MIMO - study propagation first!

Despite many valuable contributions to the theory and practice of MIMO communication systems from various scientific fields, we want to emphasize the outstanding importance of propagation aspects when dealing with MIMO systems. Radio propagation forms the basis for any radio channel including MIMO systems. On one hand, popular mathematical models and the commonly applied statistical assumptions sometimes turn out to neglect the important properties of MIMO radio channels. On the other hand, the detailed knowledge and investigations of MIMO specific phenomena (e.g. pinholes) does not imply the practical relevance. By means of four specific examples, we argue that studying propagation is indispensable in order to stay in touch with the real MIMO channels.