Spatial Limits to MIMO Capacity in General Scattering Environments

In this paper we present a new upper bound on the capacity of MIMO systems. By characterizing the fundamental communication modes of a physical aperture, we develop an intrinsic capacity which is independent of antenna array geometries and array signal processing. Using a modal expansion for free-space wave propagation we show that there exists a maximum achievable capacity for communication between spatial regions of space, which depends on the size of the regions and the statistics of the scattering environment.