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  • 301.
    Briat, Corentin
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Robust stability analysis in the *-norm and Lyapunov-Razumikhin functions for the stability analysis of time-delay systems2011Conference paper (Other academic)
    Abstract [en]

    Lyapunov-Krasovskii functionals have been shown to have connections with input-output techniques considering delay operators mapping L-2 to L-2. It is shown here that Lyapunov-Razumikhin functions can also be connected to the input-output framework by considering operators on L-infinity and the corresponding Small-Gain Theorem. Several important results from the Lyapunov-Razumikhin Theorem are retrieved and extended.

  • 302.
    Briat, Corentin
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Robust stability analysis of uncertain Linear Positive Systems via Integral Linear Constraints: L-1- and L-infinity-gain characterizations2011Conference paper (Refereed)
    Abstract [en]

    Copositive Lyapunov functions are used along with dissipativity theory for stability analysis of uncertain linear positive systems. At the difference of standard results, linear supply-rates are employed for robustness and performance analysis and lead to L-1- and L-infinity-gain characterizations. This naturally guides to the definition of Integral Linear Constraints (ILCs) for the characterization of input-output nonnegative uncertainties. It turns out that these integral linear constraints can be linked to the Laplace domain, in order to be tuned adequately, by exploiting the L-1-norm and input/output signals properties. This dual viewpoint allows to prove that the static-gain of the uncertainties, only, is critical for stability. This fact provides a new explanation for the surprising stability properties of linear positive time-delay systems. The obtained stability and performance analysis conditions are expressed in terms of (robust) linear programming problems that are transformed into finite dimensional ones using the Handelman's Theorem. Several examples are provided for illustration.

  • 303.
    Briat, Corentin
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Robust stability and stabilization of uncertain linear positive systems via integral linear constraints: L-1-gain and L-infinity-gain characterization2013In: International Journal of Robust and Nonlinear Control, ISSN 1049-8923, E-ISSN 1099-1239, Vol. 23, no 17, p. 1932-1954Article in journal (Refereed)
    Abstract [en]

    Copositive linear Lyapunov functions are used along with dissipativity theory for stability analysis and control of uncertain linear positive systems. Unlike usual results on linear systems, linear supply rates are employed here for robustness and performance analysis using L-1-gain and L-gain. Robust stability analysis is performed using integral linear constraints for which several classes of uncertainties are discussed. The approach is then extended to robust stabilization and performance optimization. The obtained results are expressed in terms of robust linear programming problems that are equivalently turned into finite dimensional ones using Handelman's theorem. Several examples are provided for illustration.

  • 304.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nonlinear state-dependent delay modeling and stability analysis of internet congestion control2010In: 49TH IEEE CONFERENCE ON DECISION AND CONTROL (CDC), 2010, p. 1484-1491Conference paper (Refereed)
    Abstract [en]

    It is shown that the queuing delay involved in the congestion control algorithm is state-dependent and does not depend on the current time. Then, using an accurate formulation for buffers, networks with arbitrary topologies can be built. At equilibrium, our model reduces to the widely used setup by Paganini et al. Using this model, the delay-derivative is analyzed and it is proved that the delay time-derivative does not exceed one for the considered topologies. It is then shown that the considered congestion control algorithm globally stabilizes a delay-free single buffer network. Finally, using a specific linearization result for systems with state-dependent delays from Cooke and Huang, we show the local stability of the single bottleneck network.

  • 305.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Yavuz, Emre Altug
    KTH, School of Electrical Engineering (EES), Communication Networks.
    An axiomatic fluid-flow model for congestion control analysis2011In: 2011 50th IEEE Conference on Decision and Control andEuropean Control Conference (CDC-ECC), 2011, p. 3122-3129Conference paper (Refereed)
    Abstract [en]

    An axiomatic model for congestion control isderived. The proposed four axioms serve as a basis for theconstruction of models for the network elements. It is shownthat, under some assumptions, some models of the literature canbe recovered. A single-buffer/multiple-users topology is finallyderived and studied for illustration.

  • 306.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dynamic equations on time-scale: Application to stability analysis and stabilization of aperiodic sampled-data systems2011In: IFAC Proc. Vol. (IFAC-PapersOnline), 2011, no PART 1, p. 11374-11379Conference paper (Refereed)
    Abstract [en]

    The stability analysis of systems with aperiodic sampling is analyzed in the framework of dynamic equations on time-scales. Lyapunov theory is used, with sample-period-dependent and independent Lyapunov functions, to obtain stability conditions expressed in terms of parameter dependent matrix inequalities. The examples illustrate the efficiency of the approach which is able to recover, for some systems, the theoretical results for the periodic sampling case even in the aperiodic case. It is also shown that some systems may have admissible varying sampling periods located in disjoint sets. Finally, stabilization results via switching statefeedback are provided; both robust and sampling-period-dependent controllers are considered. It is shown that the latter ones, using the information on the sampling period, can improve stability properties. Stabilization examples illustrate the effectiveness of the approach.

  • 307.
    Briat, Corentin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sename, O.
    Lafay, J. -F
    Design of LPV observers for LPV time-delay systems: an algebraic approach2011In: International Journal of Control, ISSN 0020-7179, E-ISSN 1366-5820, Vol. 84, no 9, p. 1533-1542Article in journal (Refereed)
    Abstract [en]

    The design of reduced order observer for linear parameter varying (LPV) time-delay systems is addressed. Necessary conditions guaranteeing critical structural properties for the observation error dynamics are first provided through nonlinear algebraic matrix equalities. An explicit parametrisation of the family of observers fulfilling these necessary conditions is then derived. Finally, an approach based on linear matrix inequalities is provided and used to select a suitable observer within this family, according to some criterion; e.g. maximisation of the delay margin or guaranteed suboptimal L(2)-gain. Examples from the literature illustrate the efficiency of the approach.

