Cellular technologies have advanced from first generation(1G) analog technologies to high-performance fourth generation (4G) and fifthgeneration (5G) systems in just four decades. While 1G cellular technologies have disappeared, 2G technologies are being replaced by newer generations. 3G and 4G cellular technologies are widely deployed worldwide. And 5G technologies have started to appear and will continue to be deployed through 2030.
Despite the increase in sophistication of wireless standards and devices over the years, cellular technologies maintain a set of common principles that form the basis behind the design of cellular systems. Certain principles are likely to be incorporated into 6G systems, whatever that standard turns out to be in the future. The implementation of these underlying principles will vary from one standard to another and sometimes within revisions of a given standard. We review these basic principles in this paper, and provide more explicit details by comparing 3G systems and 4G systems.