What is 5G?

Mobile networks have gone through distinct generations based on air interface, ranging from the original analog to second generation TDM and then a few flavors of 3G and now a small range of flavors of 4G Long Term Evolution.

Now U.K. regulator Ofcom is referring to "5G," which doesn't yet exist, for spectrum it plans to auction off in 2018, if all goes according to plan. 

Those frequencies in the 700 MHz band, which by that time will no longer be used to support TV services. 

Because the spectrum won’t be available till 2018, Ofcom, expects this will be used for the next technology following 4G or LTE, and it is therefore being referred to as “5G”. It's a fiction at the moment, since the industry has not agreed on what is to follow LTE. Nor is it clear LTE necessarily will need to be superseded by 2018. 

Roughly speaking, air interface generations have occurred about every decade, starting about 1980 for first generation, then 1990 for second generation, then 2000 for 3G and now 2010 for fourth generation networks. That implies the fifth generation will start to appear about 2020.