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  • 301.
    Chen, Phoebus
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ramesh, Chithrupa
    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.
    Reducing Packet Loss Bursts in a Wireless Mesh Network for Stochastic Bounds on Estimation Error2011In: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2011, p. 3130-3135Conference paper (Other academic)
    Abstract [en]

    A big challenge for wireless networked control systems is how to design the underlying networking algorithms and protocols to provide high reliability, defined as the end-to-end probability of packet delivery, despite the high packet loss rates of individual wireless links. This paper formulates the problem of jointly designing a set of packet forwarding policies on a multipath mesh network to meet control application requirements. We derive several results to help understand the problem space. First, we demonstrate that some common approaches, like applying a single forwarding policy to all packets or always routing packets on disjoint paths, are not optimal for the application when the links are bursty. Second, we introduce the notion of dominance to give a partial ordering to sets of forwarding policies, used to prove that an optimal policy schedules all outgoing links at each node and that an upper bound on the performance attained by unicast forwarding policies on the network graph can be computed assuming a flooding policy. Third, we demonstrate how to convert application performance metrics to packet forwarding policy objectives, using the probability that the error covariance of a Kalman filter stays within a bound as our application metric. Fourth, we provide an algorithm to compute the joint probability mass function that a sequence of packets are delivered, given a set of policies and a network graph. Finally, we describe how to obtain optimal policies via an exhaustive search, motivating future research for more computationally efficient solutions.

  • 302.
    Chen, Phoebus
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ramesh, Chithrupa
    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.
    Network Estimation and Packet Delivery Prediction for Control over Wireless Mesh Networks2011In: IFAC Proceedings Volumes (IFAC-PapersOnline), 2011, p. 6573-6579Conference paper (Refereed)
    Abstract [en]

    Much of the current theory of networked control systems uses simple point-to-point communication models as an abstraction of the underlying network. As a result, the controller has very limited information on the network conditions and performs suboptimally. This work models the underlying wireless multihop mesh network as a graph of links with transmission success probabilities, and uses a recursive Bayesian estimator to provide packet delivery predictions to the controller. The predictions are a joint probability distribution on future packet delivery sequences, and thus capture correlations between successive packet deliveries. We look at finite horizon LQG control over a lossy actuation channel and a perfect sensing channel, both without delay, to study how the controller can compensate for predicted network outages.

  • 303. Chen, S.
    et al.
    Dunkels, A.
    Österlind, F.
    Voigt, T.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Time synchronization for predictable and secure data collection in wireless sensor networks2007In: Proceedings of MedHocNet, 2007, p. 165-172Conference paper (Refereed)
    Abstract [en]

    Wireless sensor networks are trying to findtheir way from relatively undemanding applications suchas environmental monitoring to applications such as industrialcontrol, which have stronger requirements in termsof security and predictability. Predictability cannot beachieved without coordination and the coordination of distributedentities and events requires time synchronization.Towards this end, we present a secure time synchronizationservice, that as our experimental results show does notdegrade time synchronization accuracy. Based on the timesynchronization service we implement time slotted datacollection and present results that show that this way wecan provide a predictable data collection service.

  • 304.
    Chen, Shujuan
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Secure Real-time Services for Wireless Sensor Networks in Contiki2007Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With the widespread use of networked embedded systems operating over wireless sensor networks, a standardized architecture is required to enable the rapid development of applications. An embedded operating system serves as an important building block of the standardized architecture. The support of the most commonly used services and protocols should be made available in it as a system service to improve the development speed. Real-time services are commonly required by many time-sensitive applications, such as  automation control, real-time monitoring. Events need a global time notion or must happen within a deadline. Collected data should arrive at the destination before it becomes old and loses its meaning. But there is no common notion of time in a wireless sensor network in which all the nodes are physically separated and no global clock or common memory exists. Moreover, there is no guarantee that the sensed data will get to the destination before the deadline. To address these real-time issues, we develop real-time services including time synchronization and low-latency data collection to provide therapid development of time-critical applications. Meanwhile, security becomes an important issue to wireless sensor network due to the vulnerability of the wireless channel. The adversaries can simply capture and change the data and then resend it. The real-time services utilizing the wireless communication are vulnerable to the attacks and might be the weakest link for the whole system if it is not designed with security in mind.

    As the building block of real-time services, time synchronization comes into the first place to provide a global time scale for a distributed networking system. We study current time synchronization protocols for wireless sensor networks, propose our protocol design and implement it in the experimental platform, Contiki OS on the hardware platform Tmote Sky. To show the feasibility and performance of our protocol, we perform extensive experimental evaluation.

    Low-latency data collection services will also play a significant role for the time-critical applications. It aims to provide the guarantee of a time limit for the data collection. Based on the synchronized notion of time over the network, we implement a protocol for data collection aiming at low end-to-end latency for the same platform. To show the performance of data collection using this protocol, we test end-to-end latency in a multi-hop network and evaluate it based on the hop count and the estimation of the point-to-point delay in a single-hop communication.

    Security issues pose a great challenge to the applications as well as the underlying services due to vulnerability of the wireless channel, hostile environment as well as the severe resource constraint. To make the real-time services resilient to security attacks, we analyse the security attacks that might interrupt the services and present countermeasures to resist these security breaches. The hardware platform in use provides a crypto accelerator in the radio chip and frees the microcontroller from the long computation time for the security operations. We implement the security protocol utilizing hardware-assisted security operation to provide the link-layer security services. In addition, we provide data freshness service using authenticated MAC timestamping for each packet. Then we show how to secure the real-time services using these security services and integrate them into the protocol implementation.

  • 305.
    Chen, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Liu, Ji
    Chen, Yongxin
    Khong, Sei Zhen
    Wang, Dan
    Basar, Tamer
    Qiu, Li
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Characterizing the Positive Semidefiniteness of Signed Laplacians via Effective Resistances2016In: 2016 IEEE 55th Conference on Decision and Control, CDC 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 985-990, article id 7798396Conference paper (Refereed)
    Abstract [en]

    A symmetric signed Laplacian matrix uniquely defines a resistive electrical circuit, where the negative weights correspond to negative resistances. The positive semidefiniteness of signed Laplacian matrices is studied in this paper using the concept of effective resistance. We show that a signed Laplacian matrix is positive semidefinite with a simple zero eigenvalue if, and only if, the underlying graph is connected, and a suitably defined effective resistance matrix is positive definite.

  • 306.
    Chen, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. Hong Kong Univ Sci & Technol, Peoples R China.
    Qiu, Li
    Linear Quadratic Optimal Control of Continuous-Time LTI Systems With Random Input Gains2016In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 61, no 7, p. 2008-2013Article in journal (Refereed)
    Abstract [en]

    This note studies the linear quadratic ( LQ) optimal control of continuous-time linear time-invariant systems with random gains imposed on the input channels. We start from the indefinite LQ problem, in which the cost weighting matrix can be indefinite. The definite LQ problem is discussed as a special case. The main novelty originates from the point of view that in networked control, designing the channels and controller jointly often leads to an easier problem and achieves better performance than designing them separately. Specifically, we formulate the LQ problem as a channel/controller co-design problem assuming that the channel capacities can be allocated among the input channels subject to an overall capacity constraint. Necessary and sufficient conditions are obtained for the well-posedness and the attainability of the indefinite LQ problem under a given channel capacity allocation satisfying the stabilization requirement. The optimal controller is given by a linear state feedback associated with the mean-square stabilizing solution of a modified algebraic Riccati equation.

