For Tonight’s Big Game, Thank the Navy for Sharing Its Broadband Spectrum

February 12, 2023 by Chantelle Dubois

When Kansas City squares off against Philadelphia at the Big Game tonight, the NFL will have access to the Citizen Broadband Radio System as a safety net in case of internet failure.

In Arizona, for tonight's biggest football game of the year, internet failure isn't expected to be a problem. And the technology behind that fact is interesting.

The National Football League (NFL) has submitted filings to the Federal Communications Commission (FCC) to use the Citizen Broadband Radio System (CBRS) for coach-to-coach communication during the 2023 football season.

This is a continuation of the NFL’s use of CBRS since its first filing in 2021, requesting the availability of CBRS in the event of internet failure to maintain in-stadium coach-to-coach communications. 



The most recent FCC filing indicates that during the 2022 season, the NFL never had to resort to using CBRS. But with approximately 100 million viewers expected to watch live in 2023, the NFL appears motivated to ensure the games go on without a hitch. 


What Is the Citizen Broadband Radio System?

The CBRS is a spectrum-sharing scheme that uses the 3.5 GHz band (3550–3700 MHz), a 150 MHz slice that traditionally has been reserved strictly for the Department of Defense, largely for U.S. Navy radar operations. 

Spectrum-sharing was first proposed in a 2012 President’s Council of Advisors on Science and Technology (PCAST) report titled "Realizing the Full Potential of Government-Held Spectrum to Spur Economic Growth." The report posited that spectrum sharing could increase opportunities for businesses and consumers to use radio-frequency spectrums that were otherwise not operating at full capacity.

A key feature of CBRS is the three-tiered approach and mixed licensed and unlicensed use. Tier 1 are users like the Navy who have first right and priority access to the spectrum. Tier 2 is Priority Access Licenses (PAL), which may be businesses that purchase licenses for 10 MHz channel blocks that are allocated dynamically. Tier 3 is General Authorized Access (GAA) users, who can access channels dynamically in the spectrum when it is not being used by Tier 1 or Tier 2 users. For this spectrum-sharing scheme to work, Tier 1 users must be protected from harmful interference. Users are shuffled to and from the CBRS network as priority and demand dictate.


The CBRS offers a three-tiered shared spectrum

The CBRS offers a three-tiered shared spectrum. Image used courtesy of Qualcomm

Outside of the CBRS scheme, radio bands are licensed to commercial entities by the FCC through bidding, a lottery, or on a first-come-first-serve basis, depending on the exact spectrum and use case. Such licenses are awarded for terms that can be as short as one year or as long as 20 years.  

Improving the efficiency of radio band use is of great concern to the FCC since they are a limited resource. While it is limited, it is also in greater demand due to increased reliance on wireless communications. 


Technology Creating Order in the CBRS

The first among the supporting technologies are Environmental Sensing Capability (ESC) systems. The National Institute of Standards and Technology (NIST) is responsible for designing the sensors and associated software that monitors the RF environment and sends data about usage and traffic to the Spectrum Access System (SAS). If an ESC detects federal signals (Tier 1), the supporting CBRS system will implement mechanisms to ensure that the signal has priority access and is free from interference. 


Systems deployed in the neighborhood of an offshore dynamic protection area

Systems deployed in the neighborhood of an offshore dynamic protection area. Image used courtesy of NIST


The NIST has software tools and RF datasets to test and certify ESC systems using deep learning to recognize priority traffic. There is also an IEEE 1900.8 working group that defines a standardized approach for creating data sets and learning methods for this purpose.

Certain vendors, including Google, Sony, Amdocs, and Federated Wireless, are licensed by the FCC to deploy Spectrum Access Systems (SAS). These vendors can build CBRS networks. Using SAS, they can authorize users to access the CBRS spectrum. The SAS also coordinates with the ESC to ensure that the spectrum is prioritized as needed. 

Users in Tier 3 are managed by a Generalized Authorized Access scheme. When there is “white space” in the spectrum, a GAA user can be dynamically allocated to CBRS channels.


Illustration of the Dynamic Spectrum Access (DSA)

Illustration of the Dynamic Spectrum Access (DSA). Image used courtesy of NIST

National Advanced Spectrum and Communications Test Network

The National Advanced Spectrum and Communications Test Network (NASCTN) was established in 2015 to support the development of spectrum-sharing networks. It is comprised of several key partners, including NIST, the U.S. Department of Defense, NASA, the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation (NSF), and the National Telecommunications and Information Administration (NTIA).

The NASCTN has a framework to test the CBRS using real-world data and infrastructure and improve its ability to share spectrum while protecting federal use of the spectrum. In mid-2022, a report was published on simulations and tests the NASCTN conducted to collect data and characterize the ESC system and SAS.

The NIST website indicates that the CBRS Sharing Ecosystem Assessment under the NASCTN is currently in Stage 3: Test, Metrology, and Implementation Plan, and 105 licenses have been auctioned.