http://www.ifac-papersonline.net/ en Copyright 06:00 PM Tuesday 07, 2012 IFAC-PapersOnline http://www.ifacpapersonline.com 06:00 PM Tuesday 07, 2012 06:00 PM Tuesday 07, 2012 ET webmaster@ifac-papersonline.net webmaster@ifac-papersonline.net http://www.ifac-papersonline.net/Detailed/40534.html 04:00 PM Wednesday 31, 1969 Large-scale optimization problems, even when convex, can be challenging to solve directly. Recently, a considerable amount of research has focused on developing methods for solving such optimization problems in a distributed manner. The assumption that is usually made is that the global objective function is a sum of convex functions, which is restrictive. In this paper, we automatically decompose a convex function to be minimized into a sum of smaller functions that may or may not be convex and assign each sub-function to an agent in a networked system. Each agent is allowed to communicate with other agents in order to solve the original optimization problem. We propose an algorithm which will converge when the interaction between the agents is strong enough to lead to synchronization between common variables. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40563.html 04:00 PM Wednesday 31, 1969 In this paper, distributed game strategies are designed and analyzed for the multiple-pursuer single-evader problem. The proposed design is based on the integration of cooperative control theory and differential game theory. It is shown that the proposed game strategies are Nash solutions with respect to an inversely-optimal performance index and that they are fully adaptive with respect to information acquisition/communication patterns. A simple condition on topology changes is found so that performances under the distributed game strategies are comparable with those under global-knowledge game strategies. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40540.html 04:00 PM Wednesday 31, 1969 Kalman smoothers obtain state estimates in a system with stochastic dynamics and measurement noise. We consider the smoothing problem in a distributed setting, present a cooperative smoothing algorithm for Gauss-Markov linear models, and provide a convergence analysis for the algorithm. An extension of the algorithm that maximizes the likelihood with respect to a sequence of state vectors subject to inequality constraints, e.g. positivity conditions, is also described. Finally, a numerical experiment regarding cubic spline regression is included to test the new approach. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40558.html 04:00 PM Wednesday 31, 1969 Most of the literature on Distributed Model Predictive Control (DMPC) for dynamically coupled linear systems typically focuses on situations where coupling constraints between subsystems are absent. In order to address the presence of convex coupling constraints, we present a distributed version of Han's parallel algorithm for a class of convex programs. The algorithm we propose relies on local iterative updates only, instead of using system-wide information exchange as in Han's original algorithm. The new algorithm is then used to develop a new distributed MPC method that is applicable to sparsely coupled linear dynamical systems with coupled linear constraints. Convergence to the global optimum, recursive feasibility, and stability can be established using only local communications between the subsystems. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40527.html 04:00 PM Wednesday 31, 1969 The Precision Time Protocol delivered by IEEE 1588 standard has been proved to be an appropriate network synchronization protocol. The PTP protocol is based on exchanging appropriate timing information, generated by time stamping according to the local clocks, between adjacent clocks. Using the time-stamps, a slave element learns the relation between its own clock and the master clock so that it can synchronize its time to the reference time provided by the master. Uncertainties, e.g., random stamping and quantization errors, greatly affect the synchronization precision. This paper presents a probabilistic state-space model which quantifies the uncertainties and represents the relation between the system variables. Then clock synchronization is posed as a state estimation problem and solved by using Kalman filter. The performance of this approach is verified by numerical results. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40551.html 04:00 PM Wednesday 31, 1969 Object tracking in networked systems is a widely used scenario to assess newly designed methods in the field of association and estimation. This is mainly due to a great interest in object tracking applications. Current research is focused on designing dedicated tracking algorithms suitable for a particular setup of a tracking system. As a result certain choices in software design are taken implicitly, resulting in dedicated functions for which comparing and adapting the algorithm requires a significant effort. In contrast this paper describes a modular software-architecture suitable for all object tracking methods in self-organizing, networked systems. This modular architecture not only enables a designer the freedom of choice for the different tracking methodologies but it also provides the ability to re-upload parts of the algorithm or even adapt the on-line algorithm to the situation at hand. The designed architecture is demonstrated on a real-life tracking application. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40531.html 04:00 PM Wednesday 31, 1969 In this paper a distributed clock synchronization algorithm is proposed. The algorithm requires gossip asynchronous communication between the nodes of the network, and because of its proportional-integral (PI) structure it is able to compensate both initial offsets and different clock speeds. Convergence of the algorithm is proved and analysed with respect to the controller parameter, while scalability issues are addressed by simulations. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40528.html 04:00 PM Wednesday 31, 1969 This paper introduces a new algorithm to prove contraction of nonlinear dynamical systems. The algorithm is then used to devise novel strategies to achieve synchronization and consensus of networked control systems. Numerical simulations illustrate the results on a set of representative examples. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40519.html 04:00 PM Wednesday 31, 1969 The problem of reaching consensus in a heterogeneous multi-agent system is considered. The agents are modeled as linear time-invariant systems with potentially different state dimension and different dynamics. The interconnection topology between the agents is modeled as a directed and weighted graph.We propose an internal model principle for consensus translating in necessary conditions for existence of solutions to the output and state consensus problem. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40545.html 04:00 PM Wednesday 31, 1969 This paper presents a robust stabilizing decentralized model predictive control (MPC) algorithm for discrete-time nonlinear large-scale systems comprised of multiple subsystems. Each subsystem is controlled with a tube-based model predictive control algorithm that renders the subsystem input-to state stable (ISS) with respect to both the external disturbances affecting it and the interconnections to the other subsystems (treated as additional disturbance inputs). The algorithm entails redesigning the MPC control strategy periodically, taking into account newly acquired information regarding the interconnection uncertainty sets. By using a regional version of the small-gain theorem for multiple nonlinear systems, we then show that the overall closed-loop system is ISS with respect to the external disturbances. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40516.html 04:00 PM Wednesday 31, 1969 http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40524.html 04:00 PM Wednesday 31, 1969 We propose a class of distributed algorithms for computing arithmetic averages (average consensus) over networks of agents connected through digital noisy broadcast channels. Our algorithms do not require the agents to have knowledge of the network structure, nor do they assume any noiseless feedback to be available. We prove convergence to consensus, with both number of channel uses and computational complexity which are poly-logarithmic in the desired precision. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40523.html 04:00 PM Wednesday 31, 1969 This paper describes a novel consensus-based protocol, referred as Average TimeSync (ATS), for synchronizing a wireless sensor network. This algorithm is based on a cascade of two consensus algorithms, whose main idea is averaging local information. The proposed algorithm has the advantage to be totally distributed, asynchronous, robust to packet drop and sensor node failure, and it is adaptive to clock drifts and changes on the communication topology. In particular, we provide a rigorous proof of convergence to global synchronization in the absence of process noise, measurement noise and communication delay. We show its effectiveness through a number of experiments performed on a wireless sensor network. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40529.html 04:00 PM Wednesday 31, 1969 In this paper we propose a new decentralized algorithm to solve the consensus on the average problem on arbitrary strongly connected digraphs through a gossip algorithm based on broadcasts. We directly extend previous results by O. Saber et al. by not requiring that the digraph is balanced. Our algorithm is an improvement respect to known gossip algorithms based on broadcasts in that the average of the initial state is preserved after each broadcast. The nodes are assumed to know their out-degree anytime they transmit information. The algorithm convergence analysis is preliminary and performance is shown by simulations. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40535.html 04:00 PM Wednesday 31, 1969 We consider consensus problem over networks where each agent is modeled as a class of LTI systems. The objective is to make certain output of each agent converge to the (weighted) average of their initial conditions. To solve this consensus problem, we equip each plant with a local dynamic output-feedback controller. The system configuration allows us to decompose the networked system into subsystems characterized by the eigenvalues of Laplacian associated with the network topology. Having recognized that all the eigenvalues of Laplacian are bounded in a circle region, we cast each eigenvalue as an norm bounded uncertainty and use the robust control framework to evaluate the stability of each subsystem. We derive the sufficient condition to ensure that only the zero eigenvalue of Laplacian can touch the boundary of the circle. Based on that condition, we develop sufficient conditions to guarantee the marginal stability of the overall system, which allows us to use LMI approach to synthesize the controller and establish the convergence property of the system. Fianlly, we adopt a two-degree of freedom controller to improve the performance of the system as well as save the controller output energy. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40562.html 04:00 PM Wednesday 31, 1969 Mid-course guidance phase classically refers to the procedure guiding the missile to a terminal handover point in order to acquire the target motion through its on-board sensor. The mid-course guidance law differs significantly from the guidance logic for the terminal homing phase due to the inherited characteristic of the midcourse guidance: it must not only find the best condition for the terminal homing phase, but also deliver the missile to that condition using only the target motion data updated by the external source such as a plane, ship, or ground base. In this paper we revisit the mi-course guidance problem for maritime area air defense by mixing two contributions (one for mid course guidance law design and one for target allocation). The proposed solution is based on differential games (capturability considerations) for allocation of the missiles. The main idea is that a cooperative mid-course guidance strategy can defend the area as long as it assures that the depending area is always inside the defended area defined by earliest intercept geometry. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40555.html 04:00 PM Wednesday 31, 1969 This paper considers the problem of dynamic communication topologies for decentralised data fusion systems. The task of decentralised data fusion is considered as a specific instance of the general distributed inference probem in which there is a single common state of interest which is (partially) observed by a number of mobile sensor platforms. Physical communication links between mobile platforms form a connectivity graph which changes over the lifetime of the system. The challenge is to maintain a correct estimate of the common state. Our general approach is to formulate the decentralised data fusion problem using graphical model techniques. Inference is performed using the distributed Junction Tree architecture developed by Paskin and Guestrin. To address the problem of dynamic network reconfiguration, the suitability of three well-known algorithms (Hugin, Shafer-Shenoy, Covariance Intersect) is investigated. The algorithms are evaluated using a simulated tracking problem for a static and dynamic target. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40553.html 04:00 PM Wednesday 31, 1969 The problem of determining optimal observation strategies for identification of unknown parameters in distributed systems is discussed. Particularly, a setting where the measurement process is performed by collecting spatial data from mobile nodes with sensing capacity forming an organized network is considered. The framework is based on the use of the D-optimality criterion defined on the Fisher information matrix associated with the estimated parameters as a measure of the information content in the measurements. The approach is to convert the problem to a canonical optimal control one in Mayer form, in which the control forces of the sensors may be optimized. Then, through an adaptation of some pairwise communication algorithms a numerical scheme is developed, which decompose the resulting problem and distributes the computational burden between the network nodes. Numerical solutions are then obtained using widespread powerful numerical packages which handles various constraints imposed on the node motions. As a result, an adaptive scheme is outlined to determine the guidance policies for network nodes in a decentralized fashion. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40552.html 04:00 PM Wednesday 31, 1969 For large-scale processes whose dynamics can be represented as the interaction of several dynamically-coupled linear subsystems, this paper proposes a decentralized model predictive control (MPC) design approach for set-point tracking under input constraints and possible loss of information packets. Following earlier results in (Alessio and Bemporad, 2007 and 2008), the global model of the process is approximated as the decomposition of several (possibly overlapping) smaller models used for local predictions. We present sufficient criteria for asymptotic tracking of output set-points and rejection of constant measured disturbances when the overall process is in closed loop with the set of decentralized MPC controllers, under possible intermittent lack of communication of measurement data between controllers. The effectiveness of the approach is shown in a simulation example on distributed temperature control in the passenger area of a railcar. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40520.html 04:00 PM Wednesday 31, 1969 We study the stochastic consensus problem in a large population system by using the so-called Nash Certainty Equivalence (NCE) Principle. The NCE (Mean Field) methodology has been studied for dynamic games in a large population of stochastic agents. In this paper, we formalize the large population stochastic consensus problem as a dynamic game problem in which the agents have similar dynamics and are coupled via their individual costs. Then for large but finite population, we derive the standard consensus algorithm dynamics from mean field stochastic control NCE equations. While the NCE formulation requires a priori information on the mean values of the initial states, the standard consensus algorithms need no a priori information, but instead use local state feedback on the network graph. Moreover, in the NCE-Consensus formulation, each agent's behaviour is optimal with respect to other agents in a game theoretic Nash sense which shows that consensus behaviour may originate from individual incentives. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40544.html 04:00 PM Wednesday 31, 1969 The paper proposes a structure based on distributed adaptive predictive algorithms for control of water delivery open canal networks. Canals are decomposed in pools, the level of each is manipulated by a gate. To each gate/pool, a local controller is associated. In order to improve the overall as well as the local performance, communication between local controllers is provided through feedforward terms from adjacent pools. The comparison of the base line (without any communication among local controllers) performance with different configurations of the controller network proposed is made through simulation. In addition it is shown that the algorithm considered yields the best performance to each local controller, as measured by a quadratic cost, given the information pattern available in terms of sensor measurements. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40560.html 04:00 PM Wednesday 31, 1969 This two-part paper presents and analyzes a family of distributed asynchronous algorithms for solving symmetric positive definite systems of linear equations over networks. In this Part I, we develop Subset Equalizing (SE), a Lyapunov-based algorithm for solving such equations over networks of agents with arbitrary asynchronous interactions and spontaneous membership dynamics, both of which may be exogenously driven and completely unpredictable. To analyze the behavior of SE, we introduce several notions of network connectivity, capable of handling such interactions and membership dynamics, and a time-varying quadratic Lyapunov-like function, defined on a state space with changing dimension. Based on them, we derive sufficient conditions for ensuring the boundedness, asymptotic convergence, and exponential convergence of SE, and show that these conditions are mild. Finally, we illustrate the effectiveness of SE through an example, using it to perform unconstrained quadratic optimization over a volatile multi-agent system. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40561.html 04:00 PM Wednesday 31, 1969 In this Part II of the two-part paper, we study the interplay among wireless communications, distributed algorithms, and control in solving symmetric positive definite systems of linear equations over multi-hop wireless networks with fixed topologies. Building on the results from Part I, we develop and analyze Pairwise, Groupwise, Random Hopwise, and Controlled Hopwise Equalizing (PE, GE, RHE, and CHE), showing along the way how the broadcast nature of wireless transmissions may be fully utilized, how undesirable overlapping iterations may be avoided, and how iterations may be feedback controlled in a greedy, decentralized, Lyapunov-based fashion, leading to CHE. We show that CHE yields a networked dynamical system with state-dependent switching, provable exponential convergence, and quantifiable worst-case convergence rate. Finally, through extensive simulation on random geometric graphs, we show that GE, RHE, and CHE are dramatically more efficient and scalable than two existing, average-consensus-based schemes, with CHE having the best performance. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40530.html 04:00 PM Wednesday 31, 1969 In this paper we study the convergence towards consensus on information in a distributed system of agents communicating over a network. The particularity of this study is that the information on which the consensus is seeked is not represented by real numbers, rather by logical values or sets. Whereas the problems of allowing a network of agents to reach a consensus on logical functions of input events, and that of agreeing on set--valued information, have been separately addressed in previous work, in this paper we show that these problems can indeed be attacked in a unified way in the framework of Boolean distributed information systems. Based on a notion of contractivity for Boolean dynamical systems, a necessary and sufficient condition ensuring the global convergence toward a unique equilibrium point is presented. This result can be seen as a first step toward the definition of a unified framework to uniformly address all consensus problems on Boolean algebras. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/40542.html 04:00 PM Wednesday 31, 1969 In this paper we present preliminary ideas on how to develop distributed supervision strategies for networked control systems subject to coordination constraints to be enforced on-line. Such a coordination paradigm, hereafter referred to as coordination-by-constraint, is characterized by a set of spatially distributed dynamic systems, connected via communication channels, with possibly dynamical coupling amongst them which need to be supervised and coordinated in order to accomplish their overall objective. In order to evaluate the distributed method here proposed, the distributed coordination of coupled autonomous vehicles under input-saturation and formation accuracy constraints is presented as an example. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif