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How the Spectrum Access System (SAS) works

The Spectrum Access System (SAS) is a cloud-based service that manages the wireless communications of devices transmitting in the CBRS band, in order to prevent harmful interference to higher priority users. 

A CBRS device (CBSD) needs authorization from the SAS before it starts to transmit in the CBRS band. CBSDs communicate with the SAS using the SAS-CBSD API.  


  • The SAS has no way to proactively reach out to a CBSD, so the CBSD must initiate all communications.
  • The Wireless Innovation Forum (WInnForum) establishes protocols for communication between CBSDs and the SAS. Google has implemented the protocols in the SAS-CBSD API.

How CBSDs communicate with the SAS

The SAS-CBSD API defines six methods that a CBSD can use to communicate with a SAS. 

How the SAS protects higher-priority users

To make sure that higher priority users are protected, the SAS communicates with CBSDs and performs activities, like: 

  • To protect the highest-priority users, Naval radar operators, the SAS uses a sensor network of sensors to detect when they're using the spectrum. This means that sometimes, some portions of the CBRS spectrum is unavailable in regions near the coast. Learn more about deployment availability.
  • Every night, all SASes execute a process called Coordinated Periodic Activities among SASes (CPAS) to make sure that they're operating with the latest information. Learn more about CPAS and what it means to CBSDs operators.
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