1. A method for detecting a signal from a receiving device in a communication system comprising a multi-output multi-input antenna, comprising: estimating a channel matrix of a signal received from a plurality of receiving antennas; generating at least one channel matrix group by aligning the channel matrix, and generating at least one transmitting signal group by aligning a transmitting signal to be estimated to correspond thereto; determining a first candidate vector in consideration of all constellation points for a first layer of the at least one transmitting signal group; determining a second candidate vector in consideration of all constellation points for a second layer of the at least one transmitting signal group; generating a final candidate vector comprising the first candidate vector and the second candidate vector; and calculating a soft output using the final candidate vector, wherein the determining of the first candidate vector determines the first candidate vector using the upper triangular matrix with respect to remaining layers other than the first layer among the at least one transmitting signal group, and the determining of the second candidate vector determines the second candidate vector using the upper triangular matrix with respect to remaining layers other than the second layer among the at least one transmitting signal group, wherein the determining of the first candidate vector determines the first candidate vector using the upper triangular matrix with respect to remaining layers other than the first layer among the at least one transmitting signal group, and the determining of the second candidate vector determines the second candidate vector using the upper triangular matrix with respect to remaining layers other than the second layer among the at least one transmitting signal group.