A survey of consensus problems in multi-agent coordination

Abstract

As a distributed solution to multi-agent coordi- nation, consensus or agreement problems have been studied extensively in the literature. This paper provides a survey of consensus problems in multi-agent cooperative control with the goal of promoting research in this area. Theoretical results regarding consensus seeking under both time-invariant and dynamically changing information exchange topologies are summarized. Applications of consensus protocols to multi- agent coordination are investigated. Future research directions and open problems are also proposed. I. INTRODUCTION Cooperative control for multi-agent systems can be cat- egorized as either formation control problems with appli- cations to mobile robots, unmanned air vehicles (UAVs), autonomous underwater vehicles (AUVs), satellites, air- craft, spacecraft, and automated highway systems, or non- formation cooperative control problems such as task assign- ment, payload transport, role assignment, air traffic control, timing, and search. The cooperative control of multi-agent systems poses significant theoretical and practical chal- lenges. For cooperative control strategies to be successful, numerous issues must be addressed, including the definition and management of shared information among a group of agents to facilitate the coordination of these agents. In cooperative control problems, shared information may take the form of common objectives, common control algorithms, relative position information, or a world map. Information necessary for cooperation may be shared in a variety of ways. For example, relative position sensors may enable vehicles to construct state information for other vehicles (1), knowledge may be communicated between vehicles using a wireless network (2), or joint knowledge might be pre-programmed into the vehicles before a mission begins (3). For cooperative control strategies to be effective, a team of agents must be able to respond to unanticipated situations or changes in the environment that are sensed as a cooperative task is carried out. As the environment changes, the agents on the team must be in agreement as to what changes took place. A direct consequence of the assumption that shared information is a necessary condition for coordination is that cooperation requires that the group of agents reach consensus on the coordination data. In other words, the instantiation of the coordination data on each agent must asymptotically approach a sufficiently common value.