Consensus and collision detectors in wireless Ad Hoc networks

We consider the fault-tolerant consensus problem in wireless ad hoc networks with crash-prone nodes. We develop consensus algorithms for single-hop environments where the nodes are located within broadcast range of each other. Our algorithms tolerate highly unpredictable wireless communication, in which messages may be lost due to collisions, electromagnetic interference, or other anomalies. Accordingly, each node may receive a different set of messages in the same round. In order to minimize collisions, we design adaptive algorithms that attempt to minimize the broadcast contention. To cope with unreliable communication, we augment the nodes with collision detectors and present a new classification of collision detectors in terms of accuracy and completeness, based on practical realities. We show exactly in which cases consensus can be solved, and thus determine the requirements for a useful collision detector.We validate the feasibility of our algorithms, and the underlying wireless model, with simulations based on a realistic 802.11 MAC layer implementation and a detailed radio propagation model. We analyze the performance of our algorithms under varying sizes and densities of deployment and varying MAC layer parameters. We use our single-hop consensus algorithms as the basis for solving consensus in a multi-hop network, demonstrating the resilience of our algorithms to a challenging and noisy environment.