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  • 251.
    Bottegal, Giulio
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Risuleo, Riccardo Sven
    KTH, School of Electrical Engineering (EES), Automatic Control. 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.
    Blind system identification using kernel-based methods2015Conference paper (Refereed)
    Abstract [en]

    We propose a new method for blind system identification (BSI). Resorting to a Gaussian regression framework, we model the impulse response of the unknown linear system as a realization of a Gaussian process. The structure of the covariance matrix (or kernel) of such a process is given by the stable spline kernel, which has been recently introduced for system identification purposes and depends on an unknown hyperparameter. We assume that the input can be linearly described by few parameters. We estimate these parameters, together with the kernel hyperparameter and the noise variance, using an empirical Bayes approach. The related optimization problem is efficiently solved with a novel iterative scheme based on the Expectation-Maximization (EM) method. In particular, we show that each iteration consists of a set of simple update rules. Through some numerical experiments we show that the proposed method give very promising performance.

  • 252. Bouman, N.
    et al.
    Borst, S.
    Van Leeuwaarden, J.
    Proutiere, Alexandre
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Backlog-based random access in wireless networks: Fluid limits and delay issues2011In: Proceedings of the 2011 23rd International Teletraffic Congress, ITC 2011, 2011, p. 39-46Conference paper (Refereed)
    Abstract [en]

    We explore the spatio-temporal congestion dynamics of wireless networks with backlog-based random-access mechanisms. While relatively simple and inherently distributed in nature, suitably designed backlog-based access schemes provide the striking capability to match the optimal throughput performance of centralized scheduling algorithms in a wide range of scenarios. In the present paper, we show that the specific activity functions for which maximum stability has been established, may however yield excessive queue lengths and delays. The results reveal that more aggressive/persistent access schemes can improve the delay performance, while retaining the maximum stability guarantees in a rich set of scenarios. In order to gain qualitative insights and examine stability properties we will investigate fluid limits where the system dynamics are scaled in space and time. As it turns out, several distinct types of fluid limits can arise, exhibiting various degrees of randomness, depending on the structure of the network, in conjunction with the form of the activity functions. We further demonstrate that, counter to intuition, additional interference may improve the delay performance in certain cases. Simulation experiments are conducted to illustrate and validate the analytical findings.

  • 253.
    Bratt, Ola
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Robust and Adaptive Sliding Mode Controller for Machine Tool with Varying Inertia2006Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis considers the problem of designing a robust controller that achieves highperformance positioning and reference tracking of a machine tool. Specifically, the machine tool is a XY-table used in high-accuracy/high speed milling applications. The XY-table consists of a DC motor drive connected to the load using a ball screw, and can be modelled as a two-mass system. However, the presence of friction and backlash requires nonlinear models and associated control designs. Moreover, the machine tool needs to operate under a wide variety of load conditions, which necessitates a robust design.

    The starting point of this thesis is a PID controller comprised of position and velocity feedback loops, velocity and acceleration feed-forward controls and a nonlinear friction compensator. With this controller as a baseline, we develop two advanced controllers of sliding mode type: one is based on disturbance observer theory, while the other uses adaptive methods. It turns out that the controller based on disturbance observer theory fails to improve the performance of the baseline PID solution. However, the controller based on adaptive methods achieves superior performance towards the PID controller.

  • 254. Briat, C.
    et al.
    Yavuz, E.A
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The Conservation of Information, Towards an Axiomatized Modular Modeling Approach to Congestion Control2015In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 23, no 3, p. 851-865Article in journal (Refereed)
    Abstract [en]

    We derive a modular fluid-flow network congestion control model based on a law of fundamental nature in networks: the conservation of information. Network elements such as queues, users, and transmission channels and network performance indicators like sending/acknowledgment rates and delays are mathematically modeled by applying this law locally. Our contributions are twofold. First, we introduce a modular metamodel that is sufficiently generic to represent any network topology. The proposed model is composed of building blocks that implement mechanisms ignored by the existing ones, which can be recovered from exact reduction or approximation of this new model. Second, we provide a novel classification of previously proposed models in the literature and show that they are often not capable of capturing the transient behavior of the network precisely. Numerical results obtained from packet-level simulations demonstrate the accuracy of the proposed model.

  • 255.
    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
    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. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nonlinear state-dependent delay modeling and stability analysis of internet congestion control2010In: 49TH IEEE CONFERENCE ON DECISION AND CONTROL (CDC), 2010, p. 1484-1491Conference paper (Refereed)
    Abstract [en]

    It is shown that the queuing delay involved in the congestion control algorithm is state-dependent and does not depend on the current time. Then, using an accurate formulation for buffers, networks with arbitrary topologies can be built. At equilibrium, our model reduces to the widely used setup by Paganini et al. Using this model, the delay-derivative is analyzed and it is proved that the delay time-derivative does not exceed one for the considered topologies. It is then shown that the considered congestion control algorithm globally stabilizes a delay-free single buffer network. Finally, using a specific linearization result for systems with state-dependent delays from Cooke and Huang, we show the local stability of the single bottleneck network.

  • 256.
    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.

  • 257. Brighenti, C.
    et al.
    Wahlberg, Bo
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Rojas, Cristian R.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Input design using Markov chains for system identification2009In: Proceedings of the 48th IEEE Conference on  Decision and Control, 2009 held jointly with the 2009 28th Chinese Control Conference. CDC/CCC 2009, IEEE conference proceedings, 2009, p. 1557-1562Conference paper (Refereed)
    Abstract [en]

    This paper studies the input design problem for system identification where time domain constraints have to be considered. A finite Markov chain is used to model the input of the system. This allows to directly include input amplitude constraints in the input model by properly choosing the state space of the Markov chain, which is defined so that the Markov chain generates a multi-level sequence. The probability distribution of the Markov chain is shaped in order to minimize the cost function considered in the input design problem. Stochastic approximation is used to minimize that cost function. With this approach, the input signal to apply to the system can be easily generated by extracting samples from the optimal distribution. A numerical example shows how this method can improve estimation with respect to other input realization techniques.

