Distributed consensus and tracking control of second‐order time‐varying nonlinear multi‐agent systems

In this paper, the distributed consensus and tracking protocols are developed for the second‐order time‐varying nonlinear multi‐agent systems under general directed graph. Firstly, the consensus and tracking problems can be converted into a conventional stabilization control problem. Then a state transformation is employed to deal with the time‐varying nonlinearities. By choosing an appropriate time‐varying parameter and coupling strengths, exponential consensus and tracking of second‐order nonlinear multi‐agent systems can be achieved. Finally, a simulation is given to illustrate the effectiveness of the proposed consensus and tracking protocols. Copyright © 2017 John Wiley & Sons, Ltd.     

Consensus for multi‐agent systems under double integrator dynamics with time‐varying communication delays

In this paper, the consensus control problems for multi‐agent systems under double integrator dynamics with time‐varying communication delays are investigated. We assume that the interaction graphs among agents are directed. Two kinds of protocols are considered. One is an absolute damping protocol, and the other is a relative damping protocol. For the first protocol, Lyapunov–Razumikhin functional techniques are used. We derive sufficient conditions that guarantee that all agents asymptotically reach consensus under fixed topology and switching topology, respectively. Moreover, the allowable upper bound for communication delays is given. For the second protocol, Lyapunov–Krasovskii functional techniques are used. Linear matrix inequality (LMI)‐form sufficient conditions are obtained to guarantee the consensus problems to be solved under fixed topology and switching topology, respectively. The allowable upper bound for communication delays is given as well. The feasibilities of the demanded LMIs are also discussed. Finally, numerical simulations are provided to illustrate the effectiveness of our theoretical results. Copyright © 2011 John Wiley & Sons, Ltd.     

A multi‐resolution multi‐classifier system for speaker verification

This paper describes a Speaker Verification System based on the use of multi resolution classifiers in order to cope with performance degradation due to natural variations of the excitation source and of the vocal tract. The different resolution representations of the speaker are obtained by considering multiple frame lengths in the feature extraction process and from these representations a single Pseudo‐Multi Parallel Branch (P‐MPB) Hidden Markov Model is obtained. In the verification process, different resolution representations of the speech signal are classified by multiple P‐MPB systems: the final decision is obtained by means of different combination techniques. The system based on the Weighted Majority Vote technique considerably outperforms baseline systems: improvements are between 15% and 38%. The execution time of the verification process is also evaluated and it proves to be very acceptable, thus allowing the use of the approach for applications in real time systems.     

Generation of augmented video sequences combining behavioral animation and multi‐object tracking

In this paper we present a novel approach to generate augmented video sequences in real‐time, involving interactions between virtual and real agents in real scenarios. On the one hand, real agent motion is estimated by means of a multi‐object tracking algorithm, which determines real objects' position over the scenario for each time step. On the other hand, virtual agents are provided with behavior models considering their interaction with the environment and with other agents. The resulting framework allows to generate video sequences involving behavior‐based virtual agents that react to real agent behavior and has applications in education, simulation, and in the game and movie industries. We show the performance of the proposed approach in an indoor and outdoor scenario simulating human and vehicle agents. Copyright © 2009 John Wiley & Sons, Ltd.     

Adaptive lattice‐based light rendering of participating media

The visual world around us displays a rich set of light effects because of translucent and participating media. It is hard and time consuming to render these effects with scattering, caustic, and shaft because of the complex interaction between light and different media. This paper presents a new rendering method based on adaptive lattice for lighting participating media of translucent materials such as marble, wax, and shaft light. Firstly, on the basis of the lattice‐based photon tracing model, multi‐scale hierarchical lattice was constructed by mixed lattice types sampling combined cubic Cartesian and face‐centered cubic with view‐dependent adaptive resolution. Then, an adaptive method to trace diffuse photons and marked specular photons with different phase functions was suggested. Multiple lights and heterogeneous materials were also considered here. Further, the mixed rendering method and GPU accelerate technology were introduced to render different light effects under different participating media. Copyright © 2011 John Wiley & Sons, Ltd.     

