Consensus controller for multi-UAV navigation

In this paper, we design consensus algorithms for multiple unmanned aerial vehicles (UAV). We mainly focus on the control design in the face of measurement noise and propose a position consensus controller based on the sliding mode control by using the distributed UAV information. Within the framework of Lyapunov theory, it is shown that all signals in the closed-loop multi-UAV systems are stabilized by the proposed algorithm, while consensus errors are uniformly ultimately bounded. Moreover, for each local UAV, we propose a mechanism to define the trustworthiness, based on which the edge weights are tuned to eliminate negative influence from stubborn agents or agents exposed to extremely noisy measurement. Finally, we develop software for a nano UAV platform, based on which we implement our algorithms to address measurement noises in UAV flight tests. The experimental results validate the effectiveness of the proposed algorithms.     

An output-based distributed observer and its application to the cooperative linear output regulation problem

In this paper, we first extend an existing stability result for a class of linear switched systems. This extended result will relax the existence conditions of the output-based distributed observer for a leader system subject to jointly connected switching communication networks in the literature. As an application of this output-based distributed observer, we solve the cooperative output regulation problem of a linear multi-agent system subject to jointly connected switching communication networks by composing a purely decentralized control law and the output-based distributed observer based on the certainty equivalence principle.     

Ethernet based time synchronization for Raspberry Pi network improving network model verification for distributed active turbulent flow control

Friction drag primarily determines the total drag of transport systems. A promising approach to reduce drag at high Reynolds numbers(> 104) are active transversal surface waves in combination with passive methods like a riblet surface. For the application in transportation systems with large surfaces such as airplanes, ships or trains, a large scale distributed real-time actuator and sensor network is required. This network is responsible for providing connections between a global flow control and distributed actuators and sensors. For the development of this network we established at first a small scale network model based on Simulink and True Time. To determine timescales for network events on different package sizes we set up a Raspberry Pi based testbed as a physical representation of our first model. These timescales are reduced to time differences between the deterministic network events to verify the behavior of our model. Experimental results were improved by synchronizing the testbed with sufficient precision. With this approach we assure a link between the large scale model and the later constructed microcontroller based real-time actuator and sensor network for distributed active turbulent flow control.     

Generalized Moment Theorem and Its Application to Distributed-Parameter Control Systems

In this paper, we generalize the original moment theorem to the problem of existence of a linear operator with minimum norm under some constraint conditions in an abstract normed space. The results are applied to a class of largest controllable set and optimal control problems for distributed parameter systems.     

Distributed output feedback stationary consensus of multi-vehicle systems in unknown environments

In the traditional distributed consensus of multi-vehicle systems, vehicles agree on velocity and position using limited information exchange in their local neighborhoods. Recently, distributed leaderless stationary consensus has been proposed in which vehicles agree on a position and come to a stop. The proposed stationary consensus schemes are based on all vehicles'' access to their own absolute velocity measurements, and they do not guarantee this collective behavior in the presence of disturbances that persistently excite vehicles'' dynamics. On the other hand, traditional distributed disturbance rejection leaderless consensus algorithms may result in an uncontrolled increase in the speed of multi-vehicle system. In this paper, we propose a dynamic relative-output feedback leaderless stationary algorithm in which only a few vehicles have access to their absolute measurements. We systematically design the distributed algorithm by transforming this problem into a static feedback robust control design challenge for the low-order modified model of vehicles with fictitious modeling uncertainties. We further propose dynamic leader-follower stationary consensus algorithms for multi-vehicle systems with a static leader, and find closed-form solutions for the consensus gains based on design matrices and communication graph topology. Finally, we verify the feasibility of these ideas through simulation studies.     

Anti-synchronization of four-wing chaotic systems via sliding mode control

Sliding mode control is an important method used in nonlinear control systems. In robust control systems, the sliding mode control is often adopted due to its inherent advantages of easy realization, fast response and good transient performance as well as its insensitivity to parameter uncertainties and disturbances. In this paper, we derive new results based on the sliding mode control for the anti-synchronization of identical Qi three-dimensional (3D) four-wing chaotic systems (2008) and identical Liu 3D four-wing chaotic systems (2009). The stability results for the anti-synchronization schemes derived in this paper using sliding mode control (SMC) are established using Lyapunov stability theory. Since the Lyapunov exponents are not required for these calculations, the SMC method is very effective and convenient to achieve global chaos anti-synchronization of the identical Qi four-wing chaotic systems and identical Liu four-wing chaotic systems. Numerical simulations are shown to illustrate and validate the synchronization schemes derived in this paper.     

