CNRS Laboratory of Signals & Systems

GIF SUR YVETTE, France

CNRS Laboratory of Signals & Systems

GIF SUR YVETTE, France

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Lakshminarayana S.,Advanced Digital science Center | Assaad M.,CNRS Laboratory of Signals & Systems | Debbah M.,CNRS Laboratory of Signals & Systems
IEEE Journal on Selected Areas in Communications | Year: 2015

We consider a small cell network (SCN) consisting of N cells, with the small cell base stations (SCBSs) equipped with Nt ≥ 1 antennas each, serving K single antenna user terminals (UTs) per cell. Under this set up, we address the following question: given certain time average quality of service (QoS) targets for the UTs, what is the minimum transmit power expenditure with which they can be met? Our motivation to consider time average QoS constraint comes from the fact that modern wireless applications such as file sharing, multi-media etc. allow some flexibility in terms of their delay tolerance. Time average QoS constraints can lead to greater transmit power savings as compared to instantaneous QoS constraints since it provides the flexibility to dynamically allocate resources over the fading channel states. We formulate the problem as a stochastic optimization problem whose solution is the design of the downlink beamforming vectors during each time slot. We solve this problem using the approach of Lyapunov optimization and characterize the performance of the proposed algorithm. With this algorithm as the reference, we present two main contributions that incorporate practical design considerations in SCNs. First, we analyze the impact of delays incurred in information exchange between the SCBSs. Second, we impose channel state information (CSI) feedback constraints, and formulate a joint CSI feedback and beamforming strategy. In both cases, we provide performance bounds of the algorithm in terms of satisfying the QoS constraints and the time average power expenditure. Our simulation results show that solving the problem with time average QoS constraints provide greater savings in the transmit power as compared to the instantaneous QoS constraints. © 2015 IEEE.


Mazenc F.,French Institute for Research in Computer Science and Automation | Niculescu S.-I.,EPI DISCO | Bekaik M.,CNRS Laboratory of Signals & Systems
IEEE Transactions on Automatic Control | Year: 2013

We address the problem of stabilizing systems belonging to a family of time-varying nonlinear systems with distributed input delay through state feedbacks without retarded term. The approach we adopt is based on a new technique that is inspired by the reduction model technique. The control laws we obtain are nonlinear and time-varying. They globally uniformly exponentially stabilize the origin of the considered system. We illustrate the construction with a networked control system. © 2012 IEEE.


Mazenc F.,Supelec | Normand-Cyrot D.,CNRS Laboratory of Signals & Systems
IEEE Transactions on Automatic Control | Year: 2013

We propose a new construction of exponentially stabilizing sampled feedbacks for continuous-time linear time-invariant systems with an arbitrarily large constant pointwise delay in the inputs. Stability is guaranteed under an assumption on the size of the largest sampling interval. The proposed design is based on an adaptation of the reduction model approach. The stability of the closed loop systems is proved through a Lyapunov functional of a new type, from which is derived a robustness result. © 1963-2012 IEEE.


Mazenc F.,Supelec | Niculescu S.-I.,CNRS Laboratory of Signals & Systems | Bekaik M.,Supelec
Proceedings of the IEEE Conference on Decision and Control | Year: 2011

We propose a new solution to the problem of globally asymptotically stabilizing a nonlinear system in feedback form with a known pointwise delay in the input. The result covers a family of systems wider than those studied in the literature and endows with control laws with a single delay, in contrast to the existing one, which include two distinct pointwise delays or distributed delays. The design strategy is based on the construction of an appropriate Lyapunov-Krasovskii functional. © 2011 IEEE.


Cozza A.,CNRS Laboratory of Signals & Systems | Monsef F.,CNRS Laboratory of Signals & Systems
IEEE Transactions on Antennas and Propagation | Year: 2014

The ability of time-reversed signals in reproducing a given time-dependence of the electromagnetic field within random media is investigated. A general setup consisting of multiple sources cooperating in providing the best transmission is considered, where the constructive interference of their individual contributions is meant to improve the quality of the field generation with respect to a single-source setup. The medium response is described by means of tools from random-process theory, for the case of stationary media complex enough to ensure a large number of multi-path contributions. It is shown that even a very weak spatial coherence in the medium is sufficient to significantly hinder the improvement expected from the use of multiple-source scenarios. Experimental results obtained in a reverberation chamber support the validity of the proposed theory. Direct applications of these results can be found in recent proposals about the potential benefits of time-reversed signals used in wireless communications, imaging techniques, as well as in pulsed-field generation devices based on energy compression through dispersive media. © 2014 IEEE.


