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  • 51.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Aytekin, Arda
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    An Asynchronous Mini-Batch Algorithm for Regularized Stochastic Optimization2015In: 2015 54th IEEE Conference on Decision and Control (CDC), IEEE , 2015, p. 1384-1389Conference paper (Refereed)
    Abstract [en]

    Mini-batch optimization has proven to be a powerful paradigm for large-scale learning. However, the state of the art mini-batch algorithms assume synchronous operation or cyclic update orders. When worker nodes are heterogeneous (due to different computational capabilities, or different communication delays), synchronous and cyclic operations are inefficient since they will leave workers idle waiting for the slower nodes to complete their work. We propose an asynchronous mini-batch algorithm for regularized stochastic optimization problems that eliminates idle waiting and allows workers to run at their maximal update rates. We show that the time necessary to compute an ϵ-optimal solution is asymptotically O(1/ϵ2), and the algorithm enjoys near-linear speedup if the number of workers is O(1/√ϵ). Theoretical results are confirmed in real implementations on a distributed computing infrastructure.

  • 52.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Aytekin, Arda
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Asynchronous Mini-Batch Algorithm for Regularized Stochastic Optimization2016In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, ISSN 0018-9286Article in journal (Refereed)
    Abstract [en]

    Mini-batch optimization has proven to be a powerful paradigm for large-scale learning. However, the state of the art parallel mini–batch algorithms assume synchronous operation or cyclic update orders. When worker nodes are heterogeneous (due to different computational capabilities or different communication delays), synchronous and cyclic operations are inefficient since they will leave workers idle waiting for the slower nodes to complete their computations. In this paper, we propose an asynchronous mini-batch algorithm for regularized stochastic optimization problems with smooth loss functions that eliminates idle waiting and allows workers to run at their maximal update rates. We show that by suitably choosing the step-size values, the algorithm achieves a rate of the order O(1/ √ T) for general convex regularization functions, and the rate O(1/T ) for strongly convex regularization functions, where T is the number of iterations. In both cases, the impact of asynchrony on the convergence rate of our algorithm is asymptotically negligible, and a nearlinear speedup in the number of workers can be expected. Theoretical results are confirmed in real implementations on a distributed computing infrastructure.

  • 53.
    Feyzmahdavian, Hamid Reza
    et al.
    ABB Corp Res Ctr, S-72226 Vasteras, Sweden..
    Besselink, Bart
    Univ Groningen, Johann Bernoulli Inst Math & Comp Sci, NL-9712 CP Groningen, Netherlands..
    Johansson, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Stability Analysis of Monotone Systems via Max-Separable Lyapunov Functions2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 3, p. 643-656Article in journal (Refereed)
    Abstract [en]

    We analyze stability properties of monotone nonlinear systems via max-separable Lyapunov functions, motivated by the following observations: first, recent results have shown that asymptotic stability of a monotone nonlinear system implies the existence of a max-separable Lyapunov function on a compact set; second, for monotone linear systems, asymptotic stability implies the stronger properties of D-stability and insensitivity to time delays. This paper establishes that for monotone nonlinear systems, equivalence holds between asymptotic stability, the existence of a max-separable Lyapunov function, D-stability, and insensitivity to bounded and unbounded time-varying delays. In particular, a new and general notion of D-stability for monotone nonlinear systems is discussed, and a set of necessary and sufficient conditions for delay-independent stability are derived. Examples show how the results extend the state of the art.

  • 54.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Asymptotic and Exponential Stability of General Classes of Continuous-Time Power Control Laws in Wireless Networks2013In: Proceedings of 52nd IEEE Conference on Decision and Control December 10-13, 2013. Florence, Italy, IEEE conference proceedings, 2013, p. 49-54Conference paper (Refereed)
    Abstract [en]

    This paper develops a comprehensive stabilityanalysis framework for continuous-time power control algorithmsin wireless networks under bounded time-varyingcommunication delays. Our first set of results establish globalasymptotic stability of power control laws involving two-sidedscalable interference functions, and include earlier work onstandard interference functions as a special case. We thenconsider contractive interference functions and demonstratethat the associated continuous-time power control laws alwayshave unique fixed points, which are exponentially stable evenin the presence of bounded heterogeneous time-varying delays.For this class of interference functions, we derive an explicitbound on the decay rate that allows us to quantify the impactof delays on the convergence time of the algorithm. Numericalsimulations illustrate our theoretical results.

  • 55.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    ASYMPTOTIC STABILITY AND DECAY RATES OF HOMOGENEOUS POSITIVE SYSTEMS WITH BOUNDED AND UNBOUNDED DELAYS2014In: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 52, no 4, p. 2623-2650Article in journal (Refereed)
    Abstract [en]

    There are several results on the stability of nonlinear positive systems in the presence of time delays. However, most of them assume that the delays are constant. This paper considers time-varying, possibly unbounded, delays and establishes asymptotic stability and bounds the decay rate of a significant class of nonlinear positive systems which includes positive linear systems as a special case. Specifically, we present a necessary and sufficient condition for delay-independent stability of continuous-time positive systems whose vector fields are cooperative and homogeneous. We show that global asymptotic stability of such systems is independent of the magnitude and variation of the time delays. For various classes of time delays, we are able to derive explicit expressions that quantify the decay rates of positive systems. We also provide the corresponding counterparts for discrete-time positive systems whose vector fields are nondecreasing and homogeneous.

  • 56.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Asymptotic Stability and Decay Rates of Positive Linear Systems with Unbounded Delays2013In: Proceedings of the 52nd IEEE Conference on Decision and Control (CDC), IEEE conference proceedings, 2013, p. 1423-1428Conference paper (Refereed)
    Abstract [en]

    There are several results on the stability analysisof positive linear systems in the presence of constant or timevaryingdelays. However, most existing results assume thatthe delays are bounded. This paper studies the stability ofdiscrete-time positive linear systems with unbounded delays.We provide a set of easily verifiable necessary and sufficientconditions for delay-independent stability of positive linearsystems subject to a general class of heterogeneous timevaryingdelays. For two particular classes of unbounded delays,explicit expressions that bound the decay rate of the system arepresented. We demonstrate that the best bound on the decayrate that our results can guarantee can be found via convexoptimization. Finally, the validity of the results is demonstratedvia a numerical example.

