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  • 1.
    Chen, Zhiyong
    et al.
    Univ Newcastle, Sch Elect Engn & Comp Sci, Callaghan, NSW, Australia..
    Zhang, Haitao
    Huazhong Univ Sci & Technol, Dept Control Sci & Engn, Wuhan, Peoples R China..
    Zhu, Lijun
    Univ Hong Kong, Dept Elect & Elect Engn, Pokfulam, Hong Kong, Peoples R China..
    Knorn, Steffi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Cheng, Zhao
    Dartmouth Coll, Thayer Sch Engn, Hanover, NH 03755 USA..
    Advanced Techniques for Networked Systems with Applications2017In: Mathematical problems in engineering (Print), ISSN 1024-123X, E-ISSN 1563-5147, article id 3849019Article in journal (Refereed)
  • 2.
    Ferguson, Joel
    et al.
    Univ Newcastle, Sch Elect Engn & Comp, Callaghan, NSW 2308, Australia.;Univ Newcastle, PRC CDSC, Callaghan, NSW 2308, Australia..
    Donaire, Alejandro
    Univ Naples Federico II, Prisma Lab, Naples, Italy.;Univ Newcastle, Callaghan, NSW, Australia..
    Knorn, Steffi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Middleton, Richard H.
    Univ Newcastle, Sch Elect Engn & Comp, Callaghan, NSW 2308, Australia.;Univ Newcastle, PRC CDSC, Callaghan, NSW 2308, Australia..
    Decentralized control for l(2) weak string stability of vehicle platoon2017In: 20th IFAC World Congress, Elsevier, 2017, Vol. 50, no 1, p. 15012-15017Conference paper (Refereed)
    Abstract [en]

    In this paper we present a method of bidirectional control of a vehicle string that achieves l(2) weak string stability. Previous work required short-range communications between vehicles within the string. Here, we utilise some recent results on integral action to remove the requirement of communications altogether. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

  • 3.
    Herman, Ivo
    et al.
    Czech Tech Univ, Dept Control Engn, Prague, Czech Republic..
    Knorn, Steffi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Disturbance scaling in bidirectional vehicle platoons with different asymmetry in position and velocity coupling2017In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 82, p. 13-20Article in journal (Refereed)
    Abstract [en]

    This paper considers a string of vehicles where the local control law uses the states of the vehicle's immediate predecessor and follower. The coupling towards the preceding vehicle can be chosen different to the coupling with the following vehicle, which is referred to as an asymmetric bidirectional string. Further, the asymmetry for the velocity coupling can be chosen differently to the asymmetry in the position coupling. It is investigated how the effect of the disturbance on the control errors in the string depends on the string length. It is shown, that in case of symmetric position coupling and asymmetric velocity coupling, linear scaling can be achieved. For symmetric interactions, the errors scale quadratically in the number of vehicles. When the coupling in position is asymmetric, exponential scaling may occur or the system might even become unstable. The paper thus gives a comprehensive overview of the achievable performance in linear, asymmetric, bidirectional platoons. The results reveal that symmetry in the position coupling and asymmetry in velocity coupling qualitatively improve the performance of the string. Extensive numerical results illustrate the theoretical findings.

  • 4.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Deviation bounds in multi agent systems described by undirected graphs2016In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 67, p. 205-210Article in journal (Refereed)
    Abstract [en]

    The theory of port-Hamiltonian systems is used to derive upper bounds for the state deviations in multi agent systems described by undirected graphs pinned to a reference signal. The upper bounds for the deviations in networks of first or second order agents, respectively, depend on the minimal eigenvalue of the extended Laplacian of the system. In networks of first order agents, the deviations decay exponentially with a rate depending on the same minimal eigenvalue. In case networks of second order systems meet specific design properties, it can be shown that the deviations also decay exponentially with half the rate compared to first order systems.

