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

Nam Chung Ho. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 68-71). / Abstracts in English and Chinese. / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Overview and Motivation --- p.1 / Chapter 1.2 --- Organization of the Thesis --- p.5 / Chapter Chapter 2 --- Background --- p.6 / Chapter 2.1 --- Basics of 802.11 Standard --- p.6 / Chapter 2.1.1 --- Distributed Coordination Function (DCF) / Point Coordination Function (PCF) --- p.7 / Chapter 2.1.2 --- RTS/CTS --- p.8 / Chapter 2.2 --- Types of Networks --- p.9 / Chapter 2.3 --- Automatic Repeat request (ARQ) in 802.11b --- p.11 / Chapter 2.3.1 --- Importance of Link-layer ARQ in Wireless Networks --- p.12 / Chapter 2.3.2 --- MAC Algorithm of 802.11b Standard --- p.13 / Chapter 2.3.3 --- Modified MAC algorithm in 802.11b commercial products --- p.14 / Chapter 2.4 --- Automatic Adjustment of Radio Data Rate in Commercial 802.11b Products --- p.15 / Chapter Chapter 3 --- Head-of-Line Blocking in Access Points --- p.17 / Chapter 3.1 --- Cause of HOL blocking in 802.11b --- p.17 / Chapter 3.1.1 --- Calculation of Worst-Case Service Time for Packet at Head of Queue --- p.19 / Chapter 3.2 --- Simulation Settings --- p.21 / Chapter 3.2.1 --- Propagation Models Available in NS2 --- p.21 / Chapter 3.2.2 --- Variables of Shadowing Model --- p.25 / Chapter 3.3 --- Simulation Results on UDP --- p.26 / Chapter 3.4 --- Experimental Results on UDP --- p.28 / Chapter 3.5 --- Simulation Results on TCP --- p.32 / Chapter 3.6 --- Experimental Results on TCP --- p.34 / Chapter 3.7 --- Possible Solutions of HOL Blocking Problem --- p.35 / Chapter 3.7.1 --- Weakening Link-layer ARQ in 802.11b --- p.36 / Chapter 3.7.2 --- Effectiveness of ARQ in 802.11b --- p.37 / Chapter 3.7.2.1 --- Set-up for Network Experiments --- p.38 / Chapter 3.7.2.2 --- Results and Analysis --- p.39 / Chapter 3.7.3 --- Virtual Queuing --- p.45 / Chapter Chapter 4 --- Study of Uplink Traffic --- p.50 / Chapter 4.1 --- Poor Pulling Down the Rich --- p.51 / Chapter 4.2 --- Signal Capturing Effect --- p.53 / Chapter 4.2.1 --- Mathematical Analysis of Signal Capturing Effect --- p.55 / Chapter Chapter 5 --- Packet Loss Patterns in 802.11b WLAN --- p.61 / Chapter 5.1 --- """Random Loss"" vs ""Bursty Loss""" --- p.61 / Chapter 5.2 --- Experimental Evaluation --- p.62 / Chapter Chapter 6 --- Conclusion --- p.65 / Bibliography --- p.68

