The Impact of Non-Isotropic Scattering and Directional Antennas on MIMO Multicarrier Mobile Communication Channels
In outdoor environments, waves propagate nonisotropically because of non-uniform distribution of scatterers. In addition directional antennas, which are efficient for communication applications, have considerable impact on the response of the communication channel. The impact of nonisotropic propagation and directional antennas is more significant when the system employs multiple antennas. In this paper, we propose a space-time-frequency cross correlation function (CCF) for multiple-input multiple-output multicarrier channels in a two-dimensional (2D) random scattering medium. The expression of the CCF turns out to be a multiplication of three CCFs. Two of these terms characterize the impact of mobile station and base station, respectively and are linear Bessel expansions, where the coefficients are given by the linear convolution of the Fourier series coefficients (FSC)s of the employed antenna patterns and the FSCs of the probability density function describing 2D nonisotropic environment. The third expression characterizes the impact of the wireless channel. In the stationary case, we derive the expression of the fading channel power spectrum (CPS) in terms of the non-isotropic pdf and antenna patterns. Using the expression of the CCF, we also calculate coherence-bandwidth (CB)/coherence-time (CT) as a function of carrier frequency/time separations. Our numerical results show a good fit to the available experimental results obtained for the CB/CT of realistic outdoor channels.