become available?

The freeing up of the 3550-3700 MHz band stems from the 2010 National Broadband Plan issued by the FCC, which set out to make 500 MHz of additional spectrum available for new mobile uses. The FCC zeroed in on the 3.5 GHz band (which has dubbed the “innovation band”) in rules issued in April of 2015, then reaffirmed those rules about a year later. Some details about implementation are still up in the air, however, as carriers disagree amongst themselves about some technical specifics – some smaller carriers want the opportunity to expand their 5G coverage without buying fully licensed spectrum, and have therefore argued for allowing higher-powered access points in the CBRS bands, while larger providers remain on the fence. The FCC has indicated that it is interested in hearing full comment from both sides.

Who’s going to use this spectrum?

Carriers look forward to using it to extend coverage and capacity of their 4G LTE and 5G networks. They are, after all, facing a continuing spectrum crunch. But cable operators looking to get into wireless also want in on this action, as do assorted managed service providers, which includes entities such as building-management companies that need to communicate wirelessly with on-site devices. What’s more, enterprises could use the spectrum to set up their own 4G and 5G networks with which they could connect their IoT devices including factory robots. The services work both indoors and outdoors.

What applications will use CBRS?

Service providers are expected to use CBRS to replace last-mile fiber access to customer sites, deliver fixed-wireless services, and even point-to-multipoint connections. Enterprises and managed service providers could exploit it for IoT connectivity and even for Wi-Fi replacement or supplementary services. LTE services could hit 1Gbps indoors and maybe five or 10 times that for outdoor uses with line-of-sight access. 5G could be 10 times faster than LTE.

How expensive is it?

CBRS backers say the economics of this technology are much better than those of distributed-antenna systems, and they contend the speed and consistency of service will be much better than Wi-Fi. CBRS supporters also say imaginative new services will be enabled by the availability of more cheap spectrum. Federated Wireless has introduced a 4G/5G service being sold through AWS, and Microsoft Azure has sold it as connectivity to the cloud. 

Where will hardware, software, and services come from to support all this?

Here’s one clue: Almost 190 vendors, from the Big 4 carriers to service-provider equipment vendors Ericsson and Nokia to enterprise-equipment companies like Cisco and Ruckus to chipmakers like Intel and Qualcomm have banded together in the OnGo Alliance. Formerly the CBRS Alliance, the group’s membership has swelled to include just about every major player with an interest in wireless networking over the past year. Platform companies like Facebook and Google have joined, as have ISPs like Charter and Comcast, and even the venerable CTIA wireless trade industry group is an official supporter. More than 2,500 companies have been certified as professional CBRS installers as of February, according to the Wireless Innovation Forum, an industry umbrella group. Coverage plans and technical sensor specifications for the ESC system have been approved, and rollouts of that system are ongoing.