Distributed LQR control of multi-agent systems

The thesis develops optimal control methods for designing distributed cooperative control schemes in multi-agent networks. First, the model of a completely connected multi-agent network is presented, consisting of identical dynamically decoupled agents controlled by a centralized LQR (Linear Quadratic Regulator) based controller. The structure of the solution, as well as controller's spectral and robustness properties are presented. A special case of centralized control where the optimal solution for the whole network can be constructed from the solution of single agent LQR system is given. The problem is extended to distributed control where the special structure is imposed onto the information flow between agents and only local interaction is considered. A systematic method is given for computing the performance loss of various distributed control configurations relative to the performance of the optimal centralized controller. Necessary and sufficient conditions are derived for which a distributed control configuration pattern arising from the optimal centralized solution does not entail loss of performance if the initial state vector lies is a certain subspace of state-space which is identified. It is shown that these conditions are always satisfied for systems with communication/control networks corresponding to complete graphs with a single link removed. The procedure is extended for the purposes of analysing the performance loss of an arbitrary distributed configuration. Cost increase due to decentralisation is quantified by introducing three cost measures corresponding to the worst-case, best-case and average directions in which the initial state of the system lies. Finally, a cooperative scheme is presented for controlling arbitrary formations of low speed experimental UAVs (Unmanned Aerial Vehicles) based on a distributed LQR design methodology. Each UAV acts as an independent agent in the formation and its dynamics are described by a 6-DOF (six degrees-offreedom) nonlinear model. This is linearised for control design purposes around an operating point corresponding to straight flight conditions and simulated for longitudinal motion. It is shown that the proposed controller stabilises the overall formation and can control effectively the nonlinear multi-agent system. Also, it is illustrated via numerous simulations that the system provides reference tracking and that is robust to environmental disturbances such as nonuniform wind gusts acting on a formation of UAVs and to the loss of communication between two neighbouring UAVs

An empirical study of employee loyalty, service quality, cost reduction and company performance

The focus of this study was on investigating the relationships among employee loyalty, service quality, cost reduction and company performance, with the aim to investigate the impact of employee loyalty to company performance. The research model was developed and empirically tested on the sample of 100 service companies with 317 questionnaire surveys conducted in the Republic of Serbia and Bosnia and Herzegovina. Using different statistical analysis (the Kolmogorov-Smirnovljev statistic, Path analysis, A.M.O.S. statistic software and lavaan software) leads to the conclusion that employee loyalty is significantly related and has a positive influence on company performance

Securing industrial cyber-physical systems: A run-time multi-layer monitoring

Industrial Cyber-Physical Systems (ICPSs) are widely deployed in monitoring and control of the nation's critical industrial processes such as water distribution networks and power grids. ICPSs are the tight integration of cyber (software) and physical entities connected via communication networks. Communication networks are typically realised via wireless channels to reduce the cost of wires and installation. However, they are also inherently unreliable, easy to disrupt and subvert, which makes them a potential target for cyber attacks. The failure of communication can cause data loss or delays, which can compromise system functionality and have catastrophic consequences due to the strict real-time requirements of ICPSs. Current run-time security monitors protect ICPSs either at communication level (through network intrusion monitors) or application level (through threat detection monitors). Such monitors are layer-specific and thus fail to detect advanced threats arising from the multi-layer disruption. In this paper, we present a multi-layer run-time security monitor that can detect discrepancies caused by interdependent application and communication layer attacks and prevent their propagation into the system's control loops. We demonstrate the effectiveness of the approach via an example of the ICPS used for control and monitoring of a water distribution network

Performance analysis of distributed control configurations in LQR multi-agent system design

