60ghz, 80ghz, and higher frequencies (i.e. free space optics operating at or near the visible light spectrum) change the story considerably. As frequency goes

60ghz, 80ghz, and higher frequencies (i.e. free space optics operating at or near the visible light spectrum) change the story considerably. As frequency goes up and wavelengths get pencil thin, issues like "do I have clear line of sight" and "is there fog today" are more of a challenge than interference from others using the same frequencies/wavelengths. There's plenty of bandwidth available in RF, but every option has it's tradeoffs. There's a limited amount of spectrum available at frequencies with convenient propagation properties for certain use cases.