Search

International audience

IF=3.8; International audience; This article focuses on the problem of leaderfollowing consensus of second-order Multi-Agent Systems (MAS) with switching topology and partial aperiodic sampled data. MAS are subject to various constraints related to information exchange among the agents. It is considered that each agent in the network is able to measure its position only and cannot measure either its velocity or acceleration (input). Moreover, the position information is sent to the neighbors at aperiodic and asynchronous sampling rates. At last, a switching communication topology among the agents is considered. An observer-based control protocol is proposed to achieve leader-following consensus for MAS with above mentioned constraints. Using an Average Dwell Time (ADT) approach, sufficient conditions are derived through Lyapunov-based stability analysis to ensure the leader-following consensus. Numerical examples are also included to show the effectiveness of the proposed scheme.

International audience; This paper deals with the problem of time-varying formation tracking for second-order multi-agent systems under directed topology, where the follower states form a desired formation while tracking the state of the leader. It is considered that each agent, including the leader, has second-order dynamics and can only transmit its position to its neighbors. The velocities and inputs are not exchanged between neighboring agents. In this work, it should be mentioned that contrary to many existing schemes, asynchronous and aperiodic sampling is considered. For each agent, an observer is proposed to estimate its state and the state of its neighbors from the available local asynchronous and aperiodic sampled position data. Using these estimates, a time-varying formation tracking protocol is developed. The stability of the closed-loop system which combines the continuous-discrete time observer and the formation tracking controller is analysed using an appropriate Lyapunov function. The effectiveness of the proposed output-feedback controller is illustrated for various formations through simulation results.

International audience; The aim of this paper is to study the second-order practical consensus of homogeneous sampled-data multiagent systems (MASs). To do this, a new nonlinear emulation strategy based on homogeneity is developed. It is then applied to MASs under synchronously variable sampling. Finally, a comparison with the classical linear strategy is provided in the case of MASs under synchronously periodic sampling.

International audience; This paper deals with the leader-following consensus problem of multi-agent systems with the consideration that each agent can only transmit its position state to the neighbors at irregular discrete sampling times. In the proposed algorithm, a continuous-discrete time observer is designed for the continuous estimation of both position and velocity from the discrete position information of the neighbors. These estimated states are then used for designing a continuous control law which solves the leader-following consensus problem. Moreover, the dynamics of the leader is not fixed and can be controlled through an external input. The stability analysis has been carried out by employing the Lyapunov approach which provides sufficient conditions to tune the parameters according to the maximum allowable sampling period. The developed algorithm has been simulated and then tested on an actual multi-robot system consisting of three differential drive wheeled robots. Both simulation and hardware results validate the effectiveness of the control algorithm.

International audience; The article deals with the stability of discontinuous homogeneous nonlinear systems with aperiodic sampled-data inputs. We first extend results about robustness of homogeneous nonlinear systems to the discontinuous case. Then, we prove that this framework is well suited for studying the stability of discontinuous homogeneous nonlinear sampled-data systems. The results are illustrated on the double integrator.

International audience; The second-order practical consensus tracking of multi-agent systems with a fixed topology and a varying leader's velocity is obtained by using a linear control strategy and the input-to-state stability framework. Then, a new control protocol is proposed where the leader, called a perceptive leader, receives information from its followers. Finally, a study is provided in simulation and on a fleet of mobile robots showing the effectiveness of non perceptive and perceptive strategies in terms of speed of convergence, precision and connectivity maintenance.

International audience; A novel distributed consensus protocol, where only sampled position information is exchanged between neighboring agents, is designed for second-order multi-agent systems under a directed communication topology. This protocol allows to reach the consensus for asynchronous and aperiodic sampling periods, which means that every agent can send its measurements independently from its neighbors. Furthermore, the upper bound on the sampling periods can be chosen arbitrarily long by adapting the tuning parameters. This result is obtained by using a continuous-discrete time observer which allows to reconstruct the system state in real time from only discrete-time measurements. The feedback control gain is set according to the observer gain which is itself set according to the maximum sampling period.

