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  • 1.
    Abdalmoaty, Mohamed
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. KTH Royal Institute of Technology.
    Identification of Stochastic Nonlinear Dynamical Models Using Estimating Functions2019Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    Det är välkänt att datadriven modellering av icke-linjära stokastiska system är ett utmanande problem, även i fallen där det kan reduceras till ren parameterskattning. Den huvudsakliga svårigheten är att likelihoodfunktionen inte är analytiskt hanterbar, vilket medför problem vid tillämpning av standardmetoder såsom maximum likelihood. Under det senaste decenniet har numeriska algoritmer baserade på sekventiell Monte Carlo (partikelfilter) rönt stort intresse. Dessa algoritmer har imponerande prestanda på en rad benchmarkproblem; dock så är deras praktiska tillämpning än så länge begränsad till specialfall där fundamentala begränsningar kan undvikas.

    Den här avhandlingen introducerar nya metoder som kan användas för parameterestimering i en stor klass av icke-linjära stokastiska system. Metoderna baseras på enstegsprediktorer som är linjära i systemets observerade utsignal. Våra nya metoder kräver inte att likelihoodfunktionen beräknas; istället använder de, i en rad relevanta fall, analytiskt hanterbara uttryck som gör dem högst attraktiva. I fallen där prediktorerna är analytiskt ohanterbara (på grund av modellens komplexitet) kan man använda vanliga Monte Carlo-approximationer. Vi visar att klassiska resultat från asymptotisk teori kan användas under rimliga antaganden, och via dessa, att våra föreslagna skattare är konsistenta samt asymptotiskt normalfördelade. Skattarnas prestanda utvärderas i numeriska simulationer, samt nyligen föreslagna benchmarkproblem baserade på verklig data, med bra resultat.

    Vidare diskuterar vi de föreslagna metodernas asymptotiska egenskaper: deras nogrannhet beror inte enbart på hur modellen har parametriserats, utan även på datans sannolikhetsdistribution (via dess tredje och fjärde ordningens moment). Speciellt visar vi att när modellen inte uppfyller antaganden om normalfördelning, så är en prediktionsfelsmetod baserad på ett normalfördelningsantagande inte nödvändigtvis bättre än en prediktionsfelsmetod baserad på en viktad parameteroberonde kvadratisk norm. Vår slutsats är att det därför inte är uppenbart vilken prediktionsfelsmetod som bör användas. Detta resultat står i kontrast mot den vedertagna uppfattningen som finns i delar av litteraturen.

    Avhandlingen introducerar även den så kallade skattningsfunktionsmetoden (främst utvecklad inom statistiklitteraturen) som en generalisering av maximum likelihood- och prediktionsfelsmetoderna. Vi visar hur denna metod kan användas för att systematiskt konstruera optimala skattare, inom en specifierad modellklass, från enbart partiella specifikationer på den underliggande probabilistiska modellen. Detta ger skattare som asymptotiskt är likformigt mer noggrannare än linjära prediktionsfelsmetoder baserade på kvadratiska optimeringsobjektiv. Vi härleder konvergensresultat, såsom konsistens, för dessa skattare under standardantaganden.

    Slutligen behandlar vi identifieringsproblemet för återkopplade system som är stokastiska och icke-linjära. Vi behandlar ett par varianter på antaganden om mät- samt processbrus, och på kunskap om hur systemets återkoppling sker. Ett speciellt utmanande fall är när återkopplingsmekanismen är helt okänd. Metoderna vi föreslår kan ses som generaliseringar av klassiska metoder för identifiering av återkopplade system med linjärt tidsvarierande parametrar. Vi utför en asymptotisk analys av metoderna, och demonstrerar deras prestanda i numeriska experiment.

  • 2.
    Abdalmoaty, Mohamed R.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Application of a Linear PEM Estimator to a Stochastic Wiener-Hammerstein Benchmark Problem⁎2018Ingår i: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 51, nr 15, s. 784-789Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 3.
    Abdalmoaty, Mohamed R.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Consistent Estimators of Stochastic MIMO Wiener Models based on Suboptimal Predictors2018Konferensbidrag (Refereegranskat)
  • 4.
    Abdalmoaty, Mohamed R.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Linear Prediction Error Methods for Stochastic Nonlinear Models2019Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 105, s. 49-63Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

