In last few years there has been significant growth in the area of wireless communication. Quality of Service (QoS) has become an important consideration for supporting variety of applications that utilize the network resources. These applications include voice over IP, multimedia services, like, video streaming, video conferencing etc. IEEE 802.16/WiMAX is a new network which is designed with quality of service in mind. This thesis focuses on analysis of quality of service as implemented by the WiMAX networks. First, it presents the details of the quality of service architecture in WiMAX network. In the analysis, a WiMAX module developed based on popular network simulator ns-2, is used. Various real life scenarios like voice call, video streaming are setup in the simulation environment. Parameters that indicate quality of service, such as, throughput, packet loss, average jitter and average delay, are analyzed for different types of service flows as defined in WiMAX. Results indicate that better quality of service is achieved by using service flows designed for specific applications. / by Rohit Talwalkar. / Thesis (M.S.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, FL : 2008 Mode of access: World Wide Web.

"Faster, higher, stronger"---the Olympic motto is being pursued and practised in the design of broadband wireless communication systems. Motivated by the huge demands for fast and reliable communications over wireless channels, broadband communication systems are required to provide faster (low-complexity) data processing, higher data throughput and stronger (lower error rate) performance. In practice, however, broadband communication systems must cope with critical performance-limiting challenges that include time- and frequency-selective fading channels, noise, inter-symbol interference (ISI), intercarrier interference (ICI) as well as power and bandwidth constraints. To address these challenges, this thesis investigates several physical layer aspects of broadband wireless communication systems. / Incorporating OFDM into multiple-input multiple-output (MIMO) system, MIMO-OFDM has been shown to provide larger channel capacity and greater diversity gain. However, current coding schemes for MIMO-OFDM are either space-time coded (STC) OFDM without the guarantee of full diversity gains or space-frequency coding (SFC) with a greater loss of data rate. Furthermore, most existing STC and SFC have focused on quasi-static fading which is not practical for broadband wireless communications. When multi-band OFDM (MB-OFDM) is applied to ultra-wide band (UWB) communications, a high diversity can be obtained, but in the expense of a much lower (close to half) data rate. To address the limitations of existing coding schemes for broadband wireless communication systems, this thesis: (i) proposes a space-time-frequency coding (STFC) that can achieve maximum diversity and maximum symbol rate transmission over MIMO block-fading channels; (ii) derives a high-rate full-diversity SFC from STFC tailored for frequency-selective fading channels; and (iii) proposes a high-rate high-diversity algebraic time-frequency coding (ATFC) for MB-OFDM system. / Orthogonal frequency division multiplexing (OFDM) is an effective technique to eliminate ISI in broadband wireless communications. This thesis studies the problem of training-based OFDM channel estimation and proposes a training method that minimizes the number of pilots employed to achieve a desired bit error rate (BER) performance. A clustered pilot pattern is further proposed to enhance the BER performance. Focusing on OFDM frequency synchronization, this thesis also proposes a clustered pilot tones placement and a novel pilot sequence design for carrier frequency offset (CFO) compensation. The analytical and simulation results show that the root mean square error (RMSE) of the CFO estimate can be greatly reduced. / Zhang Wei. / "July 2005." / Adviser: Pak-Chung Ching. / Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0461. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 126-143). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

For packet-switched metro networks, one of the key functional blocks is the transmission, extraction and update of in-band packet control information, which is commonly known as packet label swapping. The use of phase modulation to carry the control information can facilitate easy swapping process. By combining phase modulated label with intensity modulated optical packets in non-overlapping manners, we demonstrated that optical packet label swapping using differential phase-shift keyed labels could be achieved without any sacrifices in packet signal quality. / In packet-switched optical networks, packets are routed using IP-based distributed routing algorithms. Inconsistencies in routing information among routing nodes may result in routing loop formation in the network and may cause severe impact on the network performance. We proposed a novel packet routing loop mitigation scheme based on the principle of packet 'time-to-live' value countdown. This scheme enables loop mitigation to be performed asynchronously in optical domain, causing little packet processing delay. Two implementations were proposed. One was based on differential optical phase shift keying and the other was based on self-phase modulation in semiconductor optical amplifier. / The continuous increase in Internet-bound data traffic in recent years has placed higher requirement on network bandwidth and flexibility. In view of this, packet-switched metro networks and broadband passive optical access networks have emerged as the promising network solutions in the near future. The focus of this thesis is on the improvement of functionality and reliability as well as the reduction of system complexity in optical metro area and access networks with the use of optical phase modulation techniques. In access network, constant-intensity optical phase modulation formats were studied for their applications in wavelength-division-multiplexed passive optical networks with centralized light source. Using them as downstream modulation formats, the downstream optical carrier can be utilized to carry upstream intensity-modulated data. It can greatly simplify upstream transmission and facilitate network management. Experimental and numerical analyses shows promising upstream re-modulation performance with a simple optical network unit (ONU) configuration. / Hung Wai. / Adviser: Lian-Kuan Chen. / Source: Dissertation Abstracts International, Volume: 70-09, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 130-135). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

by Philip Pak-tung To. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (p. 126). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.