The purpose of this paper is to apply filter banks to the control problem involving the rejection of multi-sinusoidal disturbance from output of slowly time-varying stable systems. The use of filter banks allows to distribute the control effort in many independent adaptive controllers, each of them taking care of a sinusoidal component of the disturbance. By varying the filter banks specifications, the method handles the trade-off between a time-behavior controller, with interesting settling time and a tonal-behavior controller showing the properties of simplified control, reduced computational time and on-line system identification with the system output noise via the feedback loop. Numerical examples are presented to illustrate this trade-off.

International audience; This article deals with the finite time boundedness (FTB) and FTB-stabilization problem for a general class of neutral high-order Hopfield neural networks (NHOHNNs) with time delay in the leakage term and mixed time delays. The mixed time delays consist of both discrete time-varying delays and infinite distributed delays. By using the topological degree theory, sufficient conditions are established to prove the existence of equilibrium points. Then, the Lyapunov-Krasovskii functional (LKF) method is used to prove sufficient conditions for the FTB. These conditions are in the form of linear matrix inequalities (LMIs) and can be numerically checked. Furthermore, a state feedback control is constructed to solve the FTB-stabilization problem. Finally, some numerical examples are presented to show the effectiveness of our main results.

International audience; Uplink transmission power control is an essential task in Wireless Cellular Networks (WCNs) due to the resource limitation of the Mobile Stations (MSs). One remaining problem is the effect of the delay caused by measuring the signal strength and decision making in the Inner-Loop Power Control (ILPC). In this article, we develop the Potential Feedback Controller (PFC) for a linear scalar discrete-time system with disturbance in order to take into account an unknown bounded time-varying input delay for uplink ILPC. The main interest of the PFC is to treat easily a stabilization problem with a constraint on the state space by using a nonlinear feedback control with a short computation time. Simulations illustrate that by applying the PFC, the communication connectivity is ensured by maintaining the signal strength above a required limit.

International audience; This article deals with a new Quality of Service (QoS) aware Two-Level Scheduler (TLS) for real-time (RT) data flows in downlink transmission of Long Term Evolution (LTE) cellular networks. It consists of two distinct scheduler levels. At the upper-level scheduler, the Potential Feedback Controller (PFC) determines the quota of data to transmit in order to meet the delay constraints of RT data flows while, at the lower-lever scheduler, the Proportional Fair (PF) scheduler is used to reach a high fairness among Users (UEs). The PFC is well suited for the upper-level scheduler since it maintains the queue length as close as possible to zero which leads to a low Packet Loss Ratio (PLR). A comparison, by using LTE-Sim simulator, with well-known QoS aware scheduling methods Frame Level Scheduler (FLS), Exponential (EXP)-rule and Logarithmic (LOG)-rule has been provided which shows that our proposed TLS outperforms the EXP-rule and LOG-rule scheduling methods and it slightly decreases the PLR of RT data flows compared to the FLS scheduling method while it significantly reduces the computation time.

The use of chaotic codes in transmission systems presents many advantages, not only in term of security, but also to combat multi-path propagations and to allow multiple access. Nevertheless, the main problem of communication with chaos is the design of an experimental and real-time synchronization decoder between transmitter and receiver. In this paper, we suggest to use the belief propagation algorithm as a new approach for synchronizing quasi-chaotic signals. In this approach, the transmitter contains a digital chaotic oscillator which is perturbed by the information signal. The receiver consists in a dual system augmented with a belief propagation processing, whose aim is to recover the information signal. We suppose that the channel is Gaussian and synchronization is forced in a first step. Once synchronization is achieved, the information signal modulated the chaotic system and is transmitted on the Gaussian channel. An adaptative belief propagation algorithm is processed to recover the signal information.

This paper presents a case of persistent harmonic active control for an HEV (Hybrid Electric Vehicle) powertrain. The active control is adapted for a hybrid powertrain consisting of a one-cylinder diesel engine, coupled with a PMSM (Permanent Magnet Synchronous Machine). The PMSM assures the propulsion of the vehicle, as in conventional mild-hybrid electrical vehicles. In addition, it provides speed ripple reductions of the diesel engine. Due to the HEV speed variation, the active control must match this variation. The speed is introduced as a parameter in order to devise an LPV (linear parameter varying) control strategy. The suitability of LPV control for engine torque ripple reduction is demonstrated through a torque control implementation of the PMSM. The control strategy uses the internal model principle of multi-sinusoidal persistent disturbances. The controller is designed to involve several steps, including LMI-based (Linear Matrix Inequalities) optimization. The results show that, for the first and second orders of the ripple, speed oscillations can be reduced when the speed varies. An industrial test bed is used to validate the effectiveness of the approach and the power consumption of the strategy is analyzed.

