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  • 201. Wang, L.
    et al.
    Wang, X.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Distributed tracking and connectivity maintenance with a varying velocity leader2012In: 2012 12th International Conference on Control, Automation, Robotics and Vision, ICARCV 2012, IEEE , 2012, p. 1824-1829Conference paper (Refereed)
    Abstract [en]

    This paper investigates a distributed tracking problem for multi-agent systems with a varying-velocity leader. The leader modeled by a double integrator can only be perceived by followers located within a sensing distance. The objective is to drive the followers with bounded control law to maintain connectivity, avoid collision and further track the leader, with no need of acceleration measurements. Two cases are considered: the acceleration of the leader is bounded; and the acceleration has a linear form. In the first case, the relative velocities of neighbors are integrated and transmitted as a new variable to account for the uncertain time-varying acceleration. In the second case, two distributed estimators are added for the leader's position and velocity. Simulations are presented to show the effectiveness of the proposed control laws.

  • 202. Almér, Stefan
    et al.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Dynamic Phasor Analysis Of Pulse-Modulated Systems2012In: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 50, no 3, p. 1110-1138Article in journal (Refereed)
    Abstract [en]

    This paper considers stability and harmonic analysis of a general class of pulse-modulated systems. The systems are modeled using the dynamic phasor model, which explores the cyclic nature of the modulation functions by representing the system state as a Fourier series expansion defined over a moving time window. The contribution of the paper is to show that a special type of periodic Lyapunov function can be used to analyze the system and that the analysis conditions become tractable for computation after truncation. The approach provides a trade-off between complexity and accuracy that includes standard state space averaged models as a special case. The paper also shows how the dynamic phasor model can be used to derive a frequency domain input-to-state map which is analogous to the harmonic transfer function.

  • 203. Ning, B.
    et al.
    Dong, H.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Tang, T.
    Sun, X.
    Emergency management of urban rail transit systems using parallel control2012In: Computers in Railways XIII: Computer System Design and Operation in the Railway and Other Transit Systems, WIT Press, 2012, Vol. 127, p. 687-695Conference paper (Refereed)
    Abstract [en]

    This paper presents a parallel control system designed for managing emergent events in an urban rail transit system (URTS). The key features of the system include cloud computing, information fusion and expert systems. A multiagent approach is used for modeling diversities and interactions in the URTS. Partially due to its ability to interact with the real system via parallel execution, such a parallel control system would provide a cost-effective solution for emergency personnel training, verification of emergency measures, and validation of emergency plans and management policies.

  • 204.
    Wei, Airong
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Wang, Yuzhen
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Estimate of Domain of Attraction for a Class of Port-Controlled Hamiltonian Systems Subject to Both Actuator Saturation and Disturbances2012In: Asian journal of control, ISSN 1561-8625, E-ISSN 1561-8625, Vol. 14, no 4, p. 1108-1112Article in journal (Refereed)
    Abstract [en]

    This paper investigates the estimate of domain of attraction for a class of nonlinear port-controlled Hamiltonian (PCH) systems subject to both actuator saturation and disturbances. Firstly, two conditions are established to determine whether an ellipsoid is contractively invariant for the systems only with actuator saturation, with which the biggest ellipsoid contained in the domain of attraction can be found. Secondly, the obtained conditions are extended to estimate the domain of attraction of the systems subject to both actuator saturation and disturbances. Study of illustrative example shows the effectiveness of the method proposed in this paper.

  • 205.
    Markdahl, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hoppe, Jens
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
    Wang, Lin
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Exact solutions to the closed loop kinematics of an almost globally stabilizing feedback law on SO(3)2012In: 2012 IEEE 51st Annual Conference on Decision and Control (CDC), IEEE , 2012, p. 2274-2279Conference paper (Refereed)
    Abstract [en]

    We propose a kinematic control law that solves the problem of stabilizing the attitude of a fully actuated rigid body to a desired rest attitude. The control law is designed on the special orthogonal group SO(3), thereby avoiding complications due to the representational singularities of local parametrizations and the unwinding phenomenon associated with global many-to-one parametrizations. We prove almost global stability, i.e. asymptotical stability from all initial conditions except for a set of zero measure. The proposed control law decouples the closed loop kinematics, allowing us to solve the state equations exactly for the rigid body attitude as a function of time, the initial conditions, and two gain parameters. The exact solutions provide an understanding of the transient behaviour of the system and can e.g. be used to tune the gain parameters. The geometric flavor of these ideas is illustrated by simulation.

  • 206.
    Gaidashev, Denis
    et al.
    Uppsala univ., Uppsala, Sweden .
    Winckler, Björn
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Existence of a Lorenz renormalization fixed point of an arbitrary critical order2012In: Nonlinearity, ISSN 0951-7715, E-ISSN 1361-6544, Vol. 25, no 6, p. 1819-1841Article in journal (Refereed)
    Abstract [en]

    We present a proof of the existence of a renormalization fixed point for Lorenz maps of the simplest non-unimodal combinatorial type ({0, 1}, {1, 0, 0}) and with a critical point of arbitrary order rho > 1.

  • 207.
    Bokrantz, Rasmus
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Miettinen, Kaisa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Improved plan quality in multicriteria radiation therapy optimization by projections onto the Pareto surface2012Report (Other academic)
    Abstract [en]

    We consider an approach to multicriteria radiation therapy optimization where the clinical treatment plan is selected from a representationof the set of Pareto optimal treatment plans in the form of a discrete setof plans and their combinations. The approximate nature of this representation implies that a selected plan in general has an approximationerror with respect to Pareto optimality. To assess and, if necessary, improve the quality of such plans, a technique is suggested that eliminatesthe approximation error of a given treatment plan by a projection ontothe Pareto surface. A more elaborate form of projection is also suggested that requires the projected solution to be not only as good asthe input plan in terms of objective function values, but also equallygood or better with respect to the three-dimensional dose distribution.The versatility of the suggested technique is demonstrated by application to planning for step-and-shoot and sliding window delivery ofintensity-modulated radiation therapy, and planning for spot-scanneddelivery of intensity-modulated proton therapy. Our numerical resultsshow that the proposed projections generally lead to improved sparingof organs at risk and a higher degree of dose conformity compared towhen projections are not performed.

