The wireless industry celebrated the FCC’s decision to relax certain restrictions within the CBRS band. This milestone, informally dubbed “CBRS 2.0,” promises to increase the availability of channels over a larger footprint along coastal lines and Federal facilities, and reduce restriction times. The industry views this as a significant advancement. However, how much of an impact this will actually have on the utilization of CBRS?
The new rules: what changed
The FCC modified the interference model parameters that SAS operators use to calculate interference between CBRS base stations and federal users, particularly radar systems. This change will expand the unencumbered area for CBRS along coastal lines and around federal radar facilities, reducing the size of Dynamic Protection Areas (DPAs). According to the NTIA, the new rules will affect approximately 72 million people in 17 states, increasing the total unencumbered CBRS area to cover roughly 240 million people nationwide. This change promises more frequency channels to become available to CBRS users. The table below highlights the population increase from the largest urban areas.
| Urban Area | Population Increase |
| Atlanta, GA | 4,232,044 |
| Phoenix–Mesa–Scottsdale, AZ | 3,328,098 |
| Las Vegas-Henderson-Paradise, NV | 1,815,938 |
| San Antonio, TX | 1,618,685 |
| Pittsburgh, PA | 1,557,003 |
| Baltimore, MD | 1,540,336 |
| Washington-Arlington, DC-VA-MD | 1,396,928 |
| Austin, TX | 1,207,721 |
| Charlotte, NC-SC | 1,050,610 |
| Sacramento, CA | 1,017,790 |
The technical detail [for the technically inclined!]
The new rules will reduce the size of the Dynamic Protection Areas (DPAs) designed to protect federal users from Category B CBRS devices (CBSD or base stations), which are high-power outdoor base stations with a maximum allowable radiated power of 47 dBm/10 MHz. These new rules effectively reduce the interference power received from CBRS devices and increase the propagation loss of interfering signals by relaxing the propagation model and factoring in clutter loss.
Specifically, the SAS administrators will be able to apply the following changes in the interference model that is used to protect federal users from CBRS devices:
- Assume 80% TDD activity factor and 20% network loading factor (traffic load of base stations). This will reduce the total interference impact of a CBRS device by 8 dB.
- Allow the use the median propagation loss, i.e. 50% reliability factor and 50% confidence factor, to calculate the received power within a DPA.
- Allow using a median clutter loss according to ITU recommendation ITU-R P.2018 to CBRS devices operating at height of less than 6 m and operating at a distance of at least 250 m from DPA boundary.
Quantifying the impact
To fully understand the impact, we need to answer several question, such as:
- How often are federal users active?
- How much bandwidth do federal users occupy?
- For how long do federal users occupy spectrum?
- How many Cat B CBRS base stations are deployed in DPA-impacted areas?
The NTIA, in collaboration with the Department of the Navy, analyzed relevant data before recommending that the FCC relax the interference model. While we don’t have direct access to this data, we can glean some insights from NTIA studies on the CBRS band, which at least answer the last question.
The state of the CBRS market (at the start of 2023!)
The Institute of Telecommunication Sciences (ITS) released an important report last year on the use of the CBRS band, titled “An Analysis of Aggregate CBRS SAS Data from April 2021 to January 2023” [See NTIA Report 23-567]. Additionally, the ITS is conducting a companion study to measure how much spectrum CBRS emissions occupy over time near DPAs [see here]. The findings from these studies have undoubtedly influenced the formation of the new rules.
Some of the key findings in the ITS report:
- At the beginning of 2023, there were approximately 287,000 active CBRS devices (here I use devices interchangeably with base stations). [See Note 1 below]. According to a recent article by RCR, this number was 340,000 by the end of 2023 [see here].
- About 45% of all active devices, or 128,351 devices, were deployed in DPA-impacted counties where spectrum is shared with the Department of Defence. These counties have a total population of 232,348,897 residents. In comparison 158,646 devices were active in non-impacted DPA counties.
- About 80% of active devices were GAA-only, which is the license tier that must accept interference from licensed and federal users. Therefore, GAA dominates CBRS deployments; and it is the sub-band most affected by the new rules.
- 85% of the active grants were for GAA, and about 66.7% of active CBRS devices with a PAL grant had at least one active GAA grant, that is, they operated using both PAL and GAA licenses.
- More than 70% of all active devices are deployed in rural census blocks.
- Category B (high-power, typically deployed outdoors) devices accounted for 96% of all deployed CBRS devices.
- Category A devices, which are limited to 20 dBm/MHz and are primarily intended for indoor deployments, increased slightly over time from 0.9% on April 1, 2021, to 3.7% on January 1, 2023. California, Texas and North Carolina are the top 3 states in number of indoor deployments.
- On January 1, 2023, the non-DPA-impacted counties has on average 0.35 more 10-MHz channel grants on average than DPA-impacted counties.
- In January 2023, the active grants are almost evenly distributed across the band; however, there is a bias towards grants in the lower part of the spectrum which borders the 3.45 GHz band (e.g. towards 3550-3560 MHz) than the upper part of the spectrum which borders the C-band (e.g. 3690 – 3700 MHz).
- 68.7% of CBRS devices operate on one 10 MHz channel. 22.6% operate with 20 MHz. About 2.6% operate with 40 MHz (all on January 1, 2023).
- The deployment of CBRS devices at the start of 2023 are shown in the graphics below for number of deployed devices and the density of devices per square kilometer:
Concluding takeaways
Considering all the data, the change in interference calculation rules represents an important optimization. However, it likely won’t significantly impact current CBRS users. Most federal users operate in the 3550 – 3650 MHz range, where 70 MHz is allocated to PAL. PAL deployments remain small compared to GAA, which federal users affect first. Two-thirds of CBRS devices use a 10 MHz channel, making it relatively easy to move within the band. The upper 50 MHz of the CBRS band (3650 – 3700 MHz) sees less utilization compared to the lower 100 MHz. Although 45% of CBRS base stations are in DPA-impacted areas, many coastal counties have among the lowest density of deployed devices per square kilometer. Overall, relaxing the interference rules will benefit future CBRS deployments as device density increases. GAA devices will benefit the most since they have the lowest access priority.
Note 1: According to the May 2023 response by WISPA to the ITS report, the number of active CBRS devices is around 335,000. A recent article by RCR (June, 2024) cites the number was 340,000 by the end of 2023 [see here]. The numbers indicate a deceleration in CBRS deployments through 2023 from the rate experienced in 2021-2022.
Note 2: For information on the CBRS auction in 2020, see my post here.