This paper describes requirement for wireless transmission of Chaotic Code Division Multiplexed Access (Chaotic CDMA) and it focuses on real-time synchronization algorithm embedded into electronic programmable device. CDMA with quasi-orthogonal codes is used to allow multi-users to transmit simultaneously in the same channel. Since the channel is shared between all users, the receiver system has to cope with channel noise and overall with interference from other users. As a result, one of the main problems of communication with quasi-orthogonal chaotic codes is to implement a real time decoder in presence of noise. Even if set-membership algorithm are efficient in real time synchronization of chaotic discrete generators in the presence of noise, these algorithms require a large memory resource. In this paper, we propose an evolution of set-membership algorithm toward genetic algorithm to be implemented into electronic programmable device. The advantage of genetic algorithm compared with set-membership algorithm is that they require a fixed size of memory.

This article presents a real-life application for the extremal harmonic active control of power [1] applied on a hybrid engine setup. The active control was adapted for a hybrid powertrain constituted of a one-cylinder diesel engine coupled with a permanent magnet synchronous machine. The problem was formulated in the harmonic domain and the control objective was to extremalize energetic criterions. Three criterions were considered: minimizing the speed ripple of the engine, maximizing the mechanical reactive power (mechanical impedance adaptation) and maximizing the active electric power for energy harvesting. The results show that, for the first and second orders of the ripple, speed oscillations can be completely cancelled and reactive power and active power can be optimized on-line. The implicit extremal controller converged rapidly, remaining stable even when the mean engine speed changed abruptly. These results confirm the robustness and the applicability of the extremal harmonic active control for industrial applications.

International audience; This paper deals with the synchronization of a chain of nonlinear and uncertain models of nonidentical oscillators. Using Lyapunov's theory of stability, a dynamical controller guaranteeing the synchronization of the oscillators is determined. The problem of synchronization is transformed into a problem of asymptotic stabilization for a nonlinear system and then is formulated as a system of linear matrix inequalities where the parameter variations of the two oscillators and their differences are modeled by polytopic matrices. The theoretical result is successfully applied to an array of transistor-based oscillators used in "smart antenna" systems.

From the unicity and orthogonality properties of chaotic sequences, it is demonstrated that a sum of N chaotic signals generated from a fixed class of chaotic systems is unique. Consequently, within a framework of a multi-user transmission, it is shown that synchronizing N chaotic carriers that emit simultaneously on the same frequency band is feasible. In this paper, the carriers are generated from Chua’s circuits and are modulated in amplitude by the information signal. Demodulation is ensured by the minimization of a cost function. Numerical simulations show that this synchronization method is robust in presence of noise and allows the integration of a high number of users.

International audience; During the past decade, coupled oscillators have shown their efficiency as simple methods for phase control in microwave antenna arrays, and hence as alternatives to conventional electronic beam steering methods. In this paper, a new writing of the nonlinear equations proposed by R. York to describe the oscillators' locked states is presented. This has allowed the elaboration of a CAD tool which provides, in a considerably short simulation time, the frequency locking region of the coupled oscillators. This region is plotted versus the oscillators' tunings referred to the resonant frequency of the coupling circuit. A prototype circuit consisting of a five oscillators array is currently under test to validate the theory.

