Downlink cell average spectral efficiency of distributed MIMO system under three dimensional model

Due to the complicated fading environment of distributed multiple-input multiple-output (d-MIMO) systems, the closed-form expression of cell average spectral efficiency (CASE) is in general difficult to be obtained, not to mention the threedimension model. Hence, by assuming appropriate number of antennas configured on the remote access unit (RAU) of d-MIMO system, we firstly derive out a simple approximate expression of spectral efficiency with fixed pathloss according to the central limit theorem. To be more realistic, the closed-form of CASE at different locations of the target cell, under three-dimensional model, i.e., with considering the height of the RAU, is then given out. The theoretical and simulation results reveal that the CASE of d-MIMO system is bounded by the density and the height of RAU, and the CASE is robust to the changes of the user's location except for the cell-edge. Further, about 50% penalty of CASE from the cell-center to the cell-edge can be found. Moreover, the analytical results fit the simulations well, which verifies our analysis.