UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item BASEBAND RADIO MODEM DESIGN USING GRAPHICS PROCESSING UNITS(2015) KIM, SCOTT C.; Bhattacharyya, Shuvra S; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A modern radio or wireless communications transceiver is programmed via software and firmware to change its functionalities at the baseband. However, the actual implementation of the radio circuits relies on dedicated hardware, and the design and implementation of such devices are time consuming and challenging. Due to the need for real-time operation, dedicated hardware is preferred in order to meet stringent requirements on throughput and latency. With increasing need for higher throughput and shorter latency, while supporting increasing bandwidth across a fragmented spectrum, dedicated subsystems are developed in order to service individual frequency bands and specifications. Such a dedicated-hardware-intensive approach leads to high resource costs, including costs due to multiple instantiations of mixers, filters, and samplers. Such increases in hardware requirements in turn increases device size, power consumption, weight, and financial cost. If it can meet the required real-time constraints, a more flexible and reconfigurable design approach, such as a software-based solution, is often more desirable over a dedicated hardware solution. However, significant challenges must be overcome in order to meet constraints on throughput and latency while servicing different frequency bands and bandwidths. Graphics processing unit (GPU) technology provides a promising class of platforms for addressing these challenges. GPUs, which were originally designed for rendering images and video sequences, have been adapted as general purpose high-throughput computation engines for a wide variety of application areas beyond their original target domains. Linear algebra and signal processing acceleration are examples of such application areas. In this thesis, we apply GPUs as software-based, baseband radios and demonstrate novel, software-based implementations of key subsystems in modern wireless transceivers. In our work, we develop novel implementation techniques that allow communication system designers to use GPUs as accelerators for baseband processing functions, including real-time filtering and signal transformations. More specifically, we apply GPUs to accelerate several computationally-intensive, frontend radio subsystems, including filtering, signal mixing, sample rate conversion, and synchronization. These are critical subsystems that must operate in real-time to reliably receive waveforms. The contributions of this thesis can be broadly organized into 3 major areas: (1) channelization, (2) arbitrary resampling, and (3) synchronization. 1. Channelization: a wideband signal is shared between different users and channels, and a channelizer is used to separate the components of the shared signal in the different channels. A channelizer is often used as a pre-processing step in selecting a specific channel-of-interest. A typical channelization process involves signal conversion, resampling, and filtering to reject adjacent channels. We investigate GPU acceleration for a particularly efficient form of channelizer called a polyphase filterbank channelizer, and demonstrate a real-time implementation of our novel channelizer design. 2. Arbitrary resampling: following a channelization process, a signal is often resampled to at least twice the data rate in order to further condition the signal. Since different communication standards require different resampling ratios, it is desirable for a resampling subsystem to support a variety of different ratios. We investigate optimized, GPU-based methods for resampling using polyphase filter structures that are mapped efficiently into GPU hardware. We investigate these GPU implementation techniques in the context of interpolation (integer-factor increases in sampling rate), decimation (integer-factor decreases in sampling rate), and rational resampling. Finally, we demonstrate an efficient implementation of arbitrary resampling using GPUs. This implementation exploits specialized hardware units within the GPU to enable efficient and accurate resampling processes involving arbitrary changes in sample rate. 3. Synchronization: incoming signals in a wireless communications transceiver must be synchronized in order to recover the transmitted data properly from complex channel effects such as thermal noise, fading, and multipath propagation. We investigate timing recovery in GPUs to accelerate the most computationally intensive part of the synchronization process, and correctly align the incoming data symbols in the receiver. Furthermore, we implement fully-parallel timing error detection to accelerate maximum likelihood estimation.Item Synchronization of Network Coupled Chaotic and Oscillatory Dynamical Systems(2013) Barlev, Gilad Samuel; Ott, Edward; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We consider various problems relating to synchronization in networks of coupled oscillators. In Chapter 2 we extend a recent exact solution technique developed for all-to-all connected Kuramoto oscillators to certain types of networks by considering large ensembles of system realizations. For certain network types, this description allows for a reduction to a low dimensional system of equations. In Chapter 3 we compute the Lyapunov spectrum of the Kuramoto model and contrast our results both with the results of