    Publikationen är tillgänglig i fulltext från 2021-04-01 16:05
  • 5.
    Abdalmoaty, Mohamed R.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Rojas, Cristian R.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Hjalmarsson, Håkan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Identification of a Class of Nonlinear Dynamical Networks⁎2018Ingår i: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 51, nr 15, s. 868-873Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 6.
    Abrardo, Andrea
    et al.
    Univ Siena, Dipartimento Ingn Informaz, I-53100 Siena, Italy. brardo, Andrea; Moretti, Marco.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Moretti, Marco
    Distributed Digital and Hybrid Beamforming Schemes With MMSE-SIC Receivers for the MIMO Interference Channel2019Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 68, nr 7, s. 6790-6804Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper addresses the problem of weighted sumrate maximization and mean squared error (MSE) minimization for the multiple-input multiple-output (MIMO) interference channel. Specifically, we consider a weighted minimum MSE architecture where each receiver employs successive interference cancellation (SIC) to separate the various received data streams and derive a hybrid beamforming scheme, where the transmitters operate with a number of radio frequency chains smaller than the number of antennas, particularly suited for millimeter-wave channels and 5G applications. To derive our proposed schemes, we first study the relationship between sum-rate maximization and weighted MSE minimization when using SIC receivers, assuming fully digital beamforming. Next, we consider the important-and, as it turns out, highly non-trivial-case where the transmitters employ hybrid digital/analog beamforming, developing a distributed joint hybrid precoding and SIC-based combining algorithm. Moreover, for practical implementation, we propose a signaling scheme that utilizes a common broadcast channel and facilitates the acquisition of channel state information, assuming minimal assistance from a central node such as a cellular base station. Numerical results show that both the proposed weighted MMSE-SIC schemes exhibit great advantages with respect to their linear counterparts in terms of complexity, feedback information, and performance.

  • 7.
    Abrardo, Andrea
    et al.
    Univ Siena, Dipartimento Ingn Informaz, I-53100 Siena, Italy..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Moretti, Marco
    Univ Pisa, Dipartimento Ingn Informaz, I-50126 Pisa, Italy..
    Telek, Miklos
    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 CSI2019Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 8, nr 1, s. 269-272Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 8.
    Adaldo, Antonio
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Event-triggered and cloud-support control of multi-robot systems2018Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    I reglering av multi-robot system är syftet att uppnå ett samordnat beteende genom lokala interaktioner bland robotarna. Ett fleragentsystem är en abstrakt modell av ett multi-robot system. I denna avhandling undersöks fleragentsystem där kommunikationen mellan agenterna modelleras som tidsdiskreta händelser som utlöses av vilkor på agenternas inre tillstånd. Vi betraktar två kommunikationsmodeller. I den första modellen utbyter två agenter direkt information med varandra. I den andra modellen utbyts all information genom asynkron tillgång till ett gemensamt minne. Avhandlingens bidrag består av fyra delar. Det första bidraget är en händelsestyrd pinningregleringsalgoritm för ett nätverk av agenter med olinjär dynamik och tidsvarierande topologi. Pinningreglering är en strategi för att styra beteendet hos ett fleragentsystem på ett önskat sätt genom att endast styra en liten del av agenterna. Vi uttrycker styrbarheten hos nätverket i form av ett medelvärde av nätverkskonnektiviteten över tiden, och vi visar att alla agenter kan drivas till en önskad referenstrajektoria. Det andra bidraget är en regleringsalgoritm för fleragentsystem där kommunikationen mellan agenterna är ersatt av ett gemensamt minne som är installerat på ett moln. Kommunikationen mellan varje agent och molnet modelleras som en följd av händelser som planeras rekursivt av agenten. Vi kvantifierar nätverkets konnektivitet och vi visar att det är möjligt att synkronisera fleragentsystemet till samma tillståndstrajektoria och att två på varandra följande uppkopplingar till molnen av samma agent separeras av ett nedåt begränsat tidsintervall. Det tredje bidraget är en samling av distribuerade regulatorer för täcknings- och övervakningsuppgifter med ett nätverk av mobila sensorer med anisotropa sensormönster. Vi utvecklar en abstrakt modell av den inspekterade miljön och definierar ett mått på den täckning som uppnås av sensornätverket. Vi visar att nätverket uppnår gradvis förbättrad täckning, och vi karaktäriserar nätverkets jämviktskonfigurationer. Det fjärde bidraget är en distribuerad, molnbaserad regleringsalgoritm för inspektion av 3D-strukturer med ett nätverk av mobila sensorer, som liknar dem som betraktas i det tredje bidraget. Vi utvecklar en abstrakt modell av strukturen som ska inspekteras och kvantifierar omfattningen av inspektionen. Vi visar att nätverket enligt den föreslagna algoritmen är garanterat att slutföra inspektionen inom begränsad tid. Alla resultat som presenteras i avhandlingen bekräftas av numeriska simuleringar och ibland av experiment med flygrobotplattformar. Experimenten visar att teorin och metoderna som utvecklas i avhandlingen är av praktisk relevans.

