1. A receiver in a MIMO multiplexing communication system in which plural signals are simultaneously transmitted from plural transmitting antenna branches using the same frequency, and the transmitted signals are retrieved by receiving the signals at plural receiving antennas, separating the received signals and searching for proper symbol metrics for each branch, comprising: a QR decomposer for QR decomposing the received signals to orthogonalize the transmitted signals; a symbol replica candidate ranking unit for subtracting surviving symbol replica candidates from the QR decomposed received signals to get remaining received signals and rank the remaining signals in increasing order of expected branch metrics of the remaining received signals; a symbol replica candidate selector for selecting the symbol replica candidates in the ranked order; a branch metric calculator for calculating the branch metrics of the selected symbol replica candidates; and a threshold comparator for comparing the calculated branch metrics with a predetermined threshold; wherein if one of the calculated branch metrics is larger than the predetermined threshold, the one of the branch metrics and successive branch metrics are deleted without further searching.