Time and again, fiber optic medium has proved to be the best means for transporting global data traffic which is following an exponential growth trajectory. Rapid development of high bandwidth applications since the past decade based on virtual reality, 5G and big data to name a few have resulted in a sudden surge of research activities across the globe to maximize effective utilization of available fiber bandwidth which until then was supporting low speed services like voice and low bandwidth data traffic. To this end, higher order modulation formats together with multi-subcarrier superchannel based fiber optic transmission systems have proved to enhance spectral efficiency and achieve multi terabit per second data rates. However, spectrally efficient systems are extremely sensitive to transmission impairments stemming from both optical devices and fiber itself. Therefore, such systems mandate the use of robust digital signal processing (DSP) to compensate and/or mitigate the undesired artifacts, thereby extending the transmission reach. The central theme of this dissertation is to propose and validate few efficient DSP techniques to compensate specific impairments as delineated in the next three paragraphs.
For short reach applications, we experimentally demonstrate a digital compensation technique to undo semiconductor optical amplifier (SOA) and photodiode nonlinearity effects by digitally backpropagating the received signal through a virtual SOA with inverse gain characteristics followed by an iterative algorithm to cancel signal-signal beat interference arising from photodiode. We characterize the phase dynamics of comb lines from a quantum dot passive mode locked laser based on a novel multiheterodyne coherent detection technique. In the context of multi-subcarrier, Nyquist pulse shaped, superchannel transmission system with coherent detection, we demonstrate through measurements and numerical simulations an efficient phase noise compensation technique called “Digital Mixing” that operates using a shared pilot tone exploiting the mutual phase coherence among the comb lines.
Finally, we propose and experimentally validate a practical pilot aided relative phase noise compensation technique for forward pumped distributed Raman amplified, digital subcarrier multiplexed coherent transmission systems.

Many radar applications today require accurate, real-time, unambiguous measurement of target range and radial velocity.  Obstacles that frequently prevent target detection are the presence of noise and the overwhelming backscatter from other objects, referred to as clutter.

In this thesis, a method of static clutter suppression is proposed to increase detectability of moving targets in high clutter environments.  An experimental dual-purpose, single-mode, monostatic FMCW radar, operating at 108 GHz, is used to map the range of stationary targets and determine range and velocity of moving targets.  By transmitting a triangular waveform, which consists of alternating upchirps and downchirps, the received echo signals can be separated into two complementary data sets, an upchirp data set and a downchirp data set.  In one data set, the return signals from moving targets are spectrally isolated (separated in frequency) from static clutter return signals.  The static clutter signals in that first data set are then used to suppress the static clutter in the second data set, greatly improving detectability of moving targets.  Once the moving target signals are recovered from each data set, they are then used to solve for target range and velocity simultaneously.

The moving target of interest for tests performed was a reusable paintball (reball).  Reball range and velocity were accurately measured at distances up to 5 meters and at speeds greater than 90 m/s (200 mph) with a deceleration of approximately 0.155 m/s/ms (meters per second per millisecond).  Static clutter suppression of up to 25 dB was achieved, while moving target signals only suffered a loss of about 3 dB.

Increasing portions of people's social and communicative activities now take place in the digital world. The growth and popularity of online social networks (OSNs) have tremendously facilitate the online interaction and information exchange. Not only normal users benefit from OSNs as more people now rely online information for news, opinions, and social networking, but also companies and business owners who utilize OSNs as platforms for gathering feedback and marketing activities. As OSNs enable people to communicate more effectively, a large volume of user  generated content (UGC) is produced daily. However, the freedom and ease of of publishing information online has made these systems no longer the sources of reliable information. Not only does biased and misleading information exist, financial incentives drive individual and professional spammers to insert deceptive content and promote harmful information, which jeopardizes the ecosystems of OSNs.
In this dissertation, we present our work of measuring the credibility of information and detect content polluters in OSNs. Firstly, we assume that review spammers spend less effort in maintain social connections and propose to utilize the social relationships and rating deviations to assist the computation of trustworthiness of users. Compared to numeric ratings, textual content contains richer information about the actual opinion of a user toward a target. Thus, we propose a content-based trust propagation framework by extracting the opinions expressed in review content. In addition, we discover that the surrounding network around a user could also provide valuable information about the user himself. Lastly, we study the problem of detecting social bots by utilizing the characteristics of surrounding neighborhood networks.

