A world of multiple different networks

There is a key trade-off in the design of wireless networks. Lower frequencies are generally preferred for their better propagation, making coverage simpler and cheaper. However, at lower frequencies there is less spectrum available, with the result that networks tend to have a lower capacity. This is a basic law of physics and not something that can be changed in the future with technological advances (although the capacity per unit amount of spectrum does tend to improve over time).

This trade-off means that there is rarely one perfect system. Instead, lower-frequency systems are used to provide coverage across much of the country but with relatively low capacity, while high-frequency systems provide much greater capacity in high-density areas. Hence, we have the current hierarchy of wireless systems, where 2G technology at 900 MHz provides wide-area coverage at data rates of about 100 kbits/s, 3G coverage at 2.1 GHz covers about 30% of a country (depending on the topography and population distribution) at data rates of about 1 Mbits/s and WiFi at 2.4 GHz or 5 GHz covers buildings and very dense urban areas at data rates of about 10 Mbits/s. Such a hierarchy has evolved over time as the most economic way to provide a service as close as possible to the user requirements.