  • 308.
    Briat, Corentin
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Seuret, Alexandre
    Convex Dwell-Time Characterizations for Uncertain Linear Impulsive Systems2012In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 57, no 12, p. 3241-3246Article in journal (Refereed)
    Abstract [en]

    New sufficient conditions for the characterization of dwell-times for linear impulsive systems are proposed and shown to coincide with continuous decrease conditions of a certain class of looped-functionals, a recently introduced type of functionals suitable for the analysis of hybrid systems. This approach allows to consider Lyapunov functions that evolve nonmonotonically along the flow of the system in a new way, broadening then the admissible class of systems which may be analyzed. As a byproduct, the particular structure of the obtained conditions makes the method is easily extendable to uncertain systems by exploiting some convexity properties. Several examples illustrate the approach.

  • 309.
    Briat, Corentin
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A conservation-law-based modular fluid-flow model for network congestion modeling2012In: 2012 Proceedings - IEEE INFOCOM, IEEE Computer Society, 2012, p. 2050-2058Conference paper (Refereed)
    Abstract [en]

    A modular fluid-flow model for network congestion analysis and control is proposed. The model is derived from an information conservation law stating that the information is either in transit, lost or received. Mathematical models of network elements such as queues, users, and transmission channels, and network description variables, including sending/ acknowledgement rates and delays, are inferred from this law and obtained by applying this principle locally. The modularity of the devised model makes it sufficiently generic to describe any network topology, and appealing for building simulators. Previous models in the literature are often not capable of capturing the transient behavior of the network precisely, making the resulting analysis inaccurate in practice. Those models can be recovered from exact reduction or approximation of this new model. An important aspect of this particular modeling approach is the introduction of new tight building blocks that implement mechanisms ignored by the existing ones, notably at the queue and user levels. Comparisons with packet-level simulations corroborate the proposed model.

  • 310.
    Briat, Corentin
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yavuz, Emre A.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Impact of Queueing Delay Estimation Error on Equilibrium and Its Stability2011In: NETWORKING 2011, PT II, 2011, p. 356-367Conference paper (Refereed)
    Abstract [en]

    Delay-based transmission control protocols need to separate round-trip time (RTT) measurements into their constituting parts: the propagation and the queueing delays. We consider two means for this; the first is to take the propagation delay as the minimum observed RTT value, and the second is to measure the queueing delay at the routers and feed it back to the sources. We choose FAST-TCP as a representative delay-based transmission control protocol for analysis and study the impact of delay knowledge errors on its performance. We have shown that while the first method destroys fairness and the uniqueness of the equilibrium, the stability of the protocol can easily be obtained through tuning the protocol terms appropriately. Even though the second technique is shown to preserve fairness and uniqueness of the equilibrium point, we have presented that unavoidable oscillations can occur around the equilibrium point.

  • 311. Brighenti, C.
    et al.
    Wahlberg, Bo
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Rojas, Cristian R.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Input design using Markov chains for system identification2009In: Proceedings of the 48th IEEE Conference on  Decision and Control, 2009 held jointly with the 2009 28th Chinese Control Conference. CDC/CCC 2009, IEEE conference proceedings, 2009, p. 1557-1562Conference paper (Refereed)
    Abstract [en]

    This paper studies the input design problem for system identification where time domain constraints have to be considered. A finite Markov chain is used to model the input of the system. This allows to directly include input amplitude constraints in the input model by properly choosing the state space of the Markov chain, which is defined so that the Markov chain generates a multi-level sequence. The probability distribution of the Markov chain is shaped in order to minimize the cost function considered in the input design problem. Stochastic approximation is used to minimize that cost function. With this approach, the input signal to apply to the system can be easily generated by extracting samples from the optimal distribution. A numerical example shows how this method can improve estimation with respect to other input realization techniques.

  • 312.
    Brodén, Daniel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Paridari, Kaveh
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    MATLAB Applications to Generate Synthetic Electricity Load Profiles of Office Buildings and Detached Houses2017In: 2017 IEEE Innovative Smart Grid Technologies - Asia: Smart Grid for Smart Community, ISGT-Asia 2017, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 1-6, 2017Conference paper (Refereed)
    Abstract [en]

    In this paper we present two MATLAB applications that generates synthetic electricity load profiles for office buildings and detached houses down to 1-minute resolution. The applications have been developed using App Designer — a MATLAB environment for application development. The applications are based on consumer load models for office buildings and detached houses published in previous research work. The aim of this paper is to present an overview of the application functionalities, code design, assumptions and limitations, and examples of their potential use in power system education and research. To the author’s knowledge these are the first applications which allow generating synthetic load profiles for office buildings and houses in practical and intuitive manner where building attributes can be easily configured.

  • 313.
    Broman, Rickard
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Practical Study of Network Coding in Distributed Storage Systems2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Highly increased data traffic over the last few years has led to a need to improve the networkefficiency. One way to achieve this is by network coding. In this thesis two codes, namelyreplication code and regenerating codes, have been examined. Most other works in this area hasbeen theoretical, so we created a testbed to perform practical tests. Then these practical resultsare compared to the theoretical results with varying finite field size. It will be shown that thepractical studies verify the theoretical work. Furthermore, we observe the probability ofsuccessful repair after several stages of repair.

    More so, the achievability of exact repair of a failed node in a tandem network has beenexamined. This has been proven possible, and also the required finite field size is presented.Another issue at focus is the number of transfers required to achieve exact repair in such anetwork. The results show that 2*k transfers is required, which is comparable to functionalrepair.

  • 314.
    Brunsell, Per R.
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Hedqvist, Anders
    KTH, School of Engineering Sciences (SCI), Physics.
    Yadikin, Dimitry
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics.
    Reversed field pinch operation with intelligent shell feedback control in EXTRAP T2R2006In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, no 11, p. 904-913Article in journal (Refereed)
    Abstract [en]

    Discharges in the thin shell reversed field pinch (RFP) device EXTRAP T2R without active feedback control are characterized by growth of non-resonant m = 1 unstable resistive wall modes (RWMs) in agreement with linear MHD theory. Resonant m = 1 tearing modes (TMs) exhibit initially fast rotation and the associated perturbed radial fields at the shell are small, but eventually TMs wall-lock and give rise to a growing radial field. The increase in the radial field at the wall due to growing RWMs and wall-locked TMs is correlated with an increase in the toroidal loop voltage, which leads to discharge termination after 3-4 wall times. An active magnetic feedback control system has been installed in EXTRAP T2R. A two-dimensional array of 128 active saddle coils (pair-connected into 64 independent m = 1 coils) is used with intelligent shell feedback control to suppress the m = 1 radial field at the shell. With feedback control, active stabilization of the full toroidal spectrum of 16 unstable m = 1 non-resonant RWMs is achieved, and TM wall locking is avoided. A three-fold extension of the pulse length, up to the power supply limit, is observed. Intelligent shell feedback control is able to maintain the plasma equilibrium for 10 wall times, with plasma confinement parameters sustained at values comparable to those obtained in thick shell devices of similar size.

