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  • 101.
    Araujo, Jose
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Design and Implementation of Resource-Aware Wireless Networked Control Systems2011Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Networked control over wireless sensor and actuator systems is of growing importancein many application domains. Energy and communication bandwidth are scarce resources in such systems. Despite that feedback control might only be needed occasionally, sensor and actuator communications are often periodic and with high frequency in today’s implementations. In this thesis, resource-constrained wireless networked control systems with an adaptive sampling period are considered.

    Our first contribution is a system architecture for aperiodic wireless networked control. As the underlying data transmission is performed over a shared wireless network, we identify scheduling policies and medium access controls that allow for an efficient implementation of sensor communication. We experimentally validate three proposed mechanisms and show that best performance is obtained by a hybrid scheme, combining the advantages of event- and self-triggered control as well as the possibilities provided by contention-based and contention-free medium accesscontrol.

    In the second contribution, we propose an event-triggered PI controller for wireless process control systems. A novel triggering mechanism which decides the transmission instants based on an estimate of the control signal is proposed. It addresses some side-effects that have been discovered in previous PI proposals, which trigger on the state of the process. Through simulations we demonstrate that the new PI controller provides setpoint tracking and disturbance rejection close to a periodic PI controller, while reducing the required network resources.

    The third contribution proposes a co-design of feedback controllers and wireless medium access. The co-design is formulated as a constrained optimization problem, whereby the objective function is the energy consumption of the network and the constraints are the packet loss probability and delay, which are derived from the performance requirements of the control systems. The design framework is illustrated in a numerical example.

  • 102.
    Araujo, Jose
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ariba, Yassine
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Park, Pangun
    KTH, School of Electrical Engineering (EES), Automatic Control. 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.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Control over a Hybrid MAC Wireless Network2010In: 2010 IEEE 1ST INTERNATIONAL CONFERENCE ON SMART GRID COMMUNICATIONS, 2010, p. 197-202Conference paper (Refereed)
    Abstract [en]

    Wireless Sensor Networks and Control Systems are an essential part of the Smart Grid. We consider the problem of performing control over large complex networked systems with packet drops. More specifically, we are interested in improving the performance of the regulation of control loops when the communication is made over low-cost wireless networks. In control over wireless networks it is common to use Contention-Free (CF) schemes where no losses occur with the price of low scalability and complicated scheduling policies. In this work we propose a hybrid MAC and control architecture, where a small number of control loops with high demand of attention are scheduled in a CF scheme and well regulated loops are scheduled in a lossy, asynchronous and highly scalable, Contention-Access (CA) scheme. We model and analyze the performance of such system with Markov Jump Linear System (MJLS) tools and compare it with other architecture types. Performance is evaluated using a quadratic cost function of the state.

  • 103.
    Araujo, Jose
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fawzi, Hamza
    Department of Electrical Engineering, University of California Los Angeles, USA.
    Mazo Jr., Manuel
    INCAS 3 & University of Groningen, The Netherlands.
    Tabuada, Paulo
    Department of Electrical Engineering, University of California Los Angeles, USA.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    An improved self-triggered implementation for linear controllers2012Conference paper (Refereed)
    Abstract [en]

    Research in networked control systems raised the importance of understanding what are thetiming requirements for control. In recent years this problem has been attacked from multiple anglesincluding the computation of Maximal Allowable Transmission Intervals, event-triggered, and selftriggered controller implementations. In a self-triggered implementation the controller is responsible forcomputing the next time instant at which the actuator values should be updated by evaluating the controllaw on fresh sensor measurements. One of the main challenges in self-triggered control is how to performthe exact calculation of the time at which these updates should take place. In this paper we present anew technique to compute lower bounds on the self-triggered update times in a computationally lightmanner. We evaluate the algorithm on numerical examples and we observe that the algorithm performswell when compared to other existing methods and provides tight lower bounds on the exact updatetimes. Additionally, we propose a Semidefinite Programming-based technique that produces triggeringconditions that are less conservative than the existing ones and for which the update times are larger.

  • 104.
    Araujo, Jose
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. 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.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Experimental Validation of a Localization System Based on a Heterogeneous Sensor Network2009In: ASCC: 2009 7TH ASIAN CONTROL CONFERENCE, NEW YORK: IEEE , 2009, p. 465-470Conference paper (Refereed)
    Abstract [en]

    The experimental implementation and validation of a localization system based on a heterogeneous sensor network is described. The sensor network consists of ultrasound ranging sensors and web cameras. They are used to localize a mobile robot under sensor communication constraints. Applying a recently proposed sensor fusion algorithm that explicitly takes communication delay and cost into account, it is shown that one can accurately trade off the estimation performance by using low-quality ultrasound sensors with low processing time and low communication cost versus the use of the high-quality cameras with longer processing time and higher communication cost. It is shown that a periodic schedule of the sensors is suitable in many cases. The experimental setup is discussed in detail and experimental results are presented.

  • 105.
    Araújo, José
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Design, Implementation and Validation of Resource-Aware and Resilient Wireless Networked Control Systems2014Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Networked control over wireless networks is of growing importance in many application domains such as industrial control, building automation and transportation systems. Wide deployment however, requires systematic design tools to enable efficient resource usage while guaranteeing close-loop control performance. The control system may be greatly affected by the inherent imperfections and limitations of the wireless medium and malfunction of system components. In this thesis, we make five important contributions that address these issues. 

    In the first contribution, we consider event- and self-triggered control and investigate how to efficiently tune and execute these paradigms for appropriate control performance. Communication strategies for aperiodic control are devised, where we jointly address the selection of medium-access control and scheduling policies. Experimental results show that the best trade-off is obtained by a hybrid scheme, combining event- and self-triggered control together with contention-based and contention-free medium access control.

    The second contribution proposes an event-based method to select between fast and slow periodic sampling rates. The approach is based on linear quadratic control and the event condition is a quadratic function of the system state. Numerical and experimental results show that this hybrid controller is able to reduce the average sampling rate in comparison to a traditional periodic controller, while achieving the same closed-loop control performance.

    In the third contribution, we develop compensation methods for out-of-order communications and time-varying delays using a game-theoretic minimax control framework. We devise a linear temporal coding strategy where the sensor combines the current and previous measurements into a single packet to be transmitted. An experimental evaluation is performed in a multi-hop networked control scenario with a routing layer vulnerability exploited by a malicious application. The experimental and numerical results show the advantages of the proposed compensation schemes.