  • 307.
    Chen, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wang, D.
    Liu, J.
    Başar, T.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Qiu, L.
    On Semidefiniteness of Signed Laplacians with Application to Microgrids2016In: IFAC-PapersOnLine, ISSN 2405-8963, Vol. 49, no 22, p. 97-102Article in journal (Refereed)
    Abstract [en]

    The paper investigates the positive semidefiniteness of signed Laplacians. It is noted that a symmetric signed Laplacian defines a unique resistive electrical network, wherein the negative weights correspond to negative resistances. As such, the positive semidefiniteness of the signed Laplacians is equivalent to the passivity of the associated resistive networks. By utilizing n-port circuit theory, we obtain several equivalent conditions for signed Laplacians to be positive semidefinite with a simple zero eigenvalue. These conditions characterize a set of negative weights that maintain the semidefiniteness of the Laplacian. The results are used to analyze the small-disturbance angle stability of microgrids as an application.

  • 308.
    Chen, Xiao
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fuel optimal powertrain control of heavy-duty vehicle based on model predictive control and quadratic programming2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The freight transport has a fundamental role in the world’s economic development.Due to the flexibility of heavy-duty vehicles, a large part of freighttransport is carried out inland. Although the use of heavy-duty vehicles contributesto the economic growth, the increased fuel consumption and globalgreenhouse gas emission that come with it constantly challenge the transportationsector to adapt and develop more fuel-efficient methods to reduce suchside effects while fulfilling the transportation requirements.This thesis considers fuel-optimal highway driving for heavy-duty vehicles.A model predictive control algorithm for minimizing fuel consumptionwhile satisfying constraints on desired speed is developed and evaluated. Thecontroller uses the available topography information of the road ahead of thevehicle in order to achieve an efficient vehicle control while satisfying a certaintrip time requirement. Under the assumption of fixed gear during the drivemission, the actual nonlinear problem is re-formulated as a real-time optimalcontrol problem based on MPC theory with a quadratic cost function and linearconstraints at each receding horizon of the drive mission. The QP problem isthen solved online and the resulting first control action is applied to the vehiclefor forward movement.The feasibility to implement such an algorithm on a control unit with limitedcomputational power is investigated and shown to be possible. Both therequirement of low computational complexity and low memory occupation arefulfilled by the tailored quadratic programming algorithm developed in thisthesis. The algorithm is fast enough to provide a solution within each samplinginterval.The overall control algorithm is implemented on a G5 control unit andtested in real life with a Scania truck during highway driving test. The resultsfrom both the real implementation and extensive simulations indicate that themethod provides a fuel-efficient vehicle behavior and is competitive with a rulebasedcontroller.

  • 309.
    Chen, Yawen
    et al.
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Shen, Hong
    Zhang, Haibo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    A Novel P-shape Tessellation Approach on Double-Loop Networks2009In: 2009 IEEE INTERNATIONAL SYMPOSIUM ON IT IN MEDICINE & EDUCATION, VOLS 1 AND 2, PROCEEDINGS, NEW YORK: IEEE , 2009, p. 507-511Conference paper (Refereed)
    Abstract [en]

    Double loop computer networks are widely used in the design and implementation of local area networks and parallel processing architectures. However the embedding problems on double-loop networks have not been well studied due to the complexity of double-loop networks. Since the traditional L-shape, designed to compute the diameter of double-loop networks, is not efficient to solve embedding problems, we propose a novel tessellation approach to partition the geometric plane of double-loop networks into a set of parallelogram shaped tiles, called P-shape. Our proposed tessellation technique, P-shape, is a useful theoretical tool for embedding meshes on double-loop networks, and can be extended to analyze other problems as a bridge between regular graphs and double-loop networks.

  • 310. Cho, Kwang-Hyun
    et al.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Wolkenhauer, Olaf
    A hybrid systems framework for cellular processes2005In: Biosystems (Amsterdam. Print), ISSN 0303-2647, E-ISSN 1872-8324, Vol. 80, no 3, p. 273-282Article in journal (Refereed)
    Abstract [en]

    With the availability of technologies that allow us to obtain stimulus-response time series data for modeling and system identification, there is going to be an increasing need for conceptual frameworks in which to formulate and test hypotheses about intra- and inter-cellular dynamics, in general and not just dependent on a particular cell line, cell type, organism, or technology. While the semantics can be quite different, biologists and systems scientists use in many cases a similar language (notion of feedback, regulation, etc.). A more abstract system-theoretic framework for signals, systems, and control could provide the biologist with an interface between the domains. Apart from recent examples to identify functional elements and describing them in engineering terms, there have been various more abstract developments to describe dynamics at the cell level in the past. This includes Rosen's (M,R)-systems. This paper presents an abstract and general compact mathematical framework of intracellular dynamics, regulation and regime switching inspired by (M,R)-theory and based on hybrid automata.

  • 311. Choi, Okyoung
    et al.
    Kim, Seokhyun
    Jeong, Jaeseong
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Lee, Hyang-Won
    Chong, Song
    Delay-Optimal Data Forwarding in Vehicular Sensor Networks2016In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 65, no 8, p. 6389-6402Article in journal (Refereed)
    Abstract [en]

    The vehicular sensor network (VSN) is emerging as a new solution for monitoring urban environments such as intelligent transportation systems and air pollution. One of the crucial factors that determine the service quality of urban monitoring applications is the delivery delay of sensing data packets in the VSN. In this paper, we study the problem of routing data packets with minimum delay in the VSN by exploiting 1) vehicle traffic statistics, 2) anycast routing, and 3) knowledge of future trajectories of vehicles such as busses. We first introduce a novel road network graph model that incorporates the three factors into the routing metric. We then characterize the packet delay on each edge as a function of the vehicle density, speed, and the length of the edge. Based on the network model and delay function, we formulate the packet routing problem as a Markov decision process (MDP) and develop an optimal routing policy by solving the MDP. Evaluations using real vehicle traces in a city show that our routing policy significantly improves the delay performance compared with existing routing protocols. Specifically, optimal VSN data forwarding (OVDF) yields, on average, 96% better delivery ratio and 72% less delivery delay than existing algorithms in some areas distant from destinations.

  • 312.
    Chotteau, Veronique
    et al.
    KTH, School of Biotechnology (BIO), Bioprocess Technology.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Tuning of dissolved oxygen and pH PID control parameters in large scale bioreactor by lag control2008In: Proceedings of the Cell Culture Engineering XI Conference, 2008Conference paper (Refereed)
    Abstract [en]

    Achieving satisfying DO and pH controllers are often challenges for pilot and large scale mammalian cultivation. Unsatisfactory DO or pH controls can imply fatal effects for the culture. Large scale bioreactors have long response times due to long mixing times compared to small scale systems where control tuning of DO and pH is not so challenging.

