Achievable sum rate analysis of ZF receivers in 3D MIMO with Rayleigh/log-normal fading channels

Three dimensions multiple-input multiple-output (3D MIMO) system is now gaining a growing interest among researchers in wireless communication, the reason can be attributed to its potential to enable a variety of strategies like user specific 3D beamforming and cell-splitting. In this paper, we pursue the performance evaluation of 3D MIMO system employing zero-forcing (ZF) receivers, accounting for both large and small-scale fading. In particular, we consider the classical log-normal model and antenna gain with tilting angle, we derive the optimal tilting angle for 3D MIMO system which maximizes the sum rate, furthermore, based on the optimal tilting angle, we propose a closed-form linear approximation on the achievable sum rate in the asymptotically high signal-to-noise ratio (SNR) and low-SNR regime, respectively. We investigate the effect of antenna tilting angle, number of base station (BS) antennas and the distance between BS and the center of building on the achievable sum rate performance of 3D MIMO.