This paper treats solutions on the ability of a chain of non identical oscilla- tors to drive antenna arrays. Frequency approaches were studied in order to solve the problem of synchronization of the oscillators. However, in this article, a new structure of chain of oscillators is introduced. Secondly, Lyapunov theory of stability is used to design a dynamical controller guarantying the oscillators synchronization. The problem of synchronization is transformed into a problem of asymptotic stabiliza- tion for a nonlinear system. It is formulated as a system of linear matrix inequalities where the parameter variations of the two oscillators and their differences are mod- eled by polytopic matrices. The theoretical result is successfully applied to an array of transistor-based oscillators used in "smart antenna" systems. Keyword : Nonlinear systems, Control applications, Antenna arrays The demand of mobile communication services is in a continuous growth, moreover, it is estimated that the rate will be maintained in the next years. This continuous development has stimulated the research of new hardware and software solutions in order to increase the volume of exchanged data and a better management of the emitted or received electromagnetic field. Smart antenna arrays comprise a number of antennas that work in conjunction with an intelligent system that processes the received and transmitted data. The processing can be realized in a hardware or in a software way and allows smart antenna arrays to focus beams into particular directions. This problem can be partially solved by using several directional antennas. This solution divides the 360-degree coverage area into sectors. However, smart antenna arrays provide a much more effective solution by focusing the transmitted power toward user and only looking in the direction of the user for the up link signal. This ensures that the user receives the optimum quality of service and the maximum coverage from a base station. The new technologies development increases the antenna array performances and minimizes the costs of production and the occupied space. It makes them implementable in domains like wireless or satellite communications, radar systems, missile defense systems, automobile industry, etc. Smart antennas or antenna arrays are a part of communication systems that can improve their global performances. This technique can increase the spectral efficiency and reduce the multi path fading, bit error rate (BER), the co-channel interferences (CCI) and the system complexity (1). This is possible by electronically adjusting the beam pattern of the antenna array in order to provide important gain for the desired signals and small gain for interference signals. At emission, the purpose of smart antennas is to minimize the interference between the different transmitters who works on the same communication channel and, thus to more efficiently use the emitted power. For this reason, the beam shape must be controlled in order to minimize the amplitude of the side lobes and to maximize the energy in the main lobe. Moreover, the direction of the main lobe must be controlled. the focused application is inter-vehicle communication. The bandwidth will be, first of all, in the area of 24Ghz and finally around 79GHz. At these frequencies, technique like "software defined radio" can not be used. One of the main objectives that is pointed out is to develop a structure which will extend in both space and time the safety information available to drivers by using the infrastructure and vehicles as sources.

International audience; This paper introduces an efficient method for predicting mobile signal reception in satellite communications. The radio wave propagation between a satellite and a land receiver leads to two kinds of fading: slow-fading due to shadowing effect and fast-fading due to multipath effect. In order to model these fluctuations in the received signal and take into consideration the local area specificities, this paper propose a novel approach combining statistical and deterministic properties of radio propagations. For slow-fading, we use an efficient estimation of the local mean based on signal's coherence distance; for fast-fading, the principal parameter of Nakagami-m model can be estimated according to multipath nature, i.e., combination of electromagnetic interactions (reflections and diffractions) between radio wave and environment. The simulations in urban scenarios are based on Ergospace software.

In this paper, the authors propose a novel control strategy of active hybrid filters. The adopted hybrid filter consists of an active filter and a passive filter connected in parallel. The power rating of the converter is reduced compared with simple active filter. The control is introduced to allow active filtering of load harmonics and active damping of passive filter connected in parallel with the active filter. When connected in power grid, the complete system is adjusted to prevent risk of resonance as well as harmonic filtering. A complete modeling of the system is achieved using a simple structure and effective corrector is developed. An important characteristic of the proposed control scheme is that it results in a simple static output feedback controller. Complete simulation of the system validates efficiency of the control law.

Pulsed flows, characterized by periodic fluctuations in flow rate, are noise-productive, but an oscillating valve positioned in the exhaust duct can attenuate the main harmonic of pulsed flow. We define a valve adaptive control in the frequency domain implemented by a digital signal processor for experimental purposes. Results show noise reduction at ground level and tracking of process unstationarity.

International audience; This paper deals with the problem of collisionfree formation tracking of second-order Multi-Agent Systems (MAS) under communication constraints. It is assumed that an agent can only transmit its position to its neighbors at asynchronous and aperiodic discrete time instants. Velocity and acceleration of the agents are not available. Moreover, the dynamics of the leader can be controlled through an external input. Using continuousdiscrete time observers, an output feedback formation controller is designed to drive the agents to a desired formation shape and to ensure that the formation tracks the leader trajectory under directed communication topology. A potential function based mechanism is incorporated into the proposed formation tracking algorithm to avoid collision between agents. The simulation results have shown the efficacy of the proposed algorithm.