    A method was developed to tune the DO controller PID parameters of a 50 L bioreactor (wv) controlled by a continuous oxygen flow of microbubbles. DO control by continuous flow of pure oxygen microbubbles can oscillate quite widely showing instable behaviour. The method, called lag control here, was based on a lead lag control design by Bode analysis where the prediction part, i.e. ‘lead’ part was omitted. A comparison of this method with a pole placement approach showed the advantage of the lag control. It was decided to omit the derivate part which could lead to instability caused by the long delay observed between the applied oxygen flow and the response detected by the DO probe. Applying the lag control method resulted in a highly satisfactory DO control. In this system, the oxygen microbubbles were almost completely consumed before reaching the liquid surface as demonstrated by the absence of foam. So the oxygen flow used to maintain the DO gave an excellent indication of the cellular oxygen consumption. The control system was robust against all the perturbations of this system, i.e. cell growth, cell bleed, addition of air-saturated fresh medium, DO set point change and a second gas sparger used to strip out the carbon dioxide. The method was first tested with the sulphite oxidation method simulating the oxygen consumption with copper as catalyst to establish the PID parameters. Then the selected parameters were successfully used during cell cultivation. Following this, an adaptation of the method was done in order to avoid the sulphite oxidation method, which leaves copper traces in the bioreactor. This was successfully used in a 400 L bioreactor (wv) for the DO controller by continuous oxygen flow of microbbubles. The lag controller method was finally modified to tune the pH controller of the same 400 L bioreactor with control upward by alkali addition or downwards by pulsed carbon dioxide addition.

  • 313.
    Chotteau, Véronique
    et al.
    KTH, School of Biotechnology (BIO), Bioprocess Technology.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tuning of dissolved oxygen and pH PID control parameters in large scale bioreactor by lag control2012In: Proceedings of the 21st Annual Meeting of the European Society for Animal Cell Technology (ESACT), 2012, p. 327-330Conference paper (Refereed)
    Abstract [en]

    A method has been developed to tune the DO and pH controller PID parameters for pilot / large scale mammalian cultivation. Our approach is to identify a model of the variable to be controlled (e.g. DO, pH) and to design several possible PID controllers based on this model. The controllers were first tested in computer simulations, followed by wet simulation and finally the best controller was tested on the real process. The approach is developed for the tuning of the DO controller of a 50 L bioreactor using microbubble continuous oxygen flow. The method, called lag control here, is based on a lead lag control design using Bode analysis where the prediction part is omitted. Experiments show that the approach results in a highly satisfactory DO control. The oxygen microbubbles were almost completely consumed before reaching the liquid surface so the oxygen flow used to maintain the DO gave an excellent indication of the cellular oxygen consumption. The control system was robust against all the perturbations, i.e. cell growth, cell bleed, addition of air-saturated fresh medium, DO set point change and a second gas sparger used to strip out the carbon dioxide. This approach was also successfully used for the tuning of a 400 L bioreactor DO controller and pH controller.

  • 314.
    Chraibi, Youssef
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Localization in Wireless Sensor Networks2005Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Similar to many technological developments, wireless sensor networks have emerged from military needs and found its way into civil applications. Today, wireless sensor networks has become a key technology for different types of ”smart environments”, and an intense research effort is currently underway to enable the application of wireless sensor networks for a wide rangeof industrial problems. Wireless networks are of particular importance whena large number of sensor nodes have to be deployed, and/or in hazardous situations.

    Localization is important when there is an uncertainty of the exact location of some fixed or mobile devices. One example has been in the supervision of humidity and temperature in forests and/or fields, where thousands of sensors are deployed by a plane, giving the operator little or no possibility to influence the precise location of each node. An effective localization algorithm can then use all the available information from the wireless sensor nodes to infer the position of the individual devices. Another application is the positioning of a mobile robot based on received signal strength from a set of radio beacons placed at known locations on the factory floor.

    This thesis work is carried out on the wireless automation testbed at the S3. Focusing on localization processes, we will first give an overview of the state of the art in this area. From the various techniques, one idea was found to have significant bearing for the development of a new algorithm. We present analysis and simulations of the algorithms, demonstrating improved accuracy compared to other schemes although the accuracy is probably not good enough for some high-end applications. A third aspect of the work concerns the feasibility of approaches based on received signal strength indication (RSSI). Multiple measurement series have been collected in the lab with the MoteIV wireless sensor node platform. The measurement campaign indicates significant fluctuations in the RSSI values due to interference and limited repeatability of experiments, which may limit the reliability of many localization schemes, especially in an indoor environment.

  • 315.
    Cioran, Anders
    KTH, School of Electrical Engineering (EES), Automatic Control.
    System Integration Testing ofAdvanced Driver Assistance Systems2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A key factor to further improve road safety is the development and implementation ofAdvanced Driver Assistance Systems (ADAS) in vehicles. Common aspects of the investigatedADAS' are their abilities of detecting and avoiding hazardous trac situations byusing sensor data and vehicle states in order to control the movement. As more complex andsafety critical ADAS are developed, new test methods have to be considered. This thesisinvestigate how to test new ADAS from a complete vehicle level by considering aspects suchas suitable test environments and trac scenarios, and thereafter compare the results withexisting testing methods. Dierent classications of ADAS have been investigated and combinedwith own classications considering complexity and trac safety aspects, have madeit possible to conclude and propose general test strategies for dierent ADAS.

  • 316.
    Cippitelli, Manuela
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Collaborative Power Control for Wireless Sensor Networks2005Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Sensor nodes within networks are often grouped to participate to a common processing task. Cooperative diversity is a technique that exploits groups of sensor node randomly placed to cooperatively relay a common received signal toward a destination with the goal to combat severe attenuation or disconnections of the signal strength.

    In recent years, cooperative diversity has received attention for cellular radio systems and ad-hoc wireless networks. Such systems, however, are usually equipped with high processing capability. On the contrary, the nodes of a WSNs have limited memory and power capabilities and are usually deployed in unfriendly environment, where recharging and maintenance is not possible.

    In this thesis, we investigate the problem of power control of nodes performing cooperative diversity. Specifically, we study the problem of minimizing the power consumption of the sensor nodes transmitters while guaranteeing a minimum quality of the signal at the data collector. After studying the most relevant algorithms existent in literature for had-hoc networks, we propose an sub-optimal algorithm suitable for nodes equipped with low computational capabilities. We implement a WSNs performing cooperative diversity with Omnet++, where the network simulator includes the sub-optimal solution. Numerical results show that for the set of parameters of practical interest, our solution exhibits good performance for low correlated channel links, while the increase of relaying nodes ensures a decreasing of total power consumption.

  • 317. Clark, William
    et al.
    Bloch, Anthony
    Colombo, Leonardo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rooney, Patrick
    Optimal Control of Quantum Purity for n=2 Systems2017In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, IEEE , 2017, p. 1317-1322Conference paper (Refereed)
    Abstract [en]

    The objective of this work is to study time-minimum and energy-minimum global optimal control for dissipative open quantum systems whose dynamics is governed by the Lindblad equation. The controls appear only in the Hamiltonian. Using recent results regarding the decoupling of such dissipative dynamics into intra- and inter-unitary orbits, we transform the control system into a bi-linear control system on the Bloch ball (the unitary sphere together with its interior). We then design a numerical algorithm to construct an optimal path to achieve a desired point given initial states close to the origin (the singular point) of the Bloch ball. This is done both for the minimum-time and minimum-energy control problems.

  • 318.
    Classon, Johan
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Map Building using Mobile Robots2006Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis two methods to solve the Simultaneous Localization And Mapping problem are presented. The classical extended Kalman filter is used as a reference from where an efficient particle filter is examined, which uses deterministic samples called sigma points. Most of the effort is put on implementing these algorithms together with the Symmetries and Permutations Model, but a preliminary comparison of the methods has been done as well. Experiments show that linearization errors make the map inaccurate over long periods of time, and methods are discussed which decrease these effects.

