Delays In Communication Channels Research Articles

Model of Optimal Placement of Cloudlets in a Wireless Metropolitan Area Network

Cloud computing has recently emerged as a new paradigm for processing and storing large amounts of data. The rapid increase in the number of mobile phones and IoT devices benefitingfrom cloud computing services reduces the Internet bandwidth, resulting in delays in delivering data processed on remote cloud servers to the user. Mobile devices use edge computing systems (cloudlet, fog computing, etc.) to overcome resource shortages, power consumption and delays in communication channels. Edge computing systems place processing devices (cloudlets) close to users. The closer the cloudlets to mobile devices, the lower the processing time and energy consumption of the mobile device, and the higher the bandwidth of communication channels. Thus, cloudlet-based mobile computing clouds are widely used to reduce the latency in the Internet communication channels and energy consumption on mobile devices. This article identifies the most popular places for cloud servers in metropolitan mobile networks and discusses the optimal placement of a limited number of cloudlets in those places.

Design of robust adaptive fuzzy control for uncertain bilateral teleoperation systems based on backstepping approach

AbstractIn this study, a novel method based on a robust adaptive fuzzy control approach is developed for nonlinear teleoperation systems. Its main objectives are to ensure system stability and properly mitigating parametric uncertainties stemming from external disturbances and un‐modelled dynamics. For the communication channel, instead of the direct transmission of environmental torque signals, the approximated environmental parameters by the fuzzy system are transmitted to the master side for the prediction of environmental torque, thus successfully avoiding the transmission of the power signals in the delayed communication channel and solving the passivity problem in the teleoperation system. Besides, a trajectory generator is employed in the master side, whereas a trajectory smoothing is provided in the slave side. Theoretically, it was proven that both position tracking and force feedback problems are attained. Using Lyapunov stability analysis, this work illustrates that the robust adaptive fuzzy controller based on the backstepping approach guarantees the system's asymptotic stability. Simulation results confirm the efficiency of the suggested control technique in achieving the stability and tracking objectives of the uncertain nonlinear teleoperation system.

Clustering Method of Mobile Cloud Computing According to Technical Characteristics of Cloudlets

The rapid increase in the number of mobile phones and IoT devices connected to the network reduces the bandwidth of the Internet communication channel, and as a result, delays occur in the delivery of data processed in remote clouds. Edge computing systems (cloudlet, fog computing, etc.) are used to eliminate resource shortages, energy consumption, and communication channel delays in mobile devices. Edge computing systems place processing devices (computers) close to users. Cloudlet-based mobile cloud computing is widely used to reduce delays in communication channels and energy consumption in mobile devices. Selection of the most suitable cloudlet allowing users to run applications fast in cloud is still a considerable problem. This paper proposes a strategy for the selection of high-performance cloudlets providing fast solutions, considering the complexity of application (file type). It offers a method for cloudlet selection out of large number of cloudlets with different technical capabilities providing faster processing of user application. The timing of user applications in cloudlets with different technical capabilities (operating frequency, number of cores, volume of RAM, etc.) also varies. The proposed method provides faster solution for the user application. User applications are grouped by type of application, and a set of cloudlets are clustered by the number of groups. Clustering is performed first by the parameters corresponding to the operating frequency of the cloudlets, then by the number of cores and the volume of RAM. The proposed method reduces energy consumption of mobile devices by providing faster processing of applications. Thus, the proposed strategy provides an energy consumption reduction on mobile devices, faster processing of results and decrease of network delays.

Adaptive Neural Network Control of Time Delay Teleoperation System Based on Model Approximation.

A bilateral neural network adaptive controller is designed for a class of teleoperation systems with constant time delay, external disturbance and internal friction. The stability of the teleoperation force feedback system with constant communication channel delay and nonlinear, complex, and uncertain constant time delay is guaranteed, and its tracking performance is improved. In the controller design process, the neural network method is used to approximate the system model, and the unknown internal friction and external disturbance of the system are estimated by the adaptive method, so as to avoid the influence of nonlinear uncertainties on the system.

Sampled-data distributed protocol for coordinated aggregation of multi-agent systems subject to communication delays

This paper studies the coordinated aggregation problem of a multi-agent system. Particularly, all the agents reach a consensus within a pre-specified target region. However, only a subset of agents have access to this target region, and each agent merely interacts with its neighbors by communication. Moreover, there exist unknown heterogeneous delays in communication channels. The underlying communication topology is characterized by a digraph. To accommodate the practical digital disposal, a sampled-data distributed protocol is proposed, where the sampling is asynchronous in the sense that the sampling periods of distinct agents are heterogeneous. The resulting closed-loop system from the proposed sampled-data distributed protocol is in a hybrid fashion that the continuous system is fed-back by using discrete states at sampling instants. The convergence performance of this hybrid closed-loop system is analyzed based on the contraction theory. More specifically, it is first shown that all the states are coordinated to aggregate within the target region, i.e., coordinated aggregation. With this result, it is next shown that all the states are coordinated towards a consensus, i.e., state agreement. These together guarantee the fulfillment of the concerned coordinated aggregation objective. Finally, a simulation example is given to validate the theoretical results.

