Hello and welcome back. Today we're going to continue with the principle that sharing is hard, which we looked at last time with cellular networks. Except today, we're going to focus on WiFi networks. And we're going to answer the question why WiFi is faster at home than it is at a hotspot, which you probably noticed for one time or another. And if you stay at home, sometimes you get much better internet connection on WiFi than if you go to Starbucks, especially if it's crowded at wherever, whichever hotspot you're at, like for instance, a coffee shop. So we'll start off today by talking about unlicensed spectrum. And so if revert to what we were talking about in the last lecture with cellular we saw that all the cellular spectrum operated on licensed bands. So all of your 3 or 4G networks all require licenses to operate. And your cellular provider needs to have a license to operate in those bands and to allocate you those frequencies. So in 1985, the FCC started to release some unlicensed bands. And a large part of reason for this is as, you know, the process [UNKNOWN] FCC in trying to terms of additional inspection took lots and lots of money, millions and millions of dollars, and a very, very long time. So this is especially inconvenient for any researchers who wanted to operate in these bands, especially in non-closed proximities. So if you're even a researcher, just as a side note, you can, as long as it's in a contained area and you're not actually projecting it out into the atmosphere, which we all have to share. But if you're trying to do any type of research, and you want some real world scenarios, it was very inconvenient. And so the FCC, we saw this logo last time, initially released this as the ISM, the Industrial Science and Medical bands. So it was for use mainly for the ISM, for these fields, like for in hospitals, for medical or any science or an industry. and they were centered around 2.4 and 5.8 gigahertz. And engineers quickly seized this opportunity, so even though it was, it was pushed out with the idea being used for people on industries of science and medicine. And engineers were very quick because they wanted to do research in these bands and try to use it for these different purposes. [LAUGH] So, in fact, the most, the most commonly encountered device that operates in these bands is the microwave oven, and that's where it gets the name microwave from. Because these are at very high frequencies, at 2.4 and 5.8 GHz, and we won't get into detail on why those are called microwave or what the microwave band is, for instance, but these are microwave range frequencies and you can look at that, for instance, more in your Wikis if you want. But we're talking low low gigahertz range like 2.4 or 5.8. Remember a gigahertz is 10 to the 9th or a billion Hertz, so this is 5.8 billion hertz. And so these bands as engineers started to seize this opportunity became increasingly used for WiFi devices. So you're probably wondering, well why didn't they just use them as additional spectrum for cellular? Well the reason is that we came to a fundamentally different paradigm and a fundamentally different way of thinking for specific devices in close proximity. Okay. And this is WiFi, as we know. So it's not the same setup as cellular anymore. These WiFi devices are used for different setup and the setup meaning that they're closer in proximity to one another. So for instance if you have laptop or a smartphone or a tablet or any other devices that can. Operate on WiFi. As you notice you generally have to be pretty close to the access point. So WiFi is typically used for a stationary devices or it's ideally used for a devices that aren't moving around a lot as well as devices that are close to the access point. So the reason we didn't allocate these for cellular is because engineers started to think, well, for devices that are stationary and close to the access point, why do they have to go, do power control with all the other cell phones that are out and about anywhere else? Why can't we just have different WiFi or small different sections where they can access the Internet differently? And that was the fundamental idea behind WiFi which is, still permeates to the present day. And as you probably know, if you've ever gone to a Starbucks or anywhere before, that as you have more and more people around it, it gets harder and harder to get a good data rate. And the data rate on WiFi fluctuates quite a bit. And we'll talk about why that is exactly, but as more and more people come, the data rate tends to go down a lot. And so its not scalable, in the sense that it can't go up to a high number of people like we can do in cellular. We can have many, many more devices in a cellular region but with WiFi, you know, if you go above. Even ten devices is getting a lot, in one specific access point, the data rates can be pretty slow.
