  It is the pursuit of a multiple-input-multiple-output (MIMO) system to
approach and even break the limit of channel capacity. However, it is always a
big challenge to efficiently characterize the MIMO systems in complex space and
get better propagation performance than the conventional MIMO systems
considering only free space, which is important for guiding the power and phase
allocation of antenna units. In this manuscript, an
Electromagnetic-Information-Theory (EMIT) based model is developed for
efficient characterization of MIMO systems in complex space. The
group-T-matrix-based multiple scattering fast algorithm, the
mode-decomposition-based characterization method, and their joint theoretical
framework in complex space are discussed. Firstly, key informatics parameters
in free electromagnetic space based on a dyadic Green's function are derived.
Next, a novel group-T-matrix-based multiple scattering fast algorithm is
developed to describe a representative inhomogeneous electromagnetic space. All
the analytical results are validated by simulations. In addition, the complete
form of the EMIT-based model is proposed to derive the informatics parameters
frequently used in electromagnetic propagation, through integrating the mode
analysis method with the dyadic Green's function matrix. Finally, as a
proof-or-concept, microwave anechoic chamber measurements of a cylindrical
array is performed, demonstrating the effectiveness of the EMIT-based model.
Meanwhile, a case of image transmission with limited power is presented to
illustrate how to use this EMIT-based model to guide the power and phase
allocation of antenna units for real MIMO applications.