  • 9.
    Adaldo, Antonio
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Dimarogonas, Dimos V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Cloud-supported effective coverage of 3D structures2018Ingår i: 2018 European Control Conference, ECC 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 95-100, artikel-id 8550377Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 10.
    Adaldo, Antonio
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Liuzza, Davide
    Univ Sannio, Dept Engn, I-82100 Benevento, Italy..
    Dimarogonas, Dimos V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Cloud-Supported Formation Control of Second-Order Multiagent Systems2018Ingår i: IEEE Transactions on Big Data, ISSN 2325-5870, E-ISSN 2168-6750, Vol. 5, nr 4, s. 1563-1574Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 11.
    Ahlberg, Sofie
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Human-in-the-Loop Control Synthesis for Multi-Agent Systems under Metric Interval Temporal Logic Specifications2019Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    I takt med att robotar blir allt vanligare i våra hem och i våra arbetsmiljöer, har det blivit allt viktigare att ta hänsyn till människan plats i systemen när regulatorerna för robotorna designas. Detta innefattar både människans fysiska närvaro och interaktion på besluts- och reglernivå. En viktig aspekt i detta är att designa regulatorer som garanterat uppfyller givna villkor. Samtidigt måste vi minimera risken att ingen lösning hittas, eftersom det skulle tvinga systemet till ett stopp. För att uppnå detta krävs det att det finns rum för att mjuka upp villkoren. En annan aspekt är att designa systemet så att det är anpassningsbart till människan och miljön.

    I den här uppsatsen närmar vi oss problemet genom att använda regulator syntes för multi-agent system under hårda och mjuka villkor där människan har direkt påverkan på hur det svaga villkoret överträds. För att hantera multi-agent strukturen undersöker vi både det klassiska centraliserade automata-baserade ramverket och ett icke-centraliserat tillvägagångsätt med krockundvikning. För att hantera mjuka villkor introducerar vi en metrik; hybrida avståndet, som kvantifierar överträdelsen. Det hybrida avståndet består av två typer av överträdelse (kontinuerligt avstånd eller missandet av deadlines, och diskret avstånd eller rumsliga överträdelser) som vägs mot varandra med en vikt konstant som vi kommer att kalla den mänskliga preferens kontanten. Som mänsklig påverkan överväger vi direkt feedback på överträdelsen genom att hon bestämmer värdet på den mänskliga preferens kontanten, och direkt påverkan på regulatorn där den mänskliga preferens konstanten bestäms genom en inverserad förstärkt inlärnings algoritm baserad på de föreslagna och följda vägarna. Metoderna valideras genom simuleringar.

  • 12.
    Aleksandrauskaite, Ruth
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Analysis of Velocity Estimation Methods for High-Performance Motion Control Systems2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Majoriteten av all kommersiell elektronikhårdvara tillverkas med ytmonteringsteknik.Ökad komplexitet och miniatyrisering av elektronik medför hårdaprestandakrav på automationsprocessen.Denna rapport behandlar test och analys av alternativa hastighetsestimeringsmetoderför inbyggda högpresterande rörelsekontrollsystem. Rörelsesystemeti Mycronics pick- and placemaskiner regleras med fram- och återkoppling.Den linjära förskjutningen mäts upp med en pulsgivare och estimering av hastighetensker med hjälp av en tillståndsobservatör. Tidigare studier indikeraratt hastighetsestimeringen är bristfällig.Diverse tekniker för rekonstruktion av tillstånd har testats och utvärderats viasimulering i MATLAB SIMULINKr. Därefter utfördes experiment på ett transportbandhämtat från en pick- and placemaskin.Resultaten påvisar att ett Kalmanfilter är den bästa tillståndsobservatören.Metoden kräver emellertid omfattande parameterjustering för att uppnå braprestanda. Robustheten samt referensspårningen förbättrades nämnvärt då enPertubation-observatör med Kalmanfiltrering användes. Däremot var insvängningstidennågot kortare då ett Kalmanfilter nyttjades enskilt.

  • 13.
    Alinia, Bahram
    et al.
    Telecom SudParis, Inst Mines Telecom, F-91000 Evry, France. alebi, Mohammad Sadegh.
    Talebi Mazraeh Shahi, Mohammad Sadegh
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Hajiesmaili, Mohammad H.
    Yekkehkhany, Ali
    Crespi, Noel
    Competitive Online Scheduling Algorithms with Applications in Deadline-Constrained EV Charging2018Ingår i: 2018 IEEE/ACM 26th International Symposium on Quality of Service, IWQoS 2018, IEEE, 2018, artikel-id 8624184Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 14.
    Alistarh, Dan
    et al.
    IST Austria, Klosterneuburg, Austria..
    Hoefler, Torsten
    Swiss Fed Inst Technol, Zurich, Switzerland..
    Johansson, Mikael
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Khirirat, Sarit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Konstantinov, Nikola
    IST Austria, Klosterneuburg, Austria..
    Renggli, Cedric
    Swiss Fed Inst Technol, Zurich, Switzerland..
    The Convergence of Sparsified Gradient Methods2018Ingår i: Advances in Neural Information Processing Systems 31 (NIPS 2018) / [ed] Bengio, S Wallach, H Larochelle, H Grauman, K CesaBianchi, N Garnett, R, Neural Information Processing Systems (NIPS) , 2018, Vol. 31Konferensbidrag (Refereegranskat)
    Abstract [en]

