If you’re deploying private LTE or 5G in the US, your radios are almost certainly running on CBRS — 3.5 GHz spectrum that doesn’t require a traditional license. What makes that possible is a system called the Spectrum Access System. If you’ve ever run a WiFi network on DFS channels, you already understand the concept.

DFS channels in the 5 GHz WiFi band exist for the same reason — radar protection. When a WiFi access point detects radar on a DFS channel it vacates and finds a clear channel. The difference is WiFi self-polices: the device handles it on its own. CBRS centralizes that coordination so it works across an entire band shared by thousands of deployments.

The 3.5 GHz band wasn’t empty when the FCC opened it for commercial use. The US Navy operates shipborne radar in that band — radar that moves and can’t be assigned a fixed exclusion zone. So the FCC built a three-tier access system that lets commercial and government users share the same spectrum:

Tier 1 — Incumbents. The Navy and fixed satellite operators. Highest priority, always protected.

Tier 2 — Priority Access Licenses (PAL). Companies that paid for licensed spectrum at auction. Protected from Tier 3, yield to Tier 1.

Tier 3 — General Authorized Access (GAA). Everyone else — including most private LTE and 5G deployments. Free to use without a license.

The SAS is what holds all of this together. Every radio registers with the SAS, which knows the location, antenna height, and transmit power of every device in its network. It assigns each radio a channel and power level that keeps the spectrum clean for everyone — protecting incumbents above, coexisting with PAL holders, and coordinating between GAA users so they don’t step on each other.

Multiple SAS operators are approved by the FCC — Google, Federated Wireless, Amdocs, and others. They coordinate with each other in real time so that radios on different SAS platforms coexist seamlessly, as if the whole band were managed by one system.

When ESC sensors along the coastline detect Navy radar, they alert the SAS, which automatically adjusts affected radios — protecting military operations while keeping the rest of the band available for commercial use.

One thing worth knowing: PAL licenses only cover 3550–3650 MHz. The upper 50 MHz — 3650–3700 MHz — is GAA only. No PAL competition, no priority users bumping you. If you’re running a private deployment, that’s your cleanest range.

The SAS is what turns a shared government band into something anyone can build on.