Linda Bushnell

Technical communique: Distributed observers design for leader-following control of multi-agent networks

This paper is concerned with a leader-follower problem for a multi-agent system with a switching interconnection topology. Distributed observers are designed for the second-order follower-agents, under the common assumption that the velocity of the active leader cannot be measured in real time. Some dynamic neighbor-based rules, consisting of distributed controllers and observers for the autonomous agents, are developed to keep updating the information of the leader. With the help of an explicitly constructed common Lyapunov function (CLF), it is proved that each agent can follow the active leader. Moreover, the tracking error is estimated even in a noisy environment. Finally, a numerical example is given for illustration.

Stability analysis of networked control systems

We introduce a control network protocol, try-once-discard (TOD), for networked control systems (NCS), and provide, for the first time, an analytic proof of global exponential stability for both the new protocol and the commonly used statically scheduled access methods. Controllers are designed without regarding the presence of the network in the feedback loop, so consequently many controller design techniques may be employed. The performance of the new network protocol and the statically scheduled protocols are compared in simulations.

Asymptotic behavior of nonlinear networked control systems

The defining characteristic of a networked control system (NCS) is having a feedback loop that passes through a local area computer network. Our two-step design approach includes using standard control methodologies and choosing the network protocol and bandwidth in order to ensure important closed-loop properties are preserved when a computer network is inserted into the feedback loop. For sufficiently high data rates, global exponential stability is preserved. Simulations are included to demonstrate the theoretical result.

A multisteering trailer system: conversion into chained form using dynamic feedback

This paper examines the kinematic model of an autonomous mobile robot system consisting of a chain of steerable cars and passive trailers, linked together with rigid bars. The state space and kinematic equations of the system are defined, and it is shown how these kinematic equations may be converted into a multiinput chained form. The advantages of the chained form are that many methods are available for the open-loop steering of such systems as well as for point-stabilization; some of these methods are discussed here. Dynamic state feedback is used to convert the system to this multiinput chained form. It is shown how the dynamic state feedback that is used in this paper corresponds to adding, in front of the steerable cars, a chain of virtual axles which diverges from the original chain of trailers. Two different example systems are also presented, along with simulation results for a parallel-parking maneuver.

Brief Error encoding algorithms for networked control systems

A networked control system is characterized by having a feedback loop closed through a local area network. This paper considers methods for scheduling the use of the network to guarantee both stability and controller performance. We propose and validate algorithms for choosing message identifiers for dynamically scheduled networked control systems. Two schemes for selecting priority levels are proposed: a fixed arbitrary grid and an auto-scaling grid. We prove that the system is uniformly ultimately bounded in the case of the fixed encoding scheme, and asymptotically stable with auto-scaling. An inverted pendulum is used to illustrate the encoding methods.

A Supermodular Optimization Framework for Leader Selection Under Link Noise in Linear Multi-Agent Systems

In many applications of multi-agent systems (MAS), a set of leader agents acts as control inputs to the remaining follower agents. In this paper, we introduce an analytical approach to selecting leader agents in order to minimize the total mean-square error of the follower agent states from their desired value in steady-state in the presence of noisy communication links. We show that, for a set of link weights based on the second-order noise statistics, the problem of choosing leaders in order to minimize this error can be solved using supermodular optimization techniques, leading to efficient algorithms that are within a provable bound of the optimum. We formulate two leader selection problems within our framework, namely the problem of choosing a fixed number of leaders to minimize the error, as well as the problem of choosing the minimum number of leaders to achieve a tolerated level of error. We study both leader selection criteria for different scenarios, including MAS with static topologies, topologies experiencing random link or node failures, switching topologies, and topologies that vary arbitrarily in time due to node mobility. In addition to providing provable bounds for all of these cases, simulation results demonstrate that our approach outperforms other leader selection methods, such as node degree-based and random selection methods, and provides comparable performance to current state of the art algorithms.

Node capture attacks in wireless sensor networks: A system theoretic approach

In this paper we address the problem of physical node capture attacks in wireless sensor networks and provide a control theoretic framework to model physical node capture, cloned node detection and revocation of compromised nodes. By combining probabilistic analysis of logical key graphs and linear control theory, we derive a dynamical model that efficiently describes network behavior under attack. Using LQR and LQG optimal control theory tools, we develop a network response strategy, which guarantees secure network connectivity and stability under attack. Detailed simulations are presented to validate the methodology.

Secure Operation, Control, and Maintenance of Future E-Enabled Airplanes

Commercial aviation is at the threshold of the era of the e-enabled airplane, brought about by the convergence of rapidly expanding worldwide data communication infrastructures, network-centric information processing, and commoditized lightweight computational hardware. With advanced avionics, processing, and wireless communication capabilities, the e-enabled airplane can revolutionize the current air transportation system. However, the use of unregulated information technology and wireless technologies introduces vulnerabilities that can be exploited to provide unauthorized access to the onboard aviation information systems and impede their operation. The emerging security threats are not covered by current aviation guidance, and regulations, hence, remain to be addressed. This paper presents a comprehensive survey of security of the e-enabled airplane with applications such as electronic distribution of loadable software and data, as well as future directions such as wireless health monitoring, networked control, and airborne ad hoc networks.

Error encoding algorithms for networked control systems

We propose and validate algorithms for choosing finite word length priorities for dynamically scheduled networked control systems. Two schemes for selecting priority levels are studied, the first with a fixed arbitrary grid and the second with an auto-scaling grid. We prove that the system is uniformly and ultimately bounded in the case of the static encoding, and asymptotically stable with the auto-scaling methodology. Simulations of an inverted pendulum controller using these schemes are compared against a controller with point-to-point wiring.

Wireless local area networks in the manufacturing industry

Based on the definition of IEEE 802.11 and the requirements of real-time control and monitoring, we introduce a new protocol-Prioritized CSMA/CA-for real-time wireless local area networking. For the first time, we propose and validate several new algorithms, a constant penalty, an estimated error order and a lag first order for dynamically scheduling the traffic of wireless networked control systems. All algorithms are compared via simulation and the results show that dynamic scheduling algorithms achieve better system performance on average than static scheduling algorithms, like fixed order polling.