Geometrical Theory of Channel Depolarization

A geometrical theory is proposed for depolarization in narrow-band fixed-to-mobile (F2M) and mobile-to-mobile (M2M) wireless channels. This novel theory is used to reveal the origin of channel depolarization and to provide a mechanism for computing cross-polarization discrimination (XPD). Based on the superposition of polarization components on conservation-of-polarization planes, a new 3-D geometry-based reference model is proposed for XPD in narrow-band F2M and M2M wireless channels. This purely theoretical approach is used to derive the XPD without the aid of measurement data or its approximation. The geometrical theory and reference model provide a relationship between channel depolarization or XPD and channel modeling factors such as the distance between the transmitter (Tx) and the receiver (Rx), the azimuth/elevation angles of arrival and departure, and the distribution of scatterers around the Tx and/or the Rx. Our geometry-based XPD model shows good agreement with previously reported empirical results from other authors and provides insight on the detailed behavior observed in their XPD measurements.