Formation tracking of multi-vehicle systems in unknown environments using a multi-region control scheme

In this paper, a multi-region control scheme is proposed for a formation of nonholonomic vehicles to track a reference trajectory while avoiding collisions and preserving network connectivity in unknown environments. The proposed control scheme defines three regions, safe region, dangerous region and transition region. In different regions, priority is given to different control objectives. In safe region where trajectory tracking holds the priority, the proposed control scheme guarantees bounded tracking of the reference trajectory for each vehicle. In dangerous region where avoidance control is the main objective, a new bounded potential function is designed to characterise constraints of obstacle and inter-vehicle collision avoidance as well as connectivity maintenance. By introducing a series of transition functions, smooth switching between trajectory tracking and avoidance control is achieved in transition region. It has been proved that each vehicle can track its reference trajectory while satisfying the constraints simultaneously with a bounded controller which means that the proposed control scheme satisfies input constraints by properly tuning parameters. Simulation results demonstrate the effectiveness of the proposed method.     

Stabilization of bilaterally controlled teleoperators with communication delay: An ISS approach

A new approach to the stabilization of bilaterally controlled teleoperators in the presence of time delay in the communication channel is presented. A control scheme is proposed which makes the teleoperator system input-to-state stable regardless of the delay in the communication channel. It is shown that in the case of digital implementation of the control system, the input-to-state stability property is preserved in the 'semiglobal' sense. Simulation results are presented which confirm the stability properties of the proposed telerobotic scheme.     

A method for designing the communication structure of networked controllers

The paper analyses the command-following behaviour of synchronised systems in dependence upon the communication structure of the networked controller. Its focus lies on the transient behaviour before the subsystems reach a common trajectory. It considers the dynamics of the subsystems as the main reason for the delay that the information about the reference trajectory is exposed to between the leader and the followers on a communication path, whereas the communication network is assumed to provide instantaneous information transmission. An abstract model of the overall system is introduced that represents the coupling structure of the agents together with a quantitative delay measure. This model is used to determine communication structures in which all agent outputs follow the reference trajectory with small delay. It helps to find a trade-off between the number of communication links and the quality of the system performance. The results are illustrated by its application to a robot formation problem.     

Minimum information rate for observability of linear systems with stochastic time delay

This paper investigates the state estimation problem for linear time-invariant systems where sensors and controllers are geographically separated and connected via stationary memoryless uncertain digital communication channels with the information rate limitation. Such channels introduce data packet dropout, stochastic time delay, and data packet reordering. In the TCP/IP model, the transport layer provides a reliable service on top of an unreliable communication channel. However, the performance of such systems is still affected by packet reordering and stochastic time delay. In particular, we present an optimal encoding and decoding scheme to guarantee observability by employing the minimum information rate, and derive a necessary and sufficient condition on the delay distribution and information rate for observability. Illustrative examples are given to demonstrate the effectiveness of the proposed scheme.     

A network level channel abstraction for multimedia communication inreal-time networks

The design of communication protocols to support guaranteed real-time communication for distributed multimedia systems is examined. A network level abstraction called φ-channel that supports the requirements of real-time applications is proposed. A φ-channel represents a fractional, simplex, end-to-end communication channel between a source and a destination. The channel is characterized by a set of specific performance parameters associated with its traffic. The required performance characteristics of a φ-channel are specified in terms of the packet maximum end-to-end delay and the maximum number of packets that can be sent over that delay. The primary attribute supported by the φ-channel is the on-time reliability. Based on the specified parameters, the underlying delivery system verifies the feasibility of supporting such a channel. The performance of an accepted φ-channel is guaranteed under any conditions, barring hardware failures. The basic scheme that the model uses to verify the feasibility of accepting a φ-channel and the run-time support used to guarantee its performance are described. The results of a simulation experiment implementing the basic functionalities of the proposed scheme are also presented     