Multi-agent systems (MAS) have gained much popularity due to their vast range of applications. MAS is deployed to achieve more complex goals which could not be realized by a single agent alone. Communication and information exchange among the agents in a MAS is crucial to control its cooperative behavior. Agents share their information with their neighbors to reach a common objective, thus do not require any central monitoring unit. However, the communication among the agents is subject to various practical constraints. These constraints include irregular and asynchronous sampling periods and the availability of partial states only. Such constraints pose significant theoretical and practical challenges. In this thesis, we investigate two fundamental problems related to distributed cooperative control, namely consensus and formation control, of double-integrator MAS under these constraints. It is considered that each agent in the network can measure and transmit its position state only at nonuniform and asynchronous sampling instants. Moreover, the velocity and acceleration are not available. First, we study the problem of distributed control of leader-following consensus. A continuous-discrete time observer based leader-following algorithm is proposed. The observer estimates the position and velocity of the agent and its neighbor in continuous time from the available sampled position data. Then these estimated states are used for the computation of the control input. Both fixed and switching topology scenarios are discussed. Secondly, a consensus based distributed formation tracking protocol is designed to achieve both fixed and time-varying formation patterns. Collision avoidance problem is also studied in this thesis. An Artificial Potential Function (APF) based collision avoidance mechanism is incorporated with the formation tracking algorithm to prevent collisions between the agents while converging to a desired position. Finally, the proposed algorithms are applied on a multi-robot network, consisting of differential drive robots using Robot Operating System (ROS). A new scheme is proposed to deal with nonholonomic constraints of the robot. Efficiency of the designed algorithms and their effectiveness in real world applications are shown through both simulation and hardware results.; Les Systèmes Multi-Agents (SMA) ont gagné en popularité en raison de leur vaste gamme d'applications. Les SMA sont utilisés pour atteindre des objectifs complexes qui ne pourraient être atteints par un seul agent. La communication et l'échange d'informations entre les agents d'un SMA sont essentiels pour contrôler son comportement coopératif. Les agents partagent leurs informations avec leurs voisins pour atteindre un objectif commun, ils n'ont donc pas besoin d'unité centrale de surveillance. Cependant, la communication entre les agents est soumise à diverses contraintes pratiques. Ces contraintes incluent des périodes d'échantillonnage irrégulières et asynchrones et la disponibilité d'états partiels uniquement. Ces contraintes posent des défis théoriques et pratiques importants. Dans cette thèse, nous étudions deux problèmes fondamentaux liés au contrôle coopératif distribué, à savoir le consensus et le contrôle de formation pour un SMA à double intégrateur sous ces contraintes. On considère que chaque agent du réseau ne peut mesurer et transmettre son état de position qu'à des instants d'échantillonnage non uniformes et asynchrones. De plus, la vitesse et l'accélération ne sont pas disponibles. Dans un premier temps, nous étudions le problème du contrôle distribué du suivi de consensus. Un algorithme de suivi de leader basé sur l'observateur à temps discret continu est proposé. L'observateur estime la position et la vitesse de l'agent et de son voisin en temps continu à partir des données de position échantillonnées disponibles. Ces états estimés sont ensuite utilisés pour le calcul de l'entrée de commande. Les scénarios de topologie fixe et de topologie commutée sont discutés. Deuxièmement, un protocole de suivi de formation distribué basé sur le consensus est conçu pour réaliser des modèles de formation fixes et variant dans le temps. Le problème d'évitement de collision est également étudié dans cette thèse. Un mécanisme d'évitement de collision basé sur la fonction de potentiel artificiel (APF) est incorporé à l'algorithme de suivi de formation pour empêcher les collisions entre les agents tout en convergeant vers la position souhaitée. Enfin, les algorithmes proposés sont appliqués sur un réseau multi-robots, composé de robots à entraînement différentiel utilisant Robot Operating System (ROS). Un nouveau schéma est proposé pour faire face aux contraintes non holonomiques du robot. L'efficacité des algorithmes sont démontrées à la fois par des résultats de simulation et des expérimentations.

