CBRS Primer

If spectrum is not being used by one tier it can be used by other tiers with a grant from the SAS.

PAL is licensed and is afforded interference protection from GAA. PAL licenses are purchased at auction. There is up to 70 MHz of PAL spectrum available in any area, which can be chosen in 10 MHz increments from the first 100 MHz of the CBRS band (3550–3650 MHz). The remainder of the spectrum (3650 – 3700) is reserved for GAA use, which is considered “licensed by rule”.

Although 7 PALs may be awarded in a given census tract, a maximum of 4 may be held by any given licensee.

The Environmental Sensing Capability (ESC) is a network of sensors located across the United States, primarily along the coastline, and used by the SAS to enforce FCC rules, manage spectrum allocation, and prevent radio interference in the 3550–3700 MHz band where U.S. Navy radar systems can operate.

The ESC informs the SAS of radar operation and the SAS reacts to ensure there is no interference between CBSDs and radar operations, specifically for Navy ships located off the coast.

Figure 1: Dynamic Protection Areas (DPAs) in the continental US

When the ESC detects an incoming transmission on the incumbent tier, it automatically creates a protection zone in that area to prevent interference from any other sources. The SAS uses a pre-calculated “move list” of CBSDs and will move them off the protected channel until the 95th percentile of allowable aggregate interference into the radar receiver antenna (-144 dBm/10 MHz) is met.

Rather than blocking all communication in that zone, the SAS can dynamically reroute PAL and GAA users to other bands of the spectrum (if available).

The NTIA, in conjunction with the FCC and DoD, publishes KML files that contain information on all DPAs, exclusion zones, and their protection requirements.

The Citizens Broadband Radio Service Device (CBSD) is a radio device that communicates in the CBRS band. A CBSD must receive a spectrum grant and authorization from a SAS before it can begin transmitting data.

There are two CBSD categories:

A CBSD obtains grants from the SAS through the SAS-CBSD interface.

According to WInnForum, a Domain Proxy (DP) is “an entity engaging in communications with the SAS on behalf of multiple individual CBSDs or networks of CBSDs. The domain proxy can also provide a translational capability to interface legacy radio equipment in the 3550-3700 MHz band with a SAS to ensure compliance with Part 96 rules.” The DP presents a consistent and secure interface to the SAS that can convey all messages pertaining to the SAS-CBSD interface on behalf of client CBSDs.

Coordinated Periodic Activities among SAS’s (CPAS) is a daily activity in which all SAS operators:

CPAS occurs between 7 am UTC - 10 am UTC each day. During CPAS, the SAS cannot issue new grants, therefore it’s recommended to do maintenance before CPAS. Once CPAS is complete, the SAS notifies CBSDs of any required changes.

Devices using CBRS must be authenticated by the SAS prior to broadcasting. The SAS has no way to proactively reach out to a CBSD, so the CBSD must initiate all communications. CBSDs can communicate with a SAS either directly or by using a DP, such as TCS. The Wireless Innovation Forum (WInnForum) establishes protocols for communication between CBSDs and the SAS. These protocols have been implemented in the SAS-CBSD API.

There are currently six different interactions a CBSD can have when communicating with a SAS:

Figure 3: CBSD Registration State

The assignment of a grant is solely at the discretion of the SAS. The following diagram shows the process of a device requesting a grant, receiving the grant, and receiving authorization. A device must successfully complete each step before it can transmit data.

Figure 4: CBSD Grant State

The following section discusses the CBSD to SAS procedures:

The CBSD initiates the Registration procedure by sending a RegistrationRequest object to the SAS.

The SAS responds to the CBSD with a RegistrationResponse object.

Figure 5: CBSD Registration Procedure

The CBSD initiates the Spectrum Inquiry procedure by sending a SpectrumInquiryRequest object to the SAS.

The SAS returns a SpectrumInquiryResponse object response to the CBSD with the results of the potential channel availability for the inquired spectrum.

Figure 6: CBSD Spectrum Inquiry Procedure

The CBSD initiates a grant request by sending a GrantRequest object to the SAS.

Figure 7: CBSD Grant Procedure (Request)

The SAS responds to the CBSD with a GrantResponse object response.

Since the CBSD cannot transition to the authorized state until the successful completion of the heartbeat procedure, the CBSD should execute the first heartbeat procedure following the GrantResponse object as soon as possible after the GrantResponse is received.

Figure 8: CBSD Grant Procedure (Response)

The CBSD initiates the heartbeat procedure by sending a HeartbeatRequest object to the SAS.

The HeartbeatRequest object informs the SAS that the CBSD needs access to the allocated spectrum.

Figure 9: CBSD Heartbeat Procedure (Request)

The SAS responds to the CBSD with a HeartbeatResponse object response. The response parameter indicates whether the request succeeded or failed.

Figure 10: CBSD Heartbeat Procedure (Response)

Figure 11: CBSD Grant Relinquishment and Deregistration Procedures

In order to operate a CBRS network, the following steps must be performed within TCS:

If it doesn’t already exist, a user account must be created in TCS for each CPI. For CBRS installations, the CPI should edit their user profile in TCS to include their CPI-ID and upload their CPI certificate and CPI certificate password. The CPI certificate is a .p12 file.

Figure 13: Editing a TCS user profile

Figure 14: Configure a TCS user as a CPI

Selection of a SAS is mandatory for CBRS operation. Tarana Wireless supports both Google and Federated Wireless SASs. The FCC OR-ID is issued by the SAS to the operator and uniquely identifies the operator and its equipment within that SAS. Changing SAS will require the operator to get a new ID.

The FCC OR-ID and SAS fields must be configured for CBRS installations within TCS before BN or RN installation. These parameters are part of the operator profile under Network Configuration. Edit the Operator page with the correct ID and SAS.

Figure 15: Configure Operator Parameters for CBRS

Certified Professional Installer (CPI) requirement

Tarana CBRS Base Node (BN) and Remote Node (RN) models are Category B and must be installed by a Certified Professional Installer (CPI). Passing CPI certification entitles the engineer to use an ID and public key certificate to authenticate themselves as the engineer of record approving an installation. A CPI must either physically install the CBSD themself or take responsibility for the accuracy of data entered by another installer.

The CPI must carefully review and sign the BN and RN installation parameters before the devices will register with a SAS.

CBRS BN Installation (Web UI)

The following steps enumerate CBRS-specific instructions for a BN installation:

For complete and the most up to date BN installation manual, including CBRS-specific instructions, see https://www.taranawireless.com/bn_manual.

Log into the BN

During the initial configuration, access the BN’s web UI from the out of band management port using the default IP address and login information:

Configure the TCS Registration URL

Step 1. When a BN is first configured, the BN must have the correct URL for TCS in order to contact it. The correct TCS URL for CBRS units is: registration.trial.cloud.taranawireless.com/443. 

Under Setup, change the Cloud URL from: registration.cloud.taranawireless.com:443 to: registration.trial.cloud.taranawireless.com:443

Figure 16: TCS registration URL in the BN web UI

BN-specific Parameter Configuration

Step 2. Click on Installation Parameters.

Figure 17: Installation Parameters button

Step 3. Verify the latitude, longitude, and tilt (received from the GPS unit on the BN) and the height and azimuth. The height should be measured above ground level (AGL) in meters.

Figure 18: BN-specific installation parameters

Enter CPI ID

Step 4. Enter your CPI-ID and click Confirm.

Figure 23: CPI ID installation parameter

BN Verification in TCS

From the BN’s Device page in TCS, click on the CBRS button in the green device summary card.

Figure 20: BN device page summary card with CBRS button

This will open a CBRS summary page. Here, you can verify that the BN has been assigned spectrum. In the example below, the dark green indicates that the spectrum has been granted and authorized by the SAS and the time until the grant expires is noted. Light green would indicate that the spectrum had been granted but not authorized.

Figure 21: CBRS summary page showing an authorized spectrum grant

CBRS RN Installation (Web UI)

The following steps enumerate CBRS-specific instructions for an RN installation:

For complete and the most up to date RN installation manual, including CBRS-specific instructions, see https://www.taranawireless.com/rn_manual.

Log into the RN

After physically installing the RN on site, access the RN’s web UI using the default IP address and login information:

RN-specific Parameters Configuration

For CBRS RNs, all five parameters are required.

Troubleshooting Note

It is especially important to make sure the latitude and longitude parameters are entered correctly. Incorrect coordinates can prevent an RN from coming up. When the device registers with the Spectrum Access System (SAS) it must provide its location which the SAS uses to verify the RN is located in a place that supports CBRS operation.

For example, in the graphic on this page, the longitude listed is -98.56300354. This will place the RN in Downs, Kansas, which is a valid location for CBRS operation. However, if the longitude is entered as a positive integer (missing the minus sign in front), you are asserting this RN is in the Gansu province in China somewhere near the Gobi Desert. This is obviously not a valid location for a CBRS device from the SAS point of view and will result in the RN continuously sending a registration request to the SAS and the SAS continuously rejecting the RN’s request. This will prevent normal operation of the RN.

Figure 22: RN web UI with installation parameters

Enter CPI ID

After Submit Changes is clicked an Installation Parameters pop-up will appear. Verify the installation parameters are correct, then enter your CPI ID and click Confirm.

Figure 23: CPI ID installation parameter

RN Verification in TCS

From the RN’s Device page in TCS, click on the CBRS button in the green device summary card.

Figure 24: RN device summary card with CBRS button

This will open a CBRS summary page. Here, you can verify that the BN has been assigned spectrum. In the example below, the dark green indicates that the spectrum has been granted and authorized by the SAS and the time until the grant expires is noted. Light green would indicate that the spectrum had been granted but not authorized.

Figure 25: CBRS summary page showing an authorized spectrum grant

Unit does not receive grant

If these values are correct, contact your SAS to verify spectrum grants are available for your area. Depending on timing, it is possible a grant must wait until after CPAS has occurred, i.e., 10 am UTC.

Grant is suspended

A grant may be suspended pending evaluation by a SAS. For example, while the SAS calculates if the new grant will impact incumbents. New grant authorizations are given after CPAS has occurred.