All students and faculty are welcome to attend the final defense of EECS graduate students completing their M.S. or Ph.D. degrees. Defense notices for M.S./Ph.D. presentations for this year and several previous years are listed below in reverse chronological order.
Students who are nearing the completion of their M.S./Ph.D. research should schedule their final defenses through the EECS graduate office at least THREE WEEKS PRIOR to their presentation date so that there is time to complete the degree requirements check, and post the presentation announcement online.
UPCOMING DEFENSE NOTICES
When & Where:March 27, 2019 - 3:00 PM
Apollo Room, Nichols Hall
Committee Members:Shannon Blunt, Chair
Stretch processing with the use of a wideband LFM transmit waveform is a commonly used technique, and its popularity is in large part due to the large time-bandwidth product that provides fine range resolution capabilities for applications that require it. It allows pulse compression of echoes at a much lower sampling bandwidth without sacrificing any range resolution. Previously, this technique has been restrictive in terms of waveform diversity because the literature shows that the LFM is the only type of waveform that will result in a tone after stretch processing. However, there are also many examples in the literature that demonstrate an ability to compensate for distortions from an ideal LFM waveform structure caused by various hardware components in the transmitter and receiver. This idea of compensating for variations is borrowed here, and the use of nonlinear FM (NLFM) waveforms is proposed to facilitate more variety in wideband waveforms that are usable with stretch processing. A compensation transform that permits the use of these proposed NLFM waveforms replaces the final fast Fourier transform (FFT) stage of the stretch processing configuration, but the rest of the RF receive chain remains the same. This modification to the receive processing structure makes possible the use of waveform diversity for legacy radar systems that already employ stretch processing. Similarly, using the same concept of compensating for distortions to the LFM structure along with the notion that a Fourier transform is essentially the matched filter bank for an LFM waveform mixed with an LFM reference, a least-squares based mismatched filtering (MMF) scheme is proposed. This MMF could likewise be used to replace the final FFT stage, and can also facilitate the application of NLFM waveforms to legacy radar systems. The efficacy of these filtering approaches (compensation transform and least-squares based MMF) are demonstrated in simulation and experimentally using open-air measurements and are applied to different scenarios of NLFM waveform to assess the results and provide a means of comparison between the two techniques.
PAST DEFENSE NOTICES
When & Where:February 4, 2019 - 1:15 PM
317 Nichols Hall
Committee Members:Carl Leuschen, Chair
Rising the yield of wheat crops is essential to meet the projected future demands of consumption and it is expected that most yield increases will be associated to improvements in biomass accumulation. Cultivars with canopy architectures that focus the light interception where photosynthetic-capacity is greater achieve larger biomass accumulation rates. Identifying varieties with improved traits could be performed with modern breeding methods, such as genomic-selection, which depend on genotype-phenotype mappings. Developing a non-destructive sensor with the capability of efficiently phenotyping wheat-canopy architecture parameters, such as height and vertical distribution of projected-leaf-area-density, would be useful for developing architecture-related genotype-phenotype maps of wheat cultivars. In this presentation, new scattering analysis tools and a new 2-18 GHz radar system are presented for efficiently phenotyping the architecture of wheat canopies.
The radar system presented was designed with the objective to measure the RCS profile of wheat canopies at close range. The frequency range (2-18 GHz), topology (Frequency-modulated-continuous-wave) and other radar parameters were chosen to meet that goal. Phase noise of self-interference signals is the main source of coherent and incoherent noise in FMCW radars. A new comprehensive noise analysis is presented, which predicts the power-spectral-density of the noise at the output of FMCW radars,
including those related to phase noise. The new 2-18 GHz chirp generator is based on a phase-locked-loop that was designed with large loop bandwidth to suppress the phase noise of the chirp. Additionally, the radar RF front-end was designed to achieve low levels of LO-leakage and antenna feed-through, which are the main self-interference signals of FMCW radars.
In addition to the radar system, a new efficient radar simulator was developed to predict the RCS waveforms collected from wheat canopies over the 2-18 GHz frequency range. The coherent radar simulator is based on novel geometric and fully-polarimetric scattering models of wheat canopies. The scattering models of wheat canopies, leaves with arbitrary orientation and curvature, stems and heads were validated using a full-wave commercial simulator and measurements. The radar simulator was used to derive retrieval algorithms of canopy height and projected-leaf-area-density from RCS profiles, which were tested with field-collected measurements.
When & Where:January 30, 2019 - 2:00 PM
317 Nichols Hall
Committee Members:Carl Leuschen, Chair
Sea ice in polar regions is typically covered with a layer of snow. The thermal insulation properties and high albedo of the snow cover insulates the sea ice beneath it, maintaining low temperatures and limiting ice melt, and thus affecting sea ice thickness and growth rates. Remote sensing of snow cover thickness plays a major role in understanding the mass balance of sea ice, inter-annual variability of snow depth, and other factors which directly impact climate change. The Center for Remote Sensing of Ice Sheets (CReSIS) at the University of Kansas has developed an ultra-wide band FMCW Snow Radar used to measure snow thickness and map internal layers of polar firn. The radar’s deployment on high-endurance, fixed-wing aircraft makes it difficult to track the surface from these platforms, due to turbulence and a limited range window. In this thesis, an automated onboard real-time surface tracker for the snow radar is presented to detect the snow surface elevation from the aircraft and track changes in the surface elevation. For an FMCW radar to have a long-range (high altitude) capability, a reference chirp delaying ability is a necessity to maintain a relatively constant beat frequency. Currently, the radar uses a filter bank to bandpass the received IF signal and store the spectral power in each band by utilizing different Nyquist zones. During airborne missions in polar regions with the radar, the operator has to manually switch the filter banks one by one as the aircraft elevation from the surface increases. The work done in this thesis aims at eliminating the manual switching operation and providing the radar with surface detection, chirp delay, and a constant beat frequency feedback loop in order to enhance its long range capability and ensure autonomous operation.
When & Where:January 3, 2019 - 8:30 AM
246 Nichols Hall
Committee Members:James Sterbenz , Chair
Mobile ad hoc networks (MANETs) consist of mobile nodes that can communicate with each other through wireless links without the help of any infrastructure. The dynamic topology of MANETs poses a significant challenge for the design of routing protocols. Many routing protocols have been developed to discover routes in MANETs through different mechanisms such as source routing and link state routing. In this thesis, we present a comprehensive performance analysis of several prominent MANET routing protocols. The protocols studied are Destination Sequenced Distance Vector protocol (DSDV), Optimized Link State Routing protocol (OLSR), Ad hoc On-demand Distance Vector protocol (AODV), and Dynamic Source Routing (DSR). We evaluate their performance on metrics such as packet delivery ratio, end-to-end delay, and routing overhead through simulations in different scenarios with ns-3. These scenarios involve different node density, node velocity, and mobility models including Steady-State Random Waypoint, Gauss-Markov, and Lévy Walk. We believe this study will be helpful for the understanding of mobile routing dynamics, the improvement of current MANET routing protocols, and the development of new protocols.