Portable multi‐gray scale video playing scheme for high‐performance electrowetting displays

Electrowetting display technology is realized by tuning the surface energy of a hydrophobic surface by applying a voltage based on electrowetting mechanism. Electrowetting displays have favorable optical properties combined with reflective paper‐like performance. It has been successfully demonstrated in reflective mode with high switching speed. In this paper, we propose a portable driving scheme that can display 4‐bit gray scale dynamic video using an active matrix electrowetting display. The proposed driving scheme includes an electronic system and a dynamic driving waveform design. High‐performance multi‐gray video playing and quick response were obtained for a Quarter Video Graphics Array electrowetting display cell fabricated by our team.     

A dual‐band eight‐antenna multi‐input multi‐output array for 5G metal‐framed smartphones

A dual‐band eight‐antenna array operating in the long‐term evolution (LTE) band 41 (2.496‐2.69 GHz) and 3.5‐GHz band (3.3‐3.7 GHz) for fifth‐generation (5G) metal‐framed smartphone is presented. The proposed dual‐band antenna array is composed of four identical dual‐antenna building blocks (DABBs). Each DABB consists of two identical antenna elements with a neutralization line between them. The antenna array is simulated, fabricated, and measured. The isolations are better than 10.5 dB and 11.0 dB in the low band (LB; LTE band 41) and high band (HB; 3.5‐GHz band). The total efficiencies are 41% to 54% and 46% to 64% in the two operation bands, respectively. In addition, the measured envelope correlation coefficients are less than 0.11 and 0.06, the calculated channel capacities are better than 34.5 and 36.3 bps/Hz in the LB and HB, respectively. Furthermore, four hand‐grip scenarios are investigated, and results show that proposed antenna array can maintain excellent multiple‐input multiple‐output performances in all scenarios.     

Adaptive fault‐tolerant time‐varying formation tracking for multiagent systems with multiple leaders

In this paper, an adaptive fault‐tolerant time‐varying formation control problem for nonlinear multiagent systems with multiple leaders is studied against actuator faults and state‐dependent uncertainties. Simultaneously, the followers form a predefined formation while tracking reference signal determined by the convex combination of the multiple leaders. Based on the neighboring relative information, an adaptive fault‐tolerant formation time‐varying control protocol is constructed to compensate for the influences of actuator faults and model uncertainties. In addition, the updating laws can be adjusted online through the adaptive mechanism, and the proposed control protocol can guarantee that all the signals in the closed‐loop systems are bounded. Lyapunov‐like functions are addressed to prove the stability of multiagent systems. Finally, two examples are provided to demonstrate the effectiveness of the theoretical results.     

Time‐varying output formation control for linear multi‐agent systems with switching topologies

Time‐varying output formation control problems for linear multi‐agent systems with switching topologies are studied, where two types of switching topologies are considered: (1) the topology is undirected and jointly connected, and 2) each topology is directed and has a spanning tree. An output formation protocol under switching topologies is constructed using the outputs of neighboring agents via dynamic output feedback. Two algorithms are proposed to design the dynamic protocols under both jointly connected topologies and switching directed topologies. Time‐varying output formation feasibility conditions are given to describe the compatible relationship among the desired time‐varying output formation, the dynamics of each agent, and the switching topologies. The stability of the closed‐loop multi‐agent systems under the proposed two algorithms is investigated based on the common Lyapunov functional theory and the piecewise Lyapunov functional theory, respectively. In the case where the topologies are jointly connected, time‐varying output formation can be achieved for multi‐agent systems using the designed protocol if the given time‐varying output formation satisfies the feasible constraint. For the case where the switching topologies are directed and have a spanning tree, the time‐varying output formation can be realized if the output formation feasibility constraint is satisfied and the dwell time is larger than a positive threshold. Moreover, approaches to determine the output formation references are provided to describe the macroscopic movement of the time‐varying output formation. Finally, numerical simulation results are presented to demonstrate the effectiveness of the theoretical results. Copyright © 2016 John Wiley & Sons, Ltd.     

