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ABSTRACT: In this paper we propose a subgradient method for solving coupled optimization problems in a distributed way given restrictions on the communication topology. The iterative procedure maintains local variables at each node and relies on local subgradient updates in combination with a consensus process. The local subgradient steps are applied simultaneously as opposed to the standard sequential or cyclic procedure. We study convergence properties of the proposed scheme using results from consensus theory and approximate subgradient methods. The framework is illustrated on an optimal distributed finite-time rendezvous problem.
Decision and Control, 2008. CDC 2008. 47th IEEE Conference on; 01/2009
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ABSTRACT: Novel event-triggered sensing and actuation strategies are presented for networked control systems with limited communication resources. Two architectures are considered: one with the controller co-located with the sensor and one with the control co-located with the actuator. A stochastic control problem with an optimal stopping rule is shown to capture two interesting instances of these architectures. The solution of the problem leads to a parametrization of the control alphabet as piecewise constant commands. The execution of the control commands is triggered by stopping rules for the sensor. In simple situations, it is possible to analytically derive the optimal controller. Examples illustrate how the new event-based control and sensing strategies outperform conventional time-triggered schemes.
Decision and Control, 2008. CDC 2008. 47th IEEE Conference on; 01/2009
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ABSTRACT: Remote control over wireless multi-hop networks is considered. Time-varying delays for the transmission of sensor and control data over the wireless network are caused by a randomized multi-hop routing protocol. The characterstics of the routing protocol together with lower-layer network mechanisms give rise to a delay process with high variance and stepwise changing mean. A new predictive control scheme with a delay estimator is proposed in the paper. The estimator is based on a Kalman filter with a change detection algorithm. It is able to track the delay mean changes but efficiently attenuate the high frequency jitter. The control scheme is analyzed and its implementation detailed. Network data from an experimental setup are used to illustrate the efficiency of the approach.
Control Applications, 2007. CCA 2007. IEEE International Conference on; 11/2007
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ABSTRACT: A control theoretic analysis of a simple error correction scheme for lossy packet-switched networks is presented. Based on feedback information from the error correction process in the receiver, the sender adjusts the amount of redundancy using a so called extremum-seeking controller, which do not rely on any accurate model of the network loss process. The closed-loop system is shown to converge to a limit cycle in a neighborhood of the optimal redundancy. The result are validated using packet-based simulations with data from wireless sensor network experiments.
Networking, Sensing and Control, 2007 IEEE International Conference on; 05/2007
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ABSTRACT: Error correction mechanisms enable control and other real-time applications to be executed over unreliable packet-switched networks. By adding carefully adjusted redundancy to transmitted data at the sender, it is possible to recover lost data at the receiver and thereby improve effective throughput. We describe simple models for packet loss, which allow us to find the optimal redundancy as a function of packet loss probability. Two feedforward control mechanisms based on the packet loss probability are presented: one that is computed off-line and another one using an on-line algorithm. A drawback with these approaches is their dependency on accurate network state information and precise loss models. To cope with these issues, we propose a new feedback solution that tracks the optimum using gradient estimation. Simulations in ns-2 illustrate the behavior of the error correction schemes, demonstrating that the feedback solution outperforms the feedforward solution in presence of model erros.
Decision and Control, 2005 and 2005 European Control Conference. CDC-ECC '05. 44th IEEE Conference on; 01/2006
