CBRS 2.0: A new era for network stability and investment
Explore the advancements in CBRS 2.0 designed to boost network performance and reliability. Find out how these changes could significantly impact the deployment of 5G networks and spectrum management.
Customer Solutions Director
Customer Solutions Director
Customer Solutions Director
CBRS 1.0, the promise and the disillusionment
Since 2019, the Citizens Broadband Radio Service (CBRS) spectrum has been used for wireless networks, with two tiers: Generally Authorized Access (GAA) and Priority Access Licenses (PAL). Service providers and private enterprises invested around USD 4.9 billion in PAL auctions to protect their operations from GAA operations.
After the initial excitement over a spectrum band intended for innovation and new use cases, many were disillusioned by the burdens of sharing spectrum with naval radar and access to spectrum is inmanaged by the Spectrum Access System (SAS), which follows highly conservative and strict procedures as detailed in FCC 47 CFR Part 96. Key drawbacks of spectrum sharing in the CBRS band that make commercial operations a challenge are as follows:
- Large incumbent protection neighborhoods – commercial operations may be interrupted as far as 430km inland from the coast
- Short Transmit Expire timer – loss of communication with SAS for >240s can cause outages
- No GAA interference protections – SAS does not provide any interference protection to operations in the GAA portion of the band.
Coastal DPA boundaries (source: ONGO Alliance)
Emergence of CBRS 2.0
The OnGo AllianceTM and other advocates for spectrum sharing have raised these issues with the Federal Communications Commission (FCC), National Telecommunications and Information Administration (NTIA), and the Department of the Navy. In response, the FCC has released new guidance over the last several months, relaxing the rules for commercial operations in the CBRS band. This new guidance from the regulatory community consists of the following:—TX Expiry extension DA-23-867A1.pdf (fcc.gov), a new aggregate interference model DA-24-553A1.pdf (fcc.gov) and the OnGo Alliance collaborative GAA coexistence specifications, (Collaborative GAA Coexistence Technical Specification - OnGo Alliance)— is collectively being referred to as CBRS 2.0. So, what was introduced and how will it propel adoption and rekindle excitement for CBRS, aka “the innovation band”? Let’s unpack the ingredients that make up CBRS 2.0.
Extension of the CBSD TX Expiry time.
The first initiative to bolster commercial operations came on September 19, 2023, when the FCC agreed to extend the TX Expiry timer to a maximum of 24 hours for the entire band outside designated DPA protection neighborhoods and within the upper 50 MHz inside. DA-23-867A1.pdf (fcc.gov). The lower 100 MHz of the band is excluded within DPA protection neighborhoods due to its criticality to naval operations. SAS providers and original equipment manufacturers (OEMs) have implemented these enhancements, extending TX Expiry time, albeit, up to six hours instead of the 24 hours allowed by the updated regulations. The choice of grant renewal was dictated by the possibility of disturbance to coordinated periodic activities (CPAS) among SAS providers. Even with a six-hour renewal period, operations will exhibit a higher tolerance for loss of heartbeat (that is, communications) with the SAS, greatly improving band utility and avoiding past issues.
What is CBRS 2.0 (source: ONGO Alliance)
Reduction of DPA neighborhood footprint.
On June 12, 2024, the FCC, in collaboration with the NTIA and DoN, approved a new aggregate interference model significantly reducing the size of DPA neighborhoods, especially for CBSDs less than six meters above ground level (AGL). According to the OnGo Alliance TM, the new model will remove service interruptions due to incumbent activity for approximately 72 million people, expanding CBRS service coverage to 240 million people (49 percent to 91 percent population coverage).
Changes in the interference model reducing the impact of DPA neighborhoods include:
- An 80 percent activity factor and 20 percent network loading for each CBSD effectively allowing reduction of the maximum allowed equivalent isotropic radiated power (EIRP) for each CBSD by 8dB, providing for clutter losses, in the aggregate interference model used by the SAS.
- SAS administrators may use median irregular terrain model (ITM) terrain dependent propagation loss (50 percent reliability and confidence factors) to calculate aggregate received power levels within a DPA, previously required to be 95 percent.
- Application of indoor to outdoor loss (15dB) to DPA neighborhood calculations (previously used in interference calculations but not in determination of neighborhood size).
The SAS administrators may apply median clutter loss, calculated using the methodology described in Recommendation ITU-R P.2108,9 section 3.2, for any CBSD with an antenna height AGL of less than or equal to six meters, that is operating at a distance of at least 250 meters from a DPA boundary.