other papers which studied similar systems and with those we would expect to arise from a low dimensional description of the macroscopic system state, demonstrating that the microscopic dynamics arise from single oscillators interacting with the mean field. Finally, Chapter 4 considers an adaptive coupling scheme for chaotic oscillators and explores under which conditions the scheme is stable, as well as the quality of the stability.Item An evaluation of the synchronization in the dynamics of blue crab (Callinectes sapidus) populations in the western Atlantic(2011) Colton, Amanda Rae; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Blue crab populations along the east coast of the United States are known to fluctuate in size annually. Previously, the degree of coherence in abundance between these populations was unknown. My research used a combination of fishery-dependent and fishery-independent data to quantify the amount of synchrony among blue crab populations and to determine the mechanisms that drive abundance fluctuations. This was done by first fitting catch-survey models to time series of survey abundance and catch to obtain absolute abundance estimates. Subsequently, I used multivariate techniques to quantify the extent and pattern of synchronization. I found that a latitudinal pattern among blue crab populations exists among all the regions except Chesapeake Bay, which appeared to be anomalous. A combination of larval mixing in the coastal ocean and a Moran effect appear to be drivers of the synchrony among blue crab populations although more investigation into these mechanisms is needed.Item Time-based Location Techniques Using Inexpensive, Unsynchronized Clocks in Wireless Networks(2011) Mah, Matthew Yew Mun; Agrawala, Ashok K; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to measure location using time of flight in IEEE 802.11 networks is impeded by the standard clock resolution, imprecise synchronization of the 802.11 protocol, and the inaccuracy of available clocks. To achieve real-time location with accuracy goals of a few meters, we derive new consensus synchronization techniques for free-running clocks. Using consensus synchronization, we improve existing time of arrival (TOA) techniques and introduce new time difference of arrival (TDOA) techniques. With this common basis, we show how TOA is theoretically superior to TDOA. Using TOA measurements, we can locate wireless nodes that participate in the location system, and using TDOA measurements, we can locate nodes that do not participate. We demonstrate applications using off-the-shelf 802.11 hardware that can determine location to within 3m using simple, existing optimization methods. The synchronization techniques extend existing ones providing distributed synchronization for free-running clocks to cases where send times cannot be controlled and adjusted precisely, as in 802.11 networks. These location and synchronization techniques may be applied to transmitting wireless nodes using any communication protocol where cooperating nodes can produce send and receive timestamps.Item Dynamics and Synchronization of Nonlinear Oscillators with Time Delay: A Study with Fiber Lasers(2007-06-20) Franz, Anthony Lawrence; Roy, Rajarshi; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The effect of time delay on nonlinear oscillators is an important problem in the study of dynamical systems. Erbium-doped fiber ring lasers have an internal time scale set by the length of the laser's electromagnetic cavity. Long cavities allow thousands of modes to experience gain making it very difficult to model the lasers. We examine the effect of adding external time delays through feedback and coupling. In the first experiment an external time delay is added to a laser by adding a feedback loop to the cavity. These delay times are varied over four orders of magnitude by changing the length of fiber in the feedback loop. The laser intensity dynamics are examined using time series, power spectra, time delay embeddings, and spatiotemporal representations. We apply Karhunen-Loeve (KL) decomposition on the spatiotemporal representations and use the Shannon entropy as calculated from the KL eigenvalue spectra as a measure of the complexity of the dynamics. For long delays we find that the complexity increases as expected, but also that the fluctuation size increases. In the second experiment two lasers are mutually coupled together with a coupling time delay that is varied over four orders of magnitude. The analysis is repeated and we find the surprising result that the dynamical complexity decreases for short coupling delays as compared to the uncoupled lasers. Measurements of the optical spectra indicate a narrowing of the spectra indicating that the simplification in dynamics could be due to the reduction in the number of electromagnetic modes experiencing gain. The fluctuation size increases for all delay times and is largest when the internal and external time delays match. Lag-synchrony is also observed for the mutually coupled lasers. Recent modeling using Ikeda ring oscillators showed that stable isochronal synchrony could be achieved if a third drive laser was unidirectionally coupled with enough strength. We experimentally find that increasing the coupling strength of a third drive laser added to the mutually coupled lasers above quenches the lag-synchrony. The two response lasers become more synchronized to the drive than to each other, however the levels of isochronal synchrony are low.