MIMO wireless channels made simple

Fundamental understanding of the interaction between the signal space and the channel is key to reliable communication. We propose a virtual channel representation for multi-antenna fading channels that captures the essence of such such interaction in the spatial dimension. The virtual representation describes the channel via spatial basis functions defined by fixed virtual angles. The resulting virtual channel matrix provides a simple geometric interpretation of the scattering environment and clearly reveals the two key factors affecting capacity: the number of parallel channels and the level of diversity. Via the concepts of spatial zooming and aliasing, the virtual representation also provides a transparent interpretation of the effects of antenna spacing on channel statistics and capacity.