The frequency spectrum allocated to cellular mobile telephone systems is very limited. Efficient channel assignment schemes can significantly increase the utilization of the available frequency channels. Virtually Fixed Channel Assignment (VFCA) is a dynamic channel assignment method. The idea behind it is simple: each cell is allocated a set of nominal channels. A call request generated in a cell is assigned a nominal channel if one is available. Otherwise, a channel from an adjacent cell is borrowed to serve this call as long as frequency interference constraints are satisfied. VFCA is a promising method because (i) it is efficient in channel assignment, and (ii) it is relatively easy to implement compared to other dynamic channel assignment methods. VFCA has been analyzed based primarily on simulation studies in the past twenty years. In this thesis, we focus our study on development of new channel borrowing strategies and analytical models for VFCA. The contribution of this work is summarized as follows. (1) Development of an queuing model for performance analysis of VFCA. This model may also be used to conduct sensitivity analysis on some system parameters when VFCA is used. (2) Proposed a new channel reservation scheme for handoffs. (In a cellular system, when a call using a channel crosses a cell boundary, it needs to be handed off to a new channel in the new cell. This is called a handoff.) An optimization model for this channel reservation scheme is developed. (3) Applied the fluid-flow approach to modeling an integrated mobile cellular system that uses VFCA to estimate the distribution of data queue length in a cell of the system. These results are useful in the design, performance analysis and optimization of VFCA schemes.

From wirelessly connected robots to car-to-car communications, and to smart cities, almost every aspect of our lives will benefit from future wireless communications. While promise an exciting future world, next-generation wireless communications impose requirements on the data rate, spectral efficiency, and latency (among others) that are higher than those for today's systems by several orders of magnitude. Full-duplex wireless, an emergent wireless communications paradigm, breaks the long-held assumption that it is impossible for a wireless device to transmit and receive simultaneously at the same frequency, and has the potential to immediately double network capacity at the physical (PHY) layer and offers many other benefits (such as reduced latency) at the higher layers. Recently, discrete-component-based demonstrations have established the feasibility of full-duplex wireless. However, the realization of integrated full duplex radios, compact radios that can fit into smartphones, is fraught with fundamental challenges. In addition, to unleash the full potential of full-duplex communication, a careful redesign of the PHY layer and the medium access control (MAC) layer using a cross-layer approach is required. The biggest challenge associated with full duplex wireless is the tremendous amount of transmitter self-interference right on top of the desired signal. In this dissertation, new self-interference-cancellation approaches at both system and circuit levels are presented, contributing towards the realization of full-duplex radios using integrated circuit technology. Specifically, these new approaches involve elimination of the noise and distortion of the cancellation circuitry, enhancing the integrated cancellation bandwidth, and performing joint radio frequency, analog, and digital cancellation to achieve cancellation with nearly one part-per-billion accuracy. In collaboration with researchers at higher layers of the stack, a cross-layer approach has been used in our full-duplex research and has allowed us to derive power allocation algorithms and to characterize rate-gain improvements for full-duplex wireless networks. To enable experimental characterization of full-duplex MAC layer algorithms, a cross-layered software-defined full-duplex radio testbed has been developed. In collaboration with researchers from the field of micro-electro-mechanical systems, we demonstrate a multi-band frequency-division duplexing system using a cavity-filter-based tunable duplexer and our integrated widely-tunable self-interference-cancelling receiver.