煤矿井下电网区域联锁保护方案及其实时性研究

针对煤矿井下供电系统通信网络无法满足数据传输实时性、可靠性的要求,很难同时实现保护速动性和选择性的问题,提出了基于交换式以太网的区域联锁保护方案,并采用OPNET网络仿真软件对交换式以太网进行了实时性研究。该方案采用树形结构的交换式以太网,在各综合保护装置上增加具备以太网通信接口的智能联锁装置,组成区域联锁系统。仿真结果表明,在同时有64个网络节点收发数据的极端情况下,网络整体延时最大值不超过0.65ms,端到端最大延时不超过1ms,整体数据收发流量比较平稳,说明交换式以太网具有很高的稳定性和可靠性,能够满足本区域联锁保护系统实时性要求,防止越级跳闸事故发生。     

Prediction and congestion control algorithm for networked motion tracking

In this paper a novel prediction method and a communication protocol is proposed for distributed motion tracking systems, for example robot control system over the Internet based on on-line visual information. It is assumed that the trajectory generator part of the control system is connected to the low level controller through wide area network (WAN). In this case the variable network delay, packet losses, irregular packet arrival can severely influence the control characteristics (transient behavior and tracking performance) in a negative sense. The proposed prediction method is based on dynamic filters and it generates the trajectory on the control system side in the control periods when no new information on the time varying reference trajectory arrives through the network. The developed application level communication protocol is meant to keep the packet loss under a predefined limit even if the network bandwidth varies below the value required by the control application. Simulations and real-time experiments show that the prediction algorithm applied jointly with the proposed communication protocol can effectively compensate the effect of networked communication on control characteristics.     

Networked control of discrete-time linear systems over lossy digital communication channels

This article addresses networked control problems for linear time-invariant systems. The insertion of the digital communication network inevitably leads to packet dropout, time delay and quantisation error. Due to data rate limitations, quantisation error is not neglected. In particular, the case where the sensors and controllers are geographically separated and connected via noisy, bandwidth-limited digital communication channels is considered. A fundamental limitation on the data rate of the channel for mean-square stabilisation of the closed-loop system is established. Sufficient conditions for mean-square stabilisation are derived. It is shown that there exists a quantisation, coding and control scheme to stabilise the unstable system over packet dropout communication channels if the data rate is larger than the lower bound proposed in our result. An illustrative example is given to demonstrate the effectiveness of the proposed conditions.     

Internet无线接入网络中应用智能天线的多址协议及性能分析

该文研究将智能天线应用于Internet无线接入网络的中心接入点(CAP)。提出了基于轮询的自适应波束形成多址接入协议(PB-ABFMA)．该协议中,CAP接收或发送数据分组前,由CAP引导用户节点发送训练序列,CAP的智能天线据此计算出与用户节点对应的权矢量．CAP以轮询及动态TDMA方式为各节点安排发送时隙。采用微时隙为处于空闲状态的节点保持连接以降低时延．设计了一种简单有效的竞争接入算法,保证新用户能快速接入信道．针对Internet中主要的“请求一回应”(request-reply)式业务,分析了协议的信道利用率与平均“请求一回应”时延．结果表明,PB-ABFMA协议能有效支持智能天线应用并具有较高的信道利用率与良好的时延性能。     

一种高吞吐量的无人机轨迹规划方法

无人机由于具有完全可控的移动性以及快速部署等优点,成为无线通信领域的研究热点。研究一种无人机支持的多播信道,利用无人机作为移动发射机向多个地面节点发送信息,在无人机的有限任务通信时间内,设计一种连续圆飞行轨迹方法。面向随机分布的多个地面节点,设定距离阈值对地面节点进行分组,通过求解新型旅行商问题确定无人机对各个分组的通信顺序,在满足无人机与地面节点通信覆盖需求的情况下,对圆心、无人机的飞行速度以及飞行半径进行求解,确定各个分组的圆形飞行轨迹,进而生成连续圆飞行轨迹。为实现吞吐量最大化目标,基于连续圆轨迹,在轨迹、功率一定情况下进行功率和轨迹优化,并通过交替联合优化无人机轨迹和功率以提高无人机对地通信系统整体性能。仿真结果表明,与基准方案相比,该方法系统吞吐量明显提高。