  • 57.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Delay-independent Stability of Cone-invariant Monotone Systems2015In: 54th IEEE Conference on Decision and Control (CDC), IEEE , 2015, p. 6361-6366Conference paper (Refereed)
    Abstract [en]

    Recent results in the literature have shown that particular classes of positive systems are insensitive to time-varying delays, giving the impression that the delay-insensitivity property stems from the fact that the system is positive. Nonetheless, it has been lately shown that a linear cone-invariant system is insensitive to time-varying delays, asserting that the property of delay-independence may stem from the fact that the system is cone-invariant rather than positive. In this paper, we provide additional evidence for this claim by analyzing the stability of cone-invariant monotone systems with bounded time-varying delays. We present a set of sufficient conditions for delay independent stability of discrete- and continuous-time cone-invariant monotone systems. For linear cone-invariant systems, we show that thestability conditions we have derived are also necessary.

  • 58.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Exponential Stability of Homogeneous Positive Systems of Degree One With Time-Varying Delays2014In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 6, p. 1594-1599Article in journal (Refereed)
    Abstract [en]

    While the asymptotic stability of positive linear systems in the presence of bounded time delays has been thoroughly investigated, the theory for nonlinear positive systems is considerably less well-developed. This paper presents a set of conditions for establishing delay-independent stability and bounding the decay rate of a significant class of nonlinear positive systems which includes positive linear systems as a special case. Specifically, when the time delays have a known upper bound, we derive necessary and sufficient conditions for exponential stability of (a) continuous-time positive systems whose vector fields are homogeneous and cooperative, and (b) discrete-time positive systems whose vector fields are homogeneous and order-preserving. We then present explicit expressions that allow us to quantify the impact of delays on the decay rate and show that the best decay rate of positive linear systems that our bounds provide can be found via convex optimization. Finally, we extend the results to general linear systems with time-varying delays.

  • 59.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the rate of convergence of continuous-time linear positive systems with heterogeneous time-varying delays2013In: 2013 European Control Conference, ECC 2013, IEEE conference proceedings, 2013, p. 3372-3377Conference paper (Refereed)
    Abstract [en]

    In this work, a set of conditions are presented for establishing exponential stability and bounds on the convergence rates of both general and positive linear systems with heterogeneous time-varying delays. First, a sufficient condition for delay-independent exponential stability of general linear systems is derived. When the time delays have a known upper bound, we present an explicit expression that bounds the decay rate of the system. We demonstrate that the best decay rate that our bound can guarantee can be easily found via convex optimization techniques. Finally, for positive linear systems, we show that the stability condition that we have developed is also necessary. The validity of the results is demonstrated via numerical examples.

  • 60.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Stability and Performance of Continuous-Time Power Control in Wireless Networks2014In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 8, p. 2012-2023Article in journal (Refereed)
    Abstract [en]

    This paper develops a comprehensive stability analysis framework for general classes of continuous-time power control algorithms under heterogeneous time-varying delays. Our first set of results establish global asymptotic stability of power control laws involving two-sided scalable interference functions, and include earlier work on standard interference functions as a special case. We then consider contractive interference functions and demonstrate that the associated continuous-time power control laws always have unique fixed points which are exponentially stable, even under bounded heterogeneous time-varying delays. For this class of interference functions, we present explicit bounds on the decay rate that allow us to quantify the impact of delays on the convergence time of the algorithm. When interference functions are linear, we also prove that contractivity is necessary and sufficient for exponential stability of continuous-time power control algorithms with time-varying delays. Finally, numerical simulations illustrate the validity of our theoretical results.

  • 61.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sub-homogeneous positive monotone systems are insensitive to heterogeneous time-varying delays2014In: 21st International Symposium on Mathematical Theory of Networks and Systems (MTNS 2014), 2014Conference paper (Refereed)
    Abstract [en]

    We show that a sub-homogeneous positive monotone system with bounded heterogeneous time-varying delays is globally asymptotically stable if and only if the corresponding delay-free system is globally asymptotically stable. The proof is based on an extension of a delay-independent stability result for monotone systems under constant delays by Smith to systems with bounded heterogenous time-varying delays. Under the additional assumption of positivity and sub-homogenousvector fields, we establish the aforementioned delay insensitivity property and derive a novel test for global asymptotic stability. If the system has a unique equilibrium point in the positive orthant, we prove that our stability test is necessary and sufficient. Specialized to positive linear systems, our results extend and sharpen existing results from the literature.

  • 62.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Gattami, Ather
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Distributed Output-Feedback LQG Control with Delayed Information Sharing2012In: Estimation and Control of Networked Systems, Volume 3, Part 1, 2012Conference paper (Refereed)
    Abstract [en]

    This paper develops a controller synthesis method for distributed LQG controlproblems under output-feedback. We consider a system consisting of three interconnected linearsubsystems with a delayed information sharing structure. While the state-feedback case haspreviously been solved, the extension to output-feedback is nontrivial as the classical separationprinciple fails. To nd the optimal solution, the controller is decomposed into two independentcomponents: a centralized LQG-optimal controller under delayed state observations, and a sumof correction terms based on additional local information available to decision makers. Explicitdiscrete-time equations are derived whose solutions are the gains of the optimal controller.