Multi-agent systems (MAS) have gained much popularity due to their vast range of applications. MAS is deployed to achieve more complex goals which could not be realized by a single agent alone. Communication and information exchange among the agents in a MAS is crucial to control its cooperative behavior. Agents share their information with their neighbors to reach a common objective, thus do not require any central monitoring unit. However, the communication among the agents is subject to various practical constraints. These constraints include irregular and asynchronous sampling periods and the availability of partial states only. Such constraints pose significant theoretical and practical challenges. In this thesis, we investigate two fundamental problems related to distributed cooperative control, namely consensus and formation control, of double-integrator MAS under these constraints. It is considered that each agent in the network can measure and transmit its position state only at nonuniform and asynchronous sampling instants. Moreover, the velocity and acceleration are not available. First, we study the problem of distributed control of leader-following consensus. A continuous-discrete time observer based leader-following algorithm is proposed. The observer estimates the position and velocity of the agent and its neighbor in continuous time from the available sampled position data. Then these estimated states are used for the computation of the control input. Both fixed and switching topology scenarios are discussed. Secondly, a consensus based distributed formation tracking protocol is designed to achieve both fixed and time-varying formation patterns. Collision avoidance problem is also studied in this thesis. An Artificial Potential Function (APF) based collision avoidance mechanism is incorporated with the formation tracking algorithm to prevent collisions between the agents while converging to a desired position. Finally, the proposed algorithms are applied on a multi-robot network, consisting of differential drive robots using Robot Operating System (ROS). A new scheme is proposed to deal with nonholonomic constraints of the robot. Efficiency of the designed algorithms and their effectiveness in real world applications are shown through both simulation and hardware results., Les Systèmes Multi-Agents (SMA) ont gagné en popularité en raison de leur vaste gamme d'applications. Les SMA sont utilisés pour atteindre des objectifs complexes qui ne pourraient être atteints par un seul agent. La communication et l'échange d'informations entre les agents d'un SMA sont essentiels pour contrôler son comportement coopératif. Les agents partagent leurs informations avec leurs voisins pour atteindre un objectif commun, ils n'ont donc pas besoin d'unité centrale de surveillance. Cependant, la communication entre les agents est soumise à diverses contraintes pratiques. Ces contraintes incluent des périodes d'échantillonnage irrégulières et asynchrones et la disponibilité d'états partiels uniquement. Ces contraintes posent des défis théoriques et pratiques importants. Dans cette thèse, nous étudions deux problèmes fondamentaux liés au contrôle coopératif distribué, à savoir le consensus et le contrôle de formation pour un SMA à double intégrateur sous ces contraintes. On considère que chaque agent du réseau ne peut mesurer et transmettre son état de position qu'à des instants d'échantillonnage non uniformes et asynchrones. De plus, la vitesse et l'accélération ne sont pas disponibles. Dans un premier temps, nous étudions le problème du contrôle distribué du suivi de consensus. Un algorithme de suivi de leader basé sur l'observateur à temps discret continu est proposé. L'observateur estime la position et la vitesse de l'agent et de son voisin en temps continu à partir des données de position échantillonnées disponibles. Ces états estimés sont ensuite utilisés pour le calcul de l'entrée de commande. Les scénarios de topologie fixe et de topologie commutée sont discutés. Deuxièmement, un protocole de suivi de formation distribué basé sur le consensus est conçu pour réaliser des modèles de formation fixes et variant dans le temps. Le problème d'évitement de collision est également étudié dans cette thèse. Un mécanisme d'évitement de collision basé sur la fonction de potentiel artificiel (APF) est incorporé à l'algorithme de suivi de formation pour empêcher les collisions entre les agents tout en convergeant vers la position souhaitée. Enfin, les algorithmes proposés sont appliqués sur un réseau multi-robots, composé de robots à entraînement différentiel utilisant Robot Operating System (ROS). Un nouveau schéma est proposé pour faire face aux contraintes non holonomiques du robot. L'efficacité des algorithmes sont démontrées à la fois par des résultats de simulation et des expérimentations.