Magíster en Ciencias de la Ingeniería, Mención Eléctrica. Ingeniero Civil Eléctrico / En la actualidad existe un crecimiento acelerado en el número de dispositivos que utilizan la red para comunicarse, sumado a que la de manda por velocidades de transmisión más altas ha aumentado. Conjuntamente con este requerimiento, existe una exigencia tácita: dispositivos más autónomos, es decir, dispositivos que tengan baterías lo suficientemente eficiente para no tener que cargarlos frecuentemente. Esto ha creado la necesidad de contar con protocolos que utilicen eficientemente el ancho de banda disponible de Internet, además de que sean considerados con la batería de los equipos. Una de las soluciones que se han planteado es la de utilizar frecuencias más elevadas de comunicación, llegando en la actualidad a transmitir a frecuencias de decenas de Gigahertz. Una banda que tiene especial interés, es la banda de 60 Ghz (58 -61 GHz), pues es una banda no licenciada y provee una alta tasa de transmisión de datos. Esta tesis presenta un protocolo Media Access Control (MAC), orientado a las ondas milimétricas (ondas que trabajan a frecuencias entre 30 y 300 GHz), que mejora el desempeño del protocolo Process-Stacking Multiplexing Access (PSMA) y adaptarlo a una red centralizada. Aquí se propone el protocolo Variable Slot Time-Time Division Multiple Access (VST-TDMA). Este usa de forma más eficiente el ancho de banda pues no desperdicia tiempo, como si ocurre en Multiplexación por División de Tiempo (TDMA, Time Division Multiple Access). Además, es energéticamente eficiente y autosustentable, pues variará su tasa de transmisión dependiendo del estado de carga (SOC, State of Charge) de la batería del dispositivo. Para diseñar este, se mantuvo el funcionamiento general del protocolo PSMA, cuya idea central es la de agendar procesos, reservando el uso de canal a medida que los equipos que integran la red soliciten usarla, asignando a cada uno de ellos el tiempo exacto que requieran de utilización del canal. No obstante, el principal cambio que se añade es que la Estación Base (BS, Base Station) envía cíclicamente un broadcast, para para incorporar y/o sincronizar cualquier dispositivo que requiera acceder la red, o si la BS necesita enviar datos a alguno de los nodos. Seguidamente, se describirá el algoritmo que se usó para la estimación de los parámetros que condicionan el comportamiento de la batería. El principal resultado de VST-TDMA, es lo relacionado con la batería. En términos de desempeño en transferencia de datos, tiene un resultado similar a PSMA. No obstante, en lo relacionado a la energía, se puede notar que la información que se puede obtener de la batería permite que el protocolo decida en qué momento debe bajar su tasa de transferencia, para no degradarla, y de esta forma tenga mayor vida útil. Además, se llegó al hecho que el parámetro que condiciona principalmente a la batería es el parámetro α, logrando errores bajos en el caso de ser estimado con precisión. Como trabajo futuro, para empezar, se propone el implementar completamente el protocolo en Opnet, tanto desde el punto de vista de funcionamiento, como de la estimación de los parámetros que modelan la batería. De esta forma, será posible conocer el comportamiento más completo del protocolo. Finalmente, se podría implementar este protocolo con algún medio físico, y a las frecuencias a la cual fue diseñado. Se podría utilizar field-programmable gate array (FPGA), dónde se programaría el protocolo y se podría observar el comportamiento en un ambiente real.

