User selection method in a zero-forcing beamforming algorithm

1. A method for selecting a transmission target terminal in a zero-forcing beamforming algorithm in which a base station with multiple transmit antennas selects a predefined number N of downlink transmission target terminals using channel information received from a plurality of terminals with at least two receive antennas, comprising the steps of:

broadcasting a pilot beam to all K terminals;

receiving information about a channel capacity of each terminal from the terminals in response to the pilot beam;

selecting a terminal with a largest channel capacity as an initial transmission target terminal;

determining whether the number of currently selected terminals, i, is equal to the predefined number N;

receiving a channel matrix of an associated terminal from the initial transmission target terminal if the number of currently selected terminals, i, is different from the predefined number N;

computing a null space of the received channel matrix;

broadcasting a null space beam based on the null space; and

receiving information about channel capacities from remaining terminals except the selected transmission target terminal in response to the null space beam, and selecting a terminal with a largest channel capacity as a transmission target terminal based on the received information about the channel capacities from the remaining terminals.

2. The method of claim 1 , wherein the pilot beam is a form of an identity matrix.

3. The method of claim 1 , further comprising:

outputting an index set of the selected terminals if the number of selected terminals, i, is equal to the predefined number N.