CBRS SAS Frequency Allocation Cheat Sheet

This document outlines how the Spectrum Access System (SAS) handles frequency and bandwidth reallocations for CBRS General Authorized Access (GAA) users, the expected impact on live deployments, and strategies for video streaming continuity.

Bandwidth & Channel Allocation

  • First-Come, Best-Fit: SAS assigns spectrum in 10, 20, or 40 MHz blocks based on what is locally open.

  • Two-Operator Example: SAS does not force operators to opposite ends of the band. If two 40 MHz blocks are available, both are approved. If requested channels overlap, SAS simply places them in adjacent, non-overlapping blocks.

Impact of New Operators & PAL Sparsity

  • Forced Adjustments: Because GAA is shared spectrum, early arrival does not grant permanent priority. If new operators enter a crowded venue or area, SAS recalculates local usage and can force active radios to shift frequencies or narrow bandwidth (e.g., 40 MHz down to 20 or 10 MHz), instantly reducing available throughput.

  • Carrier PAL Sparsity: While tier-1 carriers like Verizon hold PAL licenses in many counties, their actual physical CBRS deployments are sparse and highly localized. In practice, PAL spectrum in most suburban, industrial, or venue environments remains physically undeployed and continues to flow into the free GAA pool.

Adjustment Timing & Navy Reality

  • Navy Radar Preemption (3–5 Minutes): Higher-priority Navy radar triggers immediate preemption, requiring impacted GAA radios to vacate or shift within 3 to 5 minutes (governed by the 240-second SAS heartbeat timer).

  • Navy Events Are Rare: In practice, Navy-instigated disruptions are rare. Unless your site sits directly on the coastline or near specific inland naval testing ranges during active radar operations, Navy preemption almost never triggers in day-to-day operations.

  • GAA Crowding Adjustments (Overnight): Routine re-allocations for new GAA entrants are calculated overnight during SAS batch processing. Radios apply new channel or bandwidth limits within a few minutes of their first post-batch check-in.

Live Downtime & Network Impact

  • RF Outage: Changing channels or narrowing bandwidth causes a 5 to 60-second RF outage while the base station relinquishes its old grant, gets a new one, and retunes.

  • 5G Core Persistence: The core network retains user IP addresses and session states, so transport sockets do not drop. However, zero data moves across the air during the blackout.

  • Live Stream Impact: Single-link video feeds will stall during a retune. Use multi-path bonding (combining CBRS with public LTE/5G) or adaptive bitrate (ABR) encoding to bridge the gap smoothly.

Pro-Tip: The Upper Safe Zone (3650–3700 MHz)

To avoid Navy preemption kicks and PAL priority claims entirely, configure your radios to operate in the upper 50 MHz (3650–3700 MHz), which is exclusively reserved for GAA users.