5G is not going to be an expensive network build, according to Verizon, NTT DOCOMO, France Telecom, and Qualcomm. The latest data come from Qualcomm, the only company able to demonstrate a mobile phone sized set of chips. Qualcomm simulations, based on data from several test trials, show existing towers can cover two-thirds of most cities.“Based on our extensive over-the-air testing and channel measurements, significant outdoor coverage (> 65%) is possible utilizing actual existing LTE sites. The 65% coverage figure is outdoor only. mmWave is blocked by some wall/windows and passes through others. Verizon is using outdoor antennas but hopes to allow customer self-installs indoor.
Upgrading existing cells first drastically brings down costs. Verizon and I believe AT&T are choosing to do most mmWave from existing cells. The illustration is from a Verizon presentation. It shows a dense area where fewer cells are needed in 5G. In areas like this, the greater capacity of the new tech allows shutting down cells. Verizon hasn't given us enough data to know what percent of the network can have fewer cells. They certainly will not be able to reduce the number in rural areas, where they are needed for coverage.