A method for determining a validity of samples used to estimate a pre-distortion coefficient by a digital pre-distortion apparatus for compensating for a nonlinearity of a power amplifier, the method comprising: acquiring a predetermined number N, a natural number, of input samples from an input signal (x(n)) to be inputted into the power amplifier; first determining including: classifying the input samples into a plurality of groups based on magnitudes of the input samples thereby generating classified input samples, and determining a validity of the input samples based on a distribution of the classified input samples; and second determining including determining, when the input samples are determined to be valid, the input samples as samples to be inputted to a pre-distortion algorithm for estimating the pre-distortion coefficient, wherein the plurality of groups includes: a first group beyond a predetermined magnitude range, the predetermined magnitude range being between an upper threshold and a lower threshold, and a plurality of second groups, which respectively correspond to a plurality of sub-ranges divided from the predetermined magnitude range, and characterized in that the first determining includes determining that the input samples are valid when a ratio of the number of the input samples in the first group to the predetermined number N is equal to or smaller than a predetermined ratio and when respective ratios of the number of the input samples in each of the second groups to the predetermined number N are within a preset ratio range, wherein, when the input samples are determined to be invalid, deleting some of the input samples, acquiring, from the input signal, as many consecutive input samples as the number of deleted input samples, and classifying the consecutive input samples into the plurality of groups. acquiring a predetermined number N, a natural number, of input samples from an input signal (x(n)) to be inputted into the power amplifier; first determining including: classifying the input samples into a plurality of groups based on magnitudes of the input samples thereby generating classified input samples, and determining a validity of the input samples based on a distribution of the classified input samples; and classifying the input samples into a plurality of groups based on magnitudes of the input samples thereby generating classified input samples, and determining a validity of the input samples based on a distribution of the classified input samples; and second determining including determining, when the input samples are determined to be valid, the input samples as samples to be inputted to a pre-distortion algorithm for estimating the pre-distortion coefficient, wherein the plurality of groups includes: a first group beyond a predetermined magnitude range, the predetermined magnitude range being between an upper threshold and a lower threshold, and a plurality of second groups, which respectively correspond to a plurality of sub-ranges divided from the predetermined magnitude range, and a first group beyond a predetermined magnitude range, the predetermined magnitude range being between an upper threshold and a lower threshold, and a plurality of second groups, which respectively correspond to a plurality of sub-ranges divided from the predetermined magnitude range, and characterized in that the first determining includes determining that the input samples are valid when a ratio of the number of the input samples in the first group to the predetermined number N is equal to or smaller than a predetermined ratio and when respective ratios of the number of the input samples in each of the second groups to the predetermined number N are within a preset ratio range, wherein, when the input samples are determined to be invalid, deleting some of the input samples, acquiring, from the input signal, as many consecutive input samples as the number of deleted input samples, and classifying the consecutive input samples into the plurality of groups.