On the Power of Cohorts -- Multipoint Protocols for Fast and Reliable Safety-Critical Communications in Intelligent Vehicular Networks

We report on recent findings related to safety-critical V2V multipoint communications in ad hoc networks of fully automated vehicles, in the presence of communication failures. Neither classical failure assumptions nor multipoint protocols at the core of existing communication standards can be considered, since they do not meet the high reliability and strict timeliness requirements set for safety-critical scenarios. We introduce a novel unbounded omission failure model, the concept of proxy sets which builds on the cohort construct, and Zebra, a suite of geocast, convergecast, and multicast protocols specifically designed for safety-critical 1-hop multipoint communications. Analytical expressions of worst-case termination time bounds are given for each Zebra protocol, which is mandatory with safety requirements. These results have a number of practical implications, which are discussed. They should be of interest to safety authorities and to the transportation industry involved in future deployments of intelligent vehicular networks.