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MIMO (multiple-input - multiple output) wireless systems
are those that have antenna arrays at both transmitter
and receiver. The main problem of any MIMO system is
the increased complexity, and thus cost, it introduces
by requiring N complete RF chains. Additional antenna
elements (patch or dipole antennas) are usually cheap,
and the additional digital signal processing is becoming
less of a burden as digital processing becomes ever
more powerful. However, RF elements like low-noise amplifiers,
downconverters, and analog-to-digital converters are
a significant cost factor. Due to the reason, there
is now great interest in so-called hybrid-selection
schemes, where the "best" L out of N antennas
are chosen (either at one, or at both link ends), downconverted,
and processed. This reduces the number of required RF
chains from N to L, and thus leads to significant savings;
this comes at the price of a (usually small) performance
loss compared to the full-complexity system. This paper
gives an overview of such systems, showing how the selection
process can be applied to either diversity systems or
so-called "spatial multiplexing", and details
the performance for those two cases. In ideal channels,
full diversity can be achieved, and also the number
of independent data streams for spatial multiplexing
can be maintained if certain conditions on L are fulfilled.
Fast algorithms for the selection of the best antennas
are discussed. Finally, we discuss the impact of system
nonidealities, like noisy channel estimation, correlations
of the received signals, etc. It is demonstrated that
for many practical applications, antenna selection provides
large savings in terms of complexity with only a small
performance loss.
Biography
Andreas F. Molisch received the M. Sc., Ph.D. and habilitation
degrees, all from the Technical University of Vienna,
in 1990, 1994, and 1999 respectively. From 1994 to 2000,
he was assistant and associate professor at that university.
From 2000 to 2002, he was at AT&T Labs Research,
Middletown, NJ. Since 2002, he is with Mitsubishi Electric
Research Labs, Cambridge, MA. He is also professor and
chairholder for radio systems at Lund University, Sweden.
His research interests are MIMO systems, wireless channels,
and ultrawideband systems. He has published 2 books,
6 book chapters, 60 journal papers, and numerous conference
papers. He is a senior member of the IEEE and recipient
of several awards.
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