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Conferences, Lectures, & Seminars
Events for August
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Lattice space-time codes, MMSE-GDFE sphere decoders...
Mon, Aug 16, 2004 @ 10:00 AM - 11:00 AM
Ming Hsieh Department of Electrical and Computer Engineering
Conferences, Lectures, & Seminars
"Lattice space-time codes, MMSE-GDFE sphere decoders and the optimal diversity-multiplexing tradeoff of MIMO channels"SPEAKER: Dr. Giuseppe Caire, Institute EurecomABSTRACT: We consider the classical setting of point-to-point (single user) multiple-input multiple-output (MIMO) communications over a frequency flat slowly-varying fading channels where the channel matrix is only known to the receiver. The high-SNR behavior of optimal codes for this channel has been characterized by Zheng and Tse in terms of SNR reliability function, that is, the best possible exponent d*(r) of the decay of error probability with log SNR when codes of rate r log SNR are used. The function d*(r) also expresses the fundamental tradeoff between diversity (the exponent of error probability) and multiplexing (the pre-log factor r in the coding rate).We introduce the class of LAttice Space-Time (LAST) codes, that includes and generalizes linear codes over the complex field, such as orthogonal space time codes and linear dispersion codes. We show that LAST codes achieve the optimal diversity-vs-multiplexing tradeoff defined by Zheng and Tse. Even more remarkably, we show that LAST codes achieve the optimal d*(r) under generalized minimum Euclidean distance lattice decoding. Lattice decoding allows to exploit the algebraic structure of the underlying (infinite) lattice and obtain an efficient implementation of the decoder in terms of a variation of the well-known sphere decoder (Pohst or Schnorr-Euchner enumeration).The proposed scheme is based on a generalization of Erez and Zamir mod-Lambda scheme to the MIMO case. In our construction the ``magic'' scalar Costa scaling is replaced by the minimum mean square error generalized decision-feedback equalizer (MMSE-GDFE). This result settles the open problem posed by Zheng and Tse on the construction of explicit coding and decoding schemes that achieve the optimal diversity-vs-multiplexing tradeoff. Moreover, our results shed more light on the structure of optimal coding/decoding techniques in delay limited MIMO channels, and hence, opens the door for novel approaches for space-time code constructions. In particular; 1) we show that MMSE-GDFE plays a fundamental role in approaching the limits of delay limited MIMO channels in the high SNR regime, unlike the AWGN channel case and 2) our random coding arguments represent a major departure from traditional space-time code designs based on the rank and/or mutual information design criteria.Bio: Giuseppe Caire 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 was a recipient of the AEI G.Someda Scholarship in 1991, has been with the European Space Agency (ESTEC, Noordwijk, The Netherlands) from May 1994 to February 1995, was a recipient of the COTRAO Scholarship in 1996 and of a CNR Scholarship in 1997. He has been visiting Princeton University in summer 1997 and Sydney University in summer 2000.
He has been Assistant Professor in Telecommunications at the Politecnico di Torino and presently is Professor with the Department of Mobile Communications of the Institute Eurecom, Sophia-Antipolis, France. 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, and the Joint IT/Comsoc Best Paper Award in 2004. His current interests are in the field of communications theory, information theory and coding theory with particular focus on wireless applications.Host: Dr. Urbashi Mitra, x.04667, ubli@usc.eduLocation: Charles Lee Powell Hall (PHE) - 223
Audiences: Everyone Is Invited
Contact: Mayumi Thrasher
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Increasing reliability in ad hoc networks through diversity routing
Wed, Aug 18, 2004 @ 11:00 AM - 12:00 PM
Ming Hsieh Department of Electrical and Computer Engineering
Conferences, Lectures, & Seminars
SPEAKER: Dr. Eytan Modiano, MITABSTRACT: Key to making ad hoc networks viable is the ability to offer reliable service through an inherently unreliable medium. This talk will address novel mechanisms for increasing reliability in wireless networks through diversity routing. These mechanisms include disjoint paths routing algorithms for wireless networks and "cooperative routing" algorithms that extend physical layer diversity techniques to the network layer.As an example we will introduce a novel "outage probability" model for measuring reliability in a wireless networks. We will show how the traditional physical outage probability metric can be extended to a network setting and devise network routing algorithms for minimizing outage probability in a network. We will then show how physical layer diversity techniques can be extended to the network layer to achieve dramatic reduction in network outage probability.We will also discuss algorithms for finding minimum energy disjoint paths in a wireless network. Our major results include a novel polynomial time algorithm for the minimum energy two link-disjoint paths problem, as well as a polynomial time algorithm for the minimum energy k node-disjoint paths problem. Our results show that link-disjoint paths consume substantially less energy than node-disjoint paths and that the incremental energy of additional link-disjoint paths is decreasing.BIO: Eytan Modiano received his B.S. degree in Electrical Engineering and Computer Science from the University of Connecticut at Storrs in 1986 and his M.S. and PhD degrees, both in Electrical Engineering, from the University of Maryland, College Park, MD, in 1989 and 1992 respectively. He was a Naval Research Laboratory Fellow between 1987 and 1992 and a National Research Council Post Doctoral Fellow during 1992-1993 while he was conducting research on security and performance issues in distributed network protocols.Between 1993 and 1999 he was with the Communications Division at MIT Lincoln Laboratory where he designed communication protocols for satellite, wireless, and optical networks and was the project leader for MIT Lincoln Laboratory's Next Generation Internet (NGI) project. He joined the MIT faculty in 1999, where he is presently an Associate Professor in the Department of Aeronautics and Astronautics and the Laboratory for Information and Decision Systems (LIDS). His research is on communication networks and protocols with emphasis on satellite, wireless, and optical networks.Host: Dr. Michael Neely, x.03505, mjneely@usc.edu
Location: Hughes Aircraft Electrical Engineering Center (EEB) - 284
Audiences: Everyone Is Invited
Contact: Mayumi Thrasher
