Asymptotic analysis of RZF in large-scale MU-MIMO systems over Rician channels

Abstract : In this work, we focus on the ergodic sum rate in the downlink of a single-cell large-scale multiuser MIMO system in which the base station employs N antennas to communicate with K single-antenna user equipments. A regularized zero-forcing (RZF) scheme is used for precoding under the assumption that each link forms a spatially correlated MIMO Rician fading channel. The analysis is conducted assuming that N and K grow large with a non trivial ratio and perfect channel state information is available at the base station. New results from random matrix theory and large system analysis are used to compute an asymptotic expression of the signal-to-interference-plus-noise ratio as a function of the system parameters, the spatial correlation matrix and the Rician factor. Numerical results are used to validate the accuracy of the asymptotic approximations in the finite system regime and to evaluate the performance under different operating conditions. It turns out that the provided asymptotic expressions provide accurate approximations even for relatively small values of N and K.