Communication amongst field devices, control unit and programming unit in industrial automation networks is essential for bulk production, but largely consists of wired networks that can sometimes be bulky and substantially lack mobility as at times there can arise a need for a field device to be moved either for maintenance purposes or for rearrangement. There was therefore a need for wireless communication and PROFIBUS networks that can provide the minimum movement to field devices or the programing computer. Although wireless communication technology has penetrated the commercial network, it is still inadequately utilised in industrial settings due to electromagnetic induction and other forms of interferences due to industrial machinery. This dissertation introduced wireless communication in a PROFIBUS network where the MPI section was replaced with the wireless link. The PROFIBUS network technology is a hybrid of protocols where the PROFIBUS DP employs RS485 technology with a transmission rate of 45 kbps and above while the PROFIBUS PA employs Manchester Encoded Bus Powered (MBP) technology at a fixed rate of 31.25 kbps. In RS485 technology, data is transmitted as a voltage difference between the two wires while in MBP data is transmitted as transitions in current signal and data and power are transmitted on the same conductors. The PROFIBUS data is also transmitted in the form of telegrams which further puts a strain on any form of intermediate processing and hence the need for high speed processing. In this research task the PROFIBUS PA level transmitter measures the pressure of the fluid in the Blend Chest and sends it to the PLC. The level transmitter was installed and wired to the PROFIBUS DP/PA coupler. The PROFIBUS network, consisting of the PLC, variable speed drives, variable speed pumps, delivery pump and level transmitter, was configured and commissioned for controlling and monitoring from the programing computer. The program for the PLC was written using Siemens Step-7, compiled and downloaded to the PLC. The control and monitoring was done using the variable table. The wireless communication channel was then simulated using Matlab and Simulink. The wireless devices were then integrated into the PROFIBUS network and the MPI cable linking the programing computer and the PLC was then replaced by the wireless channel and the network was controlled and monitored from the programing computer over the wireless channel. On successful completion of this research task the research plant at MUT was controlled and monitored from the programing computer over the wireless channel and the researchers and demonstrators can now access the PLC and the PROFIBUS network using the wireless communication. / Electrical Engineering / M. Tech. (Electrical Engineering)

published_or_final_version / Computer Science / Doctoral / Doctor of Philosophy

Lam Kong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 84-85). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Related Work and Background --- p.7 / Chapter 2.1 --- Competition-free Unlimited Capacity Model´ؤOne-hop Case --- p.9 / Chapter 2.2 --- Competition-free Unlimited Capacity Model一Two-hop Case --- p.11 / Chapter 3 --- Extensions to Competition-free Unlimited Capacity Model --- p.13 / Chapter 3.1 --- Optimal Pricing for the One-hop Case under Various Utility Distributions --- p.13 / Chapter 3.2 --- Optimal Pricing for Competition-free Multi-hop Wireless Mesh Networks --- p.16 / Chapter 3.3 --- The Issue on Network Scaling --- p.22 / Chapter 4 --- Competition-free Limited Capacity Model --- p.28 / Chapter 4.1 --- One-hop Case --- p.28 / Chapter 4.2 --- Multi-hop Case --- p.36 / Chapter 5 --- Unlimited Capacity Model with Price Competition --- p.42 / Chapter 5.1 --- Renewed Game Model for Networks with Price Competition --- p.43 / Chapter 5.2 --- Pricing Equilibriums in Different Network Topologies --- p.46 / Chapter 5.2.1 --- Case A: Two Access Points Competing in a One-hop Network --- p.47 / Chapter 5.2.2 --- Case B: Two Access Points Competing in a Two-hop Network --- p.51 / Chapter 5.2.3 --- Case C: Two Resellers Competing in a Two-hop Network --- p.54 / Chapter 5.2.4 --- Case D: Extending Case A into a Multi-hop Network --- p.60 / Chapter 5.2.5 --- Case E: Extending Case C into a Multi-hop Network. --- p.66 / Chapter 5.2.6 --- The Unified Pricing Equilibrium --- p.68 / Chapter 5.2.7 --- Case F: The Characterizing Multi-hop Network --- p.75 / Chapter 5.3 --- Revisiting the Network Scaling Issue --- p.80 / Chapter 6 --- Conclusion --- p.82 / Bibliography --- p.84 / Chapter A --- Proof of the PBE for Competition-free Multi-hop Wireless Mesh Networks --- p.86 / Chapter B --- Proof of the Unified Pricing Equilibrium --- p.92