FM noise waveforms have been experimentally demonstrated to achieve high time bandwidth products and low autocorrelation sidelobes while achieving acceptable spectral containment in physical implementation. Still, it may be necessary to further reduce sidelobe levels for detection or improve spectral containment in the face of growing spectral use. The Frequency Template Error (FTE) and the Logarithmic Frequency Template Error (Log-FTE) metrics were conceived as means to achieve FM noise waveforms with good spectral containment and good autocorrelation sidelobes. In practice, FTE based waveform optimizations have been found to produce better autocorrelation responses at the expense of spectral containment while Log-FTE optimizations achieve excellent spectral containment and interference rejection at the expense of autocorrelation sidelobe levels. In this work, the notion of the FTE and Log-FTE metrics are considered as subsets of a broader class of frequency domain metrics collectively termed as the Generalized Frequency Template Error (GFTE). In doing so, many different P-norm based variations of the FTE and Log-FTE cost functions are extensively examined and applied via gradient descent methods to optimize polyphase-coded FM (PCFM) waveforms. The performance of the different P-norm variations of the FTE and Log-FTE cost functions are compared amongst themselves, against each other, and relative to a previous FM noise waveform design approach called Pseudo-Random Optimized FM (PRO-FM). They are evaluated in terms of their autocorrelation sidelobes, spectral containment, and their ability to realize spectral notches within the 3 dB bandwidth for the purpose of interference rejection. These comparisons are performed in both simulation and experimentally in loopback where it was found that P-norm values of 2 tend to provide the best optimization performance for both the FTE and Log-FTE optimizations except in the case of the Log-FTE optimization of a notched spectral template where a P-norm value of 3 provides the best results. In general, the FTE and Log-FTE cost functions as subsets of the GFTE provide diverse means to optimize physically robust FM noise waveforms while emphasizing different performance criteria in terms of autocorrelation sidelobes, spectral containment, and interference rejection.

Given a list of smartphone sensor readings, such as accelerometer, gyroscope and light sensor, is there enough information present to predict a user’s input without access to either the raw text or keyboard log? With the increasing usage of smartphones as personal devices to access sensitive information on-the-go has put user privacy at risk. As the technology advances rapidly, smartphones now equip multiple sensors to measure user motion, temperature and brightness to provide constant feedback to applications in order to receive accurate and current weather forecast, GPS information and so on. In the ecosystem of Android, sensor reading can be accessed without user permissions and this makes Android devices vulnerable to various side-channel attacks.

In this thesis, we first create a native Android app to collect approximately 20700 keypresses from 30 volunteers. The text used for the data collection is carefully selected based on the bigram analysis we run on over 1.3 million tweets. We then present two approaches (single key press and bigram) for feature extraction, those features are constructed using accelerometer, gyroscope and light sensor readings. A deep neural network with four hidden layers is proposed as the baseline for this work, which achieves an accuracy of 47% using categorical cross entropy as the accuracy metric. A multi-view model then is proposed in the later work and multiple views are extracted and performance of the combination of each view is compared for analysis.

Trends toward large-scale integration and the high-power application of green energy resources necessitate the advent of efficient power converter topologies, multilevel converters. Multilevel inverters are effective solutions for high power and medium voltage DC-to-AC conversion due to their higher efficiency, provision of system redundancy, and generation of near-sinusoidal output voltage waveform. Recently, modular multilevel converter (MMC) has become increasingly attractive. To improve the harmonic profile of the output voltage, there is the need to increase the number of output voltage levels. However, this would require increasing the number of submodules (SMs) and power semi-conductor devices and their associated gate driver and protection circuitry, resulting in the overall multilevel converter to be complex and expensive. Specifically, the need for large number of bulky capacitors in SMs of conventional MMC is seen as a major obstacle. This work proposes an MMC-based multilevel converter that provides the same output voltage as conventional MMC but has reduced number of bulky capacitors. This is achieved by introduction of an extra middle arm to the conventional MMC. Due to similar dynamic equations of the proposed converter with conventional MMC, several previously developed control methods for voltage balancing in the literature for conventional MMCs are applicable to the proposed MMC with minimal effort. Comparative loss analysis of the conventional MMC and the proposed multilevel converter under different power factors and modulation indexes illustrates the lower switching loss of proposed MMC. In addition, a new voltage balancing technique based on carrier-disposition pulse width modulation for modular multilevel converter is proposed.