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  • 208.
    Miettinen, Kaisa
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Ruiz, Francisco
    Luque, Mariano
    Improving the Computational Efficiency in a Global Formulation (GLIDE) for Interactive Multiobjective Optimization2012In: Annals of Operations Research, ISSN 0254-5330, E-ISSN 1572-9338, Vol. 197, no 1, p. 47-70Article in journal (Refereed)
    Abstract [en]

    In this paper, we present a new general formulation for multiobjective optimization that can accommodate several interactive methods of different types (regarding various types of preference information required from the decision maker). This formulation provides a comfortable implementation framework for a general interactive system and allows the decision maker to conveniently apply several interactive methods in one solution process. In other words, the decision maker can at each iteration of the solution process choose how to give preference information to direct the interactive solution process, and the formulation enables changing the type of preferences, that is, the method used, whenever desired. The first general formulation, GLIDE, included eight interactive methods utilizing four types of preferences. Here we present an improved version where we pay special attention to the computational efficiency (especially significant for large and complex problems), by eliminating some constraints and parameters of the original formulation. To be more specific, we propose two new formulations, depending on whether the multiobjective optimization problem to be considered is differentiable or not. Some computational tests are reported showing improvements in all cases. The generality of the new improved formulations is supported by the fact that they can accommodate six interactive methods more, that is, a total of fourteen interactive methods, just by adjusting parameter values.

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  • 209.
    Möller, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Modeling and Stability Analysis of Rate and Power Control Systems in Wireless Communication Networks2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wireless data traffic in cellular networks is currently undergoing a strong global expansion and the demand for high and reliable data throughput increases. Capacity is, however, a limited resource, and in radio resource management a trade-off has to be made between the congestion level, related to cell coverage and interference levels, and the Quality of Service (QoS) or data rates of the users.

    The radio channel conditions vary on a fast time scale and the measurements of the received signals are subject to disturbances and uncertainties. This motivates the use of control strategies to update the transmission powers. In fact, in implementations of uplink in cellular networks, the performance of the network is ensured by using a fast inner power control algorithm to track a QoS-target and a slower outer control algorithm to limit congestion.

    Several theoretical challenges arise in this problem setting. Due to the nature of the network, both information and control are distributed. Furthermore, measurements of the congestion and the QoS are used in the control loops, which introduces nonlinear feedback. Another complicating factor is that filtering, computations and information exchange in the network cause time-delays and dynamics.

    In this thesis we address these challenges by using modeling and analysis tools in systems and control. The objective is to provide systematic methods to quantify the fundamental limitations of the system and to point out the trade-offs for a given system design. We perform stability analysis on a high mathematical level that provides results that are simple to compute and that reveal the system structure.

    In Paper A we extend existing power control models and stability frameworks to include dynamics. For this we use a general definition of the interference. Moreover, stability is addressed by a monotonicity approach and by proposing a Lyapunov function. Paper B provides less conservative stability results using input-output analysis for the same system model. Stability of a linearization of the system model is studied in Paper C with the multivariate Nyquist criterion. Moreover, we use discrete multivariate describing functions to analyze the equilibrium oscillations that arise due to binary feedback. In Paper D we extend the model with an outer control loop, which dynamically sets the reference value to the control algorithm studied in Papers A to C. The main analysis tool for stability is input-output theory.

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  • 210.
    Bokrantz, Rasmus
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Multicriteria optimization for volumetric-modulated arc therapy by decomposition into a fluence-based relaxation and a segment weight-based restriction2012In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 39, no 11, p. 6712-6725Article in journal (Refereed)
    Abstract [en]

    Purpose: To develop a method for inverse volumetric-modulated arc therapy (VMAT) planning that combines multicriteria optimization (MCO) with direct machine parameter optimization. The ultimate goal is to provide an efficient and intuitive method for generating high quality VMAT plans. Methods: Multicriteria radiation therapy treatment planning amounts to approximating the relevant treatment options by a discrete set of plans, and selecting the combination thereof that strikes the best possible balance between conflicting objectives. This approach is applied to two decompositions of the inverse VMAT planning problem: a fluence-based relaxation considered at a coarsened gantry angle spacing and under a regularizing penalty on fluence modulation, and a segment weight-based restriction in a neighborhood of the solution to the relaxed problem. The two considered variable domains are interconnected by direct machine parameter optimization toward reproducing the dose-volume histogram of the fluence-based solution. Results: The dose distribution quality of plans generated by the proposed MCO method was assessed by direct comparison with benchmark plans generated by a conventional VMAT planning method. The results for four patient cases (prostate, pancreas, lung, and head and neck) are highly comparable between the MCO plans and the benchmark plans: Discrepancies between studied dose-volume statistics for organs at risk were-with the exception of the kidneys of the pancreas case-within 1 Gy or 1 percentage point. Target coverage of the MCO plans was comparable with that of the benchmark plans, but with a small tendency toward a shift from conformity to homogeneity. Conclusions: MCO allows tradeoffs between conflicting objectives encountered in VMAT planning to be explored in an interactive manner through search over a continuous representation of the relevant treatment options. Treatment plans selected from such a representation are of comparable dose distribution quality to conventionally optimized VMAT plans.

  • 211.
    Yang, Yuecheng
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Opinion consensus of modified Hegselmann-Krause models2012In: 2012 IEEE 51st Annual Conference on Decision and Control (CDC), IEEE , 2012, p. 100-105Conference paper (Refereed)
    Abstract [en]

    We consider the opinion consensus problem using a multi-agent setting based on the Hegselmann-Krause (H-K) Model. Firstly, we give a sufficient condition on the initial opinion distribution so that the system will converge to only one cluster. Then, modified models are proposed to guarantee convergence for more general initial conditions. The overall connectivity is maintained with these models, while the loss of certain edges can occur. Furthermore, a smooth control protocol is provided to avoid the difficulties that may arise due to the discontinuous right-hand side in the H-K model.