Challenges of Mobile Devices’ Resources and in Communication Channels and their Solutions

The article is dedicated to the development of cloudlet based mobile cloud computing (MCC) to address the restrictions that occur in the resources of mobile devices (energy consumption, computing and memory resources, etc.) and the delays occurring in communication channels. The architecture offered in the article more efficiently ensures the demand of mobile devices for computing and storage and removes the latency that occur in the network. At the same time, the tasks related to energy saving and eliminating delays in communication channels by solving the problems that require complex computing and memory resources in the cloudlets located nearby the user were outlined in the article.

Information-Theoretically Secure String Commitments Based on Packet Reordering Channels

Realizing fundamental cryptographic primitives with unconditional security is a central topic in information-theoretic cryptography. These primitives can be realized based on physical assumptions, such as the existence of noisy channels, an upper bound on the storage capacity, or the laws of quantum mechanics. Palmieri and Pereira [1] demonstrated that delays in communication channels can be used as a reasonable and effective assumption to obtain an unconditionally secure oblivious transfer protocol against honest-but-curious adversaries. While any oblivious transfer protocol secure against malicious adversaries can be used to implement commitment, the reduction does not work if the oblivious transfer protocol is only secure against honest-but-curious adversaries. Thus, the question of obtaining a secure commitment protocol based on channel delays is still open. In this paper, we provide a concrete protocol for implementing string commitments based on packet reordering – a consequence of channel delays in packet networks.

A Two-Layer Trilateral Teleoperation Architecture for Mentoring in Surgical Training

Abstract In this paper we propose a novel trilateral dual-master-single-slave teleoperation control architecture that can be used for the training of novice surgeons in surgical procedures. Starting from the concept of energy tank, we propose a flexible and stable trilateral interconnection over a delayed communication channel between the masters and the slave. Exploiting the flexibility provided by the controller, we design a training strategy for novice surgeons. The proposed architecture is experimentally validated.

Управление группой БЛА при неопределенных запаздываниях в каналах связи

The UAV groups and other unmanned robots are more and more widely used to solve production and special problems in view of their bigger efficiency in comparison with single robots. The efficiency of a group in many respects is defined by the opportunities of the communications means between members of the group and its leader, which influences the efficiency of the decisions made. The control of the UAV group is often exercised by a multivariable control system whose algorithms are implemented by a computer complex of the group UAV leader. The problem here is that in individual channels of information exchanges between the UAV-leader and other UAVs of the group there is a time delay. Any space distributions of the UAV in the neighborhood of the leader cause significantly different, uncertain delays in channels of its contact with the UAV group that can lead to a loss of control stability. It is proposed to apply a multivariable, robust to delay control system to overcome this difficulty. The design of this system is carried out on the basis of the matrix decoupling control and the method of an analytical design of systems with control on output and impact (ADSCOI) taking into account conditions of feasibility of controls on digital computing elements. Analytical expressions including the solution to the linear system algebraic equations and the creation procedure of the digital control algorithms are found in the article. This control provides robustness of the system to delays in communication channels. The efficiency of the proposed approach is illustrated by a numerical design example of the multivariable group control system of the UAV. The results obtained can be applied to create digital control systems by both single input-single-output and multi-input-multi-output objects with an uncertain delay in agricultural, food, power, machine-building and other industries.

Stabilisation of networked control systems with remote and local controllers subject to delay and packet dropout

This study considers the stabilisation problem for networked control systems (NCSs) with remote and local controllers involving delay and packet dropout. In this NCSs model, the local controller receives the precise state and sends it to the remote controller via an unreliable communication channel where packet dropout may occur. When the remote controller obtains the observation, it delivers an acknowledgement to the local controller whether the precise state is received or not. Then the two controllers make their decisions simultaneously, which shall be sent to the plant through a delayed communication channel. The authors give the necessary and sufficient condition of the stabilisation in the mean-square sense for the system without the additive noise based on two coupled algebraic Riccati equations. For the system with the additive noise, firstly, they show the stability of the optimal estimator. Then the sufficient condition of the boundedness in the mean-square sense is presented. Numerical examples are illustrated to show the effectiveness of the proposed algorithm.

