Impact Of Communication Delays Research Articles

Detectability of networked discrete event systems

Detectability of discrete event systems, defined as the ability to determine the current and subsequent states, is very important in diagnosis, control, and many other applications. So far only detectability of non-networked discrete event systems has been defined and investigated. Non-networked discrete event systems assume that all the communications are reliable and instantaneous without any delays or losses. This assumption is often violated in networked systems. In this paper, we study detectability for networked discrete event systems. We investigate the impact of communication delays and losses on detectability. We define two classes of detectabilities: network detectability for determining the state of a networked discrete event systems and network D-detectability for distinguishing certain pairs of states of the systems. Necessary and sufficient conditions for network detectability and network D-detectability are derived. Methods to check network detectability and network D-detectability are also developed. Examples are given to illustrate the results.

TeMoto: Intuitive Multi-Range Telerobotic System with Natural Gestural and Verbal Instruction Interface

Teleoperated mobile robots, equipped with object manipulation capabilities, provide safe means for executing dangerous tasks in hazardous environments without putting humans at risk. However, mainly due to a communication delay, complex operator interfaces and insufficient Situational Awareness (SA), the task productivity of telerobots remains inferior to human workers. This paper addresses the shortcomings of telerobots by proposing a combined approach of (i) a scalable and intuitive operator interface with gestural and verbal input, (ii) improved Situational Awareness (SA) through sensor fusion according to documented best practices, (iii) integrated virtual fixtures for task simplification and minimizing the operator’s cognitive burden and (iv) integrated semiautonomous behaviors that further reduce cognitive burden and negate the impact of communication delays, execution latency and/or failures. The proposed teleoperation system, TeMoto, is implemented using ROS (Robot Operating System) to ensure hardware agnosticism, extensibility and community access. The operator’s command interface consists of a Leap Motion Controller for hand tracking, Griffin PowerMate USB as turn knob for scaling and a microphone for speech input. TeMoto is evaluated on multiple robots including two mobile manipulator platforms. In addition to standard, task-specific evaluation techniques (completion time, user studies, number of steps, etc.)—which are platform and task dependent and thus difficult to scale—this paper presents additional metrics for evaluating the user interface including task-independent criteria for measuring generalized (i) task completion efficiency and (ii) operator context switching.

A distributed non-Lipschitz control framework for self-organizing microgrids with uncooperative and renewable generations

This paper investigates the design of robust distributed voltage and frequency control for a self-organized microgrid. A multiagent distributed secondary hierarchy is proposed using control Lyapunov function. Power resources are categorized as controllable and uncontrollable distributed generations (DG). Controllable DGs are exchanging information with neighbor DGs through agents at communication layer. The agents communicate to restore the voltage and frequency to their nominal references. Furthermore, the proposed scheme is robust against the insufficient data from uncontrollable DGs, since it provides an improved and stable operation even when there is no communication with uncontrollable DGs and loads. It can actively compensate for the random unknown demand and generation, by sharing the power mismatch in distributed droop architecture. It is shown that the suggested controller is capable of stabilizing an uncooperative microgrid in which not all DGs are cooperating. Also, the convergence speed of the system is improved using the finite-time controller. The performance and finite-time stability of a microgrid with partially-cooperative DGs is proved using Lyapunov theorem and is validated through numerical simulation. The results show improved transients, accurate steady state values for voltage and frequency control of a microgrid, and robustness against communication architecture variations. The impact of communication delays, the uncertainty in coupling gains of the communication links, and the time-interval between updating the controller and the states through communication are investigated.

Impact of communication delays to and from the International Space Station on self-reported individual and team behavior and performance: A mixed-methods study

Deep space explorations will involve significant delays in communication to and from Earth that will likely impact individual and team outcomes. However, the extent of these impacts and the appropriate countermeasures for their mitigation remain largely unknown. This study utilized the International Space Station (ISS), a high-fidelity analog for deep space, as a research platform to assess the impact of communication delays on individual and team performance, mood, and behavior. Three astronauts on the ISS and 18 mission support personnel performed tasks with and without communication delays (50-s one-way) during a mission lasting 166 days. Self-reported assessments of individual and team performance and mood were obtained after each task. Secondary outcomes included communication quality and task autonomy. Qualitative data from post-mission interviews with astronauts were used to validate and expand on quantitative data, and to elicit recommendations for countermeasures. Crew well-being and communication quality were significantly reduced in communication delay tasks compared to control. Communication delays were also significantly associated with increased individual stress/frustration. Qualitative data suggest communication delays impacted operational outcomes (i.e. task efficiency), teamwork processes (i.e. team/task coordination) and mood (i.e. stress/frustration), particularly when tasks involved high task-related communication demands, either because of poor communication strategies or low crew autonomy. Training, teamwork, and technology-focused countermeasures were identified to mitigate or prevent adverse impacts.

