SAS - Non-Coastal DPA Suspensions

James_S · 06-19-2023 08:36 AM

Today's article is for folks who want to know:

Why is my grant getting suspended due to DPA activation? My CBSD isn’t anywhere near the coast!

There are two primary reasons a CBSD that is very far from the coast would have its grant suspended due to DPA activation. Either the grant has not yet been held through CPAS yet, or the CBSD could be affected by a P-DPA.

Any CBSD registered within a certain proximity of a DPA is considered within its DPA Neighborhood. Per WInnForum requirements, all new grants within a DPA neighborhood that overlap with the DPA’s protected frequencies (generally 3550-3650 MHz) must be placed on one or all of that DPA’s movelists. A movelist is a list of grants per channel that the SAS has determined must be suspended to protect higher priority users from interference. This occurs when the SAS detects incumbent activity in that DPA on that channel. When the SAS does its interference calculations at CPAS, movelists are also recalculated. A grant that has gone through CPAS is likely to be removed from some or all of the movelists it was initially placed on. Grants that have not been held through CPAS are therefore more likely to be suspended due to DPA activation than grants that have. As a result, it is recommended that your CBSD hold its grants through CPAS even if they are getting suspended on the first day they were requested. This is especially the case if you think it is unlikely that your CBSD could generate interference for higher priority users near the coast. You can check the age of your suspended grant by looking at the information listed in the CBSD’s History tab in the SAS Portal. Any grant requested in the last 14 days will be listed.

To understand what a P-DPA is, it is helpful to first understand what an E-DPA is and how they differ. E-DPAs, otherwise known as ESC-controlled DPAs, are located along the entire coast of the contiguous United States. An ESC, or Environmental Sensing Capability, is used to monitor E-DPAs for incumbent user activity so that the SAS knows when they need to be protected. Conversely P-DPAs, or Portal DPAs, are only activated when an incumbent manually submits a request for interference protection. The activation of a P-DPA can cause suspensions in the bottom 100 MHz of the CBRS band (3550 MHz to 3650 MHz). They can also be located anywhere in the country, not just near the coasts.

You can check your grant in the SAS Portal to determine if it is on the movelist of a P-DPA. Simply select the device in the SAS Portal, open up the Status tab, and expand the grant you wish to investigate. If the grant is on any DPA movelists, they will be listed here by DPA name and frequency. If the name of the DPA does not conform with the following naming scheme: West1, West2, East1, East2, etc, then the DPA is likely a P-DPA. Alternatively, P-DPAs do not activate very often - it may be that the better solution is to accept the risk that the grant will occasionally be suspended in exchange for a more powerful grant.

For more information please read the following Help Center articles:

joshrogers

What would cause a DPA event that would suspend grants above 3550 MHz?

James_S

On Aug 24 2023, between 2023-08-24 14:41:10 PDT and 2023-08-24 16:12:20 PDT, grants in the following movelists were suspended by SAS.
BATH
CHINA LAKE
DAHLGREN
Hawaii7
Hawaii8
MCKINNEY
MOORESTOWN
NEWPORT NEWS
PORTSMOUTH
WALLOPS ISLAND
WHITE SANDS MISSILE RANGE
YUMA PROVING GROUNDS

This was caused by an unplanned activation of all P-DPA channels while importing a new P-DPA monitored protection area. As P-DPAs have movelists in the upper 50 MHz, some grants in that frequency range were also suspended. A fix was quickly rolled out to unsuspend grants.

We apologize for the interruption this incident may have caused to your network and are committed to providing access to the maximum CBRS spectrum available at all times.

atrivedi-tarana

@James_S is there any way the SpectrumInquiry or resonseCode/responseMessage in heartbeat/grant response tell the caller of the API that there is E-DPA or P-DPA instantiated in the area for the CBSD the request is being made to ?

James_S

For DoD Operational security reasons, SAS are barred from providing information on whether an E-DPA is active or not. We are working with DoD/Govt to see if we can provide information to users for P-DPAs as these are scheduled reservations.

CNC

I have some follow up questions:

1) Is there an FCC or NTIA doc that establishes that P-DPAs have control over the entire CBRS band (3550-3700)?

The most up-to-date P-DPA documents available to me only mentions that P-DPAs have control over the 3550-3650 band:

https://www.ntia.gov/sites/default/files/publications/p-dpas_4.kml
https://www.ntia.gov/fcc-filing/2015/ntia-letter-fcc-commercial-operations-3550-3650-mhz-band

2) You explained that "Because P-DPAs are protected across the entire CBRS band, the only way to completely avoid being on their movelists is to request grants with a lower max EIRP." What reference document should I use when to determine max EIRP values that are immune to P-DPA suspensions?

3) Can an AP request a CBRS grant in a manner that allows it to operate a high EIRP value during normal conditions and at a reduced (P-DPA-immune) EIRP value when a P-DPA move request is triggered?

