Last year, the FCC opened up 150 MHz of spectrum in the U.S. around 3.5 GHz that it named Citizens Broadband Radio Service (CBRS), not to be confused with the old CB radio. Hidden under that name is a novel approach of making more spectrum available when and where it can be used. As spectrum is the life blood of wireless communication, the FCC’s move has the potential to create new wireless opportunities, which for consumers means new and better services.
So what is the new approach in CBRS? First, it enables others to use the spectrum while it is still being used by existing incumbents, such as the military or satellite communication, see Figure 1. This in itself is not new. As a matter of fact, we helped to introduce this concept back in 2013 with Licensed Shared Access (LSA), where a license holder exclusively shares the spectrum with the incumbent. This is a powerful concept that unlocks more spectrum for wireless communication.
Figure 1: When an incumbent like the Navy is using a part of the spectrum, other users need to move to unused portions of the spectrum band.
In addition to sharing with incumbents — CBRS adds a ‘third-tier’ of general usage. In this third-tier, anyone can use the spectrum when it is not used by the higher tiers (the incumbents or users that paid for a license), see Figure 2. Of course, if there are multiple third-tier users in the same area then they will share the available spectrum with each other in a fair manner. The complexity of managing three tiers will require some additional control. To this effect, the FCC has defined a Spectrum Access System (SAS) — a type of database, in effect — and the Wireless Innovation Forum is helping to specify the details to ensure that it all works in accordance with the FCC rules.
Figure 2: CBRS consists of three tiers with different priorities: incumbents, licensed usage (PAL), and general usage (GAA).
So what exciting things will this new kind of spectrum enable? Let’s look at some examples. First it can be used by existing mobile operators to offer Gigabit LTE speeds in more places by making more spectrum available. One can also use this spectrum for small-cell deployments to extend coverage and add capacity indoors. Another example is what we call neutral host, which is a LTE deployment that can be used by subscribers irrespective of their service provider. Such a solution makes sense in places where it is not feasible for each operator to deploy its own radio systems independently; for example, in public venues such as sports stadiums, or in places where it is not cost effective to do so, like indoor coverage in malls or hotels. This approach benefits the venue owner, the mobile operator and the end users. The three-tier approach also enables new entities to offer services by creating their own so-called private LTE networks without owning any spectrum. Such private LTE networks can be used for industrial IoT or enterprise use in general. But let’s not stop there. By enabling anyone to create a LTE-based network, the sky is the limit, literally.
We are not alone at being excited about this new spectrum. Together with five partners we started the CBRS Alliance, which was announced this week, and are working toward field trials later this year. The CBRS Alliance will focus on supporting the commercialization of LTE-based solutions in the CBRS band and is encouraging companies that want to help accomplish this goal to join — for more info see their webpage. From our end, we are getting ready for CBRS by making multiple LTE-based solutions available: LTE-TDD, Licensed Assisted Access (LAA) and MulteFire. Each of these offers different benefits and can co-exist together in the CBRS spectrum. As with CBRS, all good things come in threes!