Fundamental Limits of MIMO Capacity for Spatially Constrained Arrays

In this paper we investigate the capacity behavior of spatial constrained multiple-antenna array communications. By increasing the number of antennas within a fixed region of space the antenna array becomes dense and spatial correlation inhibits capacity growth. Using a novel spatial channel model we show that the underlying physics of wave propagation limits the capacity of constrained arrays. A theoretically derived antenna saturation point is shown to exist for dense array MIMO systems, at which there is no capacity growth with increasing antenna numbers. We show this saturation point increases linearly with the radius of the region, and that it naturally lends itself to a definition for the theoretical maximum capacity for a fixed region of space.