What is CBRS?

Citizens Broadband Radio Service (CBRS) is a 150 MHz frequency band from 3550 MHz to 3700 MHz in the United States of America which was initially created for shared federal and non-federal (commercial) use. However, in January 2020, the Federal Communications Communication (FCC) authorized the entire band to be used for commercial wireless services without any restrictions. It was primarily done to accelerate and facilitate mid-band 5G deployment.

What makes CBRS unique is the way in which frequencies in this band are allocated. Instead of the usual process of spectrum auctions and licensing, it uses a three-tiered spectrum authorization framework for commercial uses on a shared basis. The three tiers of spectrum authorization are: Incumbent Access, Priority Access and General Authorized Access.

Incumbent Access - Tier 1: These users include authorized federal users in the 3550-3700 MHz band, Fixed Satellite Service (space-to-Earth) earth stations in the 3600-3650 MHz band, and, for a finite period, grandfathered wireless broadband licensees in the 3650-3700 MHz band. Incumbent Access users receive protection against harmful interference from Priority Access Licensees and General Authorized Access users.

Priority Access - Tier 2: The Priority Access tier consists of Priority Access Licenses (PALs) that will be licensed on a county-by-county basis through competitive bidding. Each PAL consists of a 10 MHz channel within the 3550-3650 MHz band. PALs are 10-year renewable licenses. For purposes of the PAL service, counties are defined using the United States Census Bureau’s 2017 counties. Up to seven PALs may be licensed in any given county, subject to a four PAL channel aggregation cap for any licensee. PALs must protect and accept interference from Incumbent Access users but receive protection from General Authorized Access users.

General Authorized Access (GAA) - Tier 3: The GAA tier is licensed-by-rule to permit open, flexible access to the band for the widest possible group of potential users. GAA users can operate throughout the 3550-3700 MHz band. GAA users must not cause harmful interference to Incumbent Access users or Priority Access Licensees and must accept interference from these users. GAA users also have no expectation of interference protection from other GAA users.

Access and operations are managed by an automated frequency coordinator, known as a Spectrum Access System (SAS) which facilitates sharing among the three tiers of authorized users in the 3.5 GHz band and authorizes the use of PALs and GAA operations with information from an approved Environmental Sensing Capability (ESC) sensor. 

Since CBRS does not require spectrum licenses, it is expected to lower the cost of transmission and also make 5G deployment quicker and easier. These frequencies were used for government purposes in the past which requires the CBRS users to “take care not to interfere with others already using nearby airwave bands is some locations, including military radar stations and satellite receiver stations”.

When a user wants access to CBRS band, they submit a request through the cloud-based SAS system. If the desired spectrum is available for use in that location, the SAS will accept the request and grand access to the CBRS spectrum. To access the CBRS spectrum, users need to use Citizens Broadband Radio Services Devices (CBSDs) which must be registered with the SAS.

In 2016, six companies formed the CBRS Alliance who were interested in promoting the commercial use CBRS. The CBRS Alliance supports common interests of members, implementers and operators for the development, commercialization, and adoption of LTE/5G solutions for the US 3.5 GHz Citizens Broadband Radio Service. As of mid-2020, it has more than 60 members which include AT&T, Comcast, CTIA, Dell, Facebook, Fujitsu, Ericsson and HCL.

The Citizen Broadband Radio Service, (CBRS), radio-frequency band, between 3.5GHz and 3.7GHz has been designated by the US Federal Communications Commission, (FCC), for shared use among three tiers of users: 

• Incumbent users, such as satellite ground stations and the US Navy
• Priority licensees who can apply for a license to use the band on the condition that they do not interfere with the incumbents and are willing to tolerate potential interference from the incumbents
• Generally authorised users, who are unlicensed and have the right to use the band on the condition that they do not interfere with the other two user categories

The FCC freed up the CBRS band as part of a 2010 initiative to make an additional 500 MHZ of spectrum available for mobile use. This shared spectrum is expected to foster innovation, particularly in the provision of 5G services. Along with the traditional mobile operators, who are looking to extend their 5G coverage and capacity, a range of managed service providers, neutral hosts and even enterprises will be able to use this spectrum to enhance in-building coverage and setup non-public networks. CBRS is one example of shared spectrum allocation, which is becoming increasingly popular on a global scale.

CBRS is know as the Citizens Broadband Radio Service. In 2015, the FCC authorized the use of the 3.5 GHz band i.e 3550 MHz to 3700 MHz for shared wireless access. This band was previously used by the US Navy and other DoD members and was not open for commercial use. The radio interface for CBRS used in this band will be the same as LTE, however the difference will be that this spectrum will be shared by all contenders who have access to this band i.e they will be able to use the spectrum when required and once they are done using it, it will be freed up for use by other requesters.

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