| This thesis investigates distributed medium access control (MAC) protocols custom tailored to both impulse-based ultra wideband (I-UWB) radios and to large ad hoc and sensor networks. I-UWB is an attractive radio technology for large ad hoc and sensor networks due to its robustness to multipath fading effects, sub-centimeter ranging ability, and low-cost, low-power hardware. Current medium access control (MAC) protocols for I-UWB target small wireless personal area networks (WPANs) and cellular networks, but they are not suitable for large, multihop ad hoc and sensor networks. Therefore, this paper proposes a new type of MAC protocol that enables ad hoc and sensor networks to realize the benefits of I-UWB radios. First, we propose a method to overcome the challenges of quickly, reliably, and efficiently sensing medium activity in an ultra wideband network. This provides a base MAC protocol similar to carrier sense multiple access (CSMA) in narrowband systems. Next, we propose to exploit the unique signaling of I-UWB to improve performance over the base MAC protocol without the associated overhead of similar improvements in narrowband systems. I-UWB enables a distributed multichannel MAC protocol, which improves throughput. I-UWB also facilitates a busy signal MAC protocol, which reduces wasted energy from corrupt packets. Finally, because the I-UWB Physical Layer and MAC Layer affect the network and application layers, we propose a cross-layer adaptive system that optimizes performance. Physical Layer simulations show that both the base protocol and the improvements are practical for an I-UWB radio. Networks level simulations characterize the performance of the proposed MAC protocols and compare them to existing MAC protocols. |
