lly distinguished through their orthogonal signatures, their overhead grows linearly with the number of transmit antennas. As we mentioned earlier, FD-MIMO systems employ 2D planar arrays; thus propagation in both vertical and horizontal directions as well as the geometry of the transmitter array and the propagation effect of the 3D objects between the base station and the mobile station should be taken into account in channel modeling. The 3D channel propagation behavior obtained through measurements show the effect of height and distance-dependent LoS chan- nel and the fact that LoS probability between the base station and the UE increases with the UE's height and increases when the distance between them decreases. Further it shows the effect of height-dependent path loss where the UE experiences less path loss on a higher floor (e.g., 0.6 dB/m gain for a macrocell and 0.3 dB/m gain for a micro cell). The height New Radio Access Physical Layer Aspects (Part 2) 579 and distance-dependent elevation spread of departure (ESD) angles effect is exhibited when the location of the base station is higher than the UE, ESD decreases with the height of the UE and as the UE moves away from the base station [46,47]. FD-MIMO systems make use of a beamformed reference signals for CSI acquisition. Beamformed reference signal transmission is a channel training technique that uses multiple precoding weights in the spatial domain. In this scheme, the UE selects the best weight among those transmitted and then feeds back this index. This scheme provides many benefits com- pared to the case with non-precoded reference signals and especially when the number of transmit antennas is large. It can be shown that this scheme has less uplink feedback overhead relative to the case with perfect CSI, where the number of feedback bits used for channel vec- tor quantization is linearly proportional to the number of transmit antennas, whereas the amount of feedback for the beamformed reference signals scales logarithmically with the num- ber of 