On the Capacity for 3D LOS MIMO Channels in Short-Range Millimeter Wave Communications

Abstract

In recent years, millimeter wave (mm-wave) wireless communications have attracted considerable research interest. The studies on the capacity of the short-range mm-wave line-of-sight (LoS) multiple-input multiple-output (MIMO) channels mainly base on the measurements and simulations. In this paper, we analytically investigate the capacity of N × 2 short-range LoS MIMO channels at mm-wave frequencies in three-dimensional (3D) space. First, the channel with arbitrary antenna orientations in 3D space is modeled using the spherical-wave model (SWM). Then, the analytical expression for the corresponding capacity without channel state information (CSI) at the transmitter is obtained. Both the analytical and simulation results show that the capacity of short-range mm-wave LoS MIMO channels is completely determined by the wavelength, the number of transmit (Tx) antennas, the interelement spacings, the transceiver distance and the orientations of the arrays. It is shown that the capacity fluctuates significantly with these parameters. Furthermore, for the shorter wavelength, the smaller inter-element spacings can be obtained for the maximum capacity with the SWM. Meanwhile, the shorter wavelength is more appropriate in short-range communications. These findings have profound guiding significance for design of mm-wave wireless communication systems.