  • 212. Mikael, Fallgren
    et al.
    Fodor, Gabor
    Forsgren, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Optimization approach to joint cell, channel and power allocation in wireless communication networks2012In: 2012 Proceedings of the 20th European Signal Processing Conference (EUSIPCO), New York: IEEE conference proceedings, 2012, p. 829-833Conference paper (Other academic)
    Abstract [en]

    In multicell wireless networks the resource allocation task includes the selection of the serving cell and the allocation of channels and transmission powers. While all of these tasks have been studied in the past, all three jointly are seldom addressed. In this paper we formulate the joint cell, channel and power allocation problem as an optimization task, whose purpose is to maximize the total user throughput. The joint problem is decomposed into separate subproblems of cell, channel and power allocation. We propose heuristic and optimization based algorithms to solve each of these tasks and present numerical results that give new and valuable insights into a sum throughput optimal joint resource allocation strategy.

  • 213.
    Miettinen, Kaisa
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hartikainen, Markus
    University of Jyväskylä, Finland.
    Wiecek, Margaret M
    Clemson University.
    PAINT: Pareto front interpolation for nonlinear multiobjective optimization2012In: Computational optimization and applications, ISSN 0926-6003, E-ISSN 1573-2894, Vol. 52, no 3, p. 845-867Article in journal (Refereed)
    Abstract [en]

    A method called PAINT is introduced for computationally expensive multiobjective optimization problems. The method interpolates between a given set of Pareto optimal outcomes. The interpolation provided by the PAINT method implies a mixed integer linear surrogate problem for the original problem which can be optimized with any interactive method to make decisions concerning the original problem. When the scalarizations of the interactive method used do not introduce nonlinearity to the problem (which is true e.g., for the synchronous NIMBUS method), the scalarizations of the surrogate problem can be optimized with available mixed integer linear solvers. Thus, the use of the interactive method is fast with the surrogate problem even though the problem is computationally expensive. Numerical examples of applying the PAINT method for interpolation are included.

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  • 214.
    Wang, Lin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Markdahl, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Wang, Xiaofan
    Position and attitude tracking for a formation of three agents2012In: Chinese Control Conference, CCC, 2012, p. 6406-6410Conference paper (Refereed)
    Abstract [en]

    In this paper we consider a trajectory tracking control problem for a multi-agent formation consisting of three agents. The agents provide a high level representation of three manipulators that have grasped a rigid object. More precisely, the agents' positions represent the end-effectors' grasp points. The agents are modelled by single integrators, and are designed to move the object such that it is located at a particular position with a particular attitude in a particular time, i.e. position and attitude tracking. The object rigidity is modelled by requiring that the agents should remain at constant relative distances from each other, reducing their three degrees of freedom each to a total of six translational and rotational degrees of freedom for the whole formation. The formation of agents is shown to be equivalent to a rigid body. The position tracking problem is solved using a standard technique whereas the attitude tracking problem is solved by adopting and adapting a recently developed approach.

  • 215.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Primal and dual criteria for robust stability applied to large scale systems2012In: Distributed Decision Making and Control, Springer, 2012, Vol. 417, p. 3-25Chapter in book (Refereed)
    Abstract [en]

    Primal and dual formulations of stability criteria based on multipliers will be discussed. The foundation for multiplier-based stability analysis is the use of a convex cone of multipliers to characterize the uncertainty in a system. The primal and dual stability criteria are formulated as convex feasibility tests involving the nominal dynamics and multipliers from the cone and the polar cone, respectively. The motivation for introducing the dual is that it provides additional insight into the stability criterion and that it is sometimes easier to use than the primal. The case considered in this chapter is that of uncertainty as it represents the interconnection of a complex network. The multipliers are used to describe characteristic properties of the network such as the spectral location or the structure of the underlying graph.

  • 216. Kragelund, Martin
    et al.
    Leth, John
    Wisniewski, Rafal
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Profit Maximization of a Power Plant2012In: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 18, no 1, p. 38-54Article in journal (Refereed)
    Abstract [en]

    This paper addresses the problem of profit maximization of a power plant by utilizing three different fuel systems in an optimal manner Pontryagin's maximum principle is used to derive properties of the optimal control strategy. These properties give rise to a switching function. Subsequently, certain heuristics are introduced and used in combination with discrete optimization to obtain an initial trajectory of the switching function. An iterative procedure is proposed, which uses the initial trajectory for the computation of the optimal control strategy. The control strategy derived is a combination of a state feedback and time-varying feedforward term. Its performance is tested against input noise.

  • 217. Cantoni, Michael
    et al.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Kao, Chung-Yao
    Robustness Analysis for Feedback Interconnections of Distributed Systems via Integral Quadratic Constraints2012In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 57, no 2, p. 302-317Article in journal (Refereed)
    Abstract [en]

    A framework is established for directly accommodating feedback interconnections of unstable distributed-parameter transfer functions in robust stability analysis via integral quadratic constraints (IQCs). This involves transfer function homotopies that are continuous in a nu-gap metric sense. As such, the development includes the extension of nu-gap metric concepts to an irrational setting and the study of uncertainty-set connectedness in these terms. The main IQC based robust stability result is established for constantly-proper transfer functions in the Callier-Desoer algebra; i.e. finitely many unstable poles and a constant limit at infinity. Problems of structured robust stability analysis and robust performance analysis are considered to illustrate use of the main result. Several numerical examples are also presented. These include stability analysis of an autonomous system with uncertain time-delay and a closed-loop control system, accounting for both the gain and phase characteristics of the distributed-parameter uncertainty associated with the nominal rational plant model used for controller synthesis.