  • 63.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    On the Convergence Rates of Asynchronous Iterations2014In: Decision and Control (CDC), 2014 IEEE 53rd Annual Conference on, IEEE conference proceedings, 2014, p. 153-159Conference paper (Refereed)
    Abstract [en]

    This paper presents a unifying convergence result for asynchronous iterations involving pseudo-contractions in the block-maximum norm. Contrary to previous results which only established asymptotic convergence or studied simplified models of asynchronism, our result allows to bound the convergence rates for both partially and totally asynchronous implementations. Several examples are worked out to demonstrate that our theorem recovers and improves on existing results, and that it allows to characterize the solution times for several classes of asynchronous iterations that have not been addressed before.

  • 64.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Contractive interference functions and rates of convergence of distributed power control laws2012In: IEEE International Conference on Communications (ICC), Ottawa, Canada., IEEE , 2012, p. 4395-4399Conference paper (Refereed)
    Abstract [en]

    The standard interference functions introduced by Yates have been very influential on the analysis and design of distributed power control laws. While powerful and versatile, the framework has some drawbacks: the existence of fixed-points has to be established separately, and no guarantees are given on the rate of convergence of the iterates. This paper introduces contractive interference functions, a slight reformulation of the standard interference functions that guarantees existence and uniqueness of fixed-points and geometric convergence rates. We show that many power control laws from the literature are contractive and derive, sometimes for the first time, convergence rate estimates for these algorithms. Finally, we show that although standard interference functions are not contractive, they are paracontractions with respect to a certain metric space. Extensions to two-sided scalable interference functions are also discussed.

  • 65.
    Feyzmahdavian, Hamid Reza
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Contractive interference functions and rates of convergence of distributed power control laws2012In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 11, no 12, p. 4494-4502Article in journal (Refereed)
    Abstract [en]

    The standard interference functions introduced by Yates have been very influential on the analysis and design of distributed power control laws. While powerful and versatile, the framework has some drawbacks: the existence of fixed-points has to be established separately, and no guarantees are given on the rate of convergence of the iterates. This paper introduces contractive interference functions, a slight reformulation of the standard interference functions that guarantees the existence and uniqueness of fixed-points along with linear convergence of iterates. We show that many power control laws from the literature are contractive and derive, sometimes for the first time, analytical convergence rate estimates for these algorithms. We also prove that contractive interference functions converge when executed totally asynchronously and, under the assumption that the communication delay is bounded, derive an explicit bound on the convergence time penalty due to increased delay. Finally, we demonstrate that although standard interference functions are, in general, not contractive, they are all para-contractions with respect to a certain metric. Similar results for two-sided scalable interference functions are also derived.

  • 66.
    Flärdh, Oscar
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    A Control Framework for Online Error Control Adaptation in Networked Applications2006In: Proceedings of IEEE Second International Symposium on Control, Communications, and Signal Processing, 2006Conference paper (Refereed)
    Abstract [en]

    For many real-time applications running over packet-switched networks, it is important to maintain delivered data quality using a limited amount of network resources. It is therefore natural to employ cost functions that allow online trade-off between the experienced application quality and the resource usage. However, minimizing such cost functions requires perfect knowledge of the network state at the transmission side, while, in general, such information is only partially available. In this paper, we introduce a new adaptive error correction algorithm that optimizes the amount of redundancy based on the available information from the application and the network. An extremum-seeking control algorithm is employed to deal with the high level of uncertainty in the network models. The validity of our approach is illustrated in simulations with varying network loads and loss correlation.

  • 67.
    Flärdh, Oscar
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Analysis of a simple feedback scheme for error correction over a lossy network2007In: 2007 IEEE INTERNATIONAL CONFERENCE ON NETWORKING, SENSING, AND CONTROL, IEEE , 2007, p. 261-266Conference paper (Refereed)
    Abstract [en]

    A control theoretic analysis of a simple error correction scheme for lossy packet-switched networks is presented. Based on feedback information from the error correction process in the receiver, the sender adjusts the amount of redundancy using a so called extremum-seeking controller, which do not rely on any accurate model of the network loss process. The closed-loop system is shown to converge to a limit cycle in a neighborhood of the optimal redundancy. The result are validated using packet-based simulations with data from wireless sensor network experiments.

  • 68.
    Flärdh, Oscar
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    A comparison of control structures for error correction in packet-switched networks2005Conference paper (Refereed)
  • 69.
    Flärdh, Oscar
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    A new feedback control mechanism for error correction in packet-switched networks2005In: 44th IEEE Conference on Decision and Control & European Control Conference, 2005, p. 488-493Conference paper (Refereed)
    Abstract [en]

    Error correction mechanisms enable control and other real-time applications to be executed over unreliable packet-switched networks. By adding carefully adjusted redundancy to transmitted data at the sender, it is possible to recover lost data at the receiver and thereby improve effective throughput. We describe simple models for packet loss, which allow us to find the optimal redundancy as a function of packet loss probability. Two feedforward control mechanisms based on the packet loss probability are presented: one that is computed off-line and another one using an on-line algorithm. A drawback with these approaches is their dependency on accurate network state information and precise loss models. To cope with these issues, we propose a new feedback solution that tracks the optimum using gradient estimation. Simulations in ns-2 illustrate the behavior of the error correction schemes, demonstrating that the feedback solution outperforms the feedforward solution in presence of model errors.

  • 70.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Demia, Penda
    Marco, Belleschi
    Abrardo, Andrea
    A Joint Power Control and Resource Allocation Algorithm for D2D Communications2012Report (Other academic)
    Abstract [en]

    We consider the problem of joint power control, signal-to-noise-and-interference-ratio (SINR)target setting, mode selection and resource allocation for cellular network assisteddevice-to-device (D2D) communications.This problem is important for fourth generation systems, such as the release under study of the Long TermEvolution Advanced (LTE-A) system standardized by the Third Generation Partnership Project (3GPP).While previous works on radio resource management (RRM) algorithms for D2D communications dealt withmode selection and power control, the problem of resource allocation for the integrated cellular-D2Denvironment and in particularthe joint problem of mode selection, resource allocation and power allocation has not been addressed.We propose a utility function maximization approach that allows to take into account the inherenttrade off between maximizing spectrum efficiency and minimizing the required sum transmit power.We implement the proposed RRM algorithms in a realistic system simulator and report numericalresults that indicate large gains of D2D communications both in terms of spectrum- and energyefficiency.

