Now that we have learned about some of the fundamentals of wireless communications and seen how a general cellular communication network looks like, let's try to get more background on a cellular network, starting with how cellular communications have evolved over the generations and what brings us to the current generation of cellular communication and potentially what might take us beyond, i.e 5G. We will learn about what are some of the fundamental premises that 5G makes pursuant to some of the strict requirements that have been put forth for 5G, which will correctly set the foundation for the rest of this class. Cellular communications, as we know today, really started in the 1970s and '80s with what is retroactively now known as the first generation of cellular communications, i.e 1G. The predominant use case at that time was to enable people to make and receive voice calls on the go wherever they were. Maybe they were in a car, maybe they were in a shopping mall, in the movie theater, whatever, the use case was to enable them to make and receive voice calls no matter where they were. That's why the hallmark application of the first generation of cellular networks was voice. Now you will see a little qualifier there, see analog voice. You might wonder, hey, isn't our voice analog by default? Why do you need to say analog voice? Well, when we think of voice or any data in terms of communication, we not only have to worry about how that data is produced but rather how that data is transmitted. In the first generation of cellular communications, our analog voice was imposed onto the outgoing carrier wave using analog modulation, something that we learned about in the previous module. Because our analog voice was transmitted over the air using analog modulation, that is the reason why you see the qualifier there as analog voice. First-generation of cellular networks is really where everything started in the 1970s and 1980s. Then came the second generation of cellular technologies, are proverbially known as 2G, sometime in the '90s. The fundamental focus was still on providing voice services but now you will see a different qualifier and that is for a well-merited reason. What you see here is not analog voice, but digital voice. What is digital voice? You might wonder. Well, our voice fundamentally, as we produce it continues to remain analog, no question about that. But in the second generation of cellular communication, the modulation technique that would be used to super-impose our voice onto the outgoing carrier wave would be digital modulation. In that modulator, in your phone, would convert your analog voice into a digital stream of bits and bytes, essentially a sequence of ones and zeros, and that sequence of ones and zeros are other than your analog voice, would be used to modulate an outgoing carrier wave. Why would we do that? Well, that is a separate discussion, but at a high level, there are certain quantifiable benefits to digitizing your voice. Not only can you compress and encrypt or encode a digital stream better than you can in analog stream, but other quality with which you can reproduce and transmit digital sound happens to be better than the quantity that analog voice can offer. That is a fundamental reason why other electronic ecosystem as a whole moved from analog voice to digital voice. But nonetheless, for second generation of cellular communication, our voice continued to be the predominant use case although text messaging had started to be popular by that time. That brought us to the third generation of cellular communication, also known as 3G, sometime in the first decade of this century. That is the first generation wherein we had seamless access to mobile Internet. For the first time, we had seamless access to all the resources available on the Internet. Be it as simple as news or weather forecast, or be it as specialized and complex as video broadcast, audio broadcast, or email, for example. So 3G was the first generation that truly offered mobile Internet. The speeds were somewhat limited compared to what we have today on the order of few 100 Kbps or a few Mbps. But suffice it to say that those speeds were more than sufficient to cover all the use cases that we had at that time. But the fundamental benefit of bringing internet connection to all the mobile phones was that it ultimately led to the invention of smartphones, which led to the advent of the next generation of cellular communications that is 4G, also known as LTE. Now, LTE made a few changes to the fundamental network architecture, which gave us some extraordinary benefits. Not only did it magnify the available data rates, from a few Mbps to a few 100 Mbps and then more than one gigabits per second, but it also greatly expanded the mobile ecosystem from just cell phones to other devices that had started cropping up at that time, for example, tablets, fitness trackers, virtual reality goggles or even connected cars, smart home devices, etc. 4G not only improved the speeds that it would offer to your mobile phones, but it also greatly expanded the Ecosystem beyond just everyday phones into the realm of tablets, smart home device, fitness trackers, etc. That was the fundamental power of 4G in that it expanded our ecosystem. Thankfully, that trend of ecosystem expansion has continued till date in that more and more devices of different varieties are asking network connectivity more reliably. Not only that, they are expecting higher and higher speeds and lower and lower lag from the network that they connect to. Given that the ecosystem has been expanding at a rapid clip. That brings us to ask one fundamental question. Is 4G or any legacy technology for that matter, truly sufficient to meet the requirements, not just for today, but continue meeting those requirements tomorrow and beyond? Is 4G truly sufficient? Is it a future-proof technology or is it going to be not sufficient beyond a certain point? Which will bring us to think about the next generation of cellular technologies, which will be called 5G. Let's try to answer that fundamental question whether there are any use cases or applications that 4G, cannot satisfactorily meet or cannot meet at all.