The following is a technical summary of the changes in the aggregate interference model:
| Category | AGL | Prop Model | Clutter Model | Indoor -> Out Loss | Activity Factor | 95% -> 50% ITM reliability* | Delta to Existing Model |
| A indoor | <= 6m | ITM | P. 2108 (nom. 30.5 dB) | 15 dB** | 8 dB | ~0.2 - 7.4 | 53.7 - 60.9 dB |
| A indoor | > 6m | ITM | None (yet) | 15 dB** | 8 dB | ~0.1 - 5.4 | 23.1 - 28.4 dB |
| B | <= 6m | ITM | P. 2108 (nom. 30.5 dB) | 0 | 8 dB | ~0.2 - 7.4 | 38.7 - 45.9 dB |
| B | > 6m | ITM | None (yet) | 0 | 8 dB | ~o.1 - 5.4 | 8.1 - 13.4 dB |
*Estimated based on a sample of point-to-point predictions
** Already used in interference calculations but not in neighborhood sizes
Source - DA 24-553, Released June 12, 2024
The biggest impact of these new propagation models is for indoor Cat A CBSD below 6 meters (roughly 2 stories) as shown in the figure below.
Pink area is CBRS 1.0 impact area for indoor coverage and white line is CBRS 2.0 impact area. This graph shows that in the new version impact area will be significantly smaller. (source: ONGO Alliance)
Enforcement of collaborative GAA coexistence rules.
In efforts to address GAA coexistence concerns, the OnGo AllianceTM approved new coexistence specifications in October 2023. The previous coexistence specifications (OnGo-TS-2001-V3.2.0_Published-May-23-2022.pdf (ongoalliance.org)) were too prohibitive, putting frequency allocation decisions solely in the hands of SAS providers. The new specifications (Collaborative GAA Coexistence Technical Specification - OnGo Alliance) establish a collaborative foundation whereby commercial network owners (CBSD Users) can mutually agree upon GAA channel allocations within a GAA coordination area (GCA), with the SAS enforcing the resulting frequency plan.
Improved GAA coexistence
- Challenge:
Multiple GAA users can cause interference in dense areas. - Solution:
New voluntary mechanism for managing interference. - Benefit:
Smoother network experience for all users.
When will these changes be implemented? The Extended TX Expiry feature has already been deployed. Federated Wireless introduced support for this feature in release 3.15 of their SAS software. Federated operates the feature on opt-in basis, requiring users to request enablement. Similarly, Google launched the feature in February and, as of May, had it enabled by default.
Deployments of the new aggregate interference model were introduced by the SAS providers on July 26. Since this is a SAS-only feature, no Interoperability testing with OEM equipment vendors is required. Collaborative coexistence guidelines were approved in December 2023. Most basic coexistence enforcement constructs have been supported by Federated Wireless and Google SAS for some time although GAA coordination zones and some other details remain to be implemented as well as interoperability testing with the OEMs. The OnGo coexistence task force is working on test cases to support these guidelines, with readiness expected around the end of this year.
Will these changes encourage continued investment in the band?
Do these changes matter? Will they renew and reinvigorate interest and investment in the band? Outside of allowing higher EIRP comparable to commercial bands, these changes will significantly level the playing field, providing non-public networks more confidence in deploying 5G networks. The benefits of 3GPP technologies including security, scalability, device availability, true mobility, and capacity, will be accessible to a wider population with greatly improved dependability and availability.
The caution is that uncertainty regarding spectrum availability is greatly reduced, but not eliminated. GAA users can still interfere with PAL, and the SAS-CBSD interface is not completely fault tolerant without business agreements establishing service level agreements between networks and SAS service providers. However, the impact of federal use of the band is less likely to cause degraded performance.
Today, CBRS is powering capacity augmentation, fixed wireless access, and private networks.
Summarizing the CBRS 2.0 initiatives and their benefits
- Extend Transmit Expire Timer: Radios (CBSDs) can continue operations for 6 hours if communications with SAS are lost.
- New aggregate interference model: Significantly reduces DPA neighborhoods for certain CBSDs, Reducing service interruptions due to incumbent activity (DPA activations).
- Collaborative coexistence rules: Voluntary and collaborative enforcement of GAA frequency planning. SAS control of channel allocation decision making is part of an agreed process between network owners, protecting against cochannel interference.
These improvements are welcome changes. Will service providers celebrate the improvements with more investment, or will they be overlooked? This decision will be in the hands of the market. IRP limitations mandated by FCC rules.
Only time will tell whether the improvements of CBRS 2.0 will reignite enthusiasm and innovation like was seen in 2020 when commercial operations in the band initially launched and operators were keen to take advantage of this mid band 3GPP technology to power various use cases. Enterprises will also recognize that these improvements will further strengthen the case for CBRS as a viable alternative to WiFi. Ericsson stands ready to meet demand from our customers with a highly competitive portfolio of CBRS radios that range from indoor radio DOTs, micro radios, andoutdoor Massive MIMO radios..