Consensus analysis of continuous‐time second‐order multi‐agent systems with nonuniform time‐delays and switching topologies

In this study, consensus problems for second‐order multi‐agent systems with nonuniform and switching topologies are investigated. Each agent has a self‐delay, and each delay is independent of the others. As a measure of the disagreement dynamics, a class of positive semi‐definite Lyapunov–Krasovskii functions are introduced. Using algebraic graph theory and these Lyapunov–Krasovskii functions, sufficient conditions are derived by contradiction under which all agents asymptotically reach consensus. Finally, the effectiveness of the obtained theoretical results is demonstrated through numerical simulations.     

Adaptive finite‐time control for nonlinear teleoperation systems with asymmetric time‐varying delays

This paper addresses the adaptive finite‐time control problem of nonlinear teleoperation system in the presence of asymmetric time‐varying delays. To achieve the finite‐time position tracking, a novel adaptive finite‐time coordination algorithm based on subsystem decomposition is developed. By introducing a switching‐technique‐based error filtering into our design framework, the complete closed‐loop master (slave) teleoperation system is modeled as a special class of switched system, which is composed of two subsystems. To analyze such system, a finite‐time state‐independent input‐to‐output stability criterion is first developed for some normal switched nonlinear delayed systems. Then based on the classical Lyapunov–Krasovskii method, the stability of complete closed‐loop systems is obtained. It is shown that the proposed scheme can make the position errors converge into a deterministic domain in finite time when the robots continuously contact with human operator and/or the environment in the presence of asymmetric time‐varying delays. Finally, the simulation results are given to demonstrate the effectiveness. Copyright © 2015 John Wiley & Sons, Ltd.     

Nonlinear adaptive learning control for unknown time‐varying parameters and unknown time‐varying delays

A new adaptive learning control approach is proposed for a class of first‐order nonlinear systems with two unknown time‐varying parameters and an unknown time‐varying delay. By reconstructing the system equation, all unknown time‐varying terms, including the time‐varying delay, are combined into an unknown periodic time‐varying vector, which is estimated by a periodic adaptive mechanism. By constructing a Lyapunov–Krasovskii‐like composite energy function (CEF), we prove the boundedness of all signals and the convergence of the tracking error. The results are extended to two classes of high‐order nonlinear systems with mixed parameters. Three simulation examples are provided to illustrate the effectiveness of the control algorithms proposed in this paper. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Consensus of multi‐agent systems with time‐varying topology: An event‐based dynamic feedback scheme

The event‐based control strategy is an effective methodology for reducing the controller update and communication over the network. In this paper, the event‐based consensus of multi‐agent systems with linear dynamics and time‐varying topology is studied. For each agent, a state‐dependent threshold with an exponentially decaying bound is presented to determine the event times, and a new event‐based dynamic feedback scheme is proposed. It is shown that the controller update for each agent is only dependent on its own event times, which reduces significantly the controller update or computation for each agent. Moreover, based on the event‐based dynamic feedback scheme and the event triggering function presented in this paper, the continuous communication among neighboring agents is avoided, and the Zeno‐behavior of the closed‐loop systems is excluded. A numerical example is given to illustrate the effectiveness of theoretical results. Copyright © 2016 John Wiley & Sons, Ltd.     

A compact multi‐band multi‐input multi‐output antenna for 4G/5G and IoT devices using theory of characteristic modes

A compact four element multi‐band multi‐input multi‐output (MIMO) antenna system for 4G/5G and IoT applications is presented in this paper. The proposed antenna is developed using the theory of characteristic modes helping in systematic design of MIMO antenna system. It consists of four L‐shaped planar inverted‐F antenna (PIFA) elements each operating at 3.5, 12.5, and 17 GHz bands with the bandwidth of 359 MHz, 1 GHz, and more than 3.7 GHz, respectively. The proposed antenna system is suitable for both 4G/5G and internet of things devices as it shows the satisfactory MIMO system performance. Good isolation characteristics are observed by implementing complimentary Metamaterial structure on the ground plane resulting in isolation level lower than ?21 dB between the antenna elements. The proposed antenna is fabricated and experimental results are also presented and discussed.     

