All Spectrum Access System (SAS) users are required to collaborate to determine
power allocation for Citizens Broadband Radio Service Devices (CBSDs). To achieve synchronous power
allocation among SASs, all SAS users perform a procedure called
[Coordinated Periodic Activities among SASs (CPAS)](https://docs.cloud.google.com/spectrum-access-system/docs/key-terms.md.txt#cpas).
WInnForum defines CPAS in the document
[WINNF-SSC-0008](https://winnf.memberclicks.net/assets/CBRS/WINNF-SSC-0008.pdf).

During CPAS, all SAS users do the following:

- Exchange information with one another.
- Retrieve the latest information from the [Federal Communications Commission (FCC)](https://docs.cloud.google.com/spectrum-access-system/docs/key-terms.md.txt#fcc) and [WInnForum](https://docs.cloud.google.com/spectrum-access-system/docs/key-terms.md.txt#winforum) databases.
- Reallocate resources among CBSDs with the Iterative Allocation Process (IAP) algorithm defined in [R2-SGN-16 of the WInnForum requirements](https://winnf.memberclicks.net/assets/CBRS/WINNF-TS-0112.pdf). In particular, grant powers are adjusted in an equitable way.
- Recalculate the [Dynamic Protected Area (DPA)](https://docs.cloud.google.com/spectrum-access-system/docs/key-terms.md.txt#dpa) move lists by using the algorithm defined in [R2-SGN-24 of the WInnForum requirements](https://winnf.memberclicks.net/assets/CBRS/WINNF-TS-0112.pdf).

SAS users synchronize these activities to make sure that all
entities are protected.

## When CPAS runs

CPAS runs from 7 AM to 10 AM UTC each day. During CPAS, SAS can't
issue new grants. When you perform CBSD maintenance that requires
new grants, we recommend that you do the maintenance before CPAS begins. This
maximizes the potential power that SAS can offer after CPAS
completes.

> [!NOTE]
> **Note:** UTC to US time zone conversion differs by one hour between US Standard Time and US Daylight Savings Time.

## What CPAS means to a CBSD operator

During CPAS, as a CBSD operator you are responsible for limiting
transmission power because grant power is not increased during CPAS. Also,
SAS recalculates the DPA move lists during CPAS. Therefore, it's
important to retain the grant suspension for the CBSDs.

### Transmission power limits

Resources are reallocated once per day during CPAS. During this reallocation, a
small portion of the resources are reserved for new grants that are requested
before the next CPAS. Any grants that are authorized the next day use
that reservation.

If a requested grant exceeds the remaining reservation, the grant request can be
approved, but the grant might not be authorized in the subsequent heartbeat.
During the next CPAS, this grant is given an equitable portion of the
resources and then authorized.

Alternatively, the CBSD might perform a spectrum inquiry before
requesting the grant. The spectrum inquiry response indicates how much of
the reservation is available for use by the CBSD. If the
CBSD requests a grant with the indicated transmission power, it's
likely to be authorized for immediate transmission with the possible exception
of DPAs. The grant power is not increased during the subsequent
CPAS; if a higher-power grant is desired, it should be requested directly.

### Grant suspension

Due to the nature of the DPA protection requirements, SAS is not
allowed to reserve even a small portion of the resources when protecting DPAs.
This means that any new grant inside a DPA neighborhood must automatically be
placed on the DPA's move list, regardless of the amount of interference that the
grant might cause to the DPA.

When CPAS runs, SAS recalculates the DPA move lists. If possible,
SAS removes the grant from the DPA move list. Learn more
about [DPA protections](https://docs.cloud.google.com/spectrum-access-system/docs/cbsd/overview.md.txt#cbsd-near-coast).

New grants are sometimes at a disadvantage in terms of their transmission power and
how likely they can be suspended. The CBSDs are encouraged to
retain their grants for a long time to avoid these disadvantages.

## How the CBSD gets notified of CPAS results

At the end of the CPAS, SAS notifies the CBSD of
any required changes through the heartbeat response. The following table
contains potential outcomes.

| Heartbeat response | Interpretation | Recommended behavior |
|---|---|---|
| `responseCode: SUCCESS` `operationParam: unset` | No changes are recommended at this time. | Continue heartbeating normally. |
| `responseCode: TERMINATED_GRANT` `operationParam: set` | A power decrease is required for this grant. Alternative operating parameters are provided. | Request a new grant by using the suggested operating parameters. |
| `responseCode: TERMINATED_GRANT` `operationParam: unset` | It's not possible to authorize even a very low-power grant on this channel. | Perform a spectrum inquiry request and request a new grant. |