Design and Analysis of MMSE Precoder for Dual-Polarized Cell-Free Massive MIMO Systems

We consider the downlink of a cell-free (CF) massive multiple-input-multiple-output (mMIMO) system, where each access point (AP) has multiple dual-polarized antennas, while a user equipment has a single dual-polarized antenna. The APs use minimum mean squared error (MMSE) precoder to precode the transmit signals. We derive the deterministic equivalent (DE) of achievable spectral efficiency (SE) for the above system, by using large-dimensional random matrix theory. The DE expression is used to analytically show that the SE gain of a dual-polarized CF mMIMO system over its single-polarized counterpart increases with increase in the number of APs, and its antennas. Crucially, the dual-polarized antennas are shown to further enhance the inherent uniform coverage provided by a CF mMIMO system.