3D Beamforming (3D BF) is a new feature of 3GPP LTE-A standard that is likely to increase spectral efficiency by exploiting the vertical dimension. If two co-located receivers are sufficiently spaced in elevation, 3D BF allows a base station (BS) to simultaneously serve them by focusing dedicated narrow beams on each receiver's vertical position. By deriving a closed-form expression of the signal-to-interference ratio which we show to be proportional to the vertical spacing between two such receivers, the accuracy of vertical spacing estimation is shown to be of paramount importance to the performance of 3D BF. A question is then how can a BS tell, with reasonable confidence, whether 2 receivers are sufficiently spaced in elevation for the beams not to significantly overlap. Thus, we provide a hypothesis testing framework under which a BS estimates such vertical spacing from the uplink signals received from the receivers, as well as a decision rule based upon which a BS decides whether or not to apply 3D BF in a given scenario.
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