The CBRS Alliance, the guardian of specifications, certification and branding in the USA’s 3.5 GHz band – has completed its 5G specs. The first CBRS devices and tests used 4G, which has standards-based ways to use shared spectrum like the general access portion of the three-tiered CBRS framework.
The priority access licences, to be auctioned later this year, will support 5G from day one, while in general access, users will have to wait for 3GPP’s Release 16, which will include standards for working in shared spectrum.
The Alliance has announced Release 3 of its specs, a little behind its original target of end of 2019. “The CBRS band is fully authorized for commercial service at a moment when enabling 5G is an important step for the wireless community,” said Gary Boudreau of Ericsson, who chairs the CBRS Alliance technical working group. “Over the past year, the CBRS Alliance worked with 3GPP and Wireless Innovation Forum (WInnForum) to develop technical specifications for shared spectrum and mobility to ensure that 5G NR use cases are supported in addition to LTE in the CBRS band. The specifications also address seamless interoperability, authentication, and roaming of data and voice.”
According to the Alliance, the new specs incorporate 5G NR definitions and standards developed by 3GPP and build on them, particularly to enable or enhance enterprise deployments and heightened security. Those new features include:
- Extended authentication support
- Local break-out of data traffic for low latency, multi-access computing and reduced backhaul
- The creation of a foundation for industry support of commercial and private roaming of data and voice
While Release 3 aligns with 3GPP Release 15, Release 4 will align with Releases 16 and 17 and will extend the 5G capabilities to the general access portion.
CBRS-style sharing system could ensure 6 GHz is opened up this year
The FCC could make a final decision about opening up the 6 GHz band in the USA as early as April. It aims to make 1,200 MHz of new spectrum available for wireless broadband technologies, if final objections from incumbent users can be overcome, perhaps with a sharing system similar to that in the CBRS band.
The WiFi community has laid claim to the frequencies, which adjoin the 5 GHz band where WiFi is the prevalent technology. The WiFi Alliance has already introduced the branding ‘WiFi 6e’ for devices that can use the whole 5 GHz/6 GHz aggregated band.
However, there is also potential to run 5G in 6 GHz, once standards for shared and unlicensed spectrum 5G usage are completed in the upcoming Release 16 (though that is possibly delayed until next year because of COVID-19). And there are incumbents to consider, and the usual claims of possible interference, especially from the utilities sector.
To address all these issues and ensure 6 GHz can be used as widely and freely as possible, the USA will need to learn lessons about spectrum sharing from its ongoing CBRS experiment in 3.5 GHz, and the resulting decisions, by regulators and operators, will be closely watched round the world.
Federated Wireless – the most prominent of the companies licensed to administer a Spectrum Access System (SAS) for CBRS – has always said the principles of its platform could be applied to sharing in any band, and it sees 6 GHz as a near term opportunity.
Currently, the 6 GHz band is used, in the USA, mainly to provide microwave links for utilities, public safety, transportation and other sectors, and for wireless backhaul. Of the incumbent users, the utilities have been the most active in opposing the FCC’s plans, citing interference concerns, but it now looks highly unlikely event that this opposition, backed by the US Department of Energy, will muster any convincing last minute evidence to scupper the new allocation for 6 GHz.
Federated Wireless says its new automated frequency controller (AFC) would protect those incumbents and remove barriers to entry for new users, using a similar approach to the one pioneered in CBRS – and before that in TV white spaces. These were less attractive in terms of spectrum capacity and quality than the midband frequencies, but hosted a significant amount of early work on techniques to manage access to spectrum to protect incumbents and minimize interference and congestion. These include a geolocation database, which can allocate free channels to requesting services, and the SAS, which support multiple access priorities (CBRS has three – incumbents, licence holders and unlicensed).
Such schemes support a middle way between the exclusivity of long term licences and the wild west of fully unlicensed bands, allowing for significant quality control while enabling a wide variety of providers and services to coexist.
Much of the legwork for a 6 GHz platform has already been done for CBRS, said Federated.
“We just want to get the process going so that we get the kinks out and can get this spectrum commercialized for new users as soon as possible,” Jennifer McCarthy, VP of legal advocacy, told FierceWireless. If the FCC does finalize the rules this spring, early commercial services in 6 GHz could be seen by late 2020 or early 2021, with some WiFi chip and equipment vendors, such as Broadcom, already showing off ‘6e’ products.
The main remaining point of dispute is whether low power indoor devices need to be managed by a device such as an AFC, or whether their lower power output is enough to prevent them interfering with incumbents or other users. If the latter is decided – as the WiFi industry is lobbying for – it will make it easier for existing indoor products and processes to be extended to 6 GHz without incurring extra cost or complexity for customers.
Incumbents prefer the guarantees offered by an AFC, while the WiFi vendors argue that the only risk is if users take their indoor devices outside, which could be prevented by ensuring the products have no weather proofing, for example. However, Federated naturally believes the AFC should be used as widely as possible. It carried out an analysis in San Francisco, New York and Dallas and found “a couple of channels where even a low power indoor device had the potential to impact an incumbent and therefore … our AFC would have blocked a particular channel for that access point”, according to McCarthy. “Our point to the FCC has always been, if you want to use the AFC to mitigate or correct for interference should it occur, the only way we can do that is if we’re in communication with the devices.”
Federated, and the whole CBRS Alliance, has also been leading the charge to introduce sharing into the 4.9 GHz band, which is currently reserved for critical infrastructure industries (CII). Utilities are calling for access to its 50 MHz of spectrum, claiming this is underused most of the time, while its incumbent public safety organizations insist they still need exclusive usage. The Alliance indicates that the spectrum sharing scheme which it supports in the 3.5 GHz band could be adapted for 4.9 GHz, which would enable the safety agencies to be prioritized, but other entities to jump on the spectrum when it was not being used for critical response.
Currently, public safety agencies use the 4.9 GHz band for point-to-point and point-to-multipoint links, often for connecting fire/rescue stations and radio networks in rural areas. They also use it in some areas for data and video backhaul, real time video surveillance, tactical robot control, airborne video, broadband connectivity and fixed wireless hotspots for high speed public safety data sharing.
Federated argues that the CBRS model could be easily adapted for 4.9 GHz and that would enable MNOs and other bodies to use the spectrum without limiting public safety use of the band.
“Dynamic spectrum sharing access is the only solution that maximizes usage of the band with the least disruption to the incumbent users,” the company wrote. It added that this could address complaints that 4.9 GHz equipment is rarefied, and therefore expensive, since gear being developed for CBRS could easily be modified to work at 4.9 GHz.