    The fourth contribution proposes a distributed reconfiguration method for sensor and actuator networks. We consider systems where sensors and actuators cooperate to recover from faults. Reconfiguration is performed to achieve model-matching, while minimizing the steady-state estimation error covariance and a linear quadratic control cost. The reconfiguration scheme is implemented in a room heating testbed, and experimental results demonstrate the method's ability to automatically reconfigure the faulty system in a distributed and fast manner.

    The final contribution is a co-simulator, which combines the control system simulator Simulink with the wireless network simulator COOJA. The co-simulator integrates physical plant dynamics with realistic wireless network models and the actual embedded software running on the networked devices. Hence, it allows for the validation of the complete wireless networked control system, including the study of the interactions between software and hardware components.

  • 106.
    Araújo, José
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Localization and tracking using an heterogeneous sensor network2008Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Taking resource limitations into account in the design of wireless sensor networks are important in many emerging applications. The need for minimizing the communication and power consumption of individual nodes and other units pose interesting challenges for estimation and control strategies.This document describes the design, implementation, obtained results and conclusions of a cooperative localization and tracking system based on two types of sensors. Practical investigations are made to reach the optimal sensor scheduling based on offline and covariance-based scheduler approaches. One sensor gives low quality measurements and is based on an ultrasound sensor and the other is a web-camera with high precision but with delayed results. The ultrasound sensor is connected to wireless sensor nodes which are part of the KTH Wireless Sensor Network Testbed and the web-camera is connected to a data processing unit and placed in the same area. An overview about localization techniques and solutions are presented. The design, development, and implementation of the KTH Wireless Sensor Network Testbed is also discussed. The software implemented on the system is fully detailed as well as the necessary hardware. A presentation of the filtering methods used to perform localization and tracking is put forward. Analysis and conclusions of all the different approaches used are discussed. Guidelines for future work are also proposed.

  • 107.
    Araújo, José
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Anta, A.
    Mazo Jr., M.
    Faria, J.
    Hernandez, Aitor
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tabuada, P.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Self-triggered control over wireless sensor and actuator networks2011Conference paper (Refereed)
    Abstract [en]

    Energy and communication bandwidth are scarce resources in wireless sensor and actuator networks. Recent research efforts considered the control of physical processes over such resource limited networks. Most of the existing literature addressing this topic is dedicated to periodically sampled control loops and scheduled communication, because it simplifies the analysis and the implementation. We propose instead an aperiodic network transmission scheme that reduces the number of transmission instances for the sensor and control nodes, thereby reducing energy consumption and increasing network lifetime, without sacrificing control performance. As an added benefit, we show the possibility of dynamically allocating the network bandwidth based on the physical system state and the available resources. In order to allow timely, reliable, and energy efficient communication, we propose a new co-design framework for the wireless medium access control, compatible with the IEEE 802.15.4 standard. Furthermore, we validate our approach in a real wireless networked control implementation.

  • 108.
    Araújo, José
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Anta, A.
    Mazo Jr., M.
    Faria, João
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hernandez, Aitor
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tabuda, P.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Self-triggered control for industrial wireless sensor and actuator networks2011Conference paper (Refereed)
    Abstract [en]

    Energy and communication bandwidth are scarceresources in wireless sensor and actuator networks. Recentresearch efforts considered the control of physical processes oversuch resource limited networks. Most of the existing literatureaddressing this topic is dedicated to periodically sampled controlloops and scheduled communication, because it simplifies theanalysis and the implementation. We propose instead an aperiodicnetwork transmission scheme that reduces the number oftransmission instances for the sensor and control nodes, therebyreducing energy consumption and increasing network lifetime,without sacrificing control performance. As an added benefit,we show the possibility of dynamically allocating the networkbandwidth based on the physical system state and the availableresources. In order to allow timely, reliable, and energy efficientcommunication, we propose a new co-design framework forthe wireless medium access control, compatible with the IEEE802.15.4 standard. Furthermore, we validate our approach in areal wireless networked control implementation.

  • 109.
    Araújo, José
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Mazo, M.
    Anta, A.
    Tabuada, P.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    System architectures, protocols and algorithms for aperiodic wireless control systems2014In: IEEE Transactions on Industrial Informatics, ISSN 1551-3203, E-ISSN 1941-0050, Vol. 10, no 1, p. 175-184Article in journal (Refereed)
    Abstract [en]

    Wide deployment of wireless sensor and actuator networks in cyber-physical systems requires systematic design tools to enable dynamic tradeoff of network resources and control performance. In this paper, we consider three recently proposed aperiodic control algorithms which have the potential to address this problem. By showing how these controllers can be implemented over the IEEE 802.15.4 standard, a practical wireless control system architecture with guaranteed closed-loop performance is detailed. Event-based predictive and hybrid sensor and actuator communication schemes are compared with respect to their capabilities and implementation complexity. A two double-tank laboratory experimental setup, mimicking some typical industrial process control loops, is used to demonstrate the applicability of the proposed approach. Experimental results show how the sensor communication adapts to the changing demands of the control loops and the network resources, allowing for lower energy consumption and efficient bandwidth utilization.

  • 110.
    Araújo, José
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Teixeira, André
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Henriksson, Erik
    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), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    A down-sampled controller to reduce network usage with guaranteed closed-loop performance2014In: Decision and Control (CDC), 2014 IEEE 53rd Annual Conference on, IEEE conference proceedings, 2014, p. 6849-6856Conference paper (Refereed)
    Abstract [en]

    We propose and evaluate a down-sampled controller which reduces the network usage while providing a guaranteed desired linear quadratic control performance. This method is based on fast and slow sampling intervals, as the closed-system benefits by being brought quickly to steady-state conditions while behaving satisfactorily when being actuated at a slow rate once at those conditions. This mechanism is shown to provide large savings with respect to network usage when compared to traditional periodic time-triggered control and other aperiodic controllers proposed in the literature.

  • 111.
    Ares, Benigno Zurita
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Energy consumption of minimum energy coding in CDMA wireless sensor networks2007In: Wireless Sensor Networks / [ed] Langendoen, K; Voigt, T, Springer Berlin/Heidelberg, 2007, Vol. 4373, p. 212-227Conference paper (Other academic)
    Abstract [en]

    A theoretical framework is proposed for accurate performance analysis of minimum energy coding schemes in Coded Division Multiple Access (CDMA) wireless sensor networks. Bit error rate and average energy consumption is analyzed for two coding schemes proposed in the literature: Minimum Energy coding (ME), and Modified Minimum Energy coding (MME). Since CDMA wireless systems are strongly limited by multi access interference, the system model includes all the relevant characteristics of the wireless propagation. Furthermore, a detailed model of the energy consumption is described as function of the coding schemes, the radio transmit powers, the characteristics of the transceivers, and the dynamics of the wireless channel. A distributed radio power minimization algorithm is also addressed. Numerical results show that ME and MME coding schemes exhibit similar bit error probabilities, whereas MME outperforms ME only in the case of low data rate and large coding codewords.

