In 2015, the Commission adopted rules for shared commercial use of the 3550-3700 MHz band (3.5 GHz band). The Commission established the Citizens Broadband Radio Service (CBRS) and created a three-tiered access and authorization framework.

https://www.fcc.gov/35-ghz-band-overview

1. Incumbents: Existing users (e.g. US Naval Radar, DoD personnel) get permanent priority as well as site-specific protection for registered sites.

2. Priority Access Licenses (PAL): Organizations can pay a fee to request up to four PALs in a limited geographic area for three years. Only the lower 100 MHz of the CBRS band will be auctioned off; with restrictions of a maximum of seven concurrent 10 MHz PALs

3. General Authorized Access (GAA): The rest of the spectrum will be open to GAA use and coexistence issues will be determined by SAS providers for spectrum allocation.

https://www.leverege.com/research-papers/cellular-lpwa

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.

https://www.networkworld.com/article/3180615/faq-what-in-the-wireless-world-is-cbrs.html

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.

https://www.fiercewireless.com/private-wireless/what-a-cbrs-spectrum-access-system

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.

https://support.google.com/sas/answer/9539282?hl=en

Five companies operate Spectrum Access Systems (SAS): Federated Wireless, Google, CommScope, Amdocs, and Sony. A sixth, Key Bridge Wireless, has a system in field trials.

Every SAS provider must develop or license an Environmental Sensing Capability (ESC).

https://www.fiercewireless.com/private-wireless/cbrs-users-learn-ins-and-outs-spectrum-access-systems

Because there is more than one SAS operating, the SAS Administrators must coordinate spectrum not only among all of the transmitting devices within their purview, but also devices being managed by the others. This occurs during each overnight period, known as a Coordinated Periodic Activity Among SASs (CPAS), so the entire system is aware of all devices operating in the band.

A User Equipment (UE) device that operates under 23 dBm EIRP (typically a handset) is not required to be registered to a SAS, but can communicate via a CBRS network. Anything that’s higher power needs to register and maintain connection to a SAS, and is known as a CBSD (CBRS Device).

https://www.cambiumnetworks.com/wp-content/uploads/2020/02/CBRS_FAQ_v1_.pdf

CPAS currently runs from 7 AM UTC–10 AM UTC each day. During CPAS, the SAS can’t issue new grants. At the end of CPAS, the SAS notifies the CBSD of any required changes through the heartbeat response.

https://support.google.com/sas/answer/9554929?hl=en