The second part of this work focuses on an improved control of MMC-based high-power DC/DC converters. Medium-voltage DC (MVDC) and high-voltage DC (HVDC) grids have been the focus of numerous research studies in recent years due to their increasing applications in rapidly growing grid-connected renewable energy systems, such as wind and solar farms. MMC-based DC/DC converters are employed for collecting power from renewable energy sources. Among various developed DC/DC converter topologies, MMC-based DC/DC converter with medium-frequency (MF) transformer is a valuable topology due to its numerous advantages. Specifically, they offer a significant reduction in the size of the MMC arm capacitors along with the ac-link transformer and arm inductors due to the ac-link transformer operating at medium frequencies. As such, this work focuses on improving the control of isolated MMC-based DC/DC (IMMDC) converters. The single phase shift (SPS) control is a popular method in IMMDC converter to control the power transfer. This work proposes conjoined phase shift-amplitude ratio index (PSAR) control that considers amplitude ratio indexes of MMC legs of MF transformer’s secondary side as additional control variables. Compared with SPS control, PSAR control not only provides wider transmission power range and enhances operation flexibility of converter, but also reduces current stress of medium-frequency transformer and power switches of MMCs. An algorithm is developed for simple implementation of the PSAR control to work at the least current stress operating point. Hardware-in-the-loop results confirm the theoretical outcomes of the proposed control method.

The worldwide energy demand is growing quickly, with an anticipated rate of growth of 48% from 2012 to 2040. Consequently, investments in all forms of renewable energy generation systems have been growing rapidly. Increased use of clean renewable energy resources such as hydropower, wind, solar, geothermal, and biomass is expected to noticeably renewable energy resources alleviate many present environmental concerns associated with fossil fuel-based energy generation.  In recent years, wind and solar energies are gained the most attention among all other renewable resources. As a result, both have become the target of extensive research and development for dynamic performance optimization, cost reduction, and power reliability assurance.  

The performance of Photovoltaic (PV) systems is highly affected by environmental and ambient conditions such as irradiance fluctuations and temperature swings. Furthermore, the initial capital cost for establishing the PV infrastructure is very high. Therefore, its essential that the PV systems always harvest the maximum energy possible by operating at the most efficient operating point, i.e. Maximum Power Point (MPP), to increase conversion efficiency and thus result in lowest cost of captured energy.

The dissertation is an effort to develop a new PV conversion system for large scale PV grid-connected systems which provides efficacy enhancements compared to conventional systems by balancing voltage mismatches between the PV modules. Hence, it analyzes the theoretical models for three selected DC/DC converters. To accomplish this goal, this work first introduces a new adaptive maximum PV energy extraction technique for PV grid-tied systems. Then, it supplements the proposed technique with a global search approach to distinguish absolute maximum power peaks within multi-peaks in case of partially shaded PV module conditions. Next, it proposes an adaptive MPP tracking (MPPT) strategy based on the concept of model predictive control (MPC) in conjunction with a new current sensor-less approach to reduce the number of required sensors in the system.  Finally, this work proposes a power balancing technique for injection of balanced three-phase power into the grid using a Cascaded H-Bridge (CHB) converter topology which brings together the entire system and results in the final proposed PV power system. The resulting PV system offers enhanced reliability by guaranteeing effective system operation under unbalanced phase voltages caused by severe partial shading.

The developed grid connected PV solar system is evaluated using simulations under realistic dynamic ambient conditions, partial shading, and fully shading conditions and the obtained results confirm its effectiveness and merits comparted to conventional systems.

