Department of Computer Science and Electrical Engineering

MS Thesis Defense

On MIMO Channel Modeling and Capacity
Using the Channel Correlation Matrix

Anush Chandrasekaran

1:00pm Wednesday, 18 July 2012, ITE 325b

Communication systems have always been affected by multipath propagation that causes a delay and distortion in receiving the signal, with a different delay for each path. Multiple-Input Multiple-Output (MIMO) communication systems were developed to combat this problem and use multipath propagation to their benefit. A MIMO communication system contains M transmitter antennas and N receiver antennas that are used to improve either the robustness of transmission or the throughput.

We assume an exponential channel correlation matrix R model for the MIMO channel with J = M = N and use it to compute the channel H-matrix, the receiver (RRx) and transmitter (RTx) correlation matrices, and the ergodic MIMO channel capacity (CH). We propose two algorithms to obtain RRx and RTx from R, which have been used to estimate/bound CH. We investigate and compare three ergodic MIMO channel capacity estimation/bound methods for our MIMO channel model in this thesis. The first two existing estimation/bound methods use the Kronecker model and an RRx-based bound, respectively. The third method is a novel method we propose and study to estimate the ergodic MIMO channel capacity using specific eigenvalues of RRx. The behavior of the eigenvalues of R and RRx are analyzed to identify the eigenvalues that can be used in this method. This method achieves less relative-error compared to the RRx-based bound. It is better than the Kronecker model for specific values of J and the correlation parameter r.

Committee: Drs. Joel M. Morris (Chair), E. F. Charles LaBerge, Mohamed Younis and Tinoosh Mohsenin

MS Thesis Defense

Finding associations among SNPs for
prostate cancer using collaborative filtering

Rohit Kugaonkar

9:00am Wed. 18 July 2012, Room ITE 325b

Prostate cancer is the second leading cause of cancer related deaths among men. Because of the slow growing nature of prostate cancer, sometimes surgical treatment is not required for less aggressive cancers. Recent debates over prostate-specific antigen (PSA) screening have drawn new attention to prostate cancer. Due to the complicated nature of prostate cancer, studying the entire genome is essential to find genomic traits. Due to the high cost of studying all Single Nucleotide Polymorphisms (SNPs), it is essential to find tag SNPs which can represent other SNPs. Earlier methods to find tag SNPs using associations between SNPs either use SNP's location information or are based on data of very few SNP markers in each sample. Our study is based on 2300 samples with 550,000 SNPs each. We have not used SNP location information or any predefined standard cut-offs to find tag SNPs. Our approach is based on using collaborative filtering methods to find pair wise associations among SNPs and thus list top-N tag SNPs. We have found 25 tag SNPs which have highest similarities to other SNPs. In addition we found 16 more SNPs which have high correlation with the known high risk SNPs that are associated with prostate cancer. We used some of these newly found SNPs with 5 different classification algorithms and observed some improvement in prediction accuracy over using the original known high risk SNPs. The classifier can be used in a decision to perform further testing in case of a "yes" answer by the classifier.

Committee: Drs. Yelena Yesha (chair), Anupam Joshi, Aryya Gangopadhyay and Micheal Grasso.

Ph.D. Dissertation Defense

Relay Node Placement for
Federating Segmented Wireless Sensor Networks

Fatih Senel

2:00pm Tuesday, 10 July 2012, ITE 325b

Recent years have witnessed a growing interest in the applications of Wireless Sensor Networks (WSNs). Most notable among these applications are those operating in hostile environments space exploration, border protection, combat field reconnaissance, and search and rescue. Due to the harsh surroundings, WSNs may suffer from a large scale damage that causes many nodes to fail simultaneously and the network to get partitioned into multiple disjoint segments and its services become very limited. In such a case, restoring the network connectivity is very important in order to avoid negative effects on the applications. Linking disjoint segments may not be feasible through coordinated repositioning of some set of nodes as the scope of the damage is so wide that cannot be determined. One of the viable solutions for federating damaged WSNs is to deploy additional resources, i.e. relay nodes, to form inter-segment multi-hop paths.

In this dissertation, we tackle technical challenges related to the federation of segmented WSNs. We present a set of effective techniques that for repairing the damaged WSN using the least number of relay nodes (RNs) as well as maintaining some desirable topology features such as robustness against failures, network coverage and balanced traffic load. The correctness and time-complexity of all proposed approaches are analyzed and their performance is validated through extensive simulation experiments.

