The method as defined in claim 25 wherein said prescribed criteria includes a first step of determining whether a value of a prescribed relationship of a sequence of said inverse discrete Fourier transform versions {em,k}, for m=0, 1, . . . , (N???1), where N is a number of OFDM sub-carriers and k is a kth OFDM symbol, is at least less than a predetermined threshold value, and when said first step