I thought of this, too. (I'm taking it as a given that this technology works as advertised at low speeds.) At higher speeds, low frequency/long wavelengths oug

I thought of this, too. (I'm taking it as a given that this technology works as advertised at low speeds.) At higher speeds, low frequency/long wavelengths ought to work better because the constructively interfering areas will be larger for any single receiver than they would be with a shorter wavelength. Also, when the receiver is traveling at constant velocity, it is very easy to predict where the receiver will be in the next frame. This covers a lot of cases (people on planes, cars, trains). In fact, I can't think of a place where an average person (e.g., not someone flying a fighter aircraft) would be moving rapidly and unpredictably.