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• 1.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
Application of a Linear PEM Estimator to a Stochastic Wiener-Hammerstein Benchmark Problem⁎2018In: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 51, no 15, p. 784-789Article in journal (Refereed)

The estimation problem of stochastic Wiener-Hammerstein models is recognized to be challenging, mainly due to the analytical intractability of the likelihood function. In this contribution, we apply a computationally attractive prediction error method estimator to a real-data stochastic Wiener-Hammerstein benchmark problem. The estimator is defined using a deterministic predictor that is nonlinear in the input. The prediction error method results in tractable expressions, and Monte Carlo approximations are not necessary. This allows us to tackle several issues considered challenging from the perspective of the current mainstream approach. Under mild conditions, the estimator can be shown to be consistent and asymptotically normal. The results of the method applied to the benchmark data are presented and discussed.

• 2.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Consistent Estimators of Stochastic MIMO Wiener Models based on Suboptimal Predictors2018Conference paper (Refereed)
• 3.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Linear Prediction Error Methods for Stochastic Nonlinear Models2019In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 105, p. 49-63Article in journal (Refereed)

The estimation problem for stochastic parametric nonlinear dynamical models is recognized to be challenging. The main difficulty is the intractability of the likelihood function and the optimal one-step ahead predictor. In this paper, we present relatively simple prediction error methods based on non-stationary predictors that are linear in the outputs. They can be seen as extensions of the linear identification methods for the case where the hypothesized model is stochastic and nonlinear. The resulting estimators are defined by analytically tractable objective functions in several common cases. It is shown that, under certain identifiability and standard regularity conditions, the estimators are consistent and asymptotically normal. We discuss the relationship between the suggested estimators and those based on second-order equivalent models as well as the maximum likelihood method. The paper is concluded with a numerical simulation example as well as a real-data benchmark problem.

The full text will be freely available from 2021-04-01 16:05
• 4.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
Identification of a Class of Nonlinear Dynamical Networks⁎2018In: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 51, no 15, p. 868-873Article in journal (Refereed)

Identification of dynamic networks has attracted considerable interest recently. So far the main focus has been on linear time-invariant networks. Meanwhile, most real-life systems exhibit nonlinear behaviors; consider, for example, two stochastic linear time-invariant systems connected in series, each of which has a nonlinearity at its output. The estimation problem in this case is recognized to be challenging, due to the analytical intractability of both the likelihood function and the optimal one-step ahead predictors of the measured nodes. In this contribution, we introduce a relatively simple prediction error method that may be used for the estimation of nonlinear dynamical networks. The estimator is defined using a deterministic predictor that is nonlinear in the known signals. The estimation problem can be defined using closed-form analytical expressions in several non-trivial cases, and Monte Carlo approximations are not necessarily required. We show, that this is the case for some block-oriented networks with no feedback loops and where all the nonlinear modules are polynomials. Consequently, the proposed method can be applied in situations considered challenging by current approaches. The performance of the estimation method is illustrated on a numerical simulation example.

• 5.
Univ Siena, Dipartimento Ingn Informaz, I-53100 Siena, Italy..
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Univ Pisa, Dipartimento Ingn Informaz, I-50126 Pisa, Italy.. Budapest Univ Technol & Econ, Dept Networked Syst & Serv, H-1117 Budapest, Hungary.;MTA BME Informat Syst Res Grp, H-1117 Budapest, Hungary..
MMSE Receiver Design and SINR Calculation in MU-MIMO Systems With Imperfect CSI2019In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 8, no 1, p. 269-272Article in journal (Refereed)

The performance of the uplink of multiuser multiple input multiple output systems depends critically on the receiver architecture and on the quality of the acquired channel state information. A popular approach is to design linear receivers that minimize the mean squared error (MSE) of the received data symbols. Unfortunately, most of the literature does not take into account the presence of channel state information errors in the MSE minimization. In this letter we develop a linear minimum MSE (MMSE) receiver that employs the noisy instantaneous channel estimates to minimize the MSE, and highlight the dependence of the receiver performance on the pilot-to-data power ratio. By invoking the theory of random matrices, we calculate the users' signal-to-interference-plus-noise ratio as a function of the number of antennas and the pilot-to-data power ratio of all users. Numerical results indicate that this new linear receiver outperforms the classical mismatched MMSE receiver.

• 6.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Event-triggered and cloud-support control of multi-robot systems2018Doctoral thesis, monograph (Other academic)

In control of multi-robot systems, the aim is to obtain a coordinated behavior through local interactions among the robots. A multi-agent system is an abstract model of a multi-robot system. In this thesis, we investigate multi-agent systems where inter-agent communication is modeled by discrete events triggered by conditions on the internal state of the agents. We consider two models of communication. In the first model, two agents exchange information directly with each other. In the second model, all information is exchanged asynchronously over a shared repository. Four contributions on control algorithms for multi-agent systems are offered in the thesis. The first contribution is an event-triggered pinning control algorithm for a network of agents with nonlinear dynamics and time-varying topology. Pinning control is a strategy to steer the behavior of the system in a desired manner by controlling only a small fraction of the agents. We express the controllability of the network in terms of an average value of the network connectivity over time, and we show that all the agents can be driven to a desired reference trajectory. The second contribution is a control algorithm for multi-agent systems where inter-agent communication is substituted with a shared remote repository hosted on a cloud. The communication between each agent and the cloud is modeled as a sequence of events scheduled recursively by the agent. We quantify the connectivity of the network and we show that it is possible to synchronize the multi-agent system to the same state trajectory, while guaranteeing that two consecutive cloud accesses by the same agent are separated by a lower-bounded time interval. The third contribution is a family of distributed controllers for coverage and surveillance tasks with a network of mobile agents with anisotropic sensing patterns. We develop an abstract model of the environment under inspection and define a measure of the coverage attained by the sensor network. We show that the network attains nondecreasing coverage, and we characterize the equilibrium configurations of the network. The fourth contribution is a distributed, cloud-supported control algorithm for inspection of 3D structures with a network of mobile sensing agents, similar to those considered in the third contribution. We develop an abstract model of the structure to inspect and quantify the degree of completion of the inspection. We demonstrate that, under the proposed algorithm, the network is guaranteed to complete the inspection in finite time. All results presented in the thesis are corroborated by numerical simulations and sometimes by experiments with aerial robotic platforms. The experiments show that the theory and methods developed in the thesis are of practical relevance.