Consensus of Continuous-Time Multiagent Systems via Delayed Output Feedback: Delay Versus Connectivity

This article studies the consensus problem for continuous-time linear time-invariant multiagent systems, in which the agents exchange information through delayed communication channels in a fixed undirected topology. Our primary objective is to characterize explicitly the delay effect on consensus in the framework of distributed dynamic output feedback control and its implication on the graph network connectivity. For this purpose, we tackle and solve the consensus problem in the spirit of gain margin problem, using analytic interpolation techniques. We develop an explicit condition for consensus. The result provides a limit on network connectivity imposed by time delays as well as by the agent's unstable poles and nonminimum phase zeros.

Discrete-time Deployment of Agents on a Line Segment: Delays and Switches Do Not Matter

This paper considers the discrete-time problem of deploying agents on a line segment under delay in communication channels and switching and also under incomplete information about the value of the delay and the law of switching. It is shown that neither delay nor switching affect the convergence of the agents' states to the uniform allocation on the line segment. The theoretical results are illustrated by numerical simulation. The evidence is based on the well-known and new approaches to the stability analysis of positive systems.

Optimized power modulation in wave based bilateral teleoperation

A common approach for stabilizing the delayed communication channel in a bilateral teleoperation architecture is using wave variables to make the exchange of information equivalent to a passive physical dynamics. However, such a dynamics is felt by the user and it affects the transparency of the system. In this article, we exploit the wave variables for storing the energy exchanged between master and slave, but we shape the incoming power for reproducing a desired, transparent behavior. First, we propose a passivity preserving modulation of the incoming power, and then, we achieve possibly scaled desired forces and velocities. Finally, we formulate an optimization problem for computing the best values of forces and velocities to be implemented. A validation of the proposed architecture and the comparison of its performances with respect to the standard wave-based approach are provided.

Analysis and Design of a Wide-Area Damping Controller for Inter-Area Oscillation With Artificially Induced Time Delay

One of the major issues in an interconnected power system is the low damping of inter-area oscillations. A proportional-derivative (PD) compensator is a popular control method which is extensively being used as an active damping control in various domains such as robotics, smart structure, etc. However, existence of noise in wide-area signal makes an ideal PD compensator unrealisable in power systems. In this endeavour, a new methodology christened as time-delayed control is proposed where artificial delay is used to provide derivative action which acts as a damping component of wide-area controller. The delay margin is computed for the closed loop system using Razumikhin approach. It is observed that the proposed controller is able to damp the oscillations adequately with reduced sensitivity to the noise in the signals. Further, the proposed controller is able to provide robustness against uncertainties arising from the system dynamics and inherent delay in communication channel.

Adaptive Fuzzy Backstepping Control for Stable Nonlinear Bilateral Teleoperation Manipulators With Enhanced Transparency Performance

Bilateral teleoperation technology has been widely concerned by its unique advantages in human–machine interaction-based cooperative operation systems. Communication delay, various nonlinearities, and uncertainties in teleoperation system are the main challenging issues to achieve system stability and good transparency performance. In this paper, a globally stable adaptive fuzzy backstepping control design is proposed for nonlinear bilateral teleoperation manipulators to handle the aforementioned issues. For the communication channel, instead of direct transmission of environmental torque signals, the fuzzy-based nonpower approximate environmental parameters are transmitted to the master side for environmental torque prediction, which effectively avoids the transmission of power signals in the delayed communication channel and solves the passivity problem in the traditional teleoperation system. A trajectory generator is implemented in the master side and a trajectory smoothing is applied in the slave side. Subsequently, nonlinear adaptive fuzzy backstepping controllers for master and slave are separately designed to handle the nonlinearities and uncertainties. Theoretically, the great transparency performance of both position tracking and force feedback can be achieved, and the global stability is still guaranteed under communication delay. Comparative experiments are conducted on the real platform, which verify the effectiveness and advantages of the proposed control design in some typical working scenarios.

Bilateral Teleoperation of Single-Master Multislave Systems With Semi-Markovian Jump Stochastic Interval Time-Varying Delayed Communication Channels.

Communication time delays in a bilateral teleoperation system often carries a stochastic nature, particularly when we have multiple masters or slaves. In this paper, we tackle the problem for a single-master multislave (SMMS) teleoperation system by assuming an asymmetric and semi-Markovian jump protocol for communication of the slaves with the master under time-varying transition rates. A nonlinear robust controller is designed for the system that guarantees its global robust H∞ stochastic stability in the sense of the Lyapunov theory. Employing the nonlinear feedback linearization technique, the dynamics of the closed-loop teleoperator is decoupled into two interconnected subsystems: 1) master-slave tracking dynamics (coordination) and 2) multislave synchronization dynamics. Employing an improved reciprocally convex combination technique, the stability analysis of the closed-loop teleoperator is conducted using the Lyapunov-Krasovskii methodology, and the stability conditions are expressed in the form of linear matrix inequalities that can be solved efficiently using numerical algorithms. Numerical studies and simulation results validate the effectiveness of the proposed controller design algorithm in both tracking and synchronization performance of the SMMS system, and robustly handling the stochastic and nondifferentiable nature of communication delays.

