Spatial Diversity in MIMO Communication Systems with Distributed or Co-located Antennas

The use of multiple antennas in wireless communication systems has gained much attention during the last decade. It was shown that multiple-antenna systems, called multiple-input multiple-output (MIMO) systems, offer huge advantages over single-antenna systems, both with regard to capacity and error performance.

Typically, quite restrictive assumptions are made in the literature on MIMO systems concerning the spacing of the individual antenna elements. On the one hand, it is typically assumed that the antenna elements at the transmitter and the receiver are co-located, i.e., they belong to some sort of antenna array. On the other hand, it is often assumed that the antenna spacings are sufficiently large, so as to justify the assumption of independent fading on the individual transmission links. From numerous publications it is known that spatially correlated links caused by insufficient antenna spacings lead to a loss in capacity and error performance.