A Virtual Mimo Channel Representation and Applications

A key to maximal exploitation of MIMO (multiple-input multiple-output) systems is a fundamental understanding of the interaction between the underlying complexphysical scattering envimnment and the space-time signal space. In timeandfrequency-selective MIMO (space-time) channels, this interaction happens in time, frequency and space. We present a four-dimensional Karhunen-Loeve-like virtual representarion for space-time channels that captures such interaction and exposes the intrinsic degrees offreedom in the channel. The virtual representation is a Fourier series dictated by thefinite array apertures, signaling duration and bandwidth and corresponds to a uniform, fixed sampling of the angle-delay-Doppler scattering space. I t provides a much-needed connection between the two existing (extreme) modeling approaches idealized statistical models and detailedphysical (ray tracing} models. In particular: it yields a simple geometric interpretation of the effects ofphysical scattering on channel statistics and capacity. We discuss various insights into the structure of space-time channels afforded by the virtual representation as well its application in capacity assessment, spatial multiplexing and space-time code design.