  • 319.
    Colledanchise, Michele
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Stabilization and Collision Avoidance of Non-point Agents in Dynamic Environments: A Potential Field Approach.2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Mobile robot navigation has found interest during the last few years in civilian and military research areas due to its main benefit of substituting human presence in dangerous tasks. Examples include bomb deactivation, fire suppression and aerial surveillance. In literature, different definitions of the environment where the vehicles’ motion takes place are considered and the main challenge for mobile robots is to navigate in such environment guaranteeing collision avoidance and convergence towards a desired target. Firstly, in the thesis these classical environments are extended considering a more general scenario characterized by workspace bounds and an arbitrary number on objects within it. The main contribution is to develop control strategies able to perform several tasks using artificial potential functions methodologies. In particular, the first studied problem consists of a single spherical shaped agent navigating among both fixed and moving obstacles. The case of study is then extended to the multi-agent navigation problem, proposing both centralized and decentralized policies. In these problems, single integrator kinematic models are considered. The methodologies are then extended to the more realistic case of mobile robots described by a double integrator kinematic model. In the thesis, theoretical results will be developed using tools from Lyapunov stability and LaSalle’s invariance principle. The derivations will be then illustrated by a set of representative numerical examples.

  • 320.
    Colledanchise, Michele
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Dimarogonas, Dimos V
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Ögren, Petter
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Robot navigation under uncertainties using event based sampling2014In: Decision and Control (CDC), 2014 IEEE 53rd Annual Conference on, IEEE conference proceedings, 2014, p. 1438-1445Conference paper (Refereed)
    Abstract [en]

    In many robot applications, sensor feedback is needed to reduce uncertainties in environment models. However, sensor data acquisition also induces costs in terms of the time elapsed to make the observations and the computations needed to find new estimates. In this paper, we show how to use event based sampling to reduce the number of measurements done, thereby saving time, computational resources and power, without jeopardizing critical system properties such as safety and goal convergence. This is done by combining recent advances in nonlinear estimation with event based control using artificial potential fields. The results are particularly useful for real time systems such as high speed vehicles or teleoperated robots, where the cost of taking measurements is even higher, in terms of stops or transmission times. We conclude the paper with a set of simulations to illustrate the effectiveness of the approach and compare it with a baseline approach using periodic measurements.

  • 321.
    Colledanchise, Michele
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Dimarogonas, Dimos
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Ögren, Petter
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Obstacle avoidance in formation using navigation-like functions and constraint based programming2013In: Proceedings of the International Conference on Intelligent Robots and Systems (IROS), 2013 IEEE/RSJ, IEEE conference proceedings, 2013, p. 5234-5239Conference paper (Refereed)
    Abstract [en]

    In this paper, we combine navigation functionlike potential fields and constraint based programming to achieve obstacle avoidance in formation. Constraint based programming was developed in robotic manipulation as a technique to take several constraints into account when controlling redundant manipulators. The approach has also been generalized, and applied to other control systems such as dual arm manipulators and unmanned aerial vehicles. Navigation functions are an elegant way to design controllers with provable properties for navigation problems. By combining these tools, we take advantage of the redundancy inherent in a multi-agent control problem and are able to concurrently address features such as formation maintenance and goal convergence, even in the presence of moving obstacles. We show how the user can decide a priority ordering of the objectives, as well as a clear way of seeing what objectives are currently addressed and what are postponed. We also analyze the theoretical properties of the proposed controller. Finally, we use a set of simulations to illustrate the approach.

  • 322.
    Colledanchise, Michele
    et al.
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL.
    Marzinotto, Alejandro
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Ögren, Petter
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL.
    The advantages of using behavior trees in multi-robot systems2016In: 47th International Symposium on Robotics, ISR 2016, VDE Verlag GmbH, 2016, p. 23-30Conference paper (Refereed)
    Abstract [en]

    Multi-robot teams offer possibilities of improved performance and fault tolerance, compared to single robot solutions. In this paper, we show how to realize those possibilities when starting from a single robot system controlled by a Behavior Tree (BT). By extending the single robot BT to a multi-robot BT, we are able to combine the fault tolerant properties of the BT, in terms of built-in fallbacks, with the fault tolerance inherent in multi-robot approaches, in terms of a faulty robot being replaced by another one. Furthermore, we improve performance by identifying and taking advantage of the opportunities of parallel task execution, that are present in the single robot BT. Analyzing the proposed approach, we present results regarding how mission performance is affected by minor faults (a robot losing one capability) as well as major faults (a robot losing all its capabilities).

  • 323. Combes, R.
    et al.
    Magureanu, Stefan
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Proutière, Alexandre
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Laroche, Cyrille
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Learning to rank: Regret lower bounds and efficient algorithms2015In: Performance Evaluation Review, ISSN 0163-5999, E-ISSN 1557-9484, Vol. 43, no 1, p. 231-244Article in journal (Refereed)
    Abstract [en]

    Algorithms for learning to rank Web documents, display ads, or other types of items constitute a fundamental component of search engines and more generally of online services. In such systems, when a user makes a request or visits a web page, an ordered list of items (e.g. documents or ads) is displayed; the user scans this list in order, and clicks on the first relevant item if any. When the user clicks on an item, the reward collected by the system typically decreases with the position of the item in the displayed list. The main challenge in the design of sequential list selection algorithms stems from the fact that the probabilities with which the user clicks on the various items are unknown and need to be learned. We formulate the design of such algorithms as a stochastic bandit optimization problem. This problem differs from the classical bandit framework: (1) the type of feedback received by the system depends on the actual relevance of the various items in the displayed list (if the user clicks on the last item, we know that none of the previous items in the list are relevant); (2) there are inherent correlations between the average relevance of the items (e.g. the user may be interested in a specific topic only). We assume that items are categorized according to their topic and that users are clustered, so that users of the same cluster are interested in the same topic. We investigate several scenarios depending on the available sideinformation on the user before selecting the displayed list: (a) we first treat the case where the topic the user is interested in is known when she places a request; (b) we then study the case where the user cluster is known but the mapping between user clusters and topics is unknown. For both scenarios, we derive regret lower bounds and devise algorithms that approach these fundamental limits.

  • 324. Combes, R.
    et al.
    Proutiere, Alexandre
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dynamic rate and channel selection in cognitive radio systems2015In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 33, no 5, p. 910-921, article id 6914537Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate dynamic channel and rate selection in cognitive radio systems that exploit a large number of channels free from primary users. In such systems, transmitters may rapidly change the selected (channel, rate) pair to opportunistically learn and track the pair offering the highest throughput. We formulate the problem of sequential channel and rate selection as an online optimization problem and show its equivalence to a structured multiarmed-bandit problem. The structure stems from inherent properties of the achieved throughput as a function of the selected channel and rate. We derive fundamental performance limits satisfied by any channel and rate adaptation algorithm and propose algorithms that achieve (or approach) these limits. In turn, the proposed algorithms optimally exploit the inherent structure of the throughput. We illustrate the efficiency of our algorithms using both test-bed and simulation experiments, in both stationary and nonstationary radio environments. In stationary environments, the packet successful transmission probabilities at the various channel and rate pairs do not evolve over time, whereas in nonstationary environments, they may evolve. In practical scenarios, the proposed algorithms are able to track the best channel and rate quite accurately without the need for any explicit measurement of and feedback on the quality of the various channels.