    Stochastic Gradient Descent (SGD) has become the standard tool for distributed training of massive machine learning models, in particular deep neural networks. Several families of communication-reduction methods, such as quantization, large-batch methods, and gradient sparsification, have been proposed to reduce the overheads of distribution. To date, gradient sparsification methods-where each node sorts gradients by magnitude, and only communicates a subset of the components, accumulating the rest locally-are known to yield some of the largest practical gains. Such methods can reduce the amount of communication per step by up to three orders of magnitude, while preserving model accuracy. Yet, this family of methods currently has no theoretical justification. This is the question we address in this paper. We prove that, under analytic assumptions, sparsifying gradients by magnitude with local error correction provides convergence guarantees, for both convex and non-convex smooth objectives, for data-parallel SGD. The main insight is that sparsification methods implicitly maintain bounds on the maximum impact of stale updates, thanks to selection by magnitude. Our analysis also reveals that these methods do require analytical conditions to converge well, justifying and complementing existing heuristics.

  • 15.
    Andersson, Sofie
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Dimarogonas, Dimos V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Human in the Loop Least Violating Robot Control Synthesis under Metric Interval Temporal Logic Specifications2018Ingår i: 2018 European Control Conference, ECC 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 453-458, artikel-id 8550179Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 16. Ansari, R. Jaberzadeh
    et al.
    Karayiannidis, Yiannis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Reducing the human effort for human-robot cooperative object manipulation via control design2017Ingår i: IFAC PAPERSONLINE, ELSEVIER SCIENCE BV , 2017, Vol. 50, nr 1, s. 14922-14927Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 17.
    Ardah, Khaled
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. Ericsson Res, Radio Dept, S-16480 Stockholm, Sweden.
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
    Freitas, Walter C., Jr.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
    Cavalcanti, Francisco R. P.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
    A Novel Cell Reconfiguration Technique for Dynamic TDD Wireless Networks2018Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, nr 3, s. 320-323Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 18.
    Ardah, Khaled
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. Ericsson Res, SE-16480 Stockholm, Sweden.
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Freitas, Walter C., Jr.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Cavalcanti, Francisco R. P.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    A Unifying Design of Hybrid Beamforming Architectures Employing Phase Shifters or Switches2018Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, nr 11, s. 11243-11247Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 19.
    Ardah, Khaled
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil..
    Freitas, Walter C., Jr.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil..
    Cavalcanti, Francisco R. P.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    An ADMM Approach to Distributed Coordinated Beamforming in Dynamic TDD Networks2017Ingår i: 2017 IEEE 7TH INTERNATIONAL WORKSHOP ON COMPUTATIONAL ADVANCES IN MULTI-SENSOR ADAPTIVE PROCESSING (CAMSAP), IEEE , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 20. Armengaud, E.
    et al.
    Zoier, M.
    Baumgart, A.
    Biel, Martin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Chen, D.
    KTH.
    Griessnig, G.
    Hein, C.
    Ritter, T.
    Tavakoli Kolagari, R.
    Model-based toolchain for the efficient development of safety-relevant automotive embedded systems2011Ingår i: SAE technical paper series, ISSN 0148-7191Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Advanced functionalities unthinkable a few decades ago are now being introduced into automotive vehicles through embedded systems for reasons like emission control, vehicle connectivity, safety and cooperative behaviors. As the development often involves stakeholders from different engineering disciplines and organizations, the complexity due to shared requirements, interdependencies of data, functions, and resources, as well as tight constraints in regards to timing, safety, and resource efficiency makes the system integration, quality control and assurance, reuse and change management increasingly more difficult. This calls for a more rigorous approach to the development of automotive embedded systems and components. This paper describes the CESAR reference technology platform (RTP) that supports the formalization of various engineering concerns in the development of safety-relevant embedded systems and thereby a model-based integration of various tools and methods to form seamless environments or toolchains for the development of such systems. 

  • 21.
    Aytekin, Arda
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Asynchronous First-Order Algorithms for Large-Scale Optimization: Analysis and Implementation2019Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    Den snabba utvecklingen inom kommunikations- och datalagringsteknik har gjort storskalig datainsamling mer tillgänglig än någonsin. För att omvandla denna data till insikt eller beslut löser man ofta någon form av numeriskt optimeringsproblem. När datavolymerna ökar blir dessa optimeringsproblem så stora att de inte längre kan lösas på en enda dator. Detta har skapat ett stort intresse för att utveckla optimeringsalgoritmer som kan exekveras effektivt på flera parallella datornoder. Ett sätt att uppnå effektivitet i parallella beräkningar är att låta noderna arbeta asynkront: på detta sätt spenderar noderna mindre tid på att koordinera med varandra och mer tid på beräkningar.  Beräkningarna måste dock ibland baseras på fördröjd information.  Asynkronism medför dock en risk att annars konvergenta optimeringsalgoritmer inte längre konvergerar, och det finns i dagsläget väldigt begränsat matematiskt stöd för analys av asynkrona optimeringsalgoritmer. I avhandlingen utvecklar vi ny teori och verktyg för att hjälpa till att förstå och implementera asynkrona optimeringsalgoritmer under tidsvarierande och begränsad informationsfördröjning.

