CBRS: How shared spectrum changes the game

Wireless system operators have traditionally had two choices for accessing spectrum: participate in an auction to buy spectrum from the regulator, with the benefit of dedicated spectrum notionally free from interference or sally forth into the wild west of unlicensed spectrum at the mercy of unknown interferers with no protection or coordination. But now, CBRS offers a third option: shared CBRS spectrum.

CBRS Band Changes The Game

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How CBRS band changes the game

How does shared spectrum work?

With the new shared spectrum scheme, a spectrum manager known as the CBRS Spectrum Access System (CBRS SAS) mediates access to spectrum by licensees in two priorities. This approach brings a new hope to users seeking the discipline of licensed spectrum without the cost of buying the airwaves. However, the utopia of this approach is complicated by the fact the band in question at 3.5 GHz is occupied by naval radar systems and by commercial Fixed Satellite Service (FSS) users. The mechanics of CBRS developed over several years protect incumbents and provide fair share access to new users as well as offering a license like concept.

There are two tiers are as follows:

Priority Access Licensed (PAL) - this layer provides access to up to 70 MHz of licensed spectrum to be auctioned later this year. PAL channels are awarded in 10 MHz license blocks.

Generally Authorized Access (GAA) – this layer is accorded no interference protection. In reality, GAA spectrum quality is dependent on how many hands are raised in a given location. The SAS uses the same 10 MHz unit as in PAL layer to apportion spectrum to GAA users. However, there are no specific rights to prevent access to spectrum eligible for GAA use. If there is no other user at that approximate location, the spectrum is all yours. Over time, GAA spectrum may become crowded in certain locations and will rely on the SAS to maintain order to avoiding suffering from issues that plague other shared spectrum bands.

How to decide what kind of license you need

The user can participate in the PAL (Priority access Layer) auction, currently being planned for June 2020, if certainty of allocation is needed. The starting bid of 2 cents per MHz per person covered is the opening ante asked by the FCC in county wide tranches. Each bidder may only secure up to 4 PAL licenses (or 40 MHz) out of a maximum of the 7 licenses allowed. An interesting wrinkle is that despite owning a PAL license, another user can use your PAL if you do not light up your spectrum at that particular location. The name of the game here is “Use it or lose it” or really use it or allow someone else to use it.

Unlocking Federal CBRS spectrum

Sharing is an important concept when it comes to federal spectrum. In the US., National security arguments often prevail when defense and government bodies argue their case against the regulator who is trying to pry valuable spectrum from their hands. Regulator end-game discussions often arrive with a “must vacate” order, so a softer gentler – well you could just share - suddenly seems attractive. This is especially true with deep rooted long lead time users like the Navy or Airforce.   Spectrum thus designated is not a replacement for traditional licensed spectrum approaches that will remain the mainstay of mobile broadband policy for telecommunications networks. After all, mobile networks have certain reliability requirements in respect to guaranteed access to capacity for critical use cases such as emergency services and call continuity for conversational services. The value proposition for CBRS is in a different dimension – that unlocking this spectrum for shared use allows the regulator and cellular industry to avail of the economies of scale for equipment that has already been designed for other bands in the same spectrum region, with some redesign due to the requirement to protect incumbent and adjacent band users.

Ecosystem development

An existential challenge for any new spectrum is the ecosystem support, and no band survives without a healthy ecosystem. This starts at the chipset level where Qualcomm, as an early supporter of the band, dug the foundation with Snapdragon capabilities in band 48 (B48) the 3GPP designation for CBRS. Other chipset vendors are following suit. Next comes OEM devices with flagship Android and IOS devices offering CBRS band support, and now the module makers enabling IOT devices for a full house of capabilities.  FWA devices are available and are stimulating that segment. 

As of February 2020, there are 43 CBSD (CBRS Devices – Base Stations) and 43 UE (Mobile Devices) approved by the FCC. 28 CBSDs are OnGo certified. The fact that Apple iPhone 11 supports the B48 CBRS band is significant and a vote of confidence from the folks in Cupertino. The Android ecosystem has likewise introduced CBRS into several smartphones, notable examples being from Google and Samsung.

Path to 5G with the CBRS alliance

The band is being initially launched as an LTE (4G) band but is rapidly progressing to 5G. The CBRS Alliance this week has announced the completion of specifications that support specific OnGo configurations under 5G, and is busy working on the SAS rules around the allocation of NR channels. Radio manufacturers, including Ericsson, can differentiate by having 5G NR radios ready in their portfolio. 3GPP work for the 5G transformation is all but complete leaving the chip guys on point.

NSA (Non-Standalone) NR comes first. This means that the user needs a licensed band anchor. Then comes Standalone, expected in 2021, which gives the enterprise the opportunity for a 5G system on CBRS independent of any licensed bands. 

Is CBRS a 5G band? Yes, it is already! The industry should work together to get to market as rapidly as possible for the benefit of 5G deployment across the nation.

What do we expect of the band?

I outlined in this blog some use cases above that will get us going, but fully expect more to emerge in a must watch saga. Having been involved in the CBRS Alliance and Winnforum activities on the Boards of both organizations, I would say it’s a somewhat unprecedented industry cooperation to get it to this point. The FCC and US Government have come together to make it happen, albeit not without bumps in the road. The industry worked together to drill for Spectrum and having struck oil will now compete to pump it to the surface.


For more information:

CBRS Alliance – FCC Authorizes full commercial deployment of OnGo service in 3.5 Ghz band unleashing billions in value with new wireless services

CBRS Alliance - CBRS Alliance Opens Gates for First U.S. Mid-band 5G Deployments

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