Design of a bandwidth-on-demand (BoD) protocol for satellite networks modelled as time-delay systems

Bandwidth-on-demand (BoD) access protocols address the problem of guaranteeing a high exploitation of the valuable satellite bandwidth in the presence of large amount of data traffic accessing the satellite network. The novelty of the proposed BoD scheme consists in the use of control theory concepts to model the satellite network as a time-delay system and to generate the bandwidth requests. The proposed scheme, based on the internal model control and on the Smith's principle, yields the following advantages: (i) when the network is not congested, it provides upper-bounds to the queue lengths and to the queuing delays of the satellite terminal buffers; (ii) it is capable of recovering from congested states; (iii) it is independent of the statistical characteristics of the traffic entering the satellite network; (iv) the requests are such that the satellite terminals have always enough traffic to use all the requested bandwidth (so that no bandwidth is wasted). The paper includes simulations showing the effectiveness of the proposed BoD scheme. The work underlying this paper has been performed within the GEOCAST project belonging to the fifth framework Information Society and Technology programme of the European Union.     

Congestion control in high-speed communication networks using the Smith principle

High-speed communication networks are characterized by large bandwidth-delay products. This may have an adverse impact on the stability of closed-loop congestion control algorithms. In this paper, classical control theory and Smith’s principle are proposed as key tools for designing an effective and simple congestion control law for high-speed data networks. Mathematical analysis shows that the proposed control law guarantees stability of network queues and full utilization of network links in a general network topology and traffic scenario during both transient and steady-state condition. In particular, no data loss is guaranteed using buffers with any capacity, whereas full utilization of links is ensured using buffers with capacity at least equal to the bandwidth-delay product. The control law is transformed to a discrete-time form and is applied to ATM networks. Moreover a comparison with the ERICA algorithm is carried out. Finally, the control law is transformed to a window form and is applied to Internet. The resulting control law surprisingly reveals that today's Transmission Control Protocol/Internet Protocol implements a Smith predictor for congestion control. This provides a theoretical insight into the congestion control mechanism of TCP/IP along with a method to modify and improve this mechanism in a way that is backward compatible.     

Neural networks in virtual reference tuning

This paper discusses the application of the virtual reference tuning (VRT) techniques to tune neural controllers from batch input-output data, by particularising nonlinear VRT and suitably computing gradients backpropagating in time. The flexibility of gradient computation with neural networks also allows alternative block diagrams with extra inputs to be considered. The neural approach to VRT in a closed-loop setup is compared to the linear VRFT one in a simulated crane example.     

A neural-network-based model reference PID-like controller for process control

This paper presents a neural-network-based PID-like control strategy applicable to a class of nonlinear control problems commonly encountered in the process-control industry. An artificial neural network is used to provide compensation of the plant's nonlinear dynamics so that the overall closed-loop system can be described in terms of an equivalent error system. In the paper, the strategy is carefully described, and then evaluated and compared with an alternative control system design which uses conventional gain-scheduled PID controllers. The paper includes real-time experimental results in applying the proposed technique for level control of a coupled-tanks system.     

A new approach to adaptive control: no nonlinearities

In adaptive control the goal is to design a controller to control an uncertain system whose parameters may be changing with time. Typically the controller consists of an identifier (or tuner) which is used to adjust the parameters of a linear time-invariant (LTI) compensator, and under suitable assumptions on the plant model uncertainty it is proven that good asymptotic behaviour is achieved, such as model matching (for minimum phase systems) or stability. However, a typical adaptive controller does not track time-varying parameters very well, and it is often highly nonlinear, which can result in undesirable behaviour, such as large transients or a large control signal. Furthermore, most adaptive controllers provide only asymptotic tracking, with no ability to design for a pre-specified settling time.Here we propose an alternative approach, which yields a linear periodic controller. Rather than estimating the plant or compensator parameters, instead we estimate what the control signal would be if the plant parameters were known. In this paper we argue the utility of this approach and then examine the first order case in detail, including a simulation. We also explore the benefits and limitations of the approach.     

飞机纵向运动模型参考反推自适应PID控制

为克服飞行控制系统设计中传统增益规划方案的缺点,提出一类飞机纵向运动模型参考反推自适应PID控制方案,并给出了该方案的具体设计过程和跟踪性能改善方法．理论分析和数值仿真结果表明．该方案兼具反推自适应控制和PID控制的优点．即：无需知道被控对象的精确数学模型,控制器结构简单,鲁棒性强,在不增大控制增益的前提下具有良好的跟踪性能．     