by Timothy Kai-Cheung Chung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references. / Chapter 1. --- INTRODUCTION --- p.1 / Chapter 2. --- ASYNCHRONOUS TRANSFER MODE SWITCHING --- p.4 / Chapter 2.1 --- Transfer Modes --- p.4 / Chapter 2.1.1 --- Circuit Switching --- p.4 / Chapter 2.1.2 --- ATM Switching --- p.6 / Chapter 2.1.3 --- Packet Switching --- p.8 / Chapter 2.2 --- Different Types of ATM Switching System --- p.8 / Chapter 2.2.1 --- Central Control Type --- p.9 / Chapter 2.2.2 --- Self-Routing Type --- p.9 / Chapter 2.3 --- Self-Routing Non-Buffering ATM Switching Node --- p.10 / Chapter 3. --- FUNCTIONAL DESCRIPTION OF MODULE ´بA´ة --- p.16 / Chapter 3.1 --- ATM Cell Format --- p.17 / Chapter 3.2 --- Concentrator --- p.17 / Chapter 3.3 --- Routing Cell --- p.19 / Chapter 4. --- PHYSICAL STRUCTURE OF MODULE ´بA´ة --- p.23 / Chapter 4.1 --- Clocking Scheme --- p.23 / Chapter 4.2 --- Concentrator --- p.25 / Chapter 4.2.1 --- 2-by-2 Sorter --- p.25 / Chapter 4.2.2 --- Input Framer --- p.30 / Chapter 4.2.3 --- Data Buffer --- p.38 / Chapter 4.3 --- Routing Cell --- p.38 / Chapter 4.3.1 --- Type I Router --- p.39 / Chapter 4.3.2 --- Type II Router --- p.42 / Chapter 4.4 --- Block By-Passed Function --- p.43 / Chapter 5. --- SIMULATION AND TEST --- p.48 / Chapter 5.1 --- Computer Simulation --- p.48 / Chapter 5.2 --- Actual Chip Testing --- p.53 / Chapter 5.3 --- Measurement Results --- p.55 / Chapter 5.3.1 --- Functionality --- p.55 / Chapter 5.3.2 --- Maximum Clock Frequency --- p.60 / Chapter 5.3.3 --- Power Dissipation --- p.61 / Chapter 6. --- CONCLUSION --- p.63 / Chapter A. --- BRIEF HISTORY OF ATM SWITCH ARCHITECTURE DEVELOPMENT --- p.65 / Chapter B. --- BIBLIOGRAPHY --- p.66 / Chapter C. --- A N-WELL CMOS PROCESS --- p.70 / Chapter D. --- CADENCE DESIGN FLOW --- p.73 / Chapter E. --- YERILOG SIMULATION PROGRAMS --- p.77 / Chapter F. --- SCHEMATIC DIAGRAMS --- p.100