  • 71.
    Fodor, Gabor
    et al.
    Ericsson Research, Sweden.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Soldati, Pablo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Near optimum power control and precoding under fairness constraints in network MIMO systems2009In: International Journal of Digital Multimedia Broadcasting, ISSN 1687-7578, Vol. 2010, p. 251719-Article in journal (Refereed)
    Abstract [en]

    We consider the problem of setting the uplink signal-to-noise-and- interference (SINR) target and allocating transmit powers for mobile stations in multicell spatial multiplexing wireless systems. Our aim is twofold: to evaluate the potential of such mechanisms in network multiple input multiple output (MIMO) systems, and to develop scalable numerical schemes that allow real-time near-optimal resource allocation across multiple sites. We formulate two versions of the SINR target and power allocation problem: one for maximizing the sum rate subject to power constraints, and one for minimizing the total power needed to meet a sum-rate target. To evaluate the potential of our approach, we perform a semianalytical study in Mathematica using the augmented Lagrangian penalty function method. We find that the gain of the joint optimum SINR setting and power allocation may be significant depending on the degree of fairness that we impose. We develop a numerical technique, based on successive convexification, for real-time optimization of SINR targets and transmit powers. We benchmark our procedure against the globally optimal solution and demonstrate consistently strong performance in realistic network MIMO scenarios. Finally, we study the impact of near optimal precoding in a multicell MIMO environment and find that precoding helps to reduce the sum transmit power while meeting a capacity target.

  • 72. Fodor, Gabor
    et al.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Soldati, Pablo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Near Optimum Power Control Under Fairness Constraints in CoMP Systems2009In: GLOBECOM 2009 - 2009 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, 2009, p. 5274-5281Conference paper (Refereed)
    Abstract [en]

    We consider the problem of setting the uplink signal-to-noise-and-interference (SINR) target and allocating transmit powers for mobile stations in multicell spatial multiplexing wireless systems. Our aim is twofold: to evaluate the potential of such mechanisms in coordinated multipoint transmission (CoMP) systems, and to develop scalable numerical schemes that allow real-time near-optimal resource allocation across multiple sites. We formulate two versions of the SINR target and power allocation problem: one for maximizing the sum rate subject to power constraints, and one for minimizing the total power needed to meet a sum-rate target. To evaluate the potential of our approach, we perform a semi-analytical study in Mathematica using the augmented Lagrangian penalty function method. We find that the gain of the joint optimum SINR setting and power allocation may be significant depending on the degree of fairness that we impose. We develop a numerical technique, based on successive convexification, for real-time optimization of SINR targets and transmit powers. We benchmark our procedure against the globally optimal solution, and demonstrate consistently strong performance in realistic CoMP scenarios.

  • 73.
    Fodor, Gabor
    et al.
    Ericsson Research, Sweden.
    Sorrentino, Stefano
    Ericsson Research, Sweden.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Soldati, Pablo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the impact of uplink power control in network MIMO systems with MMSE and SIC receivers2010In: 2010 IEEE International Symposium on 'A World of Wireless, Mobile and Multimedia Networks', 2010, Vol. WoWMoM 2010 - Digital ProceedingsConference paper (Refereed)
    Abstract [en]

    Network multiple input, multiple output (MIMO) systems are built around a broadband backbone network that allows for the fast communication of channel state information (CSI) as well as user data between different base stations. Previous works have shown that multicell channel adaptive (opportunistic) power control can minimize the sum power or maximize the sum rate when the backbone is used for the exchange of CSI in network MIMO systems. In this work we investigate the gains of multicell opportunistic power control under per user fairness constraints when both CSI and user data are shared between multiple sites. We find that multicell opportunistic power control working in concert with uplink joint signal detection is an efficient means both for the capacity and the power control problems that not only minimizes sum power or maximizes overall capacity, but is also able to provide arbitrary level of fairness.

  • 74.
    Fu, Liqun
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Energy Efficient Transmissions in Cognitive MIMO Systems With Multiple Data Streams2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 9, p. 5171-5184Article in journal (Refereed)
    Abstract [en]

    We investigate energy-efficient communications for time-division multiple access (TDMA) multiple-input multiple-output (MIMO) cognitive radio (CR) networks operating in underlay mode. In particular, we consider the joint optimization over both the time resource and the transmit precoding matrices to minimize the overall energy consumption of a single cell secondary network with multiple secondary users (SUs), while ensuring their quality of service (QoS). The corresponding mathematical formulations turn out to be non-convex, and thus of high complexity to solve in general. We give a comprehensive treatment of this problem, considering both the cases of perfect channel state information (CSI) and statistical CSI of the channels from the SUs to the primary receiver. We tackle the non-convexity by applying a proper optimization decomposition that allows the overall problem to be efficiently solved. In particular, we show that when the SUs only have statistical CSI, the optimal solution can be found in polynomial time. Moreover, if we consider additional integer constraints on the time variable which is usually a requirement in practical wireless system, the overall problem becomes a mixed-integer non-convex optimization which is more complicated. By exploring the special structure of this particular problem, we show that the optimal integer time solution can be obtained in polynomial time with a simple greedy algorithm. When the SUs have perfect CSI, the decomposition based algorithm is guaranteed to find the optimal solution when the secondary system is under-utilized. Simulation results show that the energy-optimal transmission scheme adapts to the traffic load of the secondary system to create a win-win situation where the SUs are able to decrease the energy consumption and the PUs experience less interference from the secondary system. The effect is particularly pronounced when the secondary system is under-utilized.

