1. An apparatus for transmitting in a multi-user multi-antenna system, the apparatus comprising: a precoder for orthogonalizing a channel by removing a channel element of a corresponding terminal with respect to multiple terminals, for determining an effective channel of each terminal by decomposing the orthogonalized channel using Singular Value Decomposition (SVD), for determining a precoding matrix using the effective channel, and for mapping data streams of the multiple terminals to a plurality of transmit antennas using the precoding matrix; and the plurality of the transmit antennas for transmitting the data streams of the multiple terminals.