Find a program that can measure the propagation of EM waves(for a WISP that's normally microwaves) Quite a few are listed at http://www.astrosurf.com/luxorion/qsl-review-propagation-sof...
I really liked the book Deploying License-Free Wireless Wide-Area Networks[1] if you're completely new to large scale wireless.
[1] http://www.ciscopress.com/store/deploying-license-free-wirel...