  • 325. Combes, R.
    et al.
    Talebi, Mohammad Sadegh
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Proutiere, Alexandre
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Lelarge, M.
    Combinatorial bandits revisited2015In: Advances in Neural Information Processing Systems, Neural Information Processing Systems, 2015, p. 2116-2124Conference paper (Refereed)
    Abstract [en]

    This paper investigates stochastic and adversarial combinatorial multi-armed bandit problems. In the stochastic setting under semi-bandit feedback, we derive a problem-specific regret lower bound, and discuss its scaling with the dimension of the decision space. We propose ESCB, an algorithm that efficiently exploits the structure of the problem and provide a finite-time analysis of its regret. ESCB has better performance guarantees than existing algorithms, and significantly outperforms these algorithms in practice. In the adversarial setting under bandit feedback, we propose COMBEXP, an algorithm with the same regret scaling as state-of-the-art algorithms, but with lower computational complexity for some combinatorial problems.

  • 326.
    Combes, Richard
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Altman, Z.
    Altman, E.
    Coordination of autonomic functionalities in communications networks2013In: 2013 11th International Symposium and Workshops on Modeling and Optimization in Mobile, Ad Hoc and Wireless Networks, WiOpt 2013, New York: IEEE , 2013, p. 364-371Conference paper (Refereed)
    Abstract [en]

    Future communication networks are expected to feature autonomic (or self-organizing) mechanisms to ease deployment, tune parameters automatically and repair the network. Self-organizing mechanisms are designed as stand-alone entities, even though multiple mechanisms run in parallel in operational networks. An efficient coordination mechanism will be the major enabler for large scale deployment of self-organizing networks. We model self-organizing mechanisms as control loops, and study the conditions for stability when running control loops in parallel. Based on control theory, we propose a distributed coordination mechanism to stabilize the system. In certain cases, coordination can be achieved without any exchange of information between control loops. The mechanism remains valid in the presence of noise via stochastic approximation. Instability and coordination in the context of wireless networks are illustrated with two examples. We are essentially concerned with linear systems, and the applicability of our results for non-linear systems is discussed.

  • 327.
    Combes, Richard
    et al.
    Centrale-Supelec, L2S, France.
    Magureanu, Stefan
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Proutiere, Alexandre
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Minimal Exploration in Structured Stochastic Bandits2017In: Advances in Neural Information Processing Systems, Neural information processing systems foundation , 2017, p. 1764-1772Conference paper (Refereed)
    Abstract [en]

    This paper introduces and addresses a wide class of stochastic bandit problems where the function mapping the arm to the corresponding reward exhibits some known structural properties. Most existing structures (e.g. linear, lipschitz, unimodal, combinatorial, dueling,...) are covered by our framework. We derive an asymptotic instance-specific regret lower bound for these problems, and develop OSSB, an algorithm whose regret matches this fundamental limit. OSSB is not based on the classical principle of " role="presentation" style="box-sizing: border-box; display: inline-block; line-height: 0; font-size: 16.38px; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; color: rgb(51, 51, 51); font-family: "Helvetica Neue", Helvetica, Arial, sans-serif; position: relative;">optimism in the face of uncertainty'' or on Thompson sampling, and rather aims at matching the minimal exploration rates of sub-optimal arms as characterized in the derivation of the regret lower bound. We illustrate the efficiency of OSSB using numerical experiments in the case of the linear bandit problem and show that OSSB outperforms existing algorithms, including Thompson sampling.

  • 328.
    Combes, Richard
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Proutiere, Alexandre
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Unimodal bandits: Regret lower bounds and optimal algorithms2014In: 31st International Conference on Machine Learning, ICML 2014, 2014, p. 799-807Conference paper (Refereed)
    Abstract [en]

    2014 We consider stochastic multi-armed bandits where the expected reward is a unimodal function over partially ordered arms. This important class of problems has been recently investigated in (Cope, 2009; Yu&Mannor, 2011). The set of arms is either discrete, in which case arms correspond to the vertices of a finite graph whose structure represents similarity in rewards, or continuous, in which case arms belong to a bounded interval. For discrete unimodal bandits, we derive asymptotic lower bounds for the regret achieved under any algorithm, and propose OSUB, an algorithm whose regret matches this lower bound. Our algorithm optimally exploits the unimodal structure of the problem, and surprisingly, its asymptotic regret does not depend on the number of arms. We also provide a regret upper bound for OSUB in non-stationary environments where the expected rewards smoothly evolve over time. The analytical results are supported by numerical experiments showing that OSUB performs significantly better than the state-of-the-art algorithms. For continuous sets of arms, we provide a brief discussion. We show that combining an appropriate discretization of the set of arms with the UCB algorithm yields an order-optimal regret, and in practice, outperforms recently proposed algorithms designed to exploit the unimodal structure.

  • 329.
    Combes, Richard
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Proutiere, Alexandre
    KTH, School of Electrical Engineering (EES), Automatic Control. INRIA/ENS, France .
    Yun, D.
    Ok, J.
    Yi, Y.
    Optimal Rate Sampling in 802.11 systems2014In: Proceedings - IEEE INFOCOM, 2014, p. 2760-2767Conference paper (Refereed)
    Abstract [en]

    Rate Adaptation (RA) is a fundamental mechanism in 802.11 systems. It allows transmitters to adapt the coding and modulation scheme as well as the MIMO transmission mode to the radio channel conditions, and in turn, to learn and track the (mode, rate) pair providing the highest throughput. So far, the design of RA mechanisms has been mainly driven by heuristics. In contrast, in this paper, we rigorously formulate such design as an online stochastic optimisation problem. We solve this problem and present ORS (Optimal Rate Sampling), a family of (mode, rate) pair adaptation algorithms that provably learn as fast as it is possible the best pair for transmission. We study the performance of ORS algorithms in stationary radio environments where the successful packet transmission probabilities at the various (mode, rate) pairs do not vary over time, and in non-stationary environments where these probabilities evolve. We show that under ORS algorithms, the throughput loss due to the need to explore sub-optimal (mode, rate) pairs does not depend on the number of available pairs. This is a crucial advantage as evolving 802.11 standards offer an increasingly large number of (mode, rate) pairs. We illustrate the efficiency of ORS algorithms (compared to the state-of-the-art algorithms) using simulations and traces extracted from 802.11 test-beds.

  • 330. Congiu, R.
    et al.
    Shokri-Ghadikolaei, Hossein
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Santucci, F.
    On the relay-fallback tradeoff in millimeter wave wireless system2016In: Proceedings - IEEE INFOCOM, 2016, p. 622-627Conference paper (Refereed)
    Abstract [en]

    Millimeter wave (mmWave) communications systems are promising candidate to support extremely high data rate services in future wireless networks. MmWave communications exhibit high penetration loss (blockage) and require directional transmissions to compensate for severe channel attenuations and for high noise powers. When blockage occurs, there are at least two simple prominent options: 1) switching to the conventional microwave frequencies (fallback option) and 2) using an alternative non-blocked path (relay option). However, currently it is not clear under which conditions and network parameters one option is better than the other. To investigate the performance of the two options, this paper proposes a novel blockage model that allows deriving maximum achievable throughput and delay performance of both options. A simple criterion to decide which option should be taken under which network condition is provided. By a comprehensive performance analysis, it is shown that the right option depends on the payload size, beam training overhead, and blockage probability. For a network with light traffic and low probability of blockage in the direct link, the fallback option is throughput- and delay-optimal. For a network with heavy traffic demands and semistatic topology (low beam-training overhead), the relay option is preferable.