  • 258.
    Brighenti, Chiara
    KTH, School of Electrical Engineering (EES), Automatic Control.
    On Input Design for System Identification: Input Design Using Markov Chains2009Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    When system identification methods are used to construct mathematical models of real systems, it is important to collect data that reveal useful information about the systems dynamics. Experimental data are always corrupted by noise and this causes uncertainty in the model estimate. Therefore, design of input signals that guarantee a certain model accuracy is an important issue in system identification.

    This thesis studies input design problems for system identification where time domain constraints have to be considered. A finite Markov chain is used to model the input of the system. This allows to directly include input amplitude constraints into the input model, by properly choosing the state space of the Markov chain. The state space is defined so that the model generates a binary signal. The probability distribution of the Markov chain is shaped in order to minimize an objective function defined in the input design problem.

    Two identification issues are considered in this thesis: parameter estimation and NMP zeros estimation of linear systems. Stochastic approximation is needed to minimize the objective function in the parameter estimation problem, while an adaptive algorithm is used to consistently estimate NMP zeros.

    One of the main advantages of this approach is that the input signal can be easily generated by extracting samples from the designed optimal distribution. No spectral factorization techniques or realization algorithms are required to generate the input signal.

    Numerical examples show how these models can improve system identification with respect to other input realization techniques.

  • 259.
    Brodén, Daniel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Paridari, Kaveh
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    MATLAB Applications to Generate Synthetic Electricity Load Profiles of Office Buildings and Detached Houses2017In: 2017 IEEE Innovative Smart Grid Technologies - Asia: Smart Grid for Smart Community, ISGT-Asia 2017, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 1-6, 2017Conference paper (Refereed)
    Abstract [en]

    In this paper we present two MATLAB applications that generates synthetic electricity load profiles for office buildings and detached houses down to 1-minute resolution. The applications have been developed using App Designer — a MATLAB environment for application development. The applications are based on consumer load models for office buildings and detached houses published in previous research work. The aim of this paper is to present an overview of the application functionalities, code design, assumptions and limitations, and examples of their potential use in power system education and research. To the author’s knowledge these are the first applications which allow generating synthetic load profiles for office buildings and houses in practical and intuitive manner where building attributes can be easily configured.

  • 260.
    Bromand, Homan
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Hybrid Control System for Reversing a Multibody Vehicle2004Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis deals with the problem of prototyping a vehicle, made up by a motorized body and two passive trailers using LOGO Mindstorms, and provide a hybrid control system supporting the driver while reversing the vehicle.

    The goal of the hybrid system is to switch between different linear controllers, each designed for a specific purpose, to follow a generic path. The approach, when designing the hybrid system, is similar to Dubin’s car problem.

    The prototype will be designed to perform as a stand-alone system and be controlled by its own computer.

    Information about the instant condition of the vehicle is collected by means of a set of onboard sensors. Two angle sensors are used to measure the relative angles between the different parts of the structure, one rotation sensor is used to measure the steering wheel angle and two rotation sensors are used to transform the wheel’s revolution into orientation of a specific point of the vehicle.

    The implementation of the controller consist in a java-program written on a host computer and then downloaded to a robotics command explorer (RCX), equipped with an input-output board that allows to generate the control signal and acquire data from sensors.

  • 261.
    Busson, Adélie
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Immobility control for magnetic gear tooth speed sensing: applied to  automatic metros2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 262.
    Bühler, Lukas
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fuel-Efficient Platooning of Heavy Duty Vehicles through Road Topography Preview Information2013Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Road freight transport is a growing business and serves as a centerpiece of modern economics. Traffic congestions due to the increasing amount of vehicles, growing environmental problems due to CO2 emissions and rising fuel prizes create a vast demand for solutions to these global issues.

    Look ahead cruise control and vehicle platooning can be part of a future transport concept. By using GPS localization and considering road topography data (map data), a Look Ahead Cruise Controller LAC optimizes the velocity profile of a single vehicle when facing steep up- or downhills in order to save fuel. Platooning describes the concept of driving vehicles in a convoy with short intermediate distance to reduce the aerodynamic drag and achieve considerable fuel consumption reductions for all vehicles in the platoon. However, research on platooning with road topography preview information is a novel topic. In this thesis, look ahead cruise control and platooning are analyzed and results are combined in order to develop a platoon look ahead controller (PLAC). The PLAC features low computational complexity due to a simple parametric optimization method and reaches simulated energy consumption reductions of up to 20% for a vehicle in the platoon compared to its single drive on the same road. When velocity limits are considered, the fuel saving potential is even higher. It can be shown that the reached energy consumption with a PLAC lies slightly (1.3%-1.9%) over a minimum energy consumption needed to traverse the road section. Results reveal that in practical situations, a platoon should be maintained whenever possible. Errors in parameters of the vehicle, road parameters and localization errors are analyzed in terms of their influence on the energy consumption. Strategies are presented to reduce the influence of parameter errors on the fuel consumption and especially reduce the chance of a separate of the platoon.

  • 263.
    Cabrera Molero, Inés
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Radio Network Feedback to Improve TCP Utilization over Wireless Links2005Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    During the past years, TCP has proven to be unable to perform properly in wireless environments, with high bandwidth-delay product paths and bandwidth variation. The recent development of advanced 3G networks and services makes it necessary to find ways to improve TCP’s efficiency and resource utilization, as well as improve the user’s experience and reduce latency times.

    This report presents a proxy-based solution called Radio Network Feedback, which aims at improving the performance of TCP over 3G networks. The solution proposes the use of a proxy to split the TCP connection between remote servers and mobile terminals. It manages to adapt the parameters of the connection to the wireless link characteristics, by making use of the information provided by the Radio Network Controller. The results are evaluated through a set of simulations that compare the performance of Radio Network Feedback to that of TCP.

    The simulation results show that the Radio Network Feedback solution greatly improves the link utilization when used over wireless links, compared to TCP. It manages to reduce latency times, especially during Slow Start and after and outage. It also succeeds in maintaining reduced buffer sizes,and properly adapts to varying network conditions.