Staggered Scheduling of Sensor Estimation and Fusion for Tracking Over Long-Haul Links

Networked sensing can be found in a multitude of real-world applications. We focus on the communication-and computation-constrained long-haul sensor networks, where sensors are remotely deployed over a vast geographical area to perform certain tasks. Of special interest is a class of such networks where sensors take measurements of one or more dynamic targets and send their state estimates to a remote fusion center via long-haul satellite links. The severe loss and delay over such links can easily reduce the amount of sensor data received by the fusion center, thereby limiting the potential information fusion gain and resulting in suboptimal tracking performance. In this paper, starting with the temporal-domain staggered estimation for an individual sensor, we explore the impact of the so-called intra-state prediction and retrodiction on estimation errors. We then investigate the effect of such estimation scheduling across different sensors on the spatial-domain fusion performance, where the sensing time epochs across sensors are scheduled in an asynchronous and staggered manner. In particular, the impact of communication delay and loss as well as sensor bias on such scheduling is explored by means of numerical and simulation studies that demonstrate the validity of our analysis.

Impact of Communication Delay on Frequency Regulation in Hybrid Power System Using Optimized H-Infinity Controller

ABSTRACTA communication infrastructure is essential for safe monitoring and control of isolated hybrid power system. For the hybrid system, integration of different renewable resources is required, such as wind turbine generator, diesel engine generator, aqua-electrolyser, and fuel cell along with storage unit. However, impacts of communication delay on dynamic performance on the hybrid power system, mainly load frequency control have not been reported by researchers. This paper presents the impact of communication delay profile in isolated hybrid distributed generation (DG) system for minimization of frequency deviation profile. The communication delays are one of the major problems and always present in a system during transmission of signal from remote terminal unit to control centre to individual unit. The frequency control problem is addressed for the hybrid DG system with communication delay. The delay is modelled by the second-order Padé approximation method. Particle swarm optimization (PSO)-tuned H-infinity loop shaping controller is used in this study for minimization of frequency deviation profile and compared with genetic algorithm (GA)-tuned H-infinity loop shaping controller and proportional integral-tuned H-infinity controller for different load conditions and change in system parameters. Performance of controllers is also validated with introducing nonlinearities in the system, such as generation rate constraints, time varying delay, and uncertainties. The results show that frequency deviation in presence of delay is found to be minimum for controller design by PSO-tuned H-infinity loop shaping of controller.

Impact of Communication Delays on Secondary Frequency Control in an Islanded Microgrid

Low-bandwidth communication channels are used to support the information exchange between a microgrid centralized controller and local controllers in the secondary frequency control of an islanded microgrid. However, the impact of the inherent time delay in these communication channels on the microgrid performance has not been taken into account when the secondary frequency controller is designed. This paper investigates the effect of the communication delays on the secondary frequency control of an islanded microgrid with multiple distributed generators. A small-signal model-based method is introduced for the microgrid to find delay margins below which the microgrid can remain stable. By performing a series of trial studies, the relationships between secondary frequency control gains and delay margins are obtained. A gain scheduling approach is also proposed to compensate the effect of the communication delay on the secondary frequency control. Results from the Canadian urban distribution system have verified that communication delays can adversely affect the microgrid secondary frequency control, and the proposed gain scheduling approach can improve the robustness of the microgrid secondary frequency controller to communication delays.

Reliability Analysis Models for Differential Protection Considering Communication Delays and Errors

This paper proposes three probability models to assess the impact of communication delays and bit errors on differential protection. First, the mechanism of relay protection malfunction caused by communication delays and bit errors is introduced. In general, a channel’s consistent delay or bit error results in refuse-operations, while a channel’s inconsistent delay normally causes false trips. Based on the analysis of the probability distributions of communication delays and bit errors, probabilistic models of false trips and refuse-operations are proposed. Simulation results, using typical parameters, are implemented to investigate the effects of communications on the malfunction probability of differential protection.