  • 112.
    Ares Zurita, Benigno
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Adaptive Source and Channel Coding Algorithms for Energy saving in Wireless Sensor Networks2006Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One of the major challenges to design efficient Wireless Sensors Networks (WSN) is the scarcity of energy and computational resources. We address this problem with particular reference to algorithms for efficient source and channel coding.

    Distributed source coding (DSC) is a general framework which applies to highly correlated signals that are coded separately and decoded jointly. In WSN, DSC schemes provide closed loop algorithms that exploit the correlation of data sensed by the nodes to reduce the amount of information that each node transmits, thus saving energy. A study is herein carried out along with an implementation of the aforementioned algorithms with the Matlab environment. The stability of the closed loop algorithms is then tested by means of simulations.

    Minimum energy coding schemes can be superimposed on top of the previous DSC algorithm to achieve further gains. In our work, we investigate and extend two existent energy-efficient minimum energy coding schemes [1][2]. In this context, we analyze the performance of the WSN in terms of power consumption and bit error probability, where a detailed wireless channel description is taken into account. We characterize the problem of efficient coding by means of stochastic optimization problems. This more accurate model of the system (compared to those previously existent [1][2]) allows us to propose new solutions to reduce power consumption while ensuring adequate bit error probabilities.

    As a relevant part of our work, a test-bed has been set up by using the Berkeley Telos Motes, along with a Matlab application interface, for the adaptive source coding algorithm. According to the results obtained by the ABSTRACT experimental work we have carried out, the energy consumption can be effectively reduced.

  • 113.
    Argolini, Roberto
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Bloisi, Viviana
    KTH, School of Electrical Engineering (EES), Automatic Control.
    On optimal control of the wastegate in a turbocharged SI engine2007Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The project aims to improve positive torque transient response through more advanced wastegate controllers than what are used today. All controllers are developed for a standard General Motors turbocharged engine. In many turbocharged SI engines, a wastegate is used for preventing the turbine to overrun and to decrease the pumping loss. Today, the wastegate is controlled by a PI controller, which tries to fulfill a compromise between fuel consumption and torque response by regulating the wastegate position.

    A nonlinear Mean Value Engine Model (MVEM) of this engine, with 13 states and linearized in 45 different working points, is used. The original model, implemented in Matlab/Simulink, has been enriched with new features, like lambda and spark advance efficiencies and the related exhaust temperature correction.

    The project aims to do a theoretical analysis to find the optimal control of wastegate position, investigating also spark retard and fuel enrichment during a positive torque transient. First a solution for achieving optimal wastegate control is designed, based on Linear Quadratic (LQ) approach. Since the optimal control strategy is expected to vary quite much for different working points, a gain scheduling architecture has been investigated.

    An independent lambda controller has been developed, in order to maximize the lambda efficiency and quicken the torque response during transient.

    Since the system operates near a constraint boundary, another solution based on Model Predictive Control (MPC) of the wastegate has been investigated. The MPC design has been extended also to a MIMO formulation, adding the throttle and the air to fuel ratio as control inputs, and the trade off between fast torque response and fuel economy is analyzed. A complete realtime MPC implementation, with the capability for automatic code generation in the dSpace microAutobox environment, requires the model, now with 13 states, to be reduced to a minimum state space order. The extent of model reduction that is required and the possible performance deterioration have been investigated.

  • 114. Ariba, Y.
    et al.
    Briat, C.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Simple conditions for $L_2$ stability and stabilization of networked control systems2011In: Proceeding of 8th International Federation of Automatic Control (IFAC) World Congress, 2011, p. 96-101Conference paper (Refereed)
    Abstract [en]

    The stability analysis and stabilization of networked control systems subject todata loss and time-varying transmission delays are explored. The stability result is based onquadratic separation and operator theory, which allows to capture the above phenomena intothe single formalism of aperiodic sampling. The obtained stability condition is expressed throughan LMI. The stabilization problem is a bit more involved due to the inherent structure of theobtained LMI. An approximation (dilation) is then proposed to obtain a more tractable LMIfor stabilization. Several examples illustrate the effectiveness of the proposed approach.

  • 115.
    Ariba, Yassine
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gouaisbaut, F.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Stability interval for time-varying delay systems2010Conference paper (Refereed)
    Abstract [en]

    We investigate the stability analysis of linear time-delay systems. The time-delay is assumed to be a time-varying continuous function belonging to an interval (possibly excluding zero) with a bound on its derivative. To this end, we propose to use the quadratic separation framework to assess the intervals on the delay that preserves the stability. Nevertheless, to take the time-varying nature of the delay into account, the quadratic separation principle has to be extended to cope with the general case of time-varying operators. The key idea lies in rewording the delay system as a feedback interconnection consisting of operators that characterize it. The original feature of this contribution is to design a set of additional auxiliary operators that enhance the system modelling and reduce the conservatism of the methodology. Then, separation conditions lead to linear matrix inequality conditions which can be efficiently solved with available semi-definite programming algorithms. The paper concludes with illustrative academic examples.

  • 116.
    Ariba, Yassine
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gouaisbaut, F.
    Rahme, S.
    Labit, Y.
    Traffic monitoring in transmission control protocol/active queue management networks through a time-delay observer2012In: IET Control Theory & Applications, ISSN 1751-8644, E-ISSN 1751-8652, Vol. 6, no 4, p. 506-517Article in journal (Refereed)
    Abstract [en]

    The use of the control theory tools for traffic control in communication networks, for example, the congestion control in internet protocol (IP) routers, has given rise to challenging issues in the time-delay system framework. In this study, the authors propose to design a linear time-delay observer for traffic monitoring in transmission control protocol/active queue management (TCP/AQM) networks. More precisely, the authors focus on a bottleneck topology consisting of long-lived TCP communications through a router. The developed mechanism, located at the router, aims at supervising the network via TCP flow estimations as well as detecting a class of anomalies. This issue is formulated as a stability problem for multiple delayed systems and appropriate robust control tools such as quadratic separation are adopted to address it. Then, some simulations via the network simulator NS-2 and an emulation experiment support the proposed methodology.

