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This thesis presents novel methods that are able to perform real-time estimation of the available bandwidth of a network path. In networks such as the Internet, knowledge of bandwidth characteristics is of great significance in, e.g., network monitoring, admission control, and audio/video streaming. The term bandwidth describes the amount of information a network can deliver per unit of time. For network end users, it is only feasible to obtain bandwidth properties of a path by actively probing the network with probe packets, and to perform estimation based on received measurements. In this thesis, two active-probing based methods for real-time available-bandwidth estimation are presented and evaluated. The first method, BART (Bandwidth Available in Real-Time), uses Kalman filtering for the analysis of received probe packets. BART is examined analytically and through experiments which are carried out in wired and wireless laboratory networks as well as over the Internet and commercial mobile broadband networks. The opportunity of tuning the Kalman filter and enhancing the performance by introducing change detection are investigated in more detail. Generally, the results show accurate estimation with only modest computational efforts and minor injections of probe packets. However, it is possible to identify weaknesses of BART, and a summary of these as well as general problems and challenges in the field of available-bandwidth estimation are laid out in the thesis. The second method, E-MAP (Expectation-Maximization Active Probing), is designed to overcome some of these issues. E-MAP modifies the active-probing scheme of BART and utilizes the expectation-maximization algorithm before filtering is used to generate a bandwidth estimate. Overall, this thesis shows that in many cases it is achievable to obtain efficient and reliable real-time estimation of available bandwidth by using light-weight analysis techniques and negligible probe-traffic overhead. Hence, this opens up exciting new possibilities for a range of applications and services in communication networks.

<p>Recent surveys conducted in the context of industrial automation have outlined that reliability concerns represent today one of the major barriers to the diffusion of wireless communications for sensing and control applications: this limits the potential of wireless sensor networks and slows down the adoption of this new technology. Overcoming these limitations requires that awareness on the causes of unreliability and on the possible solutions to this problem is created. With this respect, the main factor responsible for the perceived unreliability is radio interference: low-power communications of sensor nodes are in fact very sensitive to bad channel conditions and can be easily corrupted by transmissions of other co-located devices. In this thesis we investigate different techniques that can be exploited to avoid interference or mitigate its effects.We first consider interference avoidance through dynamic spectrum access: more specifically we focus on the idea of channel surfing and design algorithms that allow sensor nodes to identify interfered channels, discover their neighbors and maintain a connected topology in multi-channel environments. Our investigation shows that detecting and thus avoiding interference is a feasible task that can be performed by complexity and power constrained devices. In the context of spectrum sharing, we further consider the case of networked estimation and aim at quantifying the effects of intranetwork interference, induced by contention-based medium access, over the performance of an estimation system. We show that by choosing in an opportune manner their probability of transmitting, sensors belonging to a networked control system can minimize the average distortion of state estimates.In the second part of this thesis we focus on frequency hopping techniques and propose a new adaptive hopping algorithm. This implements a new approach for frequency hopping: in particular rather than aiming at removing bad channels from the adopted hopset our algorithm uses all the available frequencies but with probabilities that depend on the experienced channel conditions. Our performance evaluation shows that this approach outperforms traditional frequency hopping schemes as well as the adaptive implementation included in the IEEE 802.15.1 radio standard leading to a lower packet error rate.Finally, we consider the problem of sensor networks reprogramming and propose a way for ingineering a coding solution based on fountain codes and suitable for this challenging task. Using an original genetic approach we optimize the degree distribution of the used codes so as to achieve both low overhead and low decoding complexity. We further engineer the implementation of fountain codes in order to allow the recovery of corrupted information through overhearing and improve the resilience of the considered reprogramming protocol to channel errors.</p>

<p>Cooperative transmission is considered to be a key-technique for increasing the robustness, the efficiency, or the coverage of wireless communication networks. The basic concept is that the information transmission from a sender to a receiver can be aided by one or several relay nodes in a cooperative manner under constraints on power, complexity or delay.</p><p>The main part of this thesis is devoted to studies on practical realizations of cooperative communication systems. Coding solutions that implement the decode-and-forward protocol in three-node relay channels are proposed by employing convolutional and Turbo codes. Distributed Turbo coding (DTC) was the first technique to bring parallel code concatenation into relay networks. To complement the research on parallel concatenated codes, we propose distributed serially concatenated codes (DSCCs) which provide a better error-floor performance and an increased robustness compared with DTCs. Thereafter, we present a flexible distributed code design which can be adapted to the channel conditions in a simple way. For both the cases with perfect and limited channel-state information, the adaptive coding scheme outperforms static codes, like DTCs and DSCCs, in terms of transmission rate and application range.</p><p>The aforementioned implementations of relaying are based on blockwise decoding and re-encoding at the relay. In some applications, however, these techniques are not feasible due to limited processing and storage capabilities of the relay nodes. Therefore, we propose to combine instantaneous relaying strategies with bit-interleaved coded modulation. A significant gain can be obtained by using sawtooth and constellation rearrangement relaying with optimized bit-to-symbol mappings compared with conventional instantaneous relaying strategies and compared with standard mappings optimized for point-to-point communications. Both the parameters of the instantaneous relaying schemes and the bit-to-symbol mappings are optimized to maximize mutual information.</p> / QC20100607

