Browsing by Subject "Data transmission systems."
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Item Open Access Algorithms for the survivable telecommunications network design problem under dedicated protection(Bilkent University, 2010) Damcı, PelinThis thesis presents algorithms to solve a survivable network design problem arising in telecommunications networks. As a design problem, we seek to find 2-edge disjoint paths between every potential origin destination pair such that the fixed costs of installing edges and the routing costs are jointly minimized. Despite the fact that the survivable network design literature is vast, the particular problem at hand incorporating fixed and variable edge costs as well as different cost structures on the two paths has not been studied. Initially, an IP model addressing the proposed problem is developed. In order to solve problems of higher dimensions, different heuristic algorithms are designed and results of a computational study on a large bed of problem instances are reported.Item Open Access Cooperative transmission for the downlink of multiuser mimo cellular networks(Bilkent University, 2007) Yazarel, Yakup KadriIn this thesis, we propose a distributed transmission scheme for the downlink of a multiuser system. The base-stations (BSs) cooperate with each other with limited, local message-passing to find the optimum beamforming vectors, where there are individual signal-to-interference-plus-noise-ratio (SINR) targets for each user. Majority of the previous work on this problem assumed a total power constraint on the BSs. However, since each transmit antenna is limited by the amount of power it can transmit due to the limited linear region of the power amplifiers, a more realistic constraint is to place a limit on the per-antenna power. In a recent work, Yu and Lan proposed an iterative algorithm for computing the optimum beamforming vectors minimizing the power margin over all antennas under individual SINR and per-antenna power constraints. However, from a system designer point of view, it may be more desirable to minimize the total transmit power rather than minimizing the power margin, especially when the system is not symmetric. Reformulating the transmitter optimization problem to minimize the total transmit power subject to individual SINR constraints on the users and per-antenna power constraints on the base stations, the algorithm proposed by Yu and Lan is modified. Performance of the modified algorithm is compared with the existing methods for various cellular array scenarios. The modified algorithm requires inversion of a matrix, which cannot be implemented fully distributively using limited information exchange between BSs. By approximating the matrix as tridiagonal, a suboptimal distributed algorithm for computing the beamforming vectors in a cooperative system is obtained. The proposed distributed algorithm is shown to achieve near optimal performance when the target SINRs and the size of the array are small.Item Open Access Data dissemination strategies for mobile peer-to-peer information systems with applications to healthcare(Bilkent University, 2009) Özbekoğlu, Fatih MelihPeer-to-peer (P2P) architecture is becoming increasingly popular for various applications, replacing the classical Client-Server architecture. With the enhanced capabilities of mobile devices (PDAs, mobile phones, etc.) wireless networks started to take advantage of P2P paradigm along with its properties like infrastructure-free operation, scalability, balanced and distributed workload. Mobile peer-to-peer (MP2P) networks refer to the application of P2P architecture over wireless networks. Problems about dissemination of data in both P2P and MP2P networks are widely studied, and there are many proposed solutions. Healthcare information systems are helping clinicians to hold the information belonging to patients and diseases, and to communicate with each other since early 1950s. Today, they are widely used in hospitals, being constructed using Client-Server network architecture. Wireless technologies are also applied to medical domain, especially for monitoring purposes. In this thesis, we present and evaluate various data dissemination strategies to work on a mobile peer-to-peer (MP2P) network designed for a medical healthcare environment. First, the designed network system is presented along with the network topology. Then, the proposed data dissemination strategies are described. And finally, these strategies are evaluated according to the properties and needs of a medical system.