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What Wireless LAN Engineers Need to Know About CBRS

By Keith Parsons, Contributor
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There has been a lot of talk lately about CBRS or private LTE technology. Actually, CBRS, or Citizens Band Radio Service, has been talked about for years and years. But is finally nearing a stage to come to market and be installed in an enterprise near you.

First, CBRS does not use 802.11 protocols. It works off of the same type of technologies and protocols as your cellular LTE on your smartphone. It uses a set of frequencies from 3.55GHz to 3.7GHz, which is around 150MHz of bandwidth. This is about double what we have in 2.4GHz in the US, and about a third of what we have now in the 5GHz range.

The second big difference between CBRS and Wi-Fi is the FCC’s licensing model. Both 2.4GHz and 5GHz are unlicensed, which means you don’t need to check with anyone to use those frequencies. (Albeit DFS, or dynamic frequency selection, channels have a process by which APs must move off a channel if an existing incumbent primary user uses the frequencies. But this is totally automatic and not a negotiation.)

The FCC as designed an innovative licensing scheme that allows for current incumbent users of those frequencies, as well as new users to coexist and even thrive. Users of these frequencies fall into one of the following distinct groups:

  1. Incumbent Users (IU) have highest priority and all others must not use these channels in any way that could interfere with the incumbent users. This is accomplished by the use of a special spectrum database. This is called the Spectrum Allocation Service, or SAS. For any specific location, one can query SAS and be allowed access to the frequencies if no Incumbent User is already using the frequencies at that specific location.
  2. Priority Access Users (PAL) are those users of the spectrum that have been willing to pay for priority access to the frequencies. These fees are not yet defined, but are to be in the “lightly licensed” category. There are rules limiting the number of channels any one PAL can access in any given area. These users also have to query SAS to get permission as well as to register their licensed claims.
  3. General Authorized Access (GAA) users are those who want unlicensed and unpaid for access to the CBRS frequencies. They must constantly query the SAS database to determine if they can use frequencies. If no Incumbent User or no Priority Access User is using a specific frequency at a specific location, these frequencies are available for GAA use.

Potential Uses for CBRS
There are a series of potential uses for CBRS frequencies and equipment, but we are going to focus on two specific use cases.

The first is Private LTE. Where an enterprise provides a wireless infrastructure based on CBRS frequencies and equipment and uses them for in-house communications. These can deliver very high quality and dedicated capacity—something that isn’t always possible with the unlicensed Wi-Fi in 2.4GHz and 5GHz since we are required to share those with all other users.

The second option for CBRS is to integrate a system—like the Private LTE above with as an in-building cellular network. It’s kind of like a replacement for Distributed Antenna Systems (DAS) in a neutral host scenario where your internal Private LTE connects your users directly to their cell carrier of choice.

Why Wireless LAN Engineers?
Cellular networks, using other types of technologies like CDMA, TDMA, FDMA, GSM, LTE, etc. have long been the domain of a group of cellular engineers. They work in a world mostly without network protocols like TCP/IP and definitively work where the network infrastructure is owned, controlled and operated by a single entity. That infrastructure also is designed using protocols that rely on centralized control—cell towers tell cell phones what to do, what tower to be on, how loud to transmit, and what slice of spectrum and technique they should use.

By contrast, wireless LAN Engineers work in a world where the client devices make most of the decisions, where the infrastructure rides on top of a TCP/IP wired network, and where each enterprise owns and operates their own infrastructure. Then the enterprise infrastructure is connected to the wider world via WAN links.

CBRS as currently defined is far closer to the Wi-Fi world than the cellular world. Even though the transport protocol is LTE, the CBRS infrastructure resembles wireless LANs. Individual access points are each connected via Cat5e or Cat6 cable to a wired/switched infrastructure. (The CBRS term for individual access points is eNode B, base station or CBSD, citizen’s broadband service device). The data is transported over a TCP/IP infrastructure and then finally delivered to the wider world over some sort of WAN link.

The design and installation processes are very much like current wireless LAN design and installation practices.

Start Learning Now
As a wireless LAN engineer, you might want to start preparing and learning about CBRS. You are the ones that might be called on to implement these services.

Learn some of its unique language, new hardware, and how these might integrate with your existing network.

You can thank me later.

Post Script: What About Hardware?

The CBRS Alliance is a good learning resource.

As a final note, I hear the following question a lot—and figured it might make a nice postscript to this blog post.

But what about hardware? Is CBRS ready for market?

Currently, Apple’s iPhone 8 sold in Japan has CBRS frequency support, as do some Samsung Galaxy phones in that market. This means the smartphone vendors have already worked out the details to get CBRS radios, antennas, etc. working in their devices.

There are also mobile hotspots and gateways that take CBRS and convert it to standard 802.11 Wi-Fi and/or 802.3 Ethernet.

Finally, there are many vendors already CBRS access points(CBSDs), including from Corning, Ericsson, Nokia and Ruckus. And Qualcomm has been developing and shipping Wi-Fi-compatible chipsets with CBRS capabilities for a long time now.

Learn more from the CBRS Alliance.

 

Tags:

  • CBRS
  • GestaltIT
  • Private LTE
  • RF
  • Spectrum
  • Wi-Fi