  • 75.
    Ghadimi, Euhanna
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Feyzmahdavian, Hamid Reza
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Global Convergence of the Heavy-ball Method for Convex Optimization2015In: European Control Conference (ECC15), IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    This paper establishes global convergence and provides global bounds of the rate of convergence for the Heavy-ball method for convex optimization. When the objective function has Lipschitz-continuous gradient, we show that the Cesáro average of the iterates converges to the optimum at a rate of O(1/k) where k is the number of iterations. When the objective function is also strongly convex, we prove that the Heavy-ball iterates converge linearly to the unique optimum. Numerical examples validate our theoretical findings.

  • 76.
    Ghadimi, Euhanna
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shames, Iman
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Accelerated Gradient Methods for Networked Optimization2011In: 2011 AMERICAN CONTROL CONFERENCE, 2011Conference paper (Refereed)
    Abstract [en]

    This paper explores the use of accelerated gradient methods in networked optimization. Optimal algorithm parameters and associated convergence rates are derived for distributed resource allocation and consensus problems, and the practical performance of the accelerated gradient algorithms are shown to outperform alternatives in the literature. Since the optimal parameters for the accelerated gradient method depends on upper and lower bounds of the Hessian, we study how errors in these estimates influence the convergence rate of the algorithm. This analysis identifies, among other things, cases where erroneous estimates of the Hessian bounds cause the accelerated method to have slower convergence than the corresponding (non-accelerated) gradient method. An application to Internet congestion control illustrates these issues.

  • 77.
    Ghadimi, Euhanna
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Landsiedel, O.
    Soldati, Pablo
    Huawei Technologies Sweden AB, Sweden.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    A metric for opportunistic routing in duty cycled wireless sensor networks2012In: Sensor, Mesh and Ad Hoc Communications and Networks (SECON), 2012 9th Annual IEEE Communications Society Conference on, IEEE , 2012, p. 335-343Conference paper (Refereed)
    Abstract [en]

    Opportunistic routing is widely known to have substantially better performance than traditional unicast routing in wireless networks with lossy links. However, wireless sensor networks are heavily duty-cycled, i.e. they frequently enter deep sleep states to ensure long network life-time. This renders existing opportunistic routing schemes impractical, as they assume that nodes are always awake and can overhear other transmissions. In this paper, we introduce a novel opportunistic routing metric that takes duty cycling into account. By analytical performance modeling and simulations, we show that our routing scheme results in significantly reduced delay and improved energy efficiency compared to traditional unicast routing. The method is based on a new metric, EDC, that reflects the expected number of duty cycled wakeups that are required to successfully deliver a packet from source to destination. We devise distributed algorithms that find the EDC-optimal forwarding, i.e. the optimal subset of neighbors that each node should permit to forward its packets. We compare the performance of the new routing with ETX-optimal single path routing in both simulations and testbed-based experiments.

  • 78.
    Ghadimi, Euhanna
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Landsiedel, Olaf
    Department of Computer Science and Engineering, Chalmers University of Technology, Sweden .
    Soldati, Pablo
    Huawei Technologies Sweden AB, Sweden.
    Duquennoy, Simon
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Opportunistic routing in low duty-cycle wireless sensor networks2014In: ACM transactions on sensor networks, ISSN 1550-4867, E-ISSN 1550-4859, Vol. 10, no 4, p. 67-Article in journal (Refereed)
    Abstract [en]

    Opportunistic routing is widely known to have substantially better performance than unicast routing in wireless networks with lossy links. However, wireless sensor networks are usually duty cycled, that is, they frequently enter sleep states to ensure long network lifetime. This renders existing opportunistic routing schemes impractical, as they assume that nodes are always awake and can overhear other transmissions. In this article we introduce ORW, a practical opportunistic routing scheme for wireless sensor networks. ORW uses a novel opportunistic routing metric, EDC, that reflects the expected number of duty-cycled wakeups that are required to successfully deliver a packet from source to destination. We devise distributed algorithms that find the EDC-optimal forwarding and demonstrate using analytical performance models and simulations that EDC-based opportunistic routing results in significantly reduced delay and improved energy efficiency compared to traditional unicast routing. In addition, we evaluate the performance of ORW in both simulations and testbed-based experiments. Our results show that ORW reduces radio duty cycles on average by 50% (up to 90% on individual nodes) and delays by 30% to 90% when compared to the state-of-the-art.

  • 79.
    Ghadimi, Euhanna
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Shames, Iman
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Multi-Step Gradient Methods for Networked Optimization2013In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, no 21, p. 5417-5429Article in journal (Refereed)
    Abstract [en]

    We develop multi-step gradient methods for network-constrained optimization of strongly convex functions with Lipschitz-continuous gradients. Given the topology of the underlying network and bounds on the Hessian of the objective function, we determine the algorithm parameters that guarantee the fastest convergence and characterize situations when significant speed-ups over the standard gradient method are obtained. Furthermore, we quantify how uncertainty in problem data at design-time affects the run-time performance of the gradient method and its multi-step counterpart, and conclude that in most cases the multi-step method outperforms gradient descent. Finally, we apply the proposed technique to three engineering problems: resource allocation under network-wide budget constraint, distributed averaging, and Internet congestion control. In all cases, our proposed algorithms converge significantly faster than the state-of-the art.

  • 80.
    Ghadimi, Euhanna
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Soldati, Pablo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Österlind, F.
    Zhang, Haibo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Hidden Terminal-Aware Contention Resolution With an Optimal Distribution2011In: Proceedings - 8th IEEE International Conference on Mobile Ad-hoc and Sensor Systems, MASS 2011, 2011, p. 182-191Conference paper (Refereed)
    Abstract [en]

    Achieving low-power operation in wireless sensor networks with high data load or bursty traffic is challenging. The hidden terminal problem is aggravated with increased amounts of data in which traditional backoff-based contention resolution mechanisms fail or induce high latency and energy costs. We analyze and optimize Strawman, a receiver-initiated contention resolution mechanism that copes with hidden terminals. We propose new techniques to boost the performance of Strawman while keeping the resolution overhead small. We finally validate our improved mechanism via experiments.

