This thesis mainly focuses on two Internet based control applications. One is a networked control system (NCS) where the control loop is closed through the network. The other is the Networked Control System Laboratory (NCSLab) which is a global web based remote experimentation platform. The contribution in the first part of the thesis relates to the networked predictive control (NPC) which was first introduced by Liu et al. (2004). In this method, the controller uses the model predictive approach to predict a future control sequence and send it to the plant in a network packet. The plant side receives this packet and then determine the appropriate control signal to apply to the actuator according to the time delay measurement. This method is innovative and works well in theory, but it has two deficiencies in practical applications. The first deficiency is that it needs synchronization between the controller and plant side to measure the individual forward and feedback channel time delays and this is very hard to achieve on the Internet. In this thesis, a round-trip NPC is proposed in which the predictive calculations and signal selections are based on the round-trip delay. The measurement of the round-tip delay is achieved using the plant side clock only, so that the need for synchronization is avoided. The second deficiency is that the mathematical model has to be accurately known. Otherwise the accuracy of the predictive calculation is affected, which may result in a degraded control performance. An event-driven NPC scheme is introduced to solve this problem. In this scheme, the selection of the appropriate control signal is not based on the time delay measurement but on the previous system output. This method can compensate for the effect of model uncertainty, which has been verified by both simulations and real-time experiments. Some experiments carried out on other NPC schemes are also reported on in this thesis. They are the NPC in state-space form and nonlinear NPC. These methods expand the use of NPC methodology. The second part of the thesis describes the design and implementation of the Networked Control System Laboratory. The NCSLab is based in the University of Glamorgan but its test rigs are diversely located in four Institutions from both the UK and China. In order to manage these test rigs from different places, a four layer structure (Central Server/Regional Server/Sub-Server/Test Rig) is adopted. The four layers are integrated into one system via the Internet. In order to deliver the remote experimentation to the users, a web-based user interface is designed. It provides great flexibility to the users such as remote monitoring, remote tuning and remote control algorithms. The implementation of the user interface (UI) heavily adopts the AJAX technology, so the remote experiments can be conducted inside the web browsers without installing special plug-ins. In order to show how the NCSLab works, two examples are given in the thesis.

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Various wireless networks are widely deployed world wide. Current technologies employed in these networks vary widely in terms of bandwidths, latencies, frequencies, and media access methods. Most existing wireless network technologies can be divided into two categories: those that provide a low-bandwidth service over a wide geographic area, for example UMTS, and those that provide a high bandwidth service over a narrow geographic area, for example 802.11. Although it would be desirable to provide a high- bandwidth service over a wide coverage region to mobile users all the time, no single wireless network technology simultaneously satisfies these require- ments. Wireless Overlay Networks, a hierarchical structure of wireless personal area, local area, and wide area data networks, is considered as an efficient and scalable way to solve this problem. Due to the wide deployment of UMTS and 802.11 WLAN, this study attempts to combine them to implement the concept of Wireless Overlay Net- works. Furthermore, the information transmitted over this Wireless Overlay Networks is protected in terms of authentication, integrity and confidentiality. To achieve this goal, this study aims to combine GPRS, Mobile IP and IPSec to propose a framework for secure mobility in Wireless Overlay Networks. The framework is developed in three steps: Firstly, this study addresses the problem of combining GPRS and Mo- bile IP, so that GPRS users are provided with Mobile IP service. This results in presenting a uniform Mobile IP interface to peers regardless of whether mobile users use UMTS or 802.11 WLAN. Secondly, this study discovers the existing problem when combining Mobile IP and IPSec, and proposes a Dual Home Agent Architecture to achieve secure mobility. Finally, based on the output of the previous two steps, a complete framework is proposed, which achieves secure mobility in Wireless Overlay Networks, specifically, in UMTS and 802.11 WLAN. The framework also implements seamless handover when mobile users switch between UMTS and 802.11. This results in UMTS and 802.11 WLAN looking like a single network when participating in this framework, and presents seamless and secure mobility.

