CBSD stuck on suspended grant

[GerardoBarrient]

Issue: CBSD has been stuck with suspended grants due to DPA activity since April 11th at 10:00 AM. (This is an example but we have seen the same in other CBSDs)

We understand that the PAL channel is unavailable at this location due to radar or high DPA activity, as shown in the spectrum availability.

Our question is: why hasn't the CBSD automatically relocated to the top 50 MHz of the band? In similar cases, we've typically had to manually restrict the spectrum to the top 50 MHz within the CBSD configuration.

Supported spectrum configured: 150MHz

CBRS Frequency Type is set to PAL as top priority.

CBSD: AH220705115

Additional Details:

We're noticing that Google's SAS behaves differently compared to the other SAS server we’ve been working with.

With the other SAS server, it seems easier to obtain authorized grants without needing to restrict the inquired spectrum in the CBSD configuration. If a requested channel (PAL or GAA) isn’t available, the system can reallocate to a different one, allowing the CBSD to still receive grants.

With Google’s SAS, however, we often need to limit the inquired spectrum to the top 50 MHz to successfully receive grants and avoid suspended grants caused by DPAs, sometimes for an undetermined period.

We've also been trying to leverage the PAL Prioritization feature to maximize PAL usage and enhance customer benefit.

The challenge we’re facing is that when PAL channels are unavailable due to DPA activity, the grant on the PAL channel gets "stuck" in a suspended state—sometimes for several hours or even days. With the other SAS provider, if a PAL channel isn’t available, a GAA channel is automatically allocated instead.

Thanks!

[James_S]

@GerardoBarrient 

Our investigation shows that this CBSD successfully requested multiple grants in the upper 50 MHz on 04/11/2025, but then immediately relinquished them. We believe that this is the cause of the issues you've experienced. 

Let's clarify the process for handling suspended grants and how new channels are allocated:

1. Grant Suspension vs. Reallocation: When the SAS determines that an active grant would cause interference for a higher priority user (like DPA activity), the SAS instructs the CBSD via its heartbeat response to suspend transmissions on that specific frequency. The grant remains associated with that frequency but in a suspended state. Standard SAS-CBSD protocols do not involve the SAS automatically reassigning an existing, suspended grant to a completely different frequency band (like the upper 50 MHz). The SAS is also not able to issue a grant independently, the CBSD must request them from the SAS.
2. Requesting a New Grant: For the CBSD to operate on a different channel (e.g., in the upper 50 MHz), it needs send a new grant request to the SAS for a channel in the desired, available frequency range. The SAS can only approve or deny grant requests initiated by the CBSD.
3. CBSD Behavior Observed: Reviewing the history for CBSD AH220705115 around the time of the issue on April 11th, we see the following:
   • The CBSD did attempt to acquire new grants by sending several requests for channels within the upper 50 MHz band.
   • These new grant requests were all approved, but then temporarily suspended with the reason: "Interference Calculations Pending". This status typically occurs in areas with high CBSD density, like the upper 50 MHz band if many operators avoid the lower frequencies due to DPA activity. It usually means the SAS needs a brief moment (often just seconds, rarely more than a minute or two) to complete interference calculations before authorizing transmission.
   • However, the logs show that the CBSD relinquished these temporarily suspended grants almost immediately (within about a second), rather than continuing to heartbeat for the short period needed for authorization.

Conclusion:

Based on the logs, the reason the CBSD didn't successfully operate in the upper 50 MHz after the PAL channel became unavailable wasn't because the SAS didn't offer or approve channels there. Instead, the CBSD attempted to get grants in that band but then relinquished them prematurely when faced with a very short, temporary suspension related to interference calculation processing time.

The optimal behavior in response to an "Interference Calculations Pending" suspension is typically for the CBSD to continue heartbeating on the grant request, as the suspension is usually lifted very quickly. Manually restricting the CBSD's configuration to the upper 50 MHz works because it forces all grant requests into that band, bypassing the DPA issue, but it doesn't change how the CBSD handles temporary suspensions like the one observed here.

The SAS prioritizes the order of the spectrum inquiry channels in descending order of predicted channel quality. The logs for this device show that the SAS prioritized suggesting grants in the upper 50 MHz to this device. The device used those suggestions, but then relinquished the grants afterwards. 

We recommend discussing this specific relinquishment behavior with your CBSD vendor. They can help determine why the device is configured to relinquish grants so quickly under the "Interference Calculations Pending" condition, rather than waiting for authorization. Adjusting this behavior within the CBSD may resolve the issue you're observing. 

Please let us know if you have further questions or if we can assist with analyzing any other specific instances.