• 7.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Cloud-supported effective coverage of 3D structures2018In: 2018 European Control Conference, ECC 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 95-100, article id 8550377Conference paper (Refereed)

In this paper, we present a distributed algorithm for cloud-supported effective coverage of 3D structures with a network of sensing agents. The structure to inspect is abstracted into a set of landmarks, where each landmark represents a point or small area of interest, and incorporates information about position and orientation. The agents navigate the environment following the proposed control algorithm until all landmarks have reached a satisfactory level of coverage. The agents do not communicate with each other directly, but exchange data through a shared cloud repository which is accessed asynchronously and intermittently. We show formally that, under the proposed control architecture, the networked agents complete the coverage mission in finite time. The results are corroborated by simulations in ROS, and experimental evaluation is in progress.

• 8.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
Univ Sannio, Dept Engn, I-82100 Benevento, Italy.. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Cloud-Supported Formation Control of Second-Order Multiagent Systems2018In: IEEE Transactions on Big Data, ISSN 2325-5870, E-ISSN 2168-6750, Vol. 5, no 4, p. 1563-1574Article in journal (Refereed)

This paper addresses a formation problem for a network of autonomous agents with second-order dynamics and bounded disturbances. Coordination is achieved by having the agents asynchronously upload (download) data to (from) a shared repository, rather than directly exchanging data with other agents. Well-posedness of the closed-loop system is demonstrated by showing that there exists a lower bound for the time interval between two consecutive agent accesses to the repository. Numerical simulations corroborate the theoretical results.

• 9.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Analysis of Velocity Estimation Methods for High-Performance Motion Control Systems2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

The majority of all commercial electronics hardware is manufactured usingSurface Mount Technology (SMT). Nevertheless, the increased complexityand miniaturization of electronics impose tough performance requirementson the automation process.The research in this paper concerns test and analysis of alternative velocityestimation methods for high-performance embedded motion control systems.The motion system in Mycronic’s pick and place machines is regulated by amotion controller consisting of a feedforward component and a feedback controller.The linear displacement is measured with an incremental encoder andthe velocity is estimated with a state observer. Previous work suggests thatthe velocity estimation is inadequate.Different observer designs including state and disturbance estimators weretested and evaluated through simulations in MATLAB SIMULINKr. Afterthat, experiments were performed on a conveyor retrieved from a pick andplace machine.The results show that a Kalman filter is the best state estimator. However,the method requires extensive tuning to attain good performance. The trackingperformance and robustness of the motion control system was highly improvedwhen using a Perturbation observer with Kalman filtering. Nonetheless,the settling time for point-to-point movements was somewhat shorterwhen using a Kalman filter alone.

• 10.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Competitive Online Scheduling Algorithms with Applications in Deadline-Constrained EV Charging2018In: 2018 IEEE/ACM 26th International Symposium on Quality of Service, IWQoS 2018, IEEE, 2018, article id 8624184Conference paper (Refereed)

This paper studies the classical problem of online scheduling of deadline-sensitive jobs with partial values and investigates its extension to Electric Vehicle (EV) charging scheduling by taking into account the processing rate limit of jobs and charging station capacity constraint. The problem lies in the category of time-coupled online scheduling problems without availability of future information. This paper proposes two online algorithms, both of which are shown to be (2-\frac{1}{U})-competitive, where U is the maximum scarcity level, a parameter that indicates demand-to-supply ratio. The first proposed algorithm is deterministic, whereas the second is randomized and enjoys a lower computational complexity. When U grows large, the performance of both algorithms approaches that of the state-of-the-art for the case where there is processing rate limits on the jobs. Nonetheless in realistic cases, where U is typically small, the proposed algorithms enjoy a much lower competitive ratio. To carry out the competitive analysis of our algorithms, we present a proof technique, which is novel to the best of our knowledge. This technique could also be used to simplify the competitive analysis of some existing algorithms, and thus could be of independent interest.

• 11.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Human in the Loop Least Violating Robot Control Synthesis under Metric Interval Temporal Logic Specifications2018In: 2018 European Control Conference, ECC 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 453-458, article id 8550179Conference paper (Refereed)

Recently, multiple frameworks for control synthesis under temporal logic have been suggested. The frameworks allow a user to give one or a set of robots high level tasks of different properties (e.g. temporal, time limited, individual and cooperative). However, the issue of how to handle tasks, which either seem to be or are infeasible, remains unsolved. In this paper we introduce a human to the loop, using the human's feedback to determine preference towards different types of violations of the tasks. We introduce a metric of violation called hybrid distance. We also suggest a novel framework for synthesizing a least violating controller with respect to the hybrid distance and the human feedback. Simulation result indicate that the suggested framework gives reasonable estimates of the metric, and that the suggested plans correspond to the expected ones.

KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Reducing the human effort for human-robot cooperative object manipulation via control design2017In: IFAC PAPERSONLINE, ELSEVIER SCIENCE BV , 2017, Vol. 50, no 1, p. 14922-14927Conference paper (Refereed)

This study is concerned with the shared object manipulation problem in a physical Human-Robot Interaction (pHRI) setting. In such setups, the operator manipulates the object with the help of a robot. In this paper, the operator is assigned with the lead role, and the robot is passively following the forces/torques exerted by the operator. We propose a controller that is free from the well-known translation/rotation problem and enhances the operator's ability to move the object by reducing the human effort. The key point in our study is that the controller is defined based on the instantaneous center of rotation. The passivity of the system including the object and the manipulator has been evaluated. Simulation results validate the theoretical findings on different scenarios of subsequent rotations and translations of the object.

• 13.
Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson Res, Radio Dept, S-16480 Stockholm, Sweden. Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil.. Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil.. Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
A Novel Cell Reconfiguration Technique for Dynamic TDD Wireless Networks2018In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, no 3, p. 320-323Article in journal (Refereed)

In dynamic time division duplexing (DTDD) systems, the uplink (UL) and downlink (DL) resources can be configured to adapt to changing traffic conditions. Therefiwe, DTDD systems are advantageously deployed in scenarios in which the UL and DL traffic demands are asymmetric and timevarying. Unfortunately, multicell DTDD systems give rise to base station-to-base station and user equipment-to-user equipment interference, that can severely degrade the system performance. Previous works on DTDD either assumed that the UL/DL configurations are given, or they did not take into account the negative impact of multicell DTDD interference. In this letter, we propose a novel cell reconfiguration technique that considers both the prevailing traffic conditions and multicell interference levels. The proposed technique is based on an efficient solution of a mixed integer linear program, whose objective is to maximize the overall system throughput taking into account users' traffic preferences. Realistic system level simulations indicate that the proposed scheme outperforms not only the static TDD system but also other reference schemes, that disregard the DTDD specific interference effects.

