1. A computer-implemented method of detecting a transmission signal from a received signal in a multiple input multiple output (MIMO) system, the method comprising executing computer program code instructions to cause one or more computer processors to: obtain a unitary matrix Q and a triangular matrix R by performing a sorted QR-decomposition (SQRD) algorithm with respect to a matrix B indicating a channel state; calculate a vector y by multiplying a transpose matrix Q t of the unitary matrix Q by the received signal Y; divide the triangular matrix R into a plurality of sub triangular matrices; and divide the calculated vector y into a plurality of sub-vectors so as to correspond to the divided plurality of sub triangular matrices; and detect a lattice point corresponding to each of the divided sub-vectors using the divided plurality of sub triangular matrices.