The ever-growing demand for higher bandwidth broadband communication has driven transistor operation to higher and higher frequencies. However, achieving cut-o frequencies in the terahertz regime have been unsuccessful with the current state-of-the-art transistors exhibiting no better than 800 GHz. While the high-frequency transistor eld is dominated by III-V semiconductors, it has been proposed that graphene may be a competitive material. Graphene exhibits electron and hole mobilities orders of magnitude larger than conventional semiconductors and has an atomically thin form factor. Despite these benets, high-frequency graphene transis tors have yet to realize high-frequency characteristics better than III-V's. This thesis expands on the current limitations of graphene transistors in terms of improved fabrication techniques (to achieve higher carrier mobilities and lower contact resistances) and fundamental, band structure limitations (like quantum capacitance and the zero energy band gap). First, graphene, fully encapsulated in hexagonal boron-nitride crystals, transistors are fabricated with self-aligned source and drain contacts with sub-100 nm gate lengths. The encapsulation technique shields the graphene from the external environment so that graphene retains its intrinsic high mobility characteristic. In this short-channel regime, transport is determined to be ballistic with an injection velocity close to the Fermi velocity of graphene. However, the transconductance and output conductance are only 0.6 mS/mm and 0.3 mS/mm, respectively. This lack-luster performance is due to a relatively thick (3.5 nm) eective oxide thickness but also due to the eects of quantum capacitance which diminishes the total gate capacitance by up to 60%. Furthermore, the output conductance is increased due to the onset of hole conduction which leads to a second linear regime in the I-V characteristic. This is a direct consequence of graphene's zero energy band gap electronic structure. Finally, the source and drain contact resistances are large, which leads to poorer output current, transconductance and output conductance. Second, improvement to the contact resistance is explored by means of using graphite as the contact metal to graphene. Since graphite is atomically smooth, a pristine graphite-graphene interface can be formed without grain asperities found in conventional metals. Graphite is also lattice matched to graphene and exhibits the same 60 symmetry. Consequently, it is discovered that the graphite-graphene contact resistance exhibits a 60 periodicity, with respect to crystal orientation. When the two lattices align, a contact resistivity under 10 Wmm² is observed. Furthermore, contact resistivity minima are observed at two of the commensurate angles of twisted bilayer graphene. Though graphene transistor performance is band structure limited, it may still be possible to achieve competitive high-frequency operation by use of h-BN encapsulation and graphite contacts.

Thesis (Ph. D.)--University of California, San Diego, 2010. / Title from first page of PDF file (viewed Feb. 22, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 421-450).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (M.B.A.)--University of Hong Kong, 1998. / Includes bibliographical references (leaf 99-100).

Thesis (M.A.)--Eastern Illinois University, 2010. / Includes bibliographical references (leaves 72-79).

M.Phil. (Electrical & Electronic Engineering) / Without any doubt, the entire range of voice and TV signals will migrate to the packet network. The universal addressable mode of Internet protocol (IP) and the interfacing framing structure of Ethernet are the main reasons behind the success of TCP/IP and Ethernet as a packet network and network access scheme mechanisms. Unfortunately, the success of the Internet has been the problem for real-time traffic such as voice, leading to more studies in the domain of Teletraffic Engineering; and the lack of a resource reservation mechanism in Ethernet, which constitutes a huge problem as switching system mechanism, have raised enough challenges for such a migration. In that context, ITU-T has released a series of Recommendation under the umbrella of H.323 to guarantee the required Quality of Service (QoS) for such services. Although the “utilisation” is not a good parameter in terms of traffic and QoS, we are here in proposing a multiplexing scheme with a queuing solution that takes into account the positive correlations of the packet arrival process experienced at the multiplexer input with the aim to optimize the utilisation of the buffer and bandwidth on the one hand; and the ITU-T H.323 Endpoints and Terminals configuration that can sustain such a multiplexing scheme on the other hand. We take into account the solution of the models from the M/M/1 up to G/G/1 queues based on Kolmogorov’s analysis as our solution to provide a better justification of our approach. This solution, the Diffusion approximation, is the limit of the Fluid process that has not been used enough as queuing solution in the domain of networking. Driven by the results of the Fluid method, and the resulting Gaussian distribution from the Diffusion approximation, the application of the asymptotic properties of the Maximum Likelihood Estimation (MLE) as the central limit theorem allowed capturing the fluctuations and therefore filtering out the positive correlations in the queue system. This has resulted in a queue system able to serve 1 erlang (100% of transmission link capacity) of traffic intensity without any extra delay and a queue length which is 60% of buffer utilization when compared to the ordinary Poisson queue length.