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Este trabalho apresenta uma nova aplicação de wavelets em sistemas de espalhamento espectral. A aplicação apresentada foi realizada no contexto de detecção multiusuário e pode ser empregada em sistemas de acesso múltiplo por divisão de código. A detecção e a estimação são realizadas através de um algoritmo de inferência bayesiana, empregando o Amostrador de Gibbs e utilizando as wavelets para melhorar a relação sinal ruído na recepção. Na transmissão, um código específico, baseado na wavelet de Haar, modula o sinal contendo a informação preparando-o contra alterações que possam ocorrer devido a características intrínsecas do canal de ruído branco, gaussiano e aditivo. Esta técnica foi aqui denominada de modulação wavelet. Na recepção, uma transformada wavelet de Haar é aplicada ao sinal, gerando coeficientes wavelets. A ortogonalidade da wavelet de Haar torna possível executar um procedimento de cancelamento de ruído, em inglês denoising, que melhora a qualidade da recepção. Para validar a abordagem apresentada neste trabalho, foi executada uma série de simulações. Os resultados mostraram um melhor desempenho sistêmico com o emprego de wavelets. Nas simulações foram observados vários parâmetros de sistema, dentre eles e amplitude do sinal, a taxa de erro de bits (BER, bit error rate) e a variância do sinal. Os resultados foram bastante satisfatórios, indicando uma redução do ruído da ordem de 3dB em relação ao valor sem cancelamento de ruído. Este trabalho abre novas oportunidades de pesquisa para o uso de wavelets em sistemas de espalhamento espectral e telecomunicações em geral. / This work presents a new application of wavelets to spread spectrum systems. The presented application was made in the context of multiuser detection and can be used in code-division multiple access systems. Detection and estimation are performed through a Bayesian inference algorithm and, employing the Gibbs sampler and utilizing wavelets to improve the signal-to-noise ratio at the reception. At the transmission, a specific code based on the Haar wavelet modulates the signal containing the information, preparing it to alterations that may occur due to the intrinsic characteristics of the additive Gaussian noise channel. This technique was here denominated wavelet modulation. At the reception, a Haar wavelet transform is applied to the signal, generating wavelet coefficients. The orthogonality of the Haar wavelet makes it possible to perform a noise cancelling process, called denoising, which enhances the receiving quality. To validate the approach presented in this work, a number of simulations were performed. The results showed a better system performance with the use of wavelets. Several parameters were monitored in the simulations, among them the signal amplitude, de BER (bit error rate), and the signal variance. The results were very satisfactory, indicating a noise reduction of approximately 3dB referred to the value without noise cancelling. This work opens new research opportunities for the use of wavelets in spread spectrum systems and Telecommunications in general.

Wireless sensor networks (WSNs) provide rapid, untethered access to information, eliminating the barriers of distance, time, and location for many applications in national security, civilian search and rescue operations, surveillance, border monitoring, and many more. Sensor nodes are resource constraint in terms of power, bandwidth, memory, and computing capabilities. Sensor nodes are typically battery powered and depending on the application, it may be impractical or even impossible to recharge them. Thus, it is important to develop mechanisms for WSN which are energy efficient, in order to reduce the energy consumption in the network. Energy efficient algorithms result in an increased network lifetime. Data gathering is an important operation in WSNs, dealing with collecting sensed data or event reporting in a timely and efficient way. There are various scenarios that have to be carefully addressed. In this dissertation we propose energy efficient algorithms for data gathering. We propose a novel event-based clustering mechanism, and propose several efficient data gathering algorithms for mobile sink WSNs and for spatio-temporal events. Border surveillance is an important application of WSNs. Typical border surveillance applications aim to detect intruders attempting to enter or exit the border of a certain region. Deploying a set of sensor nodes on a region of interest where sensors form barriers for intruders is often referred to as the barrier coverage problem. In this dissertation we propose some novel mechanisms for increasing the percentage of events detected successfully. More specifically, we propose an adaptive sensor rotation mechanism, which allow sensors to decide their orientation angle adaptively, based on the location of the incoming events. In addition, we propose an Unmanned Aerial Vehicle UAV aided mechanism, where an UAV is used to cover gaps dynamically, resulting in an increased quality of the surveillance. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

The prevalence of wireless networks is on the increase. Society is becoming increasingly reliant on ubiquitous computing, where mobile devices play a key role. The use of wireless networking is a natural solution to providing connectivity for such devices. However, the availability of infrastructure in wireless networks is often limited. Such networks become dependent on wireless ad hoc networking, where nodes communicate and form paths of communication themselves. Wireless ad hoc networks present novel challenges in contrast to fixed infrastructure networks. The unpredictability of node movement and route availability become issues of significant importance where reliability is desired.To improve reliability in wireless ad hoc networks, predicting future connectivity between mobile devices has been proposed. Predicting connectivity can be employed in a variety of routing protocols to improve route stability and reduce unexpected drop-offs of communication. Previous research in this field has been limited, with few proposals for generating future predictions for mobile nodes. Further work in this field is required to gain a better insight into the effectiveness of various solutions.This thesis proposes such a solution to increase reliability in wireless ad hoc routing. This research presents two novel concepts to achieve this: the Communication Map (CM), and the Future Neighbours Table (FNT). The CM is a signal loss mapping solution. Signal loss maps delineate wireless signal propagation capabilities over physical space. With such a map, connectivity predictions are based on signal capabilities in the environment in which mobile nodes are deployed. This significantly improves accuracy of predictions in this and in previous research. Without such a map available, connectivity predictions have no knowledge of realistic spatial transmission ranges. The FNT is a solution to provide routing algorithms with a predicted list of future periods of connectivity between all nodes in an established wireless ad hoc network. The availability of this information allows route selection in routing protocols to be greatly improved, benefiting connectivity. The FNT is generated from future node positional information combined with the CM to provide predicted signal loss estimations at future intervals. Given acceptable signal loss values, the FNT is constructed as a list of periods of time in which the signal loss between pairs of nodes will rise above or fall below this acceptable value (predicted connectivity). Future node position information is ideally found in automated networks. Robotic nodes commonly operate where future node task movement is developed and planned into the future, ideal for use in predicted connectivity. Non-automated prediction is also possible, as there exist some situations where travel paths can be predictable, such as mobile users on a train or driving on a highway. Where future node movement is available, predictions of connectivity between nodes are possible.