  • 264.
    Cabrera Molero, Inés
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Möller, Niels
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Petersson, Justus
    Skog, Robert
    Arvidsson, Åke
    Flärdh, Oscar
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Cross-layer adaptation for TCP-based applications in WCDMA systems2005Conference paper (Refereed)
    Abstract [en]

    In this paper, we consider TCP-based applications over a high bandwidth wireless channel, such as the High-Speed Downlink Packet Access (HSDPA) channel in aWCDMAsystem, in two setups: a nominal one that employs end-to-end TCPReno and a new one that employs Cross-Layer Adaptation (CLA) in the form of Radio Network Feedback (RNF). For theCLAsetup, the Radio Resource Management unit in the Radio Network Controller (RNC) provides a proxy with reports on the radio link bandwidth and the queue level. The proxy transport layer takes appropriate actions on these reports. By doing so, it utilizes the air-interface spectrum more efficiently and keeps the layer-2 queue in the RNCclose a predetermined level. These new control mechanisms are evaluated through ns-2 simulations. In a number of realistic use cases it is shown that the new CLAsetup reduces the time to serve users, and substantially increases the radio link utilization and decreases the required buffer size in the RNC.

  • 265. Cantoni, M.
    et al.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Computing the L-2 gain for linear periodic continuous-time systems2009In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 45, no 3, p. 783-789Article in journal (Refereed)
    Abstract [en]

    A method to compute the L-2 gain is developed for the class of linear periodic continuous-time systems that admit a finite-dimensional state-space realisation. A bisection search for the smallest upper bound on the gain is employed, where at each step an equivalent discrete-time problem is considered via the well known technique of time-domain lifting. The equivalent problem involves testing a bound on the gain of a linear shift-invariant discrete-time system, with the same state dimension as the periodic continuous-time system. It is shown that a state-space realisation of the discrete-time system can be constructed from point solutions to a linear differential equation and two differential Riccati equations, all subject to only single-point boundary conditions. These are well behaved over the corresponding one period intervals of integration, and as such, the required point solutions can be computed via standard methods for ordinary differential equations. A numerical example is presented and comparisons made with alternative techniques.

  • 266. Cao, Ming
    et al.
    Olshevsky, Alex
    Xia, Weiguo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Focused First-Followers Accelerate Aligning Followers with the Leader in Reaching Network Consensus2014In: 19th IFAC World Congress 2014: Cape Town, South Africa 24-29 August 2014, 2014, Vol. 9, p. 7819-Conference paper (Refereed)
    Abstract [en]

    This paper proposes and analyzes a new strategy to accelerate the process of reaching consensus in leader-follower networks. By removing or weakening specific directed couplings pointing to the first followers from the other followers, we prove that all the followers' states converge faster to that of the leader. This result is in sharp contrast to the well known fact that when the followers are coupled together through undirected links, removing or weakening links always decelerate the converging process. Simulation results are provided to illustrate this subtle, yet somewhat surprising, provably correct result.

  • 267. Carli, Ruggero
    et al.
    Fagnani, Fabio
    Focoso, Marco
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Zampieri, Sandro
    Symmetries in the coordinated consensus problem2006In: Networked Embedded Sensing And Control / [ed] Antsaklis, PJ; Tabuada, P, Springer Berlin/Heidelberg, 2006, Vol. 331, p. 25-51Conference paper (Refereed)
    Abstract [en]

    In this paper we consider a widely studied problem in the robotics and control communities, called consensus problem. The aim of the paper is to characterize the relationship between the amount of information exchanged by the vehicles and the speed of convergence to the consensus. Time-invariant communication graphs that exhibit particular symmetries are shown to yield slow convergence if the amount of information exchanged does not scale with the number of vehicles. On the other hand, we show that retaining symmetries in time-varying communication networks allows to increase the speed of convergence even in the presence of limited information exchange.

  • 268. Carli, Ruggero
    et al.
    Fagnani, Fabio
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Zampieri, Sandro
    Communication constraints in the average consensus problem2008In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 44, no 3, p. 671-684Article in journal (Refereed)
    Abstract [en]

    The interrelationship between control and communication theory is becoming of fundamental importance in many distributed control systems, such as the coordination of a team of autonomous agents. In such a problem, communication constraints impose limits on the achievable control performance. We consider as instance of coordination the consensus problem. The aim of the paper is to characterize the relationship between the amount of information exchanged by the agents and the rate of convergence to the consensus. We show that time-invariant communication networks with circulant symmetries yield slow convergence if the amount of information exchanged by the agents does not scale well with their number. On the other hand, we show that randomly time-varying communication networks allow very fast convergence rates. We also show that by adding logarithmic quantized data links to time-invariant networks with symmetries, control performance significantly improves with little growth of the required communication effort.

  • 269.
    Carlsson, Hannes
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Development of a Depth Controller for the SEAL Carrier2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The SEAL Carrier is a hybrid marine vessel capable of traveling both fast on the water surface and completely submerged.Due to the craft's hydrodynamical properties it is taxing on the pilots to keep the SEAL Carrier at a certain depth for longer periods of time, therefore it is desirable to have a depth controller. A model was developed to describe the forces from the actuators and the depth, pitch and speed controlled through a PI controller using a backstepping approach. The resulting controller was implemented and validated in Simulink and, as there exist a Simulink model of the craft, also tested and tuned. The Simulink implementation was turned into C++ code in order to be implemented on board the SEAL Carrier.The simulations provide promising results, though further tests should be performed to ensure the robustness of the controller, as the Simulink model has difficulties capturing all of the dynamics of the craft.

