Using CBRS and haven’t heard about TARDYs3? Don’t be late to the party

CBRS today

Today’s service providers are adopting Citizens Band Radio Service (CBRS) to add capacity to licensed bands, deliver fixed wireless access(FWA) services, and bridge the digital divide in underserved markets. For them, it is a more cost effective and efficient option than other alternatives. In addition, enterprises use CBRS to power private networks. This delivers automation for manufacturing, transportation and logistics. Finally, tower companies and neutral host providers see CBRS as a radio access solution that doesn’t require licensed spectrum. As of January 2023, there have been many noteworthy developments in CBRS in the US, including:

• about 300,000 CBRS base station devices (CBSDs) deployed
• 500 end-user device models using CBRS certified by the Federal Communications Commission
• more than 4,300 professional installers certified
• USD 4.58 billion in proceeds from the priority access license spectrum auction
• introduction of 5G new radio to the band
• Data speed record of 1 Gbps in November 2022

CBRS has been the catalyst for the US telecommunications industry to reach beyond the limits of WiFi and licensed band solutions. However, this does not mean that the use of CBRS has been without its obstacles.

Challenges faced by adopters have ranged from grant suspensions due to coastal dynamic protection area (DPA) activations, reductions in available power around fixed satellite receiver stations and environmental sensing capability (ESC) whisper zones, plus generally authorized access coexistence struggles. A new challenge has also emerged recently as a result of a new Department of Defense (DoD) funded system for triggering inland DPA activations known as TARDYs3.

What is TARDYs3?

Telecom Advanced Research and Dynamic spectrum sharing system (TARDYs3) was developed by ValidaTek for the DoD to provide spectrum scheduling, interference prevention, detection, and resolution capability. This capability has been deployed from January 2023. From the perspective of commercial telecom operations, they are used by inland DoD installations to schedule activation of portal based dynamic protection areas (P-DPAs).

What are dynamic protection areas?

The backstory around the development of TARDYs3 relates to the use of CBRS as shared band. CBRS is a three-tier spectrum band where incumbents are at the top of the pyramid and all other operations must yield to them. Most incumbent activity comes from flight operation radars aboard US Navy aircraft carriers. For the purposes of allowing commercial operations within the CBRS band and protecting naval flight operations, US coastal regions have been divided into dynamic protection areas (DPAs). DPAs along the coastlines are known as E-DPAs (Environmental Sensing Capability-DPAs). These DPAs are monitored by an environmental sensing capability (ESC) network. Each Spectrum Access System (SAS) provider has their own ESC network which listens for radar signatures in the 3.55–3.65 GHz part of the CBRS band. If a signal is detected, the DPA is activated, and the SAS will suspend operations in the impacted part of the band within the DPA neighborhood. DPA neighborhoods along the coastlines have an effective distance of between 150 and 450 km depending on factors such as CBSD category and propagation distance.

Figure 1 – The coverage area of Environmental sensing capability-Dynamic protection area (ESC-DPA) (red) and neighborhoods (green) Source: Wireless Innovation Forum’s technical recommendation

E-DPAs or coastal DPAs have been operational since 2019 when commercial services in the CBRS band began. P-DPAs have also been in existence since that time (Figure 2). P-DPAs provide protection to inland DoD affiliated facilities such as shipyards, naval support and training facilities, test installations and proving grounds.

Figure 2 – Portal-dynamic protection areas (P-DPA) coverage area for manually scheduled operations (blue = category A distance, Green = Category B distance). Source: OnGo Alliance February newsletter

There are about 11 P-DPA protected installations throughout the country. They operate separately from the E-DPAs, meaning they are not integrated with the ESC networks. They are controlled separately through a portal-based system with a calendarlike interface for scheduling DPA activations.

The CBRS world before TARDYs3

Prior to TARDYs3, there was another system that was developed by Google to provide these installations a means to activate associated DPAs. Many may have forgotten about these P-DPAs because the Google developed predecessor was rarely used. Therefore, the operational impact to any commercial sector operations in the vicinity was unheard of.

What is the impact of TARDYs3?

With CBRS commercial operations proliferating across the country, we would anticipate that many CBRS adopters are comfortable thinking incumbent interruption is (or was) mostly limited to the coastlines and some satellite earth stations, so deploying inland is a safer bet. However, since TARDYs3 was commissioned by and built for the DoD many believe the DoD will want to use it or at least test it. Therefore, impact to nearby commercial systems around these inland facilities is anticipated.

The possible activation of a P-DPA by TARDYs3 could impact spectrum bandwidth in the 3.55 to 3.65 GHz range by as little as 10 MHz or as much as 100 MHz. The effective distance of these P-DPA activations range from as little as 150 km for category A CBSDs or low power CBSDs to as much as 416 km for Category B CBSDs or higher power CBSDs.

How to minimize the impact of TARDYs3

Although the introduction of this new DPA activation system seems like another blow to the CBRS band, there are considerations that soften the impact.

First, historically these P-DPAs were rarely or perhaps never activated so one could assume that nothing will change going forward. Second, per guidance in Wireless innovation Forum-technical recommendations -5003 “Incumbent protections and encumbrances overview”, not every CBSD in a DPA neighborhood is necessarily impacted upon DPA activation. Whether a CBSD is impacted or not depends on its frequency of operation and its predicted contribution (by SAS) to the overall interference estimate. This estimate is used to create a ranked list (the move list) of the interference contribution of each CBSD in the DPA neighborhood. CBSDs with the highest contribution are at the top of the list and those with the least are at the bottom.

SAS suspends or terminates grants starting with CBSDs having the highest contribution to the aggregate interference estimate and continues down the list until the aggregate interference threshold is no longer exceeded. Practically speaking, this means that CBSD max Effective Isotropic Radiated Power (EIRP) in the direction of the DPA and predicted propagation loss are key factors in determining the impact of the DPA activation to a CBSD. Put another way, the following will reduce the probability of impact:

• the farther out or away from the DPA a CBSD is
• if a CBSD is pointing away from the DPA
• if a CBSD is a category A rather than category B

How does Ericsson mitigate the impact of TARDYs3?

Intelligent logic built into Ericsson domain coordinator/domain proxy services will automatically seek alternate spectrum in the event of grant suspensions or terminations. For CBRS, our philosophy has been that of maximizing transmit up time, meaning our CBRS product automatically reacts to recover, (manual intervention is not required) in the event of incumbent activity.

Also, within our domain coordinator/proxy software, there is a channel masking capability that allows service providers to define the part of the band they want to request spectrum from. Utilizing channel masking capabilities, a service provider can prioritize channels in the lower 100 MHz as well as the upper 50 MHz (3.65–3.7GHz) of the band which is not impacted by these P-DPA locations.

Conclusion

The introduction of the TARDYs3 system brings a new challenge in deploying CBRS. The extent of the impact is yet to be seen. However, history tells us the impact is likely to be minimal. As we have discussed in the blog, when it takes place, not every CBSD in a P-DPA neighborhood will necessarily be impacted. By using the right software automation and intelligence tools, CSPs, enterprises, and neutral host operators can reduce the risk and secure their network performance.

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