Let's say Alice can hear Bob and Bob can hear Charlie, but Alice cannot hear Charlie. AFAIK, in ad-hoc mode Alice and Charlie cannot communicate. You'd need a real mesh (like 802.11s) where Bob would relay packets (and destroy his own performance and battery in the process). Then there's the 1/7th problem that hasn't been solved to my knowledge: http://pdos.csail.mit.edu/papers/grid:mobicom01/paper.pdf