  • 117. Ariba, Yassine
    et al.
    Gouaisbaut, Frederic
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Robust Stability of Time-Varying Delay Systems: The Quadratic Separation Approach2012In: Asian journal of control, ISSN 1561-8625, E-ISSN 1561-8625, Vol. 14, no 5, p. 1205-1214Article in journal (Refereed)
    Abstract [en]

    In this article, we are interested in analysing the stability of systems that incorporate time-varying delays in their dynamic. The Lyapunov-Krasovskii approach is definitely the most popular method to address this issue and many results have proposed new functionals and enhanced techniques for deriving less conservative stability conditions. In the present work, we propose an original approach: the quadratic separation. To this end, the delay operator properties are exploited to provide delay range stability conditions. In particular, L2-norm of delay-dependent operators are computed so as to reduce the conservatism of the approach. Moreover, the main result is able to assess the stability of non-small delay systems, i.e, it can detect a stability interval for systems that are unstable without any delay. Several examples illustrate the benefit of our methodology.

  • 118.
    Astier, Lionel
    KTH, School of Electrical Engineering (EES), Automatic Control.
    A management system for the electrical network of the french parliament building2007Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This report describes an exemple of management systems based on Programmable Logic Controllers. Such systems are designed in order to help monitoring and controlling of a physical system. The system which is controlled in this project is the electrical network of two buildings used by the french parliament. This network consists of several electrical boards where each board is made up of several circuit breakers that protect the electrical equipments and other boards. The goal of the management system is to monitor the network, i.e acquire data about the state of the network, and to control the network, i.e control the position of the breakers (open/closed) according to power supplies availability and network load.

    The management system is based on a multiple levels structure.

    - Level 0 : is the operating part of the network which is made up of sensors and actuators.

    - Level 1 : is the part made up of the Programmable Logic Controllers (PLC). The sensors and actuators of the level 0 are directly connected to the PLC.

    - Level 2 : This level enables to acquire the information on a computer and to monitor/control it through an ergonomic graphical interface. Thanks to that level, the operator can keep an eye on the network remotely and control it.

    This project consists in programming the Programmable Logic Controllers, and the Human

    Machine Interface, according to the specifications of the customer. Only a part of the system has so far been developped since the total duration of the project is about 2 years. The main functions of the PLC program has been programmed, and tested successfully but not in real conditions since the buildings were still under construction. Simulation tools were used in order to test Modbus communication between the levels 0 and 1. The function that controls the breakers according to power supplies availability has been tested as well, by forcing variables in the PLC (to simulate a voltage loss for example).

  • 119.
    Athanasiou, George
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Cooperative management of wireless mesh networks2012In: 2012 IFIP Wireless Days (WD), IEEE , 2012, p. 6402806-Conference paper (Refereed)
    Abstract [en]

    The association/handoff procedures are important components in a balanced operation of 802.11-based wireless mesh networks. These networks are usually consisted of a static wireless backbone. The peripheral routers serve as access points (APs) and are associated with the stations (STAs) that are distributed in the network. Due to the large number of mesh APs, the STAs must decide to be associated with the mesh APs that will provide them the best QoS. In this paper we introduce the concept of cooperative association, where the STAs can share useful information in order to improve the performance of the association/handoff procedures. Furthermore, we introduce a load balancing mechanism that can control the communication load of each mesh AP in a distributed manner. We evaluate the performance of our mechanisms through OPNET simulations.

  • 120.
    Athanasiou, George
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dynamic Resource Management in 802.11 Wireless Mesh Networks2012In: Journal of Computer Systems, Networks and Communications, ISSN 1687-7381, E-ISSN 1687-739XArticle in journal (Refereed)
    Abstract [en]

    The association/handoff procedures are important components in a balanced operation of 802.11-based wireless mesh networks. In this paper, we introduce the concept of cooperative association where the stations (STA) can share useful information in order to improve the performance of the association/reassociation procedures. Furthermore, in this work we introduce a load balancing mechanism that can be applied in mesh networks. This mechanism operates in a cross-layer manner taking into account uplink and downlink channel information, routing information, and congestion-based information. Our load balancing mechanism is based on a fairness index that is measured at each access point (AP) neighborhood. This index reflects the way the communication load is shared in the neighboring APs. The iterative heuristic algorithms that we propose controls the communication load of each mesh AP in a distributed manner. We evaluate the performance of our mechanisms through OPNET simulations.

  • 121.
    Athanasiou, George
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Energy-efficient traffic engineering for future networking infrastructures2013In: Journal of green engineering, ISSN 1904-4720, E-ISSN 2245-4586, Vol. 4, no 1, p. 1-12Article in journal (Refereed)
    Abstract [en]

    A general problem formulation for energy-efficient traffic engineering for future core networks is presented. Moreover, a distributed heuristic algorithm that provides jointly load balancing and energy efficiency is proposed. Simulation results show that the proposed algorithm approaches the optimal network operation, in terms of throughput and energy consumption.

  • 122.
    Athanasiou, George
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Green Traffic Engineering for future core networks2012In: 2012 20th IEEE/International Conference on Software, Telecommunications and Computer Networks, SoftCOM 2012, 2012, p. 6347611-Conference paper (Refereed)
    Abstract [en]

    The achieving of the best ratio of performance to energy consumption and at the same time assuring manageability is an important goal towards the design of Future Networks. This paper presents a general problem formulation for Energy-Aware Traffic Engineering (ETE) and proposes a distributed, heuristic ETE scheme that provides load balancing and energy-awareness in accordance with the operator's needs. Simulation results of ETE compared to the optimal network performance confirm the capability of ETE to meeting the needs of Future Networks.

  • 123.
    Athanasiou, George
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Tassiulas, Leandros
    Design and implementation of distributed load balancing and fast handoff for wireless mesh networks2015In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 26, no 4, p. 630-649Article in journal (Refereed)
    Abstract [en]

    The association/handoff procedures are very important towards achieving a balanced operation in 802.11-based wireless mesh networks. In this paper, we design and implement a cooperative association/handoff scheme, where stations share useful information, and handoff is executed in a seamless manner. Furthermore, we introduce a cross-layer load balancing mechanism that takes into account uplink and downlink channel conditions, routing performance and congestion control. The proposed heuristic algorithms are inspired by the rapidly designed cooperative protocols and control the communication load of each mesh access point in a distributed manner. We evaluate the performance of our mechanisms through OPNET () simulations and testbed experiments. Copyright (c) 2013 John Wiley & Sons, Ltd.

  • 124.
    Athanasiou, George
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Tassiulas, Leandros
    Design and Implementation of Distributed Resource Management Mechanisms for Wireless Mesh Networks2012In: Transactions on Emerging Telecommunications Technologies, ISSN 2161-3915Article in journal (Other academic)
    Abstract [en]

    In this paper we design and implement a resource management scheme based on cooperative association, where the STAs can share useful information in order to improve the performance of the association/handoff procedures. The cooperative association mechanism is inspired by the rapidly designed cooperative protocols in the field of wireless networks. Furthermore, we introduce a load balancing mechanism that operates in a cross-layer manner taking into account uplink and downlink channel conditions, routing performance and congestion control. The iterative heuristic algorithms that we propose, control the communication load of each mesh AP in a distributed manner. We evaluate the performance of our mechanisms through OPNET simulations and testbed experiments.