Renzo M.D.,CNRS Laboratory of Signals & Systems | Haas H.,University of Edinburgh
IEEE Transactions on Communications | Year: 2011

In this paper, we study the performance of Space Shift Keying (SSK) modulation for a generic MultipleInputMultipleOutput (MIMO) wireless system over correlated Rician fading channels. In particular, our contribution is twofold. i) First, we propose a very general framework for computing the Average Bit Error Probability (ABEP) of SSKMIMO systems over a generic Rician fading channel with arbitrary correlation and channel parameters. The framework relies upon the Moschopoulos method. We show that it is exact for MIMO systems with two transmitantenna and arbitrary receiveantenna, while an asymptoticallytight upperbound is proposed to handle the system setup with an arbitrary number of transmitantenna. ii) Second, moving from the consideration that conventional SSKMIMO schemes can offer only receivediversity gains, we propose a novel SSKMIMO scheme that can exploit the transmitantenna to increase the diversity order. The new method has its basic foundation on the transmission of signals with good timecorrelation properties, and is called TimeOrthogonalSignalDesign (TOSD) assisted SSK modulation (TOSDSSK). It is shown that the proposed method can increase twofold the diversity order for arbitrary transmit and receiveantenna. In particular, for MIMO systems with two transmitantenna and Nr receiveantenna fulldiversity equal to 2N-r can be achieved. Analytical frameworks and theoretical findings are substantiated via Monte Carlo simulations for various system setups. © 2011 IEEE.


Mazenc F.,CNRS Laboratory of Signals & Systems | Bernard O.,French Institute for Research in Computer Science and Automation
International Journal of Robust and Nonlinear Control | Year: 2014

Designing an interval observer with stability properties for nonlinear systems, which are not cooperative and not globally Lipschitz, is an open problem. This paper studies a general canonical structure for which interval observers with input to state stability (ISS) properties can be derived. This canonical block triangular nonlinear structure is rather general and may result from a change of coordinates or an output injection. We provide a general method for explicitly constructing framers for systems for which can be given such a structure. We also construct ISS interval observers when additional properties are satisfied. The systems we consider are in general not cooperative and not globally Lipschitz. We illustrate the constructions by designing a framer and an ISS interval observer for two models of bioreactors. © 2012 John Wiley & Sons, Ltd.


Bondon P.,CNRS Laboratory of Signals & Systems
Conference Record - Asilomar Conference on Signals, Systems and Computers | Year: 2013

The problem of estimating an autoregressive conditionally heteroscedastic (ARCH) model in the presence of missing data is investigated. A two-stage least squares estimator which is easy to calculate is proposed and its strong consistency and asymptotic normality are established. The behaviour of the estimator for finite samples is analyzed via Monte Carlo simulations, and is compared to a Yule-Walker estimator and to some estimators based on a complete data set obtained after filling the missing observations by imputation procedures. An application to real data is also reported. © 2013 IEEE.


Mazenc F.,French Institute for Research in Computer Science and Automation | Dinh T.N.,French Institute for Research in Computer Science and Automation | Niculescu S.I.,CNRS Laboratory of Signals & Systems
Proceedings of the IEEE Conference on Decision and Control | Year: 2012

First, time-invariant interval observers are proposed for a family of nonlinear systems. Second, it is shown that, for any time-invariant exponentially stable discrete-time linear system with additive disturbances, time-varying exponentially stable discrete-time interval observers can be constructed. The result relies on the design of time-varying changes of coordinates which transform a linear system into a nonnegative linear system. © 2012 IEEE.


Li X.-G.,Northeastern University China | Niculescu S.-I.,CNRS Laboratory of Signals & Systems | Cela A.,School of Engineering in Information and Communication Science and Technology | Wang H.-H.,Northeastern University China | Cai T.-Y.,Northeastern University China
IEEE Transactions on Automatic Control | Year: 2013

Obtaining the Puiseux series of multiple imaginary (characteristic) roots (MIRs) is a fundamental issue in the stability analysis of timedelay systems. However, to the best of the authors' knowledge, this issue has not been fully investigated up to date. This note focuses on the Puiseux series expansion of MIRs of linear time-invariant systems including commensurate delays. For anMIR of anymultiplicity, we propose an algorithm for defining the structure of the Puiseux series, as well as the explicit computation of the corresponding coefficients. By using the proposed method, we can find all the Puiseux series corresponding to all the root loci. © 2012 IEEE.

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