• 14.
Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson Res, SE-16480 Stockholm, Sweden. Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil.. Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil.. Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
A Unifying Design of Hybrid Beamforming Architectures Employing Phase Shifters or Switches2018In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, no 11, p. 11243-11247Article in journal (Refereed)

Hybrid beamfiorming (BF) architectures employing phase shifters or switches reduce the number of required radio frequency chains and the power consumption of base stations that employ a large number of antennas. Due to the inherent tradeoff between the number of radio frequency chains, the complexity of the employed analog and digital BF algorithms and the achieved spectral and energy efficiency, designing hybrid BF architectures is a complex task. To deal with this ormplexity, we propose a unifying design that is applicable to architectures employing either phase shifters or switches. In our design, the analog part (!if the hybrid BF architecture maximizes the capacity of the equivalent channel, while the digital part is updated using the well-known block diagonalizat' approach. We then employ the proposed joint analog-digital beamforming algorithm on lour recently proposed hybrid architectures and compare their performance in terms of spectral and energy efficiency, and find that the proposed analog-digital BF algorithm outperforms previously proposed schemes. We also find that phase shifterbased architectures achieve high spectral efficiency, whereas switching-based architectures can boost energy efficiency with increasing number of base station antennas.

• 15.
Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil..
Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil.. Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil.. Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil.. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
An ADMM Approach to Distributed Coordinated Beamforming in Dynamic TDD Networks2017In: 2017 IEEE 7TH INTERNATIONAL WORKSHOP ON COMPUTATIONAL ADVANCES IN MULTI-SENSOR ADAPTIVE PROCESSING (CAMSAP), IEEE , 2017Conference paper (Refereed)

We consider a dynamic time division duplexing wireless network and propose a distributed coordinated beamforming algorithm based on Alternating Direction Method of Multipliers (ADMM) technique assuming the availability of perfect channel state information. Our design objective is to minimize the sum transmit power at the base stations subject to minimum signal-to-interference-plus-noise ratio (SINR) constraints for downlink mobile stations and a maximum interference power threshold for uplink mobile stations. First, we propose a centralized algorithm based on the relaxed Semidefinite Programming (SDP) technique. To obtain the beamforming solution in a distributed way, we further propose a distributed coordinated beamforming algorithm using the ADMM technique. Detailed simulation results are presented to examine the effectiveness of the proposed algorithms. It is shown that the proposed algorithm achieves better performance in terms of the design objective and converges faster than the reference algorithm based on primal decomposition.

• 16.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Asynchronous First-Order Algorithms for Large-Scale Optimization: Analysis and Implementation2019Doctoral thesis, monograph (Other academic)

Developments in communication and data storage technologies have made large-scale data collection more accessible than ever. The transformation of this data into insight or decisions typically involves solving numerical optimization problems. As the data volumes increase, the optimization problems grow so large that they can no longer be solved on a single computer. This has created a strong interest in developing optimization algorithms that can be executed efficiently on multiple computing nodes in parallel. One way to achieve efficiency in parallel computations is to allow for asynchrony among nodes, which corresponds to making the nodes spend less time coordinating with each other and more time computing, possibly based on delayed information.  However, asynchrony in optimization algorithms runs the risk of otherwise convergent algorithms divergent, and convergence analysis of asynchronous algorithms is generally harder. In the thesis, we develop theory and tools to help understand and implement asynchronous optimization algorithms under time-varying, bounded information delay.

In the first part, we analyze the convergence of different asynchronous optimization algorithms. We first propose a new approach for minimizing the average of a large number of smooth component functions. The algorithm uses delayed partial gradient information, and it covers delayed incremental gradient and delayed coordinate descent algorithms as special cases. We show that when the total loss function is strongly convex and the component functions have Lipschitz-continuous gradients, the algorithm has a linear convergence rate. The step size of the algorithm can be selected without knowing the bound on the delay, and still, guarantees convergence to within a predefined level of suboptimality. Then, we analyze two different variants of incremental gradient descent algorithms for regularized optimization problems.  In the first variant, asynchronous mini-batching, we consider solving regularized stochastic optimization problems with smooth loss functions. We show that the algorithm with time-varying step sizes achieves the best-known convergence rates under synchronous operation when (i) the feasible set is compact or (ii) the regularization function is strongly convex, and the feasible set is closed and convex. This means that the delays have an asymptotically negligible effect on the convergence, and we can expect speedups when using asynchronous computations. In the second variant, proximal incremental aggregated gradient, we show that when the objective function is strongly convex, the algorithm with a constant step size that depends on the maximum delay bound and the problem parameters converges globally linearly to the true optimum.

In the second part, we first present POLO, an open-source C++ library that focuses on algorithm development. We use the policy-based design approach to decompose the proximal gradient algorithm family into its essential policies. This helps us handle combinatorially increasing design choices with linearly many tools, and generates highly efficient code with small footprint.  Together with its sister library in Julia, POLO.jl, our software framework helps optimization and machine-learning researchers to quickly prototype their ideas, benchmark them against the state-of-the-art, and ultimately deploy the algorithms on different computing platforms in just a few lines of code. Then, using the utilities of our software framework, we build a new, serverless'' executor for parallel Alternating Direction Method of Multipliers (ADMM) iterations. We use Amazon Web Services' Lambda functions as the computing nodes, and we observe speedups up to 256 workers and efficiencies above 70% up to 64 workers. These preliminary results suggest that serverless runtimes, together with their availability and elasticity, are promising candidates for scaling the performance of distributed optimization algorithms.

• 17.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
How to Split UL/DL Antennas in Full-DuplexCellular Networks2018In: IEEE International Conference on Communication (ICC’18): ThirdWorkshop on Full-Duplex Communications for Future Wireless Networks, Kansas City, MO, USA: IEEE Communications Society, 2018Conference paper (Refereed)

To further improve the potential of full-duplex com-munications, networks may employ multiple antennas at thebase station or user equipment. To this end, networks thatemploy current radios usually deal with self-interference andmulti-user interference by beamforming techniques. Althoughprevious works investigated beamforming design to improvespectral efficiency, the fundamental question of how to split theantennas at a base station between uplink and downlink infull-duplex networks has not been investigated rigorously. Thispaper addresses this question by posing antenna splitting as abinary nonlinear optimization problem to minimize the sum meansquared error of the received data symbols. It is shown that thisis an NP-hard problem. This combinatorial problem is dealt withby equivalent formulations, iterative convex approximations, anda binary relaxation. The proposed algorithm is guaranteed toconverge to a stationary solution of the relaxed problem with muchsmaller complexity than exhaustive search. Numerical resultsindicate that the proposed solution is close to the optimal in bothhigh and low self-interference capable scenarios, while the usuallyassumed antenna splitting is far from optimal. For large numberof antennas, a simple antenna splitting is close to the proposedsolution. This reveals that the importance of antenna splittingdiminishes with the number of antennas.