  • 81. Ghadimi, Euhanna
    et al.
    Teixeira, Andre
    Shames, Iman
    Johansson, Mikael
    On the Optimal Step-size Selection for the Alternating Direction Method of Multipliers2012Conference paper (Refereed)
    Abstract [en]

    The alternating direction method of multipliers is a powerful technique for structured large-scale optimization that has recently found applications in a variety of fields including networked optimization, estimation, compressed sensing and multi-agent systems. While applications of this technique have received a lot of attention, there is a lack of theoretical support for how to set the algorithm parameters, and its step-size is typically tuned experimentally. In this paper we consider three different formulations of the algorithm and present explicit expressions for the step-size that minimizes the convergence rate. We also compare our method with one of the existing step-size selection techniques for consensus applications.

  • 82.
    Ghadimi, Euhanna
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Teixeira, André
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rabbat, Michael G.
    McGill Univ, Dept Elect & Comp Engn, Montreal, PQ, Canada..
    Johansson, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The ADMM algorithm for distributed averaging: Convergence rates and optimal parameter selection2014In: CONFERENCE RECORD OF THE 2014 FORTY-EIGHTH ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS / [ed] Matthews, M B, IEEE COMPUTER SOC , 2014, p. 783-787Conference paper (Refereed)
    Abstract [en]

    We derive the optimal step-size and over-relaxation parameter that minimizes the convergence time of two ADMM-based algorithms for distributed averaging. Our study shows that the convergence times for given step-size and over-relaxation parameters depend on the spectral properties of the normalized Laplacian of the underlying communication graph. Motivated by this, we optimize the edge-weights of the communication graph to improve the convergence speed even further. The performance of the ADMM algorithms with our parameter selection are compared with alternatives from the literature in extensive numerical simulations on random graphs.

  • 83.
    Ghadimi, Euhanna
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Teixeira, André
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rabbat, Michael
    McGill University, Canada.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    The ADMM algorithm for distributed averaging: convergence rates and optimal parameter selection2014In: 48th Asilomar Conference on Signals, Systems, and Computers 2014, IEEE conference proceedings, 2014, p. 783-787Conference paper (Refereed)
    Abstract [en]

    We derive the optimal step-size and overrelaxationparameter that minimizes the convergence time oftwo ADMM-based algorithms for distributed averaging. Ourstudy shows that the convergence times for given step-size andover-relaxation parameters depend on the spectral propertiesof the normalized Laplacian of the underlying communicationgraph. Motivated by this, we optimize the edge-weights of thecommunication graph to improve the convergence speed evenfurther. The performance of the ADMM algorithms with ourparameter selection are compared with alternatives from theliterature in extensive numerical simulations on random graphs.

  • 84.
    Ghadimi, Euhanna
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Teixeira, André
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shames, Iman
    University of Melbourne, Australia.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Optimal parameter selection for the alternating direction method of multipliers (ADMM): quadratic problems2015In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 60, no 3, p. 644-658, article id 6892987Article in journal (Refereed)
    Abstract [en]

    The alternating direction method of multipliers (ADMM) has emerged as a powerful technique for large-scale structured optimization. Despite many recent results on the convergence properties of ADMM, a quantitative characterization of the impact of the algorithm parameters on the convergence times of the method is still lacking. In this paper we find the optimal algorithm parameters that minimize the convergence factor of the ADMM iterates in the context of l2-regularized minimization and constrained quadratic programming. Numerical examples show that our parameter selection rules significantly outperform existing alternatives in the literature.

  • 85.
    Gonga, Antonio
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fast Information Exchange in Proximity-Based Multichannel Wireless Networks2015In: Proceedings - 2015 8th IFIP Wireless and Mobile Networking Conference, WMNC 2015, IEEE conference proceedings, 2015, p. 24-31Conference paper (Refereed)
    Abstract [en]

    This paper considers the problem of distributed neighbor discovery in multi-channel wireless networks. We propose a protocol in which nodes randomly select a channel and decide whether to transmit or listen for neighbor discovery beacons. When nodes transmit, they use epidemic information dissemination to spread knowledge about all the nodes they have discovered so far. Theoretical guarantees on discovery times are complemented by extensive simulations and practical implementations. The evaluations show that multi-channel communication effectively reduces the number of collisions between nodes in the network (especially in dense networks) and that epidemic information dissemination yields both significant speed-ups and increased resilience to packet losses. Finally, we also show that our protocol compares favorably to previously proposed solutions in the literature.

  • 86.
    Gonga, António
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Neighbor discovery in multichannel wireless clique networks: An epidemic approach2013In: Proceedings - IEEE 10th International Conference on Mobile Ad-Hoc and Sensor Systems, MASS 2013, IEEE , 2013, p. 131-135Conference paper (Refereed)
    Abstract [en]

    We investigate the problem of neighbor discovery in multichannel wireless ad hoc and sensor networks with epidemic information dissemination. Previous works have considered neighbor discovery in a single channel where at most one node can be discovered per time instant. To reduce the effect of collisions observed in single channel solutions, we formulate models for multichannel neighbor discovery and allow for epidemic dissemination of information. As a result, nodes can discover all their neighbors faster, either directly or indirectly by hopping between orthogonal channels and exploring the neighbors in each of them. We show analytically, by simulations, and by experimental evaluations that the expected neighbor discovery time is reduced considerably compared to single channel neighbor discovery solutions.

  • 87.
    Gonga, António
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dunkels, A.
    MobiSense: Power-efficient micro-mobility in IPv6-based sensor networks2010In: Proceedings of the 9th ACM/IEEE International Conference on Information Processing in Sensor Networks, IPSN '10, 2010, p. 414-415Conference paper (Refereed)
    Abstract [en]

    Emerging applications in industrial automation and medical care demand support for uninterrupted connectivity and reliable data transfer from mobile sensors. We present MobiSense, an energy-efficient system for reliable data transfer supporting IPv6 micro-mobility and fast handovers. We demonstrate that a two-way end-to-end IPv6 UPD session between two mobile nodes can achieve an end-to-end reliability of up to 96% while guarateeing a hand-over latency below 2 seconds.