Third Public Television Service (Channel 3) plays important roles in enhancing sense of community and encouraging involvement in community. The Cable Television Channel Planning and Management Regulations, which was promulgated on December 13 in 2004, indicate clearly that each cable station s third channel is the public channel to practice community people s media access rights. Its major purposes are to protect the freedom of speech, to ensure citizens having channels to express their opinions, and to facilitate the diverse social developments. Recently, the issue of new immigrants has become the main issue discussed in the society. In the past, scholars apply the theories of society science to the research of the issue of new immigrants. The number of study regarding the interaction of cable station¡¦s public channel is much fewer. This paper aims to use the media access rights and theory of life adjustment of new immigrants from the concept of public channel. Taking KuanSheng CATV Co., Ltd. in Pingtung as the example, we aim to explore if cable station¡¦s third public channel can play a more positive role in enhancing the right to access to the media of new immigrants to reduce digital divide, cultural gap, and life adjustment in addition to the social work unit. For the aspect of data analysis, a questionnaire was designed according to the research goals and questions, and further in-depth interview was conducted to cover the insufficient parts of questionnaire. Data were collected via either giving away the text of questionnaire or sending email. A total of 323 questionnaires were administered, leaving 176 valid questionnaires. This research has adopted statistical package software for social science including SPSS13.0 and AMOS 4.0 as the tool for data analysis. The result of research can be described as follows: public channel has brought the positive influence to the adaptability of new immigrants. Among them, programming of public channel and support of government¡¦s policies are not only crucial to public channel¡¦s impacts on the viewing of new immigrants but also the key factors of new immigrants¡¦ adjustment to new life in Taiwan.

Unlike the traditional store-and-forward mechanism in packet-switching networks,network coding schemes could combine and modify the contents of a number of packets from different source before the packets are forwarded.It has been recently shown that network coding techniques can significantly increase the overall throughput of wireless networks by taking advantage of their broadcast nature. In wireless networks,each transmitted packet is broadcasted within a certain area and can be overheard by the neighboring nodes.When a node needs to transmit packets,it employs the coding approach that uses the knowledge of what the node's neighbors have heard in order to reduce the number of transmissions. In this thesis,I propose jointly designing the network coding scheme and the media access control scheme to improve the performance of wireless networks.

Despite a rising democratic defict in dominant Canadian media they continue to hold much influce on policy-makers, government officials and citizens. While some scholars argue that recent advancements in communication technology change the dynamics of media production, making it more accessible, others argue that online media reflects what occurs offline. To test which position is correct, this thesis compares dominant and alternative news media websites. Overall, it appears that online media practices are a reflection of offline media. At best, alternative media adopt a hybrid model of production where they chose to selectively incorporate dominant media practices in the aim to meet the goals of alternative media.

京都大学 / 新制・課程博士 / 博士(情報学) / 甲第23327号 / 情博第763号 / 新制||情||130(附属図書館) / 京都大学大学院情報学研究科通信情報システム専攻 / (主査)教授 守倉 正博, 教授 原田 博司, 教授 大木 英司 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

No description available.

本研究在減低Wimax mesh mode環境中media access階段會造成的delay現象。我們發現當subscriber station (SS)訊務繁忙時，競爭transmission opportunity (TO)以及3-way handshake的過程容易失敗，造成傳輸效率降低，封包的delay也會增加。同時我們也發現封包的延遲還來自minislot的不良配置。因為原始的Wimax mesh mode對於minislot的配置會造成預約過晚的問題，當預約時間被延長，資料就必須無條件的增加等待時間，因此我們將針對這些問題進行改善，降低在訊務繁忙的狀況下，傳輸效率低落的問題。 我們使用兩種方式來改善上述的問題，其一是由Bayer [4]所提出的動態調整holdoff指數(dynamic holdoff exponent)的方式，藉由調整holdoff指數的大小來縮短holdoff時間，以縮短傳輸延遲；另外，我們也提出一個以節點的臨接區域為配置基準(Neighborhood-Based Minislot Allocation, NBMA) 的方法，透過與其相鄰的節點交換訊息，優化minislot的配置。我們用這兩種方式減少IEEE 802.16中媒體存取階段所造成的傳輸延遲。 實驗結果顯示，在網路負載較輕的情況下，NBMA可以有效的將delay降低為原來的七分之一，改善幅度將近85%，抖動率(jitter)的部分亦有20%的改善，並略為提高傳輸效能8%左右；而當網路負載較重時，delay的改善程度仍有40%左右，jitter部分改善了12%，傳輸效能亦有6%的改善。證明了我們的方法確實可行，並且在改善delay方面有顯著的效果。 / IEEE 802.16 mesh network is a new environment of wireless network. It was designed as a self-organized, distributed scheduling, and multi-hop network. However, it is not robust enough to handle a heavy loading environment for lacking of QoS support. Our research is trying to reduce its media access delay, which comes from both TO (transmission opportunity) competition and improper minislot allocation. TO competition will extend the MSH-DSCH (mesh distributed scheduling) interval and slow down the exchanging speed of control message. Improper minislot allocation comes from the distributed scheduling of minislot. When a subscriber station (SS) allocates too much minislot for low-level traffic, it will defer the allocation of other neighbors’ high-level traffic. We use Bayer’s [4] dynamic exponent to reduce holdoff time of SS, and speed up the exchange of control message. On the other hand, we design an “importance factor” (IM-factor) to score the importance of request. Through the exchange of IM-factor, SS and its neighbors will produce a threshold of IM-factor to filter the unimportant requests, and prevent minislot from being assigned too late. In our experiments, the proposed methods can reduce 85% delay and 20% jitter, and increase bandwidth utility by 7%. It shows that our method in reducing transmission delay is pratical and effective.

