Synchronization Of Multi-agent Systems Research Articles

Insights From Robust Control Theory Into the Synchronization of Multiagent Systems

Insights From Robust Control Theory Into the Synchronization of Multiagent Systems

Redundancy-Reduction-Based Hierarchical Design in Synchronization of Multi-Agent Systems

In this paper, a layered, undirected-network-structure, optimization approach is proposed to reduce the redundancy in multi-agent information synchronization and improve the computing rate. Based on the traversing binary tree and aperiodic sampling of the complex delayed networks theory, we proposed a network-partitioning method for pinning dynamic networks, with a more simplified, analyzable structure, and all of the traversed nodes are mathematically asymptotically synchronized at the same time. Moreover, a systematic implementable approach is proposed for application. The approach could be separated into two main steps: the first is a method of network partition that reduces the trivial interaction, which does not affect the information traversal, and the second involves applying the time-dependent functional approach of Lyapunov to give global exponential conditions, under the criteria for the synchronization of multiple agents, with a lower conservatism of the decision variables compared to some other results, so that the information available could fully benefit from the actual discrete-time communication pattern. Both mathematical proofs and numerical example evidence are presented to demonstrate the effectiveness of the implemented approach. This class contains a number of practically interesting systems, for instance, unmanned aerial vehicle (UAV) formation systems or the ground-air coordinated unmanned aerial system.

Synchronization of Multi-Agent Systems under Time-Varying Network via Time-Delay Approach to Averaging

This paper studies the leader-tracking problem of Multi-Agents Systems under a periodic time-varying communication topology, without requiring the connectivity of the network for all t ≥ 0. The case of both state and communication delays is considered. A fully distributed control protocol, along with the constructive time-delay approach to periodic averaging, are combined in order to solve the problem, thus ensuring that a time-dependent switching control rule preserves the input-to-state stability (ISS) of the entire network, despite the presence of disconnected topologies, state and communication delays. The original closed-loop error systems is transformed into a neutral-type system with discrete and distributed delays. ISS analysis of the neutral system employs appropriate Lyapunov-Krasovskii functionals leading to simple ISS conditions in terms of Linear Matrix Inequalities (LMIs), whose solution allows finding upper bounds on small parameter, state and communication delays that preserve ISS. Numerical simulations illustrate the effectiveness of the theoretical results.

Consensus problems in multiagent systems: A vector based contraction approach

This paper addresses the exploitation of vector based contraction theory to synchronize the motion of agents in multiagent systems. The convergence analysis of the agents using this theory provides a flexible frame as the components of a vector distance norm follow less stringent conditions than classical contraction analysis. The key feature is that it encompasses the formulation of some comparison system, as a result, the problem of convergence analysis of a complex multiagent system reduces to the convergence analysis of a much simpler comparison system. Hence, despite the nonlinearities, the methods of designing consensus controls remain simple as compared to the existing literature. We address four different cases: 1) consensus of third-order dynamics multiagent systems subjected to acceleration and input constraints; 2) consensus of multiagent systems with heterogeneous nodes under communication imperfections; 3) synchronization of multiagent systems with connected and disconnected switching topologies; 4) synchronization in networked systems with time-varying couplings. Moreover, an effective synchronization control scheme for a class of multiagent systems with underactuated agent dynamics is developed using the method of aggregation of comparison systems. Finally, simulation results are illustrated that show the validity of the mathematical results.

マルチエージェント系のレジリエントな合意・同期：イベントに基づく通信の活用

マルチエージェント系のレジリエントな合意・同期：イベントに基づく通信の活用

Distributed Reconfiguration for Resilient Synchronization of Multi-Agent Systems

The performance in output synchronization in multi-agent systems (MAS) can degrade in the presence of misbehaving agents that are affected by external attacker actions that try to desynchronize the system. In this paper, we introduce a heuristic algorithm based on best-response games to define an online distributed reconfiguration strategy to dynamically mitigate these actions, to make the system reach a synchronization state. This algorithm provides each unattacked agent with a decision-making based on local information to reconfigure the interaction patterns with its neighbors such that the system eventually synchronizes. We present some simulations of the proposed strategy for several systems in realistic scenarios to show ability of the of the proposed algorithm to mitigate different types of attacks.

Secure impulsive synchronization in Lipschitz-type multi-agent systems subject to deception attacks

Cyber attacks pose severe threats on synchronization of multi-agent systems. Deception attack, as a typical type of cyber attack, can bypass the surveillance of the attack detection mechanism silently, resulting in a heavy loss. Therefore, the problem of mean-square bounded synchronization in multi-agent systems subject to deception attacks is investigated in this paper. The control signals can be replaced with false data from controller-to-actuator channels or the controller. The success of the attack is measured through a stochastic variable. A distributed impulsive controller using a pinning strategy is redesigned, which ensures that mean-square bounded synchronization is achieved in the presence of deception attacks. Some sufficient conditions are derived, in which upper bounds of the synchronization error are given. Finally, two numerical simulations with symmetric and asymmetric network topologies are given to illustrate the theoretical results.

