<p>Data pieces representative of in-phase components and quadrature components of a digital-modulation-resultant signal are assigned to frequencies for inverse fast Fourier transform. The inverse fast Fourier transform is executed at a predetermined sampling frequency Fs to convert the data pieces into a real-part signal and an imaginary-part signal. Phases of the real-part signal and the imaginary-part signal are shifted. Each of the phase-shifted real-part signal and the phase-shifted imaginary-part signal is divided into a sequence of even-numbered samples and a sequence of odd-numbered samples. The sequence of the even-numbered samples of the phase-shifted real-part signal is multiplied by "1" to generate a first multiplication-result signal I(2n). The sequence of the even-numbered samples of the phase-shifted imaginary-part signal is multiplied by "-1" to generate a second multiplication-result signal -Q(2n). The sequence of the odd-numbered samples of the phase-shifted real-part signal is multiplied by "-1" to generate a third multiplication-result signal -I(2n+1). The sequence of the odd-numbered samples of the phase-shifted imaginary-part signal is multiplied by "1" to generate a fourth multiplication-result signal Q(2n+1). The first multiplication-result signal I(2n), the second multiplication-result signal -Q(2n), the third multiplication-result signal -I(2n+1), and the fourth multiplication-result signal Q(2n+1) are sequentially selected at a frequency equal to twice the predetermined sampling frequency Fs to generate a digital quadrature-modulation-resultant signal. <IMAGE></p>
