Distinguished Symposium Talks

Yang-Seok Choi

Intel Corporation, USA

Full-Duplex MIMO: Algorithms and Proof-of-Concept Performance

Abstract
In this talk we present enabling technologies for full-duplex (FD) MIMO. For self-interference cancellation, we have introduced adaptive echo cancellation concept which is based on adaptive filter theory. First, open loop technique is compared to closed loop technique. Closed loop technique such as adaptive echo cancellation continuously updates the system parameters even without requiring special training signal and synchronizations such as OFDM boundary, resulting fast and continuous tracking even during random data transmission. In addition, even in the presence of stronger desired received signal than self-interference, it provides stable tracking and continuous self-interference cancellation. Secondly, in MIMO, the SIC complexity increases exponentially. We propose simpler architecture for RF cancellation which requires only one extra downconverter regardless of the number of taps without performance loss. For digital cancellation, bilinear architecture is proposed. RF components can be modeled by a linear combination of kernels. In non-bilinear, an adaptive filter is applied at each kernel. Hence, parallel adaptive filters are required. However, in bilinear architecture, two adaptations are cascaded: one for non-linear RF component modeling and the other for echo channel. Although this architecture significantly reduces the complexity, it has stability issues and creates too large dynamics of intermediate variables which prevent from efficient HW implementation. We have solved these short comings and will show demo videos of 2x2 MIMO FD system exhibiting that residual self-interference is below noise.

Biography
Yang-Seok Choi received the B.S. degree from Korea University, Seoul, South Korea, in 1990, the M.S.E.E. degree from the Korea Advanced Institute of Science and Technology, Taejon, South Korea, in 1992, and the Ph.D. degree from Polytechnic University, Brooklyn, NY, in 2000, all in Electrical Engineering. From 1992 to 1996, Dr. Choi was with Samsung Electronics, Co., Ltd., Suwon, Korea, where he developed 32-QAM modem for HDTV and QPSK ASIC for DBS. In 2000, Dr. Choi joined National Semiconductor, East Brunswick, NJ, where he was involved in the development of W-CDMA. During 2001–2002, Yang-seok was a Senior Technical Staff Member at AT&T Labs-Research, Middletown, NJ where he researched MIMO systems, OFDM systems and information theory. From 2002 to 2004 Dr. Choi was with ViVATO, Inc., Spokane, WA, working on MIMO OFDM systems, smart antenna systems, and antenna/beam selection techniques. In 2004, Dr. Yang-seok Choi joined Intel Corporation, Hillsboro, OR where his research focuses on next generation wireless communications systems, with a focus on full-duplex communication and interference cancellation. His additional research interests include MIMO, OFDM, MC-CDMA, smart antenna, blind identification/equalizer, carrier/timing recovery, space-time coding, cross-layer design and capacity of time-varying multipath channel. Dr. Choi holds several U.S. patents.

Harish Krishnaswamy

Columbia University, USA

Integrated Full-Duplex Radios: From Fundamental Physics and Integrated Circuits to Complex Systems and Networking

Abstract
Full duplex wireless has attracted significant research attention in the last five years due to its ability to potentially double network capacity at the physical layer, while offering numerous benefits at the higher layers. The basic challenge in full duplex is the tremendous transmitter self-interference at the receiver, which can be one trillion times more powerful than the desired signal and must be dealt with in all domains. There has been significant work on prototype full-duplex radios using off-the-shelf components and showing the feasibility of self-interference cancellation, and on network-layer implications of full-duplex operation.

However, the implementation of integrated full-duplex radios in commercial CMOS processes, necessary for widespread deployment, particularly in small-form-factor devices, is fraught with several fundamental challenges. Integrated CMOS electronics typically exhibit much lower dynamic range than off-the-shelf components, leading to several challenges related to full-duplex operation, including noise and distortion added by the transceiver or by the cancellers, and the bandwidth associated with the cancellation. Furthermore, shared antenna interfaces for full-duplex, such as circulators, are either impossible to integrate on chip due to a reliance on magnetic (ferrite) materials, or exhibit prohibitive loss and/or linearity penalties.

This talk will introduce several generations of integrated full-duplex transceivers developed at Columbia University that address these problems. I will discuss RF self-interference cancellation concepts that add minimal noise and distortion penalty, and are able to achieve wideband cancellation across antenna interfaces with significant frequency selectivity. At the electromagnetic (i.e. antenna) interface, I will talk about our recent work on breaking Lorentz Reciprocity using time-variance to realize the first integrated magnetic-free non-reciprocal circulator. I will also discuss how polarization can be utilized to achieve robust self-interference suppression by embedding complex signal processing functionalities like wireless channel equalization in the antenna domain. Finally, I will discuss how joint self-interference suppression across the antenna, RF/analog and digital domains can enable achievement of the 90-100dB self-interference suppression levels in integrated full-duplex radios.

Biography
Harish Krishnaswamy received the B.Tech. degree in electrical engineering from the Indian Institute of Technology, Madras, India, in 2001, and the M.S. and Ph.D. degrees in electrical engineering from the University of Southern California (USC), Los Angeles, CA, USA, in 2003 and 2009, respectively. In 2009, he joined the Electrical Engineering Department, Columbia University, New York, NY, USA, where he is currently an Associate Professor. His research interests broadly span integrated devices, circuits, and systems for a variety of RF, mmWave and sub-mmWave applications. Dr. Krishnaswamy serves as a member of the Technical Program Committee (TPC) of several conferences, including the IEEE International Solid-State Circuits Conference (2015/16-present) and IEEE RFIC Symposium (2013-present). He was the recipient of the IEEE International Solid-State Circuits Conference (ISSCC) Lewis Winner Award for Outstanding Paper in 2007, the Best Thesis in Experimental Research Award from the USC Viterbi School of Engineering in 2009, the Defense Advanced Research Projects Agency (DARPA) Young Faculty Award in 2011, a 2014 IBM Faculty Award and the 2015 IEEE RFIC Symposium Best Student Paper Award - 1st Place. He is serving as a Distinguished Lecturer of the IEEE SSCS over 2017-2018.