Dynamic Protection Area (DPA)

A DPA is not a dynamic shape; it is a pre-computed, static polygon defined by regulators. The 'dynamic' aspect refers to its activation status, not its borders.

• Definition: A fixed geographic zone established by the NTIA and FCC to protect a specific federal incumbent, typically a shipborne radar operating near a coast.
• Granularity: Boundaries are defined using high-resolution geospatial data, often encompassing a coastal exclusion zone and an inland protection contour.
• Activation Trigger: The SAS activates the DPA only when the federal incumbent's system is actively transmitting, requiring a secure, real-time signal from the Environmental Sensing Capability (ESC) network.

The SAS must ensure that the sum total of RF energy from all CBRS Devices (CBSDs) does not exceed the incumbent's interference protection criteria at the DPA boundary.

• Protection Threshold: The federal radar is protected by an Aggregate Interference Margin, typically a very low power flux density (e.g., -109 dBm/m²/MHz) at the DPA's edge.
• Computational Complexity: The SAS uses a Monte Carlo simulation or iterative optimization algorithm to calculate the cumulative interference contribution from thousands of CBSDs.
• Power Reduction: If the aggregate threshold is exceeded, the SAS commands specific high-power CBSDs to reduce their EIRP or cease transmission entirely, a process known as suspension or power back-off.

The DPA's dynamic activation is entirely dependent on a dedicated network of highly sensitive RF sensors called the Environmental Sensing Capability (ESC).

• Sensor Network: An ESC operator deploys a mesh of sensors along a coastline to detect the specific radar signatures of federal shipborne systems.
• Latency Requirement: Upon detection, the ESC must relay a 'DPA Active' signal to the SAS within 5 seconds, and the SAS must reconfigure affected CBSDs within 60 seconds of receiving that notification.
• False Positive Mitigation: ESC systems use advanced cyclostationary feature detection to distinguish federal radar pulses from commercial signals or noise, minimizing unnecessary DPA activations.

DPA activation triggers a strict, hierarchical reconfiguration of the CBRS three-tier spectrum access system to prioritize the Incumbent Access (IA) tier.

• Tier 1 - Incumbent: The federal radar's operations are sacrosanct and receive absolute protection from all CBRS users.
• Tier 2 - Priority Access License (PAL): PAL holders are guaranteed interference protection from GAA users but must yield to the Incumbent. During a DPA event, their high-power operations are suspended.
• Tier 3 - General Authorized Access (GAA): GAA users are the first to be terminated or power-reduced. They operate on an opportunistic, unprotected basis and bear the brunt of DPA-driven reconfigurations.

The SAS's response to a DPA activation is governed by strict, FCC-mandated timing windows to ensure the federal incumbent is never exposed to harmful interference.

• Heartbeat Mechanism: CBSDs must maintain a constant 'heartbeat' connection with the SAS. If a heartbeat is lost during a DPA event, the CBSD must autonomously cease transmission within 60 seconds.
• Suspension Order: The SAS transmits a suspension or power reduction order to a specific subset of CBSDs identified as contributors to the aggregate interference.
• Relinquishment Confirmation: The CBSD must acknowledge the order and vacate the channel, a process that must be completed within the 60-second window to maintain compliance.

DPAs are categorized based on the operational domain of the protected federal system, which dictates the SAS's interference calculation model.

• Coastal DPAs: Designed to protect shipborne radar systems operating in littoral waters. These DPAs extend inland from the coastline and are activated dynamically based on vessel proximity detected by the ESC.
• Inland DPAs: Protect fixed terrestrial federal systems, such as ground-based radar installations. Activation may be based on scheduled operational periods or a dedicated ESC sensor at the site.
• Propagation Modeling: The SAS must use a specific, approved irregular terrain model (e.g., ITM) to accurately predict path loss from CBSDs to the DPA boundary, accounting for coastal ducting and terrain obstructions.

The centralized, cloud-based automated frequency coordinator mandated by the FCC for the 3.5 GHz CBRS band. The SAS is the computational engine that activates a DPA by aggregating sensor data, calculating the aggregate interference margin, and issuing commands to CBSDs.

• Core Function: Authorizes transmissions and enforces protection criteria
• DPA Role: The SAS is the sole entity authorized to activate a DPA and suspend GAA/PAL operations
• Protocol: Uses the WInnForum standardized SAS-CBSD protocol for real-time control

A network of RF sensor receivers deployed along coastlines that detect federal incumbent radar signals in real-time. The ESC is the physical sensing layer that triggers DPA activation.

• Detection Target: Shipborne and airborne federal radar systems operating in the 3550-3650 MHz band
• Activation Latency: Detects radar pulses and notifies the SAS within < 5 seconds
• Deployment: Operated by ESC operators certified by the FCC and DoD

The 150 MHz wide shared spectrum band (3550-3700 MHz) governed by a three-tiered access hierarchy. The DPA is the primary mechanism for protecting the top tier.

Three Tiers:

• Tier 1 - Incumbent Access: Federal radar systems and FSS earth stations; absolute priority
• Tier 2 - Priority Access License (PAL): Licensed users with interference protection from GAA
• Tier 3 - General Authorized Access (GAA): Opportunistic, unlicensed access; first to be suspended during DPA activation