  • 125.
    Athanasiou, George
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Tassiulas, Leandros
    Dynamic Frequency Management in 802.11-based Multi-Radio Wireless Networks2014In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 25, no 7, p. 752-768Article in journal (Refereed)
    Abstract [en]

    Efficient channel selection is essential in 802.11 mesh deployments, for minimising contention and interference among co-channel devices and thereby supporting a plurality of quality of service (QoS)-sensitive applications. A few protocols have been proposed for frequency allocation in such networks; however, they do not address the problem end-to-end. In this paper, we present a general formulation of the channel selection problem, taking into account the performance of both mesh access and mesh backhaul. Moreover, we propose a routing-aware channel selection protocol for wireless mesh networks (ARACHNE). ARACHNE is distributed in nature and motivated by our measurements on a wireless testbed. The main novelty of our protocol comes from adopting a metric that captures the end-to-end link loads across different routes in the network. ARACHNE prioritises the assignment of low-interference channels to links that (i) need to serve high-load aggregate traffic and/or (ii) already suffer significant levels of contention and interference. Our protocol takes into account the number of potential interfaces (radios) per device and allocates these interfaces in a manner that efficiently utilises the available channel capacity. We evaluate ARACHNE through extensive, trace-driven simulations, and we show the approaches to the optimal channel selection. We observe that our protocol improves the total network throughput, as compared to three other representative channel allocation approaches in literature.

  • 126.
    Athanasiou, George
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tsagkaris, Kostas
    Vlacheas, Panagiotis
    Karvounas, Dimitrios
    Demestichas, Panagiotis
    Multi-Objective Traffic Engineering for Future Networks2012In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 16, no 1, p. 101-103Article in journal (Refereed)
    Abstract [en]

    An important goal towards the design of Future Networks is to achieve the best ratio of performance to energy consumption and at the same time assure manageability. This paper presents a general problem formulation for Energy-Aware Traffic Engineering and proposes a distributed, heuristic Energy-Aware Traffic Engineering scheme (ETE) that provides load balancing and energy-awareness in accordance with the operator's needs. Simulation results of ETE compared to the optimal network performance confirm the capability of ETE to meeting the needs of Future Networks.

  • 127.
    Athanasiou, George
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Weeraddana, Pradeep Chathuranga
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Association control in millimeterWave wireless access networks2014In: 2014 IEEE 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks, CAMAD 2014, 2014, p. 260-264Conference paper (Refereed)
    Abstract [en]

    The resource allocation problem of optimal assignment of the stations to the available access points in 60 GHz millimeterWave wireless access networks is investigated. The problem is posed as a multi-assignment optimization problem. The proposed solution method converts the initial problem to a minimum cost flow problem and allows to design an efficient algorithm by a combination of auction algorithms. The solution algorithm exploits the network optimization structure of the problem, and thus is much more powerful than computationally intensive general-purpose solvers. Theoretical and numerical results evince numerous properties, such as optimality, convergence, and scalability in comparison to existing approaches.

  • 128.
    Athanasiou, George
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Weeraddana, Pradeep Chathuranga
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Orten, P.
    Communication infrastructures in industrial automation: The case of 60 GHz millimeterWave communications2013In: IEEE International Conference on Emerging Technologies and Factory Automation, ETFA, 2013Conference paper (Refereed)
    Abstract [en]

    Wireless sensor networks for industrial automation applications must offer timely, reliable, and energy efficient communications at both low and high data rate. While traditional communication technologies between 2.4 GHz and 5 GHz are sometimes incapable to efficiently achieve the aforementioned goals, new communication strategies are emerging, such as millimeterWave communications. In this overview paper, the general requirements that factory and process automation impose on the network design are reviewed. Moreover, this paper presents and qualitatively evaluates the 60 GHz millimeterWave communication technology for automation. It is argued that the upcoming 60 GHz millimeterWave technology brings an enormous potential and can influence the design of the future communication infrastructures in factory and process automation.

  • 129.
    Athanasiou, Georgios
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Weeraddana, Pradeep Chathuranga
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Auction-Based Resource Allocation in MillimeterWave Wireless Access Networks2013In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 17, no 11, p. 2108-2111Article in journal (Refereed)
    Abstract [en]

    The resource allocation problem of optimal assignment of the stations to the available access points in 60 GHz millimeterWave wireless access networks is investigated. The problem is posed as a multi-assignment optimization problem. The proposed solution method converts the initial problem to a minimum cost flow problem and allows to design an efficient algorithm by a combination of auction algorithms. The solution algorithm exploits the network optimization structure of the problem, and thus is much more powerful than computationally intensive general-purpose solvers. Theoretical and numerical results evince numerous properties, such as optimality, convergence, and scalability in comparison to existing approaches.

  • 130.
    Athanasiou, Georgios
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Weeraddana, Pradeep Chathuranga
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tassiulas, Leandros
    University of Thessaly, Volos, Greece.
    Optimizing Client Association for Load Balancing and Fairness in Millimeter Wave Wireless Networks2015In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 23, no 3, p. 836-850Article in journal (Refereed)
    Abstract [en]

    Millimeter-wave communications in the 60-GHz band are considered one of the key technologies for enabling multigigabit wireless access. However, the special characteristics of such a band pose major obstacles to the optimal utilization of the wireless resources, where the problem of efficient client association to access points (APs) is of vital importance. In this paper, the client association in 60-GHz wireless access networks is investigated. The AP utilization and the quality of the rapidly vanishing communication links are the control parameters. Because of the tricky non-convex and combinatorial nature of the client association optimization problem, a novel solution method is developed to guarantee balanced and fair resource allocation. A new distributed, lightweight, and easy-to-implement association algorithm, based on Lagrangian duality theory and subgradient methods, is proposed. It is shown that the algorithm is asymptotically optimal, that is, the relative duality gap diminishes to zero as the number of clients increases.

