Defense Notices

Though languages like C and C++ are known to be memory unsafe, they are still used widely in industry because of their memory management features, low level nature and performance benefits. Also, as most of the systems software has been written using these languages, replacing them with memory safe languages altogether is currently impossible. Memory safety violations are commonplace, despite the fact that that there have been numerous attempts made to conquer them using source code, compiler and post compilation based approaches. SoftBound is a compiler-based technique that enforces spatial memory safety for C/C++ programs. However, SoftBound needs and depends on program information available in the high-level source code. The goal of our work is to develop a mechanism to efficiently and effectively implement a technique, like SoftBound, to provide spatial memory safety for binary executables. Our approach employs a combination of static-time analysis (using Ghidra) and dynamic-time instrumentation checks (using PIN). Softbound is a pointer based approach, which stores base and bound information per pointer. Our implementation determines the array and pointer access patterns statically using reverse engineering techniques in Ghidra. This static information is used by the Pin dynamic binary instrumentation tool to check the correctness of each load and store instruction at run-time. Our technique works without any source code support and no hardware or compiler alterations are needed. We evaluate the effectiveness, limitations, and performance of our implementation. Our tool detects spatial memory errors in about 57% of the test cases and induces about 6% average overhead over that caused by a minimal pintool.

Observational data produced in scientific experimentation and in day to day life is a valuable source of information for research. It can be challenging to extract meaningful inferences from large amounts of data. Data mining offers many algorithms to draw useful inferences from large pools of information based on observable patterns.

In this project I have implemented one such data mining algorithm for determining a single local probabilistic approximation, which also computes the corresponding ruleset; and compared it with two versions of the MLEM2 algorithm which induce a certain rule set and a possible rule set respectively. For experimentation, eight data sets with 35% missing values were used to induce corresponding rulesets and classify unseen cases. Two different interpretations of missing values were used, namely, lost values and do not care conditions. k-fold cross validation technique was employed with k=10 to identify error rates in classification. 

The goal of this project was to compare how accurately unseen cases are classified by the rulesets induced by each of the aforementioned algorithms. Error rate calculated from the k-fold cross validation technique was also used to observe how each type of interpretation of missing values affects the ruleset.

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.

Elastic optical networking (EON) is intended to offer flexible channel wavelength granularity to meet the requirement of high spectral efficiency (SE) in today’s optical networks. However, optical cross-connects (OXC) and switches based on optical wavelength division multiplexing (WDM) are not flexible enough due to the coarse bandwidth granularity imposed by optical filtering. Thus, OXC may not meet the requirements of many applications which require finer bandwidth granularities than that carried by an entire wavelength channel. 

 In order to achieve highly flexible and fine enough bandwidth granularities, electrical digital subcarrier cross-connect (DSXC) can be utilized in EON. As presented in this thesis, my research work focuses on the investigation and implementation of real-time digital signal processing (DSP) enabled DSXC which can dynamically assign both bandwidth and power to each individual sub-wavelength channel, known as subcarrier. This DSXC is based on digital sub-carrier multiplexing (DSCM), which is a frequency division multiplexing (FDM) technique that multiplexes a large number of digitally created subcarriers on each optical wavelength. Compared with OXC based on optical WDM, DSXC based on DSCM has much finer bandwidth granularities and flexibilities for dynamic bandwidth allocation. 

Based on a field programmable gate array (FPGA) hardware platform, we have designed and implemented a real-time DSP enabled DSXC which uses Nyquist FDM as the multiplexing scheme. For the first time, we demonstrated resampling filters for channel selection and frequency translation, which enabled real-time DSXC. This circuit-based DSXC supports flexible and fine data-rate subcarrier channel granularities, offering a low latency data plane, transparency to modulation formats, and the capability of compensating transmission impairments in the digital domain. The experimentally demonstrated 8×8 DSXC makes use of a Virtex-7 FPGA platform, which supports any-to-any switching of eight subcarrier channels with mixed modulation formats and data rates. Digital resampling filters, which enable frequency selections and translations of multiple subcarrier channels, have much lower DSP complexity and reduced FPGA resources requirements (DSP slices used in FPGA) in comparison to the traditional technique based on I/Q mixing and filtering.

