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In this paper, we introduce a new communications paradigm, namely, reliable neighborcast, and present a reliable neighborcast protocol (RNP) that operates as an overlay on the existing reliable broadcast protocols. The protocol is intended for vehicle-to-vehicle communications networks that communicate the speed, position, and state of nearby vehicles to coordinate or control their operation. The implementation of RNP that we describe operates on top of overlapping groups that use the mobile reliable broadcast protocol and provides the guarantees and characteristics of that protocol to each neighborhood. The efficiency of the overlays-defined as the fraction of the received messages that apply to a neighborhood-widely varies. We present an efficient overlay for 1-D networks, which is implemented in many highway applications. The characteristics of mobility are considered, and techniques are presented to eliminate delays as vehicles change neighborhoods and to move the underlying broadcast groups with the general flow of traffic.

Cyber-physical systems use sensing, communications, and computing to control the operation of physical devices. Sensing and computing devices have been embedded in automobiles and in the transportation infrastructure. Communications adds a new dimension to the capabilities of these systems. The embedded computers and sensors in both vehicles and the infrastructure will be networked into cyber-physical systems that reduce accidents, improve fuel efficiency, increase the capacity of the transportation infrastructure, and reduce commute times. The authors describe applications that improve the operation of automobiles, control traffic lights, and distribute the load on roadways. The requirements on the communications protocols that implement the applications are determined and a new communications paradigm, neighborcast, is described. Neighborcast communicates between nearby entities, and is particularly well suited to transportation applications.

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