ABSTRACT: For one isolated wireless link we take a unified look at simple beamforming
(BF) as contrasted with MIMO to see how both emerge and under which conditions
advantage goes to one or the other. Communication is from a high base array to
a user in clutter. The channel propagation model is derived from fundamentals.
The base knows the power angular spectrum, but not the channel instantiation.
Eigenstates of the field spatial autocorrelation are the preferred apodizations
(APODs) which are drivers of the natural modes for exciting lectric fields.
Preference for MIMO or BF depends on APOD spectra which are surveyed pointing
to various asymptotic effects, including the maximum BF gain. Performance is
studied under varying eigenmode power settings at 10% outage. We focus on (1,4)
driving the strongest mode for BF and (4,4) driving the 4 strongest for MIMO.
Results are obtained under representative parameter settings, e.g. an angular
spread of 8 deg, 2 GHz carrier, 0 dB SNR and an array aperture of 1.68m (4
field decorrelation lengths) with antenna elements spaced as close as lambda/2.
We find MIMO excelling for array apertures much larger than the decorrelation
length; BF does almost as well for smaller apertures.
IEEE Transactions on Wireless Communications. 01/2011; 10:1396-1404.
44th Annual Conference on Information Sciences and Systems, CISS 2010, Princeton, NJ, USA, 17-19 March 2010; 01/2010
Proceedings of IEEE International Conference on Communications, ICC 2008, Beijing, China, 19-23 May 2008; 01/2008
IEEE Journal on Selected Areas in Communications. 01/2003; 21:303-320.
ABSTRACT: Multielement system capacities are usually thought of as limited only by correlations between elements. It is shown here that degenerate channel phenomena called "keyholes" may arise under realistic assumptions which have zero correlation between the entries of the channel matrix H and yet only a single degree of freedom. Canonical physical examples of keyholes are presented. For outdoor environments, it is shown that roof edge diffraction is perceived as a "keyhole" by a vertical base array that may be avoided by employing instead a horizontal base array.
IEEE Transactions on Wireless Communications. 01/2002; 1:591-599.
IEEE Communications Letters. 01/2001; 5:85-87.
IEEE Transactions on Communications. 01/2000; 48:502-513.