Leung, Yiu-Wing. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 150-157). / Acknowledgments / Abstract / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Broadband Video Services --- p.1 / Chapter 1.3 --- Videoconference Services --- p.7 / Chapter 1.4 --- Videoconference Systems --- p.8 / Chapter 1.5 --- Chapter Summary and Thesis Organization --- p.18 / Chapter Chapter 2 --- Efficient Algorithms for Multiple Destinations Routing --- p.20 / Chapter 2.1 --- Background --- p.20 / Chapter 2.2 --- Integer Programming Formulation of the MDR Problem --- p.26 / Chapter 2.3 --- Heuristics for Multiple Destinations Routing --- p.27 / Chapter 2.4 --- Performance Comparisons --- p.40 / Chapter 2.5 --- Chapter Summary --- p.50 / Chapter Chapter 3 --- Connection Optimization for Two Types of Videoconferences --- p.51 / Chapter 3.1 --- Background --- p.51 / Chapter 3.2 --- The Videoconference Services --- p.52 / Chapter 3.3 --- Connection Optimization --- p.54 / Chapter 3.4 --- Performance Analysis --- p.62 / Chapter 3.5 --- Chapter Summary --- p.80 / Chapter Chapter 4 --- A TDM-based Multibus Packet Switch --- p.81 / Chapter 4.1 --- Background --- p.81 / Chapter 4.2 --- Architecture of the Multibus Switch --- p.89 / Chapter 4.3 --- Operation of the Multibus Switch --- p.93 / Chapter 4.4 --- Performance Analysis --- p.95 / Chapter 4.5 --- Numerical Results --- p.106 / Chapter 4.6 --- Discussions --- p.109 / Chapter 4.7 --- Chapter Summary --- p.113 / Chapter Chapter 5 --- A Modular Shared Media Video Switch --- p.114 / Chapter 5.1 --- System Architecture and Operation --- p.114 / Chapter 5.2 --- Slot Assignment for Point-to-Point Transmissions --- p.129 / Chapter 5.3 --- Slot Assignment for Point-to-Multipoint Transmissions --- p.132 / Chapter 5.4 --- Network Design Example --- p.136 / Chapter 5.5 --- Chapter Summary --- p.143 / Appendix --- p.144 / Chapter Chapter 6 --- Conclusions --- p.147 / References --- p.150

An Zhuo. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 62-65). / Abstracts in English and Chinese. / Acknowledgments --- p.i / 摘要 --- p.ii / Abstract --- p.iii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Circuit switching and Packet switching --- p.2 / Chapter 1.2 --- Virtual paths in high-speed networks --- p.6 / Chapter 1.3 --- BEF in cross-path switch --- p.8 / Chapter 1.4 --- Organization --- p.11 / Chapter Chapter 2 --- Analysis models --- p.12 / Chapter 2.1 --- Routing schemes in Clos network --- p.12 / Chapter 2.2 --- Path Switching --- p.15 / Chapter 2.3 --- Traffic Model of Input Modules --- p.17 / Chapter 2.4 --- Traffic Model of Output Modules --- p.19 / Chapter 2.5 --- Summary --- p.23 / Chapter Chapter 3 --- Throughput Performance of Input Modules in Path Switching --- p.24 / Chapter 3.1 --- Throughput performance vs. BEF --- p.24 / Chapter 3.2 --- Throughput performance vs. number of virtual paths --- p.30 / Chapter 3.2.1 --- Throughput performance vs. integer group size m/k --- p.33 / Chapter 3.2.2 --- Throughput performance vs. group size 0<R<2 --- p.39 / Chapter 3.2.3 --- Throughput performance vs. look-ahead scheme window size ω --- p.46 / Chapter 3.3 --- Summary --- p.48 / Chapter Chapter 4 --- Traffic Balancing Control in Path Switching --- p.50 / Chapter 4.1 --- Loss Probability in Output Modules --- p.50 / Chapter 4.1.1 --- Loss probability vs. number of central modules m --- p.51 / Chapter 4.1.2 --- Loss probability vs. knockout group size R and cluster size g --- p.52 / Chapter 4.2 --- Simulation Comparison of look-ahead scheme --- p.53 / Chapter 4.3 --- Simulation result of throughput vs. BEF --- p.55 / Chapter 4.4 --- Traffic Balancing Control --- p.55 / Chapter 4.5 --- Summary --- p.53 / Chapter Chapter 5 --- Conclusion --- p.60 / Bibliography --- p.62

