  Dynamic Time Division Duplexing (D-TDD) allows cells to accommodate
asymmetric traffic variations with high resource assignment flexibility.
However, this feature is limited by two additional types of interference
between cells in opposite transmission direction: downlink (DL) to uplink (UL)
and UL to DL interference. Therefore, using this mode with macro-cell
deployments requires interference mitigation techniques to reduce the strong DL
to UL interference. 3D beamforming is an efficient technique that minimizes
interference and enhances performance by exploiting a large 2D array of
antennas intelligently. Combining D-TDD and 3D beamforming can make D-TDD
feasible for macro-cells. The aim of this work is to provide a 3D beamforming
analytical model in a D-TDD based macro-cells' deployment where beamforming
horizontal and vertical radiation patterns depend on the spatial distribution
of random users' locations. We evaluate interference in terms of Interference
to Signal Ratio (ISR). We show that the cumulative ISR can be written in terms
of convergent series and its expectation is an almost sure convergent series.
Different numerical results are presented to justify the applicability of this
scheme.