  • 131.
    Avventi, Enrico
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wahlberg, Bo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Graphical Models of Autoregressive Moving-Average Processes2010In: The 19th International Symposium on Mathematical Theory of Networks and Systems (MTNS 2010), 2010Conference paper (Refereed)
    Abstract [en]

    Consider a Gaussian stationary stochastic vector process with the property that designated pairs of components are conditionally independent given the rest of the components. Such processes can be represented on a graph where the components are nodes and the lack of a connecting link between two nodes signifies conditional independence. This leads to a sparsity pattern in the inverse of the matrix-valued spectral density. Such graphical models find applications in speech, bioinformatics, image processing, econometrics and many other fields, where the problem to fit an autoregressive (AR) model to such a process has been considered. In this paper we take this problem one step further, namely to fit an autoregressive moving-average (ARMA) model to the same data. We develop a theoretical framework which also spreads further light on previous approaches and results.

  • 132.
    Aytekin, Arda
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Asynchronous Algorithms for Large-Scale Optimization: Analysis and Implementation2017Licentiate thesis, monograph (Other academic)
    Abstract [en]

    This thesis proposes and analyzes several first-order methods for convex optimization, designed for parallel implementation in shared and distributed memory architectures. The theoretical focus is on designing algorithms that can run asynchronously, allowing computing nodes to execute their tasks with stale information without jeopardizing convergence to the optimal solution.

    The first part of the thesis focuses on shared memory architectures. We propose and analyze a family of algorithms to solve an unconstrained, smooth optimization problem consisting of a large number of component functions. Specifically, we investigate the effect of information delay, inherent in asynchronous implementations, on the convergence properties of the incremental prox-gradient descent method. Contrary to related proposals in the literature, we establish delay-insensitive convergence results: the proposed algorithms converge under any bounded information delay, and their constant step-size can be selected independently of the delay bound.

    Then, we shift focus to solving constrained, possibly non-smooth, optimization problems in a distributed memory architecture. This time, we propose and analyze two important families of gradient descent algorithms: asynchronous mini-batching and incremental aggregated gradient descent. In particular, for asynchronous mini-batching, we show that, by suitably choosing the algorithm parameters, one can recover the best-known convergence rates established for delay-free implementations, and expect a near-linear speedup with the number of computing nodes. Similarly, for incremental aggregated gradient descent, we establish global linear convergence rates for any bounded information delay.

    Extensive simulations and actual implementations of the algorithms in different platforms on representative real-world problems validate our theoretical results.

  • 133.
    Aytekin, Arda
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Feyzmahdavian, Hamid Reza
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Asynchronous incremental block-coordinate descent2014In: 52nd Annual Allerton Conference on Communication, Control, and Computing (Allerton), IEEE conference proceedings, 2014, p. 19-24Conference paper (Refereed)
    Abstract [en]

    This paper studies a flexible algorithm for minimizing a sum of component functions, each of which depends on a large number of decision variables. Such formulations appear naturally in “big data” applications, where each function describes the loss estimated using the data available at a specific machine, and the number of features under consideration is huge. In our algorithm, a coordinator updates a global iterate based on delayed partial gradients of the individual objective functions with respect to blocks of coordinates. Delayed incremental gradient and delayed coordinate descent algorithms are obtained as special cases. Under the assumption of strong convexity and block coordinate-wise Lipschitz continuous partial gradients, we show that the algorithm converges linearly to a ball around the optimal value. Contrary to related proposals in the literature, our algorithm is delay-insensitive: it converges for any bounded information delay, and its step-size parameter can be chosen independently of the maximum delay bound.

  • 134.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fast-Lipschitz Power Control and User-Frequency Assignment in Full-Duplex Cellular Networks2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 10, p. 6672-6687Article in journal (Refereed)
    Abstract [en]

    In cellular networks, the three-node full-duplex transmission mode has the po-tential to increase spectral efficiency without requiring full-duplex capability ofusers. Consequently, three-node full-duplex in cellular networks must deal with self-interference and user-to-user interference, which can be managed by power controland user-frequency assignment techniques. This paper investigates the problem ofmaximizing the sum spectral efficiency by jointly determining the transmit powersin a distributed fashion, and assigning users to frequency channels. The problem is for-mulated as a mixed-integer nonlinear problem, which is shown to be non-deterministicpolynomial-time hard. We investigate a close-to-optimal solution approach by dividingthe joint problem into a power control problem and an assignment problem. The powercontrol problem is solved by Fast-Lipschitz optimization, while a greedy solution withguaranteed performance is developed for the assignment problem. Numerical resultsindicate that compared with the half-duplex mode, both spectral and energy efficienciesof the system are increased by the proposed algorithm. Moreover, results show that thepower control and assignment solutions have important, but opposite roles in scenarioswith low or high self-interference cancellation. When the self-interference cancellationis high, user-frequency assignment is more important than power control, while powercontrol is essential at low self-interference cancellation.

  • 135.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    On the Spectral Efficiency and Fairness in Full-Duplex Cellular Networks2017In: 2017 IEEE International Conference on Communications (ICC), Paris: Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1-6, article id 7996391Conference paper (Refereed)
    Abstract [en]

    To increase the spectral efficiency of wireless networks without requiring full-duplex capability of user devices, a potential solution is the recently proposed three-node full-duplex mode. To realize this potential, networks employing three-node full-duplex transmissions must deal with self-interference and user-to-user interference, which can be managed by frequency channel and power allocation techniques. Whereas previous works investigated either spectral efficient or fair mechanisms, a scheme that balances these two metrics among users is investigated in this paper. This balancing scheme is based on a new solution method of the multi-objective optimization problem to maximize the weighted sum of the per-user spectral efficiency and the minimum spectral efficiency among users. The mixed integer non-linear nature of this problem is dealt by Lagrangian duality. Based on the proposed solution approach, a low-complexity centralized algorithm is developed, which relies on large scale fading measurements that can be advantageously implemented at the base station. Numerical results indicate that the proposed algorithm increases the spectral efficiency and fairness among users without the need of weighting the spectral efficiency. An important conclusion is that managing user-to-user interference by resource assignment and power control is crucial for ensuring spectral efficient and fair operation of full-duplex networks.

  • 136.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Spectral Efficient and Fair User Pairing for Full-Duplex Communication in Cellular Networks2016In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, no 11, p. 7578-7593Article in journal (Refereed)
    Abstract [en]

    —A promising new transmission mode in cellular networks is the three-node full-duplex mode, which involves a base station with full-duplex capability and two half-duplex user transmissions on the same frequency channel for uplink and downlink. The three-node full-duplex mode can increase spectral efficiency, especially in the low transmit power regime, without requiring full-duplex capability at user devices. However, when a large set of users is scheduled in this mode, self-interference at the base station and user-to-user interference can substantially hinder the potential gains of full-duplex communications. This paper investigates the problem of grouping users to pairs and assigning frequency channels to each pair in a spectral efficient and fair manner. Specifically, the joint problem of user uplink/downlink frequency channel pairing and power allocation is formulated as a mixed integer nonlinear problem that is solved by a novel joint fairness assignment maximization algorithm. Realistic system level simulations indicate that the spectral efficiency of the users having the lowest spectral efficiency is increased by the proposed algorithm, while a high ratio of connected users in different loads and self-interference levels is maintained.