  • 218.
    Demirel, Burak
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Briat, Corentin
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Supervisory control design for networked systems with time-varying communication delays2012In: Analysis and Design of Hybrid Systems, IFAC , 2012, p. 133-140Conference paper (Refereed)
    Abstract [en]

    This paper proposes a supervisory control structure for networked systems with time-varying delays. The control structure, in which a supervisor triggers the most appropriate controller from a multi-controller unit, aims at improving the closed-loop performance relative to what can be obtained using a single robust controller. Our analysis considers average dwelltime switching and is based on a novel multiple Lyapunov-Krasovskii functional. We develop analysis conditions that can be verified by semi-definite programming, and show that associated state feedback synthesis problem also can be solved using convex optimization. Small and large scale networked control systems are used to illustrate the effectiveness of our approach.

  • 219.
    Thunberg, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Ögren, Petter
    Aeronautical and Systems Technology, Swedish Defence Research Agency (FOI), Sweden.
    A Boolean Control Network Approach to Pursuit Evasion Problems in Polygonal Environments2011In: 2011 IEEE International Conference on obotics and Automation (ICRA), 2011, p. 4506-4511Conference paper (Refereed)
    Abstract [en]

    In this paper, the multi pursuer version of the pursuit evasion problem in polygonal environments is addressed. This problem is NP-hard, and therefore we seek good enough, but not optimal solutions. By modeling the problem as a Boolean Control Network, we can efficiently keep track of which regions are cleared, and which are not, while the input nodes of the network are used to represent the motion of the pursuers. The environment is partitioned into a set of convex regions, where each region correspond to a set of nodes in the network. The method is implemented in ANSI C, and efficiently solves complex environments containing multiple loops and requiring so-called recontamination. The provided examples demonstrate the effectiveness of the method in terms of computational time

  • 220.
    Lovisari, Enrico
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jonsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A framework for robust synchronization in heterogeneous multi-agent networks2011In: Proc IEEE Conf Decis Control, 2011, p. 7268-7274Conference paper (Refereed)
    Abstract [en]

    A general framework for the analysis of networks of heterogeneous agents is presented. By modeling each agent as a nominal linear time-invariant system plus a possibly nonlinear perturbation and the interconnection among the agents via a memoryless operator, a general result is offered which ensures robust synchronization of the network to a subspace of R N. The result is applied to the case when the interconnection operator is a constant normal matrix and the perturbations nonlinear. The criterion is reduced to a graphical Popov criterion for the synchronization of the network. 

  • 221.
    Thunberg, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Ögren, Petter
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    A Mixed Integer Linear Programming approach to Pursuit Evasion Problems with optional Connectivity Constraints2011In: Autonomous Robots, ISSN 0929-5593, E-ISSN 1573-7527, Vol. 31, no 4, p. 333-343Article in journal (Refereed)
    Abstract [en]

    In this paper, we address the multi pursuer version of the pursuit evasion problem in polygonal environments. By discretizing the problem, and applying a Mixed Integer Linear Programming (MILP) framework, we are able to address problems requiring so-called recontamination and also impose additional constraints, such as connectivity between the pursuers. The proposed MILP formulation is less conservative than solutions based on graph discretizations of the environment, but still somewhat more conservative than the original underlying problem. It is well known that MILPs, as well as multi pursuer pursuit evasion problems, are NP-hard. Therefore we apply an iterative Receding Horizon Control (RHC) scheme where a number of smaller MILPs are solved over shorter planning horizons. The proposed approach is implemented in Matlab/Cplex and illustrated by a number of solved examples.

  • 222. Wei, A.
    et al.
    Wang, Y.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Adaptive H∞control of uncertain port-controlled Hamiltonian systems subject to actuator saturation2011In: Proceedings of the 30th Chinese Control Conference, CCC 2011, 2011, p. 391-396Conference paper (Refereed)
    Abstract [en]

    This paper deals with the problem of adaptive control of uncertain nonlinear port-controlled Hamiltonian systems subject to actuator saturation, and proposes a number of results on the control design. Firstly, an adaptive H∞ control design approach is presented by using both the dissipative Hamiltonian structural and saturated actuator properties for the case that there are both parametric uncertainties and external disturbances in the AS systems. Secondly, the results obtained for Hamiltonian systems are applied to adaptive control for a class of uncertain nonlinear affine systems subject to actuator saturation, and several interesting results are obtained. Finally, study of an example of power systems with simulations shows that the adaptive controller proposed in this paper is effective.

  • 223.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Yavuz, Emre Altug
    KTH, School of Electrical Engineering (EES), Communication Networks.
    An axiomatic fluid-flow model for congestion control analysis2011In: 2011 50th IEEE Conference on Decision and Control andEuropean Control Conference (CDC-ECC), 2011, p. 3122-3129Conference paper (Refereed)
    Abstract [en]

    An axiomatic model for congestion control isderived. The proposed four axioms serve as a basis for theconstruction of models for the network elements. It is shownthat, under some assumptions, some models of the literature canbe recovered. A single-buffer/multiple-users topology is finallyderived and studied for illustration.

  • 224. Karasalo, Maja
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    An optimization approach to adaptive Kalman filtering2011In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 47, no 8, p. 1785-1793Article in journal (Refereed)
    Abstract [en]

    In this paper, an optimization-based adaptive Kalman filtering method is proposed. The method produces an estimate of the process noise covariance matrix Q by solving an optimization problem over a short window of data. The algorithm recovers the observations h(x) from a system (x) over dot = f (x), y = h(x) + v without a priori knowledge of system dynamics. Potential applications include target tracking using a network of nonlinear sensors, servoing, mapping, and localization. The algorithm is demonstrated in simulations on a tracking example for a target with coupled and nonlinear kinematics. Simulations indicate superiority over a standard MMAE algorithm for a large class of systems.

  • 225.
    Fallgren, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Oddsdóttir, H. Æ
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Fodor, G.
    An optimization approach to joint cell and power allocation in multicell networks2011In: IEEE Int Conf Commun, 2011, p. 5963591-Conference paper (Refereed)
    Abstract [en]

    Since the seminal paper by Knopp and Humblet that showed that the system throughput of a single cell system is maximized if only one terminal transmits at a time, there has been a large interest in opportunistic communications and its relation to various fairness measures. On the other hand, in multicell systems there is a need to allocate transmission power such that some overall utility function is maximized typically under fairness constraints. Furthermore, in multicell systems the degree of resource allocation freedom includes the serving cell selection that allows for load balancing and thereby the efficient use of radio resources. In this paper we formulate the joint serving cell selection (link selection) and power allocation problem as an optimization task whose purpose is to maximize either the minimum user throughput or the multicell sum throughput. Both the max-min and the max-throughput problems are non-polynomial hard and we therefore propose heuristic solution approaches. We present numerical results that give new and valuable insights into the trade off between fair and sum throughput optimal joint resource allocation strategies.

