Effects Of Network Delay Research Articles

Design of Networked Control Systems With Explicit Compensation for Time-Delay Variations

In this paper, the effects of network delay among interconnecting elements of a distributed computer network control system are analyzed. Experimental tests have been accomplished to show the influence of the combined effects of the network delay (between sensor/controller and controller/actuator) on the overall performance of a feedback control system. For this purpose, a proportional-plus-integral (PI) controller has been used. This controller has been designed, using the well-known direct synthesis method and implemented in a didactic networked control system platform. Corresponding ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> -transform) difference equations have been used, assuming time-triggered (regular) samplings. The augmented PI controller (with compensation of the control signal and estimation of missing measurements) is developed. Stability analysis is performed to verify the validity of this scheme. The results presented in the paper show that the dynamic behavior of the closed-loop system can be improved using the proposed technique.

On the Effects of Network Delays on an Energy-based Controller

In this paper, the design of an energy-based controller for a platoon of nonholonomic vehicles is presented and its performance is analysed for the case of random time delays in the network. The nonholonomic constraints of the models are taken into account during the design process by considering them in the goal virtual Lagrange function. The introductory section gives an overview of the energy methods for the case of mass point vehicles. Subsequently, the strategy is extended to apply to the case of nonholonomic vehicles. The controller is analysed by means of simulation tools in order to evaluate the effects of random Rayleigh distributed delays on the network.

L 2-gain analysis for networked predictive control systems based on switching method

This article deals with the problem of L 2-gain for a class of networked control systems with time-varying network delay in both forward and feedback channels. An improved network predictive control scheme is proposed to compensate the effects of network delay and data dropout using a switching control strategy. Based on the average dwell time method, the restrictions that the original delay-compensation strategy imposes on the subsystems are relaxed and a sufficient condition for weighted L 2-gain is developed for a class of switching signal. An example illustrates the effectiveness of the proposed method.

Discrimination of visual and haptic rendering delays in networked environments

Many networked human-machine interface systems have a distributed structure for certain purposes such as more computational power, tele-presence, collaboration, and portability. However, network delays are inevitable in the distributed structure, and often make sensory information delivered behind time to the user. In the literature, the effect of network delays on the quality of information presentation has been considered with respect to task performances in most cases. In this paper, we pay attention to a more stringent criterion, namely whether perceptual artifacts caused by network delays are perceptible by the user. We examined minimum perceptible visual and/or haptic rendering delays by measuring their discrimination thresholds between normal and delayed virtual environments with and without a task, and report the results in this paper. We also provide a simple guideline for determining whether active delay compensation algorithms are required in a networked human-machine interface system by comparing representative network delays to the measured discrimination thresholds.

The Effects of Simulated Inertia and Force Prediction on Delayed Telepresence

This paper presents two methods aimed at alleviating the negative effects of network delays on teleoperation. The problem of telepresence across delayed networks is well known. A delay in feedback information such as visual and haptic data can make the task at hand very unintuitive and difficult for the operator. The first presented method investigates the hypothesis that simulated inertia in the haptic input device can be a supporting factor during teleoperation across delayed networks. An experiment involving 36 human subjects was carried out under varying network and inertia conditions. Psychophysical experiments were conducted to determine suitable values of inertia. However, simulated inertia was found to be neither a supporting factor nor a detrimental factor to operator performance and immersion in the presence of both delayed and non-delayed networks. The second presented method is a force prediction approach, which extends the teleoperation system with a local force model. This is a learned force model situated locally at the operator-side. Instead of relying on the delayed force signals from the teleoperator-side, haptic information can be extracted from this local force model. An experiment has been created to demonstrate the benefits of this approach in compensating for the instabilities due to time delay.

