Global Connectivity Maintenance Research Articles

A connectivity preserving node permutation local method in limited range robotic networks

Limited communication range, together with mobility of robots, makes it crucial to design the control plans such that connectivity of a multi-robot network is maintained. Recently, many local and global connectivity maintenance schemes have been proposed to preserve connectivity of a robotic network. The traditional local connectivity maintenance method (LCM) is known to preserve every existing link, even though some of the existing connections might not be necessary for maintaining a path between each pair of robots, which is the aim of global connectivity maintenance (GCM) methods. However, the flexibility of movement provided by the global method costs restriction on speed and bandwidth. In this paper, a modified local connectivity maintenance method is provided to gain more flexibility of movement, while preserving the properties and simplicity of a local method. The proposed method is based on traditional local connectivity maintenance equipped with a basic operation to exchange the neighbors between two adjacent robots. Permutation of robots could be beneficial in many robotic applications such as exchanging the leader role in a V-formed robotic group or providing a path for a robot to reach its desired position while preserving the networks connectivity.

Decentralized local-global connectivity maintenance for networked robotic teams

A prerequisite for a team of robots to cooperate is to maintain connectivity among robots. Connectivity maintenance has been extensively studied recently and several local and global connectivity maintenance algorithms have been proposed for the distance dependent communication topology. Local methods are known to be very restrictive and it will be shown that global methods, based on power iteration estimation, could be sluggish in the presence of communication delay and non-converging in large and sparse robot teams. Therefore, a method based on k-hop routing is proposed, where k is a design parameter to determine the locality level of the proposed method. Before any link disconnection, a test for an alternative k-hop path is executed and, based on its result, the disconnection is allowed or blocked. Blocking displacement for maintaining connectivity will eventually immobilize (freeze) the network. Therefore, a procedure for unfreezing the network is also proposed. Simulation results are provided to further investigate the proposed method.

Bounded Control Law for Global Connectivity Maintenance in Cooperative Multirobot Systems

In this paper, we address the connectivity maintenance problem for a multirobot system that moves according to a given bounded collective control objective. We assume that the interaction among the robotic units is limited by a given visibility radius both in terms of sensing and communication capabilities. For this scenario, we propose a decentralized bounded control law that can provably preserve the connectivity of the multirobot system over time. We characterize the effect of the connectivity control term on the achievement of the collective control objective by resorting to an input-to-state stability-like analysis. We provide numerical and experimental results to corroborate the theoretical findings and assess the effectiveness of the proposed bounded connectivity maintenance control law.

Distributed Global Connectivity Maintenance and Control of Multi-Robot Networks

In this paper, we propose a distributed global connectivity maintenance and control framework of multi-robot networks, which can adapt connectivity online. Based on a series of energy functions, the control framework can make each robot autonomously move along the direction of gradient descent of the energy functions in order to reach the desired global connectivity of the multi-robot networks. This framework has enhanced adaptability and flexibility of multi-robot systems, because adapting connectivity online enables the system to maintain, promote or degrade connectivity at different stages of an integrated mission which require different desired connectivity values. Online connectivity adaptation can also help to change connectivity when the environment becomes more complicated, unknown and dynamic. Theorems are proposed to prove that the framework can not only maintain global connectivity, but can also effectively adapt global connectivity to desired values online, which has rarely been studied. Furthermore, connectivity promotion in the presence of bounded external control terms, such as collision avoidance, is also investigated, which helps to expand the scope of the framework. Finally, simulation and experiment results are presented so as to validate our unified control framework.

Decentralized global connectivity maintenance for interconnected Lagrangian systems in the presence of data corruption

In order to accomplish cooperative tasks, multi-robot systems are required to communicate among each other. Thus, maintaining the connectivity of the communication graph is a fundamental issue. In this paper we develop a strategy based on Sabattini et al., Decentralized Connectivity Maintenance for Networked Lagrangian Dynamical Systems, 2012 for guaranteeing connectivity in the presence of data corruption. In fact, when dealing with real systems, several sources of data corruption can appear. For instance, sensor noise is one of the primary sources of data corruption. Moreover, when dealing with interconnected robotic systems, assuming instantaneous exchange of data is often unrealistic; communication delays are then another important source of data corruption. For this reason, we provide a solution to the connectivity maintenance problem for interconnected Lagrangian dynamical agents, in the presence of data corruption.

Distributed Control of Multirobot Systems With Global Connectivity Maintenance

This study introduces a control algorithm that, exploiting a completely decentralized estimation strategy for the algebraic connectivity of the graph, ensures the connectivity maintenance property for multi robot systems, in the presence of a generic (bounded) additional control term. This result is obtained by driving the robots along the negative gradient of an appropriately defined function of the algebraic connectivity. The proposed strategy is then enhanced with the introduction of the concept of critical robots, that is robots for which the loss of a single communication link might cause the disconnection of the communication graph. Limiting the control action to critical robots will be shown to reduce the control effort that is introduced by the proposed connectivity maintenance control law and to mitigate its effect on the additional (desired) control term.

Decentralized connectivity maintenance for cooperative control of mobile robotic systems

To accomplish cooperative tasks, robotic systems are often required to communicate with each other. Thus, maintaining connectivity of the communication graph is a fundamental issue in the field of multi-robot systems. In this paper we present a completely decentralized control strategy for global connectivity maintenance of the communication graph. Considering the disk communication model, we describe a gradient-based control strategy that exploits decentralized estimation of the algebraic connectivity. Unlike previous approaches available in the literature, the proposed control algorithm solves the global connectivity problem in a decentralized manner providing theoretical guarantees, without requiring maintenance of the local connectivity between robotic systems. Moreover, results obtained with simulations and experiments on real robots are described for demonstrating the efficacy of the proposed algorithm.

Decentralized Global Connectivity Maintenance for Interconnected Lagrangian Systems with Communication Delays

In order to accomplish cooperative tasks, multi–robot systems are required to communicate among each other. Thus, maintaining the connectivity of the communication graph is a fundamental issue. In this paper we extend the connectivity maintenance control strategy introduced in (Sabattini et al., 2012), in order to explicitly take into account the presence of communication delays. When dealing with interconnected robotic systems, in fact, assuming instantaneous exchange of data is often unrealistic. For this reason, we provide a solution to the connectivity maintenance problem for interconnected Lagrangian dynamical agents, in the presence of communication delays.