Achievable rate of multiuser downlink for LOS-MIMO systems with uniform circular arrays

In this paper, we investigate the achievable downlink rate of line-of-sight (LOS) multiple-input multiple-output (MIMO) systems, where uniform circular arrays (UCAs) is deployed at Base station (BS). Based on an existing three-dimensional channel model developed by considering both the azimuth and elevation dimensions. We first analyze channel vectors by assuming that users are randomly distributed in a cell, which indicates that the inner product of channel vectors in LOS-MIMO systems satisfies Bessel function when the number of transmit antenna is sufficiently large. Based on the properties of Bessel function, novel closed-form lower bound of achievable sum-rate are derived by considering two different cases with azimuth angles or elevation angles of users being identical. Our results show that with increasing the radius of UCAs, the achievable sum-rate converges to a saturated value. Finally, the theoretical analysis is validated via numerical simulations.