Not to nitpick, but wifi is radio. The propagation of radio waves depends on their frequency. The frequency wifi operates on is in the GHz, which mostly is line

Not to nitpick, but wifi is radio. The propagation of radio waves depends on their frequency. The frequency wifi operates on is in the GHz, which mostly is line-of-sight only. This is not always practical. See [1] for an overview of frequency and propagation. [1]: http://en.wikipedia.org/wiki/Radio_propagation http://en.wikipedia.org/wiki/Radio_propagation