  • 88.
    Gonga, António
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Landsiedel, O.
    Soldati, P.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Revisiting multi-channel communication to mitigate interference and link dynamics in wireless sensor networks2012In: Proceedings - IEEE International Conference on Distributed Computing in Sensor Systems, DCOSS 2012, IEEE Computer Society, 2012, p. 186-193Conference paper (Refereed)
    Abstract [en]

    Multichannel communication has been proposed as alternative to adaptive (single-channel) routing protocols for mitigating the impact of interference and link dynamics in wireless sensor networks. While several studies have advocated features of both techniques (not without running up against contradicting arguments) a comprehensive study that aligns these results is still lacking. This paper aims at filling this gap. We present an experimental test bed setup used to perform extensive measurements for both single-channel and multichannel communication. We first analyze single-channel and multichannel communication over a single-hop in terms of packet reception ratio, maximum burst loss, temporal correlation of losses, and loss correlations across channels. Results show that multichannel communication with channel hopping significantly reduces link burstiness and packet loss correlation. For multi-hop networks, multi-channel communication and adaptive routing show similar end-to-end reliability in dense topologies, while multichannel communication can outperform adaptive routing in sparse networks with bursty links.

  • 89.
    Gonga, António
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Landsiedel, Olaf
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    MobiSense: power-efficient micro-mobility in wireless sensor networks2011In: 2011 International Conference on Distributed Computing in Sensor Systems and Workshops, DCOSS'11, 2011Conference paper (Refereed)
    Abstract [en]

    Emerging applications in industrial automation as well as tracking and monitoring applications of humans, objects or animals share common requirements: micro-mobility, high-throughput, and two-way end-to-end communications. In this paper we present MobiSense, a MAC layer and routing architecture for micro-mobility environments providing reliable and energy-efficient communication and low-latency handoffs. MobiSense's energy-efficiency and reliability comes from a set of carefully chosen design elements: rapid network information gathering, rapid network (re)admission and convergence, distributed network formation, and dynamic scheduling. Testbed evaluations show that a mobile sensor achieves: (i) reliability above 95% even in scenarios with high data rates of 6pps/node; (ii) low latency-handoffs typically below 1 second; (iii) a high aggregate system throughput of more than 95kbps; (iv) two-way communication without the need for flooding; and (v) communication at very low duty-cycles below 4% at 6pps/node.

  • 90. Gunnar, A.
    et al.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Cautious weight tuning for link-state routing2010In: Proceedings of the 2010 International Conference on Network and Service Management, CNSM 2010, IEEE , 2010, p. 346-349Conference paper (Refereed)
    Abstract [en]

    Link-state routing protocols are widely used for intradomain routing in the Internet. These protocols are simple to administer and automatically update paths between sources and destinations when the topology changes. However, finding link weights that optimize network performance for a given traffic scenario is computationally hard. The situation is even more complex when the traffic is uncertain or time-varying. We present an efficient heuristic for finding link settings that give uniformly good performance also under large changes in the traffic. The heuristic combines efficient search techniques with a novel objective function. The objective function combines the network performance with a cost of deviating from desirable features of robust link weight settings. We assess performance of our method using traffic data from an operational IP backbone.

  • 91.
    Gunnar, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Cautious Weight Tuning for Link State Routing Protocols2011Report (Other academic)
    Abstract [en]

    Link state routing protocols are widely used for intradomain routing in the Internet. These protocols are simple to administer and automatically update paths between sources and destinations when the topology changes. However, finding link weights that optimize network performance for a given traffic scenario is computationally hard. The situation is even more complex when the traffic is uncertain or time-varying.  We present an efficient heuristic for finding link settings that give uniformly good performance also under large changes in the traffic. The heuristic combines efficient search techniques with a novel objective function. The objective function combines network performance with a cost of deviating from desirable features of robust link weight settings. Furthermore, we discuss why link weight optimization is insensitive to errors in estimated traffic data from link load measurements. We assess performance of our method using traffic data from an operational IP backbone.

  • 92.
    Gunnar, Anders
    et al.
    Swedish Institute of Computer Science.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Robust load balancing under traffic uncertainty-tractable models and efficient algorithms2011In: Telecommunications Systems, ISSN 1018-4864, E-ISSN 1572-9451, Vol. 48, no 1-2, p. 93-107Article in journal (Refereed)
    Abstract [en]

    Routing configurations that have been optimized for a nominal traffic scenario often display significant performance degradation when they are subjected to real network traffic. These degradations are due to the inherent sensitivity of classical optimization techniques to changes in model parameters combined with the significant traffic variations caused by demand fluctuations, component failures and network reconfigurations. In this paper, we review important sources for traffic variations in data networks and describe tractable models for capturing the associated traffic uncertainty. We demonstrate how robust routing settings with guaranteed performance for all foreseen traffic variations can be effectively computed via memory efficient iterative techniques and polynomial-time algorithms. The techniques are illustrated on real data from operational IP networks.

  • 93.
    Gunnar, Anders
    et al.
    KTH, School of Electrical Engineering (EES).
    Johansson, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Robust load-balancing under statistical uncertainty: models and polynomial-time algorithms2009In: 2009 NEXT GENERATION INTERNET NETWORKS, IEEE , 2009, p. 99-+Conference paper (Refereed)
    Abstract [en]

    We study the problem of guaranteed-performance routing under statistical traffic uncertainty. Relevant traffic models are presented and a polynomial-time algorithm for solving the associated robust routing problem is given. We demonstrate how our techniques, in combination with fundamental limitations on the accuracy of estimated traffic matrices, enable us to compute bounds on the achievable performance of OSPF-routing optimized using only topology information and link count data. We discuss extensions to other types of traffic uncertainties and describe an alternative, more memory efficient, algorithm based on combined constraint and column generation. The proposed techniques are evaluated in several numerical examples to highlight the features of our approach.

