Hi I'm Kate Harrison, and I work as a senior software engineer in the wireless services team at Google. Welcome to the first module of our training to become a CBRS CPI, and thank you for choosing Google as your training program administrator. You might have only a vague idea of what those terms mean, but don't worry, you're in the right place and we're going to walk you through all of it. This course will train you to be a certified professional installer, or CPI, of devices that use the CBRS band. CBRS stands for Citizens Broadband Radio Service. This lesson covers CBRS basics, and you'll get all the info you need about the CBRS band and spectrum sharing so you can understand the rest of this course. Ready to get started? In this first part, we're going to cover the very basics, and give you all the background you need on CBRS and spectrum sharing. We'll get more into the details of the CPI role in other lessons. The Citizens Broadband Radio Service, or CBRS, is a special frequency band with an exciting new purpose, and it's part of what we're calling the spectrum sharing revolution. Wireless spectrum is traditionally assigned by the Federal Communications Commission, or FCC, one band at a time, with each band managed by a specific user, such as a cellular provider who has exclusive rights to use the band. But in 2015, the FCC did something new. They took the frequencies in the 3550 to 3700 megahertz range and used them to establish the Citizens Broadband Radio Service, which is being managed in a completely new and different way. Before 2015, most of those frequencies were reserved for certain parts of the US military. But with the creation of the CBRS band, the military hasn't lost access, and their service hasn't diminished either. They're just sharing these frequencies with a huge number of new users. So now, the CBRS band is a 150 megahertz of spectrum shared by multiple different systems with different owners, and that's what we call shared spectrum. The problem with the traditional approach - licensing spectrum in an exclusive way - is that certain users are going to utilize their spectrum mostly in just part of the allocated geographic area or for a small fraction of the time. So assigning a whole band to just one user 100 percent of the time is not an efficient way to distribute this valuable resource. Look at the 3.5 gigahertz band, which is now the CBRS band. It was reserved nationwide for military radar systems, but it was only used on occasion, in only a few locations, and all along the shoreline. So that's a lot of wasted opportunity and bandwidth. The vision for CBRS is 150 megahertz of new wireless bandwidth in the 3550 to 3700 megahertz range that can be used for fixed and mobile broadband access. Here are a few use cases. It can be used for localized wireless broadband access in businesses and homes or cellular-like broadband access across larger outdoor areas. It can provide broadband service to homes, businesses, or schools from a central transmitting tower. This is just a taste of what's possible with CBRS. Here, let's compare traditional exclusively licensed spectrum with the new spectrum sharing model of the CBRS band and see how they're different. With exclusively licensed spectrum, there's a lot of unused capacity. For example, naval radar gets spectrum allocated nationwide even if they only need it occasionally along the coastlines. But shared spectrum is more efficient. Parts of the spectrum that are underused by the primary user of the band can be opened up to new users and new uses whenever the original users don't need it. Under the old system, the time to market, and by that I mean how long it takes for a user to obtain rights from the FCC to use a particular band, can be more than 10 years from start to finish. A lot happens in 10 years. Whereas, with shared spectrum, it's very easy for a new company to start operating in a new band, and you'll see why as we learn more. Then, when you consider cost, distributing spectrum the old way is also expensive for the operator and the consumer. Forty five billion dollars was spent on 65 megahertz of spectrum in 2015, which is a large upfront expenditure which will eventually be passed on to consumers. The high cost of spectrum means that it's harder to get started for new businesses or use cases or any systems with a decentralized cost structure, like Wi-Fi. If we look at how Wi-Fi systems are deployed and used today, it's clear that their success comes from their low cost and the wide variety of equipment and service providers, which never could have happened if we had needed to buy spectrum at auction before even knowing that Wi-Fi would be so successful. Shared spectrum creates opportunities to test out new ideas and create products that wouldn't have succeeded otherwise. Although the CBRS band is free to use, its users can actually choose to pay if they want higher priority access and a better experience. For example, a small business may utilize free spectrum at first, then opt to invest more as it grows. We believe that these two properties - a low minimum cost, and the option to pay for improved quality - will inspire exciting new uses of spectrum, just like we saw years ago with Wi-Fi. Usable spectrum is a finite resource, and it gets harder every year to find enough spectrum to meet the growing demand. There's no totally unused spectrum left at the most usable frequencies. So for one new user to acquire exclusively licensed spectrum, it has to be taken away from someone else. Whereas, with the new approach of shared spectrum, there are tons of opportunities that haven't been explored yet. Shared spectrum means more opportunities for more users. But why didn't the FCC do this in the past? Why weren't we always sharing spectrum? Why is this revolution happening only now? For spectrum sharing to work, higher priority users need to be sure that they won't be dealing with excessive interference from other users. That requires someone to enforce what's called an aggregate interference constraint. An aggregate interference constraint means that the total amount of noise caused to each higher priority user is kept to acceptable levels. Users could do what's called spectrum sensing, meaning that they would listen to see if any higher priority users are transmitting, before transmitting themselves. But one major problem with this is that each interferer only knows about themselves, not the other potential interferers around them, so no one entity has enough information to guarantee that the aggregate interference constraint is met. It takes a centralized system with a lot of computing power to know who's transmitting where, when, and how powerfully. The best tool for this task is a scalable cloud service. But in the past, Internet connections were not so ubiquitous or reliable, so depending on an internet connection to keep your network alive was a much scarier proposition. The scalable cloud service that manages CBRS transmissions is called a spectrum access system, or SAS. The SAS manages information about all users of the CBRS band, in order to ensure that higher priority users are protected from harmful interference. A SAS is a tremendously powerful tool that enables the use of the CBRS band. But any cloud service is only as smart as the data that gets fed into it, and that's where you as the CPI play your role, ensuring that the SAS gets the right data about the devices transmitting in the CBRS band.
