Browsing by Subject "Broadband communication systems."
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Item Open Access A framework for handling connectionless services in ATM networks(Bilkent University, 1997) Abdelati, MohamedATM networks, which are connection-oriented transport inediums, are well-suited to handle interactive and real-time applications such as telephony and video conferencing. However, they will be underutilized if used directly in aipplications characterized by sporadic behaivior and short service time requirements such as mail and file transfer. For such applications, in which the user information typically consists of a single block of data., connection-oriented services are inefficient due to connection establishment and teardown overhead. These applications are more efficiently handled by a connectioidess service which multiplexes data from individual applications into a pre-established virtual connection. In this work a method for providing connectionless services in ATM networks is proposed. This method is based on a pricing scheme which allocates the communication resources in a Pareto-optimal way that achieves maximum total surplus. The key idea, is to decompose the service provision procedure among three separate parties whose interactions are governed by a. set of competitive pricing mechanisms.Item Open Access Implementation of a coded-reference ultra-wideband system(Bilkent University, 2011) Gürlevik, OsmanCoded-reference ultra-wideband (CR UWB) systems provide orthogonalization of the reference and data signals in the code domain to facilitate communications without the need for complex channel estimation and have significant advantages over the previous techniques in terms of performance and/or implementation complexity. This thesis presents a UWB testbed as a general experimental platform to explore pulse-based UWB communications and discusses design and implementation issues. A testbed is built as a flexible solution for hardware implementation of a CR UWB system.Item Open Access Receiver design and performance analysis for code-multiplexed transmitted-reference ultra-wideband systems(Bilkent University, 2010) Tutay, Mehmet EminIn transmitted-reference (TR) and frequency-shifted reference (FSR) ultrawideband (UWB) systems, data and reference signals are shifted relative to each other in time and frequency domains, respectively. The main advantage of these systems is that they remove strict requirements of channel estimation. In order to implement TR UWB systems, an analog delay line, which is difficult to build in an integrated fashion, is needed. Although FSR systems require frequency conversion at the receiver, which is much simpler in practice, they have data rate limitations. Instead, a code-multiplexed transmitted-reference (CM-TR) UWB system that transmits data and reference signals using two distinct orthogonal codes can be considered. This system requires a simpler receiver and has better performance than TR and FSR. In the first part of the thesis, CM-TR systems are investigated and probability of error expressions are obtained. For the single user case, a closed-form expression for the exact probability of error is derived. For the multiuser case, a closed-form expression is derived based on the Gaussian approximation, and the results are compared in different scenarios. In the second part of the thesis, some optimal and suboptimal receivers are studied. First, low complexity receivers, such as the blinking receiver (BR) and the chip discriminator, are presented. The requirements for these types of receivers are explained, and the conditions under which their performance can be improved are discussed. Then, an analytical analysis of the linear minimum mean-squared error (MMSE) receiver and the requirements to implement this MMSE receiver are provided. Lastly, the optimal maximum-likelihood (ML) detector is derived, which has higher computational complexity and more strict requirements than the other receivers. Finally, simulation results are presented in order to verify the theoretical results and to compare the performance of the receivers.Item Open Access A system level simulation study of WiMAX(Bilkent University, 2010) Başçiftçi, Yüksel OzanIn this thesis, we implement a WiMAX system level simulator compliant with the evaluation methodology document published by the IEEE 802.16m Task Group. We study the PHY abstraction of polar codes and integrate polar codes into the simulator. We compare the system level performances of polar code and convolutional turbo code (CTC) and observe that CTC outperforms polar code. On the simulator, we study the downlink (DL) performance of WiMAX under various configurations such as scheduling methods, subchannelization methods, and frequency reuse models. We study there types of scheduling methods, namely round robin (RR) scheduling, proportional fair (PF) scheduling, and maximum sum rate (MSR) scheduling. We observe that MSR scheduling has the best throughput performance but does not support the users far from the base station. We study three frequency reuse models, namely 1×3×1, 1×3×3, and 3×3×1. We observe that 1 ×3×1 reuse model has the best throughput performance and maximum spectral efficiency is obtained in 1 × 3 × 3 reuse model. We study two subchannelization methods, namely PUSC and band AMC. We observe that in low mobility cases, band AMC outperforms PUSC and in high mobility cases, PUSC is better than band AMC.