  • 270. Carlsson, Mats
    et al.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Larson, Jeffrey
    Scheduling double round-robin tournaments with divisional play using constraint programming2017In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 259, no 3, p. 1180-1190Article in journal (Refereed)
    Abstract [en]

    We study a tournament format that extends a traditional double round-robin format with divisional single round-robin tournaments. Elitserien, the top Swedish handball league, uses such a format for its league schedule. We present a constraint programming model that characterizes the general double round-robin plus divisional single round-robin format. This integrated model allows scheduling to be performed in a single step, as opposed to common multistep approaches that decompose scheduling into smaller problems and possibly miss optimal solutions. In addition to general constraints, we introduce Elitserien-specific requirements for its tournament. These general and league-specific constraints allow us to identify implicit and symmetry-breaking properties that reduce the time to solution from hours to seconds. A scalability study of the number of teams shows that our approach is reasonably fast for even larger league sizes. The experimental evaluation of the integrated approach takes considerably less computational effort to schedule Elitserien than does the previous decomposed approach.

  • 271.
    Caro Terrón, Jorge
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Web-based Virtual Laboration of Water Tanks Control System2003Student paper other, 20 credits / 30 HE creditsStudent thesis
  • 272.
    Carretti, Cesare Maria
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Comparison of Distributed Optimization Algorithms in Sensor Networks: Simulations and results2008Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    We consider a peer-to-peer approach to wireless sensor networks using the IEEE 802.15.4 standard, with sensors not synchronized, and without any routing protocol. Only communications between neighbors are allowed. In this scenario we do a comparison between four distributed algorithms that solve a special class of optimization problems, which are of great interest in networking applications. We want to retrieve, without a central node, the average of a scalar measurement from all sensors in the network. In the nal state, each sensor should have the global average of the considered measurement. To evaluate performances of the algorithms, we build an application for the network simulator ns2, and we do several simulations to evaluate convergence delay, and nal error, respect to time and to number of packets sent. In this thesis we present the algorithms from theoretical and practical point of views, we describe our application for ns2, and we show the results obtained, which show that this types of algorithms, if tuned properly, work well and are ready to be practically implemented in a real sensor network.

  • 273.
    Carvalho Bittencourt, André
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Friction change detection in industrial robot arms2007Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Industrial robots have been used as a key factor to improve productivity, quality and safety in manufacturing. Many tasks can be done by industrial robots and they usually play an important role in the system they are used, a robot stop or malfunction can compromise the whole plant as well as cause personal damages. The reliability of the system is therefore very important.

    Nevertheless, the tools available for maintenance of industrial robots are usually based on periodical inspection or a life time table, and do not consider the robot’s actual conditions. The use of condition monitoring and fault detection would then improve diagnosis.

    The main objective of this thesis is to define a parameter based diagnosis method for industrial robots. In the approach presented here, the friction phenomena is monitored and used to estimate relevant parameters that relate faults in the system. To achieve the task, the work first presents robot and friction models suitable to use in the diagnosis. The models are then identified with several different identification methods, considering the most suitable for the application sought.

    In order to gather knowledge about how disturbances and faults affect the friction phenomena, several experiments have been done revealing the main influences and their behavior. Finally, considering the effects caused by faults and disturbances, the models and estimation methods proposed, a fault detection scheme is built in order to detect three kind of behavioral modes of a robot (normal operation, increased friction and high increased friction), which is validated within some real scenarios.

  • 274.
    Carvalho, J. Frederico
    et al.
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Pequito, S.
    Aguiar, A. P.
    Kar, S.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Composability and controllability of structural linear time-invariant systems: Distributed verification2017In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 78, p. 123-134Article in journal (Refereed)
    Abstract [en]

    Motivated by the development and deployment of large-scale dynamical systems, often comprised of geographically distributed smaller subsystems, we address the problem of verifying their controllability in a distributed manner. Specifically, we study controllability in the structural system theoretic sense, structural controllability, in which rather than focusing on a specific numerical system realization, we provide guarantees for equivalence classes of linear time-invariant systems on the basis of their structural sparsity patterns, i.e., the location of zero/nonzero entries in the plant matrices. Towards this goal, we first provide several necessary and/or sufficient conditions that ensure that the overall system is structurally controllable on the basis of the subsystems’ structural pattern and their interconnections. The proposed verification criteria are shown to be efficiently implementable (i.e., with polynomial time-complexity in the number of the state variables and inputs) in two important subclasses of interconnected dynamical systems: similar (where every subsystem has the same structure) and serial (where every subsystem outputs to at most one other subsystem). Secondly, we provide an iterative distributed algorithm to verify structural controllability for general interconnected dynamical system, i.e., it is based on communication among (physically) interconnected subsystems, and requires only local model and interconnection knowledge at each subsystem.

  • 275.
    Castell Hernández, Colette
    KTH, School of Electrical Engineering (EES), Automatic Control.
    HCCI Timing Control Using Iterative Feedback Tuning2006Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Homogeneous Charge Compression Ignition (HCCI) is an engine which combines some of the characteristics of the Diesel and Otto engines. As a result an engine with a high efficiency and low emissions is constructed. Unfortunately, there is not a direct way to control its start of combustion (SOC). One way to phase the SOC is using valve timings. There are two main methods, the Overlap, which consists in trapping more or less residual gas, and the IVC method, which acts affecting the effective compression ratio.

    Iterative Feedback Tuning (IFT) is a control method that appeared in 1994, which has presented good performances in the tuning of PID and more complex controllers. The tuning is done by using data of closed loop experiments with the controller that is being tuned in the loop. Therefore, knowledge of the system and disturbances is not required. That is one of the principal advantages of this method.

    At the department of Machine Design at the Royal Institute of Technology (KTH) there is a single cylinder HCCI engine. It is based on a SCANIA truck engine and it includes an Active Valve Train System. In this equipment a control system based on non-linear compensation is used. Furthermore, a model of the real engine is available.

    In this project a procedure which allows the application of IFT in the HCCI has been developed. The method was tested, first, on a model and, secondly, in the test bed of the HCCI engine explained above. Controllers were tuned for three different operating points of the engine. The overlap method was used in two of them and the IVC method in the third one.

    However, more experience is required to determine how much improvement can be gained with the method. It was also noted that speed transients were very difficult to control due to long time delays.