  • 226. Pedicini, C.
    et al.
    Vasca, F.
    Iannelli, L.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    An overview on averaging for pulse-modulated switched systems2011In: Proceedings of the IEEE Conference on Decision and Control, 2011, p. 1860-1865Conference paper (Refereed)
    Abstract [en]

    Averaging of fast switching systems is an effective technique used in many engineering applications. Practical stability and control design for a nonsmooth switched system can be inferred by analyzing the smooth averaged system. In this paper we overview the few formal approaches proposed in the literature to deal with the averaging of nonsmooth systems. The dithering, the phasor dynamics and the hybrid framework techniques are recast and compared by considering pulse-modulated switched linear systems as the common modeling platform.

  • 227. Bhattacharyya, Tirthankar
    et al.
    Sasane, Amol
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    COHERENCE OF THE REAL SYMMETRIC HARDY ALGEBRA2011In: OPERATORS AND MATRICES, ISSN 1846-3886, Vol. 5, no 2, p. 303-308Article in journal (Refereed)
    Abstract [en]

    Let D denote the open unit disk in C centered at 0. Let H-R(infinity) denote the set of all bounded and holomorphic functions defined in D that also satisfy f(z) = )over bar> for all z is an element of D. It is shown that H-R(infinity) is a coherent ring.

  • 228.
    Möller, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Blomgren, Mats
    Gunnarsson, Fredrik
    Congestion-based Rate and Power Control in Wireless Cellular Networks2011In: 2011 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE (GLOBECOM 2011), New York: IEEE , 2011, p. 6133508-Conference paper (Refereed)
    Abstract [en]

    In a cellular network it is necessary to make a trade-off between congestion and Quality of Service (QoS) of the users. To ensure good system performance in uplink of a WCDMA network, control loops are used to adapt to changing radio and interference conditions. A fast inner power control loop updates the transmission powers of the mobiles based on measurements related to QoS, which are compared to a reference value. The reference value is set dynamically by a slower outer rate control loop that uses measurements of congestion. There is a time-scale difference between the loops, but joint dynamics cannot be neglected. In this paper we derive a high order system model with distributed feedback control based on locally measurable information. We model the time-scale difference between the loops and include this in the model. We give sufficient conditions for stability using control theoretic methods and validate the model and results by simulations.

  • 229. Wang, L.
    et al.
    Wang, X.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Connectivity maintenance and collective consensus for multi-agent system with an active leader2011In: Proceedings of the 30th Chinese Control Conference, CCC 2011, 2011, p. 6025-6029Conference paper (Refereed)
    Abstract [en]

    In this paper, we study a leader-following consensus problem with an active leader and distance-determinant topology. In the scenario we consider, only the leader has the information of the desired motion, and only the followers located within a sensing zone can access to the information of the leader. To reach a desired global consensus, a neighbor-based local controller is developed for the followers. We prove that, under some initial conditions, the proposed control scheme can enable the followers to maintain connectivity, avoid collision, and track the varying-velocity leader. Simulations are also presented to illustrate the theoretical results.

  • 230.
    Hartikainen, Markus
    et al.
    University of Jyväskylä, Finland.
    Miettinen, Kaisa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Wiecek, Margaret M
    Clemson University.
    Constructing a Pareto front approximation for decision making2011In: Mathematical Methods of Operations Research, ISSN 1432-2994, E-ISSN 1432-5217, Vol. 73, no 2, p. 209-234Article in journal (Refereed)
    Abstract [en]

    An approach to constructing a Pareto front approximation to computationally expensive multiobjective optimization problems is developed. The approximation is constructed as a sub-complex of a Delaunay triangulation of a finite set of Pareto optimal outcomes to the problem. The approach is based on the concept of inherent nondominance. Rules for checking the inherent nondominance of complexes are developed and applying the rules is demonstrated with examples. The quality of the approximation is quantified with error estimates. Due to its properties, the Pareto front approximation works as a surrogate to the original problem for decision making with interactive methods.

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  • 231.
    Briat, Corentin
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Convergence and Equivalence Results for the Jensen's Inequality-Application to Time-Delay and Sampled-Data Systems2011In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 56, no 7, p. 1660-1665Article in journal (Refereed)
    Abstract [en]

    The Jensen's inequality plays a crucial role in the analysis of time-delay and sampled-data systems. Its conservatism is studied through the use of the Gruss Inequality. It has been reported in the literature that fragmentation (or partitioning) schemes allow to empirically improve the results. We prove here that the Jensen's gap can be made arbitrarily small provided that the order of uniform fragmentation is chosen sufficiently large. Nonuniform fragmentation schemes are also shown to speed up the convergence in certain cases. Finally, a family of bounds is characterized and a comparison with other bounds of the literature is provided. It is shown that the other bounds are equivalent to Jensen's and that they exhibit interesting well-posedness and linearity properties which can be exploited to obtain better numerical results.

  • 232.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sename, O.
    Lafay, J. -F
    Design of LPV observers for LPV time-delay systems: an algebraic approach2011In: International Journal of Control, ISSN 0020-7179, E-ISSN 1366-5820, Vol. 84, no 9, p. 1533-1542Article in journal (Refereed)
    Abstract [en]

    The design of reduced order observer for linear parameter varying (LPV) time-delay systems is addressed. Necessary conditions guaranteeing critical structural properties for the observation error dynamics are first provided through nonlinear algebraic matrix equalities. An explicit parametrisation of the family of observers fulfilling these necessary conditions is then derived. Finally, an approach based on linear matrix inequalities is provided and used to select a suitable observer within this family, according to some criterion; e.g. maximisation of the delay margin or guaranteed suboptimal L(2)-gain. Examples from the literature illustrate the efficiency of the approach.

