Smart antennas and MIMO systems

Andreas F. Molisch, Mitsubishi Electric Research Lab, and Lund University, Sweden
Juha Laurila, Nokia Research Center, Helsinki, Finland
Klaus Hugl, Nokia Research Center, Helsinki, Finland
Ernst Bonek, Technische Universität Wien, Austria

Smart antennas and MIMO (multiple-input multiple-output) systems utilize multiple antennas at one and at both wireless link ends, respectively. These techniques can be used to increase the capacity of mobile radio systems, both for upgrading second-generation systems and for use in third- and fourth generation systems. Thus, multi-antenna systems have attracted enormous interest and a lot of effort has been spent for its system development and standardization. The tutorial will give a comprehensive overview over all relevant aspects of smart antenna and MIMO systems.

The mobile radio channel, especially its directional nature defined by the directions-of-arrival and directions-of-departure of the waves propagating from transmitter to receiver, determines the performance of multi-antenna systems. Therefore, we start out with an introduction of spatial channel sounding techniques forming the basis for spatial channel measurements and spatial channel characterization. We present measurement results of the directional channel properties as seen from the base station and from the mobile terminal only, as well as measurements of the double-directional propagation characteristics. We then explain how these measurement results can be utilized and included in spatial channel models, which are required for the design and development of adaptive antenna and MIMO systems.

Next, we describe transceiver structures and algorithms for smart antennas at one link end. After an introduction to the basic smart antenna technology, we describe different adaptation techniques for multi-antenna reception in detail. Thereby, we consider temporal reference, spatial reference as well as blind adaptation algorithms and present their performance in different propagation conditions. Moreover, the fundamental differences of reception and transmission using several antennas will be explained and transmission strategies including downlink beamforming and transmission diversity will be derived. The more practical aspects of roll-out and capacity of smart antenna base stations – especially in the context of 3G systems - will complete the considerations of multiple antennas at one link end.

Next, we present the two operation modes of MIMO systems applying multiple antennas for transmission and reception: diversity enhancement, and BLAST-like schemes. In the former case, the multiple antennas at both link ends are used to provide a high degree of diversity, resulting in a high-quality link. We explain what diversity degree and beamforming gain can be achieved in different types of wireless channels. Then, we describe BLAST schemes where independent data streams are sent from the different transmit antennas, and the multiple receive antennas are used to receive and separate those different data streams. We show how the capacity of these systems can increase linearly with the number of transmit and receive antennas. Different BLAST implementations are explained, and their advantages and drawbacks are discussed. Finally, we demonstrate the principles of space-time codes, and show how those can be applied for diversity and capacity increase. A discussion of interference-limited MIMO systems, and of waterfilling schemes, will round off the presentation.

Andreas F. Molisch received the Dipl. Ing., Dr. techn. (with highest honors), and habilitation degrees from the Technical University Vienna in 1990, 1994, and 1999, respectively. From 1991 to 2001, he was with the Institut für Nachrichtentechnik und Hochfrequenztechnik (INTHFT) of the TU Vienna, most recently as associate professor. From 2001 to 2002, he was with AT&T Laboratories - Research; since 2002 he has been with Mitsubishi Electric Research Laboratory, Murray Hill. He is also professor and chairholder for Radio Communications at Lund University, Sweden His current research interests are MIMO systems, UWB, characterization of mobile radio channels, and wideband systems. He is senior member of the IEEE, and (co)author of two books, five book chapters, some 50 journal papers, four patents, and numerous conference contributions. He is also editor for IEEE Trans. Wireless Comm., chairman of the COST273 working group on MIMO channels, and active in the 3GPP adhoc group for this topic.

Juha Laurila was born 1970 in Korpilahti, Finland. He received the M.Sc. (E.E.) degree from the Helsinki University of Technology, Finland (Institute of Radio Communications) in 1995 and the Dr. Tech. degree from the Vienna University of Technology, Austria (Institut fuer Nachrichtentechnik und Hochfrequenztechnik) in 2000. In his doctoral thesis he investigated semi-blind algorithms for mobile communications concentrating on the reception with multiple antennas at the base station. In 1995-96 he was with the Helsinki University of Technology and from 1996 to 2000 with the Vienna University of Technology, working as research engineer at both universities. Since 2000 he has been working as senior research engineer and most recently as research manager at Nokia Research Center (Radio Communications Laboratory) Helsinki, Finland. His current research activities are related to the utilisation of multiple antenna techniques in cellular systems. His main interests are in link-level algorithm development, but he is also involved with spatial propagation studies and system-level investigations. J. Laurila has authored or co-authored one book chapter and some 30 international reviewed journal and conference publications. He holds one patent and several applications are pending.

Klaus Hugl was born in Mistelbach, Austria, 1974. He received his Dipl. Ing. and Dr. techn. degrees (with highest honors) from Technische Universität Wien (TU-Wien) in 1998 and 2002, respectively. From 1998 to 2002, he was with the Institut für Nachrichtentechnik und Hochfrequenztechnik (INTHF) of TU-Wien, working as a research engineer. Since 2002, he has been with Nokia Research Center (Radio Communications Laboratory) Helsinki, Finland. His current research interests are adaptive antenna systems and spatial channel modeling/characterization. He (co)-authored more than 10 international reviewed journal and conference publications, and holds one patent in the field of multi-antenna systems.

Ernst Bonek was born in Vienna, Austria, 1942. He received the Dipl. Ing. and Dr. techn. degrees (with highest honors) from the Technische Universität (TU) Wien. In 1984, he was appointed Full Professor of Radio Frequency Engineering at the TU Wien. His present field of interest is mobile communications at large. Recent contributions concern the characterization of mobile radio channels, cordless telephony, and advanced antennas and receiver designs. Altogether, he authored or co-authored some 100 journal publications. He holds three patents, and seven more applications on mobile radio technology are pending. His current positions in scientific organizations include: chairman of the "Antennas and Propagation" working group in the European research initiative "COST 273"; Area Editor of "Wireless Personal Communications"; Chairman of URSI (Union of radio scientists) commission Chairman of a COST 259/260 workshop on "Spatial channel models and adaptive antennas"; Senior Member of IEEE.