Impact of Communication Delay on the Bullwhip Effect in a Supply Chain Where Demand Information is Shared

Impact of Communication Delay on the Bullwhip Effect in a Supply Chain Where Demand Information is Shared

Performance Analysis of a Model-Free Predictor for Delay Compensation in Networked Systems

One important challenge with networked systems is that communication delays can significantly deteriorate system performance. This paper considers a model-free predictor framework to compensate for communication delays and improve networked system performance, where the term "model-free" indicates that the predictor does not need to know the dynamic equations governing the system. Stability analysis of this predictor is available in the literature; however, ensuring stability does not guarantee a good performance. Understanding when the predictor can perform well and what its limitations are is critical, but the performance characteristics of the predictor are unknown. Hence, this paper aims to fill this gap by providing a predictor performance analysis for constant time delays. First, a frequency-domain analysis is performed for the predictor and the relationship between the predictor design parameter, time delay, and steady-state performance is revealed. Fundamental limitations of the predictor at higher frequencies are laid out. Next, this analysis is confirmed on a case study. The case study further allows for testing the transient performance of the predictor in closed-loop with the networked system, and shows that the predictor holds significant potential to alleviate the negative impact of communication delays, even if its higher frequency performance may be limited.

The Impact of Communication Delay and Medium on Team Performance and Communication in Distributed Teams

Long duration space missions will involve communication delays of up to 20 minutes one way, a reality that will make it challenging for space crews and flight controllers to coordinate and pool their efforts, especially when unforeseen problems occur that may require extensive collaboration. The present study was conducted to examine how communication delay will impact distributed team performance, and whether communication media will moderate or exacerbate its effect. Method: Twenty-four teams of three were assigned the roles of space crewmember (2 participants) or flight controller (1 participant) and had to collaborate remotely on computer-based tasks simulating failures in the spacecraft’s life support system. Communication medium (text vs. voice) was a between-group variable; presence/absence of communication delay was a within-group variable. Performance variables included time to repair system failures and number of incorrect repairs. Audio-recordings of team members’ voice communications were transcribed and logs of their chats uploaded for further analysis. Results and discussion: Teams took significantly longer to repair system failures when team communication was asynchronous rather than synchronous. While communication medium had a significant effect when team interactions were synchronous, it had no differential impact under time-delayed conditions. Preliminary communication analyses suggest that under time-delayed conditions, successful teams in each media condition were those who adapted to the constraints of their communication medium to establish shared task understanding.

Performance optimization of parallel algorithms

The high intensity of research and modeling in fields of mathematics, physics, biology and chemistry requires new computing resources. For the big computational complexity of such tasks computing time is large and costly. The most efficient way to increase efficiency is to adopt parallel principles. Purpose of this paper is to present the issue of parallel computing with emphasis on the analysis of parallel systems, the impact of communication delays on their efficiency and on overall execution time. Paper focuses is on finite algorithms for solving systems of linear equations, namely the matrix manipulation (Gauss elimination method, GEM). Algorithms are designed for architectures with shared memory (open multiprocessing, openMP), distributed-memory (message passing interface, MPI) and for their combination (MPI + openMP). The properties of the algorithms were analytically determined and they were experimentally verified. The conclusions are drawn for theory and practice.

Centralized Reactive Power Control for a Wind Farm under Impact of Communication Delay

Generally, a wind turbine may have inferior reactive power dynamic performance where constant power control is adopted by a wind farm equipped with doubly fed induction generators (DFIGs). As a result, power system disturbance may incur grid faults where the wind farm cannot provide enough reactive power to the grid. This paper proposes a novel reactive power control strategy with centralized management for a wind farm. The real-time signal representing the voltage at a specified remote location -- a point of common coupling (PCC), is taken into account as an increment of the given value of the reactive power before being transmitted into each wind turbine by the distributed communication networks. In order to implement real-time regulation with reactive power output to the entire wind farm, this signal is meanwhile fed into the control loop in the rotor-side converter. Considering the issue of widely geographical distribution for each individual wind turbine, this paper studies the impact of communication delay on the system performance. As simulation results showing, in both of the cases of grid faults and wind speed fluctuation, the system with this control strategy can provide reactive power complement and keep the bus voltage stable. By using frequency domain analysis, this research also explores that different delay time may result in control failure due to multi-frequency harmonic incurred in the cases of long-term delay.

Decentralized Delayed-State Information Filter (DDSIF): A new approach for cooperative decentralized tracking

This paper presents a decentralized data fusion approach to perform cooperative perception with data gathered from heterogeneous sensors, which can be static or carried by robots. In particular, a decentralized delayed-state information filter (DDSIF) is described, in which full-state trajectories (that is, delayed states) are considered to fuse the information. This approach allows obtaining an estimation equal to that provided by a centralized system and reduces the impact of communication delays and latency in the estimation. The sparseness of the information matrix maintains the communication overhead at a reasonable level. The method is applied to cooperative tracking, and some results in disaster management scenarios are shown. In this kind of scenario, the target might move in both open-field and indoor areas, so the fusion of data provided by heterogeneous sensors is beneficial. The paper also shows experimental results with real data and integrating several sources of information.

