Systems and Communications Commons^™

Monostatic Airborne Synthetic Aperture Radar Using Commercial Wimax Transceivers In The License-Exempt Spectrum, Kai Liu

Electronic Thesis and Dissertation Repository

The past half-century witnessed an evolution of synthetic aperture radar (SAR). Boosted by digital signal processing (DSP), a variety of SAR imaging algorithms have been developed, in which the wavenumber domain algorithm is mature for airborne SAR and independent of signal waveforms. Apart from the algorithm development, there is a growing interest in how to acquire the raw data of targets’ echoes before the DSP for SAR imaging in a cost-effective way. For the data acquisition, various studies over the past 15 years have shed light on utilizing the signal generated from the ubiquitous broadband wireless technology – orthogonal frequency …

A Collaborative Access Control Model For Shared Items In Online Social Networks, Hanaa Al Shareef

Electronic Thesis and Dissertation Repository

The recent emergence of online social networks (OSNs) has changed the communication behaviors of thousand of millions of users. OSNs have become significant platforms for connecting users, sharing information, and a valuable source of private and sensitive data about individuals. While OSNs insert constantly new social features to increase the interaction between users, they, unfortunately, offer primitive access control mechanisms that place the burden of privacy policy configuration solely on the holder who has shared data in her/his profile regardless of other associated users, who may have different privacy preferences. Therefore, current OSN privacy mechanisms violate the privacy of all …

Joint Use Of On-Board Reconfigurable Antenna Pattern And Adaptive Coding And Modulation In Satellite Communications At High Frequency Bands, Marco Luccini

Electronic Thesis and Dissertation Repository

The Telecommunication market is driven by the increasing need of the end users for multimedia services which require high data rates. Within the fixed satellite service, frequency bandwidths wide enough to carry such high data rates are to be found in Ka band (26-40 GHz), and Q/V bands (40-50 GHz). However, at Ka band and above, transmitted signals can be severely affected by tropospheric attenuation for substantial percentages of time, resulting in the degradation of the quality and of the availability of communication services. Fade Mitigation Techniques (FMTs) must be used to counteract these severe propagation impairments. In this thesis …

Spectrum Sensing And Multiple Access Schemes For Cognitive Radio Networks, Oscar G. Filio Rodriguez

Electronic Thesis and Dissertation Repository

Increasing demands on the radio spectrum have driven wireless engineers to rethink approaches by which devices should access this natural, and arguably scarce, re- source. Cognitive Radio (CR) has arisen as a new wireless communication paradigm aimed at solving the spectrum underutilization problem. In this thesis, we explore a novel variety of techniques aimed at spectrum sensing which serves as a fundamental mechanism to find unused portions of the electromagnetic spectrum.

We present several spectrum sensing methods based on multiple antennas and evaluate their receiving operating characteristics. We study a cyclostationary feature detection technique by means of multiple cyclic frequencies. …

Resource Allocation In Uplink Long Term Evolution, Aidin Reyhanimasoleh

Electronic Thesis and Dissertation Repository

One of the most crucial goals of future cellular systems is to minimize transmission power while increasing system performance. This master thesis work presents two channel-queue-aware scheduling schemes to allocate channels among active users in uplink LTE. Transmission power, packet delays and data rates are three of the most important criteria critically affecting the resource allocation designs. Therefore, each of these two scheduling algorithms proposes a practical method that assigns resources in such a way so as to optimally maximize data rate and minimize transmission power and packet delays while ensuring the QoS requirements. After converting the resource allocation problem …

Physical-Layer Security Enhancement In Wireless Communication Systems, Hao Li

Electronic Thesis and Dissertation Repository

Without any doubt, wireless infrastructures and services have fundamental impacts on every aspect of our lives. Despite of their popularities, wireless communications are vulnerable to various attacks due to the open nature of radio propagation. In fact, communication security in wireless networks is becoming more critical than ever. As a solution, conventional cryptographic techniques are deployed on upper layers of network protocols. Along with direct attacks from lower layer, wireless security challenges come with the rapid evolution of sophisticated decipher techniques. Conventional security mechanisms are not necessarily effective against potential attacks from the open wireless environment anymore. As an alternative, …

Reduced Order Estimation Of Time Varying Wireless Channels In Real Life Scattering Environment, Elena Uchiteleva

Electronic Thesis and Dissertation Repository

This thesis deals with theoretical study and numerical simulation of 2x1 MISO system with Alamouti coding and imperfect channel estimation at the receiver. We adopt two channel models to represent scattering environment. One is Sum of Sinusoids model, which is simple, but does not properly reflect the geometry of scattering environment. The second model uses a set of Modulated Discrete Prolate Spheroidal Sequences to represent the channel in a scenario with scattering from one or more clusters with predefined geometry. The effect of clusters location on estimation quality is examined. Furthermore, we derive reduced complexity Wiener filters for slow flat …

Modeling And Optimization Of Next-Generation Wireless Access Networks, Maysam Mirahmadi

Electronic Thesis and Dissertation Repository

The ultimate goal of the next generation access networks is to provide all network users, whether they are fixed or mobile, indoor or outdoor, with high data rate connectivity, while ensuring a high quality of service. In order to realize this ambitious goal, delay, jitter, error rate and packet loss should be minimized: a goal that can only be achieved through integrating different technologies, including passive optical networks, 4th generation wireless networks, and femtocells, among others.

