Hi there. I'm Kate Harrison, and this is the third module of your training to become a Certified Professional Installer, or CPI, of devices that transmit in the CBRS band. In this lesson, we're going to get into some more background on CBRS that you'll need to know. Remember CBSDs, the devices which transmit in the CBRS band and communicate with the spectrum access system, also called the SAS? Now we're going to cover how a CBSD and a SAS communicate with each other, and go over some procedures and protocols used by CBRS equipment. We'll also have a quick overview of the CBSD life cycle. But first, let's talk about the larger CBRS ecosystem. You might be asking, who is actually making all of these decisions about what happens in the CBRS band? More specifically, who has defined the way CBRS works, the language we use to describe it, and the rules around it? It mostly boils down to three main entities. The FCC, that's the Federal Communications Commission, is the government regulatory agency that assigns spectrum, and they created the high-level rules for using CBRS. FCC rules, particularly the one called Part 96, define the CBRS band and the general rules for its use. Then, there's the Wireless Innovation Forum, which its members call WInnForum. WInnForum is an industry-led group that defines requirements and protocols for using the CBRS band. Members of WInnForum include SAS administrators, CBRS equipment manufacturers, network operators, and training program administrators like Google. The FCC and Department of Defense employees also regularly participate in WinnForum to help ensure that incumbent users will be protected. One WinnForum document we recommend you read is the SAS-CBSD specification, which defines how CBSDs talk to a SAS. That document is the source for a lot of material in this presentation, and Section 10 is particularly important to read. There'll be a second release in the future and, as your TPA, we'll keep you informed of any changes that are relevant to your role. Finally, there's the CBRS Alliance, an industry group that manages the ongoing certification program for LTE use and the CBRS band. So those are the big three entities you should know that are making the big decisions about what happens in the CBRS band. Now let's get into the relationship between a SAS and a CBSD. Just for ease right now, we're going to talk about direct communication between the two. But don't forget that in some cases, a domain proxy might be needed to talk to the SAS on behalf of one or multiple CBSDs. Even in that case, they'll exchange exactly the same kinds of messages. The first thing you should know is that it's always the CBSD which sends a request to the SAS, and the SAS which responds. The SAS can't proactively reach out to a CBSD. A response from the SAS always includes a response code. The response code is a number that represents the outcome of the request. If you want to read up on all of the possible codes, you can check out table 39 of WInnForum's SAS-CBSD specification, but we'll describe some key ones later in this course too. Before it can begin to transmit in the CBRS band, a CBSD needs to send a registration request to the SAS. This is a message that includes information identifying the CBSD, where and how it's installed, and who owns it. The SAS receives those parameters, and if they're approved, the SAS sends back a unique identifier it's going to use to identify this CBSD. This is called the CBSD ID. This registration process is where all of the action happens for the CPI. They need to ensure that the parameters that are sent to the SAS are complete and correct. Remember, the SAS can't do its job without 100 percent correct information, and as the CPI, you're responsible for the accuracy of all information you send to the SAS. The SAS-CBSD specification defines three types of parameters: A required parameter, meaning that the CBSD absolutely must provide this in the registration request that it sends to the SAS. An optional parameter, meaning the CBSD might choose to omit this parameter, but if it's included, its value will need to be validated by the SAS. And a REG-Conditional parameter. This is a parameter the CPI must provide. We'll go over these parameters in more detail in the next lesson, including the cases where these parameters are actually optional. After a CBSD is installed, it registers with the SAS. But just completing registration doesn't mean CBSD can immediately start transmitting. Once the CBSD is registered, it may ask the SAS about what spectrum is available at its location. This is done with a spectrum inquiry request. The SAS will respond with the list of frequency ranges which are most likely available for this CBSD to use, and also the transmit power levels that it could use in each of these ranges. Once the CBSD picks an available frequency range and transmit power that it would like to use, it will send a grant request to the SAS. The grant that the CBSD is asking for is a spectrum lease provided by the SAS to the CBSD. It's restricted to a specific set of operating parameters, so to operate on a different frequency, the CBSD would first need to obtain a new grant. If the SAS approves the request, its response will include a grant ID, which is a unique identifier for this particular spectrum grant. A CBSD can actually have multiple grants as long as their frequency ranges don't overlap. But a CBSD can't have simultaneous grants from different SASes. Got all that? So now let's say your CBSD is registered and it has a grant. Now it must be able to transmit, right? It's really close, but the CBSD still has to send a heartbeat request. The heartbeat request is checking with the SAS to verify that it's authorized to transmit using its grant. As always, the SAS will respond with a response code. Here are descriptions of the most common ones. "Success" means that the CBSD can now transmit with this grant. CBSD is ready to go. "Terminated grant" means that the SAS had to revoke the grant and the CBSD is going to have to start over and try to get a new one. "Suspended grant" means the CBSD still has the grant, but can't use it to transmit right now. In this situation, the CBSD should keep heart beating on the grant, and hopefully it will be able to transmit soon. If that doesn't work, the CBSD can try to get another grant, and use that one to transmit. Be aware that some CBSD interfaces will show you these names, and others might show you a numeric code. To see the full list, you can reference the WInnForum document we suggested earlier. CBSDs are actually required to heartbeat at least once every four minutes. This is so the SAS can update their permissions in response to shifts in higher-priority user activity. Remember that the SAS can't reach out to CBSDs, which is why it needs the CBSDs to phone home so frequently. Remember, the SAS' top priority is to protect incumbents, so if a CBSD misses a heartbeat, it has to stop transmitting until it successfully heartbeats again. That's it for lesson three. Now you know more about the CBRS band, CBSDs, and the SAS. Come back for our next lesson, where we'll get into the nitty-gritty details of doing the CPI job. See you back here real soon.