Consensus seeking via iterative learning for multi‐agent systems with switching topologies and communication time‐delays

This paper deals with the high‐precision consensus seeking problem of multi‐agent systems when they are subject to switching topologies and varying communication time‐delays. By combining the iterative learning control (ILC) approach, a distributed consensus seeking algorithm is presented based on only the relative information between every agent and its local (or nearest) neighbors. All agents can be enabled to achieve consensus exactly on a common output trajectory over a finite time interval. Furthermore, conditions are proposed to guarantee both exponential convergence and monotonic convergence for the resulting ILC processes of multi‐agent consensus systems. In particular, the linear matrix inequality technique is employed to formulate the established convergence conditions, which can directly give formulas for the gain matrix design. An illustrative example is included to validate the effectiveness of the proposed ILC‐motivated consensus seeking algorithm. Copyright © 2016 John Wiley & Sons, Ltd.     

Adaptive tracking for MIMO nonlinear systems with Unknown fast time‐varying parameters

In this paper, we consider a class of MIMO nonlinear systems with fast time‐varying parametric uncertainties. First, the tracking problem of general nonlinearly time‐varyingly parameterized systems is solved. Then, a Lyapunov‐based singularity free adaptive controller is proposed for the considered system. Specifically, an estimation approach with a proportional plus integral adaptation scheme is utilized to update the estimations of the unknown parameters under a mild assumption that the signs of the leading minors of the input gain matrix are known. The asymptotic stability is achieved with full state feedback. Furthermore, we design an output feedback controller by utilizing a standard high‐gain observer and achieve uniformly ultimately bounded convergence. Simulation examples illustrate the effectiveness of the proposed methods.     

A multi‐plane optical see‐through head mounted display design for augmented reality applications

Augmented reality (AR) display technology greatly enhances users' perception of and interaction with the real world by superimposing a computer‐generated virtual scene on the real physical world. The main problem of the state‐of‐the‐art 3D AR head‐mounted displays (HMDs) is the accommodation‐vergence conflict because the 2D images displayed by flat panel devices are at a fixed distance from the eyes. In this paper, we present a design for an optical see‐through HMD utilizing multi‐plane display technology for AR applications. This approach manages to provide correct depth information and solves the accommodation‐vergence conflict problem. In our system, a projector projects slices of a 3D scene onto a stack of polymer‐stabilized liquid crystal scattering shutters in time sequence to reconstruct the 3D scene. The polymer‐stabilized liquid crystal shutters have sub‐millisecond switching time that enables sufficient number of shutters to achieve high depth resolution. A proof‐of‐concept two‐plane optical see‐through HMD prototype is demonstrated. Our design can be made lightweight, compact, with high resolution, and large depth range from near the eye to infinity and thus holds great potential for fatigue‐free AR HMDs.     

Reduced‐order state estimation for linear time‐varying systems

We consider reduced‐order and subspace state estimators for linear discrete‐time systems with possibly time‐varying dynamics. The reduced‐order and subspace estimators are obtained using a finite‐horizon minimization approach, and thus do not require the solution of algebraic Lyapunov or Riccati equations. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

A necessary and sufficient condition for the controllability of single‐leader multi‐chain systems

In this work, the controllability of single‐leader multi‐agent systems with chain structures is studied. It is shown that the necessary and sufficient condition for the multi‐chain system to be controllable is that there exist no two chain lengths in the form ? ₁=i + k ₁(2i + 1) and ? ₂=i + k ₂(2i + 1), where i is some natural number and k ₁ and k ₂ some nonnegative integers. Using this condition, the author derives an upper bound based on the length of the longest chain and proves that if the number of chains exceeds this bound, the multi‐chain system must be uncontrollable. In addition, the author investigates an augmented system constructed by connecting some follower nodes of the multi‐chain system and obtains a sufficient condition for the augmented system to be uncontrollable. Finally, the author shows how to select a minimum number of additional leaders to make an uncontrollable multi‐chain system controllable. Numerical examples are provided to illustrate the results. Copyright © 2016 John Wiley & Sons, Ltd.