  In this paper, we perform a coverage analysis of a cellular massive
multiple-input multiple-output (MaMIMO) network which adopts 3D beamforming. In
contrast to the previous works on 3D beamforming which assume that all users
are placed on the ground (i.e, in a 2D environment), we consider a more
practical scenario where the users of the network are dropped in a 3D
environment with different heights. In this scenario, by adopting a stochastic
geometry framework, first we calculate the coverage probability of the network
as a function of the users height. Then considering this coverage probability
as the objective function, the optimum tilt angle of the base station antenna
pattern is found and the effect of users' heights on this tilt angle is
investigated. Our numerical results show that by taking the users' heights into
account and using the proposed method, a considerable improvement is achieved
in the performance of the network compared to other similar 3D beamforming
methods that ignore the users'height distribution.