Committee: Drs. Mohamed Younis (Chair), Charles Nicholas, Samuel Lomonaco, Tim Oates, Kemal Akkaya and Waleed Youssef

MS Thesis Defense

Integrating Domain Knowledge in Supervised Machine Learning
to Assess the Risk of Breast Cancer Using Genomic Data

Aniket Bochare

9:00am Friday 29 June 2012, ITE 325b

Breast cancer is the most common form of cancer in women. Breast cancer comprises 22.9% of the invasive cancers in women and 16% of all the female cancers. Currently, treatment decisions are based primarily on clinical parameters, with little use of genomic data. Our study takes into consideration the data of postmenopausal women of European descent and their single nucleotide polymorphism (SNP) information to assess the risk of developing breast cancer. We used various supervised machine learning and data mining techniques to generate a model for predicting risk of breast cancer using only genomic data.

In this research we propose an approach to select the nine best SNPs using various feature selection algorithms to improve binary classification accuracy and validate our results with the existing literature. The machine learning model generated without the domain knowledge yields poor prediction results. After the addition of the domain knowledge of the 11 SNPs into the original training set we performed classification using the best features obtained by feature selection techniques. The machine learning model generated using both the domain knowledge and the feature selection techniques performed much better compared to the naive approach of classification.

Committee: Drs. Yelena Yesha (chair), Anupam Joshi, Aryya Gangopadhyay and Micheal Grasso

Ph.D. Dissertation Defense

Fabrication and Operation of Integrated Distributed-Bragg-Reflector
Thermally Tunable Quantum Cascade Lasers

Liwei Cheng

10:00am Friday, 22 June 2012
Center for Advanced Studied in Photonics Research Conference Room

Quantum cascade lasers (QCLs) that emit in the mid-infrared (IR) range between 3 and 10 μm of the electromagnetic spectrum play an important role in optical gas sensing and molecular spectroscopic applications because several important environmental molecules such as CO, CO2, CH4, and NH3 are known to exhibit strong absorption lines in this mid-IR range. To differentiate such fine absorption features as narrow as a few angstroms, a single-mode QCL with an extremely narrow spectral linewidth, broadly tunable over the molecular absorption fingerprints and operating at sufficient optical power at room temperature, is highly desirable. We present, in this dissertation, two major studies on mid-IR QCLs, one being an improvement in device performance through a buried-heterostructure (BH) regrowth study, and the other being a realization of single-mode tunable QCLs integrated with distributed-Bragg-reflector (DBR) grating and thermal tuning mechanism.

Efficient heat dissipation in the QCL active region, which is crucial for high optical-power operation, can be effectively achieved using BH waveguides laterally embedded with InP grown by metal-organic chemical vapor disposition. We have experimentally studied the effects of the structural features of mesas, such as mesa orientation, geometry, sidewall-etched profile, and the length of the oxide overhang, on the BH regrowth. We find that the mesa oriented in the [01 1 ] direction with smoothly etched sidewalls produces a satisfactory planar growth profile and uniform lateral growth coverage and that a mesa-height–to–overhang-length ratio between 2.5 and 3.0 is effective in reducing anomalous growth in the vicinity of oxide edges. As a result, high-power QCLs capable of producing multi-hundred milliwatts at room temperature at ~4.6 μm and ~7.9 μm through reproducible BH regrowth results have been demonstrated.

We have also demonstrated single-mode tunable QCLs operating at ~7.9 μm with an internal DBR grating structure and thermal tuning scheme incorporated. A special flip-chip bonding configuration and device assembly utilizing two copper heatsinks—one for the gain section and the other for the DBR grating section—were devised and constructed to achieve separate temperature controls in both sections. A miniature thermoelectric (TE) cooler dedicated to the DBR grating section was implemented to control the DBR grating temperature while the gain section was kept at a different temperature to achieve single-wavelength tuning. Under ±1000 mA bias conditions, a quasi-single-wavelength tuning range of ~7.2 cm-1 was realized across the TE cooler temperature span, combined with an additional temperature contrast of 56 °C between the two heatsinks (gain/DBR = 10/66 °C) owing to the implementation of additional temperature-controlling elements. We have also developed a two-dimensional thermal model to investigate the thermal dynamics in the device, including the temperature distribution and thermal dependency of each section, and the thermal response time, which ultimately dictates the wavelength tuning speed. We find that a 250-μm passive section located between the gain and DBR grating section can significantly improve temperature uniformity in both the sections as it absorbs most temperature gradients. Further, a swift thermal response time of ~7 ms is simulated if the DBR grating section is directly bonded on the miniature TE cooler.