Reachability analysis is one of the earliest and most common techniques for protocol validation. It is well suited to checking the protocol syntactic properties since they are a direct consequence of the structure of the reachability tree. However, validations of unbounded protocols via reachability analysis always lead to the "state explosion" problem. To overcome this, a new approach in reachability analysis has been proposed by Vuong et al [Vuong 82a, 83a]. While not loosing any information on protocol syntactic properties, the Teachability tree constructed by the new approach for all non-FIFO and for a particular set of FIFO protocols (called well-ordered protocols) will become finite. This thesis is concerned with the implementation of an integrated package called VALIRA (VALIdation via Reachability Analysis) which bases on both the proposed technique and the conventional technique. Details and implementation of the various approaches used in VALIRA are presented in order to provide an insight to the package. Various features of the package are demonstrated with examples on different types of protocols, such as the FIFO, the non-FIFO, and the priority protocols. The use of VALIRA was found to be practical in general, despite some limitations of the package. Further enhancements on the VALIRA are also suggested. / Science, Faculty of / Computer Science, Department of / Graduate

Unidirectional broadcast structures constitute a class of high performance local network architectures. They are very flexible and well suited for fiber optic implementation. The access methods used in these networks are often based on certain implicit token-passing mechanisms to provide superior delay-vs-throughput characteristics. The performance of these unidirectional broadcast protocols is evaluated in this thesis via a study on the classical token-ring system. Emphasis is placed on the analysis of mean delay-vs-throughput performance for the gated exhaustive service discipline under asymmetric traffic. The analysis involves examination of the statistical behaviour of interacting queues. A number of exact results are derived and based on these results, a very good approximation for the average delays is developed. The approximation agrees closely with exact numerical solutions over a wide range of system parameters. The implications of the approximation are also discussed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This thesis presents the development and implementation of two fundamental communication sublayers, medium access and logical link, for a new Local Area Network (LAN) which utilizes the intra-building power distribution circuit as physical transmission medium. This medium provides a low cost means for data communications with a high degree of portability. A low-to-medium data rate and a relatively high error rate are two of the major disadvantages associated with the use of the medium. The Logical Link Control (LLC) protocol adopted is a modified version of the IEEE 802.2 protocol; whereas, the Medium Access Control (MAC) protocol used is a simple hub polling scheme. For efficiency reason, both LLC and MAC sublayers are implemented in the kernel of the UNIX¹ operating system. The schemes used, justifications for the decisions made and their implementations are discussed in details in the thesis. The performance of the power line LAN formed with four Sun workstations² using modems with a data rate of 14.4 kilo-bit per second is measured and analyzed. ¹UNIX is a trademark of AT & T Bell laboratories. ²Sun workstation is a trademark of Sun Microsystems. / Science, Faculty of / Computer Science, Department of / Graduate

A high-speed local area communication network--the Expressnet--is investigated in this thesis with regard to voice and data transmissions. Performance criteria, such as channel utilizations, delay characteristics, and queue lengths are determined from computer simulation and numerical calculation approaches. The protocol is particularly suitable for the transmission of packetized voice as it is able to guarantee an upper bound on the transmission delay for each packet. The network under study thus will find major application in future office automation, where large amounts of voice will be integrated with data. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

A wireless mesh network (WMN) is a multihop wireless network consisting of a large number of wireless nodes of which some are called gateway nodes and connected with a wired network. Wireless mesh network have attracted much research attention recently due to its flexibility, low-cost and robustness, which facilitate its usability in many potential applications, including last-mile broadband Internet access, neighborhood gaming, Video-on-Demand (VoD), distributed file backup, video surveillance, etc. The broadcast nature, the lack of infrastructure as well as the flexible deployment nature of wireless mesh networks make it different from wired networks, therefore more attention in designing the wireless mesh network is needed to maintain a good performance of this promising technology. We, in this study, investigate the wireless mesh network design taking into consideration three design factors seeking an improvement in the network performance by reducing the interference influence in the network, improving the network reliability to satisfy more requests, and securing the network against malicious eavesdropping attacks. Our design is presented into three sub-problems; sub-problem (1), which seeks an interference-aware robust topology control scheme, sub-problem (2) which seeks a multipath routing scheme, and sub-problem (3) which seeks a secure key management scheme. Through simulations and comparisons with previous work, we show that our proposed solutions outperform previous schemes in providing a better network performance in terms of reducing the network interference, satisfying more number of requests and increasing the network resistance to malicious eavesdropping attacks.

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