Receiver-initiated medium access control protocols for wireless sensor networks

One of the fundamental building blocks of a Wireless Sensor Network (WSN) is the Medium Access Control (MAC) protocol, that part of the system governing when and how two independent neighboring nodes activate their respective transceivers to directly interact. Historically, data exchange has always been initiated by the node willing to relay data, i.e. the sender. However, the Receiver-Initiated paradigm introduced by Lin et al. in 2004 with RICER and made popular by Sun et al. in 2008 with RI-MAC, has spawned a whole new stream of research, yielding tens of new MAC protocols. Within such paradigm, the receiver is the one in charge of starting a direct communication with an eligible sender. This allows for new useful properties to be satisfied, novel schemes to be introduced and new challenges to be tackled. In this paper, we present a survey comprising of all the MAC protocols released since the year 2004 that fall under the receiver-initiated category. In particular, keeping in mind the key challenges that receiver-initiated MAC protocols are meant to deal with, we analyze and discuss the different protocols according to common features and design goals. The aim of this paper is to provide a comprehensive and self-contained introduction to the fundamentals of the receiver-initiated paradigm, providing newcomers with a quick-start guide on the state of the art of this field and a palette of options, essential for implementing applications or designing new protocols.     

一类直接模型参考Backstepping自适应控制

提出一种新的直接模型参考Backstepping自适应控制系统结构:谈系统在直接模型参考卓适应控制(MRAC)结构的基础上,增加了Beckstepping控制信号发生器,通过Backstepping方法的灵活设计获得良好的过渡过程品质,得到直接MRAC在稳定性和鲁棒性设计等方面的优点.采用高阶调节器设计了未具规范化的直接模型参考Backstepping自适应律,克服了传统自适应律引入规范化信号后使系统过渡过程品质下降的缺点.     

机械臂轨迹跟踪控制--基于EC-RBF神经网络的机械臂模型参考自适应控制

针对机械臂运动轨迹控制中存在的跟踪精度不高的问题,采用了一种基于EC-RBF神经网络的模型参考自适应控制方案对机械臂进行模型辨识与轨迹跟踪控制。该方案采用了两个RBF神经网络,运用EC-RBF学习算法,采用离线与在线相结合的方法来训练神经网络,一个用来实现对机械臂进行模型辨识,一个用来实现对机械臂轨迹跟踪控制。对二自由度机械臂进行仿真,结果表明,使用该控制方案对机械臂进行轨迹跟踪控制具有较高的控制精度,且因采用EC-RBF学习算法使网络具有更快的训练速度,从而使得控制过程较迅速。     

Feedback linearization-based satellite attitude control with a life-support device without communications

This paper develops a control strategy for a life-support device to be attached to an orbiting satellite to extend its operational life. The objective is met in such a way that the original satellite keeps operating without communications between the two systems (also valuable for energy efficiency). The case in which the original satellite is equipped with a feedback-linearization based controller is considered and the control law for the life-support is developed with the same methodology, obtaining a compensating control which recovers the performance of the original control strategy. Simulations validate the approach considering a real case study in various scenarios.     

一种卫星网络中RTT公平性增强算法

为解决卫星网络中由于链路长时延、网络拓扑动态变化等造成的TCP连接RTT不公平性问题,给出了一个卫星网络中RTT不公平性增强方案TCP Riff。TCP Riff中引入了参考连接RTT的概念,通过一个基准RTT,使得异构RTT的TCP连接窗口的增长,继而传输速率的增长独立于连接的RTT,从而获得了很好的RTT公平性。NS仿真实验表明TCP Riff明显地减少对长RTT连接的性能差异,并且,在出现拥塞和链路差错情况下,相对于TCP标准版本具有明显的吞吐量优势,以及良好的公平性和友好性。值得提出的是TCP Riff没有破坏TCP协议端到端的语义,并且与其他TCP增强方案是兼容的。     

An extremum-seeking control approach for constrained robotic motion tasks

In this paper, we propose two adaptive control schemes for multiple-input systems for execution of robot end-effector movements in the presence of parametric system uncertainties. The design of these schemes is based on Model Reference Adaptive Control (MRAC) while the adaptation of the controller parameters is achieved by Extremum Seeking Control (ESC). The two control schemes, which are called Multiple-Input ESC–MRAC and Multiple-Input Adaptive-Dynamic-Inversion ESC–MRAC, are suitable for linear and nonlinear systems respectively. Lyapunov and averaging analysis shows that the proposed schemes achieve practical asymptotic reference state tracking. The proposed methods are evaluated in simulations and in a real-world robotic experiment.     

An MPC-based reference governor approach for offset-free control of constrained linear systems

This paper presents a model predictive control (MPC) based reference governor approach for control of constrained linear systems. A nominal closed-loop system is first designed to guarantee that, in the unconstrained case, asymptotic zero-error regulation for (piecewise) constant reference signals is achieved. Then, a couple of exogenous signals are added to the reference signal and to the control variable and their value is determined by formulating a MPC problem in order to guarantee that (i) when the state and control constraints are not active, the nominal closed-loop system is recovered, (ii) in transient conditions the constraints are always satisfied and the difference of the performances between the real and the nominal closed-loop systems is minimised, and (iii) when the reference signal is infeasible, the output is brought to the nearest feasible value. A simulation example is reported to witness the potentialities of the approach.     

