Hello. Today, we're going to talk about wireless technologies and about wireless networks that use these radio access technologies. We start first, with a little bit of an overview and background how to set the scene for the later content that we have in this presentation. Original networks made use of physical medium in the form of cables to transmit information from one point to another, but with the invention of radio, it was possible to use the air as such medium. And this came with the benefits of mobility-- users weren't tied to the end of a cable to be the transmitter or the receiver of such communications. The air is a medium that can be shared, unlike a cable where it can be really shared between multiple users. The air as a medium can be reused by many different transmitters and receivers. But there need to be certain rules so that they can do that. In order to do that, typically, there is air or the spectrum has been divided into frequency bands that are then used by each type of communication. And as long as its network is using their own portion of the spectrum, they can do so without interfering with each other. Wireless technologies and radio technologies have been used for many different types of uses, from wireless networks-- which is the main topic for today-- but it also has been used for things like radar-- for example-- as well. The first wireless telephone network was created in the 1950s. And since then, we have gone throughout multiple generations of this type of cellular networks that were originally created [? then. ?] How the spectrum is used is heavily regulated. We'll see in this slide, the example of how the UK allocates their spectrum between all the many different end users they can have. This slide shows the complexity of how that is managed. So at the national level, there is usually a regulator that, very carefully, uses and manages this spectrum and makes the most use of it because its a public resource. When we look at the spectrum-- how it is used-- there are many-- mainly, three types of classification of the spectrum. We talk about licensed spectrum, unlicensed spectrum, or shared spectrum. Licensed spectrum is typically leased to a single owner. This single owner-- typically, a service provider-- will be the only user of that spectrum. And with the knowledge that there is not going to be a known interference from other transmitters in that network. And that capability gives the service provider the tools to deliver quality of service to the users by managing completely the spectrum and how it is being used. Examples of licensed spectrum and wireless technologies that use the licensed spectrum are cellular technologies such as LT or 5G and all the previous generations. Unlicensed spectrum, on the other hand, doesn't have a single owner. It's still regulated, but there are multiple users that can use that spectrum as long as they follow the rules that have been set. Such rules will include things like transmit power, certain limitations of transmit power, or certain coexistence rules to ensure that multiple transmitters and multiple receivers can actually make efficient use of that spectrum. Examples of wireless technologies are wireless networks that use unlicensed spectrum are Wi-Fi or different types of generations of Wi-Fi and Bluetooth, as well. In between licensed and unlicensed, we also have shared spectrum. Shared spectrum sits between the two. It typically operates in short leases so its very dynamic in the way it is being used. Examples of shared spectrum are CBRS, which is common [INAUDIBLE] in the US. When we look at wireless networks, we can also classify them in the range that they have and the coverage area that they provide, we have personal area networks. Usually very short range. They're within a person or within a small area, such as a room. Coverage is about 10 meters or so. Examples of this type of technologies are Bluetooth-- for example. Local are networks, on the other hand, provide a little bit bigger coverage. These would give coverage around a building, around our campus. Could be a residential property or it could be a stadium. For example, in the range of hundreds of meters, a kilometer to the most. Examples of local area networks are Wi-Fi and similar type of technologies. Providing bigger coverage and wider coverage are wide area networks or WANs. These provides a metropolitan coverage or even national coverage. Even in the case of satellites, they can provide international coverage, as well-- worldwide. Finally, we have the services that are being delivered on top of these networks and radio access technologies. We have on one side, consumer-oriented services. These type are services go from voice and telephony to short messaging, media streaming, mobile broadband-- these type of services that are given to consumers. On the other hand, we have services that are delivered to things and machines. So this is where IoT or the internet of things and machine-to-machine communications come into place. There is also a wide variety within these type of services. For example, you can have a sensor that is just delivered in short bursts of data once or twice a day. Or on the other hand, you could have a streaming video camera streaming video at very high definition. We have new types of machines required in different types of services within this domain, as well. Could have a robot that requires very reliable and very low latency type of communication. Or you can have an automotive that requires, again, very reliable, very low latency type of communications.