Polarization characteristics of multiple-input multiple-output channels

In this paper, we investigate the polarization characteristics of the multiple-input multiple-output (MIMO) channels. The cross polarization discrimination (XPD) is found to change over time, while its variation in frequency domain is relatively small. The probability density function (PDF) of the XPD follows a Gaussian distribution. Analysis and measurement results show that the polarization preserves better in the line of sight (LOS) scenario. In the case of non line of sight (NLOS) scenario, the polarization of the signals is destroyed due to multiple reflections, diffractions or scattering. The difference between the XPDs of the vertically polarized and horizontally transmission highly depends on the specific propagation environment between the transmitter and the receiver. Comparison of the capacity in different scenarios further shows that the polarization diversity gain is less in NLOS scenarios compared with that in LOS scenarios.