MODELING ANTENNA COUPLING AND CORRELATION IN RAPIDLY FADING MIMO CHANNELS

Node mobility in rich multipath environments limits the quality of attainable channel state information (CSI) due to wavelength-scale fading, leading to effectively lower channel capacities. Recent work on the capacity of blockfading MIMO channels considers the impact of antenna correlation at the transmitter [1], proving that correlation guarantees capacity growth with additional antennas and suggests that for rapidly fading channels, antennas should be paced as close together as possible. This work augments the MIMO modeling strategy in [1] to include the effects of electromagnetic coupling of the antennas. Constraining the radiated power of the transmit array reveals that the reported gains result from simple beamforming mechanisms, and that capacity growth only comes from increased channel correlation, not antenna correlation whose gain is offset by increased coupling. The new model also predicts that optimal antenna placement for rapidly fading channels is not arbitrarily close, but rather on the order of 0.3 to 0.6 wavelengths.