  In this paper, we investigate the use of chirp spread spectrum signaling over
air-ground channels. This includes evaluation of not only the traditional
linear chirp, but also of a new chirp signal format we have devised for
multiple access applications. This new format is more practical than prior
multi-user chirp systems in the literature, because we allow for imperfect
synchronism. Specifically we evaluate multi-user chirp signaling over
air-ground channels in a quasi-synchronous condition. The air-ground channels
we employ are models based upon an extensive NASA measurement campaign. We show
that our new signaling scheme outperforms the classic linear chirp in these
air-ground settings.
