Unexpected Frequency Grant Behavior in DPA Zone with Google SAS – Need Clarification

[heisenberg600]

Hi everyone,

I’m operating a CBSD using Google SAS within a DPA (Dynamic Protection Area) zone and I’ve encountered some puzzling behavior:

1. Often, the frequency I request via the domain proxy is not granted. Instead, SAS grants a different frequency.

2. In some cases, even after a grant is issued, it is later moved to a different frequency.

3. Additionally, I’ve observed that even the newly granted frequency may be revoked shortly after—especially when the DPA activates.

I’m trying to understand what’s happening here. A few questions:

• Does Google SAS internally prioritize certain frequencies over others, perhaps based on its interference calculations or protection algorithms?

• Is it avoiding frequencies that are likely to be on the DPA move list, hence auto-assigning something “safer”?

• Why might even an alternate frequency grant be short-lived or suspended?

Any insights from others who’ve operated radios in DPA zones or with Google SAS would be appreciated. Documentation references or links are also welcome. Also if we can get any historical DPA event related data wrt a location that can help in choosing frequency, it would be super helpful.

Thanks!

[James_S]

@heisenberg600 

The SAS doesn't issue grants independently. Any grants your DP gets from the SAS, it has to request and specify the channel(s). If your DP  is losing grants due to DPA suspensions or getting grants on unexpected frequencies, that is almost certainly because your DP is manually requesting grants on new frequencies.

Google SAS does prioritize spectrum inquiry results based on estimated channel quality. it tries to take into account both available max EIRP and interference from other CBRS users in the area when prioritizing channels. The channels with the highest channel quality are generally prioritized first in the SI results. 

The main takeaway here is this: your DP is the one that is in charge of requesting grants and specifying the frequencies of those grants. It also decides how long to keep those grants. Google SAS will occasionally terminate grants, but these grant terminations only happen a single time a day: at the end of CPAS. These grant terminations usually occur because of a PPA in the area, not a DPA. The behavior you are describing sounds like you are losing grants much more often than that. That's indicative that this is something that your DP is choosing to do. If you want to know why your DP is choosing to behave in this manner, your device vendor is likely going to be the best place to ask.

[heisenberg600]

Thanks for the response. I have a follow-up question:

Does the spectrum inquiry ranking of channels also factor in the historical DPA or PPA activity on those frequencies? For example, do channels that have had frequent DPA/PPA-related suspensions show up lower in the spectrum inquiry results?

Also, is there any way to pre-check a location (before deploying a CBSD) to estimate the likelihood of it being impacted by DPA or PPA activity—maybe based on past events or any insights exposed by the SAS? This would help in planning in coastal or sensitive areas.

Would appreciate any pointers or clarification.

[James_S]

@heisenberg600 

It's important to remember that DPAs and PPAs are distinct and managed differently:

Regarding Dynamic Protection Areas (DPAs):

• Spectrum Inquiry Ranking and Historical DPA Activity: The SAS aims to provide the most current and best available channel information in its spectrum inquiry results. However, DPAs are dynamic and activate based on real-time needs of higher-priority users, often naval operations near coastal areas. Because of this, it's not possible to predict precisely which channels will be affected when a DPA activates. Therefore, the spectrum inquiry ranking does not deprioritize channels based on historical DPA-related suspensions. If you need to eliminate the risk of DPA-related grant suspensions, you could consider requesting grants exclusively in the upper 50 MHz of the band. DPAs only activate in the bottom 100 MHz.
• Pre-checking a Location for DPA Likelihood: While the SAS cannot predict future DPA activations, we do offer DPA neighborhood overlays in the SAS Portal. These visual tools can help you estimate areas more prone to DPA suspensions. We have several available, depending on device category  and device height. Keep in mind that these overlays are guidelines. The actual impact on your specific CBSD will also depend on its registration parameters (like height, azimuth, beamwidth) and the geographical features of its installation site.

Regarding PAL Protection Areas (PPAs):

• Spectrum Inquiry Ranking and PPA Activity: PPAs are designed to be "always on" to protect Priority Access License (PAL) holders from interference. This directly influences spectrum inquiry results:
• If your CBSD is registered inside another entity's PPA, the spectrum inquiry results will typically omit the specific PAL channel(s) allocated to that PPA.
• If your CBSD is registered just outside a PPA, the spectrum inquiry results would likely show very low available power on the PAL channel(s) to prevent interference.
• Pre-checking a Location for PPA Likelihood: You can use tools within the SAS Portal to estimate PPA impact:
• Heatmaps Overlay: This feature can give you a general idea of PPA locations by highlighting areas with reduced channel availability.
• Point Analysis Tools: These tools can provide more specific information about which channels are impacted at a given location. This tool is best used as a guideline, as the results it provides are based on a theoretical “average CBSD”.
• Test CBSD Configuration: For more detailed insights similar to a spectrum inquiry, you can create a CBSD configuration in the SAS Portal for your potential deployment location and observe the resulting channel ranking.
• Historical PPA Data: There isn't "historical data of PAL activations" in the sense of them turning on and off. Once a PPA is established to protect a PAL grant, it generally remains active. PPAs can expand if PAL customers register new CBSDs and request additional PAL grants. A publicly available list of current PAL channel assignments can provide some insight, but remember that PPAs are only drawn when a PAL grant is actually requested. This means that even in counties with channels allocated for PAL use, actual channel availability can vary significantly until those PAL grants are actively requested.

Hope this helps!