Internet telephony has had a tremendous impact on how people communicate.Many now maintain contact using some form of Internet telephony.Therefore the motivation for this work has been to address the quality aspectsof real-world Internet telephony for both fixed and wireless telecommunication.The focus has been on the quality aspects of voice communication,since poor quality leads often to user dissatisfaction. The scope of the workhas been broad in order to address the main factors within IP-based voicecommunication. The first four chapters of this dissertation constitute the backgroundmaterial. The first chapter outlines where Internet telephony is deployedtoday. It also motivates the topics and techniques used in this research.The second chapter provides the background on Internet telephony includingsignalling, speech coding and voice Internetworking. The third chapterfocuses solely on quality measures for packetised voice systems and finallythe fourth chapter is devoted to the history of voice research. The appendix of this dissertation constitutes the research contributions.It includes an examination of the access network, focusing on how calls are multiplexed in wired and wireless systems. Subsequently in the wireless case, we consider how to handover calls from 802.11 networks to the cellularinfrastructure. We then consider the Internet backbone where most of ourwork is devoted to measurements specifically for Internet telephony. The applications of these measurements have been estimating telephony arrival processes, measuring call quality, and quantifying the trend in Internet telephony quality over several years. We also consider the end systems, since they are responsible for reconstructing a voice stream given loss and delay constraints. Finally we estimate voice quality using the ITU proposal PESQ and the packet loss process. The main contribution of this work is a systematic examination of Internet telephony. We describe several methods to enable adaptable solutions for maintaining consistent voice quality. We have also found that relatively small technical changes can lead to substantial user quality improvements.A second contribution of this work is a suite of software tools designed to a certain voice quality in IP networks. Some of these tools are in use within commercial systems today. / QC 20100802

Interruptions have a profound impact on our attentional orientation in everyday life. Recent advances in mobile information technology increase the number of potentially disruptive notifications on mobile devices by an increasing availability of services. Understanding the contextual intricacies that make us receptive to these interruptions is paramount to devising technology that supports interruption management. This thesis makes a number of contributions to the methodology of studying mobile experiences in situ, understanding receptivity to interruptions, and designing context-sensitive systems. This thesis presents a series of real-world studies that investigate opportune moments for interruptions in mobile settings. In order to facilitate the study of the multi-faceted ways opportune moments surface from participants' involvement in the world this thesis develops: - a model of the contextual factors that interact to guide receptivity to interruptions, and - an adaptation of the Experience-Sampling Method (ESM) to capture behavioural response to interruptions in situ. In two naturalistic experiments, participants' experiences of being interrupted on a mobile phone are sampled as they go about their everyday lives. In a field study, participants' experiences are observed and recorded as they use a notification-driven mobile application to create photo-stories in a theme park. Experiment 1 explores the effects of content and time of delivery of the interruption. The results show that receptivity to text messages is significantly affected by message content, while scheduling one's own interruption times in advance does not improve receptivity over randomly timed interruptions. Experiment 2 investigates the hypothesis that opportune moments to deliver notifications are located at the endings of episodes of mobile interaction such as texting and calling. This notification strategy is supported by significant effects in behavioural measures of receptivity, while self-reports and interviews reveal complexities in the subjective experience of the interruption. By employing a mixed methods approach of interviews, observations and an analysis of system logs in the field study, it is shown that participants appreciated location-based notifications as prompts to foreground the application during relative 'downtimes' from other activities. However, an unexpected quantity of redundant notifications meant that visitors soon habituated to and eventually ignored them, which suggests careful, sparing use of notifications in interactive experiences. Overall, the studies showed that contextual mediation of the timing of interruptions (e.g. by phone activity in Experiment 2 and opportune places in the field study) is more likely to lead to interruptions at opportune moments than when participants schedule their own interruptions. However, momentary receptivity and responsiveness to an interruption is determined by the complex and situated interactions of local and relational contextual factors. These contextual factors are captured in a model of receptivity that underlies the interruption process. The studies highlight implications for the design of systems that seek to manage interruptions by adapting the timing of interruptions to the user's situation. In particular, applications to manage interruptions in personal communication and pervasive experiences are considered.