Preserving the Physical Coupling in Teleoperation despite Time Delay through Observer-Based Gradient Control

In recent past, a variety of control approaches were proposed that serve the stabilization of coupled network systems despite time delay. Especially in teleoperation setups, where the input device displays the interaction forces and torques of the remote coupled robot with its environment to a human operator. This force feedback should represent the physical behavior of a coupling at zero time delay. However, most control approaches aim to limit the force feedback for the sake of stability which does not necessarily lead to a reasonable presentation of the remote side impedances. Recently, Singh et al. (2019) proposed an observer-based gradient controller to eliminate the force jittering on the master side. It rectified the delayed feedback force by removing the undesired increase in force which is generated by the delay in communication channel. The stability of the system was assured via the Time Domain Passivity Approach which leads to an undesired position drift. In this work the observer-based gradient approach is modified to increase it’s force transparency and implemented to another recently developed position-drift free Time Domain Passivity Approach, Panzirsch et al. (2019). The new amalgamated approach is validated and compared to the state-of-the-art in experiments.

A Scaled Bilateral Teleoperation System for Robotic-Assisted Surgery with Time Delay

The master-slave teleoperated robotic systems have advanced the surgeries in the past decades. Time delay is usually caused due to the data transmission between communication channel connecting the master and slave in bilateral teleoperation, which is crucial because even small time delay could destabilize the whole teleoperation system. Motivated to solve the instability caused by time delay in bilateral teleoperation, wave variable transformation (WVT) structure has been proposed to passivate the delayed communication channel. However, conventional WVT structure provides poor velocity, position and force tracking performances which are not sufficient for surgical applications. In this paper, a new wave variable compensation (WVC) structure is proposed to improve the tracking performances with less conservative condition and comprehensive analysis to keep stable and improved tracking performance is also provided. In order to better facilitate certain surgical procedures with special requirements, e.g. robotic-assisted neurosurgery, velocity/position and force scalings are designed in the proposed structure with guaranteed system passivity, and transparency of the scaled WVC structure is also analyzed. Simulation and experimental studies were carried out to verify the performance of the proposed structure with time delay. System performance comparisons with several existing wave based bilateral teleoperation structures are also provided through simulation studies to show the improvements brought by the proposed teleoperation structure.

Stability analysis of nonlinear telerobotic systems with time-varying communication channel delays using general integral inequalities

Existing controller synthesis schemes for teleoperation of nonlinear master-slave systems with time-varying communication channel are subject to conservative stability criteria. This paper presents a new stability criteria for bilateral tele-operation systems with proportional-derivative, position-position and position-force control architectures, considering both passive/non-passive human operator. The communication channel pertains unknown asymmetric time-varying delays with given lower and upper-bounds. Using the Lyapunov Krasovskii approach, the stability analysis of the dynamic system is examined and the stability conditions are derived in the form of Linear Matrix Inequalities (LMIs). Advanced techniques have been employed to find less conservative integral inequalities in the process of stability analysis of the closed-loop teleoperator. Illustrative numerical examples and simulation results emphasize the effectiveness of the proposed stability criteria in enlarging the stability bounds and providing efficient control performances.

Position-Force Domain Passivity of the Human Arm in Telerobotic Systems

In order to guarantee safe human–robot interaction in single-master/single-slave teleoperation systems, passivity-based controllers have traditionally been developed for communication delay compensation in the velocity-force domain (VD) with the assumption of passivity of the human arm. The same controllers can also make the delayed communication channel passive in the position-force domain (PD), which provides a convenient position-drift-free control strategy for more complicated scenarios such as multi-master/single-slave systems. This would, however, only work if the operator's arm also remains passive in the PD. Whether the arm remains passive in the PD is a critical question yet to be answered. In this paper, passivity of the human arm in the PD is investigated through mathematical analysis, experimentation, and statistical user studies involving 12 subjects and 48 trials. It is shown that unlike in the VD, the human operator will not remain passive in the PD for all frequency ranges. This implies the need for appropriate control strategies to make the human operator termination passive in the PD. For future design of suitable controllers, statistical analyses are performed to investigate correlations between the levels of PD passivity of the left and the right arms of the human participants, as well as the levels of passivity of the subjects’ arms and their physical characteristics, e.g., weight, height, and body mass index. Possible control strategies through which the passivity of the operator termination can be guaranteed are also discussed.