Protocols for Controlling Platoon Maneuvers for the AHS

This paper describes the development of a protocol to coordinate platoon maneuvers in the context of an automated highway system (AHS). Such a protocol would need to have access to both communication and control information, and would thus exist at the boundary of what has been referred to as the coordination and regulation layers of the AHS control architecture, and is referred to in this paper as the configuration manager. The main feature of these protocols is the ability to verify the receipt of all messages broadcast on the wireless media (in this case, radio), and in the case that a critical message is lost, to take corrective action. For the most part, the design of the configuration manager is independent of the communications system employed in the platoon. However, it must take into account the effect that reconfiguring the local area network in a platoon will have on the control algorithms which govern the vehicles themselves. The protocol takes the form of a finite state machine which takes radio messages, and controller flags as inputs, and can provide outputs to both the coordination layer, and the regulation layer software modules. At this time, only the platoon split protocol has been worked out in detail, with the main challenge in the merge protocol being taking into account the ability of the communications system to initiate contact between platoons. Introduction Much research has been done towards the development of an automated highway system (AHS) by the California PATH program in the Institute of Transportation Studies at Berkeley. The prevalent design proposed by researchers on the Berkeley campus involves the use of platoons of vehicles. A platoon is defined as a group of closely spaced vehicles traveling at highway speeds. It has been determined by Swaroop (1994) that in order to maintain the required spacing of two to three meters between vehicles in a platoon, the controllers in each vehicle need information both from their preceding vehicle and some reference vehicle (which is chosen to be the leader of the platoon). Thus vehicles within a platoon are grouped together not only by close proximity to one another, but also by a local communications network, as shown in figure 1. By comparison, the spacing between platoons is fairly large, in order that they may avoid collisions with each other using only sensor information.