Citizens Broadband Radio Service (CBRS)

CBRS organizes users into a strict priority structure to protect critical operations while maximizing commercial access:

• Incumbent Access (Tier 1): The highest priority, reserved for federal radar systems (e.g., naval radar) and Fixed Satellite Service (FSS) earth stations. These users are protected from all interference.
• Priority Access (Tier 2): Licenses acquired via auction for specific geographic areas (PALs), providing interference protection from General Authorized Access users.
• General Authorized Access (Tier 3): Unlicensed, opportunistic access similar to Wi-Fi, available to any FCC-certified device when spectrum is not claimed by higher tiers.

The ESC is a dedicated sensor network that acts as the eyes and ears for protecting Tier 1 incumbents, specifically naval radar operations in coastal areas:

• Detection: A network of highly sensitive RF sensors deployed along coastlines to detect specific radar signatures from federal shipborne systems.
• Notification: Upon detection, the ESC instantly signals the SAS, which triggers a mandatory channel vacation for all lower-tier CBSDs operating on the affected frequencies.
• Security: The ESC network is designed to be tamper-proof and highly reliable to ensure the absolute protection of critical national security operations.

Citizens Broadband Radio Service Devices (CBSDs) are the end-user radios that operate under SAS control, classified into two categories:

• Category A CBSD: A lower-power device for indoor or outdoor small cell deployments, limited to 30 dBm/10 MHz EIRP. Subject to more conservative interference management.
• Category B CBSD: A higher-power device for macrocell deployments, permitted up to 47 dBm/10 MHz EIRP, but with stricter professional installation and antenna registration requirements to enable precise interference modeling by the SAS.

Priority Access Licenses (PALs) are not defined by traditional large geographic areas but by census tracts, enabling granular and flexible spectrum rights:

• Granularity: The U.S. is divided into approximately 74,000 census tracts, each representing a potential license area.
• Auction Mechanism: Licenses for 10 MHz channels are awarded via competitive bidding, with a cap of four PALs per census tract to prevent spectrum hoarding.
• Flexible Use: Licensees can deploy any technology within the band, enabling 4G LTE, 5G NR, and other proprietary wireless systems under the same regulatory framework.

The SAS enforces strict, mathematically defined protection contours to ensure coexistence between tiers:

• Co-Channel Separation: PALs receive protection from GAA users on the same channel within a defined geographic contour, calculated using the Irregular Terrain Model (ITM).
• Adjacent Channel Limits: Out-of-band emission limits are enforced to prevent GAA users on adjacent channels from desensitizing PAL receivers.
• Aggregate Interference Control: The SAS models the cumulative effect of all GAA users to ensure the total interference at a PAL coverage boundary does not exceed a -80 dBm/10 MHz threshold.

A network of dedicated RF sensors deployed along coastlines to detect federal incumbent radar operations in the 3550-3650 MHz band. When an ESC sensor identifies a naval radar signature, it immediately notifies the SAS, which triggers dynamic protection zones and reallocates PAL and GAA users to alternative channels within 300 seconds. This hard real-time sensing layer is what distinguishes CBRS from purely database-driven sharing models like TV White Spaces.

A three-year, renewable license auctioned by census tract that guarantees interference protection from GAA users but requires yielding to incumbents. Key characteristics:

• Each PAL grants a 10 MHz channel (3550-3650 MHz)
• Maximum of 4 PALs per census tract (40 MHz total)
• Licensees may aggregate PALs for wider carriers
• Auctioned via clock auction format beginning in 2020
• PAL holders receive co-channel and adjacent-channel protection from GAA devices within their geographic boundary

The unlicensed, opportunistic tier that enables any FCC-certified device to operate in CBRS spectrum without individual licenses. GAA users access any portion of the 150 MHz band not assigned to incumbents or PAL holders, using a hierarchical channel assignment algorithm managed by the SAS. This tier supports LTE-TDD and 5G NR deployments for private enterprise networks, neutral host infrastructure, and fixed wireless access, making it the primary driver of CBRS adoption for industrial IoT and in-building coverage.

The highest-priority tier encompassing federal radar operations (primarily U.S. Navy shipborne and ground-based systems), fixed satellite service earth stations, and grandfathered wireless broadband licensees. Incumbents receive absolute interference protection through two mechanisms:

• ESC-triggered dynamic protection zones for coastal radar
• Static exclusion zones and protection contours for inland sites The SAS must enforce a -129 dBm/MHz interference threshold at the incumbent receiver, calculated using terrain-aware propagation models like Irregular Terrain Model (ITM).