Abstract
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.
Highlights
Space-time-frequency (STF) models are required to realistically evaluate the performance and to comprehensively understand the behavior of multiple-input multiple-output (MIMO) multicarrier communication systems in the presence of fading(s) [1]
This result is expected based on the Fourier analysis on the stationary cross-correlation function (CCF), as the Doppler effect certainly appears as a function of different parameters of the nonisotropic propagation medium and parameters of the employed antenna
Using the same curve-fitting technique, we suggest the following approximations between Δx measured in wavelength λ1 = c/ f1 and Δ f measured in GHZ: SCx =Δ Δx ≈ k1(Δ f )k2
Summary
Space-time-frequency (STF) models are required to realistically evaluate the performance and to comprehensively understand the behavior of multiple-input multiple-output (MIMO) multicarrier communication systems in the presence of fading(s) [1]. Most of existing MIMO models for outdoor environments assume wave propagation in a twodimensional (2D) horizontal space, considering a special geometry for the scatterers combined with appropriate probability density functions (pdfs) for the physical parameters, for example, [2, 3]. Our literature review shows that available CCFs for 3D-MIMO outdoor environments are mostly based on specific geometries of scatterers in the space and each model is just capable to predict the behavior of that particular propagation scenario. They are not able to investigate the spatial, the temporal, and the frequency aspects of the wireless channel in one single model.
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