  • 5.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Chen, Z
    Univ Newcastle, Sch Elect Engn & Comp Sci, Callaghan, NSW 2308, Australia.
    Middleton, RH
    Univ Newcastle, Sch Elect Engn & Comp Sci, Callaghan, NSW 2308, Australia.
    Overview: Collective control of multi-agent systems2016In: IEEE Transactions on Control of Network Systems, E-ISSN 2325-5870, Vol. 3, no 4, p. 334-347Article in journal (Refereed)
    Abstract [en]

    Collective control of amultiagent system is concerned with designing strategies for a group of autonomous agents operating in a networked environment. The aim is to achieve a global control objective through distributed sensing, communication, computing, and control. It has attracted many researchers from a wide range of disciplines, including the literature of automatic control. This paper aims to give a general framework that is able to accommodate many of these outcomes. Within this framework, the development on this topic is systematically reviewed and the representative outcomes can be sorted out from four aspects: 1) agent dynamics; 2) network topologies; 3) feedback and communication mechanisms; and 4) collective behaviors. Thus, the state-of-the-art approach and technology is described. Moreover, within this framework, further interesting and promising directions on this research topic are envisioned.

  • 6.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Dey, Subhrakanti
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Optimal energy allocation for linear control over a packet-dropping link with energy harvesting constraints2015Conference paper (Refereed)
  • 7.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Dey, Subhrakanti
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Optimal energy allocation for linear control with packet loss under energy harvesting constraints2017In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 77, p. 259-267Article in journal (Refereed)
    Abstract [en]

    This paper studies a closed loop linear control system over a lossy communication link. A sensor computes a state estimate of the observed discrete-time system and sends it (in the form of packetized transmission) to the controller in the receiver block over a randomly time-varying (fading) packet dropping link. The receiver sends an ACK/NACK packet to the transmitter over an acknowledgement channel which might also be prone to packet loss. It is assumed that the energy used in packet transmission depletes a battery of limited capacity at the sensor, but is also replenished by an energy harvester which has access to a source of everlasting but random harvested energy. Under an assumption of finite-state Markov chain models of the energy harvesting and the fading channel gain processes, the objective is to design an optimal energy allocation policy at the transmitter and an optimal control policy at the receiver so that an average infinite horizon linear quadratic Gaussian (LQG) control cost is minimized. It is shown that in the case of perfect channel feedback a separation principle holds, the optimal LQG controller is linear and the optimal energy allocation policy at the transmitter can be obtained via solving the Bellman dynamic programming equation. A Q-learning algorithm is used to approximate the optimal energy allocation policy in case the system parameters are unknown. Numerical simulation examples show that the dynamic programming based policies outperform various simple heuristic policies, especially at higher battery capacities.

  • 8.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Dey, Subhrakanti
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Optimal sensor transmission energy allocation for linear control over a packet dropping link with energy harvesting2015In: 2015 54Th IEEE Conference On Decision And Control (CDC), 2015, p. 1199-1204Conference paper (Refereed)
    Abstract [en]

    This paper studies a closed loop linear control system. The sensor computes a state estimate and sends it to the controller/actuator in the receiver block over a randomly fading packet dropping link. The receiver sends an ACK/NACK packet to the transmitter over a link. It is assumed that the transmission energy per packet at the sensor depletes a battery of limited capacity, replenished by an energy harvester. The objective is to design an optimal energy allocation policy and an optimal control policy so that a finite horizon LQG control cost is minimized. It is shown that in case the receiver to sensor feedback channel is free of errors, a separation principle holds. Hence, the optimal LQG controller is linear, the Kalman filter is optimal and the optimal energy allocation policy is obtained via solving a backward dynamic programming equation. In case the feedback channel is erroneous, the separation principle does not hold. In this case, we propose a suboptimal policy where the controller still uses a linear control, and the transmitter minimizes an expected sum of the trace of an "estimated" receiver state estimation error covariance matrix. Simulations are used to illustrate the relative performance of the proposed algorithms and various heuristic algorithms for both the perfect and imperfect feedback cases. It is seen that the dynamic programming based policies outperform the simple heuristic policies by a margin.