    I den första delen av avhandlingen analyserar vi konvergensen för olika asynkrona optimeringsalgoritmer. Vi föreslår först ett nytt tillvägagångssätt för att minimera medelvärdet av ett stort antal differentierbara komponentfunktioner. Algoritmen använder fördröjd partiell gradientinformation, och inkluderar fördröjda inkrementella gradientalgoritmer och koordinatreduktionsalgoritmer som specialfall. Vi visar att när den totala förlustfunktionen är strarkt konvex och komponentfunktionerna har Lipschitz-kontinuerliga gradienter så konvergerar algoritmen linjärt.  Steglängden för algoritmen kan väljas utan vetskap om den övre gränsen på informationsfördröjningen och garanterar ändå konvergens till en given nivå av suboptimalitet. Därefter analyserar vi två varianter av inkrementella gradientalgoritmer för regulariserade optimeringsproblem. Den första varianten, asynkron mini-batching, används för att lösa regulariserade stokastiska optimeringsproblem med deriverbara förlustfunktioner. Vi visar att algoritmen med tidsvarierande steglängd uppnår de bäst kända konvergenshastigheterna för motsvarande synkrona algoritm när (i) den tillåtna mängden är kompakt eller (ii) regulariseringsfunktionen är starkt konvex och den tillåtna mängden är sluten och konvex. Detta innebär att tidsfördröjningen har en asymptotiskt försumbar effekt på konvergensen, och vi kan förvänta oss att asynkrona beräkningar ger en kortare beräkningstid. För den andra varianten, proximal inkrementell aggregerad gradientnedstigning, visar vi att när målfunktionen är starkt konvex, så konvergerar algoritmen linjärt till den korrekta lösningen ifall man använder en konstant stegstorlek som beror på den maximala tidsfördröjningen.

    I den andra delen av avhandlingen presenterar vi först POLO, ett öppen källkodsbibliotek för algoritmutveckling skrivet i C++. Vi använder en policy-baserad designmetod för att dekomponera proximala gradientalgoritmer till deras grundläggande byggstenar. Detta tillåter oss att hantera en kombinatorisk mängds designval med linjärt många komponenter och resulterar i effektiv kod med litet fotavtryck. Tillsammans med sitt systerbibliotek skrivet i Julia, POLO.jl, ger vårat ramverk forskare inom optimering och maskininlärning en möjlighet att snabbt skapa prototyper av sina idéer, testa dem mot algoritmer från forskningens framkant, och senare distribuera algoritmerna på olika datorplattformar med bara några rader av kod. Vidare framställer vi en ny ``serverlös'' exekverare för en parallell variant av den alternerande riktningsmetoden för multiplikatorer (ADMM) med hjälp av verktygen i vårat ramverk. Vi använder Amazon Web Services Lambda-funktioner som datornoder, och vi observerar kortare körtid upp till 256 arbetare och en parallella effektiviteten på över 70% upp till 64 arbetare. Dessa preliminära resultat tyder på att serverlösa exekveringsmiljöer, med deras tillgänglighet och elasticitet, är lovande kandidater för att skala upp distribuerade optimeringsalgoritmer.

  • 22.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    Ghauch, Hadi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    How to Split UL/DL Antennas in Full-DuplexCellular Networks2018Ingår i: IEEE International Conference on Communication (ICC’18): ThirdWorkshop on Full-Duplex Communications for Future Wireless Networks, Kansas City, MO, USA: IEEE Communications Society, 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 23.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    Sabharwal, Ashutosh
    Rice University.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    Low Resolution Phase Shifters Suffice for Full-Duplex mmWave Communications2019Ingår i: IEEE International Conference on Communications: Workshop on Full-Duplex Communications for Future Wireless Networks, Shangai, China: IEEE Communications Society, 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Full-duplex base-stations with half-duplex nodes,allowing simultaneous uplink and downlink from different nodes,have the potential to double the spectrum efficiency withoutadding additional complexity at mobile nodes. Hybrid beam-forming is commonly used in millimeter-wave systems for itsimplementation efficiency. An important element of hybrid beam-forming is quantized phase shifters. In this paper, we ask iflow-resolution phase shifters suffice for beamforming-based full-duplex millimeter-wave systems. We formulate the problem ofjoint design for both self-interference suppression and downlinkbeamforming as an optimization problem, which we solve usingpenalty dual decomposition to obtain a near-optimal solution.Numerical results indicate that low-resolution phase shifters canperform close to systems that use infinite phase shifter resolution,and that even a single quantization bit outperforms half-duplextransmissions in both low and high residual self-interferencescenarios.