Multiple-Input Multiple-Output (MIMO) systems with large-scale transmit antenna arrays, often called massive MIMO, are a very promising direction for 5G due to their ability to increase capacity and enhance both spectrum and energy efficiency. To get the benefit of massive MIMO systems, accurate downlink channel state information at the transmitter (CSIT) is essential for downlink beamforming and resource allocation. Conventional approaches to obtain CSIT for FDD massive MIMO systems require downlink training and CSI feedback. However, such training will cause a large overhead for massive MIMO systems because of the large dimensionality of the channel matrix. In this dissertation, we improve the performance of FDD massive MIMO networks in terms of downlink training overhead reduction, by designing an efficient downlink beamforming method and developing a new algorithm to estimate the channel state information based on compressive sensing techniques. First, we design an efficient downlink beamforming method based on partial CSI. By exploiting the relationship between uplink direction of arrivals (DoAs) and downlink direction of departures (DoDs), we derive an expression for estimated downlink DoDs, which will be used for downlink beamforming. Second, By exploiting the sparsity structure of downlink channel matrix, we develop an algorithm that selects the best features from the measurement matrix to obtain efficient CSIT acquisition that can reduce the downlink training overhead compared with conventional LS/MMSE estimators. In both cases, we compare the performance of our proposed beamforming method with traditional methods in terms of downlink achievable rate and simulation results show that our proposed method outperform the traditional beamforming methods.​

As people gather during different social, political or musical events, automated crowd analysis can lead to effective and better management of such events to prevent any unwanted scene as well as avoid political manipulation of crowd numbers. Crowd counting remains an integral part of crowd analysis and also an active research area in the field of computer vision. Existing methods fail to perform where crowd density is either too high or too low in an image, thus resulting in either overestimation or underestimation. These methods also mix crowd-like cluttered background regions (e.g. tree leaves or small and continuous patterns) in images with actual crowd, resulting in further crowd overestimation. In this work, we present a novel deep convolutional neural network (CNN) based framework ZiZoNet for automated crowd counting in static images in very low to very high crowd density scenarios to address above issues. ZiZoNet consists of three modules namely Crowd Density Classifier (CDC), Decision Module (DM) and Count Regressor Module (CRM). The test image, divided into 224x224 patches, passes through crowd density classifier (CDC) that classifies each patch to a class label (no-crowd (NC), low-crowd (LC), medium-crowd (MC), high-crowd (HC)). Based on the CDC information and using either heuristic Rule-set Engine (RSE) or machine learning based Random Forest based Decision Block (RFDB), DM decides which mode (zoom-in, normal or zoom-out) this image should use for crowd counting. CRM then performs patch-wise crowd estimate for this image accordingly as decided or instructed by the DM module. Extensive experiments on three diverse and challenging crowd counting benchmarks (UCF-QNRF, ShanghaiTech, AHU-Crowd) show that our method outperforms current state-of-the-art models under most of the evaluation criteria.​

This project report presents results of experiments on rule induction from incomplete data using probabilistic approximations. Mining incomplete data using probabilistic approximations is a well-established technique. Main goal of this report is to present research on a comparison carried out on two different approaches to mining incomplete data using probabilistic approximations: single local probabilistic approximations approach and concept probabilistic approximations. These approaches were implemented in python programming language and experiments were carried out on incomplete data sets with two interpretations of missing attribute values: lost values and do not care conditions. Our main objective was to compare concept and single local approximations in terms of the error rate computed using double hold-out method for validation. For our experiments we used seven incomplete data sets with many missing attribute values. The best results were accomplished by concept probabilistic approximations for five data sets and by single local probabilistic approximations for remaining two data sets.

A learning map is an unweighted directed graph containing relationships between discrete skills and concepts with edges defining the prerequisite hierarchy. They arose as a means of connecting student instruction directly to standards and curriculum and are designed to assist teachers in lesson planning and evaluating student response. As learning maps gain popularity there is an increasing need for teachers to quickly evaluate which nodes have been mastered by their students. Psychometrics is a field focused on measuring student performance and includes the development of processes used to link a student's response to multiple choice questions directly to their understanding of concepts. This dissertation focuses on developing modeling and visualization capabilities to enable efficient analysis of data pertaining to student understanding generated by psychometric techniques.

Such analysis naturally includes that done by classroom teachers. Visual solutions to this problem clearly indicate the current understanding of a student or classroom in such a way as to make suggestions that can guide future learning. In response to these requirements we present various experimental approaches which augment the original learning map design with targeted visual variables.

