Things you need to know - CBRS Webinar


Great CBRS overview, thanks Matt! I have a few questions/comments...

1. If you request, let's say a 30MHz channel from the SAS, and it's denied, will it automatically ask for the next smaller sized channel width i.e 20MHz and if that's denied... then down to 10MHz?

2. There was talk of Cambium having some CPI training how can we find out more about this and are there any CPI training/certification courses at WISPAPALOOZA this year?

3. Aren't there different power levels for radios that do not require SAS or CPI? Can you avoid CPI certification and the SAS monthly if you only use the lower power uplink TX for clients... IIRC isn't it 23dBm?

4. How does back to back frequency reuse work with this system? Will the SAS 'know' my other AP's at a location and how they're physically arranged and be able to intelligently assign channels? My fear is that a lot of spectrum will be wasted by not taking advantage of frequency reuse due to the SAS just blindly assigning unique channels for every AP at a site.

5. This SAS channel plan obviously doesn't take into account any guard bands. Things could get ugly for you and a competitor if you're both assigned channels next to each other, on the same site/tower, and aren't using the same frame settings :-(

Thank you for Matt for information. I know you are mentioning a whitepaper in the webinar. Can someone please share link to that particular whitepaper?

The MU-MIMO whitepaper mentioned at the beginning discusses all the innovation and features of cnMedusa (in the 450m product) and can be found here.

Eric, good questions:

1. This depends a bit on how it is requested, and we are still working with the SAS vendors on what this will end up like... it CAN happen as you describe. There is also a function called a spectrum inquiry which will return what is avaialble, prior to actually requesting the grant. We are looking at how this tool can be implemented to get the desired results.  This will evolve over time.

2.  Cambium will not be doing our own CPI training. We will, however, have a training module that covers how to install, use and provision our equipment for Part 96 operation (which will compliment CPI training). Currently, all the major SAS vendors have CPI training courses available for you to get certified (Google, Federated Wireless and Commscope).

3. The limit for Category A devices is 23 dBm EIRP. However, the device must be certified as a Category A CBSD and be installed at lower than 6 meters HAAT (height above average terrain). All Cambium Networks devices are certified as Category B devices, so even if the ATPC (Automatic Transmit Power Control) turns down the power to be lower than 23 dBm EIRP (because the SM is close to the AP for example), it is still considered a Category B CBSD and is required to talk to the SAS.

4. We are working with the SAS vendors and carefully walking through our use cases, including this aspect (of frequency re-use capabilities). There is still ongoing work being done, but the goal of this work is to eliminate wasted spectrum as you describe.

5. Coexistence groups take this into account. As the SAS evolves, there will be more of this factored into the assignment of channels, power levels, etc. An area that is entirely made up of LTE equipment might have a different interference level calculation than an area where Cambium 450 is nearby LTE equipment, and other coexistence calculations take place, possibly changing the grant results, moving the frequency further or reducing power to avoid interference.


Minor correction: An End User Device (EUD) is limited to +23 dBm EIRP. That is a client that does not register with a SAS. Think "cell phone", but if you have a really good path it could legally be an SM. A Category A device is limited to +30 dBm and all indoor base station devices must be Category A. Whether you're Category A or B doesn't matter much to the SAS in terms of process; you still need the SAS (this will cost something) and you still need a Grant. If the Category A has approved GPS, it won't need a SAS, but GPS isn't accurate enough in elevation to be used to register the required elevation, so don't count on it.

"Coexistence" is entirely outside of the FCC rules but the big SAS players are most concerned about the big mobile players so it becomes  a tool for them. Devices that transmit in sync with one another, like LTE-TDD with a common profile, will be more likely to be allowed to share a channel. Cambium, however, did a clever tweak in 16.0.1.that lets it sync up with what is likely to be a common LTE profile, so even without being LTE it may be able to "coexist" with it. In CBRS terms, that's about as clever as Elevate is in the 802.11-radio world, without the legal issues. So C450 is a lower risk than other non-LTE technologies.

But it would still be nice if we had a SAS vendor who cared about fixed users, not just mobile.

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Thanks for the correction and commentary Fred.

All 450 platform devices are considered Category B devices and are being issued the grant as such, so we really won't have a way to allow Category A devices onto a 450 network. However, when cnRanger is released in 3 GHz (early 2020), this platform (because it utilizes LTE protocol) will have many more options.