  • 276.
    Celik, Haris
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Identication and Prediction of Discrete-Time Bilinear State-Space Models: Interaction Matrices and Superstates2010Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this master thesis, an extension of the interaction matrix formulation to the discrete-time bilinear state-space model is derived. Several identication techniques are presented from this formulation to identify the bilinear state-space matrices using a superstate vector, derived from a single set of su-ciently rich input-output measurements. The initial state can be non-zero and unknown. Unlike other approaches, no specialized inputs are required, such as sinusoidal or white inputs, or duration-varying unit pulses involving multiple experiments. For that reason, the bilinear state-space identication problem is di-cult to solve, since it can be seen as a linear time-varying system with input-dependent system matrix or state-dependent input-influence matrix.

    The resultant input-output map from this state-space formulation can be used for output prediction. A relationship between the coe-cients of this input-output map and the bilinear state-space model matrices is obtained via two interaction matrices, corresponding to the linear and bilinear portions of the model, respectively.

    Numerical examples are provided to illustrate these bilinear state-space model identication techniques and the input-output model identication method. It is concluded that the proposed identication algorithms can correctly identify the original bilinear state-space model, and the identied input-output map correctly predict its system output response, despite the fact that the interaction matrices are only implicitly assumed to exist.

  • 277. Chaporkar, P.
    et al.
    Proutière, Alexandre
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Optimal distributed scheduling in wireless networks under SINR interference model2013In: 2013 51st Annual Allerton Conference on Communication, Control, and Computing, Allerton 2013, IEEE conference proceedings, 2013, p. 1372-1379Conference paper (Refereed)
    Abstract [en]

    Radio resource sharing mechanisms are key to ensuring good performance in wireless networks. In their seminal paper [1], Tassiulas and Ephremides introduced the Maximum Weighted Scheduling algorithm, and proved its throughput-optimality. Since then, there have been extensive research efforts to devise distributed implementations of this algorithm. Recently, distributed adaptive CSMA scheduling schemes [2] have been proposed and shown to be optimal, without the need of message passing among transmitters. However their analysis relies on the assumption that interference can be accurately modelled by a simple interference graph. In this paper, we consider the more realistic and challenging SINR interference model. We present the first distributed scheduling algorithms that (i) are optimal under the SINR interference model, and (ii) that do not require any message passing. They are based on a combination of a simple and efficient power allocation strategy referred to as Power Packing and randomization techniques. These algorithms are rate-optimal in the sense that they perform as well as the best centralized scheduling schemes in scenarios where each transmitter is aware of the rate at which it should send packets to the corresponding receiver. As shown in [3], rate-optimal algorithms can be extended easily so that they reach throughput-optimality.

  • 278. Chaporkar, Prasanna
    et al.
    Magureanu, Stefan
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Proutiere, Alexandre
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Optimal Distributed Scheduling in Wireless Networks Under the SINR Interference Model2016In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 24, no 4, p. 2033-2045Article in journal (Refereed)
    Abstract [en]

    In wireless networks, the design of radio resource sharing mechanisms is complicated by the complex interference constraints among the various links. In their seminal paper (IEEE Trans. Autom. Control, vol. 37, no. 12, pp. 1936-1948), Tassiulas and Ephremides introduced Maximum Weighted Scheduling, a centralized resource sharing algorithm, and proved its optimality. Since then, there have been extensive research efforts to devise distributed implementations of this algorithm. Recently, distributed adaptive CSMA scheduling schemes have been proposed and shown to be optimal, without the need of message passing among transmitters. However, their analysis relies on the assumption that interference can be accurately modeled by a simple interference graph. In this paper, we consider the more realistic and challenging signal-to-interference-plus-noise ratio (SINR) interference model. We present distributed scheduling algorithms that: 1) are optimal under the SINR interference model; and 2) do not require any message passing. These algorithms are based on a combination of a simple and efficient power allocation strategy referred to as Power Packing and randomization techniques. The optimality of our algorithms is illustrated in various traffic scenarios using numerical experiments.

  • 279. Charalambous, Charalambos D.
    et al.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hadjicostis, Christoforos N.
    Team Optimality Conditions of Differential Decision Systems with Nonclasssical Information Structures2014In: 2014 European Control Conference (ECC), IEEE , 2014, p. 2851-2856Conference paper (Refereed)
    Abstract [en]

    We derive team optimality conditions for differential decision systems with nonclassical information structures. The necessary conditions of optimality are given in terms of Hamiltonian system of equations consisting of a coupled backward and forward differential equations and a Hamiltonian projected onto the subspace generated by the information structures. Under certain global convexity conditions it is shown that person-by-person optimality implies team optimality.

  • 280.
    Charalambous, Charalambos D.
    et al.
    University of Cyprus.
    Tziortzis, Ioannis
    University of Cyprus.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dynamic programming with total variational distance uncertaint2012In: Decision and Control (CDC), 2012 IEEE 51st Annual Conference on, IEEE , 2012, p. 1909-1914Conference paper (Refereed)
    Abstract [en]

    The aim of this paper is to address optimality of stochastic control strategies via dynamic programming subject to total variational distance uncertainty on the conditional distribution of the controlled process. Utilizing concepts from signed measures, the maximization of a linear functional on the space of probability measures on abstract spaces is investigated, among those probability measures which are within a total variational distance from a nominal probability measure. The maximizing probability measure is found in closed form. These results are then applied to solve minimax stochastic control with deterministic control strategies, under a Markovian assumption on the conditional distributions of the controlled process. The results include: 1) Optimization subject to total variational distance constraints, 2) new dynamic programming recursions, which involve the oscillator seminorm of the value function.

  • 281.
    Charalambous, Charalambos D.
    et al.
    University of Cyprus.
    Tziortzis, Ioannis
    University of Cyprus.
    Loyka, Sergey
    University of Ottawa.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Extremum Problems with Total Variation Distance2013In: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC), IEEE conference proceedings, 2013, p. 1204-1209Conference paper (Refereed)
    Abstract [en]

    The aim of this paper is to investigate extremum problems with pay-off the total variational distance metric subject to linear functional constraints both defined on the space of probability measures, as well as related problems. Utilizing concepts from signed measures, the extremum probability measures of such problems are obtained in closed form, by identifying the partition of the support set and the mass of these extremum measures on the partition. The results are derived for abstract spaces, specifically, complete separable metric spaces, while the high level ideas are also discussed for denumerable spaces endowed with the discrete topology.

