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2023 Seminars


Research on ORAN at Hanyang University with an Emphasis on Front-Haul

Prof. Seungwon Choi - 09/22/2023

Abstract: The crucial part of this presentation is an introduction to a hardware implementation of oRU, which composes the ORAN system with oDU and oCU. Recently, we developed an oRU for two different network operators, each with their oDU provided by many different vendors. Before we show the details of our oRU, we will summarize the basic concept of ORAN by briefly observing the evolution of the RAN system and the basic structure of eCPRI. Then, we will expose the details of our POC system consisting of oDU, oRU, and UE emulators. Finally, the oRU implemented for the 2 customers will be shown.

Bio: Seungwon Choi got his Ph.D. in electrical engineering from Syracuse University in 1988. Seungwon has been a professor at Hanyang University, Seoul, Korea, since 1992 and is particularly interested in wireless communications, smart antenna and MIMO, software-defined radio, 5G-related technologies like Filter Bank Multi Carrier and open RAN, etc. He has published around 85 SCI-registered journal papers. He also has held more than 100 patents registered internationally. Recently, Prof. Choi's research has focused on the Radio Unit of the Open RAN system for commercial applications so that the Radio Unit can be connected to various Distributed Units provided by many different vendors.

Near-optimal packet scheduling with end-to-end deadline constraints in multihop networks

Prof. Javad Ghaderi - 02/24/2023

Abstract: Scheduling packets with end-to-end deadline constraints in multi-hop networks is an important but notoriously difficult problem. Recently, there has been progress on this problem in the worst-case traffic setting with the objective of maximizing the weighted sum of packets delivered within their deadlines. The proposed algorithms were shown to achieve Ω(1/log(𝐿)) approximation if the minimum link capacity in the network is Cmin= Ω(log(𝐿)), where 𝐿 is the maximum length of any route that a packet in the network follows (which is bounded by the packet’s deadline). However, such guarantees can be quite pessimistic due to the worst-case traffic assumption, and the derived algorithms do not necessarily perform well in practical settings. In this work, we show that it is possible to design algorithms that attain a constant approximation by relaxing the worst-case traffic assumption. In fact, in a stochastic traffic setting, with i.i.d. packet arrivals, it is possible to design near-optimal, (1 − 𝜖)-approximation algorithms if Cmin=Ω(log(L/ϵ)/ϵ^2). To the best of our knowledge, this is the first result that shows this problem can be solved near optimally under nontrivial assumptions on traffic and links' capacity. We further generalize our assumptions and provide extended simulations using real network traces that show that our algorithms indeed outperform the worst-case-based algorithms in practical settings.

Bio: Javad Ghaderi is an Associate Professor of Electrical Engineering at Columbia University. His research interests include algorithms, optimization, and stochastic processes with application to wireless networks and data centers. He received his B.Sc. from the University of Tehran, Iran, in 2006, M.Sc. from the University of Waterloo, Canada, in 2008, and Ph.D. from the University of Illinois at Urbana-Champaign in 2013. He spent a one-year Simons Postdoctoral Fellowship at the University of Texas at Austin before joining Columbia. He is a recipient of several awards, including Best Student Paper Finalist Award at ACC 2013, Best Paper Award at ACM CoNEXT 2016, NSF CAREER Award in 2017, Best Student Paper Award at IFIP Performance 2020, and Best Paper Award at IEEE INFOCOM 2020.

Leveraging RIS-Enabled Smart Signal Propagation for Solving Minimal Localization Problems

Prof. Henk Wymeersch - 02/17/2023

Abstract: Reconfigurable intelligent surfaces (RISs) have tremendous potential for communication, localization, and sensing. While communication benefits are now well-understood, the breakthrough nature of the technology may well lie in its capability to provide location estimates when conventional approaches fail, (e.g., due to insufficient available infrastructure). Hence, RISs are a green enabler for providing positioning and bi-static sensing coverage. We present an overview of localization scenarios with various numbers of RISs, single- or multi-antenna base stations, narrowband or wideband transmissions, and near- and far-field operation. Then we dive deeper into 2 examples: (i) localization with 1 base station and 1 RIS, and (ii) localization without any RIS.

Bio: Henk Wymeersch obtained the Ph.D. degree in Electrical Engineering/Applied Sciences in 2005 from Ghent University, Belgium. He is currently a Professor of Communication Systems with the Department of Electrical Engineering at Chalmers University of Technology, Sweden. He is also a Distinguished Research Associate with Eindhoven University of Technology. Prior to joining Chalmers, he was a postdoctoral researcher from 2005 until 2009 with the Laboratory for Information and Decision Systems at the Massachusetts Institute of Technology. Prof. Wymeersch served as Associate Editor for IEEE Communication Letters (2009-2013), IEEE Transactions on Wireless Communications (since 2013), and IEEE Transactions on Communications (2016-2018) and is currently Senior Member of the IEEE Signal Processing Magazine Editorial Board. During 2019-2021, he was an IEEE Distinguished Lecturer with the Vehicular Technology Society. His current research interests include the convergence of communication and sensing, in a 5G and Beyond 5G context.

Vector OFDM Systems

Prof. Xiang-Gen Xia - 10/2/2023

Abstract: Over the past decades, dealing with intersymbol interference (ISI) has been the main subject in physical layer communications systems, such as in wireline computer modem designs and wireless cellular and WiFi systems. The increasing of a channel bandwidth causes the increasing of the ISI channel length. In this talk, I will talk about single antenna vector OFDM (VOFDM) systems first appeared in ICC 2000. VOFDM is a bridge of OFDM and single carrier frequency domain equalizer (SC-FDE) that are the downlink and uplink, respectively, in LTE. VOFDM provides the flexibility of choosing a level of ISI for any fixed channel length (or channel bandwidth) and is scalable to a channel bandwidth. I will talk about linear receivers and their properties for VOFDM systems. Interestingly, the transmission of the recent OTFS is the same as that of VOFDM despite the channel is stationary or not, and OTFS can be thought of as an application of VOFDM in time-varying channels.

Bio: Xiang-Gen Xia received his Ph.D. in electrical engineering from University of Southern California in 1992, and is currently the Charles Black Evans Professor, Department of Electrical and Computer Engineering, University of Delaware, Newark, Delaware, USA. Dr. Xia was the Kumar’s Chair Professor Group Professor (guest) in Wireless Communications, Tsinghua University, during 2009-2011, the Chang Jiang Chair Professor (visiting), Xidian University, during 2010-2012, and the WCU Chair Professor (visiting), Chonbuk National University, during 2009-2013. He received the National Science Foundation (NSF) Faculty Early Career Development (CAREER) Program Award in 1997, the Office of Naval Research (ONR) Young Investigator Award in 1998, the Outstanding Overseas Young Investigator Award from the National Nature Science Foundation of China in 2001, and the Information Theory Outstanding Overseas Chinese Scientist Award from the Chinese Information Theory Society of Chinese Institute of Electronics in 2019. Dr. Xia was the General Co-Chair of ICASSP 2005 in Philadelphia. He is a Fellow of IEEE. His current research interests include space-time coding, MIMO and OFDM systems, digital signal processing, and SAR and ISAR imaging. He is the author of the book Modulated Coding for Intersymbol Interference Channels (New York, Marcel Dekker, 2000), and a co-author of the book Array Beamforming Enabled Wireless Communications (CRC Press, 2023).

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For information on the Wireless @ Virginia Tech Seminar Series, please contact Dr. Harpreet Dhillon.