Electromagnetic Effective Degree of Freedom of MIMO System in Nonfree Space

The effects of inhomogeneous environments on nearfield multi-input-multi-output (MIMO) communications are discussed by using full-polarization channel matrix that contains all necessary information. In particular, reflections from grounds are taken into account by full-wave simulations. It is found that the dielectric parameters of the grounds, the relative heights and distances between the transmitters and receivers can affect the electromagnetic effective degree of freedom, which represents the equivalent number of independent single-input-single-output systems. The simulated results also reveal that the extra propagation paths brought by the ground reflection have potential benefits and values in near-field MIMO communication when the number of the antennas of the MIMO system reaches a critical value.