Space-Time-Frequency Characterization of 3D Nonisotropic MIMO Multicarrier Propagation Channels Employing Directional Antennas

Channel models for outdoor wireless systems usually assume two-dimensional (2D) random scattering media. In the practical outdoor wireless channels, the impact of the wave propagation in the third-dimension is definitely important; especially when the communication system efficiently exploits potentials of multiple antennas. In this paper, we propose a new model for multiple-input multiple-output (MIMO) multicarrier propagation channels in a three-dimensional (3D) environment. Specifically, the proposed model describes the cross-correlation function (CCF) between two subchannels of an outdoor MIMO channel employing directional antennas and in the presence of nonisotropic wave propagation in 3D space. The derived CCF consists of some correlation terms. Each correlation term is in the form of a linear series expansion of averaged Bessel functions of the first kind with different orders. In practice, each correlation term has a limited number of Bessel components. Our numerical evaluations show the impact of different parameters of the propagation environment as well as the employed antennas on the resulting CCF. Using the proposed CCF, we also establish simple formulas to approximate the coherence time, the coherence bandwidth and the spatial coherence of such channels. The numerical curve fitting results fit to the empirical results reported in the channel modeling literature.