Mobile Network Usage is Highly Non-Uniform

Coverage and capacity have been the big trade-offs when designing mobile networks, particularly as customer usage is highly non-uniform. 

In the 3G era, about 20 percent of mobile cell sites handled 60 percent of total traffic, while half of sites handled 95 percent of traffic. In the 4G era, perhaps 80 percent of traffic has been carried by 20 percent of cell sites.  

source: T-Mobile

For any single user, perhaps half of all usage occurs in just one macrocell. About 80 percent of usage happens in three cells. About 20 percent of usage happens in 28 additional cells. 

source: T-Mobile

U.K. population density suggests very similar rules of thumb about cell site usage. Maximum density is more than 160 times higher than the national mean and 12 times higher than the most densely populated 80 percent of areas, according to the Wireless Broadband Alliance. 

source: Wireless Broadband Alliance

All of that has capital investment and business model implications. In the fixed networks business, it long was the rule of thumb that service providers made money in urban areas, broke even in suburban areas and lost money in rural areas.

That same rule seems to hold for mobile networks as well. Mobile operators see most of the customer usage in urban areas, and relatively little in rural areas. Traffic offload solutions therefore make sense, where possible.