We have also investigated the feasibility of using the distributed arithmetic (DA) architecture for real-time DSXC to completely eliminate the need of DSP slices in FPGA implementation. For the first time, we experimentally demonstrated the implementation of real-time frequency translation and channel selection based on the DA architecture in the same FPGA platform. Compared with resampling filters that leverage multipliers, the DA-based approach eliminates the need of DSP slices in the FPGA implementation and significantly reduces the hardware cost. In addition, by requiring the time of only a few clock cycles, a DA-based resampling filter is significantly faster when compared to a conventional FIR filter whose overall latency is proportional to the filter order. The DA-based DSXC is, therefore, able to achieve not only the improved spectral efficiency, programmability of multiple orthogonal subcarrier channels, and low hardware resources requirements, but also much reduced cross-connection latency when implemented in a real-time DSP hardware platform. This reduced latency of cross-connect switching can be critically important for time-sensitive applications such as 5G mobile fronthaul, cloud radio access network (C-RAN), cloud-based robot control, tele-surgery and network gaming.

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.

Rough set theory is a tool to deal with uncertain and incomplete data. It has been successfully used in classification, machine learning and automated knowledge acquisition. A maximal consistent block defined using rough set theory, is used for rule acquisition.

Maximal consistent block technique is applied to acquire knowledge in incomplete data sets by analyzing the structure of a similarity class. 

The main objective of this project is to implement and compare the algorithms for computing the maximal consistent blocks. The brute force method, recursive method and hierarchical method were designed for the data sets with missing attribute values interpreted only as “do not care” conditions. In this project, we extend these algorithms so they can be applied to arbitrary interpretations of missing attribute values, and an approach for computing maximal consistent blocks on the data sets with lost values is introduced in this project. Besides, we found that the brute force method and recursive method have problems dealing with the data sets for which characteristic sets are not transitive, so the limitations of the algorithms and a simplified recursive method are provided in the project as well.

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.

Machine learning is all about automation. Many tools have been created to help data scientists automate repeated tasks and train models. These tools require varying levels of user experience to be used effectively. The ``machine learning WOrk fLow management Framework" (WOLF) aims to automate the machine learning pipeline. One of its key uses is to discover which machine learning model and hyper-parameters are the best configuration for a dataset. In this project, features were explored that could be added to make WOLF behave as a full pipeline in order to be helpful for novice and experienced data scientists alike. One feature to make WOLF more accessible is a website version that can be accessed from anywhere and make using WOLF much more intuitive. To keep WOLF aligned with the most recent trends and models, the ability to train a neural network using the TensorFlow framework and Keras library were added. This project also introduced the ability to pickle and save trained models. Designing the option for using the models to make predictions within the WOLF framework on another collection of data is a fundamental side-effect of saving the models. Understanding how the model makes predictions is a beneficial component of machine learning. This project aids in that understanding by calculating and reporting the relative importance of the dataset features for the given model. Incorporating all these additions to WOLF makes it a more functional and user-friendly framework for machine learning tasks.

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.

In data mining, decision rules induced from known examples are used to classify unseen cases. There are various rule induction algorithms, such as LEM1 (Learning from Examples Module version 1), LEM2 (Learning from Examples Module version 2) and MLEM2 (Modified Learning from Examples Module version 2). In the real world, many data sets are imperfect, may be incomplete. The idea of the probabilistic approximation, has been used for many years in variable precision rough set models and similar approaches to uncertainty. The objective of this project is to test whether proper probabilistic approximations are better than concept lower and upper approximations. In this project, experiments were conducted on six incomplete data sets with lost values. We implemented the local probabilistic version of MLEM2 algorithm to induce certain and possible rules from incomplete data sets. A program called Rule Checker was also developed to classify unseen cases with induced rules and measure the classification error rate. Hold-out validation was carried out and the error rate was used as the criterion for comparison.