SAS

The SAS is the brain that makes CBRS's shared-spectrum scheme actually work. Every CBRS radio (a CBSD) has to register with and obey a SAS before it can transmit. The SAS knows where the incumbents are, who holds which PAL, and who's using GAA, and it dynamically grants, modifies, and revokes channel assignments so the three tiers never collide — protecting Navy radar first, PAL holders next, GAA last.

The behaviour that surprises people new to CBRS is that grants aren't permanent. If an incumbent (a radar ship, say) appears in an area, the SAS will tell GAA — and if necessary PAL — devices to vacate or change channel, in near real time, via an Environmental Sensing Capability (ESC) network that detects the incumbent. So a CBRS radio's spectrum is genuinely conditional, granted by an external authority and subject to recall. That's a different mental model from licensed spectrum you simply own, and it's worth internalising when you design a CBRS network: your channel can move underneath you, so the system has to handle that gracefully.