More importantly, we have realized a monolithic photonic integration platform, both thermally and electrically, for mid-IR QCLs. The QCLs fabricated in this dissertation possess two major functionalities. The gain section, an active component, is electrically pumped to provide optical gain and is kept at a temperature different from the DBR grating section, and the DBR grating section, a passive component, provides optical feedback for single-wavelength emission and subsequently tunes the emission wavelength through a local temperature variation. Such thermal and optoelectronic integration opens new perspectives for mid-IR QC technology.

Committee: Drs. Fow-Sen Choa, Anthony Johnson, Li Yan, Ryan Robucci, Terrance Worchesky and Jocob Khurgin

In its second year, the Baltimore Hackathon invites teams or individuals to build a hardware or software project from start to finish. Sporting the slogan "Meet People. Build Stuff. Have Fun.", this year's competition was held in Tide Point from June 8–10.

Among the more than ninety participants was UMBC student Ahmad Abbas, who took home the competition's DIY/Hacker prize for his hardware project. Originally from Egypt, Ahmad is finishing up his Master's degree in Computer Engineering under the supervision of Dr. Mohamed Younis in the ESNet Lab. He hopes to graduate this summer and begin Ph.D. studies at UMBC this Fall.

In the interview below, Ahmad talks about his experience at the Baltimore Hackathon and explains what made it "one of the most exciting experiences of [his] life."

How did you hear about the Baltimore Hackathon?  I heard about the Baltimore Hackathon 2012 after reading a post by Dr.Tim Finin on myUMBC on Wednesday, just two days before the competition, and I decided to join at the same day.

What is the Baltimore Hackathon? The Hackathon is a competition where you work individually or on teams with the purpose of building hardware or software in a single weekend. Participants may submit an existing project as well, but they need to indicate this before entering the competition.

In a few words, explain your winning project. When I registered, I wasn't sure about my project's idea. My idea was to build a digital camera using 1.3 MPixel CMOS camera sensor, 2.4" LCD and SD card. I decided later, during the competition, to build shields, daughter boards, for Arduino kits. These boards can be connected to Arduino kits and used in different projects.

Where did you come up with the idea? I came up with this ides because I am skilled in designing and implementing electronic circuits. Some people need these circuits to build their own projects, but they can't design or implement it. I build these circuits to help them. This idea was not only for the competition. I built my first Arduino shield last semester in Dr.Ryan Robucci's class. It is an FPGA board that can be connected to Arduino kits. This board was one of my boards in the competition, too.

I designed another two boards during the competition. One of them was a WiFi board for Arduino and the second was a Camera board for the Arduino. I built the WiFi, but I couldn't finish the camera board. Also, I built another USB enabled kit using a low-cost micro-controller and a small number of components. Last board was a DIY digital camera,  which was the original idea. I designed the board but I didn't have time to build it.       

Describe the Baltimore Hackathon. Was it stressful? Exciting? Were you intimidated by the other competitors, or did you collaborate and support one another? The Baltimore Hackathon turned out to be one of the most exciting experiences of my life. Although I was highly stressed during the competition, I was inspired by all the creative and hardworking participants.  In order to reduce the stress, participants played different games, where I earned the title of "ping pong master" and a prize to go with the title.    

I had the fortune over the course of the competition to meet Gary Mauler, Founder of Robot Fest and DIY Expo, and Amy Hurst, Assistant Professor of Human-Centered Computing at UMBC. Gary provided me with insights on how to move forward with my passion for building hardware. 

The Hackathon would not have been such an incredible experience if it were not for the organizers and volunteers who made it possible.  I would like to personally thank Jason, Kafu, Paris, and John.

Did you think you would win, or was the award a pleasant surprise? I won the Hacker DIY prize which comes with $500. I expected to win a prize because most of the participants were doing software projects.  