• 18. Bagloee, S. A.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
A hybrid machine-learning and optimization method for contraflow design in post-disaster cases and traffic management scenarios2019In: Expert systems with applications, ISSN 0957-4174, E-ISSN 1873-6793, Vol. 124, p. 67-81Article in journal (Refereed)

The growing number of man-made and natural disasters in recent years has made the disaster management a focal point of interest and research. To assist and streamline emergency evacuation, changing the directions of the roads (called contraflow, a traffic control measure) is proven to be an effective, quick and affordable scheme in the action list of the disaster management. The contraflow is computationally a challenging problem (known as NP-hard), hence developing an efficient method applicable to real-world and large-sized cases is a significant challenge in the literature. To cope with its complexities and to tailor to practical applications, a hybrid heuristic method based on a machine-learning model and bilevel optimization is developed. The idea is to try and test several contraflow scenarios providing a training dataset for a supervised learning (regression) model which is then used in an optimization framework to find a better scenario in an iterative process. This method is coded as a single computer program synchronized with GAMS (for optimization), MATLAB (for machine learning), EMME3 (for traffic simulation), MS-Access (for data storage) and MS-Excel (as an interface), and it is tested using a real dataset from Winnipeg, and Sioux-Falls as benchmarks. The algorithm managed to find globally optimal solutions for the Sioux-Falls example and improved accessibility to the dense and congested central areas of Winnipeg just by changing the direction of some roads.

• 19. Balaghi I., M. H.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
An Optimal LQG Controller for Stochastic Event-triggered Scheduling over a Lossy Communication Network2018In: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 51, no 23, p. 58-63Article in journal (Refereed)

We consider a networked control loop in which the sensors acquire partial state information and communicate to a remote controller through a lossy communication network. A scheduler, collocated with the sensors, decides to transmit a locally estimated state to the controller based on an event-triggered transmission policy with stochastic thresholds. Assuming that the local estimator either senses the communication channel or receives an ideal acknowledgment from the remote estimator, then the optimal control law can be shown to be a linear function of the conditional expectation of the state. However, the probability distribution of the state conditioned on the information available to the controller based on the mentioned transmission policy and network is not Gaussian, but rather described by a sum of Gaussians with an increasing number of terms at every time-step. We show that the optimal LQG control law can be determined without tracking this probability distribution for finding its expected value. Moreover, we establish that the stochastic event-triggered scheduler can be appropriately regulated in order to achieve a desired triggering probability at every time-step.

• 20.
Eindhoven Univ Technol, Dept Mech Engn, Control Syst Technol Grp, Eindhoven, Netherlands..
Eindhoven Univ Technol, Dept Mech Engn, Control Syst Technol Grp, Eindhoven, Netherlands.. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Tech Univ Munich, Chair Informat Oriented Control, Munich, Germany..
A Decentralized Consistent Policy for Event-triggered Control over a Shared Contention-based Network2018In: 2018 IEEE Conference on Decision and Control  (CDC), IEEE , 2018, p. 1719-1724Conference paper (Refereed)

We consider a network of several independent linear systems controlled over a shared communication network. Data transmissions pertaining to each control loop are arbitrated by a scheduler collocated with the plant's sensors that transmits the state information to the corresponding remote controller collocated with the plant's actuators. The shared communication channel is assumed to be operating based on a contention-based protocol, endowing the networked control system with desirable reconfigurable and scalable features. We propose a class of scheduling policies which admit a decentralized optimal control implementation and an event-triggered policy within this class which is shown to be consistent, i.e. it results in a better control performance for any linear system, measured by an average quadratic cost than its non-event-based counterpart.

• 21.
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. Royal Inst Technol, KTH, Stockholm, Sweden..
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
How to Split UL/DL Antennas in Full-Duplex Cellular Networks2018In: 2018 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE, 2018Conference paper (Refereed)

To further improve the potential of full-duplex communications, networks may employ multiple antennas at the base station or user equipment. To this end, networks that employ current radios usually deal with self-interference and multi-user interference by beamforming techniques. Although previous works investigated beamforming design to improve spectral efficiency, the fundamental question of how to split the antennas at a base station between uplink and downlink in full-duplex networks has not been investigated rigorously. This paper addresses this question by posing antenna splitting as a binary nonlinear optimization problem to minimize the sum mean squared error of the received data symbols. It is shown that this is an NP-hard problem. This combinatorial problem is dealt with by equivalent formulations, iterative convex approximations, and a binary relaxation. The proposed algorithm is guaranteed to converge to a stationary solution of the relaxed problem with much smaller complexity than exhaustive search. Numerical results indicate that the proposed solution is close to the optimal in both high and low self-interference capable scenarios, while the usually assumed antenna splitting is far from optimal. For large number of antennas, a simple antenna splitting is close to the proposed solution. This reveals that the importance of antenna splitting diminishes with the number of antennas.

• 22.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Max Planck Institute for Intelligent Systems.
Fast and Resource-Efficient Control of Wireless Cyber-Physical Systems2019Licentiate thesis, monograph (Other academic)

Cyber-physical systems (CPSs) tightly integrate physical processes with computing and communication to autonomously interact with the surrounding environment.This enables emerging applications such as autonomous driving, coordinated flightof swarms of drones, or smart factories. However, current technology does notprovide the reliability and flexibility to realize those applications. Challenges arisefrom wireless communication between the agents and from the complexity of thesystem dynamics. In this thesis, we take on these challenges and present three maincontributions.We first consider imperfections inherent in wireless networks, such as communication delays and message losses, through a tight co-design. We tame the imperfectionsto the extent possible and address the remaining uncertainties with a suitable controldesign. That way, we can guarantee stability of the overall system and demonstratefeedback control over a wireless multi-hop network at update rates of 20-50 ms.If multiple agents use the same wireless network in a wireless CPS, limitedbandwidth is a particular challenge. In our second contribution, we present aframework that allows agents to predict their future communication needs. Thisallows the network to schedule resources to agents that are in need of communication.In this way, the limited resource communication can be used in an efficient manner.As a third contribution, to increase the flexibility of designs, we introduce machinelearning techniques. We present two different approaches. In the first approach,we enable systems to automatically learn their system dynamics in case the truedynamics diverge from the available model. Thus, we get rid of the assumption ofhaving an accurate system model available for all agents. In the second approach, wepropose a framework to directly learn actuation strategies that respect bandwidthconstraints. Such approaches are completely independent of a system model andstraightforwardly extend to nonlinear settings. Therefore, they are also suitable forapplications with complex system dynamics.