"As streaming techniques and wireless access networks become more widely deployed, a streaming multimedia connection with the "last mile" being a wireless network is becoming increasingly common. However, since current streaming techniques are primarily designed for wired networks, streaming multimedia applications can perform poorly in wireless networks. Recent research has shown that the wireless network conditions, such as the wireless link layer rate adaptation, contending traffic, and interference can significantly degrade the performance of streaming media applications. This performance degradation includes increased multimedia frame losses and lower image quality caused by packet loss, and multiple rebuffering events that stop the media playout. This dissertation presents the model, design, implementation and evaluation of an application layer solution for improving streaming multimedia application performance in IEEE 802.11 wireless networks by using enhanced bandwidth estimation techniques. The solution includes two parts: 1) a new Wireless Bandwidth estimation tool (WBest) designed for fast, non-intrusive, accurate estimation of available bandwidth in IEEE 802.11 networks, which can be used by streaming multimedia applications to improve the performance in wireless networks; 2) a Buffer and Rate Optimization for Streaming (BROS) algorithm using WBest to guide the streaming rate selection and initial buffer optimization. WBest and BROS are implemented and incorporated into an emulated streaming client-server system, Emulated Streaming (EmuS), in Linux and evaluated under a variety of wireless conditions. The evaluations show that with WBest and BROS, the performance of streaming multimedia applications in wireless networks can be significantly improved in terms of multimedia frame loss, rebuffer events and buffer delay."

Improving end-to-end Quality of Service (QoS) in existing network systems is a fundamental problem, as it can be affected by many factors, including congestion, packet scheduling, attacks, and air-time allocation. This dissertation addresses QoS in two critical environments: home WiFi and cloud networks. In home networks, we focus on improving QoS over WiFi networks, the dominant means for home Internet access. Three major reasons for end-to-end QoS efforts fail in WiFi networks are its: 1) inherent wireless channel characteristics, 2) approach to access control of the shared broadcast channel, and 3) impact on transport layer protocols, such as TCP, that operate end-to-end, and over-react to the loss or delay caused by the single WiFi link. We present our cross-layer design, Virtual Wire, leveraging the philosophy of centralization in modern networking to address the problem at the point of entry/egress into the WiFi network. Based on network conditions measured from buffer sizes, airtime, and throughput, flows are scheduled to the optimal utility. Unlike most existing WiFi QoS approaches, our design only relies on transparent modifications, requiring no changes to the network (including link layer) protocols, applications, or user intervention. Through extensive experimental investigation, we show that our design significantly enhances the reliability and predictability of WiFi performance, providing a ``virtual wire''-like link to the targeted application. In cloud networks, we explore mechanisms to improve availability during DDoS attacks. The availability of cloud servers is impacted when excessive loads induced by DDoS attacks cause the servers to crash or respond too slowly to legitimate session requests. We model and analyze the effectiveness of a shuffling mechanism: the periodic, randomized re-assignment of users to servers. This shuffling mechanism not only complicates malicious users’ abilities to target specific servers but also, over time, allows a system to identify who the malicious users are. We design and evaluate improved classifiers which can, with statistical accuracy and well-defined levels of confidence, identify malicious users. We also propose and explore the effectiveness of a two-tiered system in which servers are partitioned in two, where one partition serves only ”filtered” users who have demonstrated non-malicious behavior. Our results show how shuffling with these novel classifiers can improve the QoS of the system, which is evaluated by the survival probability, the probability of a legitimate session not being affected by attacks.

Solving NP-hard facility location problems in wireless network planning is a common scenario. In our research, we study the Covering problem, a well known facility location problem with applications in wireless network deployment. We focus on networks with a sparse structure. First, we analyzed two heuristics of building Tree Decomposition based on vertex separator and perfect elimination order. We extended the vertex separator heuristic to improve its time performance. Second, we propose a dynamic programming algorithm based on the Tree Decomposition to solve the Covering problem optimally on the network. We developed several heuristic techniques to speed up the algorithm. Experiment results show that one variant of the dynamic programming algorithm surpasses the performance of the state of the art mathematical optimization commercial software on several occasions. / ix, 89 leaves : ill. ; 29 cm

Thesis (M.Eng.) - Carleton University, 2005. / Includes bibliographical references (p. 123-129). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 243-251) Also available in print.

