Inter-user interference reduction factor for 3-D massive MIMO systems

Massive MIMO has recently attracted considerable attention, regarded as a way to improve both spectrum and energy efficiency for broadband wireless communication systems. In traditional MIMO or 2-D MIMO only the horizontal beam (azimuth angle) is exploited, not considering the potential advantage of the elevation angle. In order to evaluate the elevation angle effect, over the inter-user interference, a 3-D massive MIMO scenario is proposed through a correlation-based stochastic model. Expressions to assess the inter-user interference are derived as an interference reduction factor (IRF) for linear, planar and cubical antennas array. A performance comparison between 2-D and 3-D massive MIMO systems is presented. Finally, the tradeoff between IRF and array compaction for linear, planar and cubical arrays for unlimited and limited physical space is analyzed.