Distributed adaptive consensus protocol with decaying gains

SummaryThis article brings a distributed adaptive protocol for consensus and synchronization in multiagent systems on directed communication networks. Agents are modeled as general linear time‐invariant systems. The proposed protocol introduces a novel adaptation scheme allowing control coupling gains to decay to their reference values. This approach improves upon existing adaptive consensus protocols which may result in overly large or even unbounded coupling gains. The protocol design in this article does not rely on any centralized information; hence it is distributed. Nevertheless, the price to pay for this is the need to estimate those reference values. Convergence of the overall network dynamics is guaranteed for correctly estimated references; otherwise, the trajectory of the system is only uniformly ultimately bounded. Two estimation algorithms are proposed: one based on the interval‐halving method and the other based on a distributed estimation of Laplacian eigenvalues. Numerical simulations validate the proposed approach.

Synchronization of Multi-Agent Systems With Time-Varying Control and Delayed Communications

This paper investigates the synchronization problem of nonlinear multi-agent systems with time-varying control in the presence of transmission delay over a communication network. To facilitate the study, a novel delayed differential inequality with time-varying coefficients is first established. Then, the synchronization problem is recast into the stability problem of a delayed differential system with certain time-dependent parameter. A sufficient criterion is further formulated to guarantee the synchronization. The mathematical proof reveals that the time average of the control strength is crucial for reaching synchronization. Together with the agent dynamics and the topology, this average also governs the largest admissible delay. Moreover, the criterion is applied to synchronization problems with general on-off coupling under data sampling and delayed communications, respectively. Some useful corollaries are consequently deduced. Finally, numerical simulations are presented to illustrate the validity of our theoretical results.

Synchronization of Multiagent Systems Using Event-Triggered and Self-Triggered Broadcasts

This paper addresses the problem of synchronizing a group of identical linear time-invariant agents that exchange information through a communication network. The agents may only broadcast information at discrete-time instants and the decision to execute a broadcast is based on an event-triggered communication protocol. We prove that with the proposed control architecture the state of each agent converges to and remains in a neighborhood of a desired reference signal and the closed-loop system does not exhibit Zeno solutions. A self-triggered implementation of the proposed event-triggered communication protocol is also derived.

Synchronisation of linear high-order multi-agent systems via event-triggered control with limited communication

ABSTRACTIn this paper, the synchronisation problems of multi-agent systems with asynchronous and synchronous event-triggered control under a novel event-triggered condition are solved. Our event-triggered control protocols only require each agent to send its state information to its neighbouring agents when an event-triggered condition is satisfied. Such control protocols substantially reduce the cost of communication. It is worth mentioning that the proposed protocols also ensure that the synchronisation of the multi-agent system with asynchronous and synchronous event-triggered can be achieved asymptotically without Zeno-behaviour. Meanwhile, an ultimate synchronisation trajectory is given. Moreover, our results are applied to solve the formation control problem. Some numerical simulations are presented to illustrate the effectiveness of our protocols.

Synchronization of multi-agent systems with heterogeneous controllers

This paper studies synchronization in a multi-agent system, which is defined as a situation where all the agents in a group are required to achieve a common velocity direction. The agents are assumed to be coupled through controller gains that are not necessarily identical or homogeneous, which addresses a practical scenario where the gains may vary nominally due to minor implementation errors or drastically due to major faults or errors. The paper analyzes the effect of heterogeneous gains on the common velocity direction at which the system of agents synchronizes. Conditions under which heterogeneous controller gains result in a synchronized formation are derived and it is shown that the resulting common velocity direction lies in the conic hull of the initial velocity vectors of agents. A detailed analysis of the two agents system shows that there exists a less restrictive condition on heterogeneous gains that results in synchronization. Effect of saturation is also studied for two cases when the controller gains are bounded and when the control efforts are bounded. Both all-to-all and limited communication topologies are considered. Simulations are given to support the theoretical findings.

Synchronization of multi-agent systems with metric-topological interactions.

A hybrid multi-agent systems model integrating the advantages of both metric interaction and topological interaction rules, called the metric-topological model, is developed. This model describes planar motions of mobile agents, where each agent can interact with all the agents within a circle of a constant radius, and can furthermore interact with some distant agents to reach a pre-assigned number of neighbors, if needed. Some sufficient conditions imposed only on system parameters and agent initial states are presented, which ensure achieving synchronization of the whole group of agents. It reveals the intrinsic relationships among the interaction range, the speed, the initial heading, and the density of the group. Moreover, robustness against variations of interaction range, density, and speed are investigated by comparing the motion patterns and performances of the hybrid metric-topological interaction model with the conventional metric-only and topological-only interaction models. Practically in all cases, the hybrid metric-topological interaction model has the best performance in the sense of achieving highest frequency of synchronization, fastest convergent rate, and smallest heading difference.

