Let's note the "not used by anything else" is probably the most important thing, because of https://ieeexplore.ieee.org/document/1208921 https://ieeexplore.ieee

Let's note the "not used by anything else" is probably the most important thing, because of https://ieeexplore.ieee.org/document/1208921 https://ieeexplore.ieee.org/document/1208921 Basically, because WiFi gives an equal opportunity (sort of) of transmission to all devices, old devices or devices far away will slow down the network for fast devices as they will take a big amount of transmission time because of their lower transmission rates. Greenfield was already a try at "ignoring" old devices but never really took off.