  • 9.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Dey, Subhrakanti
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Quevedo, Daniel E.
    Distortion Minimization in Multi-Sensor Estimation Using Energy Harvesting and Energy Sharing2015In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 63, no 11, p. 2848-2863Article in journal (Refereed)
    Abstract [en]

    This paper investigates an optimal energy allocation problem for multisensor estimation of a random source where sensors communicate their measurements to a remote fusion center (FC) over orthogonal fading wireless channels using uncoded analog transmissions. The FC reconstructs the source using the best linear unbiased estimator (BLUE). The sensors have limited batteries but can harvest energy and also transfer energy to other sensors in the network. A distortion minimization problem over a finite-time horizon with causal and noncausal centralized information is studied and the optimal energy allocation policy for transmission and sharing is derived. Several structural necessary conditions for optimality are presented for the two sensor problem with noncausal information and a horizon of two time steps. A decentralized energy allocation algorithm is also presented where each sensor has causal information of its own channel gain and harvested energy levels and has statistical information about the channel gains and harvested energies of the remaining sensors. Various other suboptimal energy allocation policies are also proposed for reducing the computational complexity of dynamic programming based solutions to the energy allocation problems with causal information patterns. Numerical simulations are included to illustrate the theoretical results. These illustrate that energy sharing can reduce the distortion at the FC when sensors have asymmetric fading channels and asymmetric energy harvesting processes.

  • 10.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Dey, Subhrakanti
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Quevedo, Daniel E
    Univ Newcastle, Sch Elect Engn & Comp Sci, Callaghan, NSW 2308, Australia.
    Multi-sensor estimation using energy harvesting and energy sharing2015Conference paper (Refereed)
    Abstract [en]

    This paper investigates an optimal energy allocation problem for multi sensor estimation of a random source where sensors communicate their measurements to a remote fusion centre (FC) over orthogonal fading wireless channels using uncoded analog transmissions. The FC reconstructs the source using the best linear unbiased estimator (BLUE). The sensors have limited batteries but can harvest energy and also transfer energy to other sensors in the network. A distortion minimization problem over a finite-time horizon with causal and non-causal information is studied and the optimal energy allocation policy for transmission and sharing is derived. Several structural necessary conditions for optimality are presented for the two sensor problem with non-causal information and a horizon of two time steps. Numerical simulations are included to illustrate the theoretical results.

  • 11.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Donaire, A
    Agüero, JC
    Middleton, RH
    Scalability of bidirectional vehicle strings with static and dynamic measurement errors2015In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 62, p. 208-212Article in journal (Refereed)
    Abstract [en]

    Poor scalability arises in many vehicle platoon problems. Bidirectional strings appear to show some promise for mitigating these problems. In some cases these solutions have the undesirable side effect of non-scalable response to measurement errors. We examine this problem and show how information exchange between neighbouring vehicles may eliminate scalability difficulties due to measurement errors.

  • 12.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Donaire, Alejandro
    University of Newcastle, Australien.
    Agüero, Juan C
    University of Newcastle, Australien.
    Middleton, Richard H
    University of Newcastle, Australien.
    Passivity-based control for multi-vehicle systems subject to string constraints2014In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 50, no 12, p. 3224-3230Article in journal (Refereed)
    Abstract [en]

    In this paper, we show how heterogeneous bidirectional vehicle strings can be modelled as port-Hamiltonian systems. Analysis of stability and string stability within this framework is straightforward and leads to a better understanding of the underlying problem. Nonlinear local control and additional integral action is introduced to design a suitable control law guaranteeing 12 string stability of the system with respect to bounded disturbances. 