<p>The present development of the demography of elderly people in the western world will generate a shortage of caregiver’s for elderly people in the near future. There are major risk that the lack of qualified caregivers will result in deterioration in the quality of elderly care. One possible </p><p>solution is the use of modern information and communication technology (ICT) to enable staff to work more efficiently. However, if ICT system is introduced into the elderly care it must done in a way which is acceptable from a humane perspective while at the same time increasing the efficiency of the personal that working in elderly care centers. This thesis investigates the </p><p>technical feasibility of using a wireless mesh network for a social alarm system, in the elderly care. The System as such is not intended to replace the staff at an elderly care center but instead is intended to reduce staff workloads while providing more time for elderly care.</p>

Localization and coverage are two important and closely related problems in wireless ad hoc networks. Localization aims to determine the physical locations of devices in a network, while coverage determines if a region of interest is sufficiently monitored by devices. Localization systems require a high degree of coverage for correct functioning, while coverage schemes typically require accurate location information. This thesis investigates the relationship between localization and coverage such that new schemes can be devised which integrate approaches found in each of these well studied problems. This work begins with a thorough review of the current literature on the subjects of localization and coverage. The localization scheduling problem is then introduced with the goal to allow as many devices as possible to enter deep sleep states to conserve energy and reduce message overhead, while maintaining sufficient network coverage for high localization accuracy. Initially this sufficient coverage level for localization is simply a minimum connectivity condition. An analytical method is then proposed to estimate the amount of localization error within a certain probability based on the theoretical lower bounds of location estimation. Error estimates can then be integrated into location dependent schemes to improve on their robustness to localization error. Location error estimation is then used by an improved scheduling scheme to determine the minimum number of reference devices required for accurate localization. Finally, an optimal coverage preserving sleep scheduling scheme is proposed which is robust to localization error, a condition which is ignored by most existing solutions. Simulation results show that with localization scheduling network lifetimes can be increased by several times and message overhead is reduced while maintaining negligible differences in localization error. Furthermore, results show that the proposed coverage preserving sleep scheduling scheme results in fewer active devices and coverage holes under the presence of localization error.

Localization and coverage are two important and closely related problems in wireless ad hoc networks. Localization aims to determine the physical locations of devices in a network, while coverage determines if a region of interest is sufficiently monitored by devices. Localization systems require a high degree of coverage for correct functioning, while coverage schemes typically require accurate location information. This thesis investigates the relationship between localization and coverage such that new schemes can be devised which integrate approaches found in each of these well studied problems. This work begins with a thorough review of the current literature on the subjects of localization and coverage. The localization scheduling problem is then introduced with the goal to allow as many devices as possible to enter deep sleep states to conserve energy and reduce message overhead, while maintaining sufficient network coverage for high localization accuracy. Initially this sufficient coverage level for localization is simply a minimum connectivity condition. An analytical method is then proposed to estimate the amount of localization error within a certain probability based on the theoretical lower bounds of location estimation. Error estimates can then be integrated into location dependent schemes to improve on their robustness to localization error. Location error estimation is then used by an improved scheduling scheme to determine the minimum number of reference devices required for accurate localization. Finally, an optimal coverage preserving sleep scheduling scheme is proposed which is robust to localization error, a condition which is ignored by most existing solutions. Simulation results show that with localization scheduling network lifetimes can be increased by several times and message overhead is reduced while maintaining negligible differences in localization error. Furthermore, results show that the proposed coverage preserving sleep scheduling scheme results in fewer active devices and coverage holes under the presence of localization error.