協作多點 (CoMP)是一種最近興起的傳輸技術，其主要作用為應付新一代無線通訊系統中的小區間干擾問題。在過去十數年內，研究員研發了 CoMP中一些關鍵的新技術，當中包括 MIMO合作和干擾協調。本論文考慮一個聯合用戶排程和干擾協調的問題。在傳統的研究中，用戶排程和干擾協調通常作為獨立的問題進行研究。可是，從本質上這兩個問題是相互影響的，因此傳統的研究將導致系統性能退化。為此，本論文探討了一個聯合用戶排程和波束形成（JACoB）的問題，這當中採用了一種稱為協同波束形成（CoBF）的干擾協調技術。具體而言，本文把 JACoB問題表達成了一個可支持用戶數最大化的問題，而其中的 CoBF設計將盡可能地配合用戶的需求而改變。 / 本論文有兩個主要的貢獻。第一，本文把 JACoB問題轉換成一個 ℓ₀範數最小化問題。其後本文採用 ℓ₁範數近似法將 JACoB問題近似為一個凸優化問題。第二，本文提出一種新型的分佈 JACoB方法。本文提出的分佈方法是基於塊坐標下降法。該方法不同於傳統的基於次梯度方法的分佈方法，如原始/對偶分解。 / 仿真結果顯示，採用本文提出的 JACoB方法（無論是集中的或是分佈的）所能支持的用戶數量遠超過現有的固定波束形成方法。此外，本文提出的分佈 JACoB方法能達到與集中JACoB方法相近的性能，而且其收斂速度亦是相當快的。 / Coordinated MultiPoint (CoMP) cooperative transmission has recently emerged as a promising technique for mitigating intercell interference in next generation wireless communication systems. Several key techniques for CoMP have been endeavored over the past decades, for example, MIMO cooperation and interference coordination. The present work studies a joint user scheduling and interference coordination problem in the CoMP downlink systems. Conventionally, user scheduling and interference coordination are treated as separate problems. This may result in a degradation of the system performance as the two problems are actually intertwined with each other. As such, this thesis considers a joint admission control and beamforming (JA-CoB) problem which employs a popular interference coordination technique called coordinated beamforming (CoBF). In particular, the JA-CoB problem is stated as a user number maximization problem where the CoBF design can be adapted to the set of selected users. / There are two major contributions in this thesis. Firstly, the JA-CoB problem is cast as an ℓ₀ norm minimization problem and then tackled by the now popularized ℓ₁ approximation technique. Secondly, a novel decentralized JACoB method is developed. The proposed de-centralized method is based on the simple block coordinate descent method, which is different from the conventional approaches which em-ploy subgradient-based method such as dual/primal decomposition. / The simulation results indicate that: i) the proposed centralized method yields a performance close to the optimum JACoB design while the complexity is significantly reduced; ii) employing the proposed JA-CoB methods (either centralized or decentralized) gives a significant gain over a fixed beamformers design in terms of the number of supported users. Moreover, the decentralized JACoB method achieves a performance close to its centralized counterpart, whilst the convergence speed is considerably fast. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wai, Hoi To. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 77-80). / Abstracts also in Chinese. / Abstract --- p.i / Acknowledgement --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Overview of techniques for CoMP --- p.2 / Chapter 1.2 --- Overview of user scheduling algorithms --- p.4 / Chapter 1.3 --- Contributions --- p.6 / Chapter 2 --- The JACoB problem and the related works --- p.8 / Chapter 2.1 --- System model --- p.8 / Chapter 2.2 --- Joint admission control and beamforming (JACoB) --- p.10 / Chapter 2.2.1 --- Coordinated beamformers design --- p.11 / Chapter 2.2.2 --- Semide nite relaxation for the CoBF problem --- p.13 / Chapter 2.3 --- Related works --- p.14 / Chapter 2.3.1 --- Common trend in JACoB - deflation heuristic . --- p.18 / Chapter 2.4 --- Decentralized methods --- p.19 / Chapter 3 --- Centralized JACoB method --- p.21 / Chapter 3.1 --- Step 1 - a new formulation to JACoB --- p.21 / Chapter 3.2 --- Step 2 - ℓ₁ approximation to JACoB --- p.24 / Chapter 3.2.1 --- Properties of the ℓ₁ JACoB problem --- p.26 / Chapter 3.3 --- Proposed JACoB method --- p.28 / Chapter 3.3.1 --- Prescreening procedure --- p.28 / Chapter 4 --- Decentralized JACoB method --- p.31 / Chapter 4.1 --- Block coordinate descent method --- p.32 / Chapter 4.2 --- Smooth approximation to ℓ₁ JACoB --- p.34 / Chapter 4.2.1 --- Empirical iteration complexity of the BCD method --- p.38 / Chapter 4.3 --- Proposed decentralized JACoB method --- p.40 / Chapter 5 --- Simulation results --- p.43 / Chapter 5.1 --- Performance of centralized JACoB methods --- p.44 / Chapter 5.2 --- Performance of decentralized JACoB methods --- p.48 / Chapter 5.3 --- Summary --- p.52 / Chapter 6 --- Conclusions and future directions --- p.53 / Chapter 6.1 --- Future directions --- p.53 / Chapter 6.1.1 --- From a practical point of view --- p.54 / Chapter 6.1.2 --- From a theoretical point of view --- p.54 / Chapter A --- A primal decomposition method for (3.4) --- p.56 / Chapter B --- A projected gradient method for (4.3) --- p.60 / Chapter C --- Proofs --- p.67 / Chapter C.1 --- KKT conditions for (2.6) and (3.5) --- p.67 / Chapter C.2 --- Proof of Proposition 2.1 --- p.68 / Chapter C.3 --- Proof of Proposition 3.3 --- p.69 / Chapter C.4 --- Proof of Proposition 3.2 --- p.69 / Chapter C.5 --- Proof of Proposition 3.5 --- p.71 / Chapter C.6 --- Proof of Fact 4.1 --- p.75 / Bibliography --- p.77

