Cyclic network automata and cohomological waves

Following Baryshnikov-Coffman-Kwak [2], we use cyclic network automata (CNA) to generate a decentralized protocol for dynamic coverage problems in a sensor network, with only a small fraction of sensors awake at every moment. This paper gives a rigorous analysis of CNA and shows that waves of awake-state nodes automatically solve pusuit/evasion-type problems without centralized coordination. As a corollary of this work, we unearth some interesting topological interpretations of features previously observed in cyclic cellular automata (CCA). By considering CCA over networks and completing to simplicial complexes, we induce dynamics on the higher-dimensional complex. In this setting, waves are seen to be generated by topological defects with a nontrivial degree (or winding number). The simplicial complex has the topological type of the underlying map of the workspace (a subset of the plane), and the resulting waves can be classified cohomologically. This allows one to 'program' pulses in the sensor network according to cohomology class. We give a realization theorem for such pulse waves.