  • 282. Charalambous, Charalambos D.
    et al.
    Tzortzis, Ioannis
    Loyka, Sergey
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Extremum Problems With Total Variation Distance and Their Applications2014In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 9, p. 2353-2368Article in journal (Refereed)
    Abstract [en]

    The aim of this paper is to investigate extremum problems with pay-off being the total variation distance metric defined on the space of probability measures, subject to linear functional constraints on the space of probability measures, and vice-versa; that is, with the roles of total variation metric and linear functional interchanged. Utilizing concepts from signed measures, the extremum probability measures of such problems are obtained in closed form, by identifying the partition of the support set and the mass of these extremum measures on the partition. The results are derived for abstract spaces; specifically, complete separable metric spaces known as Polish spaces, while the high level ideas are also discussed for denumerable spaces endowed with the discrete topology. These extremum problems often arise in many areas, such as, approximating a family of probability distributions by a given probability distribution, maximizing or minimizing entropy subject to total variation distance metric constraints, quantifying uncertainty of probability distributions by total variation distance metric, stochastic minimax control, and in many problems of information, decision theory, and minimax theory.

  • 283.
    Charalambous, T.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Power control inwireless ad hoc networks: Stability and convergence under uncertainties2013In: Springer Optimization and Its Applications, Springer, 2013, p. 143-174Conference paper (Refereed)
    Abstract [en]

    A successful distributed power control algorithm requires only local measurements for updating the power level of a transmitting node, so that eventually all transmittersmeet their QoS requirements, i.e. the solution converges to the global optimum. There are numerous algorithmwhich claim to work under ideal conditions in which there exist no uncertainties and the model is identical to the real-world implementation. Nevertheless, the problem arises when real-world phenomena are introduced into the problem, such as uncertainties (such as changing environment and time delays) or the QoS requirements cannot be achieved for all the users in the network. In this chapter, we study some distributed power control algorithms for wireless ad hoc networks and discuss their robustness to real-world phenomena. Simulations illustrate the validity of the existing results and suggest directions for future research.

  • 284.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Charalambous, Charalambos D.
    Rezaei, Farzad
    Optimal Merging Algorithms for Lossless Codes With Generalized Criteria2014In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 60, no 9, p. 5486-5499Article in journal (Refereed)
    Abstract [en]

    This paper presents lossless prefix codes optimized with respect to a payoff criterion consisting of a convex combination of maximum codeword length and average codeword length. The optimal codeword lengths obtained are based on a new coding algorithm, which transforms the initial source probability vector into a new probability vector according to a merging rule. The coding algorithm is equivalent to a partition of the source alphabet into disjoint sets on which a new transformed probability vector is defined as a function of the initial source probability vector and scalar parameter. The payoff criterion considered encompasses a tradeoff between maximum and average codeword length; it is related to a payoff criterion consisting of a convex combination of average codeword length and average of an exponential function of the codeword length, and to an average codeword length payoff criterion subject to a limited length constraint. A special case of the first related payoff is connected to coding problems involving source probability uncertainty and codeword overflow probability, whereas the second related payoff compliments limited length Huffman coding algorithms.

  • 285.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Hadjicostis, C. N.
    Average consensus in the presence of dynamically changing directed topologies and time delays2014In: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2014, no February, p. 709-714Conference paper (Refereed)
    Abstract [en]

    We have recently proposed a robustified ratio consensus algorithm which achieves asymptotic convergence to the global average in a distributed fashion in static strongly connected digraphs, despite the possible presence of bounded but otherwise arbitrary delays. In this work, we propose a protocol which reaches asymptotic convergence to the global average in a distributed fashion under possible changes in the underlying interconnection topology (e.g., due to component mobility), as well as time-varying delays that might affect transmissions at different times. More specifically, we extend our previous work to also account for the case where, in addition to arbitrary but bounded delays, we may have time varying communication links. The proposed protocol requires that each component has knowledge of the number of its outgoing links, perhaps with some bounded delay, and that the digraphs formed by the switching communication topologies over a finite time window are jointly strongly connected.

  • 286.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Hadjicostis, Christoforos N.
    Electrical and Computer Engineering Department, University of Cyprus.
    Distributed Formation of Balanced and Bistochastic Weighted Digraphs in Multi-Agent Systems2013In: 2013 European Control Conference (ECC), IEEE , 2013, p. 1752-1757Conference paper (Refereed)
    Abstract [en]

    We propose two distributed algorithms, one for solving the weight-balance problem and another for solving the bistochastic matrix formation problem, in a distributed system whose components (nodes) can exchange information via interconnection links (edges) that form an arbitrary, possibly directed, strongly connected communication topology (digraph). Both distributed algorithms achieve their goal asymptotically and operate iteratively by having each node adapt the (nonnegative) weights on its outgoing edges based on the weights of its incoming links. The weight-balancing algorithm is shown to admit geometric convergence rate, whereas the second algorithm, which is a modification of the weight-balancing algorithm, leads asymptotically to a bistochastic digraph with geometric convergence rate for a certain set of initial values. The two algorithms perform better than existing approaches, as illustrated by the examples we provide.

  • 287.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hadjicostis, Christoforos N.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Minimum-Time Weight Balancing over Digraphs2014Conference paper (Refereed)
    Abstract [en]

    We address the weight-balancing problem for a distributed system whose components (nodes) can exchange information via interconnection links (edges) that form an arbitrary, possibly directed, communication topology (digraph). A weighted digraph is balanced if, for each node, the sum of the weights of the edges outgoing from that node is equal to the sum of the weights of the edges incoming to that node. Weight-balanced digraphs play a key role in a variety of applications, such as coordination of groups of robots, distributed decision making, and distributed averaging which is important for a wide range of applications in signal processing. We propose a distributed algorithm for solving the weight balancing problem in a minimum number of iterations, when the weights are nonnegative real numbers. We also provide examples to corroborate the proposed algorithm.

