To find out more about the spectrum, see the links in Resources. To convert metric measurements discussed in this feature to standard, see NOVA's conversion chart. Rick Groleau is managing editor ...

A variety of airwaves are being used or explored for private network spectrum around the world, from 400 MHz to mmWave. This ...

(since each country ultimately manages its own spectrum,) and you'll start to understand how hard it can be to coordinate these things globally. In the chart above, the lower bands came first.