Fault-tolerant Control Systems—An Introductory Overview

This paper presents an introductory overview on the development of fault-tolerant control systems. For this reason, the paper is written in a tutorial fashion to summarize some of the important results in this subject area deliberately without going into details in any of them. However, key references are provided from which interested readers can obtain more detailed information on a particular subject. It is necessary to mention that, throughout this paper, no efforts were made to provide an exhaustive coverage on the subject matter. In fact, it is far from it. The paper merely represents the view and experience of its author. It can very well be that some important issues or topics were left out unintentionally. If that is the case, the author sincerely apologizes in advance.After a brief account of fault-tolerant control systems, particularly on the original motivations, and the concept of redundancies, the paper reviews the development of fault-tolerant control systems with highlights to several important issues from a historical perspective. The general approaches to fault-tolerant control has been divided into passive, active, and hybrid approaches. The analysis techniques for active fault-tolerant control systems are also discussed. Practical applications of fault- tolerant control are highlighted from a practical and industrial perspective. Finally, some critical issues in this area are discussed as open problems for future research/development in this emerging field.     

Information theoretic conditions for tracking in leader-follower systems with communication constraints

In this paper, we introduce a general framework for tracking in leader-follower systems under communication constraints, in which the leader and follower systems as well as the corresponding controllers are spatially distributed and connected over communication links. We provide necessary conditions on the channel data rate of each communication link for tracking of the leader-follower systems. By considering the forward and feedback channels as one cascade channel, we also provide a lower bound for the data rate of the cascade channel for the system to track a reference signal such that the tracking error has finite second moment. Examples and simulations are provided to demonstrate some of the results.     

A dynamical inequality for the output of uncertain nonlinear systems

An important task in control theory is to study the limitations of feedback principle in dealing with uncertainties.Although some progresses have been achieved in this area,they are all focused on some special classes of linearly parameterized nonlinear uncertain systems.In this paper,we will present a dynamic inequality for the output process of a quite general class of nonlinear dynamical control systems with nonlinearly parameterized uncertain parameters.This inequality will be established using a stochastic imbedding approach based on a Cramér-Rao inequality for dynamical systems,and will be shown to play a crucial role in investigating the fundamental limitations of the feedback mechanism.     

Consensus control of multi‑manipulator systems based on disturbance observer under Markov switching topologies

In this paper, to solve the consensus control problem of multi-manipulator systems under Markov switching topologies, we propose a distributed consensus control strategy based on disturbance observer. In multi-manipulator systems, external disturbance described by heterogeneous exogenous systems is considered, and all communication topologies are directed. First, a disturbance observer is presented to suppress the influence of unknown external disturbance, and the equivalent compensation is introduced into the control protocol in multi-manipulator systems. Then, a novel control protocol based on neighbor information is designed, which guarantees that multi-manipulator systems reach consensus under Markov switching topologies. Finally, two simulation examples verify the validity of the theoretical result.     

End-to-end analysis of distributed video-on-demand systems

The focus of the research presented in this paper is the end-to-end analysis of a distributed Video-on-Demand (VoD) system. We analyze the distributed architecture of a VoD system to design global request handling and admission control strategies and evaluate them using global metrics. The performance evaluation methodology developed in this paper helps in determining efficient ways of using all resources in the VoD architecture within the constraints of providing guaranteed high quality service to each request. For instance, our simulation results show that request handling policies based on limited redirection of blocked requests to other resources perform better than load sharing policies. We also show that request handling policies based on redirection have simpler connection establishment semantics than load sharing policies and, therefore, are easily incorporated into reservation or signaling protocols.     

The Analysis and Performance of Multi-Rate Service in Distributed Video-on-Demand Systems

In this paper, we develop an end-to-end analysis of a distributed Video-on-Demand (VoD) system that includes an integrated model of the server and the network subsystems with analysis of its impact on client operations. The VoD system provides service to a heterogeneous client base at multiple playback rates. A class-based service model is developed where an incoming video request can specify a playback rate at which the data is consumed on the client. Using an analytical model, admission control conditions at the server and the network are derived for multi-rate service. We also develop client buffer requirements in presence of network delay bounds and delay jitter bounds using the same integrated framework of server and network subsystems. Results from an extensive simulation show that request handling policies based on limited redirection of blocked requests to other resources perform better than load sharing policies. The results also show that downgrading the service for blocked requests to a lower bitrate improves VoD system performance considerably. Combining the downgrade option with restrictions on access to high bitrate request classes is a powerful tool for manipulating an incoming request mix into a workload that the VoD system can handle.     

P2P VoD系统的关键技术研究进展

结合现有的对等网络视频点播系统,分析了P2P VoD系统的关键技术及其研究进展,主要包括视频点播系统结构的构建、节点失效时的修复策略、数据片断的缓存和调度策略、对VCR操作的支持策略、以及QoS保证机制等等.     

