Band-limited Networks Research Articles

Quantized-output-feedback practical prescribed-time design strategy for decentralized tracking of a class of interconnected nonlinear systems with unknown interaction delays

This paper proposes a decentralized practical prescribed-time (PT) tracking design using quantized output feedback (QOF) for uncertain interconnected lower-triangular systems with unknown time-delay interconnections. The local output signals are assumed to be only measured and quantized for the PT tracker design under a band-limited network. By employing a PT-dependent scaling function, a decentralized memoryless PT observer based on quantized local outputs is developed to estimate local unmeasurable state variables. Owing to output quantization, the available output feedback signals become discontinuous. As a result, the tracking error between the actual (i.e., unquantized) local output and the local desired signal cannot be utilized in the local virtual controller. To address this issue, a novel adaptive compensation mechanism is derived to design the local PT neural network tracking laws using only quantized local outputs and estimated states. The proposed PT tracking controller does not require information on the interconnected nonlinear functions and interaction delays. During the Lyapunov stability analysis, the boundary layer error decomposition approach is employed to address the issue of non-differentiability in the local virtual control laws. The proposed QOF control system achieves practical PT stability. It is shown that the settling time of local tracking errors can be predetermined, regardless of the design parameters and initial conditions. Finally, the proposed QOF decentralization strategy is supported with illustrative examples and a comparison to demonstrate its benefits.

Robust trajectory tracking with adjustable performance of underactuated surface vessels via quantized state feedback

This paper investigates a robust quantized state feedback tracking problem with preselected performance of uncertain underactuated surface vessels (USVs) with state and input quantization under a band-limited network. With the feedback of all quantized states and control inputs, a preselected-performance-based tracking strategy using quantized states is proposed to achieve robust tracking that does not require any knowledge of the USV dynamics and function approximators. Design conditions of performance functions are introduced to ensure the stability of the closed-loop system using quantized feedback. In the Lyapunov sense, it is analyzed that all error surfaces remain within the preselected performance functions for all time. Finally, some convincing simulation comparison results are provided to illustrate the theoretical results.

Quantized-State-Feedback-Based Neural Control for a Class of Switched Nonlinear Systems With Unknown Control Directions

This paper investigates the problem of unknown virtual control directions in a state-quantized adaptive recursive control design for a class of arbitrarily switched uncertain pure-feedback nonlinear systems in a band-limited network. State quantization is considered for state feedback control in a band-limited network. The primary contribution of this study is to provide a quantized state feedback adaptive control strategy to address the unknown control direction and arbitrarily switched nonaffine nonlinearities. Herein, a coupling problem between Nussbaum functions and quantization errors caused by quantized state feedback control laws is considered in the Lyapunov-based design and stability analysis. A state-quantized adaptive recursive control scheme using the function approximation is constructed without a priori knowledge of the signs of the control gain functions, where the estimated parameters and Nussbaum-type functions are adaptively updated via quantized states. Theoretical lemmas are derived to show that the adaptive parameters and quantization errors of the closed-loop signals are bounded using the proposed control scheme. The boundedness of the closed-loop signals and the convergence of tracking error to a neighborhood of the origin are proved using the common Lyapunov function approach. Two simulation examples are shown to illustrate the effectiveness of the proposed theoretical result.

Networked scheduling for decentralized load frequency control

This paper investigates the scheduling process for multi-area interconnected power systems under shared but band-limited networks and decentralized load frequency controllers. To cope with sub-area information and avoid node collision of large-scale power systems, round-robin and try-once-discard scheduling are used to schedule sampling data among different sub-grids. Different from existing decentralized load frequency control methods, this paper studies multi-packet transmission scheme and introduces scheduling protocols to deal with multi-node collision. Considering the scheduling process and decentralized load frequency controllers, an impulsive power system closed-loop model is well established. Furthermore, sufficient stabilization criteria are derived to obtain decentralized output feedback controller gains and scheduling protocol parameters. Under the designed decentralized output feedback controllers, the prescribed system performances have been achieved. Finally, a three-area power system example is used to verify the effectiveness of the proposed scheduling method.

Adaptive event-based robust passive fault tolerant control for nonlinear lateral stability of autonomous electric vehicles with asynchronous constraints

This work solves the robust passive fault-tolerant control problem for autonomous electric vehicles based on an adaptive event triggered mechanism. Firstly, given the system uncertainties from the tire dynamics and the longitudinal speed, the T–S fuzzy model method is used to approximate the vehicle lateral dynamics. Secondly, taking the communication constraints caused by band-limited networks into account, an adaptive event-triggered scheme is introduced in the process of the control design. Moreover, the asynchronous constraint of the weight function between the controller and system is considered. Thirdly, considering that the actuator faults are inevitably encountered in the control system, a robust passive fault-tolerant control method is proposed to improve vehicle performances. Finally, simulations are carried out to illustrate the effectiveness and robustness of the proposed approach.

A survey on sliding mode control for networked control systems

In the framework of the networked control systems (NCSs), the components are connected with each other over a shared band-limited network. The merits of NCSs include easy extensibility, resource sharing, high reliability and so forth. However, the insertion of the communication network brings many challenges, such as network-induced phenomena and cyber-security, which should be handled properly. On the other hand, the sliding mode control (SMC) has become an effective scheme for the synthesis of NCSs due to its strong robustness and SMC has wide applications in NCSs. In this paper, some recent advances on SMC for NCSs are reviewed. In particular, some new SMC schemes for NCSs subject to time-delay, packet losses, quantisation and uncertainty/disturbance are summarised firstly. Subsequently, the problem of SMC for NCSs under scheduling protocols is discussed, where different communication protocols are introduced for the energy saving purpose during the synthesis of NCSs. Next, some recent results on SMC for NCSs with actuator/sensor fault and cyber-attack are recalled. Finally, the conclusion is provided and the potential research challenges on SMC for NCSs are pointed out.

