Guest editorial: special issue on Consensus‐based Applications in Networked Systems

Abstract

Consensus, as an efficient distributed computing method, has been studied for several decades. The researchers within this area mainly focus on theoretical analysis of general consensus algorithm for different scenarios, for example, stability analysis under dynamic topologies and time delays, asynchronous and quantized consensus, and performance evaluation including convergence speed, accuracy, robustness, etc. However, existing works have rarely considered consensus in practical application scenarios, especially for the newly emerging distributed networked systems such as wireless sensor networks, cyber physical systems and smart grids, where there exist rich research opportunities in both theoretical and practical aspects. The objective of this special issue is to link the practical challenges and requirements with the theoretical advances in consensus. This special issue contains 17 papers that represent the state of the art in the research area of the consensus and its applications in networked systems. The papers address a variety of applications and cover a breadth of topics, ranging from theory to high-performance algorithms. Lu and Liu 1 focus on theoretical analysis of consensus, where the consensus problem for linear multi-agent systems subject to non-uniform time-varying communication delays and jointly connected switching networks is investigated. Both state feedback law and output feedback law are proposed to handle the consensus problem. Wu and Wang 2 investigate the problem of the mixed H2/H∞ synchronization control for the coupled partial differential systems. The sufficient conditions guaranteeing the existence of the solution are provided. Lei et al. 3 investigate security issues of consensus-based distributed estimation problem, considering the false data-injection attack. An optimal estimator is designed by minimizing the estimation error of each sensor under hostile attackers, and a set of suboptimal attacking sequence is provided. Nguyen and Dankowicz 4 investigate the synchronization and consensus problem of networked manipulators working on an underactuated-dynamic platform with communication delays. A leader-follower consensus scheme is proposed to track the constant and time-varying reference values. The tracking synchronization objective is achieved despite the effects of the communication delay and the unknown dynamics of the platform. Liu et al. 5 describe a dynamic coupling structure for the cluster synchronization problem with coupled-nonidentical linear systems. Lyapunov stability analysis method is used to obtain algebraic and graph topological conditions for cluster synchronization. Ou et al. 6 introduce methods for decentralized minimal-time formation control problems, including static and dynamic cases, respectively. The decentralized minimal-time static-formation method utilizes minimal polynomial to compute the final formation positions, and a Kronecker-theorem-based algorithm is proposed for the dynamic cases. Kempton et al. 7 propose a distributed-control approach to maximize the robustness of the network to time delays in linear-consensus protocol. The method uses a multi-layer distributed estimation strategy to solve the constrained optimization problem. Wen et al. 8 describe the distributed-tracking problem for multi-agent systems with general-linear dynamics under directed-fixing topologies. A distributed information communication protocol and containment tracking law are proposed for multi-leader multi-agent systems. Experiment results are performed to validate the obtained results. Dal Col et al. 9 propose a consensus-based approach to PI gains tuning for quality-fair video delivery. The PI gain tuning problem is reduced to a linear static output feedback problem with linear consensus results. A necessary and sufficient condition for the quality-fair delivery of multimedia contents to mobile users is obtained. Munoz et al. 10 describe an adaptive leader-follower consensus algorithm for multi-agent systems affected by switching events. Distributed control laws are designed for the systems, where the coupling gain of the communication graph changes dynamically. A real-time experimental application is presented to show the effectiveness of the proposed schemes. Yang et al. 11 design the disturbances compensators to attenuate the unknown disturbances for the distributed multiple-unicycles rendezvous and tracking problems. The system convergence is proofed by employing LaSalle's invariance principle and Barbalat's lemma, respectively. The control laws avoiding inter-agent collision are constructed by the potential function approach, with which the tracking error can be made upper bounded and the agents can keep a safe distance from each other. Yan et al. 12 apply the consensus theory to solve the target localization problem in underwater acoustic sensor networks. They apply a hybrid architecture to underwater acoustic sensor networks, where autonomous underwater vehicles provide self-location and clock synchronization for sensor nodes. Then, a trilateration method coupled with a regional optimal solution is provided to estimate the rough localization of a target. A consensus estimation-based solution is provided to further improve the localization accuracy. Wang et al. 13 consider the robust output consensus problem for linear multi-agent systems with disturbances on directed graphs. A distributed-control protocol with integral action and observer is proposed to solve the problem. Dong et al. 14 construct a time-varying group-formation protocol by local neighboring relative information and apply the singular transformation to the closed-loop multi-agent system. Sufficient conditions for multi-agent system to achieving the time-varying group formation and the feasibility constraints are presented. Moreover, the subgroup formation reference functions and the time-varying group formation protocol design are provided. Cai and Xiang 15 consider the finite-time consensus tracking problem of multiple uncertain mechanical systems under switching topologies. An adaptive finite-time tracking protocol is proposed using distributed observers. Rezaee and Abdollahi 16 propose an adaptive protocol to guarantee the consensus in the network based on the local position information among the agents. The sufficient conditions to achieve the consensus in the presence of jointly connected switching topologies are obtained. Zhou and Li 17 introduce a neighbor screening protocol based on the relative motion between each pair of neighboring agents, and further propose a distributed-model predictive control-flocking algorithm. The formation of the flock is guaranteed by using the geometric properties of the optimal path. In closing, the guest editors would like to acknowledge the contributions of the many experts who submitted their work, participated in the review process, and provided constructive and helpful comments to the authors to improve the technical content and presentation quality of the papers. They would also like to extend their sincere thanks to Professor Mike J. Grimble, the Editor-in-Chief of the International Journal of Robust and Nonlinear Control, and Martin Wells, the Journals Editor, for their support and help in bringing this special issue to press. We hope you will enjoy the papers in this collection.