  • 315.
    Brunsell, Per
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Yadikin, Dmitriy
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Marchiori, Giuseppe
    Feedback stabilization of resistive wall modes in a reversed-field pinch2005In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, no 9, p. 092508-Article in journal (Refereed)
    Abstract [en]

    An array of saddle coils having Nc =16 equally spaced positions along the toroidal direction has been installed for feedback control of resistive wall modes (RWMs) on the EXTRAP T2R reversed-field pinch [P. R. Brunsell, H. Bergsaker, M. Cecconello, Plasma Phys. Controlled Fusion 43, 1457 (2001)]. Using feedback, multiple nonresonant RWMs are simultaneously suppressed for three to four wall times. Feedback stabilization of RWMs results in a significant prolongation of the discharge duration. This is linked to a better sustainment of the plasma and tearing mode toroidal rotation with feedback. Due to the limited number of coils in the toroidal direction, pairs of modes with toroidal mode numbers n, n′ that fulfill the condition ∫n- n′ ∫ = Nc are coupled by the feedback action from the discrete coil array. With only one unstable mode in a pair of coupled modes, the suppression of the unstable mode is successful. If two modes are unstable in a coupled pair, two possibilities exist: partial suppression of both modes or, alternatively, complete stabilization of one target mode while the other is left unstable.

  • 316.
    Brunsell, Per
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Yadikin, Dmitriy
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Cecconello, Marco
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Zanca, P.
    Active control of multiple resistive wall modes2005In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 47, no 12 B, p. B25-B36Article in journal (Refereed)
    Abstract [en]

     A two-dimensional array of saddle coils at M-c poloidal and N-c toroidal positions is used on the EXTRAP T2R reversed-field pinch (Brunsell P R et al 2001 Plasma Phys. Control. Fusion 43 1457) to study active control of resistive wall modes (RWMs). Spontaneous growth of several RWMs with poloidal mode number m = 1 and different toroidal mode number n is observed experimentally, in agreement with linear MHD modelling. The measured plasma response to a controlled coil field and the plasma response computed using the linear circular cylinder MHD model are in quantitive agreement. Feedback control introduces a linear coupling of modes with toroidal mode numbers n, n' that fulfil the condition vertical bar n - n'vertical bar = N-c. Pairs of coupled unstable RWMs are present in feedback experiments with an array of Mc x Nc = 4 x 16 coils. Using intelligent shell feedback, the coupled modes are generally not controlled even though the field is suppressed at the active coils. A better suppression of coupled modes may be achieved in the case of rotating modes by using the mode control feedback scheme with individually set complex gains. In feedback with a larger array of Mc x Nc = 4 x 32 coils, the coupling effect largely disappears, and with this array, the main internal RWMs n = -11, -10, +5, +6 are all simultaneously suppressed throughout the discharge (7-8 wall times). With feedback there is a two-fold extension of the pulse length, compared to discharges without feedback.

  • 317.
    Brännström, Fredrik
    et al.
    Chalmers University of Technology.
    Rasmussen, Lars Kildehöj
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Classification of 8PSK mappings for BICM2007In: IEEE International Symposium on Information Theory, 2007, p. 2136-2140Conference paper (Refereed)
    Abstract [nb]

    The performance of bit-interleaved coded modulation with iterative decoding is significantly influenced by the mapping of bits to the symbol constellation. A range of mappers have been suggested in the literature, however, no attempt has been made to systematically enumerate all unique mappers for a given signal constellation. In this paper, we classify 8PSK mappers based on bit-wise distance spectra for no prior information, and full prior information, respectively.

  • 318.
    Brännström, Fredrik
    et al.
    Chalmers University of Technology.
    Rasmussen, Lars Kildehöj
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Classification of Unique Mappings for 8PSK Based on Bit-Wise Distance Spectra2009In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 55, no 3, p. 1131-1145Article in journal (Refereed)
    Abstract [en]

    The performance of bit-interleaved coded modulation (BICM) with (or without) iterative decoding (ID) is significantly influenced by the mapping of bits to the symbol constellation. Our main objective in this paper is to develop a systematic design approach for BICM-ID schemes, ensuring the best possible performance with iterative decoding. Although useful mappings for BICM-ID have been found based on various search strategies, no attempt has been made to systematically enumerate and classify all unique mappers for a given constellation. As the basis for a systematic enumeration and classification, we define the average bit-wise distance spectrum for a mapping from bits to symbols. Different bit-wise distance spectra are derived assuming no prior information or full prior information, respectively. The bit-wise distance spectra determine correspondingbit-wise error probability and bit-wise mutual information. The latter allows us to use theclassification of mappings with unique bit-wise distance spectra to also classifymappings with unique extremal points in the corresponding extrinsic information transfer (EXIT) curves. As an example of our approach, we classify 8PSK mappings into 86 classes of unique mappings according to bit-wise distance spectra. The classificationcan be used to significantly reduce the complexity of the search for suitable mappers for BICM-ID. For 8PSK and a given encoder, only 86 different mappings need to be investigated. As examples of the systematic design approach, the best 8PSK mappingsfor minimizing the convergence threshold are found for concatenation with the rate 1/2 (5, 7)8 and (133,1718 convolutional codes, and the rate 1/2 UMTS turbo code with identical constituent convolutional codes (15/13)8.