Haptic Data Prediction and Extrapolation for Communication Traffic Reduction of Four-Channel Bilateral Control System

Robotic teleoperation with a bilateral control system has attracted attention owing to its haptic transmission performance. However, conventional bilateral control systems require broadband communication to transmit the vivid haptic sensation. This problem limits the application range of the bilateral control systems. The communication traffic can be reduced by predicting and extrapolating the incoming data. However, in the conventional prediction-based methods, only one type (e.g., position, velocity, or force) of data is transmitted per one direction because of the difficulty of predicting multiple independent data. The novelty of this article is the realization of the prediction-based traffic reduction in the four-channel bilateral control system that transmits accurate haptic sensation by communicating both position and force data. By equivalently transforming this control scheme in the structure of impedance control, the transmit data are summed up to one data, equilibrium force. The equilibrium force is not only transmitted but extrapolated on the receiver side. As a result, the communication frequency becomes low without degrading haptic transmission performance. The validity of the proposed method was confirmed through experiments and succeeded to reduce the communication data size to less than 3.0%. The proposed method helps to realize a high-performance bilateral control system on band-limited networks.

Plant input-mapping-based predictive control of systems through band-limited networks

A new control method for network-based control systems, with guaranteed closed-loop stability, is proposed. The method substantially enhances the conventional networked model-based predictive control (NMBPC) schemes. In conventional NMBPC methods, associated with a pre-specified range of possible time delays, a vector of stabilising control signals is determined and transmitted to the plant side of the network, where, based on the actually occurred time delay, just one entry of the control vector is selected and applied to the plant. In practice, stability issues may arise when the network time delay is not small enough. A modified method, using the plant-input mapping (PIM) discretisation technique, with the possibility of guaranteeing the closed-loop stability is introduced. In order to alleviate the deficiency of some existing transfer function-based methods, which implicitly assume a non-realistic zero initial condition at the outset of every sampling instant, a state-space representation is proposed. Simulation studies on well-known benchmark problems demonstrate the effectiveness of the proposed PIM-based NMBPC method.

Special issue on ubiquitous multimedia services

1 IntroductionEmerging ubiquitous multimedia services are expected tobe available anytime, anywhere, and using differentcomputing devices. Services such as audio/video streaming,digital libraries, on-line businesses, and live camera remotesurveillance are widely deployed. Users will be able toaccess these services anytime, anywhere, and using anycomputing device in a pervasive way. For example, a usermay bring a PDA on a field trip, carry a laptop (with bothwireless and wired network cards) on a business trip, usehigh performance workstations at work, and use desktopPCs at home (with dial-up, cable, or DSL connection). Inanother example, a user continues to watch the soccer gameover home TV, while he watches the game through a mobiledevice out of home. Some other ubiquitous multimediaservices include mobile games and entertainment, mobileblog, mobile community, home network, and so on.Since ubiquitous multimedia services are constructedon the convergence of various networks (wired or wirelessnetworks, broadcasting or multicasting networks, broad-band or band-limited networks, etc.) and devices (PC, PDA,Cell Phone, TV, Camera, etc.), the new challenge inmultimedia service management is to deal with heteroge-neous client capabilities and dynamic end-to-end resourcesavailability, and to ensure satisfactory service quality foreach client. Additionally, privacy, security and ethicalissues are becoming increasingly important topics inubiquitous services.This special issue of the Information Systems Frontiersaims to expose the readership to the latest research resultson ubiquitous multimedia services. It is composed of sevenselected papers, covering the interesting topics, e.g., mobilechatting system, ubiquitous surveillance system, personal-ized news consuming system, home networking systems,etc., demonstrating pioneer work, investigating the novelsolutions and discussing the future trends in this field.2 The papers in this special issueThe first paper, “MILC: A Secure and Privacy-PreservingMobile Instant Locator with Chatting” by (A. Loukas et al.2010), presents a mobile application scheme, named MILC,that not only supports location-based services and mobileinstant messaging but also provides real security andprivacy solutions. Thus, the users can chat, interchangegeographic coordinates and make Splashes in real-time incontrol of their own personal information and privatesphere. The scheme’s architecture, protocols, security andprivacy issues are presented and discussed in detail.Additionally, the prototype implemented in Google’sAndroid OS shows the system’s good properties.

Adaptive QoS control of multimedia transmission over band-limited networks

Consumers increasingly demand high quality of service (QoS) for multimedia applications. Application-layer QoS control mechanisms that do not make specific references to coding semantics tend to provide the most robust solutions for delivery of multimedia data over band-limited networks. We propose an adaptive and robust QoS algorithm for band-limited networks that integrates explicit receiver-sender rate control, rate shaping with multiple quantization parameters and adaptive forward error correction (FEC). Experimental results indicate that an average improvement of 0.5 dB PSNR can be achieved compared to other methods.

Oscillatory Decay of Band-Limited Impulse Responses

This paper presents a simple derivation of the general form of impulse responses corresponding to strictly band-limited networks, showing that all such responses must decay in an oscillatory manner.