We use cellular networks to place phone calls from our mobile phones when we are on the road. WiFi to access data when we are at home. Bluetooth to connect our wireless headsets. And play music from our phones and bar codes to scan information. All of them are amazing wireless technologies that give us mobility. But why do we need so many of them? Which business context can be best served by each of these technologies? In this module, we are going to find answers to these questions. So let's begin at the basics. Wireless communication systems use electromagnetic waves. These are coupled electrical and magnetic waves which can occupy different frequencies. Ranging from the visible spectrum. That is the colors of the rainbow and sunlight to the invisible ones like the x-rays, gamma rays, and microwaves. Some of these waves, depending on its frequency, can pass to solid obstacles just like sunlight can pass through glass. WiFi and cellular signals can pass through brick walls. The frequency of a electromagnetic wave is measured in the units of hertz, and it's written as H and a small z. And it's also written in kilohertz, megahertz, and gigahertz, depending on the magnitude. So thus, the whole wireless spectrum can be divided into frequency bands that correspond to different types of waves. Different wireless technologies use different types of waves, and hence, they occupy different frequency bands. For example, in this diagram, you can see that the WiFi operates at a very different frequency your cellular and GPS devices. So here we have the frequencies increasing from megahertz to gigahertz. The radio waves, or the radio signals occupy lower frequencies then it's the remote control TV and then finally you have cellphones, GPS, medical devices, microwave and so on as you go up higher in the frequency. The U.S. government has been trying to free up some of the spectrum that has been allocated to the TV providers, to the TV broadcasters, which is in that area between 500 megahertz to 1 gigahertz. And reallocate those frequencies to cell phone operators so that they can meet the demand for growing data. So, if the frequency of the waves that a particular technology uses is higher, then it needs a smaller antenna. If the technology operates at a lower frequency, then it needs a larger antenna. For example, radio needs a larger antenna than your cellphone because radio operates a lower frequency than cellular networks. There's also a relationship between the mobility that a technology offers and the data speeds that that technology can provide. So, if we look at the trade off between mobility and speed by plotting mobility on the x axis and the speed or the data rates on the y axis. You can see that WiFi provides a small mobility because it only works in the tens or hundreds of meters. But it offers very high data speed. So WiFi operates at 2 gigahertz so it has a high frequency and therefore it would require a smaller antenna compared to cell towers. And since it operates at a higher frequency it provides higher speed but it also provides less mobility tens to hundreds of meters. In contrast, if you look at cellular networks like UMTS, 3G, TSM, these operate at a much lower frequency, for a 2G is around 900 to 1800 megahertz. And for 3G, it's about 2100 megahertz. So they are operating at much lower frequency than WiFi, and therefore they would need larger antennas for broadcasting these signals. But they also provide a larger range of ability. And that's why we use cellular networks to use our cellphones when we are on the road, but the data rate that they provide is also lower, so that's why WiFi is much faster than your 3G or GSM networks. And so this curve shows the trade off between mobility and speed and where the different technologies lie in that curve. So WiMax, which is a metropolitan network is somewhere in between cellular networks and your local area networks like WiFi. It provides a coverage over a larger area than WiFi but a smaller area than a traditional 3G or GSM network or cellular network. And since it's an intermediate technology it provides intermediate range of speed and mobility. So let's also look at these different technologies by plotting them slightly differently. Again, this is a picture with the range on the x axis. That is the range over which this technology would work. And the y axis represents the data rate. Near Field Communication which is what you would use in your iPhones to pay for Apple Pay. That requires very close contact between the receiver and the phone. And so they have a very small range and they have a very small data rate. On the other hand you have WiFi which has a much higher data rate, and it also has a range of about tens of meters. And Bluetooth provides the shorter range than WiFi and a lower data rate as well. Now, if you Look at technologies that offer larger range, such as 3G, 4G, GSM, or WiMax. They would offer larger range, but typically they have lower speeds or data rates that they would offer compared to technologies like WiFi or Bluetooth. So this is another visualization that shows where the different technologies lie in with respect to the trade off between range or mobility and speeds of the data rates that they support. So in the next video we are now going to look at how these technologies actually work.
