On Spectrum Sharing Between Radar and Communication Systems

Athina P. Petropulu is Distinguished Professor at the Electrical and Computer Engineering (ECE) Department at Rutgers, having served as chair of the department during 2010-2016.  Prior to joining Rutgers she was a Professor of ECE at Drexel University (1992-2010). She held Visiting Scholar appointments at SUPELEC, Universite’ Paris Sud, Princeton University and University of Southern California. Dr. Petropulu's research interests span the area of statistical signal processing, wireless communications, signal processing in networking, physical layer security, and radar signal processing. Her research has been funded by various government industry sponsors including the National Science Foundation (NSF), the Office of Naval research, the US Army, the National Institute of Health, the Whitaker Foundation, Lockheed Martin and Raytheon. Dr. Petropulu is Fellow of IEEE and AAAS and recipient of the 1995 Presidential Faculty Fellow Award given by NSF and the White House. She is President-Elect for the IEEE Signal Processing Society for 2020-2021, and in the past, has served as Editor-in-Chief of the IEEE Transactions on Signal Processing (2009-2011) and IEEE Signal Processing Society Vice President-Conferences (2006-2008). She was the General Chair of the 2005 International Conference on Acoustics Speech and Signal Processing (ICASSP-05), Philadelphia PA, and is General Co-Chair of the 2018 IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC). She is recipient of the 2005 IEEE Signal Processing Magazine Best Paper Award, and the 2012 IEEE Signal Processing Society Meritorious Service Award. She was Distinguished Lecturer for the Signal Processing Society for 2017-2018, and is currently Distinguished Lecturer for the IEEE Aerospace & Electronics Systems Society.

Spectrum congestion in commercial wireless communications is a growing problem as high-data-rate applications become prevalent. On the other hand, frequency bands earmarked for exclusive use by radar are underutilized.  Spectrum sharing is a new line of work that aims to enable radar and communication systems to share the same frequency bands efficiently. There are two lines of research on spectrum sharing. The first one considers radar and communication systems on separate platforms, and addresses the design of signaling schemes that minimize the interference one system exerts to the other. The second line of research addresses the design of radars that communicate information at the same time they are performing their sensing functionality. Such systems, referred to as dual function radar communications (DFRC) systems, are implemented on the same platform.

In the first part of the talk we present our recent work on cooperative spectrum sharing framework, where the signaling schemes of the radar and communication systems are jointly designed to me a quality of service (QoS) metric for the radar, while meeting power and rate constraints for the communication system. Compared to non-cooperative approaches in the literature, our approach has the potential to improve the spectrum utilization because it introduces more degrees of freedom. We focus on a special case of MIMO radar, namely the matrix completion based MIMO radar (MIMO-MC), which perform sub-Nyquist rate sampling of the received signals and then recovers the missing samples via matrix completion. In addition to reducing the amount of data required, MIMO-MC radar offer a significant advantage for spectrum sharing. The advantage stems from the way the sub-sampling scheme at the radar receivers modulates the interference channel from the communication system transmitters, rendering it symbol dependent and reducing its row space. This makes it easier for the communication system to design its waveforms in an adaptive fashion so that it minimizes the interference to the radar subject to meeting rate and power constraints. In the second part of the talk, we present our current work on another form of spectrum sharing along the lines of dual functional radar communication systems (DFRC). In DFRC systems communication information is conveyed by the radar probing signals, thus there is no interference between radar and communication functionalities. We present a novel DFRC system, consisting of a sparse MIMO radar whose active antennas transmit orthogonal frequency division multiplexing (OFDM) waveforms. The system communicates information via the transmitted data symbols and also via the pattern of active transmit antennas in a generalized spatial modulation (GSM) fashion. Unlike existing literature, the active antennas use most OFDM subcarriers in a shared fashion and only one in an exclusive fashion (private subcarrier). The shared subcarriers among antennas enable high communication rate. The private subcarriers facilitate the construction of a virtual array for higher angular resolution, and also the recovery of the active transmit antenna indices. The OFDM waveforms allow both systems to easily mitigate the effect of frequency selective fading.