The paper considers a distributed Linear Quadratic Regulator (LQR) design framework for a network of identical dynamically decoupled multi-agent systems. It is known that in this case a stabilizing distributed controller for the network can be obtained by solving a centralized LQR problem whose size depends on the maximum vertex degree of the graph. A systematic method is presented for computing the performance loss of various distributed control configurations relative to the performance of the centralized controller. A procedure is developed for analyzing the performance loss for general distributed control configurations and state-space directions. It is also shown that by removing a single link we can always define a control configuration for which there is no performance loss, provided the initial state of the aggregate system lies in a particular direction of state-space which is identified. The results are illustrated by an exhaustive analysis of the network consisting of six identical agents

A survey of potential security issues in existing wireless sensor network protocols

The increasing pervasiveness of wireless sensor networks (WSNs) in diverse application domains including critical infrastructure systems, sets an extremely high security bar in the design of WSN systems to exploit their full benefits, increasing trust while avoiding loss. Nevertheless, a combination of resource restrictions and the physical exposure of sensor devices inevitably cause such networks to be vulnerable to security threats, both external and internal. While several researchers have provided a set of open problems and challenges in WSN security and privacy, there is a gap in the systematic study of the security implications arising from the nature of existing communication protocols in WSNs. Therefore, we have carried out a deep-dive into the main security mechanisms and their effects on the most popular protocols and standards used in WSN deployments, i.e., IEEE 802.15.4, Berkeley media access control for low-power sensor networks, IPv6 over low-power wireless personal area networks, outing protocol for routing protocol for low-power and lossy networks (RPL), backpressure collection protocol, collection tree protocol, and constrained application protocol, where potential security threats and existing countermeasures are discussed at each layer of WSN stack. This paper culminates in a deeper analysis of network layer attacks deployed against the RPL routing protocol. We quantify the impact of individual attacks on the performance of a network using the Cooja network simulator. Finally, we discuss new research opportunities in network layer security and how to use Cooja as a benchmark for developing new defenses for WSN systems

Failures from the Environment, a Report on the First FAILSAFE workshop

This document presents the views expressed in the submissions and discussions at the FAILSAFE workshop about the common problems that plague embedded sensor system deployments in the wild. We present analysis gathered from the submissions and the panel session of the FAILSAFE 2017 workshop held at the SenSys 2017 conference. The FAILSAFE call for papers specifically asked for descriptions of wireless sensor network (WSN) deployments and their problems and failures. The submissions, the questions raised at the presentations, and the panel discussion give us a sufficient body of work to review, and draw conclusions regarding the effect that the environment has as the most common cause of embedded sensor system failures

Disadvantages of electrocoagulation-flotation treatment of offset printing effluents

The efficiency of electrocoagulation-flotation (ECF) treatment was estimated based on the quantity of pollutants (cooper, turbidity, and organic substances) in printing effluents (waste offset printing developer and waste offset fountain solution) at selected process parameters. Four sets of aluminum or/and iron electrode combinations were applied, each with a current density of 2, 4, and 8 mA cm−2 and interelectrode distances of 0.5, 1.0, and 1.5 cm. In the progress of the ECF treatment, samples were taken at certain process times (1, 5, 10, 20, 40, and 60 min). Based on the obtained results, the disadvantages of ECF treatment of offset printing effluents are defined

The heavy metals in the processing screen printing inks

The contents of heavy metals were analyzed in the two types (solvent-based and water-based) of processing screen printing inks. Mass concentrations of heavy metals (copper, iron, zinc, manganese, chromium, nickel, cadmium, and lead) were determined in the tested screen inks by combining the gravimetric method and atomic absorption spectroscopy. The results indicated that the measured mass concentration of copper (2049.9 mg kg-1 ) in solvent-based cyan ink is 2.4 times higher than in water-based cyan. Other detected metals show higher concentration values with water-based processing inks

Electrocoagulation removal of heavy metals from wastewater generated by washing a screen printing plate

The possibility of applying electrocoagulation treatment to remove heavy metals (zinc, copper, and chromium) from wastewater generated during the washing process of the screen printing plate was carried out. The electrocoagulation efficiency is estimated based on reducing the concentrations of detected heavy metals in the screen wastewater at defined process parameters such as electrode material, current density, interelectrode distance, and operating times