James_S

P-DPA activations can no longer cause suspensions in the upper 50 MHz. The original article will be updated to reflect this change.
Interference calculations are determined by many factors such as installation parameters, higher priority users in the area, aggregate interference, etc. These variables are constantly changing, and the only time the SAS has perfect access to all variables is when all the SASes share their databases at CPAS. As a result, the SAS is only able to determine whether or not a grant will permanently be on a DPA movelist after that grant has been held through CPAS. I would recommend requesting the grants you want, hold them until after CPAS has completed, and see if they are still on DPA movelists by checking them in the "Status" tab of the SAS Portal. If they are, you may need to request a lower power grant. Please note that P-DPA related suspensions are relatively infrequent, so it may be more valuable in the long term to operate with a more powerful grant.
No, a CBSD can only have a single max EIRP and a CBSD can only hold a single grant on each channel. We generally recommend requesting a temporary grant in addition to your suspended grant, rather than replacing it. Your CBSDs could heartbeat on both until the suspension on the original grant has been lifted.

CNC

@James_S Thank you for the additional clarification!

Can you please provide the source documentation (preferably from FCC, NTIA or some other similarly authoritative source) for the details you provided? Using original source material is critical to develop durable implementation strategies and provide accurate training to my team.

James_S

Could you please specify which details you require documentation for? Most of your questions were specific to Google SAS. Online documentation for Google SAS is available here. The SAS-CBSD API is outlined here.

CNC

I'm hoping for documentation confirming:

1) P-DPA activations cannot cause suspensions in the upper 50 MHz.

2) In the lower 100MHz, grants with lower max EIRP values are immune to P-DPA move requests. More specifically, in the China Lake P-DPA what maximum EIRP values avoid suspension during P-DPA activation.

James_S

@CNC

1. The definition of a P-DPA in our online documentation specifies that a P-DPA can only cause suspensions in the 3550-3650 MHz range.

2. This is a function of how the SAS works. As a result, there is not a single document that will outline SAS behavior. Only grants on DPA movelists will be suspended if a DPA is activated. This is true regardless of DPA type. If a grant is weak enough that the SAS determines it is impossible for it to cause interference to a higher priority user, that grant will not be placed on any movelists. This prevents any DPA suspensions. The calculations the SAS uses to determine which grants might interfere are too complicated and specific to the device in question for us to say categorically that grants can prevent suspensions in perpetuity by requesting a certain power level. This is why I encouraged you to check the movelists of your grants after CPAS, as this is the only way of knowing for sure that a grant is not going to be suspended due to DPA activation on that day. The SAS recalculates movelists every day, so there is a very slim possibility that a borderline grant could be re-added to a movelist later. This would likely only happen if the amount of aggregate interference in an area rises between days, which would require a large amount of grants on the same channel be requested.

CNC

Thank you. I appreciate your thorough responses!

1) I understand the P-DPA definition (and corresponding frequency control limitation) as stated in the Google list of key terms. But while the Google SAS implements this definition, certainly it is not responsible for the definition itself – that must be something established by the FCC. Otherwise, each SAS could define and also implement P-DPA scopes in different ways.

What I've been looking for (and have so far failed to find) is a FCC document certifying this specification. The closest thing I've found is the NTIA docs (also listed above):

https://www.ntia.gov/sites/default/files/publications/p-dpas_4.kml
https://www.ntia.gov/fcc-filing/2015/ntia-letter-fcc-commercial-operations-3550-3650-mhz-band

I know that you don't represent the FCC. However, because the P-DPA limitation (as listed inhttps://cloud.google.com/spectrum-access-system/docs/key-terms) of not being able to suspend grants in the 3.65-3.7GHz range is drawn from FCC specifications, I was hoping you (or some other member of the Google SAS team) might know where that information is to be found in FCC documentation and share it with the rest of us.

2) The information you have provided above is extremely helpful. I will make a habit of reviewing move lists for each of my CBRS access points each day after CPAS (which completes each day by 2 a.m. PST or 3 a.m. PDT).

2a) Do you have anything more to report regarding your statement above? "We are working with DoD/Govt to see if we can provide information to users for P-DPAs as these are scheduled reservations." It would be wonderful for CBRS admins to have advance warning regarding P-DPA move requests to allow for sufficient time (multiple CPAS cycles) to successfully request different channel grants as needed.

2b) Is there a way for me to set up a notification within the Google SAS to send me a text or email whenever (at the conclusion of the CPAS cycle) a P-DPA move request is going to affect one of my CBRS access points?

Advancements in both of these areas (2a and 2b) will be immensely helpful to any WISPs operating in P-DPA-controlled areas.

James_S

@CNC

CBRS Incumbent Protections and Encumbrances Overview from Winnforum outlines the mechanisms by which a SAS protects a DPA (either E-DPA or P-DPA). The P-DPA KML from NTIA shows where all of those P-DPAs are, and what frequency range must be protected. Combined, these two documents show that P-DPAs are not protected by the SAS on frequencies 3650-3700 MHz. If you need documentation that comes from the FCC, please reach out to the FCC.

No additional details regarding advance P-DPA activation warning is available at this time. However, I will forward your two feature requests to the appropriate parties. Keep an eye out for more feature announcements in the future!

atrivedi-tarana

@James_S The ticket was opened before the transmitExpiry features were implemented back in 08/2023. Now I have the new documentation about it.