• 23. Beerens, R.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Hybrid PID control for transient performance improvement of motion systems with friction2018In: 2018 Annual American Control Conference (ACC), Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 539-544, article id 8431613Conference paper (Refereed)

We present a novel reset control approach to improve transient performance of a PID-controlled motion system subject to friction. In particular, a reset integrator is applied to circumvent the depletion and refilling process of a linear integrator when the system overshoots the setpoint, thereby significantly reducing settling times. Moreover, robustness for unknown static friction levels is obtained. A hybrid closed-loop system formulation is derived, and stability follows from a discontinuous Lyapunov-like function and a meagre-limsup invariance argument. The working principle of the controller is illustrated by means of a numerical example.

• 24.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Univ Western Ontario, Dept Elect & Comp Engn, London, ON, Canada.;Lakehead Univ, Dept Elect Engn, Thunder Bay, ON, Canada.. Univ Calif Santa Barbara, Dept Elect & Comp Engn, Santa Barbara, CA 93106 USA..
Hybrid Constrained Estimation For Linear Time-Varying Systems2018In: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2018, p. 4643-4648Conference paper (Refereed)

For linear time-varying systems with possibly constrained states, we propose a hybrid observer that guarantees the containment of the estimated state variables in a prescribed domain of interest. The hybrid observer employs a Kalmantype continuous estimator during the flows while, during the jumps, projects the state estimates onto the set described by the constraint equation. A suitable choice of the flow and jump sets allows to conclude uniform global asymptotic stability of the zero estimation error set.

• 25.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Efficient Trajectory Reshaping in a Dynamic Environment2018In: 2018 IEEE 15TH INTERNATIONAL WORKSHOP ON ADVANCED MOTION CONTROL (AMC), IEEE, 2018, p. 54-59Conference paper (Refereed)

A general trajectory planner for optimal control problems is presented and applied to a robot system. The approach is based on timed elastic bands and nonlinear model predictive control. By exploiting the sparsity in the underlying optimization problems the computational effort can be significantly reduced, resulting in a real-time capable planner. In addition, a localization based switching strategy is employed to enforce convergence and stability. The planning procedure is illustrated in a robotics application using a realistic SCARA type robot.

• 26.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Distributed L-shaped Algorithms in Julia2018In: PROCEEDINGS OF PAW-ATM18: 2018 IEEE/ACM PARALLEL APPLICATIONS WORKSHOP, ALTERNATIVES TO MPI (PAW-ATM) / [ed] NDERS JF, 2005, NUMER MATH, V2, P3 okhmal P., 2005, APPLICATIONS OF STOCHASTIC PROGRAMMING, V5, P609 nderoth J, 2003, COMPUTATIONAL OPTIMIZATION AND APPLICATIONS, V24, P207 well Warren B., 2005, APPLICATIONS OF STOCHASTIC PROGRAMMING, V5, P185, IEEE , 2018, p. 57-69Conference paper (Refereed)

We present LShapedSolvers.jl, a suite of scalable stochastic programming solvers implemented in the Julia programming language. The solvers, which are based on the L-shaped algorithm, run efficiently in parallel, exploit problem structure, and operate on distributed data. The implementation introduces several flexible high-level abstractions that result in a modular design and simplify the development of algorithm variants. In addition, we demonstrate how the abstractions available in the Julia module for distributed computing are exploited to simplify the implementation of the parallel algorithms. The performance of the solvers is evaluated on large-scale problems for finding optimal orders on the Nordic day-ahead electricity market. With 16 worker cores, the fastest algorithm solves a distributed problem with 2.5 million variables and 1.5 million linear constraints about 19 times faster than Gurobi is able to solve the extended form directly.

• 27.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
A hybrid barrier certificate approach to satisfy linear temporal logic specifications2018In: 2018 Annual American Control Conference (ACC), Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 634-639, article id 8430795Conference paper (Refereed)

In this work we formulate the satisfaction of a (syntactically co-safe) linear temporal logic specification on a physical plant through a recent hybrid dynamical systems formalism. In order to solve this problem, we introduce an extension to such a hybrid system framework of the so-called eventuality property, which matches suitably the condition for the satisfaction of such a temporal logic specification. The eventuality property can be established through barrier certificates, which we derive for the considered hybrid system framework. Using a hybrid barrier certificate, we propose a solution to the original problem. Simulations illustrate the effectiveness of the proposed method. 2018 AACC.

• 28.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Performance Quantification of Interarea Oscillation Damping Using HVDC2019Licentiate thesis, monograph (Other academic)

With the transition towards renewable energy, and the deregulation of the electricity market, generation patterns and grid topology are changing. These changes increase the need for transfer capacity. One limiting factor, which sometimes leads to underutilization of the transmission grid, is interarea oscillations. These system-wide modes involve groups of generators oscillating relative to each other and are sometimes hard to control due to their scale and complexity. In this thesis we investigate how high-voltage direct current (HVDC) transmission can be used to attenuate interarea oscillations. The thesis has two main contributions.

In the first contribution we show how the stability of two asynchronous grids can be improved by modulating the active power of a single interconnecting HVDC link. One concern with modulating HVDC active power is that the interaction between interarea modes of the two grids may have a negative impact on system stability. By studying the controllability Gramian, we show that it is always possible to improve the damping in both grids as long as the frequencies of their interarea modes are not too close. For simplified models, it is explicitly shown how the controllability, and therefore the achievable damping improvements, deteriorates as the frequency difference becomes small.

The second contribution of the thesis is to show how coordinated control of two (or more) links can be used to avoid interaction between troublesome interarea modes. We investigate the performance of some multivariable control designs. In particular we look at input usage as well as robustness to measurement, communication, and actuator failures. Suitable controllers are thereby characterized.

• 29.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
Fundamental Performance Limitations in Utilizing HVDC to Damp Interarea Modes2019In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 34, no 2, p. 1095-1104Article in journal (Refereed)

This paper considers power oscillation damping (POD) using active power modulation of high-voltage dc transmissions. An analytical study of how the proximity between interarea modal frequencies in two interconnected asynchronous grids puts a fundamental limit to the achievable performance is presented. It is shown that the ratio between the modal frequencies is the sole factor determining the achievable nominal performance. To illustrate the inherent limitations, simulations using a proportional controller tuned to optimize performance in terms of POD are done on a simplified two-machine model. The influence of limited system information and unmodeled dynamics is shown. The analytical result is then further validated on a realistic model with two interconnected 32-bus networks.

