1. A signal detection method executed by a processor provided in a receiver of a multiple-input multiple-output system, comprising: dividing a constellation set into a plurality of subsets by grouping the constellation set; dividing a tree search process of a QR-decomposition with M-algorithm (QRDM) algorithm into a plurality of partial detection phases based on the grouped constellation set; and performing the plurality of partial detection phases in parallel, wherein each of the partial detection phases calculates a distance of each branch and calculates minimum accumulated distance per partial detection phase or performing plurality of partial detection phases iteratively, wherein at each detecting level, optimal estimated signals and the accumulated distances of the corresponding estimated signals are obtained wherein dividing the constellation set into the plurality of subsets divides the constellation set into a plurality of subsets having same cardinality by continuous or dispersive grouping.