The Spectrum Access System (SAS) is a frequency coordination system that manages the Citizens Broadband Radio Service (CBRS) spectrum in the 3.5 GHz band. It manages spectrum sharing on a dynamic, as-needed basis across three tiers.
The three tiers in the CBRS band include: Incumbent Access licenses, Priority Access licenses (PALs), and General Authorized Access licenses (GAA). The Federal Communications Commission (FCC) requires the use of a SAS administrator to coordinate and manage operations of the three tiers to prevent interference to higher priority users.
The SAS dynamically manages spectrum for all three tiers with first priority for incumbents, second priority for PALs and third priority for GAA users.
Currently, the FCC has designated five SAS administrators. These include Google, CommScope, Federated Wireless, Sony and Amdocs.
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The SAS administrators tap Environmental Sensing Capability (ESC) sensors. These ESC sensors are deployed along the U.S. coastlines, and they detect when CBRS spectrum is being used by Navy ships. If an ESC sensor detects a Naval transmission, it activates a protection zone and alerts the SAS.
Currently, ESCs from CommScope, Federated Wireless and Google have been approved by the U.S. government.
When someone wants to use the CBRS spectrum, they must contact a SAS administrator and use the cloud-based SAS database to indicate where they want to deploy their CBRS access points. They input precise data about latitude, longitude, and height into the SAS database. And then the SAS administrator determines if the spectrum is available. The SAS administrator can then assign spectrum channels and grant authority for CBRS Devices (CBSDs) to operate in the channel. The SAS administrator also authorizes the appropriate transmit power levels.
According to the FCC, SAS administrators must make aggregated spectrum usage data for any particular area of interest available to the public.