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An important problem in a multi-user mobile communication scenario is to provide adequate suppression of interfering signals at each receiver. This can be effectively achieved in two steps by using a multi-sensor array at the transmitter and the receiver. First, the array at the transmitter is used to form a main beam along the desired receiver direction under the constraint that the total transmitted power along the undesired receiver directions is minimized. Because of the large number of receivers present in the scene, exact null placement will not be possible. However, each receiver also forms a beam under similar constraints, and the combined effect of these beams are shown to result in adequate interference suppression. The desired weight vectors in each case depend on a set of intermediate parameters that can be determined as the least square solution of an over determined system of equations.
Lee et al. (Tue,) studied this question.