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The research presented in this thesis aims to demonstrate that fuzzy logic is a useful tool for developing mechanisms for controlling traffc flow in ATM based multimedia networks to maintain quality of service (QoS) requirements and maximize resource utilization. The study first proposes a hierarchical, multilevel control structure for ATM networks to exploit the reported strengths of fuzzy logic at various control levels. Then, an extensive development and evaluation is presented for a subset of the proposed control architecture at the congestion control level. An ATM based multimedia network must have quite sophisticated traffc control capabilities to effectively handle the requirements of a dynamically varying mixture of voice, video and data services while meeting the required levels of performance. Feedback control techniques have an essential role for the effective and efficient management of the resources of ATM networks. However, development of conventional feedback control techniques relies on the availability of analytical system models. The characteristics of ATM networks and the complexity of service requirements cause the analytical modeling to be very difficult, if not impossible. The lack of realistic dynamic explicit models leads to substantial problems in developing control solutions for B-ISDN networks. This limits the ability of conventional techniques to directly address the control objectives for ATM networks. In the literature, several connection admission and congestion control methods for B-ISDN networks have been reported, and these have achieved mixed success. Usually they either assume heavily simplified models, or they are too complicated to implement, mainly derived using probabilistic (steady-state) models. Fuzzy logic controllers, on the other hand, have been applied successfully to the task of controlling systems for which analytical models are not easily obtainable. Fuzzy logic control is a knowledge-based control strategy that can be utilized when an explicit model of a system is not available or, the model itself, if available, is highly complex and nonlinear. In this case, the problem of control system design is based on qualitative and/or empirically acquired knowledge regarding the operation of the system. Representation of qualitative or empirically acquired knowledge in a fuzzy logic controller is achieved by linguistic expressions in the form of fuzzy relational equations. By using fuzzy relational equations, classifications related to system parameters can be derived without explicit description. The thesis presents a new predictive congestion control scheme, Fuzzy Explicit Rate Marking (FERM), which aims to avoid congestion, and by doing so minimize the cell losses, attain high server utilization, and maintain the fair use of links. The performance of the FERM scheme is extremely competitive with that of control schemes developed using traditional methods over a considerable period of time. The results of the study demonstrate that fuzzy logic control is a highly effective design tool for this type of problems, relative to the traditional methods. When controlled systems are highly nonlinear and complex, it keeps the human insight alive and accessible at the lower levels of the control hierarchy, and so higher levels can be built on this understanding. Additionally, the FERM scheme has been extended to adaptively tune (A-FERM) so that continuous automatic tuning of the parameters can be achieved, and thus be more adaptive to system changes leading to better utilization of network bandwidth. This achieves a level of robustness that is not exhibited by other congestion control schemes reported in the literature. In this work, the focus is on ATM networks rather than IP based networks. For historical reasons, and due to fundamental philosophical differences in the (earlier) approach to congestion control, the research for control of TCP/IP and ATM based networks proceeded separately. However, some convergence between them has recently become evident. In the TCP/IP literature proposals have appeared on active queue management in routers, and Explicit Congestion Notication (ECN) for IP. It is reasonably expected that, the algorithms developed in this study will be applicable to IP based multimedia networks as well.

This research deals with optimal resource management in an overloaded broadband multimedia network. Optimisation is with respect to user satisfaction, where user satisfaction reflects both the quality of service experienced by connected users and the dissatisfaction of users blocked from access to the network. The research focuses on Asynchronous Transfer Mode (ATM) networks and the Internet, because these are the dominant emerging broadband networks which present some fundamental unsolved problems, related to the sharing of resources between mixed traffic types. ATM networks use conservative admission control, which protects network resources and ensures a high level of service for those admitted to the network, but results in low network efficiency because of low utilisation of resources due to blocking of many potential users. The Internet does not use admission control, with the result that performance degrades progressively as load increases. This causes frustration among users, and lowers the network efficiency due to high levels of congestion. We propose an optimisation model for each network (ATM networks and the Internet)which is intended to represent the distribution and consumption of key network resources by different traffic types. The model is aimed at maximising performance such that users admitted to the network are offered no less than some minimum acceptable level of quality of service (QoS). The solution is a set of traffic flow rates on each path which results in maximising an objective function value (revenue based on network operator interest or throughput based on customer interest) for a given network configuration with given user demand. As an example using the ATM network model, we illustrate the application of the model to an ATM network carrying both connection oriented and connectionless traffic. We explore the optimal response to a link failure which in turn causes node overload. As an example using the Internet model, we consider an overloaded network with link bottlenecks and an overloaded Web server, and explore the effect of transferring some server capacity to a mirror site and a proxy server. For real-time traffic control, the optimisation model is used to assign quotas for bandwidth or connections to selected paths. A control algorithm is implemented to provide maximum performance by admitting requests within the quotas which are obtained from the optimisation model. In an ATM network simulation, the algorithm is used to manage the virtual path (VP) pool in a network which suffers a link failure. A comparison is made between fixed virtual path management (FVPM) and dynamic virtual path management (DVPM), comparing the revenue achieved by each. This illustrates how DVPM adapts the VP pool in a robust fashion to achieve maximum revenue in the face of a link failure. However, the transient response suggests that benefit could be obtained using non-steady-state solutions. The model is extended by taking network state and traffic parameters into account to control changes in the VP pool to recognise limits to the rate at which traffic can be moved (through the natural birth-death processes). This scheme is called state dependent virtual path management (SDVPM). Performance evaluation of the new model shows that SDVPM achieves higher revenue than DVPM when the network suffers a link failure that requires a major change to the VP pool. In an Internet simulation, two algorithms are compared for control of access to a proxy server and a set of primary servers. An algorithm based on optimal flow solutions provides substantially better network performance than a localised heuristic algorithm. In each simulation case (ATM and Internet examples), the performance using a control system based on the steady state optimum flow model is close to the ideal optimal result.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.