V této práci se zabývám firemní komunikací. Pro její plánování a rozvoj je třeba udržovat aktuální komunikační a informační strategii. Pro zjednodušení jsem systém firemní komunikace rozdělil na 4 subsystémy: Kultura, informační systém, komerční komunikace a firemní styl, z nichž každým se podrobně zabývám. Společným působením těchto čtyř disciplín vzniká unikátní identita organizace a toto jsou její základní kameny. Jedním ze způsobů, jak docílit silné identity, je budování promyšleného a stabilního firemního stylu. Firemní styl je úžeji vymezen jako vizuální tvář podniku, tzv. Corporate Design. Jeho základními elementy jsou: logotyp, barevnost a typografie. Přestože firmy si mohou být v těchto základních elementech podobné, odlišují se jejich aplikacemi na komunikační aktivity. Každá vizuální identita se stává unikátním otiskem složitého firemního organismu. Účelem aplikací není pouze marketingový úspěch či vizuální dokonalost; ten spočívá v jejich funkčnosti. Proto je při jejich tvorbě nutné respektovat daleko více kritérií.

The determination of the optimal location of transceivers is a critical design factor when deploying a wireless local area network (WLAN). The performance of the WLAN will improve in a variety of aspects when the transceivers' locations are adequately determined, including the overall cell coverage to the battery life of the client units. Currently, the most common method to determine the appropriate location of transceivers is known as a site survey, which is normally a very time and energy consuming process. The main objective of this research was to improve current methodologies for the optimal or near-optimal placement of APs in a WLAN installation. To achieve this objective, several improvements and additions were made to an existing computational tool to reflect the evolution that WLAN equipment has experienced in recent years. Major additions to the computational tool included the addition of the capability to handle multiple power levels for the transceivers, the implementation of a more adequate and precise representation of the passive interference sources for the path loss calculations, and the definition of a termination criterion to achieve reasonable computational times without compromising the quality of the solution. An experiment was designed to assess how the improvements made to the computational tool provided the desired balance between computational time and the quality of the solutions obtained. The controlled factors were the level of strictness of the termination criterion (i.e., high or low), and the number of runs performed (i.e., 1, 5, 10, 15, and 20 runs). The low level of strictness proved to dramatically reduce (i.e., from 65 to 70%) the running time required to obtain an acceptable solution when compared to that obtained at the high level of strictness. The quality of the solutions found with a single run was considerably lower than that obtained with the any other number of runs. On the other hand, the quality of the solutions seemed to stabilize at and after 10 runs, indicating that there is no added value to the quality of the solution when 15 or 20 runs are performed. In summary, having the computational tool developed in this research execute 5 runs with the low level of strictness would generate high quality solutions in a reasonable running time. / Graduation date: 2004

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Not available / text

No description available.

A case study of collaborative storyboarding in an animation studio grounded this investigation of visual discourse---discourse about and with visual displays. The focus was on a problem occurring during a 40-minute task between the head storyboard artist and his junior colleague in reviewing a rough, conceptual storyboard. The research investigated the role of different semiotic modalities produced by the artists', i.e., speech, gesture, and drawing, in mediating spatial (frames of reference) and motion (action and path) representations and inferences from the storyboard. One aim was to determine if particular modalities were used to represent particular spatial and motion ideas. / Both qualitative discourse and quantitative analyses were undertaken to associate the individual discourse modality in co-occurring external representations (speech, gesture, or drawing), with spatial and motion ideas required to understand the storyboard. The results showed that (a) most modalities did not consistently or uniquely represent specific types of spatial and motion ideas, (b) representations frequently demonstrated a mismatching between spoken and gestured or drawn ideas, (c) spatial representation in particular required the artists to represent specific goal domains as contexts that determined the frame of reference and local sense of the representation, and (d) a more complex drawing style was used at the beginning of the problem than in the latter solution stages. / These findings are discussed in terms of the artists' (a) flexibility needed to traverse between 2-D and 3-D imagined worlds requiring the representation of different spatial coordinate systems, (b) handling of the modalities in visual discourse as supporting this flexibility, and (c) strategic use of drawing styles to assist inferring 3-D dynamic action from an incomplete, 2-D, static storyboard. The study demonstrates the importance of considering activity goals and interacting semiotic modalities as contributing to the knowledge needed to represent and infer space and motion. These findings are significant to research on the knowledge and tools used to infer space and motion from static visual displays in authentic collaborative design activities, and have implication for research on technologies and environments supporting collaborative visual thinking in design settings.

Thesis (M.F.A.)--Rochester Institute of Technology, 1995. / Typescript. Includes bibliographical references (leaves 24-28).