• 30.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. ABB, Corp Res, Vasteras, Sweden.. Svenska kraftnat, R&D, Sundbyberg, Sweden..
Analysis of Coordinated HVDC Control for Power Oscillation Damping2018In: Conference Record of the 3rd IEEE International Workshop on Electronic Power Grid, eGrid 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 19-24, article id 8598674Conference paper (Refereed)

Controlling the active power of high-voltage de (HVDC) transmission that interconnects two asynchronous ac grids can be used to improve the power oscillation damping in both of the interconnected ac systems. Using one HVDC link, achievable performance are limited since control actions may excite modes of similar frequencies in the assisting network. However, with coordinated control of two or more HVDC links, the limitations can be circumvented. With decoupling control the system interactions can be avoided all together. This paper investigates the conditions suitable for decoupling control. It is also shown that decoupling between system modes can be achieved using a proportional controller. The control method is compared to decentralized and H-2 optimal control. The best control method for different system topologies is investigated by looking on input usage and stability following dc link failure.

• 31. Boem, F.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Distributed Pareto-optimal state estimation using sensor networks2018In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 93, p. 211-223Article in journal (Refereed)

A novel model-based dynamic distributed state estimator is proposed using sensor networks. The estimator consists of a filtering step – which uses a weighted combination of information provided by the sensors – and a model-based predictor of the system's state. The filtering weights and the model-based prediction parameters jointly minimize – at each time-step – the bias and the variance of the prediction error in a Pareto optimization framework. The simultaneous distributed design of the filtering weights and of the model-based prediction parameters is considered, differently from what is normally done in the literature. It is assumed that the weights of the filtering step are in general unequal for the different state components, unlike existing consensus-based approaches. The state, the measurements, and the noise components are allowed to be individually correlated, but no probability distribution knowledge is assumed for the noise variables. Each sensor can measure only a subset of the state variables. The convergence properties of the mean and of the variance of the prediction error are demonstrated, and they hold both for the global and the local estimation errors at any network node. Simulation results illustrate the performance of the proposed method, obtaining better results than state of the art distributed estimation approaches.

• 32. Bombois, X.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Optimal identification experiment design for the interconnection of locally controlled systems2018In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 89, p. 169-179Article in journal (Refereed)

This paper considers the identification of the modules of a network of locally controlled systems (multi-agent systems). Its main contribution is to determine the least perturbing identification experiment that will nevertheless lead to sufficiently accurate models of each module for the global performance of the network to be improved by a redesign of the decentralized controllers. Another contribution is to determine the experimental conditions under which sufficiently informative data (i.e. data leading to a consistent estimate) can be collected for the identification of any module in such a network.

• 33.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Decentralized abstractions for multi-agent systems under coupled constraints2019In: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 45, p. 1-16Article in journal (Refereed)

The goal of this paper is to define abstractions for multi-agent systems with feedback interconnection in their dynamics. In the proposed decentralized framework, we specify a finite or countable transition system for each agent which only takes into account the discrete positions of its neighbors. The dynamics of each agent consist of a feedback component which can guarantee certain system and network requirements and induces the coupled constraints, and additional input terms, which can be exploited for high level planning. In this work, we provide sufficient conditions for space and time discretizations which enable the abstraction of the system's behavior through a discrete transition system. Furthermore, these conditions include design parameters whose tuning provides the possibility for multiple transitions, and hence, the construction of transition systems with motion planning capabilities. Published by Elsevier Ltd. All rights reserved.

• 34.
Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson Res, SE-16480 Stockholm, Sweden. Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil.. Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
Distributed Beamforming in Dynamic TDD MIMO Networks With BS to BS Interference Constraints2018In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, no 5, p. 788-791Article in journal (Refereed)

This letter proposes distributed beamforming as a means of reducing interference in dynamic time division duplexing multiple input multiple output networks. Specifically, we formulate an optimization task, whose objective is to minimize the base station (BS) transmit power, while satisfying a predefined signal-to-interference-plus-noise ratio threshold for each downlink user equipment and keeping the BS to BS interference power below a tolerable level. An iterative decentralized solution requiring reduced signaling load based on primal decomposition is proposed. This decentralized algorithm is shown to iterate towards the centralized solution, while feasible but suboptimal solutions can be obtained at any iteration.

• 35.
Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy..
Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy.. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy.. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy..
Cloud-supported self-triggered control for multi-agent circumnavigation2018In: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2018, p. 5090-5095Conference paper (Refereed)

In this paper, we propose a cloud-supported control framework for multi-agent circumnavigation missions. We consider a network of planar autonomous agents. Our objective is for the agents to circumnavigate a target with a desired angular speed, while forming a regular polygon around the target. We propose self-triggered rules to schedule the bearing measurements and the cloud accesses for each agent.

• 36.
Aalto Univ, Dept Elect Engn & Automat, Espoo, Finland..
Korea Polytech Univ, Dept Elect Engn, Shihung, South Korea.. Univ Aegean, Dept Informat & Commun Syst Engn, Samos, Greece.. KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Relay-pair selection in buffer-aided successive opportunistic relaying using a multi-antenna source2019In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 84, p. 29-41Article in journal (Refereed)

We study a cooperative network with a buffer-aided multi-antenna source, multiple half-duplex (HD) buffer-aided relays and a single destination. Such a setup could represent a cellular downlink scenario, in which the source can be a more powerful wireless device with a buffer and multiple antennas, while a set of intermediate less powerful devices are used as relays to reach the destination. The main target is to recover the multiplexing loss of the network by having the source and a relay to simultaneously transmit their information to another relay and the destination, respectively. Successive transmissions in such a cooperative network, however, cause inter-relay interference (IRI). First, by assuming global channel state information (CSI), we show that the detrimental effect of IRI can be alleviated by precoding at the source, mitigating or even fully cancelling the interference. A cooperative relaying policy is proposed that employs a joint precoding design and relay-pair selection. Note that both fixed rate and adaptive rate transmissions can be considered. For the case when channel state information is only available at the receiver side (CSIR), we propose a relay selection policy that employs a phase alignment technique to reduce the IRI. The performance of the two proposed relay pair selection policies are evaluated and compared with other state-of-the-art relaying schemes in terms of outage and throughput. The results show that the use of a powerful source can provide considerable performance improvements.

• 37.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Secure patching of an output-feedback controller for a class of nonlinear systems under adversarial attack2018In: 2018 IEEE CConference on Decision and Control  (CDC), Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 7255-7260, article id 8618972Conference paper (Refereed)

We consider a class of nonlinear systems for which an observer-based output-feedback controller is updated at discrete time instances. However, the received update or patch can be compromised by the attacker to drive the system to instability. In this paper, we provide a checkable condition to ensure that the received patch has not been tampered with to cause instability in the control system. Moreover, we guarantee that the application of the tamper-free patch ensures global asymptotic stability of the control system by choosing the update time instances appropriately. The secure patch update protocol is illustrated on an example involving the output-feedback synchronization of two neuron population models, where the observer gains are updated at discrete time instances.