Networked Predictive Control of Systems With Random Network Delays in Both Forward and Feedback Channels

The design problem of networked control systems (NCS) with constant and random network delay in the forward and feedback channels, respectively, is considered in this paper. A novel networked predictive control (NPC) scheme is proposed to overcome the effects of network delay and data dropout. Stability criteria of closed-loop NPC systems are presented. The necessary and sufficient conditions for the stability of closed-loop NCS with constant time delay are given. Furthermore, it is shown that a closed-loop NPC system with bounded random network delay is stable if its corresponding switched system is stable. Both simulation study and practical experiments show the effectiveness of the control scheme

Stable task load balancing strategies for Cooperative control of networked autonomous air vehicles

We introduce a mathematical model for the study of cooperative control problems for multiple autonomous air vehicles (AAVs) connected via a communication network. We propose a cooperative control strategy based on task-load balancing that seeks to ensure that no vehicle is underutilized and we show how to characterize task-load balancing as a stability property. Then, using Lyapunov stability analysis, we provide conditions under which task-load balancing is achieved even in the presence of communication delays. Finally, we investigate performance properties of the cooperative controller using Monte Carlo simulations. This shows the benefits of cooperation and the effects of network delays and communication topology on performance

Haptic Media Synchronization for Remote Surgery through Simulation

Network delay affects the operational instability of haptic displays for telehaptic remote surgery applications using simulation. A synchronization control mechanism for haptic media reduces network delay's effects and enhances telehaptic capability in these applications

INFLUENCE OF NETWORK DELAYS IN RESIDUAL COMPUTATION

A challenging problem that motivates this work is the network delay effects in residual computation. Residuals are assumed to be identically zero in fault-free situations whereas deviations from zero alert the presence of fault in the system. In practice residuals are not identically zero due to various factors (measurements noises, modelling uncertainties, delays, and so on). This work is focused on the study of the availability of data, due to delays in the communication network, to compute residuals. An optimal dynamic alignment of data in a time window (Dynamic Time Warping) is proposed and tested to reduce errors when computing residuals.

PREDICTIVE CONTROL OF NETWORKED SYSTEMS WITH RANDOM DELAYS

This paper is concerned with the design of networked control systems with random network delay in the forward and feedback channels and gives stability criteria of closed-loop networked predictive control systems. The principle of the predictor is adopted to overcome the effects of network delay. The necessary and sufficient conditions on the stability of the closed-loop networked control system are derived, which provide useful analytical stability criteria. It is shown that closed-loop system with bounded random network delay is stable if the corresponding switched system is stable.

Gain Scheduler Middleware: A Methodology to Enable Existing Controllers for Networked Control and Teleoperation—Part I: Networked Control

Conventionally, in order to control an application over a data network, a specific networked control or teleoperation algorithm to compensate network delay effects is usually required for controller design. Therefore, an existing controller has to be redesigned or replaced by a new controller system. This replacement process is usually costly, inconvenient, and time consuming. In this paper, a novel methodology to enable existing controllers for networked control and teleoperation by middleware is introduced. The proposed methodology uses middleware to modify the output of an existing controller based on a gain scheduling algorithm with respect to the current network traffic conditions. Since the existing controller can still be utilized, this approach could save much time and investment cost. Two examples of the middleware applied for networked control and teleoperation with IP network delays are given in these two companion papers. Part I of these two companion papers introduces the concept of the proposed middleware approach. Formulation, delay modeling, and optimal gain finding based on a cost function for a case study on DC motor speed control with a proportional-integral (PI) controller are also described. Simulation results of the PI controller shows that, with the existence of IP network delays, the middleware can effectively maintain the networked control system performance and stabilize the system. Part II of this paper will cover the use of the proposed middleware concept for a mobile robot teleoperation.

Gain Scheduler Middleware: A Methodology to Enable Existing Controllers for Networked Control and Teleoperation—Part II: Teleoperation

Conventionally, in order to control an application over a data network, a specific networked control or teleoperation algorithm to compensate network delay effects is usually required for controller design. Therefore, an existing controller has to be redesigned or replaced by a new controller system. This replacement process is usually costly, inconvenient, and time consuming. In this paper, a novel methodology to enable existing controllers for networked control and teleoperation by middleware is introduced. The proposed methodology uses middleware to modify the output of an existing controller based on a gain scheduling algorithm with respect to the current network traffic conditions. Since the existing controller can still be utilized, this approach could save much time and investment cost. Two examples of the middleware applied for networked control and teleoperation with IP network delays are given in these two companion papers. Part I of these two companion papers introduces the concept of the proposed middleware approach. Formulation, delay modeling, and optimal gain finding based on a cost function for a case study on DC motor speed control with a proportional-integral (PI) controller are also described. Simulation results of the PI controller shows that, with the existence of IP network delays, the middleware can effectively maintain the networked control system performance and stabilize the system. Part II of this paper will cover the use of the proposed middleware concept for a mobile robot teleoperation.

