Evaluation of the effect of base station antenna polarization on the performance of CoMP transmission techniques based on synchronous multi-link measurements

In this paper, the effect of polarization on the downlink sum-rate capacity of multi-user Cooperative Multi-Point (CoMP) systems using synchronous multi-link measurement data, for two different antenna arrangements, is studied. In the first setup, four antenna patches each of which with dual-polarized antenna elements at the base station (BS) with inter-patch distance varied from half wavelength to 8 m is considered. In the second setup, two BSs located 60 m apart are used each is provided with dual-polarized antennas spaced half a wavelength apart. Based on the BS antenna element selection, scenarios with different antenna polarizations at the BSs are considered. We assume the existence of four virtual users each equipped with two dual-polarized antennas with half-wavelength inter-element distance. The users are equally spaced with inter-user distance of about 0.5 m and moving in different routes. For each scenario, 8x4 MIMO channels of each user are used to evaluate the sum-rate capacity of the system, where the minimum mean square error (MMSE) beamforming at both the BS and the mobile station (MS) is used. It is found that the performance improvement gained from using dual-polarized antennas at the BS vanishes if the BS antenna elements are distributed over large distance (i.e., having a large antenna array). However, in the measured environment, for the case of having two BSs each of which is provided with closely-located antennas, using dual-polarized antennas provide about 40% improvement in the ergodic sum-rate capacity compared to using single-polarized antennas.