A Randomized Linear Algorithm for Clock Synchronization in Multi-Agent Systems

A broad family of randomized clock synchronization protocols based on a second order consensus algorithm is proposed. Under mild conditions on the graph connectivity, it is proved that the parameters of the algorithm can always be tuned in such a way that the clock synchronization is achieved in the probabilistic mean—square sense. This family of algorithms contains, as particular cases, several known approaches which range from distributed asynchronous to hierarchical synchronous protocols. This is illustrated by specializing the algorithm for the well-known broadcast and gossip scenarios in wireless communications, and for the standard hierarchical protocol used in the context of wired communications in data networks. In these cases, we show how the feasible range for the algorithm parameters can be explicitly computed. Finally, the performance of this strategy is validated by actual implementation in a real testbed and by numerical simulations.

Uniform synchronization in multi-agent systems with switching topologies

Summary This paper deals with uniform synchronization analysis of multi-agent systems with switching topologies. The agents are assumed to have general, yet identical, linear dynamics. The underlying communication topology may switch arbitrarily within a finite set of admissible topologies. We establish conditions under which the network is uniformly synchronized meaning that synchronization is valid under all possible switching scenarios. The primary conditions established are in terms of a pair of Lyapunov strict inequalities. Following those conditions, small gain and passivity types of conditions are proposed under which uniform synchronization is guaranteed. The proposed results are also extended to the case of observer-based protocols. Copyright © 2015 John Wiley & Sons, Ltd.

Synchronization of multi-agent systems with event-based communication

Abstract This paper investigates the synchronization problem of multi-agent systems with event-based communication. It is assumed that contionuous-time synchronization protocolls guarentee the asymptotic synchronization of the agents. It will be shown that event-based synchronization protocols reduce the communication effort in comparison to the continuous-time synchronization algorithms, while the convergence of the subsystems to a bounded region around the synchronous trajectory is guaranteed.

Extended-state-observer-based adaptive control for synchronisation of multi-agent systems with unknown nonlinearities

This paper studies the problem of synchronisation to a desired trajectory for non-linear multi-agent systems. By introducing extended state observer approach, decentralised adaptive controllers are designed for distributed systems which have non-identical unknown non-linear dynamics. The non-identical unknown non-linear dynamics allows for a tracked command dynamics which is also non-linear and unknown. State variables of agents can be obtained only in the case where leader agent and the network communication topology for multi-agent systems is strongly connected digraph network structures. A Lyapunov-function-based approach is given to show that the tracking error is ultimately bounded. Some simulation results are given to demonstrate the effectiveness of the developed techniques in this paper.

Synchronization Conditions for Multiagent Systems With Intrinsic Nonlinear Dynamics

This brief studies local and global synchronization in multiagent systems with nonlinear dynamics with respect to equilibrium points and periodic orbits. For local synchronization, a method is proposed based on the transformation of the original system into an uncertain polytopic system and on the use of homogeneous polynomial Lyapunov functions. For global synchronization, another method is proposed based on the search for a suitable polynomial Lyapunov function. The proposed methods exploit linear matrix inequalities and have several advantages. In particular, the proposed methods require the solution of convex optimization problems. Also, the proposed methods exploit more complex Lyapunov functions than the quadratic Lyapunov functions typically considered in the literature and included in this brief as a special case.

Synchronization of multi-agent systems with similar dynamics

This paper deals with the synchronization problem for a class of linear heterogeneous multi-agent systems. The agents are assumed to be similar in the sense that a part of the dynamics is common and the remaining part is individual. Based on the common dynamics, LQR control methods are used for the design of a synchronizing networked controller. By choosing the objective function so as to reflect the behavior of synchronization errors between modified outputs of the agents, an optimal controller is obtained. It is shown that the optimal controller requires an information exchange between all agents to solve the synchronization problem. For this reason, an approximation of the optimal controller is proposed to synchronize the autonomous agents by a networked controller for arbitrary directed communication topologies.

Synchronization of multi-agent systems with topological interaction

AbstractThe recent research by a group of European scientists shows that, each starling bird adjusts its flight in the light of topological interaction, that according to a fixed number of its nearest neighbors, rather than all agents within a fixed Euclidean distance. A theoretical study to understand such topological interaction is given in this paper, and a sufficient synchronization condition imposing only on the initial states is developed. Furthermore, the number of neighbors needed for the synchronization is discussed, which shows that for the sake of connectivity the number of neighbors should increase as the density of group increasing.