  • 319.
    Brännström, Fredrik
    et al.
    Chalmers University of Technology.
    Rasmussen, Lars Kildehöj
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Grant, Alex J.
    University of South Australia.
    Optimal Puncturing Ratios and Energy Allocation for Multiple Parallel Concatenated Codes2009In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 55, no 5, p. 2062-2077Article in journal (Refereed)
    Abstract [en]

    We propose a systematic design framework for optimal, low-complexity punctured multiple parallel concatenated codes (MPCCs), based on minimizing the convergence threshold using extrinsic information transfer (EXIT) charts. As the convergence threshold is related to the area between the two EXIT curves, the corresponding optimization problem is equivalent to a curve-fitting problem. The EXIT curves are determined by the respective EXIT functions of the constituents, which can be conveniently shaped through the use of random puncturing and unequal energy allocations across parallel coding streams. The design task is therefore to find the optimal combination of constituents, puncturing ratios, and energy allocation for matching the EXIT curves. A search over all rate-one convolutional codes of memory length four or less is performed, identifying 98 classes of codes with unique EXIT functions out of a total of 310 codes. Low-complexity MPCCs with up to four constituents are found, where the convergence thresholds are observed to be within 0.1 dB or less of the fundamental minimum signal-to-noise ratio (SNR) corresponding to the binary phase-shift keying (BPSK) capacity for code rates 1/3 ≤ R < 7/8. Further allowing for unequal energy allocation, the convergence thresholds for lower code rates are similarly improved.

  • 320.
    Burden, Tony
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Cohen, Ian
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Dodd, D.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Online tutoring2006In: SEFI 2006 - 34th Annual Conference: Engineering Education and Active Students, Uppsala universitet, 2006Conference paper (Refereed)
    Abstract [en]

    Tutoring has been a central part of the educational system at the long established universities of Cambridge and Oxford in the UK. Previously, at most two students could be tutored in the mathematical sciences, one on each side of the supervisor. Today in the age of computing and Internet, any number of students, in principal, could be supervised at a distance, as each student will be sitting in front of his or her own computer. This paper describes an attempt to carry out tutoring in the subject area of mechanics in small groups and at a distance, i.e. the tutors and the students communicate via an Internet based e-meeting system rather being present in the same physical room. This is used at a KTH (Sweden) mechanics distance course supported with tutoring from AUT (New Zealand) and the reverse tutoring of students at a regular mechanics course at AUT tutored from KTH.

  • 321.
    Byrnes, Christopher
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Georgiou, T. T.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Megretski, A.
    Generalized interpolation in H-infinity with a complexity constraint2006In: Transactions of the American Mathematical Society, ISSN 0002-9947, E-ISSN 1088-6850, Vol. 358, no 3, p. 965-987Article in journal (Refereed)
    Abstract [en]

    In a seminal paper, Sarason generalized some classical interpolation problems for H-infinity functions on the unit disc to problems concerning lifting onto H-2 of an operator T that is defined on K=H-2 circle minus phi H-2 (phi is an inner function) and commutes with the (compressed) shift S. In particular, he showed that interpolants (i.e., f is an element of H-infinity such that f(S)=T) having norm equal to parallel to T parallel to exist, and that in certain cases such an f is unique and can be expressed as a fraction f=b/a with a, b is an element of K. In this paper, we study interpolants that are such fractions of K functions and are bounded in norm by 1 (assuming that parallel to T parallel to<1, in which case they always exist). We parameterize the collection of all such pairs (a, b)is an element of K x K and show that each interpolant of this type can be determined as the unique minimum of a convex functional. Our motivation stems from the relevance of classical interpolation to circuit theory, systems theory, and signal processing, where phi is typically a finite Blaschke product, and where the quotient representation is a physically meaningful complexity constraint.

  • 322. Byrnes, Christopher I.
    et al.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The moment problem for rational measures: convexity in the spirit of Krein2009In: MODERN ANALYSIS AND APPLICATIONS: MARK KREIN CENTENARY CONFERENCE / [ed] Adamyan, V; Berezansky, Y; Gohberg, I; Gorbachuk, M; Gorbachuk, V; Kochubei, A; Langer, H; Popov, G, Birkhäuser Verlag, 2009, Vol. 190, p. 157-169Conference paper (Refereed)
    Abstract [en]

    The moment problem as formulated by Krein and Nudel'man is a beautiful generalization of several important classical moment problems, including the power moment problem, the trigonometric moment problem and the moment problem arising in Nevanlinna-Pick interpolation. Motivated by classical applications and examples, in both finite and infinite dimensions, we recently formulated a new version of this problem that we call the moment problem for positive rational measures. The formulation reflects the importance of rational functions in signals, systems and control. While this version of the problem is decidedly nonlinear, the basic tools still rely on convexity. In particular, we present a solution to this problem in terms of a nonlinear convex optimization problem that generalizes the maximum entropy approach used in several classical special cases.

  • 323.
    Byrnes, Christopher
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Important moments in systems, control and optimizations2009In: Decision and Control, 2009 held jointly with the 2009 28th Chinese Control Conference. CDC/CCC 2009. Proceedings of the 48th IEEE Conference on, IEEE , 2009, p. 91-96Conference paper (Refereed)
    Abstract [en]

    The moment problem matured from its various special forms in the late 19th and early 20th Centuries to a general class of problems that continues to exert profound influence on the development of analysis and its applications to a wide variety of fields. In particular, the theory of systems and control is no exception, where the applications have historically been to circuit theory, optimal control, robust control, signal processing, spectral estimation, stochastic realization theory and the use of the moments of a probability density. Many of these applications are also still works in progress. In this paper, we consider the generalized moment problem, expressed in terms of a basis of a finite-dimensional subspace β of the Banach space C[a, b] and a "positive" sequences c, but with a new wrinkle inspired by the applications to systems and control. We seek to parameterize solutions which are positive "rational" measures, in a suitably generalized sense. Our parameterization is given in terms of smooth objects. In particular, the desired solution space arises naturally as a manifold which can be shown to be diffeomorphic to a Euclidean space and which is the domain of some canonically defined functions. Moreover, on these spaces one can derive natural convex optimization criteria which characterize solutions to this new class of moment problems.