  • 331.
    Congiu, Roberto
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fundamental performance analysis ofmillimeter wave relay networks2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    unicationtechnologies, the millimeter wave (mmWave) bands are consideredas a promising candidate to extremely high data rate access in futurewireless networks. MmWave communications exhibit high attenuations,vulnerability to obstacles, and sparse-scattering environments. The smallwavelengths of mmWave signals make it possible to incorporate many antennaelements both at the transmitters and at the receivers, which lead tohigh antenna gains. This demands a reconsideration of almost all designaspects in mmWave networks compared to the traditional networks, especiallyat the medium access control (MAC) layer. Blockage affects heavilythe performance of mmWave networks. How to model blockage and itsimpacts on the key performance indicators are largely open problems.In this thesis, a new blockage model is introduced, which allows evaluatingthe impact of penetration loss due to obstacles on the fundamental performanceindicators including achievable throughput and delay. Using thisblockage model, the achievable throughput and delay of two solution approachesto overcome blockage, namely fallback and relay, is investigated.The analysis highlights an interesting correlation between blockage periodand the importance of using one technique or the other one. Afterwards, adelay analysis is proposed to focus on more realistic scenarios. Such an analysisis then used to characterize the throughput-delay tradeoff. The lattersection allows to explore the impact of the main network parameters suchas beamwidth, obstacle occurrence, blockage period, transmission time andalignment overhead. A general framework is proposed, in which it is shownunder which condition which option is preferable, from throughput-delayperspective, at the transmitter to mitigate the blockage problem. Moreover,it shows the situations under which these two techniques are notfeasible in order to fulfil some throughput-delay requirements. Simulationsare presented in order to validate the equations used at the performanceanalysis.

  • 332.
    Cornell, Axel
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Probabilistic Fault Isolation in Embedded Systems Using Training Data2008Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the heavy vehicle industry customers, laws and increasingly complex processes demand methods of supervising every aspect of a truck. Fault isolation systems are introduced to do just that. In order to assure a sustainable development new types of isolation systems are investigated to substitute the consistency based isolation systems of today.

    In this thesis an application of a probabilistic isolation method that ranks possible faults on their likeliness of being a fault in the process is implemented and evaluated as a possible future replacement of today's system. This method bases the isolation on training data collected from measurements on the process and observation of the process.

    The probabilistic isolation method is evaluated on hos it performs under different circumstances such as the effort of different amounts of training data and how well it performs if the tests and observations of the process are of varying quality.

    Solution to several problems that arise when this method is implemented are also investigated such as how the system handles cases where several faults occur at the same time, what happens if there are missing data in the observations of the system and how to solve problems that involve execution times which is important in embedded systems.

    The results that are derived show that this probabilistic isolation system performs well on the process as it is today and that this is a good substitute when developing for future processes. There is however a need for further development of the system such as improved isolation when there are several faults present in the process and questions on how to collect and store the training data still remain to be answered. A full scale implement would allow for better comparison with the current system and give more information on runtime and storage problems.

  • 333.
    Cornell, Ivar
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Implementation of a Collection Tree Routing Protocol and a Predictive Outage Compensator2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Wireless communication is widely used in modern devices but has not yet conquered industry. Introducing wireless control in industry will result in an economical bene t since installing cables is time consuming and expensive. Wireless control brings other problems to the table such as delays and packet loss which are discussed in this thesis. The original problem scenario is set in an industry with wireless control loops. A fork lift parks in a way so that communication on a wireless path is broken, creating a so called communication outage. Two solutions to this problem are proposed.

    The first contribution of this thesis solves the communication outage by re-routing. The solution is a Collection Tree routing Protocol (CTP) that detects the broken link and nds another way of sending the information. This solution proves to be eective as only between one and eight packets is lost. The implementation of this protocol is implemented on wireless communication modules called Tmote sky motes.

    The second contribution deals with lost packets. A Kalman lter based Predictive Outage Compensator (POC) is introduced and implemented on a Quanser Two Tank process together with the routing protocol above. The POC is benchmarked against a naive and commonly used Hold compensator that simply holds the last received value. Results show that the Kalman POC eectively estimates lost information where the Hold compensator causes over ooding of the water tanks.

  • 334. Daafouz, J.
    et al.
    Benedetto, M. D. Di
    Blondel, V. D.
    Ferrari-Trecate, G.
    Hetel, L.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Juloski, A. L.
    Paoletti, S.
    Pola, G.
    Santis, E. De
    Vidal, R.
    Switched and  piecewise affine systems2009In: Handbook of Hybrid Systems Control: Theory, Tools, Applications / [ed] Lunze, J.; Lamnabhi-Lagarrigue, F., Cambridge Press , 2009, p. 87-138Chapter in book (Other academic)
  • 335. Dai, Li
    et al.
    Xia, Yuanqing
    Gao, Yulong
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cannon, Mark
    Distributed Stochastic MPC of Linear Systems With Additive Uncertainty and Coupled Probabilistic Constraints2017In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 62, no 7, p. 3474-3481Article in journal (Refereed)
    Abstract [en]

    This technical note develops a new form of distributed stochastic model predictive control (DSMPC) algorithm for a group of linear stochastic subsystems subject to additive uncertainty and coupled probabilistic constraints. We provide an appropriate way to design the DSMPC algorithm by extending a centralized SMPC (CSMPC) scheme. To achieve the satisfaction of coupled probabilistic constraints in a distributed manner, only one subsystem is permitted to optimize at each time step. In addition, by making explicit use of the probabilistic distribution of the uncertainties, probabilistic constraints are converted into a set of deterministic constraints for the predictions of nominal models. The distributed controller can achieve recursive feasibility and ensure closed-loop stability for any choice of update sequence. Numerical examples illustrate the efficacy of the algorithm.

  • 336.
    Dalin, Erik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Automatic control of servo systems for positioning of parabolic antenna in two-way satellite communication at sea2004Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 337. D'Angelo, M.
    et al.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    How to select the OOK detection threshold in wireless ad hoc and sensor networks2009In: IEEE Vehicular Technology Conference / [ed] 69th IEEE Vehicular Technology Conference Barcelona, SPAIN, APR 26-29, 2009, 2009Conference paper (Refereed)
    Abstract [en]

    On-off keying (OOK) is an attractive modulation technique to reduce energy consumption of power-constrained wireless networks. The OOK detection threshold, however, must be carefully selected to minimize the bit error probability (BER). This is a challenging task to accomplish on resource-limited nodes or on networks with high-mobility. In this paper, an efficient algorithm to compute the optimal threshold is proposed. The system scenario considers nodes simultaneously transmitting over same frequencies in Rayleigh-log-normal or Rice-log-normal fading conditions. It is shown that by using the Stirling expansion for the BER, and a log-normal approximation, a quick contraction-mapping can be built to achieve the threshold numerically. The mapping is simple to implement and converges quickly. Numerical simulations verify the validity of the theoretical analysis, and show that the new algorithm performs quite well in scenarios of practical interest.