  • 233.
    Wang, Lin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. Department of Automation, Shanghai Jiao Tong University, China .
    Markdahl, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Distributed attitude control of multi-agent formations2011In: IFAC Proceedings Volumes: (IFAC-PapersOnline), 2011, no PART 1, p. 4513-4518Conference paper (Refereed)
    Abstract [en]

    This paper addresses the problem of how to coordinate the spatial motion of individual agents in a multi-agent system in such a way that the distance between any two agents is maintained at a constant value (but not stabilized) throughout the evolution of the system while simultaneously rotating the formation of agents to a pre-set reference attitude. We propose a distributed control law based on locally available information. The stability of the proposed control law is analyzed using Lyapunov theory in the special case of three agents. The region of attraction is found to encompass the entire statespace, save a single point. A generalization to the case of n agents is performed using the theory of rigid graphs. The geometric underpinnings of these ideas are illustrated by simulation.

  • 234.
    Thunberg, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Montijano, Eduardo
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Distributed Attitude Synchronization Control2011In: 2011 50th IEEE Conference of Decision and Control and European Control Conference (CDC-ECC), NEW YORK: IEEE conference proceedings, 2011, p. 1962-1967Conference paper (Other academic)
    Abstract [en]

    In this paper we consider the problem of constructing feedback control laws for a system of n agents that shall synchronize their attitudes in SO(3). We propose distributed controllers for two synchronization problems, in which the objective is the same, to synchronize the orientations, but what the agents can perceive or communicate differs. In the first problem the agents can measure their orientation to a common reference object, and either communicate with the neighbors or estimate the relative orientation to their neighbors. In the second problem the agents can, without communication, only measure the relative orientation to the neighbors. For the first problem we present a controller which will lead to synchronization, provided the neighborhood graph is connected. For the second problem we present a controller that will lead to synchronization provided the neighborhood graph is connected and the agents initially are contained within a geodesic ball of radius pi/2, which is the maximal convex set in SO(3).

  • 235. Wang, L.
    et al.
    Wang, X.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Distributed coordination for connectivity-preserving flocking without velocity measurement2011In: ASCC - Asian Control Conf. - Final Program Proc., 2011, p. 788-793Conference paper (Refereed)
    Abstract [en]

    In this paper, we address the design of decentralized controller for connectivity-preserving flocking without velocity measurement. An output vector based on neighbors' position information alone is constructed to replace the role of velocity, then some bounded attractive and repulsive forces are integrated together to design the controller. Under some initial conditions, we prove that the controller not only can synchronize all agents, but also can avoid collision as well as preserving connectivity among agents for all the time. Moreover, a leader-follower method is used to guide the group to a desired direction, where the neighboring relationship is totally determined by the distance.

  • 236.
    Bokrantz, Rasmus
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. RaySearch Labs, Stockholm, Sweden..
    Eriksson, K.
    RaySearch Labs, Stockholm, Sweden..
    Hardemark, B.
    RaySearch Labs, Stockholm, Sweden..
    DOES DOSE RATE AND GANTRY SPEED PROVIDE SUFFICIENT DEGREES OF FREEDOM TO ALLOW FOR MULTI-CRITERIA VMAT PLANNING?2011In: Radiotherapy and Oncology, ISSN 0167-8140, E-ISSN 1879-0887, Vol. 99, p. S99-S99Article in journal (Other academic)
  • 237.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dynamic equations on time-scale: Application to stability analysis and stabilization of aperiodic sampled-data systems2011In: IFAC Proc. Vol. (IFAC-PapersOnline), 2011, no PART 1, p. 11374-11379Conference paper (Refereed)
    Abstract [en]

    The stability analysis of systems with aperiodic sampling is analyzed in the framework of dynamic equations on time-scales. Lyapunov theory is used, with sample-period-dependent and independent Lyapunov functions, to obtain stability conditions expressed in terms of parameter dependent matrix inequalities. The examples illustrate the efficiency of the approach which is able to recover, for some systems, the theoretical results for the periodic sampling case even in the aperiodic case. It is also shown that some systems may have admissible varying sampling periods located in disjoint sets. Finally, stabilization results via switching statefeedback are provided; both robust and sampling-period-dependent controllers are considered. It is shown that the latter ones, using the information on the sampling period, can improve stability properties. Stabilization examples illustrate the effectiveness of the approach.

  • 238.
    Fischione, Carlo
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Fast-Lipschitz optimization with wireless sensor networks applications2011In: Proceedings of the 10th ACM/IEEE International Conference on Information Processing in Sensor Networks, IPSN'11, 2011, p. 378-389Conference paper (Refereed)
    Abstract [en]

    Motivated by the need for fast computations demanded by wireless sensor networks, the new F-Lipschitz optimization theory is introduced for a novel class of optimization problems. These problems are defined by simple qualifying properties specified in terms of increasing objective function and contractive constraints. It is shown that feasible F-Lipschitz problems have always a unique optimal solution that satisfies the constraints at equality. The solution is obtained quickly by asynchronous algorithms of certified convergence. F-Lipschitz optimization can be applied to both centralized and distributed optimization. Compared to traditional Lagrangian methods, which often converge linearly, the convergence time of centralized F-Lipschitz problems is at least superlinear. Distributed F-Lipschitz algorithms converge fast, as opposed to traditional La-grangian decomposition and parallelization methods, which generally converge slowly and at the price of many message passings. In both cases, the computational complexity is much lower than traditional Lagrangian methods. Examples of application of the new optimization method are given for distributed detection and radio power control in wireless sensor networks. The drawback of the F-Lipschitz optimization is that it might be difficult to check the qualifying properties. For more general optimization problems, it is suggested that it is convenient to have conditions ensuring that the solution satisfies the constraints at equality.