  • 13.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Donaire, Alejandro
    University of Newcastle, Australien.
    Agüero, Juan C
    University of Newcastle, Australien.
    Middleton, Richard H
    University of Newcastle, Australien.
    Scalability of bidirectional vehicle strings with measurement errors2014Conference paper (Refereed)
  • 14.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Middleton, Richard H.
    Univ Newcastle, Ctr Complex Dynam Syst & Control, Callaghan, NSW 2308, Australia..
    Asymptotic and exponential stability of nonlinear two-dimensional continuous-discrete Roesser models2016In: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 93, p. 35-42Article in journal (Refereed)
    Abstract [en]

    Sufficient conditions guaranteeing Lyapunov stability, asymptotic stability and exponential stability of nonlinear two-dimensional continuous-discrete systems are proposed. Special attention is paid to neutrally stable systems such as some two-dimensional system descriptions of vehicle platoons, which may be stable or asymptotically stable but never exponentially stable. Our conditions for Lyapunov stability and asymptotic stability only require the corresponding two-dimensional Lyapunov function to have a negative semidefinite divergence. They are thus suitable for the analysis of non-exponential versions of 2D stability. Examples are given to illustrate the results.

  • 15.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Middleton, Richard H
    University of Newcastle, Australien.
    Lymph compartment models and HIV intra patient infection dynamics2014In: IEEE International Conference on Control Applications, 2014, p. 1699-1704Conference paper (Refereed)
    Abstract [en]

    A compartment model is proposed to describe the HIV infection in humans. The compartments describe the blood, several lymph nodes and connecting lymph vessels. The dynamics in each compartment are described by a simplified HIV model considering the healthy and infected T-cells. A bifurcation analysis based on the variation of the proliferation rate is discussed and supported by simulations. Additional simulations illustrate the effect of a simple mutation model.

  • 16.
    Knorn, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Varagnolo, Damiano
    Lulea Univ Technol, Dept Comp Sci Elect & Space Engn, Lulea, Sweden..
    Melles, Reinhile
    Maastricht Univ, Med Ctr, Dept Psychol & Neurosci, Clin Psychol Sci,Behav Med, Maastricht, Netherlands..
    Dewitte, Marieke
    Maastricht Univ, Med Ctr, Dept Psychol & Neurosci, Clin Psychol Sci,Behav Med, Maastricht, Netherlands..
    Mathematical Modelling Of Pressure Versus Pain Relations In Women Suffering From Dyspareunia2017In: Journal of Sexual Medicine, ISSN 1743-6095, E-ISSN 1743-6109, Vol. 14, no 5, p. E335-E335Article in journal (Other academic)
  • 17.
    Varagnolo, Damiano
    et al.
    Luleå Univ Technol, Dept Comp Sci Elect & Space Engn, Luleå, Sweden.
    Knorn, Steffi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    MeIles, Reinhilde
    Maastricht Univ Medisch Centrum, Dept Psychol & Neurosci, Clin Psychol Sci, Behav Med, Maastricht, Netherlands.
    Dewitte, Marieke
    Maastricht Univ Medisch Centrum, Dept Psychol & Neurosci, Clin Psychol Sci, Behav Med, Maastricht, Netherlands.
    Qualitative modeling of pressure vs. pain relations in women suffering from dyspareunia2017In: IFAC-PapersOnLine, ISSN 1045-0823, E-ISSN 1797-318X, Vol. 50, no 1, p. 2043-2050Article in journal (Refereed)
    Abstract [en]

    Genital pain / penetration disorders affect a significant portion of the female population and diminish significantly the quality of life of the subjects. Treatments, that often consist in stretching opportunely the vaginal duct by means of opportune vaginal dilators, are known to be invasive, lengthy and uncomfortable. Designing better treatments (e.g., more efficient locations and levels of pressures) nonetheless requires understanding better how the pressure developed in the vaginal channel affects the patient and leads to subjective pain. Here we take a control-oriented approach to the problem, and aim at describing the dynamics of the pressure vs. pain mechanisms by means of opportune state space representations. In particular, we first collect and discuss the medical literature, that describes how the variables that are involved in the treatment of genital pain / penetration disorders with vaginal dilators, are logically related. After this we translate (and complete) this set of logical relations into a qualitative model that allows control oriented analyses of the dynamics. The obtained state space model is then proved to both mimic correctly what is expected from logical perspectives and reproduce behaviors measured in clinical settings.

1 - 17 of 17
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