The Internet Engineering Task Force (IETF) has recently released routing standards that allow deployment of TCP/IP local area networks (LANs) onboard a moving vehicle and yet maintain permanent connectivity of the onboard LAN to the Internet via a vehicular mobile router. This recent development opens up new opportunities for providing efficient mobile computing for users on the move, especially for commuters traveling on public transports. Supporting real-time communications, e.g. IP Telephony, on-line video on demand, etc., over such onboard mobile networks is the main motivation of this thesis. Due to the volatility of the wireless bandwidth available to connect the moving LAN to the Internet at different locations of the trip, supporting on-line services that require bandwidth guarantees becomes a challenging task. The main problem investigated is how to provide bandwidth guarantee efficiently, effectively, and in a scalable manner in the context of moving onboard networks. To achieve the goal, a systematic approach is taken that involves (i) designing a signalling protocol that allows transparent bandwidth reservation for the aggregate demand of all onboard users in the vehicle, and (ii) proposing effective aggregation and bandwidth reservation policies that aim to maximize the chances of successful reservation and minimize the bandwidth and processing overhead in critical network elements. Mathematical models are derived to evaluate the performance of proposed solutions. These models are validated using discrete event simulation. One important conclusion reached is that onboard mobile communication provides significant aggregation and centralized management opportunities that must be exploited to provide a scalable solution to the bandwidth guarantee problem in mobile communications. The techniques proposed and analyzed in this thesis to exploit such aggregation opportunities constitute the original contribution to knowledge.

Quality of service differentiation has never achieved much attention and relevance until the advent of the convergence of mobile wireless network and the fixed Internet, that is, Internet Protocol ( IP ) based mobile wireless networks, or wireless Internet. These networks are poised to support multimedia applications ' traffic with diverse QoS sensitivities. To date, most traffic transferred over the Internet still undergo best - effort forwarding, which does not guarantee whether or not traffic sent by a source gets to the intended destination, let alone loss and timing bounds. The major contribution of this thesis is three - fold. First, the thesis proposes a QoS - enabled wireless Internet access architecture, which leverages the micromobility in wireless standards to reduce mobile IP weaknesses, such as long handoff delay, to achieve effective interworking between mobile wireless networks and the global, fixed Internet. Although the idea here is applicable to any wireless standard, the design examples in this thesis are based on the IEEE 802.11b wireless local area network ( WLAN ) standard. Second, it proposes a framework for a class of wireless channel state dependent packet scheduling schemes, which consider the QoS requirements of the applications ' traffic ; the wireless channel state ( reflected in instantaneous data rate or noise level ) ; and optimises the usage of the expensive wireless resource. The operation of the QoS - enabled, channel state - dependent packet scheduler is analysed using optimisation theory, eigenanalysis and stochastic modelling. Third, the thesis analyses the effects of wireless channel properties on differentiated QoS ( DQoS ) schemes, using two - dimensional, channel - state - dependent queuing theory, matrix analytic methods to stochastic modelling and eigenanalysis. The ana - lytical model of DQoS schemes, especially models accounting for user scenarios such as speed of motion and wireless channel properties, such as fading, spatio - temporarily varying quality and low rate, is not properly covered in the open literature, and hence was a motivation for this part of the thesis. The wireless channel is discretized into discrete - time Markovian states based on the received signal - to - noise plus interference ratio ( SNIR ), which also reflects on the instantaneous link quality. The link quality, in turn, influences the QoS experienced by the transported applications sitting on top of the ISO / OSI protocol hierarchy. The parameters of the Markovian states are evaluated using realistic physical channel noise models and transceiver characteristics, such as modem. [ Different modems ( modulator / demodulator ) yields different transceiver properties such as sensitivity. The analysis in the thesis adopts QPSKand BPSK modulation. ] Source traffic models are used in the analysis. Lastly, the thesis provides an extensive introduction to, and provides a detailed background material for the new area of mobile wireless Internet systems, upon which considerable future research can be based. / Thesis (Ph.D.)--School of Electrical and Electronic Engineering, 2003.