Before diving into the technical aspects of frequencies and network speeds, it helps to have a benchmark to put everything against. Think about a time you wanted to download something to watch for a long plane ride. For a 3 GB movie, it would take over an hour if you were still on a 3G network. With 5G, that gets cut down to less than a minute. But how did we get there?
Wireless technology's first generation, retroactively named 1G, launched in 1979 before arriving in the US in 1983. It used frequencies in the 800 MHz spectrum, and it helped usher in the first analog cell phones. 2G came in 1991, and with it came expansion into the 1.9 GHz spectrum and such features as SMS (simple text messages), MMS (multimedia messages) and voicemail. This bandwidth expansion marked a significant shift in the capabilities of cellphones—the wider the frequency range, the more data that's able to transfer—and is a hallmark of delineating the different generations.
3G was introduced in Japan in 2001 and in the US in 2002 by Verizon, expanded the frequency range into the 2.1 GHz spectrum, providing the network speeds that smartphones need. The core technology of this generation was MIMO (multiple-input multiple-output), which expanded the network's bandwidth and upped its device capacity. 3G could theoretically reach speeds of 40 Mbps, and its higher data-transfer rates enabled now-standard functionalities like mobile web browsing, image sharing and GPS location-tracking.
4G was introduced commercially in 2009 and added frequencies in the 600 MHz, 700 MHz, 1.7 GHz, 2.1 GHz and 2.5 GHz spectrums. 4G network speeds could reach up to 400 Mbps, which has facilitated high-definition video gaming, video streaming and video conferencing. 4G LTE, which most networks currently use, further reduced latency and increased efficiency. (LTE, by the way, is not a technology—it stands for Long Term Evolution, denoting the road to 4G.)
Millimeter wave-based 5G is anticipated to provide very high levels of peak downlink throughput performance--ranging approximately from 4 Gbps on the lower end to 20 Gbps on the higher end, all under ideal channel conditions. These speeds represent a massive opportunity for practically every industry and vertical. Expect real-time monitoring, low-latency communication in remote areas, the development of "smart cities" and so much more in the very near future.