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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Error Resilient Coding Using Flexible Macroblock Ordering In Wired And Wireless Communications

Demirtas, Ali Murat 01 September 2008 (has links) (PDF)
Error Resilient Coding tools are the methods to avoid or reduce the amount of corruption in video by altering the encoding algorithm. One of them is Flexible Macroblock Ordering (FMO) which provides us with ordering macroblocks of the frames flexibly. Six of them have definite ordering pattern and the last one, called explicit type, can get any order. In this thesis two explicit type algorithms, one of which is new, are explained and the performance of different FMO types in wired and wireless communication are evaluated. The first algorithm separates the important blocks into separate packets, so it equalizes the importance of packets. The proposed method allocates the important macroblocks according to a checkerboard pattern and employs unequal error protection to protect them more. The simulations are performed for wired and wireless communication and Forward Error Correction is used in the second stage of the simulations. Lastly the results of the new algorithms are compared with the performance of the other FMO types. According to the simulations the Proposed algorithm performs better than others when the error rate is very high and FEC is employed.
2

User Efficient Authentication Protocols with Provable Security Based on Standard Reduction and Model Checking

Lin, Yi-Hui 12 September 2012 (has links)
Authentication protocols are used for two parties to authenticate each other and build a secure channel over wired or wireless public channels. However, the present standards of authentication protocols are either insufficiently secure or inefficient for light weight devices. Therefore, we propose two authentication protocols for improving the security and user efficiency in wired and wireless environments, respectively. Traditionally, TLS/SSL is the standard of authentication and key exchange protocols in wired Internet. It is known that the security of TLS/SSL is not enough due to all sorts of client side attacks. To amend the client side security, multi-factor authentication is an effective solution. However, this solution brings about the issue of biometric privacy which raises public concern of revealing biometric data to an authentication server. Therefore, we propose a truly three factor authentication protocol, where the authentication server can verify their biometric data without the knowledge of users¡¦ templates and samples. In the major wireless technologies, extensible Authentication Protocol (EAP) is an authentication framework widely used in IEEE 802.11 WLANs. Authentication mechanisms built on EAP are called EAP methods. The requirements for EAP methods in WLANs authentication have been defined in RFC 4017. To achieve user efficiency and robust security, lightweight computation and forward secrecy, excluded in RFC 4017, are desired in WLAN authentication. However, all EAP methods and authentication protocols designed for WLANs so far do not satisfy all of the above properties. We will present a complete EAP method that utilizes stored secrets and passwords to verify users so that it can (1) meet the requirements of RFC 4017, (2) provide lightweight computation, and (3) allow for forward secrecy. In order to prove our proposed protocols completely, we apply two different models to examine their security properties: Bellare¡¦s model, a standard reduction based on computational model, that reduces the security properties to the computationally hard problems and the OFMC/AVISPA tool, a model checking approach based on formal model, that uses the concept of the search tree to systematically find the weaknesses of a protocol. Through adopting Bellare¡¦s model and OFMC/AVISPA tool, the security of our work is firmly established.
3

Optical millimeter-wave signal generation, transmission and processing for symmetric super-broadband optical-wireless access networks

Jia, Zhensheng 01 July 2008 (has links)
Three 40/60-GHz optical-wireless bidirectional architectures are designed with a centralized light source in the central office based on wavelength reuse. Three super-broadband access networks are proposed and experimentally demonstrated for simultaneously delivering wired and wireless services over an optical fiber and an air link in a single transport platform. The transport feasibility in metro and wide-area access networks with multiple reconfigurable optical add-drop multiplexers (ROADMs) nodes is explored for 40-GHz and 60-GHz optical millimeter-wave signals. Additionally, the optical-wireless systems using the orthogonal frequency division multiplexing (OFDM) modulation format are analytically and experimentally demonstrated to mitigate the chromatic dispersion in optical fiber. This thesis also successfully implements the testbed trial for the delivery of uncompressed 270-Mb/s standard-definition television (SDTV) and 1.485-Gb/s high-definition television (HDTV) video signals over optical fiber and air links. The demonstration represents the first ever reported real applications over hybrid wired and wireless access networks, showing that our developed up-conversion schemes and designed architectures are highly suitable for super-broadband applications in next-generation optical-wireless access networks.

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