  • 94. Gunnar, Anders
    et al.
    Johansson, Mikael
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Telkamp, Thomas
    Traffic matrix estimation for a global IP network2004In: 17th Nordic Teletraffic Seminar, 2004Conference paper (Refereed)
  • 95. Gunnar, Anders
    et al.
    Johansson, Mikael
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Thomas, Telkamp
    Traffic matrix estimation on a large IP backbone: a comparison on real data2004In: IMC '04 Proceedings of the 4th ACM SIGCOMM conference on Internet measurement, 2004, p. 149-160Conference paper (Refereed)
    Abstract [en]

    This paper considers the problem of estimating the point-to-point traffic matrix in an operational IP backbone. Contrary to previous studies, that have used a partial traffic matrix or demands estimated from aggregated Netflow traces, we use a unique data set of complete traffic matrices from a global IP network measured over five-minute intervals. This allows us to do an accurate data analysis on the time-scale of typical link-load measurements and enables us to make a balanced evaluation of different traffic matrix estimation techniques. We describe the data collection infrastructure, present spatial and temporal demand distributions, investigate the stability of fan-out factors, and analyze the mean-variance relationships between demands. We perform a critical evaluation of existing and novel methods for traffic matrix estimation, including recursive fanout estimation, worst-case bounds, regularized estimation techniques, and methods that rely on mean variance relationships. We discuss the weaknesses and strengths of the various methods, and highlight differences in the results for the European and American subnetworks.

  • 96.
    Johansson, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Adam, Constantin
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Stadler, Rolf
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Distributed resource allocation strategies for achieving quality of service in server clusters2006In: PROCEEDINGS OF THE 45TH IEEE CONFERENCE ON DECISION AND CONTROL, 2006, p. 1990-1995Conference paper (Refereed)
    Abstract [en]

    We investigate the resource allocation problem for large-scale server clusters with quality-of-service objectives, where key functions are decentralized. Specifically, the optimal service selection is posed as a discrete utility maximization problem that reflects management objectives and resource constraints. We develop an efficient centralized algorithm that solves this problem, and we propose three suboptimal schemes that operate with local information. The performance of the suboptimal schemes is evaluated in simulations, both under idealized conditions and in a full-scale system simulator.

  • 97.
    Johansson, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Carretti, Cesare Maria
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    On Distributed Optimization using Peer-to-Peer Communications in Wireless Sensor Networks2008In: Proceedings of IEEE SECON, 2008, p. 497-505Conference paper (Refereed)
    Abstract [en]

    We describe and evaluate a suite of distributed and computationally efficient algorithms for solving a class of convex optimization problems in wireless sensor networks. The problem class has wide applications in estimation, detection, localization, coordination and resource sharing. We focus on peer-to-peer algorithms where nodes only exchange data with their immediate neighbors, and consider three distinct alternatives: a dual-based broadcast algorithm, a novel stochastic unicast algorithm, and a linear broadcast algorithm tailored for least-squares problems. We implement the algorithms in the network simulator NS2 and present extensive simulation results for random topologies.

  • 98.
    Johansson, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed non-smooth resource allocation over a network2009In: IEEE Conference on Decision and Control, 2009, p. 1678-1683Conference paper (Refereed)
    Abstract [en]

    Networked systems are common and crucial. Oneof the canonical problems in such systems is distributed resourceallocation. From this rather broad class of problems, weconsider a convex non-smooth resource allocation problem witha global resource constraint. Specifically, the objective functionis separable and consists of a sum of convex functions, eachassociated with a node in a given network. Each component ofthe objective depends on a single variable local to the associatednode and the sum of all local variables must remain constantat all times. For scalability, we constrain the nodes to onlycommunicate and exchange resources with their immediateneighbors. We propose an algorithm that combines subgradientoptimization with distributed averaging. Starting the algorithmfrom a feasible point, the nodes iteratively exchange resourceswith their neighbors to get close to the optimal set whilesatisfying the total resource constraint at all times.We show thatunder mild technical conditions the algorithm converges in anepsilon-sense, as long as the stepsize is chosen sufficiently smalland the distributed averaging process is sufficiently accurate.We derive expressions for how the stepsize and the number ofconsensus iterations affect the accuracy of the final result.

  • 99.
    Johansson, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Faster Linear Iterations for Distributed Averaging2008In: Proceedings of the 17th IFAC World Congress, 2008, 2008Conference paper (Refereed)
    Abstract [en]

    Distributed averaging problems are a subclass of distributed consensus problems,which have received substantial attention from several research communities. Although many ofthe proposed algorithms are linear iterations, they vary both in structure and state dimension.In this paper, we investigate the performance benefits of adding extra states to distributedaveraging iterations. We establish conditions for convergence and discuss possible ways ofoptimizing the convergence rates. By numerical examples, it is shown that the performance canbe significantly increased by adding extra states. Finally, we provide necessary and sufficientconditions for convergence of a more general version of distributed averaging iterations.

  • 100.
    Johansson, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Primal and Dual Approaches to Distributed Cross-layer Optimization2005In: IFAC Proceedings Volumes (IFAC-PapersOnline), 2005, p. 113-118Conference paper (Refereed)
    Abstract [en]

    Several approaches for cross-layer design, e.g., coordinating the traditionally separated layers in wireless networks, have been proposed. However, protocols that are close to achieving the performance bounds are still lacking. We propose three distributed algorithms for joint congestion control and resource allocation in networks with variable capacities subject to a global resource constraint. Examples include spectrum assignment in wireless networks and wavelength allocation in optical networks. For scalability, we impose the additional constraint that nodes can only negotiate and exchange resources with their neighbors. The proposed algorithms consist of two complementary approaches based on decomposition techniques, in which congestion control and resource allocations are performed on different time-scales. Two of the algorithms can be shown to converge without network delays. Copyright 2005 IFAC

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