  • 288. Charalambous, Themistoklis
    et al.
    Hadjicostis, Christoforos N.
    Rabbat, Michael G.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Totally asynchronous distributed estimation of eigenvector centrality in digraphs with application to the PageRank problem2016In: 2016 IEEE 55th Conference on Decision and Control, CDC 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 25-30, article id 7798241Conference paper (Refereed)
    Abstract [en]

    We propose a distributed coordination mechanism which enables nodes in a directed graph to accurately estimate their eigenvector centrality (eigencentrality) even if they update their values at times determined by their own clocks. The clocks need neither be synchronized nor have the same speed. The main idea is to let nodes adjust the weights on outgoing links to compensate for their update speed: the higher the update frequency, the smaller the link weights. Our mechanism is used to develop a distributed algorithm for computing the PageRank vector, commonly used to assign importance to web pages and rank search results. Although several distributed approaches in the literature can deal with asynchronism, they cannot handle the different update speeds that occur when servers have heterogeneous computational capabilities. When existing algorithms are executed using heterogeneous update speeds, they compute incorrect PageRank values. The advantages of our algorithm over existing approaches are verified through illustrative examples.

  • 289.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Kalyviannaki, Evangelia
    City University London.
    Hadjicostis, Christoforos N.
    Electrical and Computer Engineering Department, University of Cyprus.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Distributed Offline Load Balancing in MapReduce Networks2013In: 2013 IEEE 52ND ANNUAL CONFERENCE ON DECISION AND CONTROL (CDC), IEEE conference proceedings, 2013, p. 835-840Conference paper (Refereed)
    Abstract [en]

    In this paper we address the problem of balancing the processing load of MapReduce tasks running on heterogeneous clusters, i.e., clusters with different capacities and update cycles. We present a fully decentralized algorithm, based on ratio consensus, where each mapper decides the amount of workload data to handle for a single user job using only job specific local information, i.e., information that can be collected from directly connected neighboring mappers, regarding their current workload and capacity. In contrast to other algorithms in the literature, the proposed algorithm can be deployed in heterogeneous networks and can operate asynchronously in both directed and undirected communication topologies. The performance of the proposed algorithm is demonstrated via simulation experiments on large-scale strongly connected topologies. 

  • 290.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Klerides, Evelina
    Imperial College London.
    Wiesemann, Wolfram
    Imperial College London.
    Vassiliou, Angelos
    University of Cyprus.
    Hadjitheophanous, Stavros
    Deliparaschos, Kyriakos
    Cyprus University of Technology.
    On the Minimum Latency Transmission Scheduling in Wireless Networks with Power Control under SINR Constraints2013In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 26, no 3, p. 367--379Article in journal (Refereed)
    Abstract [en]

    In order to alleviate interference and contention in a wireless network, we may exploit the existence of multiple orthogonal channels or time slots, thus achieving a substantial improvement in performance. In this paper, we study a joint transmission scheduling and power control problem that arises in wireless networks. The goal is to assign channels (or time slots) and transmitting powers to communication links such that all communication requests are processed correctly, specified quality-of-service requirements are met, and the number of required time slots is minimised. First, we formulate the problem as a mixed-integer linear programming. Then, we show that the problem considered is non-deterministic polynomial-time hard, and subsequently, we propose non-trivial bounding techniques to solve it. Optimisation methods are also discussed, including a column generation approach, specifically designed to find bounds for the transmission scheduling problem. Moreover, we develop optimisation techniques in which the bounding techniques are integrated in order to derive the optimal solution to the problem faster. We close with an extensive computational study, which shows that despite the complexity of the problem, the proposed methodology scales to problems of non-trivial size. Our algorithms can therefore be used for static wireless networks where propagation conditions are almost constant and a centralised agent is available (e.g. cellular networks where the base station can act as a centralised agent or wireless mesh networks), and they can also serve as a benchmark for the performance evaluation of heuristic, approximation or distributed algorithms that aim to find near-optimal solutions without information about the whole network. 

  • 291.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Krikidis, I.
    Medium access control via contention-based distributed power control2012In: 2012 8th International Wireless Communications And Mobile Computing Conference (IWCMC), IEEE , 2012, p. 555-560Conference paper (Refereed)
    Abstract [en]

    A successful distributed power control algorithm requires only local measurements for updating the power level of a transmitting node, so that eventually all transmitters meet their QoS requirements. Nevertheless, the problem arises when the QoS requirements cannot be achieved for all the users in the network. In this paper, a distributed algorithm for wireless ad hoc networks which is contention-based and makes use of a back off mechanism is proposed. This algorithm aims to eliminate overhead communication, improve fairness, allow nodes to operate asynchronously while establishing some performance level. The performance of the algorithm is evaluated via simulations.

  • 292.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Krikidis, I.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Precoding decision for full-duplex X-relay channel with Decode-And-Forward2014In: IWCMC 2014 - 10th International Wireless Communications and Mobile Computing Conference, IEEE , 2014, p. 791-796Conference paper (Refereed)
    Abstract [en]

    In this paper, we study a simple X-relay configuration where the shared relay operates in full-duplex (FD) mode. The relay node may have limited spatial degrees of freedom, and as a result, it may not be able to handle both the loop interference and the multiuser interference. Hence, a decision on the precoding scheme is necessitated. It is often the case that the relay does not have the option of real-Time switching between different precoding schemes, either due to hardware limitations of the relay or increased complexity of the problem. Hence, we investigate a 'static' precoding decision where the relay node decides on its precoding scheme based only on statistical knowledge of the channel conditions. To perform this decision, the behavior of the system is formulated as a Markov chain and the outage probability of the system is derived in a closed-form with the precoding decision as a parameter. The outage probability is minimized by optimally choosing the precoding scheme, using easily verifiable conditions on the statistical knowledge of the channel conditions. Simulations validate the investigated scheme.