  • 338.
    Dargaud, Etienne
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Pick-Up and Delivery Planning in Multi-Agent Systems under Temporal Logic Specications2013Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis describes an approach for solving planning problems for a team of robots involving picking up and moving objects. The temporal goals are described using linear temporal logic over subsets of the workspace. Temporal logic is a convenient formalism to capture the usual control specications such as reachability and invariance as well as more complex specications like sequencing and obstacle avoidance. Those goals include the positions of the robots and the positions of the objects, e.g, go to a given location, bring an object there or pick up this object. We consider robots moving in a 2D environment which is partitioned into non-overlapping regions. A cost representing the total number of actions done by all the robots will be used to evaluate the quality of the runs. Our goal is to create a plan in a decentralized way for the robots that has a small cost and makes the robots collaborate to decrease the cost even more.

    The approach is divided in several steps. First a plan is created for each robot using an abstraction of the robot and its specication. This plan describes the sequence of abstract actions the robot will do to full its specifications. Second those actions are ordered in order to make their global cost as small as possible. Third and nally, the robot path for executing each action is found using automata theory. Such path is guaranteed to respect the global specication of the robot. We support the proposed theory with experimental results, showing that it gives an optimal solution in some simple examples.

  • 339.
    De Angelis, Alessio
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    A distributed information fusion method for localization based on Pareto optimization2011In: 7th IEEE International Conference on Distributed Computing in Sensor Systems(DCOSS), 2011Conference paper (Refereed)
    Abstract [en]

    To overcome the limitations of specific positioning techniques for mobile wireless nodes and achieve a high accuracy, the fusion of heterogeneous sensor information is an appealing strategy. In this paper, the problem of optimal fusion of ranging information typically provided by Ultra-Wideband radio with speed and absolute orientation information is addressed. A new distributed recursive estimation method is proposed. The method does not assume any motion model of mobile nodes and is based on a Pareto optimization. The challenging part of the new estimator is the characterization of the statistical information needed to model the optimization problem. The proposed estimator is validated by Monte Carlo simulations, and the performance is compared to several Kalman-based filters commonly employed for localization and sensor fusion. Much better performance is achieved, but at the price of an increased computational complexity.

  • 340.
    De Angelis, Alessio
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing.
    A Sensor Fusion Algorithm for Mobile Node Localization2011In: 18th World Congress of the International Federation of Automatic Control (IFAC), 2011Conference paper (Refereed)
    Abstract [en]

    Accurate  distributed  estimation  of the position  of network  nodes  is essential  formany  applications,  including  localization,  geographic  routing,  and  vehicular  networks.  When nodes are mobile and their mobility pattern is unknown,  there are not yet adequate techniques to achieve high accuracy  and  low estimation errors.  In this paper,  a new distributed estimator of the position of mobile nodes is proposed.  No model of the mobility is assumed.  The estimator combines heterogeneous  information coming from pre-existing ranging, speed, and angular measurements,  which  is jointly  fused  by  an  optimization  problem  where  the squared  mean and variance  of the localization error is minimized. Challenges of this optimization are the characterization  of the moments  of the noises  that affect  the measurements.  The  estimator is distributed  in that it  requires  only  local processing  and  communication  among  the nodes of the network.  Numerical  results  show that the proposed  estimator  outperforms traditionalapproaches based on the extended Kalman  filter.

  • 341.
    De Biasi, Mauro
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Implementation of a wirelessHART simulator and its use in studying packet loss compensation in networked control2008Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis is part of the SOCRADES project, a European research and advanced development project with the primary objective to develop a design, execution and management platform for next-generation industrial automation systems. In the speci¯c case of work it concerns the networked control systems. These are becoming more important in the industrial automation ¯eld thanks to the many advantages introduced by the networks. In fact, the use of a network to connect the devices permits to eliminate unnecessary wirings, reducing the complexity and the overall cost in designing and implementing the control systems. In the last years the fast spread of the wireless technologies has opened new scenarios for the communication in the automation ¯eld. The bene¯ts introduced by the use of wireless communication in the networked control system are many. First of all the simplicity and the convenience of the sensors placement. The price to be paid is a lower reliability due to the interference that can easily a®ect the medium (radio frequencies) with the consequent possible loss of communication. This work is focused on the study of the problem of losing packets (the information in a wireless network is formed by packets of bits) in a WirelessHART networked control system and on the possible solutions to avoid the problem. WirelessHART is a wireless protocol that provides a low cost, relatively low speed (e.g., compared to IEEE 802.11g) wireless connection. The aims of the thesis are multiple, ¯rst of all the implementation of a tool that permits to simulate a wirelessHART network. In fact, since it is a quite new protocol, the most used network simulators do not give the possibility to simulate WirelessHART networks. This simulator has been implemented modifying the original version of the TrueTime network simulator, adding this new protocol and some other functions to make the simulator as close as possible to the reality. Another objective of the thesis is to study the e®ects, and the possible solutions, of the loss of communication in a wirelessHART network.

    The last part of the thesis deals with a level control problem in a mineral flotation plant and with the possibility to use a wirelessHART network for that plant.

  • 342. De Castro, N. C.
    et al.
    De Wit, C. C.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On energy-aware communication and control co-design in wireless networked control systems2010In: Estimation and Control of Networked Systems, 2010, p. 49-54Conference paper (Refereed)
    Abstract [en]

    Energy is a key resource in Networked Control Systems, in particular in applications concerning wireless networks. This paper reviews the multi-layer architecture of those systems in the light of their energy-use, and points out major contributions in the area of energy-management policies, layer per layer. This review of the literature is organized according to the layered communication architecture covering from bottom to top the Physical, Data Link, Network, and Application layers. We specifically focus on advances that concern energy-aware management in wireless communication and control co-design. It is argued that existing work is limited to single layer approaches, with a lack of design methods taking into account several layers.

  • 343.
    De Lucia, Silvia
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Optimization of Handover Algorithms for Wireless Networks2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    We are witnessing a continuous development of heterogeneous wireless networks, such as cellular systems (e.g., the LTE, or long term evolution of the third generation wireless system), sensor networks, and satellite networks. The coexistence of all these networks requires the design of control mechanisms to allow the seamless communication from one network to another, and even between communication standards. The handover is one such control mechanism. Specifically, the handover is the mechanism of transferring the connection of a mobile node from an access point (which could be a base station or a network using some communication standard) to another AP. During the handover, a node that is being disconnected from an AP and connected to another AP may experience a sudden degradation of the bandwidth or outage of the communication. This leads to frequent and unnecessary handovers that may reduce significantly the quality of service perceived by the node. Therefore, in order for the node to achieve high quality of service, an optimization of the handover algorithm is essential. In this thesis we study some optimization algorithms for the handover procedure. We show that the variables available at the node to control the handover are the hysteresis margin, which is used to compare the quality of signals of the APs, and the estimation window length, which is the number of samples to estimate with a desired accuracy these signals. Then, we study two optimization problems in which the parameters that affect the handover are optimized by considering as a cost function a convex combination of the probability of outage and the probability of handover. The first problem is based on a static optimization, whereas the second problem on a dynamic optimization. We show that both problems offer better performance with respect to existing algorithms from the literature. We  show that the dynamic optimization gives better results, but at the cost of an increased computational complexity.

