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2014 Weekly Seminar Series


Recaps of previous seminars are posted below.


Spectrum Sharing Between Radars and Communication Systems

Speakers: Mo Ghorbanzadeh and Awais Khawar
(Hume Center for National Security and Technology)

Advisor: Dr. Charles Clancy
Date: November 21, 2014
Time: 2:30pm-30:30pm
Location: SEB-135

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Abstract: Spectrum sharing between radars and communication systems is an emerging area of research due to the interest of federal regulatory agencies such as the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA) in the U.S. Recently, the FCC has proposed the use of the 3550-3650 MHz band (primarily a federal radar band) for commercial broadband. Interference analysis and mitigation is the biggest concern that needs to be addressed in order to realize spectrum sharing between radars and communication systems.

In the first half of the talk, the focus will be on radar interference analysis at Long Term Evolution (LTE) systems. We study the interference from a rotating ship borne radar system, spectrally and spatially coexistent with a LTE cellular communications network, in the 3.5 GHz band. We evaluate the throughput of the LTE system in the uplink direction for various distances between the radar and the cellular system using NTIA- and LTE-compliant simulation parameters. Our simulation results indicate that the LTE system operates well inside the exclusion zones set by NTIA and such large geographic separations are not realistic. We also study the feasibility of sharing the spectrum between sectorized cellular systems and stationary radars interfering with certain sectors of the communications infrastructure. We explore allocating optimal resources to mobile devices in order to provide with the quality of service for all running applications whilst growing the communications network spectrally coexistent with the radar systems.

In the second half of the talk we focus on radar interference mitigation approaches. A new projection based scheme is proposed where MIMO radar projects its waveform onto null space of interference channel present between radar and communication systems. This approach mitigates radar interference to communication systems but results in some degradation in radar performance. This degradation in radar performance is studied using metrics like Cramer Rao bound and maximum likelihood estimate of target’s angle of arrival, transmit/receive beampattern, and target detection probability. In addition, BPSK and QPSK waveforms for MIMO radars are designed with spectrum sharing constraints for spectral environments where radars and communication systems are sharing spectrum.

Bios: Mo Ghorbanzadeh is with the Hume Center for National Security and Technology, where he is a PhD student working on QoS-minded resource allocation in cellular networks within congested and contested environments. He has a bachelor’s degree from Azad University of Arak, and a Master’s degree from the Southern Illinois University in Edwardsville.

Awais Khawar received his BS in telecommunication engineering from the National University of Computer and Emerging Sciences, Pakistan (2007) and MS in electrical engineering from the University of Maryland at College Park (2010). At the University of Maryland his research focused on the security aspect of spectrum sensing in cognitive radio networks. His work on spectrum sensing security was featured in the IEEE COMSOC Best Readings in Cognitive Radio. Currently, he is working towards the Ph.D. degree in electrical engineering at Virginia Tech where he is affiliated with the Hume Center for National Security and Technology. His research interests are in the areas of spectrum sharing, security, optimization, and resource allocation for coexisting wireless communication and radar systems.


November 14, 2014

Wireless Fronthauling: An Alternative Architecture for Heterogeneous Cellular Networks

Speaker: (Wireless@VT)
Email: eyoseph at

Adviser: Dr. Jeffrey Reed
Date: November 14, 2014
Time: 2:30pm-30:30pm
Location: SEB-135


Fronthauling is a relatively new type of cellular network architecture. In a fronthauled cell, the RF radio-heads of a base-station are detached from the baseband processing unit, and are scattered across the coverage area of the cell. "Fronthaul" is the link between the remote radio-head and the centralized baseband processor.

Fronthauled cells, similar to backhauled heterogeneous cells, use multiple access points within a macro-cell. However, fronthauled cells do not suffer from the lack of coordination between the access points and the resulting rise of interference temperature. This is because the access points of a fronthauled cell can be operated in a coordinated MIMO fashion such that interference becomes a friend instead of being an enemy. In this presentation, we will discuss some of the advantages that "fronthauling" has compared to "backhauling". Furthermore, we will be discussing about the role of massive MIMO and millimeter-wave technologies in wireless fronthauls. At the end, we will talk about existing research challenges related to wireless fronthauling, massive MIMO and millimeter-wave technologies.

Bio: Eyosias Yoseph received B.Sc. degree in electrical engineering from Bahir Dar University, Ethiopia, in 2007, and M.Sc. degree in electrical engineering from Florida Institute of Technology, in 2009. In 2010, he came to the Bradley Department of Electrical and Computer Engineering at Virginia Tech to pursue his Ph.D. He interned at Analog Devices during summer 2014 where he participated in R&D works related to wirelessly-fronthauled commercial base-stations.


November 7, 2014

Chipless RFID System: Tag Design and Detection Technique

Speaker: Reza Rezaiesarlak (Virginia Tech)
Email: surlak at

Advisor: Majid Manteghi
Date: November 7, 2014
Time: 2:30pm-3:30pm
Location: SEB-125

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Abstract: In this seminar, an introduction to chipless RFID systems and their practical applications are presented. The components of the system are introduced and their effects on the received signal are studied in detail in the presence of the background objects and noise in the reader area. After mathematical modelling of the scenario, a systematic anti-collision algorithm is presented by which multiple multi-bit chipless RFID tags in the reader area are detected, identified and localized in a space-time-frequency diagram. The effects of the various parameters on the resolution in time, frequency and rang are presented in this seminar.

