Hi Google-SAS team, we have a question regarding Google SAS behavior.
Lets say a CBSD has an authorized grant at 37 dBm/MHz and primary user starts using spectrum which results in lower available power of say, 27 dBm/MHz, Google SAS will suspend then grant for the CBSD…
In the response, would Google SAS provide the OperationParam power of 27 dBm/MHz?
Also if at a later time the primary user switches frequencies, would we ever get OperationParam power of 37 dBm/MHz in a HeartbeatSuccess or HeartbeatSuspended Heartbeat Response? (since the higher power would be available)
In general, we would like to understand under which scenarios of grant-suspension (response code501) would Google-SAS “not” provide operationalParams? We are currently seeing for DPA Suspension, there is no OperationParams present. Thanks!
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Great question!
The SAS will only provide suggested operating parameters in a grant termination message. At all other times, the CBSD must send a spectrum inquiry request to the SAS to receive recommended power levels for each channel. This is because most suspension reasons are temporary, and older grants are generally of higher quality than newly requested ones. The approved power of a grant cannot change, so to reduce power from 37 dBm/MHz to 27 dBm/MHz would require relinquishing the existing grant and replacing it with a less powerful one. The replacement grant would probably be more likely to be suspended than the old one, even with a lower power level because it would likely be on more movelists. As a result, we do not recommend requesting a less powerful grant on the same channel when a suspension occurs. It is better to request a grant on a different channel that is not being affected by the presence of a higher priority user.
At any time, a CBSD can send a spectrum inquiry request to the SAS and receive a list of available channels in the range specified in the request. The channels will be listed in descending order of channel quality, with channels that are currently being affected due to DPA activation deprioritized. Each channel included in the spectrum inquiry response will contain the highest Max EIRP that the SAS can authorize for immediate transmission. This does not account for higher priority users whose presence in an area is temporary, such as a DPA suspension. It does account for higher priority users who require around the clock protection, such as PAL Protection Areas (PPAs).
If your CBSD supports it, we recommend responding to DPA suspensions by performing a spectrum inquiry request and using that information to request a temporary grant. The SAS allows a CBSD to hold multiple grants if their channels do not overlap. Once the temporary grant has been requested, the CBSD should send heartbeat requests for both grants until the suspension on the original grant has been lifted. The temporary grant can then be relinquished and transmission can resume on the original grant. This allows the CBSD to operate when a higher priority user is in the area while still holding onto the original grant. We would recommend consulting with your CBSD vendor to see if this functionality is supported with your individual device. Please see CBSD operator best practices in the Help Center for more information.
You may find yourself asking, “why are older grants generally of higher quality than brand new grants”? Well, depending on the installation parameters of the associated CBSD, grants that have been held through the interference calculations that happen at CPAS are removed from some or all DPA movelists. This means that older grants are usually less likely to be suspended due to DPA activation than new ones. Older grants are also less likely to be suspended to protect a higher priority user that requires constant protection, like a PPA. This is because the SAS must treat the interference level of new grants much more conservatively than those that have gone through the more extensive interference calculations that happen at CPAS.
For more information, please see Operate CBSDs near the coast in the Help Center.
If you have any follow up questions, please let me know!
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Hi James,
Thanks for the response, it was very enlightening. 
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@James_S As a follow up to above question, I wanted to understand how long does SAS keep grants given to a CBSD in granted state if the CBSD is not heartbeating, will it keep as long as GrantExpiryTime or shorter ? If it is shorter what is that time ?
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