  • 344. de Sousa, Joao Borges
    et al.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Silva, Jorge
    Speranzon, Alberto
    A verified hierarchical control architecture for co-ordinated multi-vehicle operations2007In: International journal of adaptive control and signal processing (Print), ISSN 0890-6327, E-ISSN 1099-1115, Vol. 21, no 02-3, p. 159-188Article in journal (Refereed)
  • 345. Deghat, M.
    et al.
    Davis, E.
    See, T.
    Shames, Iman
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Anderson, B. D. O.
    Yu, C.
    Target localization and circumnavigation by a non-holonomic robot2012In: Intelligent Robots and Systems (IROS), 2012 IEEE/RSJ International Conference on, 2012, p. 1227-1232Conference paper (Refereed)
    Abstract [en]

    This paper addresses a surveillance problem in which the goal is to achieve a circular motion around a target by a non-holonomic agent. The agent only knows its own position with respect to its initial frame, and the bearing angle of the target in that frame. It is assumed that the position of the target is unknown. An estimator and a controller are proposed to estimate the position of the target and make the agent move on a circular trajectory with a desired radius around it. The performance of the proposed algorithm is verified both through simulations and experiments. Robustness is also established in the face of noise and target motion.

  • 346. Deghat, M.
    et al.
    Shames, Iman
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Anderson, B. D. O.
    Moura, J. M. F.
    Distributed localization via barycentric coordinates: Finite-time convergence2011In: IFAC Proceedings Volumes: (IFAC-PapersOnline), 2011, no PART 1, p. 7824-7829Conference paper (Refereed)
    Abstract [en]

    We consider distributed localization in a sensor network in ℝ 2 from inter-agent distances. Sensors and anchors exchange data with their neighbors. No centralized data processing is required. We establish a differential equation for the unknown sensor positions, and show that the estimated positions of sensors converge to their actual values in finite time (assuming noise-free measurements). The key assumption is that all sensors are in the convex hull of three or more anchors. The proposed localization method uses the barycentric coordinates of each sensor with respect to some of its neighbors (which may not include those anchors), assuming the sensor falls in the convex hull of these neighbors.

  • 347. Del Favero, S.
    et al.
    Varagnolo, Damiano
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pillonetto, G.
    Bayesian learning of probability density functions: A Markov chain Monte Carlo approach2012In: Decision and Control (CDC), 2012 IEEE 51st Annual Conference on, IEEE , 2012, p. 1512-1517Conference paper (Refereed)
    Abstract [en]

    The paper considers the problem of reconstructing a probability density function from a finite set of samples independently drawn from it.We cast the problem in a Bayesian setting where the unknown density is modeled via a nonlinear transformation of a Bayesian prior placed on a Reproducing Kernel Hilbert Space. The learning of the unknown density function is then formulated as a minimum variance estimation problem. Since this requires the solution of analytically intractable integrals, we solve this problem by proposing a novel algorithm based on the Markov chain Monte Carlo framework. Simulations are used to corroborate the goodness of the new approach.

  • 348. Delellis, P.
    et al.
    Di Bernardo, M.
    Liuzza, Davide
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Department of Electrical Engineering and Information Technology, University of Naples Federico II, Naples, Italy.
    Convergence and synchronization in heterogeneous networks of smooth and piecewise smooth systems2015In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 56, p. 1-11Article in journal (Refereed)
    Abstract [en]

    This paper presents a framework for the study of convergence in networks where the nodes’ dynamics may be both piecewise smooth and/or nonidentical. Sufficient conditions are derived for global convergence of all node trajectories towards the same bounded region in the synchronization error space. The analysis is based on the use of set-valued Lyapunov functions and bounds are derived on the minimum coupling strength required to make all nodes in the network converge towards each other. We also provide an estimate of the asymptotic bound on the mismatch between the node state trajectories. The analysis is performed both for linear and nonlinear coupling protocols. The theoretical analysis is extensively illustrated and validated via its application to a set of representative numerical examples.

  • 349. Deliparaschos, K. M.
    et al.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Christodoulides, P.
    Klerides, E.
    Reduced power expenditure in the minimum latency transmission scheduling problem2014In: 6th International Symposium on Communications, Control and Signal Processing, ISCCSP 2014, 2014, p. 206-209Conference paper (Refereed)
    Abstract [en]

    In large networks due to the large number of transmissions it is unlikely that a slot will be used only by a single wireless node. In this paper, a Cutting Plane approach is proposed in order to combine the minimum latency transmission scheduling problem with power expenditure minimization. The problem is partitioned into a Master Problem and a Subproblem; the main objective of the Subproblem is to minimize the total power expenditure. The Cutting Plane algorithm used is evaluated with regard to its performance and the outcome is that the power expenditure is reduced significantly, while achieving the minimum latency transmission scheduling. One of the drawbacks of the proposed approach, however, is the fact that although it reduces the power significantly, the computational time required is quite large, pointing to further research towards that direction.

  • 350.
    Della Penda, Demia
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Resource management for network-assisted D2D communication2016Licentiate thesis, monograph (Other academic)
    Abstract [en]

    During the last decade, the widespread use of smart devices and mobile applications has led to a massive growth of the mobile traffic demand. Efficiency and scalability are therefore key criteria for the development of future cellular systems, in which device-to-device (D2D) communication is recognized as one of the promising technologies. D2D communication allows mobile users in physical proximity to communicate directly, bypassing the base station as in conventional cellular networks.In this thesis, we investigate some of the possible benefits and challenges brought by the introduction of D2D communication in cellular systems. In particular, we focus on resource management techniques for network-assisted D2D communication using cellular spectrum. Our main contributions lie in the context of mode selection, power control and (frequency/time) resource allocation mechanisms, recognized as key techniques to realize the promises of this technology.First, we investigate how the integration of D2D communication in cellular systems operating under dynamic Time Division Duplex (TDD) can enhance their energy efficiency. We perform joint optimization of mode selection, uplink/downlink transmission period, and power allocation to minimize the transmission energy consumption. The resource management problems for different scenarios are formulated as mixed-integer nonlinear programming problems. In several cases, we exploit the problems’ structure to design efficient algorithms that achieve optimal solutions in polynomial time. In the remaining cases, we propose a heuristic algorithm that computes near-optimal solutions while respecting practical constraints in terms of execution times and signalling overhead. Our simulations demonstrate that D2D communications in dynamic TDD systems can yield significant energy savings and improved spectral efficiency compared to traditional cellular communication.Second, we study the performance of various power control strategies applicable to D2D communications in 3GPP LTE networks. We compare them with an utility maximization approach that trades off spectrum efficiency and total transmit power consumption. Our numerical results suggest that the LTE power control scheme is well prepared for network-assisted D2D communications, especially from the cellular user perspective. However, for D2D users, the utility based scheme can provide gains in terms of SINR and power consumption.Finally, we investigate the subcarrier allocation problem for uplink transmissions ina D2D-enabled network. We focus on maximizing the aggregate transmission rate of the system. In addition to the traditional inter-cell interference, we also account for the intra-cell interference caused by D2D pairs reusing cellular resources. This problem is computationally hard due to its nonconvex and combinatorial nature. However, we show that it can be described as a potential game; hence, we can find a Nash equilibrium using iterative algorithms based on best/better response dynamics.

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