As well as looking forward, we also consider ways in which data visualization can be used to evaluate and improve existing teaching methods. We present several graphics based on modelling student progression as information flow. These methods rely on conservation of data to increase edge information, reducing the load carried by the nodes and encouraging path comparison.

In addition to visualization schemes and methods, we present contributions made to the field of Computer Science in the form of algorithms developed over the course of the research project in response to gaps in prior art. These include novel approaches to simulation of student response patterns, ranked layout of weighted directed graphs with variable edge widths, and enclosing certain groups of graph nodes in envelopes.

Finally, we present a final design which combines the features of key experimental approaches into a single visualization tool capable of meeting both predictive and validation requirements along with the methods used to measure the effectiveness and correctness of the final design.

   Ice bottom topography layers are an important boundary condition required to model the flow dynamics of an ice sheet. In this work, using low frequency multichannel radar data, we locate the ice bottom using two types of automatic trackers.

   First, we use the multiple signal classification (MUSIC) beamformer to determine the pseudo-spectrum of the targets at each range-bin. The result is passed into a sequential tree-reweighted message passing belief-propagation algorithm to track the bottom of the ice in the 3D image. This technique is successfully applied to process data collected over the Canadian Arctic Archipelago ice caps, and produce digital elevation models (DEMs) for 102 data frames. We perform crossover analysis to self-assess the generated DEMs, where flight paths cross over each other and two measurements are made at the same location. Also, the tracked results are compared before and after manual corrections. We found that there is a good match between the overlapping DEMs, where the mean error of the crossover DEMs is 38+7 m, which is small relative to the average ice-thickness, while the average absolute mean error of the automatically tracked ice-bottom, relative to the manually corrected ice-bottom, is 10 range-bins.

  Second, a direction of arrival (DOA)-based tracker is used to estimate the DOA of the backscatter signals sequentially from range bin to range bin using two methods: a sequential maximum a posterior probability (S-MAP) estimator and one based on the particle filter (PF). A dynamic flat earth transition model is used to model the flow of information between range bins. A simulation study is performed to evaluate the performance of these two DOA trackers. The results show that the PF-based tracker can handle low-quality data better than S-MAP, but, unlike S-MAP, it saturates quickly with increasing numbers of snapshots. Also, S-MAP is successfully applied to track the ice-bottom of several data frames collected over Russell glacier, and the results are compared against those generated by the beamformer-based tracker. The results of the DOA-based techniques are the final tracked surfaces, so there is no need for an additional tracking stage as there is with the beamformer technique.

Dynamic Binary Translators(DBTs) have a variety of uses, like instrumentation,
profiling, security, portability, etc. In order for the desired application to run
with these enhanced additional features(not originally part of its design), it is to be run
under the control of Dynamic Binary Translator. The application can be thought of as the
guest application, to be run with in a controlled environment of the translator,
which would be the host application. That way, the intended application execution
flow can be enforced by the translator, thereby inducing the desired behavior in
the application on the host platform(combination of Operating System and Hardware).

However, there will be a run-time/execution-time overhead in the translator, when performing the
additional tasks to run the guest application in a controlled fashion. This run-time
overhead has been limiting the usage of DBT's on a large scale, where response times can be critical.
There is often a trade-off between the benefits of using a DBT against the overall application response
time. So, there is a need to research/explore ways to faster application execution through DBT's(given
their large code-base).

With the evolution of the multi-core and GPU hardware architectures, multilpe concurrent threads can get
more work done through parallelization. A proper design of parallel applications or parallelizing parts of existing
serial code, can lead to improved application run-time's through hardware architecture support.

We explore the possibility of improving the performance of a DBT named DynamoRIO. The basic idea is to improve
its performance by speeding-up the process of guest code translation, through multiple threads translating
multiple pieces of code concurrently. In an ideal case, all the required code blocks for application
execution are readily available ahead of time without any stalls. For efficient eager translation, there is
also a need for heuristics to better predict the next code block to be executed. That could potentially
bring down the less productive code translations at run-time. The goal is to get application speed-up through
eager translation and block prediction heuristics, with execution time close to native run.

​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.

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.​