This thesis presents an evaluation of the performance, in terms of throughput and latency, of two Media Access Control (MAC) mechanisms in Underwater Acoustic Networks (UANs), using a model designed in the COTS simulation tool OPNET 10.5. The carrier sense multiple access with collision avoidance is the predominant approach for implementing the MAC mechanism in UANs. However, the underwater acoustic environment is characterized by extreme propagation delays and limited bandwidth, which suggests that an Aloha-like scheme may merit consideration. The performance of these two schemes was compared with respect to two topologies: tree and grid. The results showed that an Aloha-like scheme that does not segment messages outperforms the contention-based scheme under all load conditions, in terms of both throughput and latency, for the two topologies. This thesis is the first to establish that Aloha-like MAC mechanisms can be more than a limited alternative for lightly loaded networks; more specifically, they can be the preferred choice for an environment with large propagation delays. / Lieutenant Commander, Portuguese Navy

Approved for public release; distribution in unlimited. / In spite of the fact that wireless network technology has been available for long period of time, there has been very limited wireless networks deployments around the world before 1997 due to the lack of widely recognized standard for wireless networks. Thanks to the approval of the IEEE 802.11 family of standards in 1997, the world has witnessed tremendous deployment and proliferation of wireless networks in all aspects of life. Although the IEEE 802.11 family of standards has been ratified to design radio transceivers for wireless computer stations capable of interconnecting with other wireless computer stations in close proximity, the technology has been successfully employed to design and implement wireless networks with great number of distant wireless computer stations with reasonable data throughput and flexibility. This thesis explores the wireless network technology and the primary building blocks and components of a wireless network. It also explores the IEEE 802.11 standard and its technical specifications including the Physical layer (PHY), the Media Access Control layer (MAC) and the ongoing task forces. Additionally, the thesis examines the wireless network security including the vulnerabilities, ongoing improvements and recommendations. Next, it investigates the market for available wireless devices compatible with the IEEE 802.11 standard that can be used to build a wireless network with high data throughput and high level of security. Subsequently, the thesis formulates a design plan for civilian wireless network with different scenarios in order to provide a speedy solution to the limited broadband service availability in the Sultanate of Oman. Additionally, the thesis formulates a generic design plan for a military wireless network with different scenarios that can be rapidly deployed in the field of operations. / Computer Engineer, Royal Army of Oman

The objective of this dissertation is to improve the service quality of broadband optical access networks by developing advanced link- and transport- layer protocols. Current access technologies represent a significant bottleneck in bandwidth and service quality between a high-speed residential/enterprise network and a largely overbuilt core network. Although it is believed that passive optical network (PON) will be the most promising solution to provide truly broadband connections to end users, a suit of protocols are required to provide quality of service (QoS). In this dissertation, we design a new reservation MAC scheme that arbitrates upstream transmission, prevents collisions, and varies bandwidth according to demand and priority. The new access scheme exploits both WDM and TDM to cater for both light and heavy bandwidth requirements. Next, we introduce delta compression as an efficient method for fast content download. In the third part of this dissertation, we enhance the transport performance of Ethernet services by addressing the throughput optimization issue at the edge of the network. A novel SLA-aware transport control scheme is proposed to utilize reserved bandwidth more efficiently using a shifted additive increase multiplicative decrease (AIMD) algorithm, and to detect congestion more accurately based on hypothesis test. The performance of the proposed scheme is compared with traditional TCP through theoretical analyses and simulations.