Multi-antenna Spectrum Sensing: From GLRTs to LMPITs

Dr. Javier Via
University of Cantabria, Spain

2:00pm Friday 22 June 2012, ITE 325b

Spectrum Sensing represents one of the critical aspects of the Cognitive Radio paradigm, where spectral monitors need to determine the presence or absence of primary users under very low SNR conditions. In this talk, we briefly revisit the main spectrum sensing techniques, with special emphasis in multi-antenna detectors, and we will see that the heuristic eigenvalue-based approaches can be outperformed by making use of some important results in the hypothesis testing literature. In particular, we will consider two related hypothesis testing problems, and derive the locally (under low SNR) best detectors among those preserving the problem invariances. Interestingly, this challenging task can be accomplished thanks to Wijsman's theorem, which allows us to obtain the optimal test statistic without the explicit knowledge of the maximal invariant distributions.

Javier Vía received his Telecommunication Engineer Degree and his Ph.D. in Electrical Engineering from the University of Cantabria, Spain in 2002 and 2007, respectively. In 2002 he joined the Department of Communications Engineering, University of Cantabria, Spain, where he is currently an Associate Professor. He has spent visiting periods at Stanford University, Hong Kong University of Science and Technology, and more recently at SUNY at Buffalo. Prof. Vía has actively participated in several European and Spanish research projects. His current research interests include hypothesis testing and spectrum sensing, quaternion signal processing, and financial engineering.

Host: Tulay Adali

MS Thesis Defense

An Operational Study of DNSSEC and its Practical
Application in Establishing a Secure PKI Framework

Colin Roby

4:00pm 19 June 2012, ITE 325b

With the recent completion of signing the DNS Root and various TLD (top level domain), DNSSEC is gradually progressing towards an internet-wide adoption. The extension of DNSSEC security measures addresses many of the security flaws plagued the underlying DNS architecture since its inception. Once widely deployed, DNSSEC will pave the way for extending security service to a wide range of applications. This study focuses on the practicability of current iteration of DNSSEC implementation. Through a virtual network configuration which mimics a typical corporate environment, we explore viable options to establish a secure PKI framework based on DNSSEC in spite of its current limitations. In this endeavour, we propose a simple yet effective method to combine a corporate existing LDAP based directory service with DNSSEC to form a PKI key exchange infrastructure – one which is intuitive to administer and easy to scale to any large corporate network. We demonstrate the advantage of such a PKI framework in one area of its application – the common use of email. Using a prototype email client application, we illustrate how such a framework can promote and facilitate a more secure email system in terms of authenticity, integrity and confidentiality.

Committee: Dr. Deepinder Sidhu (Chair), Dr. Chein-I Chang, Dr. Yun Peng

The Second Baltimore Hackathon will be held this weekend, starting at 6:00pm Friday June 8 and ending at 6:00pm Sunday. At a hackathon people get together to build a hardware or software project from idea to prototype, in this case in one weekend. You can do it individually or as a team. You can come as part of a team or find one when you get there. It’s a great way to meet people and have fun.

The hackathon will take place at Advertising.com‘s offices in Tide Point (1020 Hull Street, 1st Floor Ivory Building, Baltimore, MD 21230).

You can register online (tickets are limited) for just $10, which includes a t-shirt and food for the weekend. Significant prizes will be awarded in six different categories: technical complexity, smart design, civic service, aesthetics, crowd favorite, and hacker/DIY.

See the Baltimore Hackathon site for more information.

Congratulations to Computer Science Ph.D. student Yasaman Haghpanah, who will be receiving one of three prestigious Dissertation Fellowships from UMBC’s Graduate School to help complete her Ph.D. dissertation this summer.

Originally from Iran, Yasaman began her Ph.D. studies at UMBC in Spring 2009. Her dissertation, entitled “A novel trust and reputation mechanism through behavioral modeling of reviewers,” focuses on trust and reputation modeling for online markets.

“My research interests lie in the broad area of trust and reputation modeling and their effect on various domains such as online markets, supply chain management, auctions, social networks, smart grids, and e-commerce applications,” explains Yasaman. She credits the success of online auction site eBay to its reputation system: “Feedback Forum.” “I have extensively modeled trust and reputation through behavioral modeling of the reviewers using formal probabilistic modeling. My model is general and can be applied to several domains.”

Planning to defend her dissertation in August 2012, Yasaman credits the fellowship with helping her to wrap up her research over the summer. Once she graduates, she will be looking for postdoc positions or work in a research lab. She aspires to one day become a professor.