On the performance of randomly directional beamforming between line-of-sight and rich scattering channels

In this paper, the performance of random beamforming (RBF) which requires only partial channel state information (CSI) feedback is investigated for millimeter-wave (mmwave) multiple-input multiple-output (MIMO) downlink systems under a new channel model that captures both the independent and identically-distributed (i.i.d.) Rayleigh fading MIMO channel model and the uniform random line-of-sight (UR-LoS) channel model and bridges the two channel models. Under the proposed channel model, we answer the basic question “how many users in the cell are required for RBF to achieve linear sum rate scaling with respect to (w.r.t.) the number of transmit antennas?”