• 38.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Estimating the Wigner distribution of linear time-invariant dynamical systems2018In: 2018 European Control Conference, ECC 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 1220-1225Conference paper (Refereed)

An estimation algorithm for the Wigner distribution (time-frequency representation) of the unmeasured states of a linear time-invariant system is presented. Given that the inputs and outputs are measured, the algorithm involves designing a Luenberger-like observer for each frequency of interest. Under noise-free conditions, we show that the es- timates converge to the true Wigner distribution under a detectability assumption on the time-frequency representation. The estimation algorithm provides estimates which converge to a neighbourhood of the true Wigner distribution where its norm is dependent on the norm of the measurement noise. We also illustrate the efficacy of the estimation algorithm on an academic example and a model of neuron populations.

• 39.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH Royal Inst Technol, Dept Automat Control, Stockholm, Sweden..
Traffic regulation via individually controlled automated vehicles: a cell transmission model approach2018In: 2018 21ST INTERNATIONAL CONFERENCE ON INTELLIGENT TRANSPORTATION SYSTEMS (ITSC), IEEE , 2018, p. 766-771Conference paper (Refereed)

The advent of automated, infrastructure-controlled vehicles offers new opportunities for traffic control. Even when the number of controlled vehicles is small, they can significantly affect the surrounding traffic. One way of regulating traffic is by using the automated vehicles as controlled moving bottlenecks. We present an extension of the cell transmission model that includes the influence of moving bottlenecks, consistently with the corresponding PDE traffic model. Based on this model, a control strategy is derived for traffic jam resolution. The strategy is tested in simulations, and shown to reduce the average travel time of surrounding vehicles, while also helping dissipate the traffic jam faster and ensuring the controlled vehicle avoids it.

• 40.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
Time reversal symmetries and zero dynamics for simple hybrid Hamiltonian control systems2018In: 2018 Annual American Control Conference (ACC), Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 2218-2223Conference paper (Refereed)

This paper studies Hamel's formalism for simple hybrid mechanical control systems and explores the role of time-reversal symmetries and hybrid zero dynamics to predict the existence of periodic orbits in these control system. A time reversal symmetry in the phase-space permits us to construct a time reversible hybrid Hamiltonian system. If the Hamiltonian function describing the continuous dynamics and the impact map are invariants under a time reversal symmetry on the zero hybrid dynamics, under some mild conditions, we find sufficient conditions for the existence of periodic solutions for the class of simple hybrid Hamiltonian control systems.

• 41.
KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
Optimal Control of Left-Invariant Multi-Agent Systems with Asymmetric Formation Constraints2018In: 2018 European Control Conference, ECC 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 1728-1733, article id 8550238Conference paper (Refereed)

In this work we study an optimal control problem for a multi-agent system modeled by an undirected formation graph with nodes describing the kinematics of each agent, given by a left invariant control system on a Lie group. The agents should avoid collision between them in the workspace. Such a task is done by introducing some potential functions into the cost functional for the optimal control problem, corresponding to fictitious forces, induced by the formation constraint among agents, that break the symmetry of the individual agents and the cost functions, and rendering the optimal control problem partially invariant by a Lie group of symmetries. Reduced necessary conditions for the existence of normal extremals are obtained using techniques of variational calculus on manifolds. As an application we study an optimal control problem for multiple unicycles.

• 42.
Cent Supelec & L2S, Telecommun Dept, Gif Sur Yvette, France. gureanu, Stefan; Proutiere, Alexandre.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Generic Asymptotically Optimal Algorithms for Multi-Armed Bandits2018In: 2018 56TH ANNUAL ALLERTON CONFERENCE ON COMMUNICATION, CONTROL, AND COMPUTING (ALLERTON), IEEE , 2018, p. 235-241Conference paper (Refereed)
• 43.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Autonomous racing using model predictive control2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Autonomous vehicles are expected to have a significant impact on our societies by freeinghumans from the driving task, and thus eliminating the human factor in one of themost dangerous places: roads. As a matter of facts, road kills are one of the largest sourceof human deaths and many countries put the decrease of these casualties as one of their toppriorities. It is expected that autonomous vehicles will dramatically help in achieving that.Moreover, using controllers to optimize both the car behaviour on the road and higher leveltraffic management could reduce traffic jams and increase the commuting speed overall.To minimize road kills, an approach is to design controllers that would handle the car atits limits of handling, by integrating complex dynamics such as adherence loss it is possibleto prevent the car from leaving the road. A convenient setup to evaluate this type ofcontrollers is a racing context: a controller is steering a car to complete a track as fast aspossible without leaving the road and by brining the car to its limits of handling.In this thesis, we design a controller for an autonomous vehicle with the goal of driving itfrom A to B as fast as possible. This is the main motivation in racing applications. Thecontroller should steer the car with the goal to minimize the racing time.This controller was designed within the model predictive controller (MPC) framework,where we used the concept of road-aligned model. In contrast with the standard mpc techniques,we use the objective function to maximize the progress along the reference path,by integrating a linear model of the vehicle progression along the centerline. Combinedwith linear vehicle model and constraints, a optimization problem providing the vehiclewith the future steering and throttle values to apply is formulated and solved with linearprogramming in an on-line fashion during the race. We show the effectiveness of our controllerin simulation, where the designed controller exhibits typical race drivers behavioursand strategies when steering a vehicle along a given track. We ultimately confront it withsimilar controllers from the literature, and derive its strength and weaknesses compared tothem.

• 44.
Politecn Milan, Dept DEIB, Via Ponzio 34-5, I-20133 Milan, Italy..
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Univ Toulouse, CNRS LAAS, Equipe MAC, 7 Ave Colonel Roche,BP 54200, F-31031 Toulouse 4, France.. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Distributed control of compact formations for multi-robot swarms2018In: IMA Journal of Mathematical Control and Information, ISSN 0265-0754, E-ISSN 1471-6887, Vol. 35, no 3, p. 805-835Article in journal (Refereed)

This article proposes a distributed algorithm for the compact deployment of robots, using both distance-and angular-based arguments in the controllers' design. Our objective is to achieve a configuration maximizing the coverage of the environment while increasing the graph's connectivity. First, we provide: (i) a dispersion protocol guaranteeing connectivity maintenance; and (ii) a compactness controller with static and variable control gains that minimizes the inter-agent angles. Second, we present a sequential, multi-stage strategy and analyse its stability. Finally, we validate our theoretical results with simulations, where a group of robots are deployed to carry out sensing or communication tasks.