Regulator independence has been widely acknowledged by a large segment of experts as significant for the growth and development of the telecoms industry. However, the impact of regulatory independence on industry growth has not been prominently analysed from the perspective of developing countries. This study was therefore conceived and designed to determine whether the degree of independence of the Nigerian Communication Commission (NCC) has had any effect on the growth and development of the telecoms industry in Nigeria. The parameters for regulator independence examined include; stability of tenure, relationship between the regulator and the various arms of government, fiscal and organisational autonomy, regulator legitimacy as well as the regulator authority to regulate. While the parameters for growth examined include: access to service, usage of service, geographical spread, and quality of service, competition and pricing. A connection between the degree of regulator independence and industry growth and development was subsequently established. A descriptive method of analysis was adopted using the TRE technique of assessment and the study confirmed that the NCC is fairly/reasonably independent. Furthermore, evidence from both primary and secondary sources indicated a remarkable but modest growth and development in the Nigeria telecoms industry from 2001 to 2010. The study found that Nigeria’s communication sector development was positively affected by the degree of independence of the regulator and government policy choices in the 1990s. The result of this study may be an indicator of the success of the telecoms market liberalisation programme embarked upon by the Nigerian government. ii The telecoms market liberalisation facilitated the entry of many telecoms companies providing various services as a result of which Nigeria attracted considerable foreign investments making the country one of the fastest growing and biggest telecoms market in Africa. As a consequence of this development, the mobile sector of the telecoms industry has seen triple digit growth rates for five years in a row since competition was introduced. A number of additional players have also entered the market under a new unified licensing regime which is expected to boost the country’s underdeveloped Internet and broadband sector. Third generation mobile and wireless broadband services are being rolled out at a rapid pace. All this development is supposedly as a result of the creation of an independent regulator, the Nigeria Communication Commission (NCC). On the other hand, this study shows that regulatory independence by itself is not a sufficient condition to promote sector growth. This is because, despite the fact that the study found the regulator (NCC) to be fairly and reasonably independent, Nigeria remains at relatively moderate levels of market penetration ― around 50% ― as reported by Baez and Kechiche (2010, p.5).

Cheung, Wing Kai = 互連網絡上的崩塌行為 / 張永佳. / Thesis M.Phil. Chinese University of Hong Kong 2015. / Includes bibliographical references (leaves 96-99). / Abstracts also in Chinese. / Title from PDF title page (viewed on 14, September, 2016). / Cheung, Wing Kai = Hu lian wang luo shang de beng ta xing wei / Zhang Yongjia.

by Yan Zhaoxu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references. / LIST OF FIGURES AND TABLES --- p.iii / ABBREVIATIONS --- p.v / INTRODUCTION --- p.1 / Chapter CHAPTER 1 --- TOWARD A PLURALISTIC APPROACH TO TELECOMMUNICATIONS --- p.10 / Chapter 1.1 --- "A Synthetic Review of Technological, Economic and Political Inquiries into Telecommunications" --- p.11 / Chapter 1.2 --- Toward a Pluralistic Approach to Telecommunications --- p.24 / Chapter CHAPTER 2 --- THE ANALYTIC FRAMEWORK OF THE CHINA-HONGKONG RELATIONSHIP IN TELECOMMUNICATIONS --- p.29 / Chapter 2.1 --- "Technological, Economic and Political Interdependence in International Telecommunications: An Extension of the Pluralistic Approach" --- p.30 / Chapter 2.2 --- The Analytic Framework of the China-Hongkong Relationship in Telecommunications --- p.37 / Chapter CHAPTER 3 --- TELECOMMUNICATIONS ENVIRONMENT IN CHINA： A POLICY-DRIVEN MODEL --- p.41 / Chapter 3.1 --- Policy Perspective --- p.41 / Chapter 3.2 --- Technology Perspective --- p.46 / Chapter 3.3 --- Market Perspective --- p.48 / Chapter 3.4 --- Changing Environment --- p.50 / Chapter CHAPTER 4 --- TELECOMMUNICATIONS ENVIRONMENT IN HONGKONG: A MARKET-DRIVEN MODEL --- p.61 / Chapter 4.1 --- Policy Perspective --- p.61 / Chapter 4.2 --- Technology Perspective --- p.66 / Chapter 4.3 --- Market Perspective --- p.70 / Chapter 4.4 --- Changing Environment --- p.73 / Chapter CHAPTER 5 --- THE CHINA´ؤHONGKONG RELATIONSHIP IN TELECOMMUNICATIONS I: A HISTORICAL BACKGROUND --- p.78 / Chapter CHAPTER 6 --- THE CHINA-HONGKONG RELATIONSHIP IN TELECOMMUNICATIONS II: THE HONGKONG INFLUENCES --- p.86 / Chapter 6.1 --- Trade with China in Telecommunications --- p.86 / Chapter 6.2 --- Direct Investment in and Technology Transfer to China's Telecommunications --- p.91 / Chapter 6.3 --- Political influence from Hongkong --- p.97 / Chapter 6.4 --- Assessing the Hongkong Influence --- p.100 / Chapter CHAPTER 7 --- THE CHINA-HONGKONG RELATIONSHIP IN TELECOMMUNICATIONS III: THE CHINA INFLUENCES --- p.104 / Chapter 7.1 --- Trade with Hongkong in Telecommunications --- p.104 / Chapter 7.2 --- Direct Investment in and Technology Transfer to Hongkong's Telecommunications --- p.107 / Chapter 7.3 --- Political Influence from China --- p.112 / Chapter 7.4 --- Assessing the China Influence --- p.116 / CONCLUSION --- p.122 / APPENDIX --- p.131 / BIBLIOGRPHY --- p.135