Signal processing mini-symposium

Roberto López Valcarce, Visa Koivunen, Yonina Eldar
University of Vigo, Vigo, Spain. Aalto University, Helsinki, Finland. Technion, Haifa, Israel.

Facilitator: Prof. dr. ir. Geert Leus, Circuits and Systems group

1. Carving the Multicarrier Spectrum

Roberto López Valcarce University of Vigo, Vigo, Spain

Multicarrier modulation has become the format of choice in modern high-speed wireless and wireline systems, due to its many well-known qualities. Nevertheless, the large IFFT sidelobes result in substantial leakage across subcarriers with the ensuing adjacent channel interference. The usual approach of deactivating a number of guard subcarriers at the edges of the signal spectrum is very inefficient in terms of data rate. In order for OFDM to be adopted by future high-performance systems, e.g., 5G, a number of enhancements will become necessary to overcome this and other drawbacks. The leakage problem is also of concern in wideband OFDM-based cognitive systems, in which deep notches must be sculpted in the spectrum to avoid interfering to narrowband licensed users. Judiciously modulating (a few) cancellation subcarriers in order to reduce leakage is an appealing alternative, which originally incurred in high online implementation complexity. We will review this Active Interference Cancellation approach and present efficient designs recently developed in our group, with extensions to linear symbol precoding.

Roberto Lopez-Valcarce received the Ph.D. degree in electrical engineering from the University of Iowa, Iowa City, in 2000. He was a Postdoctoral Fellow of the Spanish Ministry of Science and Technology from 2001 to 2006, with the Signal Theory and Communications Department, University of Vigo, Spain, where he currently is an Associate Professor. His main research interests lie in the areas of adaptive signal processing, digital communications, and sensor networks, having coauthored over 50 papers in leading international journals. He holds several patents in collaboration with industry. Roberto was the recipient of a 2005 Best Paper Award of the IEEE Signal Processing Society. He served as an Associate Editor of the IEEE TRANSACTIONS ON SIGNAL PROCESSING from 2008 to 2011, and as a member of the IEEE Signal Processing for Communications and Networking Technical Committee from 2011 to 2013.

2. Optimal Array Signal Processing in the Face of Non-Idealities

Visa Koivunen Aalto University, Helsinki, Finland

In this talk we describe techniques that facilitate applying high performance array processing algorithms using real-world sensor arrays with nonidealities. The theoretical background is in wavefield modeling that allows one to develop computationally-efficient and asymptotically-optimal array processing methods regardless of the array geometry (conformal arrays). Wavefield modeling also facilitates incorporating array nonidealities into array processing methods and performance bounds. Parameter estimation and beamforming in the azimuth-elevation-polarimetric domain will be addressed. We acquire a realistic array steering vector model by taking into account array nonidealities such as mutual coupling, mounting platform reflections, cross-polarization effects, errors in element positions as well as individual directional beampatterns. This facilitates achieving optimal or close-to-optimal performance and retaining high-resolution capability despite the nonidealities. Moreover, tighter performance bounds may be established for parameter estimation. We describe how the various approaches can be applied in practice in the context of high-resolution direction finding as well as beamforming so that problems related to beamsteering, SOI and interference cancellation are mitigated. This is joint work with Dr. Mario Costa.

Visa Koivunen received his Ph.D in electrical engineering from the University of Oulu, Finland. He was visiting researcher at the Univ of Pennsylvania in 1992-1995. Since 1999 he has been full professor of signal processing at Aalto University (Helsinki Univ of Technology), Finland where he currently holds the Academy Professor position. He has been an adjunct professor at Penn and visiting fellow at Nokia Research Center. He has spent multiple research visits and sabbaticals terms at Princeton University. His research interests include statistical, communication and array signal processing. Dr. Koivunen is an IEEE Fellow and 2015 IEEE SPS Distinguished Lecturer. He received the 2007 IEEE Signal Processing Society best paper award.

3. Sub-Nyquist Sampling: Bounds, Algorithms and Hardware

Yonina Eldar Technion, Haifa, Israel

The famous Shannon-Nyquist theorem has become a landmark in the development of digital signal processing. However, in many modern applications, the signal bandwidths have increased tremendously, while the acquisition capabilities have not scaled sufficiently fast. Consequently, conversion to digital has become a serious bottleneck. Furthermore, the resulting high rate digital data requires storage, communication and processing at very high rates which is computationally expensive and requires large amounts of power. In this talk, we present a framework for sampling and processing a wide class of wideband analog signals at rates far below Nyquist. We refer to this methodology as sampling:combination of compression and sampling, performed simultaneously.

Using the Cramer-Rao bound we develop a generic low-rate sampling architecture that is optimal in a mean-squared error sense, and can be applied to a wide variety of wideband inputs. The resulting system can be readily implemented in hardware, and is easily modified to incorporate correlations between signals. We consider application of these ideas to a variety of problems including low rate ultrasound imaging, radar detection, ultra wideband communication, and cognitive radio, and show several demos of real-time sub-Nyquist prototypes.

Yonina Eldar received the B.Sc. degree in physics and the B.Sc. degree in electrical engineering both from Tel-Aviv University (TAU), Tel-Aviv, Israel, in 1995 and 1996, respectively, and the Ph.D. degree in electrical engineering and computer science from the Massachusetts Institute of Technology (MIT), Cambridge, in 2002. She is currently a Professor in the Department of Electrical Engineering at the Technion—Israel Institute of Technology, Haifa. She is also a Research Affiliate with the Research Laboratory of Electronics at MIT and a Visiting Professor at Stanford University, Stanford. Dr. Eldar was a Horev Fellow of the Leaders in Science and Technology program at the Technion and an Alon Fellow. In 2004, she was awarded the Wolf Foundation Krill Prize for Excellence in Scientific Research, in 2005 the Andre and Bella Meyer lectureship, in 2007 the Henry Taub Prize for Excellence in Research, in 2008 the Hershel Rich Innovation Award, the Award for Women with Distinguished Contributions, the Muriel & David Jacknow Award for Excellence in Teaching, and the Technion Outstanding Lecture Award, in 2009 the Technion's Award for Excellence in Teaching, in 2010 the Michael Bruno Memorial Award from the Rothschild Foundation, and in 2011 the Weizmann Prize for Exact Sciences. In 2012 she was elected to the Young Israel Academy of Science and to the Israel Committee for Higher Education, and elected an IEEE Fellow. In 2013 she received the Technion's Award for Excellence in Teaching, the Hershel Rich Innovation Award, and the IEEE Signal Processing Technical Achievement Award. In 2014 she was awarded the IEEE/AESS Fred Nathanson Memorial Radar Award. She received several best paper awards together with her research students and colleagues. She is the Editor in Chief of Foundations and Trends in Signal Processing. In the past, she was a Signal Processing Society Distinguished Lecturer, a member of several Signal Processing technical committees, and an associate editor for several IEEE and SIAM journals.

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Overview of Signal Processing Seminar