OFDM modulator and OFDM modulation method for digital modulated wave having guard interval

An orthogonal frequency division multiplex modulator of such a system as to add guard intervals to a temporal waveform generated by modulating an input data train into a large number of carriers, said orthogonal frequency division multiplex modulator comprising:

• an IFFT circuit for conducting inverse fast Fourier transform processing to modulate said input data train into a large number of carriers;
• a guard interval adder for adding a guard interval to each effective symbol duration of a composite carrier signal supplied from said IFFT circuit and outputting a resultant signal;
• a control signal generator for generating, in synchronism with each guard interval of the composite carrier signal supplied from said guard interval adder, such a control signal as to attenuate signal amplitude of said composite carrier signal over an interval substantially equal in length to said each guard interval;
• and
• an amplitude controller responsive to said control signal, to attenuate the amplitude of the composite carrier signal supplied from said guard interval adder and output a resultant signal, only over an interval substantially equal in length to said each guard interval, said amplitude controller outputting, in remaining intervals, said composite carrier signal supplied from said guard interval adder as it is;
• and
• a quadrature processor for conducting quadrature modulation on the signal supplied from said amplitude controller and outputting an OFDM signal.

An orthogonal frequency division multiplex modulation method of such a system as to add guard intervals to a temporal waveform generated by modulating an input data train into a large number of carriers, conducting quadrature modulation, and outputting an OFDM signal, said orthogonal frequency division multiplex modulation method comprising the steps of:

• (a) conducting inverse fast Fourier transform processing to modulate said input data train into a large number of carriers;
• (b) adding a guard interval to each effective symbol duration of a composite carrier signal obtained by said step (a);
• and
• (c) attenuating signal amplitude of said composite carrier signal having the guard intervals added thereto and outputting a resultant signal, only over an interval substantially equal in length to said each guard interval, and outputting, in remaining intervals, said composite carrier signal obtained by said step (b) as it is.