Control gain adaptation in virtual reality mediated human-telerobot interaction

The Internet connects millions of computers worldwide, and provides a new potential working environment for remote-controlled telerobotic systems. The main limitation of using the Internet in this application is random delays between communicating nodes, which can cause disturbances in human–machine interaction and affect telepresence experiences. This is particularly important in systems integrating virtual reality technology to present interfaces. Telepresence, or the sense of presence in a remote environment, hypothetically is positively related to teleoperation task performance. This research evaluated the effect of constant and random network (communication) delays on remote-controlled telerover performance, operator workload, and telepresence experiences. The research also assessed the effect of using a system gain adaptation algorithm to offset the negative impact of communication delays on the various response measures. It was expected that with gain adaptation, system stability, performance, and user telepresence experiences would improve with a corresponding decrease in workload. Results indicated that gain adaptation had a significant effect on the performance measures. The study demonstrated that gain adaptation could reduce deterioration in telepresence experiences and improve user performance in teleoperated and telerobotic control. © 2005 Wiley Periodicals, Inc. Hum Factors Man 15: 259–274, 2005.

The Effects of Gain Adaptation on Qos Deterioration in an Internet-Based Teleoperation Using a Virtual Reality Interface

The Internet connects millions of computers worldwide, and provides a new potential working environment for remote-controlled telerobotic systems. The main drawback of using the Internet in this application is random delays between communicating nodes. These delays are considered disturbances in human-machine interaction and may affect telepresence experiences in teleoperation systems, particularly those integrating virtual reality technology for interface presentation. This research evaluated the effect of constant and random network (communication) delays on remote-controlled telerover performance, operator workload and telepresence experiences. The research also assessed the effect of using a system gain adaptation algorithm to offset the negative impact of communication delays on various response measures. It was expected that with gain adaptation, system stability, performance and user telepresence experiences would improve with a corresponding decrease in workload. Results indicated that gain adaptation had a significant effect on performance measures. The study demonstrated that gain adaptation could reduce deterioration in telepresence experiences and improve user performance in teleoperated and telerobotic control.

An adaptive scheduler for distributed real-time database systems

In a distributed real-time database system, a remote transaction usually accesses some data located at remote sites. However, traditional real-time schedulers do not consider the impact of communication delay in transferring remote data, resulting in a high MissRatio for remote transactions. This study proposes a new real-time scheduler called flexible high reward (FHR) to reduce the MissRatio and lessen the unnecessary waiting time due to communication delay for a remote transaction. This scheduler gives a remote transaction a slightly higher priority and adjusts a remote transaction’s waiting status such that the resources held by a waiting remote transaction can be released as soon as possible. Through the underlying operating system, local transactions can also be executed while a remote transaction is waiting for remote data. Simulation results demonstrate that the FHR outperforms current real-time schedulers such as earliest deadline, highest value, and highest reward and urgency.

The Impact of Communication Delays on Air Traffic Controllers' Vectoring Performance

An experiment was conducted to investigate the impact of communication delays in the pilot—controller communication loop on air traffic controllers' performance and workload. Four levels of constant systemic audio delay (AD), 150, 250 ms, 350 ms, and 1,000 ms, and two levels of variable pilot delay (PD), zero delay and realistic delay, were employed. Vectoring accuracy and the controller's final turn initiation served as dependent variables. Subjective workload was measured by the NASA-TLX workload index. Eight subjects proficient in the task participated in the experiment. Random PD had significant effects on both vectoring accuracy and final turn initiation; accuracy was reduced and initiation times were earlier when PD was added. However, data showed no effect of AD on vectoring accuracy, and no evidence of compensatory strategies in response to increasing AD levels. Results suggest that variability in the subjects' turn initiation effectively masked the impact of even the longest AD of 1,000 ms on vectoring accuracy. The NASA-TLX showed no effect of AD on workload in either PD condition.

Delay-independent design for distributed systems

Methods of limiting the impact of communication delays on the logical behavior of distributed systems are considered. It is assumed that a distributed system is described in terms of a number of interconnected modules, and each module is described in terms of its possible states and the possible state transitions. Transitions may be initiated spontaneously by a module and may give rise to output messages, which will be received, after some possible delay, by another module as an input. Otherwise, transitions may be initiated by received input. If the system has the property called regularity, its behavior is logically independent of the communication delays. A simple condition for regularity is given. This condition is the basis for the implementation of counter-based synchronization conditions in a distributed environment. Weaker forms of regularity, which make abstraction of internal operations invisible from the point of view of an outside observer, are also considered. The application of these concepts to the design of module interfaces involving 'collisions' and to communication including timeouts is discussed in some detail with examples. >