  • 324.
    Byrnes, Christopher
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the Stability and Instability of Padé Approximants2010In: Lecture notes in control and information sciences, ISSN 0170-8643, E-ISSN 1610-7411, Vol. 398, p. 165-175Article in journal (Refereed)
    Abstract [en]

    Over the past three decades there has been interest in using Pade approximants K with n = deg(K) < deg(G) = N as "reduced-order models" for the transfer function G of a linear system The attractive feature of this approach is that by matching the moments of G we can reproduce the steady-state behavior of G by the steady-state behavior of K. for certain classes of Inputs Indeed, we illustrate this by finding a first-order model matching a fixed set of moments for G. the causal inverse of a heat equation A key feature of this example is that the heat equation is a minimum phase system, so that its inverse system has a stable transfer function G and that K can also be chosen to be stable On the other hand, elementary examples show that both stability and instability can occur in reduced order models of a stable system obtained by matching moments using Pade approximants and, in the absence of stability, it does not make much sense to talk about steady-state responses nor does it make sense to match moments In this paper, we review Pack approximains. and their intimate relationship to continued fractions and Riccati equations, in a historical context that underscores why Pade approximation, as useful as it is, is not an approximation in any sense that reflects stability. Our main results on stability and instability states that if N >= 2 and l, r >= 0 with 0<l+r=n<N there is a non-empty open set U-lr of stable transfer functions G, having infinite Lebesque measure, such that each degree n proper rational function K matching the moments of G has e poles lying in C- and r poles lying in C+ The proof is constructive.

  • 325.
    Cao, Le Phuong
    et al.
    KTH, School of Electrical Engineering (EES), Information Science and Engineering. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Oechtering, Tobias J.
    KTH, School of Electrical Engineering (EES), Information Science and Engineering. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Optimal transmit strategy for MIMO channels with joint sum and per-antenna power constraints2017In: 2017 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), IEEE, 2017, p. 3569-3573Conference paper (Refereed)
    Abstract [en]

    This paper studies optimal transmit strategies for multiple-input multiple-output (MIMO) Gaussian channels with joint sum and per-antenna power constraints. It is shown that if an unconstraint optimal allocation for an antenna exceeds a per-antenna power constraint, then the maximal power for this antenna is used in the constraint optimal transmit strategy. This observation is then used in an iterative algorithm to compute the optimal transmit strategy in closed-form. Finally, a numerical example is provided to illustrate the theoretical results.

  • 326. Cao, Ming
    et al.
    Olshevsky, Alex
    Xia, Weiguo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Focused First-Followers Accelerate Aligning Followers with the Leader in Reaching Network Consensus2014In: 19th IFAC World Congress 2014: Cape Town, South Africa 24-29 August 2014, 2014, Vol. 9, p. 7819-Conference paper (Refereed)
    Abstract [en]

    This paper proposes and analyzes a new strategy to accelerate the process of reaching consensus in leader-follower networks. By removing or weakening specific directed couplings pointing to the first followers from the other followers, we prove that all the followers' states converge faster to that of the leader. This result is in sharp contrast to the well known fact that when the followers are coupled together through undirected links, removing or weakening links always decelerate the converging process. Simulation results are provided to illustrate this subtle, yet somewhat surprising, provably correct result.

  • 327.
    Cao, Phuong
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Oechtering, Tobias J.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Schaefer, Rafael
    Princeton University.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Optimal Transmission Rate for MISO Channels with Joint Sum and Per-antenna Power Constraints2015In: IEEE International Conference on Communications (ICC), London, June 08-12, 2015, 2015, p. 4727-4732Conference paper (Refereed)
    Abstract [en]

    We consider multiple-input single-output (MISO) Gaussian channels with joint sum and per-antenna power constraints. A closed-form solution of the optimal beamforming vector is derived which achieves the maximal transmission rate. The result shows that if the sum power constraint only optimal power allocation violates a per-antenna power constraint then the joint power constraint optimal power allocation is at the intersection of the sum power constraint and the per-antenna power constraints.

  • 328.
    Carlqvist, Per
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    A remarkable double helix in the V838 Mon nebula2005In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 436, no 1, p. 231-239Article in journal (Refereed)
    Abstract [en]

    In the beginning of 2002 the previously unnoted star V838 Mon had a powerful outburst. The star is surrounded by pre-existing, dusty clouds which are illuminated by the star in an expanding, parabolic layer. Spectacular images captured by the Hubble Space Telescope Advanced Camera for Surveys show that the clouds are to a great extent built up by filaments and concentric shells. One of the most remarkable features is a filamentary structure forming a double helix. The structure, which has a projected length and width of similar to 9 '' and similar to 1.'' 4, respectively, points almost radially towards V838 Mon. In order to reveal the geometry of the double helix in some more detail, a three-dimensional computer model of the structure has been constructed. The model also assists in determining the expansion rate of the light echoes along the double helix. By means of the expansion rate and the tilt of the double helix the distance to V838 Mon is determined to be 2.4 +/- 0.5 kpc. A theory of the double helix, based on a magnetized and twisted filament, is presented. Dynamic and magnetic forces play an essential role in the shaping of the double helix. The theory is supported by a mechanical analogy model. Double helices in other cosmic environments are also discussed.

  • 329.
    Casamitjana, Adrià
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sundin, Martin
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ghosh, P.
    Chatterjee, S.
    Bayesian learning for time-varying linear prediction of speech2015In: 2015 23rd European Signal Processing Conference, EUSIPCO 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 325-329Conference paper (Refereed)
    Abstract [en]

    We develop Bayesian learning algorithms for estimation of time-varying linear prediction (TVLP) coefficients of speech. Estimation of TVLP coefficients is a naturally underdeter-mined problem. We consider sparsity and subspace based approaches for dealing with the corresponding underde-termined system. Bayesian learning algorithms are developed to achieve better estimation performance. Expectation-maximization (EM) framework is employed to develop the Bayesian learning algorithms where we use a combined prior to model a driving noise (glottal signal) that has both sparse and dense statistical properties. The efficiency of the Bayesian learning algorithms is shown for synthetic signals using spectral distortion measure and formant tracking of real speech signals. © 2015 EURASIP.