This thesis focuses on medium access control and physical layers of future networks. In this regard, the first part of this thesis discusses techniques …

Secure Ofdm System Design For Wireless Communications, Hao Li

Electronic Thesis and Dissertation Repository

Wireless communications is widely employed in modern society and plays an increasingly important role in people's daily life. The broadcast nature of radio propagation, however, causes wireless communications particularly vulnerable to malicious attacks, and leads to critical challenges in securing the wireless transmission. Motivated by the insufficiency of traditional approaches to secure wireless communications, physical layer security that is emerging as a complement to the traditional upper-layer security mechanisms is investigated in this dissertation. Five novel techniques toward the physical layer security of wireless communications are proposed. The first two techniques focus on the security risk assessment in wireless networks …

Detection, Receivers, And Performance Of Cpfsk And Cpck, Mohammed Zourob

Electronic Thesis and Dissertation Repository

Continuous Phase Modulation (CPM) is a power/bandwidth efficient signaling technique for data transmission. In this thesis, two subclasses of this modulation called Continuous Phase Frequency Shift Keying (CPFSK) and Continuous Phase Chirp Keying (CPCK) are considered and their descriptions and properties are discussed in detail and several illustrations are given. Bayesian Maximum Likelihood Ratio Test (MLRT) is designed for detection of CPFSK and CPCK in AWGN channel. Based on this test, an optimum receiver structure, that minimizes the total probability of error, is obtained. Using high- and low-SNR approximations in the Bayesian test, two receivers, whose performances are analytically …

Situation-Aware Rate And Power Adaptation Techniques For Ieee 802.11, Jay Nadeau

Electronic Thesis and Dissertation Repository

The current generation of IEEE 802.11 Wireless Local Area Networks (WLANs) provide multiple data rates from which the different physical (PHY) layers may choose. The rate adaptation algorithm (RAA) is an essential component of 802.11 WLANs which completely determines the data rate a device may use. Some of the key challenges facing data rate selection are the constantly varying wireless channel, selecting the data rate that will result in the maximum throughput, assessing the conditions based on limited feedback and estimating the link conditions at the receiver.

Current RAAs lack the ability to sense their environment and adapt accordingly. 802.11 …

Performance Analysis Of Channel-Aware Media Access Control Schemes, Abdulfattah Noorwali

Electronic Thesis and Dissertation Repository

This thesis proposes a new Channel-Aware MAC (CA-MAC) protocol that allows more than two simultaneous transmissions to take place within a single wireless collision domain. In this proposed work, Multiple-Input Multiple-Output (MIMO) system is used to achieve higher spectral efficiency. The MIMO-based PHY layer has been adopted to help in controlling the transmission and to avoid any collisions by using weights gains technique on the antenna transmission, and by recovering any possible collisions using ZigZag decoding. In order to develop CA-MAC algorithm, to exploit the full potential of MIMO system, the library of 802.11x standard has been modified. NS-2 based …

Delay Extraction Based Equivalent Elmore Model For Rlc On-Chip Interconnects, Shamsul Arefin Siddiqui

Electronic Thesis and Dissertation Repository

As feature sizes for VLSI technology is shrinking, associated with higher operating frequency, signal integrity analysis of on-chip interconnects has become a real challenge for circuit designers. For this purpose, computer-aided-design (CAD) tools are necessary to simulate signal propagation of on-chip interconnects which has been an active area for research. Although SPICE models exist which can accurately predict signal degradation of interconnects, they are computationally expensive. As a result, more effective and analytic models for interconnects are required to capture the response at the output of high speed VLSI circuits. This thesis contributes to the development of efficient and closed …

Security On Medical Wireless Sensor Networks, Eric D. Southern

Electronic Thesis and Dissertation Repository

Wireless technology is fast becoming a very important tool for all aspects of communication. An area that lacks a strong implementation for wireless communication is the medical field. Wireless systems could be used by clinicians to be better able to diagnose and monitor patients. The reason behind the lack of adoption in healthcare is due to the need to meet the legislated and perceived requirements of security and privacy when dealing with clinical information. The current methods of wireless authentication are investigated and an existing issue in mobile networks is described and solved with two novel solutions; one solution within …

A Total Electron Content Receiver For The E-Pop Mission, Dmitry Shatskiy

Electronic Thesis and Dissertation Repository

Ionospheric parameters, such as electron density have a highly irregular structure and vary greatly throughout the day and with the seasons. Complete knowledge of the ionospheric structure usually requires expensive and/or stationary equipment such as rocket probes or incoherent scatter radars.

A height-integrated electron density along the satellite – ground-based receiver path, called total electron content (TEC), is often used as a measure of ionospheric inhomogeneities and, when possible, for ionospheric tomography.

An inexpensive portable digital receiver was used to assess the background ionospheric TEC. GNU Radio, an open-source software radio toolkit, GNU/Linux Bash scripts, a code in Python, a …

Enabling Techniques Design For Qos Provision In Wireless Communications, Penghui Mi

Electronic Thesis and Dissertation Repository

Guaranteeing Quality of Service (QoS) has become a recognized feature in the design of wireless communications. In this thesis, the problem of QoS provision is addressed from different prospectives in several modern communication systems.

In the first part of the thesis, a wireless communication system with the base station (BS) associated by multiple subscribers (SS) is considered, where different subscribers require different QoS. Using the cross-layer approach, the conventional single queue finite state Markov chain system model is extended to multiple queues' scenario by combining the MAC layer queue status with the physical layer channel states, modeled by finite state …