Bio: Reza Rezaiesarlak was born in Iran. He received the B.S. degree from Shahid Beheshti University, Tehran, Iran, in 2004 and the M.S. degree from Iran University of Science and Technology (IUST), Tehran, Iran, in 2007, both in electrical engineering. He is currently working toward the Ph.D. degree at the Virginia Polytechnic Institute and State University (Virginia Tech). He was a research assistant in the Microwave group at Shahid Beheshti University from 2008 to 2012, where he worked on various active and passive microwave circuits and antennas. In spring 2012, he jointed Virginia Tech Antenna Group (VTAG). His research area includes time domain electromagnetics, Chipless RFID and Space-Time-Frequency target identification techniques.

October 31, 2014

A Statistical Spectrum Sensing Approach for Asynchronously Received Digital Amplitude-Phase Modulated Signals

Speaker: William Christopher Headley (Wireless@VT and the Hume Center for National Security and Technology)
Email: cheadley at

Advisor: Prof. Jeffrey Reed
Date: October 31, 2014
Time: 2:30pm-3:30pm
Location: SEB 135

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Abstract: The task of spectrum sensing, defined here to consist of signal detection, signal parameter estimation, and signal classification, is a critically important task in a wide variety of commercial and military wireless communication applications. In this talk, first a generalized overview of the concept of spectrum sensing will be discussed, with an emphasis on statistical signal processing techniques. Next, we will introduce the concept of the statistical measurement of kurtosis and how it can be used to classify the modulation scheme of digital amplitude-phase modulated signals (PAM, PSK, QAM, etc.). Finally, the impact of unknown channel and timing effects on the kurtosis will be presented, and an estimation approach using statistical moments to estimate these unknown parameters will be presented.

Bio: William "Chris" Headley received his B.S. degree in electrical engineering from Virginia Tech in the fall of 2006. In the spring of 2009, he graduated with his M.S. degree in electrical engineering as a Bradley Fellow under Dr. Claudio da Silva. In the summer of 2009, he interned with MIT Lincoln Laboratories. His research interests include spectrum sensing, statistical signal processing, and machine learning.

October 24, 2014

Learning Using Delayed Information - A Case of Jamming

Speaker: SaiDhiraj Amuru (Wireless@VT)
Email: adhiraj at

Advisor: Prof. R. Michael Buehrer
Date: October 24, 2014
Time: 2:30pm-3:30pm
Location: SEB 125

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Abstract: Recent advances in cognitive radios create the potential for dynamically changing conditions in practical wireless environments. Under such scenarios, more often that not, it is not possible to have instantaneous information about the environment. For instance, when a jammer disrupts a data packet, it is not aware whether the jamming was successful or not until an acknowledgement packet is sent by the receiver. In this talk, we will first discuss the concept of reinforcement learning and then explore how delayed knowledge can be exploited in a reinforcement learning framework. We will then use these concepts to address a MAC layer jamming attack against an 802.11 network. If time permits, we will briefly talk about some recent work on physical layer jamming attacks that use the concept of multi-armed bandits.

Bio: SaiDhiraj Amuru received the B.Tech. degree in electrical engineering from the Indian Institute of Technology, Madras, in 2009. In between 2009 and 2011, he worked with Qualcomm, India as a modem engineer. Since 2011, he is pursuing his Ph.D. in the Bradley Department of Electrical and Computer Engineering, Virginia Tech. He visited the Networks, Economics, Communication Systems, Informatics and Multimedia Research lab at UCLA during Summer 2014. His research interests include cognitive radio, statistical signal processing and machine learning.

October 17, 2014

On the Physical Layer Security of Wireless Backscatter Systems

Speaker: Prof. Walid Saad (Wireless@VT)

Date: October 17, 2014
Time: 2:30pm-3:30pm
Location: SEB 135

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Abstract: Backscatter wireless communication lies at the heart of many practical low-cost, low-power, distributed systems such as the Internet of Things (IoT). The inherent cost restrictions coupled with the modest computational and storage capabilities of passive sensors, such as RFID tags, render the adoption of classical security techniques challenging; which motivates the introduction of physical layer security approaches. Despite their promising potential, little has been done to study the prospective benefits of such physical layer techniques in backscatter systems. In this talk, we study and analyze the physical layer security of wireless backscatter systems. First, we study the secrecy rate of a basic single-reader, single-tag model. Then, we investigate how the unique features of the backscatter channel are exploited to maximize this secrecy rate. In particular, we show how one can achieve perfect secrecy by allowing backscatter system’s reader to inject a noise-like signal, added to the conventional continuous wave signal, in order to interfere with eavesdropper’s reception of the tag’s information signal. The benefits of this approach are studied for a variety of scenarios while assessing the impact of key factors, such as antenna gains and location of the eavesdropper, on the overall secrecy of the backscatter transmission. We conclude this talk with a discussion on the multi-reader, multi-tag case and a future outlook on this emerging area.

Bio: Walid Saad (S'07, M'10) received his B.E. degree in Computer and Communications Engineering from the Lebanese University, in 2004, his M.E. in Computer and Communications Engineering from the American University of Beirut (AUB) in 2007, and his Ph.D degree from the University of Oslo in 2010. Currently, he is an Assistant Professor at the Bradley Department of Electrical and Computer Engineering at Virginia Tech, where he leads the Network Science, Wireless, and Security (NetSciWiS) laboratory, within the Wireless@VT research group. Prior to joining VT, he was a faculty at the Electrical and Computer Engineering Department at the University of Miami and he has held several research positions at institutions such as Princeton University and the University of Illinois at Urbana-Champaign. His research interests include wireless and small cell networks, game theory, cybersecurity, smart grid, network science, cognitive radio, and self-organizing networks. He has published one textbook and over 100 papers in these areas. Dr. Saad is the recipient of the NSF CAREER award in 2013. He was the author/co-author of three conference best paper awards at WiOpt in 2009, ICIMP in 2010, and IEEE WCNC in 2012. He currently serves as an editor for the IEEE Transactions on Communications and the IEEE Communication Tutorials & Surveys.