1. A maximum likelihood detection method, comprising: processing received data to obtain preliminary parameters; determining an initial radius r; multiplying r 2 by a corresponding scaling factor according to a partial Euclidean distance (PED) constraint function to determine the upper limit values of PED for each layer; and examining whether a sub-lattice exceeds a search scope according to the upper limit values of PED for each layer to search a better solution by utilizing the preliminary parameters.