Self-adaptive clock synchronization for computational grid

This paper presents an innovative method to synchronize physical clocks for a computational grid, in particular for a computational grid linked through the asynchronous Intranet or Internet environments. The method discussed is an asynchronous self-adaptive clock synchronization mechanism. Two strategies for clock synchronisation are introduced. (1) Use continuous time intervals to calculate the precision of clocks, which can reduce the effect of network delay efficiently. (2) Every node synchronizes its clock with its leader actively. In addition, a node self-adaptive model is presented, and the relationship between the clock precision and synchronization time is induced, hence a node can predict when it should begin the synchronization process. Detailed simulation and extension of this issue are provided at the end of the paper. The presented model is both practical and feasible.

An experimental study on the effects of Network delay in Cooperative Shared Haptic Virtual Environment

A cooperative shared haptic virtual environment (CSHVE), where the users can kinesthetically interact and simultaneously feel each other over the network, is beneficial for many distributed VR simulations. A little is known about the influences of the network delay on the quality of haptic sensation and the task performance in such environments. This paper has addressed these issues by conducting a subjective evaluation to the force feedback and the task performance in a tele-handshake cooperative shared haptic system for different delay setting. Also, four subjective measures to evaluate the quality of haptic in CSHVEs have been proposed. These measures are the feeling of force, the consistency between the haptic-visual feedback, the vibration, and the rebound in the haptic device. In addition, a detailed description of the haptic sensation for different time delays is also described. A network emulator was utilized to simulate the real network cloud. An objective evaluation of the force feedback and the performance showed that there was no effect of the delay on the force feedback. It had a negative impact on the task performance. In general, the quality of haptic deteriorated as the delay increased and vibration and rebound hampered the users for large time delay. The haptic-visual consistency was robust in the presented system even for large time delays. Nevertheless, the examined tele-handshake system was able to deliver a high quality of haptic sensation, good performance, and stability for large time delay over the network.

Obtaining high performance for storage outsourcing

The viability of storage outsourcing is critically dependent on the access performance of remote storage. We study this issue by measuring the behavior of a broad variety of I/O-intensive benchmarks as they access remote storage over an IP network. We measure the effect of network latencies that correspond to distances ranging from a local neighborhood to halfway across a continent. We then measure the effect of latency-hiding mechanisms. Our results indicate that, in many cases, the adverse effects of network delay can be rendered inconsequential by clever file system and operating system techniques.

Twenty years of telecommunications research in BIT

This paper reflects on 20 years of behavioural research in telecommunications published in BIT. The past 20 years have seen major changes in telecommunications technology and applications. They have also seen the deregulation of telecommunications markets and the pervasive penetration of the working environment by networked systems. Papers published in BIT have reflected these changes. Some research topics have attracted continuing interest throughout this period, and two are reviewed briefly: the effect of network delays on users and the relative effectiveness of different media and user choices between them. In addition many new technical and theoretical developments have been reported. Two major theoretical trends have been the convergence between behavioural research in telecommunications and computing, and the rise in social-science-based research. The question whether published behavioural research has been able to influence the development of the technologies studied is considered. Finally, the paper speculates on future topics for research.

The effect of network delay and media on user perceptions of web resources

This research experimentally examines the effects of network delays, document type, and various user characteristics on the perceived usability of distributed documents on the internet. Six experimental conditions were analysed: text only documents and documents including text and graphics at three levels of delay. Users were undergraduate and graduate students who reported spending zero to 50 hours per week on the internet. Usability was assessed by analysing responses to questions about ease of locating information, information organization, information quality, and navigation problems. The results showed significant interactions of network delay and document type on subjects' perceptions of quality, organization, navigation, and several additional factors that are important to organizations providing information on the internet. Both the number of hours subjects reported spending using the internet and subjects' self-reported command of the English language were significantly correlated with perceptions of various aspects of the internet sites examined. While the results indicate that internet users may prefer highly graphical web sites, it appears that they are unwilling to tolerate substantial delays. As a result, users in the study preferred plain text documents as delays increased.