Abstract:

Massive MIMO, proposed by Marzetta, is the regime of multiuser MIMO where the number of base station antennas is much larger than the number of spatially multiplexed data streams. In this regime, using Time-Division Duplexing (TDD) and channel reciprocity, it is possible to saturate the channel available multiplexing gain and achieve a number of additional benefit provided by the large number of antennas. While the initial results and most of the analysis developed for massive MIMO consider i.i.d. channel vectors, in this talk we consider antenna correlation motivated by a specific propagation model where each user is seen by the base station under a small angular spread. We show that antenna correlation can be leveraged as an additional source of ``diversity'', in order to achieve further significant advantages in complexity and performance. In particular, we show that this type of channel correlation with structure is very relevant in the case of mmWaves, and yields naturally to hybrid analog-digital beamforming structures that provide very significant hardware and  power savings with respect to the standard scheme based on digital-only beamforming, implemented in the baseband processing unit. We conclude by pointing out some interesting connections with compressed sensing for efficient channel estimation, and some results on large-scale antenna calibration in order to achieve uplink-downlink reciprocity with TDD.

Biography of the speaker:

Giuseppe Caire (S '92 -- M '94 -- SM '03 -- F '05) was born in Torino, Italy, in 1965. He received the B.Sc. in Electrical Engineering from


Politecnico di Torino (Italy), in 1990, the M.Sc. in Electrical Engineering from Princeton University in 1992 and the Ph.D. from Politecnico


di Torino in 1994. He has been a post-doctoral research fellow with the European Space Agency (ESTEC, Noordwijk, The Netherlands) in 1994-1995,


Assistant Professor in Telecommunications at the Politecnico di Torino, Associate Professor at the University of Parma, Italy, Professor with


the Department of Mobile Communications at the Eurecom Institute, Sophia-Antipolis, France, and he is currently a professor of Electrical


Engineering with the Viterbi School of Engineering, University of Southern California, Los Angeles and an Alexander von Humboldt Professor


with the Electrical Engineering and Computer Science Department of the Technical University of Berlin, Germany.
He served as Associate Editor for the IEEE Transactions on Communications in 1998-2001 and as Associate Editor for the IEEE Transactions on


Information Theory in 2001-2003. He received the Jack Neubauer Best System Paper Award from the IEEE Vehicular Technology Society in 2003,


the IEEE Communications Society & Information Theory Society Joint Paper Award in 2004 and in 2011, the Okawa Research Award in 2006,


the Alexander von Humboldt Professorship in 2014, and the Vodafone Innovation Prize in 2015.
Giuseppe Caire is a Fellow of IEEE since 2005. He has served in the Board of Governors of the IEEE Information Theory Society from 2004 to 2007,


and as officer from 2008 to 2013. He was President of the IEEE Information Theory Society in 2011. His main research interests are in the


field of communications theory, information theory, channel and source coding with particular focus on wireless communications.