  • 24. Bagloee, S. A.
    et al.
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Asadi, M.
    A hybrid machine-learning and optimization method for contraflow design in post-disaster cases and traffic management scenarios2019Ingår i: Expert systems with applications, ISSN 0957-4174, E-ISSN 1873-6793, Vol. 124, s. 67-81Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 25. Balaghi I., M. H.
    et al.
    Antunes, D. J.
    Mamduhi, Mohammad Hossein
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Hirche, S.
    An Optimal LQG Controller for Stochastic Event-triggered Scheduling over a Lossy Communication Network2018Ingår i: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 51, nr 23, s. 58-63Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 26.
    Balaghi, M. Hadi I.
    et al.
    Eindhoven Univ Technol, Dept Mech Engn, Control Syst Technol Grp, Eindhoven, Netherlands..
    Antunes, Duarte J.
    Eindhoven Univ Technol, Dept Mech Engn, Control Syst Technol Grp, Eindhoven, Netherlands..
    Mamduhi, Mohammad H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Hirche, Sandra
    Tech Univ Munich, Chair Informat Oriented Control, Munich, Germany..
    A Decentralized Consistent Policy for Event-triggered Control over a Shared Contention-based Network2018Ingår i: 2018 IEEE Conference on Decision and Control  (CDC), IEEE , 2018, s. 1719-1724Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 27.
    Barbosa, Fernando S.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Robotik, perception och lärande, RPL.
    Lindemann, Lars
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Dimarogonas, Dimos V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Tumova, Jana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Robotik, perception och lärande, RPL.
    Integrated motion planning and control under metric interval temporal logic specifications2019Ingår i: 2019 18th European Control Conference, ECC 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, s. 2042-2049, artikel-id 8795925Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper proposes an approach that combines motion planning and hybrid feedback control design in order to find and follow trajectories fulfilling a given complex mission involving time constraints. We use Metric Interval Temporal Logic (MITL) as a rich and rigorous formalism to specify such missions. The solution builds on three main steps: (i) using sampling-based motion planning methods and the untimed version of the mission specification in the form of Zone automaton, we find a sequence of waypoints in the workspace; (ii) based on the clock zones from the satisfying run on the Zone automaton, we compute time-stamps at which these waypoints should be reached; and (iii) to control the system to connect two waypoints in the desired time, we design a low-level feedback controller leveraging Time-varying Control Barrier Functions. Illustrative simulation results are included.

  • 28.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik. Royal Inst Technol, KTH, Stockholm, Sweden..
    Ghauch, Hadi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    How to Split UL/DL Antennas in Full-Duplex Cellular Networks2018Ingår i: 2018 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE, 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 29.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    Sabharwal, Ashutosh
    Rice Univ, Houston, TX USA..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. Ericsson Res, Kista, Sweden..
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Nätverk och systemteknik.
    Low Resolution Phase Shifters Suffice for Full-Duplex mmWave Communications2019Ingår i: 2019 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE , 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Full-duplex base-stations with half-duplex nodes, allowing simultaneous uplink and downlink from different nodes, have the potential to double the spectrum efficiency without adding additional complexity at mobile nodes. Hybrid beam forming is commonly used in millimeter wave systems for its implementation efficiency. An important element of hybrid beam-forming is quantized phase shifters. In this paper, we ask if low-resolution phase shifters suffice for beamforming-based full-duplex millimeter wave systems. We formulate the problem of joint design for both self-interference suppression and downlink beamforming as an optimization problem, which we solve using penalty dual decomposition to obtain a near-optimal solution. Numerical results indicate that low-resolution phase shifters can perform close to systems that use infinite phase shifter resolution, and that even a single quantization bit outperforms half-duplex transmissions in both low and high residual self-interference scenarios.

  • 30.
    Baumann, Dominik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. Max Planck Institute for Intelligent Systems.
    Fast and Resource-Efficient Control of Wireless Cyber-Physical Systems2019Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 31. Beerens, R.
    et al.
    Bisoffi, Andrea
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Zaccarian, L.
    Heemels, W. P. M. H.
    Nijmeijer, H.
    Van De Wouw, N.
    Hybrid PID control for transient performance improvement of motion systems with friction2018Ingår i: 2018 Annual American Control Conference (ACC), Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 539-544, artikel-id 8431613Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 32.
    Beerens, R.
    et al.
    Eindhoven Univ Technol, Dept Mech Engn, NL-5600 MB Eindhoven, Netherlands..
    Bisoffi, Andrea
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Zaccarian, L.
    Univ Toulouse, LAAS, CNRS, F-31400 Toulouse, France.;Univ Trento, I-38122 Trento, Italy..
    Heemels, W. P. M. H.
    Eindhoven Univ Technol, Dept Mech Engn, NL-5600 MB Eindhoven, Netherlands..
    Nijmeijer, H.
    Eindhoven Univ Technol, Dept Mech Engn, NL-5600 MB Eindhoven, Netherlands..
    van de Wouw, N.
    Eindhoven Univ Technol, Dept Mech Engn, NL-5600 MB Eindhoven, Netherlands.;Univ Minnesota, Civil Environm & Geoengn Dept, Minneapolis, MN 55455 USA..
    Reset integral control for improved settling of PID-based motion systems with friction2019Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 107, s. 483-492Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a reset control approach to improve the transient performance of a PID-controlled motion system subject to Coulomb and viscous friction. A reset integrator is applied to circumvent the depletion and refilling process of a linear integrator when the solution overshoots the setpoint, thereby significantly reducing the settling time. Robustness for unknown static friction levels is obtained. The closed-loop system is formulated through a hybrid systems framework, within which stability is proven using a discontinuous Lyapunov-like function and a meagre-limsup invariance argument. The working principle of the proposed reset controller is analyzed in an experimental benchmark study of an industrial high-precision positioning machine.