热电偶检定炉炉温模型参考自适应控制的研究

热电偶校检定炉在对热偶进行高温点的校验时,炉温难于稳定,主要原因在于控高温时加热时间较长环境温度产生较大变化,从而造成检定炉加热模型产生时变,导致控制器效果明显变差,本文利用模型参考自适应控制方法在线调整PID控制器参数以适应环境温度变化而造成的加热炉模型时变,试验结果表明该方法适应性良好,从而为热电偶检定炉的温度控制提供了新的方法。     

Model predictive pressure control of steam networks

The control scheme of industrial power plants leads typically to a complex multivariable control structure with active constraints to be taken care of. Then Model Predictive Control method (MPC) handles multivariate control problems naturally and optimal control result is calculated considering actuator limitations and constraints of process variables. MPC is applied to control the pressure stability in a multilevel steam network. The system is demonstrated in a simulator environment. MPC can also be used as a convenient tool for analyzing and designing the structure of the steam network. A power plant simulator controlled by MPC helps to decide the location and the capacity of steam levelling components needed to stabilize the operation of the process.     

基于概率的三维无线传感器网络K-覆盖控制方法

针对无线传感器网络在三维空间监测中存在的固有的不确定性与系统应具有较强的容错能力、鲁棒性之间的矛盾,提出了一种基于概率的三维无线传感器网络K-覆盖控制方法.对三维待监测区域以网格建模,用迭代的贪婪启发式方法确定传感器节点在网格中的位置,每一步迭代完成一个节点的放置,直到节点总数达到预设的上界或每个网格点以概率T达到K-覆盖为止.仿真结果表明,相对于传统的随机和均匀配置方法,本方法能使用较少的节点满足相同的覆盖度和监测精度的要求,或使用相同的节点达到更高的覆盖度.并对整个待监测区域中有优先覆盖要求(覆盖度优先和监测精度优先)的局部区域的情况进行了分析.     

State tracking model reference adaptive control for switched nonlinear systems with linear uncertain parameters

Model reference adaptive control(MRAC)is considered for a class of switched nonlinear systems in which the unknown parameters appear linearly.The linear uncertain parameters in each subsystem can be expressed as a vector and the uncertain vectors in different subsystems are estimated individually by different vector variables.Update laws are designed such that the parameter estimation will ’freeze’ until its corresponding subsystem is active.Controllers for subsystems are given to ensure asymptotic states tracking under arbitrary switchings.Two examples are presented to validate the proposed method.     

On the convergence of a model reference adaptive control algorithm with unknown high frequency gain

A model reference adaptive control algorithm is shown not to be exponentially convergent when the high frequency gain of the plant is unknown. The implication is that such an algorithm will be lacking in some way in robustness.     

A distributed predictive control approach for periodic flow-based networks: application to drinking water systems

This paper proposes a distributed model predictive control approach designed to work in a cooperative manner for controlling flow-based networks showing periodic behaviours. Under this distributed approach, local controllers cooperate in order to enhance the performance of the whole flow network avoiding the use of a coordination layer. Alternatively, controllers use both the monolithic model of the network and the given global cost function to optimise the control inputs of the local controllers but taking into account the effect of their decisions over the remainder subsystems conforming the entire network. In this sense, a global (all-to-all) communication strategy is considered. Although the Pareto optimality cannot be reached due to the existence of non-sparse coupling constraints, the asymptotic convergence to a Nash equilibrium is guaranteed. The resultant strategy is tested and its effectiveness is shown when applied to a large-scale complex flow-based network: the Barcelona drinking water supply system.     

A detailed review of energy-efficient medium access control protocols for mobile sensor networks

This article reviews the state-of-the-art energy-efficient contention-based and scheduled-based medium access control (MAC) protocols for mobile sensor networks (MSNs) by first examining access schemes for wireless sensor networks (WSNs). Efficient and proper mobility handling in sensor networks provides a window of opportunity for new applications. Protocols, such as S-MAC, reduce energy consumption by putting nodes to sleep after losing to channel contention or to prevent idling. Sleeping is a common method for energy-efficient MAC protocols, but delay depends on sleep duration or frame time, and longer delays lead to higher packet lost rate when nodes are unsynchronized due to network mobility. MS-MAC extends S-MAC to include mobility-awareness by decreasing this sleep duration when mobility is detected. S-MAC with extended Kalman filter (EKF) reduces mobility-incurred losses by predicting the optimal data frame size for each transmission. MMAC utilizes a dynamic mobility-adaptive frame time to enhance TRAMA, a scheduled-based protocol, with mobility prediction. Likewise, G-MAC utilizes TDMA for cluster-based WSNs by combining the advantages of contention and contention-free MACs. Z-MAC also combines both methods but without clustering and allows time slot re-assignments during significant topology changes. All of the above MAC protocols are reviewed in detail.