  • 137.
    Babu, George Jithin
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Look-Ahead Platooning through Guided Dynamic Programming2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 138.
    Back, Per
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Simulering av simulinkmodeller med Extended Kalman Filter2005Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Simulations of simulink models using Kalman filters are often very time-consuming. This problem depends mainly on the fact that the Kalman correction has to be performed at each sample instance through the whole simulation. The goal for this thesis work is to reduce that time-consumption for the filtering part (the integration partis treated in a complementary report) of a simulation. Furthermore a Matlab routine to perform parameter tuning and finally a graphical user interface is developed.

    The filtering part of the simulation in this thesis is based on an Extended Kalman Filter (EKF). The time optimization of this filter considers searching for the possibility to replace the today’s existing Matlab functions that is used to perform the filtering calculations. Examples of such functions are routines for linearization and integration. To decrease the time-consumption, we have also developed a routine to make it possible to convert a simulink model to a state-space description. This conversion makes it possible to avoid a lot of time-consuming calls to the simulink model.

    In this case it is the built-in functions in Matlab that causes the large time-consumption. The main time-consuming parts in the filter are the built-in routines for linearization (linmod) and the numerical method that is used to calculate the prediction error (riccatiequation). By creating new routines to solve these problems, the total time-consumption for the filtering part is reduced by approximately a factor of eighteen.

    As a final step the time optimized Kalman filter and the time optimized integration (treated in a complementary report) are brought together in a time efficient routine for simulation. This final routine for simulation may further be used to perform a time efficient simulation, but also to form a routine, which can be used to estimate unknown parameters in a simulink model. Using the time optimized parts of the simulation routine will make it possible to reduce the execution time for a filtering simulation by approximately a factor of ten.

    Three kinds of models are used to confirm that the different element of the Kalman filter and the new developed routines work properly. These models consist of one fermentation system that describes a biological process, and two different tank systems that describe the level and the torrent of water in several water tanks.

  • 139.
    Badia Canal, Jordi
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fuel Saving Potentials of HDVs through Platooning based on Real GPS Traces.2014Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the last years, the increase of the fuel price and the need to reduce the greenhouse gas emissions have triggered the research on lowering the fuel consumption within the transport sector. The research not only involves the development of more efficient engines but also the exploration of new transportation paradigms. One promising approach is to create vehicle platoons, i.e. convoys of vehicles driving close to each other. Vehicles driving close behind benefit from the reduction of the air drag and hence their overall fuel consumptions are reduced.

    This work focuses on studying platoons of heavy-duty vehicles (HDVs). More specifically, the work analyzes real position data of an HDV fleet from one manufacturer. The objective is to determine the potentials to reduce the fuel consumption of the fleet through platoon formations, using low sampled GPS traces obtained from the fleet management system. Map matching and path inference algorithms have been developed to reconstruct the path of the vehicles on a given road network.

    The reconstructed paths are used to analyze the vehicles’ positions and inter-vehicle distances. Results show that the vehicles are widely spread. The average distance to the closest vehicle is greater than 20km, which limits the platoon opportunities. Although with limited platoon opportunities, potential fuel savings up to 0.14% of the whole fleet’s consumption have been obtained. Results suggest that fuel savings can be largely improved if the density of vehicles in the road network is increased.

  • 140.
    Balland, Olivier
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Collaborative motion planning of humanoid robots2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    For a matter of efficiency and robustness, it is often better to use a team of robots

    instead of a single agent to solve a given problem. A key challenge with multi-robot

    systems is the collaboration in order to accomplish complex tasks. To coordinate

    them, we can pre-compute their behavior. However, this method might not be

    robust to some events such as modification of environment or robots team. To

    overcome this issue, an adaptive decentralized coordination framework is needed for

    heterogeneous multiple robot systems.

    We consider a team of two robots NAOs which can only exchange information when

    they are close to each other, or via symbols grounded to each embodiment. They

    are initially in a room a few meters away from each other. The goal is to make them

    meet and then perform an action such as exchanging an object or some information.

    In this thesis, we study first robots specifications and adopt tools used for robot control.

    A tracking method in a simple situation is then described. The robots’ strategy

    is structured and improved adding obstacles limiting the two agents’ motion.

    The achieved robust framework allows two humanoid robots to meet, even if one

    has a problem and can not move.

  • 141.
    Balland, Olivier
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Collaborative motion planning of humanoid robots2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    For a matter of efficiency and robustness, it is often better to use a team of robots instead of a single agent to solve a given problem. A key challenge with multi-robot systems is the collaboration in order to accomplish complex tasks. To coordinate them, we can pre-compute their behavior. However, this method might not be robust to some events such as modification of environment or robots team. To overcome this issue, an adaptive decentralized coordination framework is needed for heterogeneous multiple robot systems.

    We consider a team of two robots NAOs which can only exchange information when they are close to each other, or via symbols grounded to each embodiment. They are initially in a room a few meters away from each other. The goal is to make them meet and then perform an action such as exchanging an object or some information.

    In this thesis, we study first robots specifications and adopt tools used for robot control. A tracking method in a simple situation is then described. The robots’ strategy is structured and improved adding obstacles limiting the two agents’ motion.

    The achieved robust framework allows two humanoid robots to meet, even if one has a problem and can not move.

  • 142. Balluchi, A.
    et al.
    Benvenuti, L.
    Engell, S.
    Geyer, T.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Lamnabhi-Lagarrigue, F.
    Lygeros, J.
    Morari, M.
    Papafotioug, G.
    Sangiovanni-Vincentelli, A. L.
    Santuchi, F.
    Stursberg, O.
    Hybrid control of networked embedded systems2005In: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 11, no 4-5, p. 478-508Article in journal (Refereed)
    Abstract [en]

    Hybrid systems that involve the interaction of continuous and discrete dynamics have been an active area of research for a number of years. In this paper, we start by briefly surveying the main theoretical control problems that have been treated in the hybrid systems setting and classify them into stabilization, optimal control and language specification problems. We then provide an overview of recent developments in four of the most prominent areas where these hybrid control methods have found application: control of power systems, industrial process control, design of automotive electronics and communication networks.