Distributed Throughput Maximization in P2P VoD Applications

In peer-to-peer (P2P) video-on-demand (VoD) systems, a scalable source coding is a promising solution to provide heterogeneous peers with different video quality. In this paper, we present a systematic study on the throughput maximization problem in P2P VoD applications. We apply network coding to scalable P2P systems to eliminate the delivery redundancy. Since each peer receives distinct packets, a peer with a higher throughput can reconstruct the video at a higher quality. We maximize the throughput in the existing buffer-forwarding P2P VoD systems using a fully distributed algorithm. We demonstrate in the simulations that the proposed distributed algorithm achieves a higher throughput compared to the proportional allocation scheme or the equal allocation scheme. The existing buffer-forwarding architecture has a limitation in total upload capacity. Therefore we propose a hybrid-forwarding P2P VoD architecture to improve the throughput by combining the buffer-forwarding approach with the storage-forwarding approach. The throughput maximization problem in the hybrid-forwarding architecture is also solved using a fully distributed algorithm. We demonstrate that the proposed hybrid-forwarding architecture greatly improves the throughput compared to the existing buffer-forwarding architecture. In addition, by adjusting the priority weight at each peer, we can implement the differentiated throughput among different users within a video session in the buffer-forwarding architecture, and the differentiated throughput among different video sessions in the hybrid-forwarding architecture.      

一个具有高可用性的动态容错VoD系统

提出了一个在VoD系统中具有高可用性的动态容错算法。针对分布式应用的特点，能对控制节点实现服务器切换的容错，数据服务节点负载均衡分配和故障节点提供服务的恢复。同时按照文章一致性保证机制可以实现媒体服务故障恢复对客户端的透明。通过对系统可用性分析和仿真试验表明，该算法可以有救地提高系统的可用性。     

一种适用于VoD/P2P的存储调度策略

近年来,基于对等网络的视频点播系统(VoD/P2P)备受人们关注.在这类系统中,存储的难点主要表现为VoD应用中庞大的视频数与P2P网络中有限的存储资源之间的矛盾.提出对等数据随机访问的存储策略(Equivalent Data Random Access,EDRA),并重点研究了如何采用EDRA对VoD/P2P系统的存储进行优化调度,以最小化系统的资源占用或最大化系统的容量.实验表明,EDRA可以达到很高的节点带宽利用率,在相同条件下支持的最大点播数可能比传统方案高出58-73%.     

VoD系统性能的综合研究

分析了可能成为VoD系统瓶颈的几个主要因素，给出了在VOD系统的设计与实现中进行许可控制的方法，从而有助于提高VoD系统的性能。     

Distributed admission control for anycast flows

Anycasting has recently become an important research topic, especially for replicated servers. With anycasting, applications can request the "nearest" server for provision of desired (multimedia) service. In this paper, we study efficient distributed admission control (DAC) for anycast flows. We focus on algorithms that perform destination selection and efficient path establishment. Taking advantage of anycasting, our distributed algorithms differ from each other in their dependence on system status information. Performance data obtained through mathematical analysis and simulations show that, in terms of admission probabilities, DAC systems that are based on local status information have performance levels close to those that utilize global and dynamic status information. This renders our DAC algorithms useful not only for the network layer, but also for the application layer admission control for anycast flows.     

DPVoD:基于P2P的视频点播体系结构

可扩展性和可靠性是视频点播系统大规模应用的关键,提出了一种P2P点播系统结构DPVoD.系统基于应用层组播,用户以订制的缓存为其他节点提供服务,并形成相对独立的共享并发流组播树,组播树之问根据拥有的视频数据的重合程度而建立不同的组邻居关系,以此为基础,采用多种机制来提高系统性能:组协同工作、父亲点选择策略、状态控制协议和失效恢复等.定义并分析了可能对系统性能有严重影响的结尾雪崩问题并提出解决方案.对系统基本性能进行了理论分析.仿真结果表明,在静态和动态环境中,DPVoD系统的并发流占用数和利用率、可靠性等性能均优于类似系统.     

基于代理的视频点播系统设计

视频点播（Video-on-Demand,VoD)是现代网络上的一个重要多媒体应用。在传统的集中式视频点播系统中，如果用户数目过多，将会出现服务器I/O及网络带宽的瓶颈，而采用基于代理服务器的分布式体系结构，可以把VoD系统的负载分布到放置在网络不同位置的各个代理服务器上，能很好地解决系统瓶颈问题，阐述了基于代理的VoD系统的特点，设计原则，以及设计的关键问题，并提出了一种基于代理服务器的VoD系统模型。