why use Ghz frequencies at all?
Lower frequencies in the VHF (30-300Mhz) range have a longer distance perspective than the Ghz frequencies mentioned in this article.
Only the 900Mhz band comes close to these characteristics.
This has partially to do with reflections as well as that higher frequencies have more trouble penetrating materials, specially those containing metals.
And yes that's also why WiFI networks have trouble in your home between rooms. Specifically if the walls contain metal like in reinforced concrete.
Lower than then 30Mhz is unwise as that comes with larger antenna's as well as very different distance propagation characteristics (which may or may not work depending on time of day, sun spots etc.).