The performance of 802.11b wireless LANs is well understood for indoor environments. However, their behavior in outdoor and mobile environments has remained largely unexplored. We have performed experiments to bridge this knowledge gap by empirically measuring the performance of an 802.11b system in a broad spectrum of emulated environments. The goal of our work is to contribute to the evolution of currently existing wireless standards by measuring the effects of different channel phenomena on 802.11b. Our results show that current implementations of the 802.11b standard may not be well suited to use in a mobile environment, but that they could conceivably be modified to have better performance in such situations.