Analysis of the Capacity Statistics for 2 $\times$ 2 3D MIMO Channels in Short-Range Communications

In this letter, we investigate the capacity of 2 × 2 short-range line-of-sight (LOS) multiple-input multiple-output (MIMO) channels in three-dimensional (3D) space. The corresponding channel with arbitrary antenna orientations in 3D space is modeled using the spherical-wave model (SWM) , based on which the capacity without channel knowledge at the transmitter is obtained. The exact analytical expressions for the probability density function (PDF), cumulative distribution function (CDF) , and expectation of the capacity are then derived and compared with those obtained by the plane-wave model (PWM) . Both the analytical and simulation results show that the capacity is determined by a factor depending on the transceiver distance, the wavelength, and the array size.