by Vincent Wing-Shing Tse. / Thesis submitted in: December 1997. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 62-[64]). / Abstract also in Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Principles of Multirate Circuit Switching in Quantized Clos Network --- p.10 / Chapter 2.1 --- Formulation of Multirate Circuit Switching --- p.11 / Chapter 2.2 --- Call Level Routing in Quantized Clos Network --- p.12 / Chapter 2.3 --- Cell Level Routing in Quantized Clos Network --- p.16 / Chapter 2.3.1 --- Traffic Behavior in ATM Network --- p.17 / Chapter 2.3.2 --- Time Division Multiplexing in Multirate Circuit Switching and Cell-level Switching in ATM Network --- p.19 / Chapter 2.3.3 --- Cell Transmission Scheduling --- p.20 / Chapter 2.3.4 --- Capacity Allocation and Route Assignment at Cell-level --- p.29 / Chapter 3 --- Performance Evaluation of Different Implementation Schemes --- p.31 / Chapter 3.1 --- Global Control and Distributed Switching --- p.32 / Chapter 3.2 --- Implementation Schemes of Quantized Clos Network --- p.33 / Chapter 3.2.1 --- Classification of Switch Modules --- p.33 / Chapter 3.2.2 --- Bufferless Switch Modules Construction Scheme --- p.38 / Chapter 3.2.3 --- Buffered Switch Modules Construction Scheme --- p.42 / Chapter 3.3 --- Complexity Comparison --- p.44 / Chapter 3.4 --- Delay Performance of The Two Implementation Schemes --- p.47 / Chapter 3.4.1 --- Assumption --- p.47 / Chapter 3.4.2 --- Simulation Result --- p.50 / Chapter 4 --- Conclusions --- p.59 / Bibliography --- p.62

Finally, we extend the threshold optimization algorithm to solve a more general N-state distributed estimation problem. We combine multiple observations of a signal process via the maximum function for decision-making and find out that the optimal decision function can be implemented by means of thresholds under suitable technical conditions. We propose here a training sequence based algorithm for threshold adjustment. The algorithm is a variation of the Kiefer-Wolfowitz algorithm with expending truncations and randomized differences. Convergence of this algorithm is also established. / Prior to timing jitter robust receiver design, a measurement campaign was carried out on indoor UWB signal propagation in order to characterize the UWB indoor channel and provide a simulation platform. Channel parameters are analyzed based on measurement data, including path loss, RMS delay spread, amplitude distribution and correlation properties. / Ultra-wideband (UWB) technique has been the subject of extensive research in recent years due to its unique capabilities and potential applications, particularly in short-range multiple access wireless communications. Despite of many advantages over traditional narrow band systems, UWB impulse radio is sensitive to timing jitter effect. In this thesis, we devote to design a high speed UWB receiver which is robust under timing jitter. The basic idea is that the received signal is over-sampled within the sampling window and its maximum value or maximum absolute value is selected as the decision variable and to be compared with a threshold. A main advantage of this scheme is that its performance will not degrade if the timing jitter is shorter than half of the window length. Therefore, the proposed scheme is robust against timing jitter and no precise synchronization between the transmitter and receiver is required. However, how to determine the optimal threshold value is a critical issue for this new scheme. In this thesis, we propose a simple stochastic approximation (SA) approach to adjust the threshold recursively. The approach is based on a version of SA known as the Kiefer-Wolfowitz (KW) algorithm with expanding truncations and randomized differences. Corresponding to two different decision-making structures, two SA algorithms are presented and their convergence properties are analyzed, respectively. The proposed algorithms are effective in threshold optimization and the convergence rate is fast, as demonstrated by the numerical results. / Li Qiang. / "June 2005." / Adviser: Wing Shing Wong. / Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0440. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 133-138). / 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.