Elevation Beamforming in a Multi-Cell Full Dimension Massive MIMO System

Abstract : The 3GPP Release-13 has recently introduced full-dimension multiple-input multiple-output (FD-MIMO) technology as a practical way to deploy massive MIMO arrays within feasible base station (BS) form factors through the use of active antenna systems (AAS) with two-dimensional (2D) planar array structures. The 2D arrangement of antenna elements, where the elements in each antenna port are fed with downtilt weights, provides the additional ability of adaptive electronic beam control in the elevation dimension. This work focuses on the previously unaddressed problem of determining the optimal downtilt weight vectors for the antenna ports in each cell of a multi-cell multiuser system. The optimization criteria is to maximize the minimum signal-to-intra-cell-interference ratio within a cell while constraining the inter-cell interference leakage. A quasi-optimal solution is obtained for the weight vectors through the application of semi-definite relaxation and Dinkelbach's method. The proposed algorithm is shown to perform better than the existing schemes even under the effects of pilot contamination.