  • 143.
    Balsemin, Antonio
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Applications Oriented Input design for MPC: An analysis of a quadruple water tank process2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Model predictive control (MPC) has become an increasingly popular control strategy thanks to its ability to handle multivariable systems and constraints. This control technique makes use of a model of the system, therefore performances are highly dependent on the accuracy of the model chosen. The process of obtaining the model is often costly, for this reason system identi cation for MPC is an important topic. Applications oriented optimal input design enables optimization of the system identi cation experiments, leading to a set of models with the necessary accuracy for the intended application. In this thesis a method of system identi cation for MPC applications is simulated on a multivariable nonlinear system consisting of four interconnected water tanks. An analysis of the impact of MPC settings, such as active or no active constraints and dierent weight settings, is carried out. The initial hypothesis is that d erent MPC settings inuence the obtained set of models. Simulations show that the hypothesis is correct and the result give rise to some interesting interpretations.

  • 144. Bao, L.
    et al.
    Skoglund, M.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rate allocation with power constraints for quantized control over binary symmetric channelsManuscript (preprint) (Other academic)
  • 145. Bao, L.
    et al.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. 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.
    Encoder-decoder design for feedback control over the binary symmetric channel2006In: 2006 IEEE International Symposium on Information Theory, Vols 1-6, Proceedings, IEEE , 2006, p. 2481-2485Conference paper (Refereed)
    Abstract [en]

    Encoder-decoder design is considered for a closed-loop scalar control system with feedback transmitted over a binary symmetric channel. We propose an iterative procedure which can jointly optimize adaptive encoder-decoder pairs for a certainly equivalence controller. The goal is to minimize a design criterion, in particular, the linear quadratic (LQ) cost function over a finite horizon. The algorithm leads to a practically feasible design of time-varying non-uniform encoding and decoding. Numerical results demonstrate the promising performance obtained by employing the proposed iterative optimization algorithm.

  • 146.
    Bao, Lei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On rate allocation for multiple plants in a networked control system2012In: 2012 American Control Conference (ACC), IEEE Computer Society, 2012, p. 2024-2029Conference paper (Refereed)
    Abstract [en]

    The problem of allocating communication resources to multiple plants in a networked control system is investigated. In the presence of a shared communication medium, a total transmission rate constraint is imposed. For the purpose of optimizing the rate allocation to the plants over a finite horizon, two objective functions are considered. The first one is a single-objective function, and the second one is a multi-objective function. Because of the difficulty to derive the closed-form expression of these functions, which depend on the instantaneous communication rate, an approximation is proposed by using high-rate quantization theory. It is shown that the approximate objective functions are convex in the region of interest both in the scalar case and in the multi-objective case. This allows to establish a linear control policy given by the classical linear quadratic Gaussian theory as function of the channel. Based on this result, a new complex relation between the control performance and the channel error probability is characterized.

  • 147.
    Bao, Lei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    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.
    Optimized Rate Allocation for State Estimation over Noisy Channels2009In: 2009 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY, NEW YORK: IEEE , 2009, p. 2684-2688Conference paper (Refereed)
    Abstract [en]

    Optimal rate allocation in a networked control system with limited communication resources is instrumental to achieve satisfactory overall performance. In this paper, a practical rate allocation technique for state estimation in linear dynamic systems over a noisy channel is proposed. The method consists of two steps: (i) the overall distortion is expressed as a function of rates at all time instants by means of high-rate quantization theory, and (ii) a constrained optimization problem to minimize the overall distortion is solved by using Lagrange duality. Monte Carlo simulations illustrate the proposed scheme, which is shown to have good performance when compared to arbitrarily selected rate allocations.

  • 148.
    Bao, Lei
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    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.
    Optimized rate allocation for state feedback control over noisy channels2009In: Decision and Control, 2009 held jointly with the 2009 28th Chinese Control Conference. CDC/CCC 2009. Proceedings of the 48th IEEE Conference on, IEEE , 2009, p. 573-578Conference paper (Refereed)
    Abstract [en]

    Optimal rate allocation in a networked control system with highly limited communication resources is instrumental to achieve satisfactory overall performance. In this paper, we propose a rate allocation technique for state feedback control in linear dynamic systems over a noisy channel. Our method consists of two steps: (i) the overall distortion is expressed as a function of rates at all time instants by means of high-rate quantization theory, and (ii) a constrained optimization problem to minimize the overall distortion is solved. We show that a non-uniform quantization is in general the best strategy for state feedback control over noisy channels. Monte Carlo simulations illustrate the proposed scheme, which is shown to have good performance compared to arbitrarily selected rate allocations.

  • 149.
    Bao, Lei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    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.
    Rate Allocation for Quantized Control Over Binary Symmetric Channels2012In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, no 6, p. 3188-3202Article in journal (Refereed)
    Abstract [en]

    Utility maximization in networked control systems (NCSs) is difficult in the presence of limited sensing and communication resources. In this paper, a new communication rate optimization method for state feedback control over a noisy channel is proposed. Linear dynamic systems with quantization errors, limited transmission rate, and noisy communication channels are considered. The most challenging part of the optimization is that no closed-form expressions are available for assessing the performance and the optimization problem is nonconvex. The proposed method consists of two steps: (i) the overall NCS performance measure is expressed as a function of rates at all time instants by means of high-rate quantization theory, and (ii) a constrained optimization problem to minimize a weighted quadratic objective function is solved. The proposed method is applied to the problem of state feedback control and the problem of state estimation. Monte Carlo simulations illustrate the performance of the proposed rate allocation. It is shown numerically that the proposed method has better performance when compared to arbitrarily selected rate allocations. Also, it is shown that in certain cases nonuniform rate allocation can outperform the uniform rate allocation, which is commonly considered in quantized control systems, for feedback control over noisy channels.

  • 150.
    Bao, Lei
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Theory.
    Fischione, Carlo
    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.
    Rate allocation for quantized control over noisy channels2009In: Final Proceedings of the 2009 7th International Symposium on Modeling and Optimization in Mobile, Ad Hoc and Wireless Networks, 2009, Vol. WiOpt 2009, p. 595-603Conference paper (Refereed)
    Abstract [en]

    To achieve satisfactory overall performance, optimal rate allocation in a networked control system with highly limited communication resources is instrumental. In this paper, a rate allocation technique for state feedback control in linear dynamic systems over a noisy channel is proposed. The method consists of two steps: (i) the overall cost is expressed as a function of rates at all time instants by means of high-rate quantization theory, and (ii) a constrained optimization problem to minimize the overall distortion is solved. It is shown that a non-uniform quantization is in general the best strategy for state feedback control over noisy channels. Monte Carlo simulations illustrate the proposed scheme, which is shown to have good performance when compared to arbitrarily selected rate allocations.

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