  • 33.
    Berkane, Soulaimane
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Bisoffi, Andrea
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Dimarogonas, Dimos V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    A hybrid controller for obstacle avoidance in an n-dimensional euclidean space2019Ingår i: 2019 18th European Control Conference, ECC 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, s. 764-769, artikel-id 8795713Konferensbidrag (Refereegranskat)
    Abstract [en]

    For a vehicle moving in an n-dimensional Euclidean space, we present a construction of a hybrid feedback that guarantees both global asymptotic stabilization of a reference position and avoidance of an obstacle corresponding to a bounded spherical region. The proposed hybrid control algorithm switches between two modes of operation: stabilization (motion-to-goal) and avoidance (boundary-following). The geometric construction of the flow and jump sets of the hybrid controller, exploiting a hysteresis region, guarantees robust switching (chattering-free) between stabilization and avoidance. Simulation results illustrate the performance of the proposed hybrid control approach for a 3-dimensional scenario.

  • 34.
    Berkane, Soulaimane
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Tayebi, A.
    Attitude estimation with intermittent measurements2019Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 105, s. 415-421Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a framework for attitude estimation on the Special Orthogonal group SO(3) using intermittent body-frame vector measurements. We consider the case where the vector measurements are synchronously-intermittent (all measurements are received at the same time) and the case where the vector measurements are asynchronously-intermittent (not all measurements are received at the same time). The proposed observers have a measurement-triggered structure where the attitude is predicted using the continuously measured angular velocity when the vector measurements are not available, and adequately corrected upon the arrival of the vector measurements. A hybrid framework is proposed to capture the behaviour of the closed-loop system by extending the state with timers that are reset at each jump of the observer state. Almost global asymptotic stability is shown using rigorous Lyapunov techniques for hybrid systems.

  • 35.
    Berkane, Soulaimane
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Tayebi, Abdelhamid
    Univ Western Ontario, Dept Elect & Comp Engn, London, ON, Canada.;Lakehead Univ, Dept Elect Engn, Thunder Bay, ON, Canada..
    Teel, Andrew R.
    Univ Calif Santa Barbara, Dept Elect & Comp Engn, Santa Barbara, CA 93106 USA..
    Hybrid Constrained Estimation For Linear Time-Varying Systems2018Ingår i: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2018, s. 4643-4648Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 36.
    Biel, Martin
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Aytekin, Arda
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Mikael
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    POLO.J1: Policy-based optimization algorithms in Julia2019Ingår i: Advances in Engineering Software, ISSN 0965-9978, E-ISSN 1873-5339, Vol. 136, artikel-id UNSP 102695Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present POLO. j1- a Julia package that helps algorithm developers and machine-learning practitioners design and use state-of-the-art parallel optimization algorithms in a flexible and efficient way. POLO. j1 extends our C+ + library POLO, which has been designed and implemented with the same intentions. POLO. j1 not only wraps selected algorithms in POLO and provides an easy mechanism to use data manipulation facilities and loss function definitions in Julia together with the underlying compiled C+ + library, but it also uses the policy-based design technique in a Julian way to help users prototype optimization algorithms from their own building blocks. In our experiments, we observe that there is little overhead when using the compiled C+ + code directly within Julia. We also notice that the performance of algorithms implemented in pure Julia is comparable with that of their C+ + counterparts. Both libraries are hosted on GitHub(1)under the free MIT license, and can be used easily by pulling the pre-built 64-bit architecture Docker images.(2)

  • 37.
    Biel, Martin
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Mikael
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Distributed L-shaped Algorithms in Julia2018Ingår i: 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, s. 57-69Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 38.
    Biel, Martin
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Norrlof, Mikael
    Efficient Trajectory Reshaping in a Dynamic Environment2018Ingår i: 2018 IEEE 15TH INTERNATIONAL WORKSHOP ON ADVANCED MOTION CONTROL (AMC), IEEE, 2018, s. 54-59Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 39.
    Bisoffi, Andrea
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Dimarogonas, Dimos V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    A hybrid barrier certificate approach to satisfy linear temporal logic specifications2018Ingår i: 2018 Annual American Control Conference (ACC), Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 634-639, artikel-id 8430795Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 40.
    Björk, Joakim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Performance Quantification of Interarea Oscillation Damping Using HVDC2019Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [sv]

    Övergången till förnybar energi och avregleringen av elmarknaden leder till förändrade produktions-och överföringsmönster. Dessa förändringar medför behov av en ökad överföringskapacitet. En begränsande faktor, som kan leda till ett underutnyttjande av stamnätet, är interareapendlingar. Dessa systemövergripande pendlingar involverar grupper av generatorer som svänger i förhållande till varandra. Interareapendlingar är ibland svåra att styra på grund av deras skala och komplexitet. I denna avhandling undersöker vi hur förbindelser med högspänd likström, engleska high-voltage direct current (HVDC), kan användas för att dämpa interareapendlingar. Avhandlingen har två huvudbidrag.

    I det första bidraget visar vi hur stabiliteten hos två olika synkrona nät kan förbättras genom att modulera den aktiva effekten hos en enda HVDC-länk. Ett bekymmer med aktiv effektmodulering är att växelverkan mellan interareapendlingar hos de två näten kan ha en negativ inverkan på systemets stabilitet. Genom att studera styrbarhetsgramianen visar vi att det alltid är möjligt att förbättra dämpningen i båda näten så länge som frekvenserna hos deras interareapendlingar inte ligger för nära varandra. För förenklade modeller visas det uttryckligen hur styrbarheten och därmed de möjliga dämpningsförbättringarna, försämras då frekvensskillnaden blir liten.

    Avhandlings andra bidrag visar hur koordinerad styrning av två (eller fler) länkar kan användas för att undvika växelverkan mellan besvärliga interareapendlingar. Vi undersöker prestandan hos olika typer av flervariabla regulatorer. I synnerhet undersökers styrsignalsanvändning samt robusthet mot mät-, kommunikations- och aktuatorfel. Därigenom karakteriseras lämpliga regulatortyper.

  • 41.
    Björk, Joakim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Fundamental Performance Limitations in Utilizing HVDC to Damp Interarea Modes2019Ingår i: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 34, nr 2, s. 1095-1104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 42.
    Björk, Joakim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Harnefors, Lennart
    ABB, Corp Res, Vasteras, Sweden..
    Eriksson, Robert
    Svenska kraftnat, R&D, Sundbyberg, Sweden..
    Analysis of Coordinated HVDC Control for Power Oscillation Damping2018Ingår i: Conference Record of the 3rd IEEE International Workshop on Electronic Power Grid, eGrid 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 19-24, artikel-id 8598674Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 43. Boem, F.
    et al.
    Zhou, Y.
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Parisini, T.
    Distributed Pareto-optimal state estimation using sensor networks2018Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 93, s. 211-223Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 44. Bombois, X.
    et al.
    Korniienko, A.
    Hjalmarsson, Håkan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Scorletti, G.
    Optimal identification experiment design for the interconnection of locally controlled systems2018Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 89, s. 169-179Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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. 

  • 45.
    Boskos, Dimitris
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Dimarogonas, Dimos V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Decentralized abstractions for multi-agent systems under coupled constraints2019Ingår i: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 45, s. 1-16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 46.
    Cavalcante, Eduardo de Olivindo
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. Ericsson Res, SE-16480 Stockholm, Sweden.
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Freitas Jr, Walter C.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Distributed Beamforming in Dynamic TDD MIMO Networks With BS to BS Interference Constraints2018Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, nr 5, s. 788-791Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 47.
    Cavaliere, Clara
    et al.
    Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy..
    Mariniello, Dario
    Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy..
    Adaldo, Antonio
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Lo Iudice, Francesco
    Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy..
    Dimarogonas, Dimos V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Karl H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    di Bernardo, Mario
    Univ Naples Federico II, Dept Elect Engn & Informat Technol, Naples, Italy..
    Cloud-supported self-triggered control for multi-agent circumnavigation2018Ingår i: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2018, s. 5090-5095Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 48.
    Charalambous, Themistoklis
    et al.
    Aalto Univ, Dept Elect Engn & Automat, Espoo, Finland..
    Kim, Su Min
    Korea Polytech Univ, Dept Elect Engn, Shihung, South Korea..
    Nomikos, Nikolaos
    Univ Aegean, Dept Informat & Commun Syst Engn, Samos, Greece..
    Bengtsson, Mats
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Johansson, Mikael
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Relay-pair selection in buffer-aided successive opportunistic relaying using a multi-antenna source2019Ingår i: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 84, s. 29-41Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 49.
    Chong, Michelle S.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Sandberg, Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Secure patching of an output-feedback controller for a class of nonlinear systems under adversarial attack2018Ingår i: 2018 IEEE CConference on Decision and Control  (CDC), Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 7255-7260, artikel-id 8618972Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 50.
    Chong, Michelle
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Sandsten, M.
    Rantzer, A.
    Estimating the Wigner distribution of linear time-invariant dynamical systems2018Ingår i: 2018 European Control Conference, ECC 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 1220-1225Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

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