  • 293.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nomikos, Nikolaos
    Krikidis, Ioannis
    Vouyioukas, Demosthenes
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Modeling Buffer-Aided Relay Selection in Networks With Direct Transmission Capability2015In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 19, no 4, p. 649-652Article in journal (Refereed)
    Abstract [en]

    We consider a wireless relay network that consists of a source, half-duplex decode-and-forward buffer-aided relays and a destination. While the majority of previous works on relay selection assume no direct transmission between source and destination in such a setting, we lift this assumption and propose a link selection policy that exploits both the buffering ability and the opportunity for successful reception of a packet directly from the source. The proposed relay selection scheme incorporates the instantaneous strength of the wireless links and adapts the relay selection decision based on the strongest available link. The evolution of the network as a whole is modeled by means of a Markov chain and thus, the outage probability is associated with the steady state of the Markov chain. It is deduced that even if the link between the source and the destination is in principle a very unreliable link, it is always beneficial for the source to multicast a packet to both the relay with the strongest available link and the destination.

  • 294.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rabbat, M. G.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hadjicostis, C. N.
    Distributed Finite-Time Computation of Digraph Parameters: Left-Eigenvector, Out-Degree and Spectrum2016In: IEEE Transactions on Control of Network Systems, ISSN 2325-5870, Vol. 3, no 2, p. 137-148, article id 7100912Article in journal (Refereed)
    Abstract [en]

    Many of the algorithms that have been proposed in the field of distributed computation rely on assumptions that require nodes to be aware of some global parameters. In this paper, we propose algorithms to compute some network parameters in a distributed fashion and in a finite number of steps. More specifically, given an arbitrary strongly connected network of interconnected nodes, by adapting a distributed finite-time approach, we develop distributed strategies that enable nodes to compute the following network parameters: the left-eigenvector, the out-degree, and the spectrum of weighted adjacency matrices.

  • 295.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yuan, Ye
    University of Cambridge.
    Yang, Tao
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pan, Wei
    Imperial College London.
    Hadjicostis, Christoforos N.
    University of Cyprus.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Decentralised Minimum-Time Average Consensus in Digraphs2013In: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC), IEEE conference proceedings, 2013, p. 2617-2622Conference paper (Refereed)
    Abstract [en]

    Distributed algorithms for average consensus in directed graphs are typically asymptotic in the literature. In this work, we propose a protocol to distributively reach average consensus in a finite number of steps on interconnection topologies that form strongly connected directed graphs (digraphs). The average consensus value can be computed, based exclusively on local observations at each component, by running a protocol that requires each component to observe and store its own value over a finite and minimal number of steps, and to have knowledge of the number of its out-going links (i.e., the number of components to which it sends information). The proposed algorithm is demonstrated via illustrative examples.

  • 296.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yuan, Ye
    Yang, Tao
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pan, Wei
    Hadjicostis, Christoforos N.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Distributed Finite-Time Average Consensus in Digraphs in the Presence of Time Delays2015In: IEEE TRANSACTIONS ON CONTROL OF NETWORK SYSTEMS, ISSN 2325-5870, Vol. 2, no 4, p. 370-381Article in journal (Refereed)
    Abstract [en]

    Most algorithms for distributed averaging only guarantee asymptotic convergence. This paper introduces a distributed protocol that allows nodes to find the exact average of the initial values in a finite and minimum number of steps on interconnection topologies described by strongly connected directed graphs (digraphs). More specifically, under the assumption that each component has knowledge of the number of its outgoing links (i.e., the number of components to which it sends information), we show that the average value can be computed based on local observations over a finite time interval. The average can be obtained in a finite number of steps even when the information exchange is subject to delays. The proposed algorithm is the first in the literature that allows for distributed computation of the exact average in digraphs in finite time, with and without delays.

  • 297.
    Chatzis, Ioannis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Motion Planning of Multi-Agent Systems under Temporal Logic Specifications2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis, a top-down hierarchical framework is proposed to deal with multiagentsymbolic motion planning and control. Agents are assigned a distributable globalmission, and are partitioned into leaders and followers. The global mission is distributedamong the followers and each one synthesizes a discrete motion plan. By exploitingthe concept of network controllability, an open-loop optimal control law is synthesizedcentrally and executed in a distributed manner. This control law guarantees the concurrentexecution and fulfillment of the followers’ discrete motion plans. Simulations areperformed to verify the proposed control law both for single- and multi-leader, leaderfollowernetworks.

  • 298. Chen, J.
    et al.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Olariu, S.
    Paschalidis, I.Ch.
    Stojmenovic, I.
    Guest Editorial Special Issue on Wireless Sensor and Actuator Networks2011In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 56, no 10, p. 2244-2246Article in journal (Refereed)
  • 299. Chen, J.
    et al.
    Wei, Jieqiang
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Chen, Wei
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. University of California at Berkeley, United States.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Protecting Positive and Second-Order Systems against Undetectable Attacks2017In: IFAC-PapersOnLine, ISSN 2405-8963, Vol. 50, no 1, p. 8373-8378Article in journal (Refereed)
    Abstract [en]

    Undetectable attacks in security studies of cyber-physical systems render the measurements of the system equal to a possible physical response. In this paper, we investigate defense strategies against the undetectable single-attack for positive systems and second-order systems, which both can be reinterpreted in terms of graphs with nodes and edges, while the undetectable attack is added through one of the nodes. We show that an arbitrary placement of a sensor prevents undetectable single-attack for these classes of systems. It is worth emphasising that we do not need to measure at the corrupted node to prevent the undetectable single-attack, but can measure at any node. The defense strategy is of a low complexity and can be readily implemented.

  • 300.
    Chen, Phoebus
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Ramesh, Chithrupa
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Reducing Packet Loss Bursts in a Wireless Mesh Network for Stochastic Guarantees on Estimator Performance2011In: 2011 50th IEEE Conference on Decision and Control andEuropean Control Conference (CDC-ECC), 2011Conference paper (Refereed)
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