Reliable group communications for vehicular networks and aircraft safety applications

Research in mobile ad hoc networks and intelligent transportation research has resulted in vehicle ad hoc networks that use wireless inter-vehicle communication to improve traffic flow, fuel efficiency, and passenger safety. This communication can be used to coordinate vehicle motion through shared planning of future movements and instant-to-instant control inputs to onboard engine and braking systems. This strategy holds particular value for the air transport system, which has suffered from limited runway capacity and safety issues due to the inability to safely reduce the separation between aircraft near airports largely due to the centralized, manual nature of existing Air Traffic Control operations. However, nearly all of the communication protocols developed for inter-vehicle communications fail to provide adequate mechanisms to support failsafe collaboration, such as assurance that all parties are working with the same information and that each individual knows when they are missing information or that another party has failed.;We found that our arrival technique provides a much lower risk of incursion (e.g., 10-8 per landing) at moderate throughputs (e.g., 60% of peak) than state-of-the-art control methods, even when aircraft are provided with a relatively inaccurate estimation of prior aircrafts' Runway Occupancy Times. When the estimation is accurate, the runway throughput can be maintained to within 5.5% of its theoretical peak at extremely low risk levels. We estimate that the effect of implementing this technology at the three largest airports serving New York City would be a 29% improvement in total capacity, which would eliminate the need for a new airport, a project under consideration at this time. We determine that the Mobile Reliable Broadcast Protocol provides the best throughput versus safety profile for this application amongst several protocols of interest. The protocol is also analyzed and simulated to check its correctness and explore its performance characteristics.;This dissertation investigates reliable group communications in vehicular ad hoc networks, with particular attention to aircraft safety applications. We develop a reliable broadcast protocol based on a token ring architecture, called the Mobile Reliable Broadcast Protocol, that is specifically designed to contend with the high packet loss and frequently-changing vehicle groups encountered in these applications. The protocol uses a distributed voting procedure to ensure that all members of the vehicle group agree on the existence of messages, their ordering, and changes to the set of collaborators. The votes are contained in tokens that are transmitted at scheduled times. Because the protocol is time-driven, the group is able to agree on the use of messages in bounded time. These properties permit the protocol to support a decentralized Air Traffic Control model that makes use of direct communication within groups of aircraft to carry out automated arrival spacing and runway clearances, among other critical tasks. The aspect of delivering aircraft to a runway in a manner that maintains high utilization while minimizing the probability that two successive arrivals occupy the runway at the same time is analyzed in detail.