• 45.
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Device-to-Device Communication in Future Cellular Networks: Resource allocation and mode selection2018Doctoral thesis, monograph (Other academic)

• 46.
Ericsson AB, S-16480 Kista, Sweden..
Univ Siena, Dept Informat Engn, I-53100 Siena, Italy.;Consorzio Nazl Interuniv Telecomunicaz, I-43124 Parma, Italy.. Consorzio Nazl Interuniv Telecomunicaz, I-43124 Parma, Italy.;Univ Pisa, Dept Informat Engn, I-56122 Pisa, Italy.. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Distributed Channel Allocation for D2D-Enabled 5G Networks Using Potential Games2019In: IEEE Access, E-ISSN 2169-3536, Vol. 7, p. 11195-11208Article in journal (Refereed)

Frequency channel allocation is a key technique for improving the performance of cellular networks. In this paper, we address the channel allocation problem for a 5G multi-cell system. We consider a heterogeneous network in which cellular users, micro-cell users, and device-to-device (D2D) communications coexist within the radio footprint of the macro cell. We maximize the aggregate transmission rate, exploiting channel diversity and managing both the inter-cell interference, typical of cellular networks and the intra-cell interference generated by the nonorthogonal transmissions of the small-cell and D2D users. By modeling the allocation problem as a potential game, whose Nash equilibria correspond to the local optima of the objective function, we propose a new decentralized solution. The convergence of our scheme is enforced by using a better response dynamic based on a message passing approach. The simulation results assess the validity of the proposed scheme in terms of convergence time and achievable rate under different settings.

• 47.
KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH Royal Inst Technol, ACCESS Linnaeus Ctr, Sch Elect Engn, Osquldas Vag 10, SE-10044 Stockholm, Sweden..
KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH Royal Inst Technol, ACCESS Linnaeus Ctr, Sch Elect Engn, Osquldas Vag 10, SE-10044 Stockholm, Sweden.. Univ Newcastle, Sch Elect Engn & Comp Sci, Callaghan, NSW 2308, Australia.. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH Royal Inst Technol, ACCESS Linnaeus Ctr, Sch Elect Engn, Osquldas Vag 10, SE-10044 Stockholm, Sweden..
To wait or to drop: on the optimal number of retransmissions in wireless control2015In: 2015 EUROPEAN CONTROL CONFERENCE (ECC), IEEE , 2015, p. 962-968Conference paper (Refereed)

The dimensioning of wireless communication protocols for networked control involves a non-trivial trade-off between reliability and delay. Due to the lossy nature of wireless communications, there is a risk that sensor messages will be dropped. The end-to-end reliability can be improved by retransmitting dropped messages, but this comes at the expense of additional delays. In this work, we determine the number of retransmissions that strikes the optimal balance between communication reliability and delay, in the sense that it achieves the minimal expected linear-quadratic loss of the closed-loop system. An important feature of our setup is that it accounts for the random delays and possible losses that occur when unreliable communication is combatted with retransmissions. The resulting controller dynamically switches among a set of infinite-horizon linear-quadratic regulators, and is simple to implement. Numerical simulations are carried out to highlight the trade-off between reliability and delay.

• 48.
Huawei Technol Sweden AB, SE-16494 Kista, Sweden.. Paderborn Univ, Chair Automat Control EIME, D-33098 Paderborn, Germany.. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
Optimal Control of Linear Systems With Limited Control Actions: Threshold-Based Event-Triggered Control2018In: IEEE Transactions on Big Data, ISSN 2325-5870, E-ISSN 2168-6750, Vol. 5, no 3, p. 1275-1286Article in journal (Refereed)

We consider a finite-horizon linear-quadratic optimal control problem where only a limited number of control messages are allowed for sending from the controller to the actuator. To restrict the number of control actions computed and transmitted by the controller, we employ a threshold-based event-triggering mechanism that decides whether or not a control message needs to be calculated and delivered. Due to the nature of threshold-based event-triggering algorithms, finding the optimal control sequence requires minimizing a quadratic cost function over a nonconvex domain. In this paper, we first provide an exact solution to this nonconvex problem by solving an exponential number of quadratic programs. To reduce computational complexity, we then propose two efficient heuristic algorithms based on greedy search and the alternating direction method of multipliers technique. Later, we consider a receding horizon control strategy for linear systems controlled by event-triggered controllers, and we further provide a complete stability analysis of receding horizon control that uses finite-horizon optimization in the proposed class. Numerical examples testify to the viability of the presented design technique.

• 49.
MIT, Dept Mech Engn, Cambridge, MA 02139 USA..
KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. MIT, Dept Mech Engn, Cambridge, MA 02139 USA.. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. North Carolina State Univ, Dept Elect Engn, Raleigh, NC USA..
Secure Control of Wide-Area Power Systems: Confidentiality and Integrity Threats2018In: 2018 IEEE Conference on Decision and Control  (CDC), Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 7269-7274, article id 8618862Conference paper (Refereed)

A cyber-physical model for wide-area control of power systems is considered, where the state variables of each generator are measured and sent to the cyber-network and the corresponding control inputs are computed distributively. The secure control of such wide-area power systems is considered in the presence of cyber attacks that introduce threats that compromise their integrity and confidentiality. Detection, prevention, and resilience for these attacks and algorithms for accomplishing these goals are proposed. In particular, an algorithm to overcome confidentiality attacks of the underlying control gains is presented. Also proposed is an algorithm for defense against integrity attacks that might take place on the cyber-network. For this purpose, a resilient information retrieval approach is leveraged which recovers the true state variables despite the malicious attacks on both virtual machines and communication links. The retrieved states are then used to detect possible attacks on phasor measurement units (PMU) in the next time-step. Simulation studies are included to validate our proposed approaches.

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KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
Developing a System for Robust Planning using Linear Temporal Logic2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Human robot-collaborative search missions have gotten more and more attention in recent years.Especially in scenarios where the robot first scouts the scene before sending in human agents. Thissaves time and avoids unnecessary risks for the human agents. One possible configuration of such arescue team is, a human operator instructing a unmanned aerial vehicle (UAV) via speech-commandshow to traverse through an environment to investigate areas of interest. A first step to address thisproblem is presented in this master thesis by developing a framework for mapping temporal logicinstructions to physical motion of a UAV.The fact that natural language has a strong resemblance to the logic formalism of Linear-TemporalLogic (LTL) is exploited. Constraints expressed as an LTL-formula are imposed on a provided labeledmap of the environment. An LTL-to-cost-map converter including a standard input-skeleton is developed.Respective cost maps are obtained and a satisfaction-measure of fulfilling these constraints ispresented. The input-skeleton and the map-converter are then combined with a cost-map-based pathplanning algorithm in order to obtain solution sets. A clarification request is created such that theoperator can choose which solution set should be executed. The proposed framework is successivelyvalidated, first by MATLAB-experiments to ensure the validity of the cost-map-creation followed bysimulation experiments in ROS incorporating the entire framework. Finally, a real-world experimentis performed at the SML to validate the proposed framework.

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