Characterizing Polarization-MIMO Antennas in Random-LOS Propagation Channels

In the 5G system, we foresee the use of LOS-dominated mm-wave radio links to moving users being subject to slow fading resulting from the users' random locations and orientations. We refer to this as a random-LOS channel. MIMO processing algorithms will be used in 5G to improve performance in slow fading, similar to how they are used in Rayleigh fading. To this end, we study the probability of detection in the random-LOS channel when there are dual-polarized antennas on both sides of the link. We introduce two polarization deficiencies: the polarization non-orthogonality and the amplitude imbalance between the ports of a two-port antenna. The MIMO efficiency is evaluated as a function of these deficiencies. In the analysis, we consider the MRC algorithm for one bitstream, and the ZF and SVD algorithms for two bitstreams. We also present two analytical formulas for the MIMO efficiency that can be used to determine performance. We use the formulas on two ideally orthogonal dipoles, and show by means of coverage plots how much the 1- and 2-bitstream performances degrade due to the polarization deficiencies in off-boresight directions.