<p>Assuming that each of subcarriers has an amplitude 1 and carries in-phase data, the envelope waveform of a time axis signal includes guard bands (304) in IDFT process frequency ranges, resulting in being centered on the time zero with side lobes (306) widely spreading as shown in Fig. 3(c). In order to suppress these side lobes (306), the amplitude at the ends of the frequency range of transmission spectrum is smoothly reduced. In this way, the optimization of the spectrum of the auxiliary pilot subcarriers makes it possible to reduce the spread of the waveform on the time axis in a communication apparatus.</p>