  • 239. Sasane, Sara Maad
    et al.
    Sasane, Amol
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Generators for Rings of Compactly Supported Distributions2011In: Integral equations and operator theory, ISSN 0378-620X, E-ISSN 1420-8989, Vol. 69, no 1, p. 63-71Article in journal (Refereed)
    Abstract [en]

    Let C denote a closed convex cone in R-d with apex at 0. We denote by E'(C) the set of distributions on R-d having compact support contained in C. Then E'(C) is a ring with the usual addition and with convolution. We give a necessary and sufficient analytic condition on (f) over cap (1), ..., (f) over cap (n) for f(n) is an element of E'(C) to generate the ring E'(C). (Here (center dot) over cap denotes Fourier-Laplace transformation.) This result is an application of a general result on rings of analytic functions of several variables by Lars Hormander. En route we answer an open question posed by Yutaka Yamamoto.

  • 240.
    Luque, Mariano
    et al.
    University of Malaga.
    Ruiz, Francisco
    University of Malaga.
    Miettinen, Kaisa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Global Formulation for Interactive Multiobjective Optimization2011In: OR Spectrum, ISSN 0171-6468, Vol. 33, no 1, p. 27-48Article in journal (Refereed)
    Abstract [en]

    Interactive methods are useful and realistic multiobjective optimization techniques and, thus, many such methods exist. However, they have two important drawbacks when using them in real applications. Firstly, the question of which method should be chosen is not trivial. Secondly, there are rather few practical implementations of the methods. We introduce a general formulation that can accommodate several interactive methods. This provides a comfortable implementation framework for a general interactive system. Besides, this implementation allows the decision maker to choose how to give preference information to the system, and enables changing it anytime during the solution process. This change-of-method option provides a very flexible framework for the decision maker.

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  • 241.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Martinez, J. J.
    H ∞ bounded resilient state-feedback design for linear continuous-time systems -a robust control approach2011In: IFAC Proceedings Volumes: (IFAC-PapersOnline), 2011, no PART 1, p. 9307-9312Conference paper (Refereed)
    Abstract [en]

    The quadratic stabilization of LTI systems by bounded resilient state-feedback controllers is addressed. The controllers are guaranteed to be non-fragile with respect to either uniform or nonuniform maximal implementation errors. The design of resilient controller relies on an LMI problem while boundedness of the coefficients (a NP-Hard problem) can be guaranteed by solving a nonconvex problem involving a BMI. The latter problem is solved using proposed locally convergent iterative LMI algorithms. Finally, an example is considered in order to illustrate the effectiveness of the approach.

  • 242.
    Heinrich, Benjamin C.
    et al.
    University of Stuttgart.
    Möller, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Local Stability of High Order Power Control in Cellular Networks2011In: 2011 50th IEEE Conference on Decision and Control and European Control Conference, 2011, p. 4528-4534Conference paper (Refereed)
    Abstract [en]

    We address three major control challenges present in power control of wireless cellular networks: time-delays, interference and the binary control feedback. The power control is distributed and based on measurements of the Signal-to-Interference Ratio (SIR). This implies that the users are coupled through the mutual interference.

    In this paper we show that the interference feedback plays a fundamental role for system stability and behavior. The interference is captured by the so-called feasibility matrix, which contains the interference couplings weighted with SIR-requirements. First, we consider a simplified system and derive a Nyquist stability criterion which separates the system dynamics from the eigenvalues of the feasibility matrix. This criterion is also used to derive bounds on the rate of convergence. Second, we investigate oscillations caused by the binary feedback using harmonic balance techniques. Here, we obtain a similar separation result. Using the structure of the feasibility matrix we derive bounds on the eigenvalue location, which can be seen as a robustness result to disturbances. In an example we illustrate the stability results and predict and observe oscillation modes that are caused by the interference feedback.

  • 243.
    Fredriksson, Albin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Forsgren, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hardemark, Björn
    Minimax optimization for handling range and setup uncertainties in proton therapy2011In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 38, no 3, p. 1672-1684Article in journal (Refereed)
    Abstract [en]

    Purpose: Intensity modulated proton therapy (IMPT) is sensitive to errors, mainly due to high stopping power dependency and steep beam dose gradients. Conventional margins are often insufficient to ensure robustness of treatment plans. In this article, a method is developed that takes the uncertainties into account during the plan optimization. Methods: Dose contributions for a number of range and setup errors are calculated and a minimax optimization is performed. The minimax optimization aims at minimizing the penalty of the worst case scenario. Any optimization function from conventional treatment planning can be utilized by the method. By considering only scenarios that are physically realizable, the unnecessary conservativeness of other robust optimization methods is avoided. Minimax optimization is related to stochastic programming by the more general minimax stochastic programming formulation, which enables accounting for uncertainties in the probability distributions of the errors. Results: The minimax optimization method is applied to a lung case, a paraspinal case with titanium implants, and a prostate case. It is compared to conventional methods that use margins, single field uniform dose (SFUD), and material override (MO) to handle the uncertainties. For the lung case, the minimax method and the SFUD with MO method yield robust target coverage. The minimax method yields better sparing of the lung than the other methods. For the paraspinal case, the minimax method yields more robust target coverage and better sparing of the spinal cord than the other methods. For the prostate case, the minimax method and the SFUD method yield robust target coverage and the minimax method yields better sparing of the rectum than the other methods. Conclusions: Minimax optimization provides robust target coverage without sacrificing the sparing of healthy tissues, even in the presence of low density lung tissue and high density titanium implants. Conventional methods using margins, SFUD, and MO do not utilize the full potential of IMPT and deliver unnecessarily high doses to healthy tissues.

  • 244.
    Yang, Yuecheng
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Högberg, M.
    Multirate asynchronous state and parameter estimation for centrifugal compressors2011Conference paper (Refereed)
    Abstract [en]

    A number of strategies for state and parameter estimation for a centrifugal compressor system are investigated using a nonlinear dynamical model. It is found that high frequency measurements can be combined with lower frequency measurements to achieve high fidelity state estimation for stable equilibria, limit cycles, as well as transients using either a multirate discrete extended Kalman filter or a data fusion based algorithm with one independent estimator per measurement. When there is a change in one of the parameters of the system only a filter designed to adapt to such changes produces estimates with acceptable errors for a locally stable equilibrium.