  • 330. Castaldo, C.
    et al.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Pericoli, V.
    Rypdal, K.
    De Angelis, U.
    Morfill, G. E.
    Pieroni, L.
    Capobianco, G.
    De Angeli, M.
    Gabellieri, L.
    Giovannozzi, E.
    Maddaluno, G.
    Marmolino, C.
    Orsitto, F.
    Romano, A.
    Rufoloni, A.
    Tuccillo, A. A.
    Fast dust particles in tokamak plasmas: Detection and effects2007In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, European Physical Society , 2007, no 2, p. 848-851Conference paper (Refereed)
  • 331.
    Cecconello, Marco
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Yadikin, Dmitriy
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Drake, James Robert
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Rotation evolution of tearing modes during feedback stabilization of resistive wall modes in a reversed field pinch2005Conference paper (Refereed)
  • 332.
    Cecconello, Marco
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Hedqvist, Anders
    KTH, School of Engineering Sciences (SCI), Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Current profile modifications with active feedback stabilization of resistive wall modes in a reversed field pinch2006In: Proceedings of the 33rd European Physical Society Conference on Plasma Physics, 2006, p. 1680-1683Conference paper (Refereed)
  • 333.
    Cecconello, Marco
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Engineering Sciences (SCI), Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Kuldkepp, Mattias
    KTH, School of Engineering Sciences (SCI), Physics.
    Rotation in a reversed field pinch with active feedback stabilization of resistive wall modes2006In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 48, no 9, p. 1311-1331Article in journal (Refereed)
    Abstract [en]

    Active feedback stabilization of multiple resistive wall modes (RWMs) has been successfully proven in the EXTRAP T2R reversed field pinch. One of the features of plasma discharges operated with active feedback stabilization, in addition to the prolongation of the plasma discharge, is the sustainment of the plasma rotation. Sustained rotation is observed both for the internally resonant tearing modes (TMs) and the intrinsic impurity oxygen ions. Good quantitative agreement between the toroidal rotation velocities of both is found: the toroidal rotation is characterized by an acceleration phase followed, after one wall time, by a deceleration phase that is slower than in standard discharges. The TMs and the impurity ions rotate in the same poloidal direction with also similar velocities. Poloidal and toroidal velocities have comparable amplitudes and a simple model of their radial profile reproduces the main features of the helical angular phase velocity. RWMs feedback does not qualitatively change the TMs behaviour and typical phenomena such as the dynamo and the `slinky' are still observed. The improved sustainment of the plasma and TMs rotation occurs also when feedback only acts on internally non- resonant RWMs. This may be due to an indirect positive effect, through non- linear coupling between TMs and RWMs, of feedback on the TMs or to a reduced plasma- wall interaction affecting the plasma flow rotation. Electromagnetic torque calculations show that with active feedback stabilization the TMs amplitude remains well below the locking threshold condition for a thick shell. Finally, it is suggested that active feedback stabilization of RWMs and current profile control techniques can be employed simultaneously thus improving both the plasma duration and its confinement properties.

  • 334. Cedervall, Simon
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nonlinear observers for unicycle robots with range sensors2007In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 52, no 7, p. 1325-1329Article in journal (Refereed)
    Abstract [en]

    For nonlinear mobile systems equipped with exteroceptive sensors, the observability does not only depend on the initial conditions, but also on the control and the environment. This presents an interesting issue: how to design an observer together with the exciting control. In this note, the problem of designing an observer based on range sensor readings is studied. A design method based on periodic excitations is proposed for unicycle robotic systems.

  • 335. Celani, A.
    et al.
    Bo, Stefano
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB. KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Eichhorn, Ralf
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Aurell, Erik
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Anomalous thermodynamics at the microscale2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 26, p. 260603-Article in journal (Refereed)
    Abstract [en]

    Particle motion at the microscale is an incessant tug-of-war between thermal fluctuations and applied forces on one side and the strong resistance exerted by fluid viscosity on the other. Friction is so strong that completely neglecting inertia - the overdamped approximation - gives an excellent effective description of the actual particle mechanics. In sharp contrast to this result, here we show that the overdamped approximation dramatically fails when thermodynamic quantities such as the entropy production in the environment are considered, in the presence of temperature gradients. In the limit of vanishingly small, yet finite, inertia, we find that the entropy production is dominated by a contribution that is anomalous, i.e., has no counterpart in the overdamped approximation. This phenomenon, which we call an entropic anomaly, is due to a symmetry breaking that occurs when moving to the small, finite inertia limit. Anomalous entropy production is traced back to futile phase-space cyclic trajectories displaying a fast downgradient sweep followed by a slow upgradient return to the original position.

  • 336. Chan, Wai Ming
    et al.
    Kim, Taejoon
    Ghauch, Hadi
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Subspace Estimation and Hybrid Precoding for Wideband Millimeter-Wave MIMO Systems2016In: 2016 50th Asilomar Conference on Signals, Systems and Computers, IEEE Computer Society, 2016, p. 286-290, article id 7869043Conference paper (Refereed)
    Abstract [en]

    There has been growing interest in millimeter wave (mmWave) multiple-input multiple-output (MIMO) systems, which would likely employ hybrid analog-digital precoding with large-scale analog arrays deployed at wide bandwidths. Primary challenges here are how to efficiently estimate the large-dimensional frequency-selective channels and customize the wideband hybrid analog-digital precoders and combiners. To address these challenges, we propose a low-overhead channel subspace estimation technique for the wideband hybrid analog-digital MIMO precoding systems. We first show that the Gram matrix of the frequency-selective channel can be decomposed into frequency-flat and frequency-selective components. Based on this, the Arnoldi approach, leveraging channel reciprocity and time-reversed echoing, is employed to estimate a frequency-flat approximation of the frequency-selective mmWave channels, which is used to design the analog parts. After the analog precoder and combiner design, the low-dimensional frequency-selective channels are estimated using conventional pilot-based channel sounding. Numerical results show that considerable improvement in data-rate performance is possible.

  • 337. Chang, Z.
    et al.
    Lei, L.
    Zhang, H.
    Ristaniemi, T.
    Chatzinotas, S.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Han, Z.
    Energy-Efficient and Secure Resource Allocation for Multiple-Antenna NOMA With Wireless Power Transfer2018In: IEEE Transactions on Green Communications and Networking, ISSN 2473-2400, Vol. 2, no 4, p. 1059-1071Article in journal (Refereed)
  • 338. Charalambous, Charalambos D.
    et al.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hadjicostis, Christoforos N.
    Team Optimality Conditions of Differential Decision Systems with Nonclasssical Information Structures2014In: 2014 European Control Conference (ECC), IEEE , 2014, p. 2851-2856Conference paper (Refereed)
    Abstract [en]

    We derive team optimality conditions for differential decision systems with nonclassical information structures. The necessary conditions of optimality are given in terms of Hamiltonian system of equations consisting of a coupled backward and forward differential equations and a Hamiltonian projected onto the subspace generated by the information structures. Under certain global convexity conditions it is shown that person-by-person optimality implies team optimality.

  • 339.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Charalambous, Charalambos D.
    Rezaei, Farzad
    Optimal Merging Algorithms for Lossless Codes With Generalized Criteria2014In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 60, no 9, p. 5486-5499Article in journal (Refereed)
    Abstract [en]

    This paper presents lossless prefix codes optimized with respect to a payoff criterion consisting of a convex combination of maximum codeword length and average codeword length. The optimal codeword lengths obtained are based on a new coding algorithm, which transforms the initial source probability vector into a new probability vector according to a merging rule. The coding algorithm is equivalent to a partition of the source alphabet into disjoint sets on which a new transformed probability vector is defined as a function of the initial source probability vector and scalar parameter. The payoff criterion considered encompasses a tradeoff between maximum and average codeword length; it is related to a payoff criterion consisting of a convex combination of average codeword length and average of an exponential function of the codeword length, and to an average codeword length payoff criterion subject to a limited length constraint. A special case of the first related payoff is connected to coding problems involving source probability uncertainty and codeword overflow probability, whereas the second related payoff compliments limited length Huffman coding algorithms.

  • 340.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hadjicostis, Christoforos N.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Minimum-Time Weight Balancing over Digraphs2014Conference paper (Refereed)
    Abstract [en]

    We address the weight-balancing problem for a distributed system whose components (nodes) can exchange information via interconnection links (edges) that form an arbitrary, possibly directed, communication topology (digraph). A weighted digraph is balanced if, for each node, the sum of the weights of the edges outgoing from that node is equal to the sum of the weights of the edges incoming to that node. Weight-balanced digraphs play a key role in a variety of applications, such as coordination of groups of robots, distributed decision making, and distributed averaging which is important for a wide range of applications in signal processing. We propose a distributed algorithm for solving the weight balancing problem in a minimum number of iterations, when the weights are nonnegative real numbers. We also provide examples to corroborate the proposed algorithm.

  • 341. Charalambous, Themistoklis
    et al.
    Hadjicostis, Christoforos N.
    Rabbat, Michael G.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Totally asynchronous distributed estimation of eigenvector centrality in digraphs with application to the PageRank problem2016In: 2016 IEEE 55th Conference on Decision and Control, CDC 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 25-30, article id 7798241Conference paper (Refereed)
    Abstract [en]

    We propose a distributed coordination mechanism which enables nodes in a directed graph to accurately estimate their eigenvector centrality (eigencentrality) even if they update their values at times determined by their own clocks. The clocks need neither be synchronized nor have the same speed. The main idea is to let nodes adjust the weights on outgoing links to compensate for their update speed: the higher the update frequency, the smaller the link weights. Our mechanism is used to develop a distributed algorithm for computing the PageRank vector, commonly used to assign importance to web pages and rank search results. Although several distributed approaches in the literature can deal with asynchronism, they cannot handle the different update speeds that occur when servers have heterogeneous computational capabilities. When existing algorithms are executed using heterogeneous update speeds, they compute incorrect PageRank values. The advantages of our algorithm over existing approaches are verified through illustrative examples.

  • 342.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nomikos, Nikolaos
    Krikidis, Ioannis
    Vouyioukas, Demosthenes
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Modeling Buffer-Aided Relay Selection in Networks With Direct Transmission Capability2015In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 19, no 4, p. 649-652Article in journal (Refereed)
    Abstract [en]

    We consider a wireless relay network that consists of a source, half-duplex decode-and-forward buffer-aided relays and a destination. While the majority of previous works on relay selection assume no direct transmission between source and destination in such a setting, we lift this assumption and propose a link selection policy that exploits both the buffering ability and the opportunity for successful reception of a packet directly from the source. The proposed relay selection scheme incorporates the instantaneous strength of the wireless links and adapts the relay selection decision based on the strongest available link. The evolution of the network as a whole is modeled by means of a Markov chain and thus, the outage probability is associated with the steady state of the Markov chain. It is deduced that even if the link between the source and the destination is in principle a very unreliable link, it is always beneficial for the source to multicast a packet to both the relay with the strongest available link and the destination.

  • 343.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rabbat, M. G.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hadjicostis, C. N.
    Distributed Finite-Time Computation of Digraph Parameters: Left-Eigenvector, Out-Degree and Spectrum2016In: IEEE Transactions on Control of Network Systems, ISSN 2325-5870, Vol. 3, no 2, p. 137-148, article id 7100912Article in journal (Refereed)
    Abstract [en]

    Many of the algorithms that have been proposed in the field of distributed computation rely on assumptions that require nodes to be aware of some global parameters. In this paper, we propose algorithms to compute some network parameters in a distributed fashion and in a finite number of steps. More specifically, given an arbitrary strongly connected network of interconnected nodes, by adapting a distributed finite-time approach, we develop distributed strategies that enable nodes to compute the following network parameters: the left-eigenvector, the out-degree, and the spectrum of weighted adjacency matrices.

  • 344.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yuan, Ye
    University of Cambridge.
    Yang, Tao
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pan, Wei
    Imperial College London.
    Hadjicostis, Christoforos N.
    University of Cyprus.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Decentralised Minimum-Time Average Consensus in Digraphs2013In: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC), IEEE conference proceedings, 2013, p. 2617-2622Conference paper (Refereed)
    Abstract [en]

    Distributed algorithms for average consensus in directed graphs are typically asymptotic in the literature. In this work, we propose a protocol to distributively reach average consensus in a finite number of steps on interconnection topologies that form strongly connected directed graphs (digraphs). The average consensus value can be computed, based exclusively on local observations at each component, by running a protocol that requires each component to observe and store its own value over a finite and minimal number of steps, and to have knowledge of the number of its out-going links (i.e., the number of components to which it sends information). The proposed algorithm is demonstrated via illustrative examples.

  • 345.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yuan, Ye
    Yang, Tao
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pan, Wei
    Hadjicostis, Christoforos N.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Distributed Finite-Time Average Consensus in Digraphs in the Presence of Time Delays2015In: IEEE TRANSACTIONS ON CONTROL OF NETWORK SYSTEMS, ISSN 2325-5870, Vol. 2, no 4, p. 370-381Article in journal (Refereed)
    Abstract [en]

    Most algorithms for distributed averaging only guarantee asymptotic convergence. This paper introduces a distributed protocol that allows nodes to find the exact average of the initial values in a finite and minimum number of steps on interconnection topologies described by strongly connected directed graphs (digraphs). More specifically, under the assumption that each component has knowledge of the number of its outgoing links (i.e., the number of components to which it sends information), we show that the average value can be computed based on local observations over a finite time interval. The average can be obtained in a finite number of steps even when the information exchange is subject to delays. The proposed algorithm is the first in the literature that allows for distributed computation of the exact average in digraphs in finite time, with and without delays.

  • 346.
    Chatterjee, Saikat
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Flåm, John T.
    NTNU - Norwegian University of Science and Technology.
    Kansanen, Kimmo
    NTNU - Norwegian University of Science and Technology.
    Ekman, Tobjorn
    NTNU - Norwegian University of Science and Technology.
    On MMSE estimation: A linear model under Gaussian mixture statistics2012In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, no 7, p. 3840-3845Article in journal (Refereed)
    Abstract [en]

    In a Bayesian linear model, suppose observation y = Hx + n stems from independent inputs x and n which are Gaussian mixture (GM) distributed. With known matrix H, the minimum mean square error (MMSE) estimator for x , has analytical form. However, its performance measure, the MMSE itself, has no such closed form. Because existing Bayesian MMSE bounds prove to have limited practical value under these settings, we instead seek analytical bounds for the MMSE, both upper and lower. This paper provides such bounds, and relates them to the signal-to-noise-ratio (SNR).

  • 347.
    Chatterjee, Saikat
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kleijn, W. Bastiaan
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Auditory Model-Based Design and Optimization of Feature Vectors for Automatic Speech Recognition2011In: IEEE Transactions on Audio, Speech, and Language Processing, ISSN 1558-7916, E-ISSN 1558-7924, Vol. 19, no 6, p. 1813-1825Article in journal (Refereed)
    Abstract [en]

    Using spectral and spectro-temporal auditory models along with perturbation-based analysis, we develop a new framework to optimize a feature vector such that it emulates the behavior of the human auditory system. The optimization is carried out in an offline manner based on the conjecture that the local geometries of the feature vector domain and the perceptual auditory domain should be similar. Using this principle along with a static spectral auditory model, we modify and optimize the static spectral mel frequency cepstral coefficients (MFCCs) without considering any feedback from the speech recognition system. We then extend the work to include spectro-temporal auditory properties into designing a new dynamic spectro-temporal feature vector. Using a spectro-temporal auditory model, we design and optimize the dynamic feature vector to incorporate the behavior of human auditory response across time and frequency. We show that a significant improvement in automatic speech recognition (ASR) performance is obtained for any environmental condition, clean as well as noisy.

  • 348.
    Chatterjee, Saikat
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Koslicki, David
    Dept of Mathematics, Oregon State University, Corvallis, USA.
    Dong, Siyuan
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Innocenti, Nicolas
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Cheng, Lu
    Dept of Mathematics and Statistics, University of Helsinki, Finland.
    Lan, Yueheng
    Dept of Physics, Tsinghua University, Beijing, China.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Theory.
    K. Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Aurell, Erik
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Corander, Jukka
    Dept of Signal Processing, Aalto University, Finland.
    SEK: Sparsity exploiting k-mer-based estimation of bacterial community composition2014In: Bioinformatics, ISSN 1460-2059, Vol. 30, no 17, p. 2423-2431Article in journal (Refereed)
    Abstract [en]

    Motivation: Estimation of bacterial community composition from a high-throughput sequenced sample is an important task in metagenomics applications. As the sample sequence data typically harbors reads of variable lengths and different levels of biological and technical noise, accurate statistical analysis of such data is challenging. Currently popular estimation methods are typically time-consuming in a desktop computing environment.

    Results: Using sparsity enforcing methods from the general sparse signal processing field (such as compressed sensing), we derive a solution to the community composition estimation problem by a simultaneous assignment of all sample reads to a pre-processed reference database. A general statistical model based on kernel density estimation techniques is introduced for the assignment task, and the model solution is obtained using convex optimization tools. Further, we design a greedy algorithm solution for a fast solution. Our approach offers a reasonably fast community composition estimation method, which is shown to be more robust to input data variation than a recently introduced related method.

    Availability and implementation: A platform-independent Matlab implementation of the method is freely available at http://www.ee.kth.se/ctsoftware; source code that does not require access to Matlab is currently being tested and will be made available later through the above Web site.

  • 349.
    Chatterjee, Saikat
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Structured Gaussian Mixture model based product VQ2010In: 18th European Signal Processing Conference (EUSIPCO-2010), EUROPEAN ASSOC SIGNAL SPEECH & IMAGE PROCESSING-EURASIP , 2010, p. 771-775Conference paper (Refereed)
    Abstract [en]

    In this paper, the Gaussian mixture model (GMM) based parametric framework is used to design a product vector quantization (PVQ) method that provides rate-distortion (R/D) performance optimality and bitrate scalability. We use a GMM consisting of a large number of Gaussian mixtures and invoke a block isotropic structure on the covariance matrices of the Gaussian mixtures. Using such a structured GMM, we design an optimum and bitrate scalable PVQ, namely an split (SVQ), for each Gaussian mixture. The use of an SVQ allows for a trade-off between complexity and R/D performance that spans the two extreme limits provided by an optimum scalar quantizer and an unconstrained vector quantizer. The efficacy of the new GMM based PVQ (GMPVQ) method is demonstrated for the application of speech spectrum quantization.

  • 350.
    Chatterjee, Saikat
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sundman, Dennis
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Look ahead orthogonal matching pursuit2011In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, 2011, p. 4024-4027Conference paper (Refereed)
45678910 301 - 350 of 2628
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