  • 245. Montijano, E.
    et al.
    Thunberg, J.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Sagues, C.
    Multi-robot distributed visual consensus using epipoles2011In: Proc IEEE Conf Decis Control, IEEE, 2011, p. 2750-2755Conference paper (Refereed)
    Abstract [en]

    In this paper we give a distributed solution to the problem of making a team of non-holonomic robots achieve the same heading (attitude consensus problem) using vision sensors with limited field of view. The use of cameras with constrained field of view limits the information the robots perceive compared to other omnidirectional sensors. This makes the consensus problem more complicated, because the robots will not always be able to observe other robots. By using structure from motion computed from images, the robots can estimate the difference in their headings from common observations of the environment without the necessity of directly observe each other. In this way, the robots achieve the consensus in their headings while observing the environment instead of each other. The contribution of the paper is a new controller that uses the epipoles computed from pairs of images to estimate the misalignment between neighbor robots. In addition, the control is robust to changes in the topology of the network and does not require to know the calibration of the cameras in order to achieve the desired configuration. To the best of our knowledge, this is the first time that the epipoles are used in multi-robot consensus, putting their properties in value.

  • 246. Curtain, Ruth
    et al.
    Sasane, Amol
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    ON RICCATI EQUATIONS IN BANACH ALGEBRAS2011In: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 49, no 2, p. 464-475Article in journal (Refereed)
    Abstract [en]

    Let R be a commutative complex Banach algebra with the involution .* and suppose that A is an element of R-nxn, B is an element of R-nxm, C is an element of R-pxn. The question of when the Riccati equation PBB*P - PA - A*P - C*C = 0 has a solution P is an element of R-nxn is investigated. A counterexample to a previous result in the literature on this subject is given, followed by sufficient conditions on the data guaranteeing the existence of such a P. Finally, applications to spatially distributed systems are discussed.

  • 247.
    Thunberg, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Optimal output consensus control for systems of agents with continuous linear dynamics2011In: IFAC Proc. Vol. (IFAC-PapersOnline), 2011, no PART 1, p. 10050-10055Conference paper (Refereed)
    Abstract [en]

    In this paper we study the output consensus problem for systems of agents with linear continuous, time invariant dynamics. We derive control laws with minimal energy that solves the problem, while using only relative information. Instead of considering a fixed communication topology for the agents, and derive the optimal control for that topology, we derive the optimal control law for any communication topology between the agents. We show that the optimal control uses only relative information but requires the connectivity graph to be complete and in general requires measurements of the state errors. We identify the cases where the optimal control is only based on output errors, and show that in the infinite time horizon case, the optimal controller can always be expressed as a dynamic controller that is only based on the output errors. Regarding the theoretic contributions of this paper, the control laws are derived using methods from linear vector space optimization and are given in closed form. To the authors knowledge these methods have not been used within this context before.

  • 248.
    Eriksson, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Svanberg, Krister
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Optimization in simulations of human movement planning2011In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 87, no 12, p. 1127-1147Article in journal (Refereed)
    Abstract [en]

    This paper discusses optimization algorithms in movement simulations for models of humans, humanoid robots or other mechanisms. Targeted movements between two configurations define a dynamically redundant system, for which there is freedom in the choice of control force time variations. A previously developed formulation for the treatment of targeted dynamics for mechanisms was used as a basis. The paper describes the development of an algorithm related to the method of moving asymptotes for the necessary optimization. The algorithm is specifically adapted to problems which are large and non-linear but sparse, and which include very high numbers of design variables as well as constraints. In particular, non-linear equality constraints from dynamic equilibrium equations are important. The optimization algorithm was developed to include these, but also in order to allow successively increasing penalty factors for constraint violations. The resulting setting was shown to be able to handle the systems established, robustly giving convergence to at least a local minimum also for very distant start iterates. The existence of very closely situated local optima, representing very similar movements, was discovered for the problem formulation, calling for an ad hoc method for finding the best of these local optima.

  • 249.
    Fallgren, Mikael
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Optimization of Joint Cell, Channel and Power Allocation in Wireless Communication Networks2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis we formulate joint cell, channel and power allocation problems within wireless communication networks. The objectives are to maximize the user with mini- mum data throughput (Shannon capacity) or to maximize the total system throughput, referred to as the max-min and max-sum problem respectively. The complexity is stud- ied together with proposed optimization- and heuristic-based approaches.

    In the first paper an overall joint cell, channel and power allocation max-min prob- lem is formulated. We show that the decision problem is NP-hard and that the op- timization problem is not approximable unless P is equal to NP, for instances with a sufficiently large number of channels. Further, it follows that for a feasible binary cell and channel allocation, the remaining continuous power allocation optimization problem is still not approximable unless P is equal to NP. In addition, it is shown that first-order optimality conditions give global optimum of the single channel power al- location optimization problem, although the problem is in general not convex.

    In the following two papers heuristics for solving the overall problem are proposed. In the second paper we consider the single channel problem with convex combinations of the max-min and the max-sum objective functions. This variable utility provides the ability of tuning the amount of fairness and total throughput. The third paper investi- gates the multiple channel setting. On a system with three cells, eight mobile users and three channels, we perform an exhaustive search over feasible cell and channel alloca- tions. The exhaustive search is then compared to the less computationally expensive heuristic approaches, presenting potential earnings to strive for. A conclusion is that several of the proposed heuristics perform very well.

    The final paper incorporates fixed relay stations into the overall joint cell, channel and power allocation max-min problem. The complexity is inherited from the formula- tion without relay stations. Further, we propose a heuristic channel allocation approach that shows good performance, compared to an optimization based approach, in numer- ical simulations on the relay setting.

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  • 250. Hartikainen, Markus
    et al.
    Miettinen, Kaisa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Wiecek, Margaret M
    Clemson University.
    PAINT: An Interpolation method for Computationally Expensive Multiobjective Optimization Problems2011Report (Other academic)
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