OFDM transmitter device having a symbol generator for generating non-zero control symbols, and OFDM transmission method including generating non-zero control symbols

1. An OFDM receiver for receiving a signal transmitted from an OFDM transmitter, the OFDM receiver comprising:

a receiver that, in operation, receives the signal, the signal carrying a frame including a plurality of control symbols transmitted successively and a plurality of other symbols following the plurality of control symbols, the plurality of control symbols including a first control symbol allocated at the beginning of the frame and a second control symbol allocated immediately after the first control symbol, a time-domain signal of the first control symbol including a first useful symbol part and a first guard interval part, the first guard interval part being identical to at least a portion of the first useful symbol part which has been frequency-shifted by a first non-zero frequency-shift amount and a time-domain signal of the second control symbol including a second useful symbol part and a second guard interval part, the second guard interval part being identical to at least a portion of the second useful symbol part which has been frequency-shifted by a second non-zero frequency-shift amount, the first non-zero frequency-shift amount being different from the second non-zero frequency-shift amount;

a first demodulator that, in operation, (i) performs a first frequency shift procedure on the received signal using a third non-zero frequency-shift amount, the third non-zero frequency-shift amount having an identical absolute value as the first non-zero frequency-shift amount, and the third non-zero frequency-shift amount having a different sign from the first non-zero frequency-shift amount, (ii) detects the first control symbol as the head of the frame by using the received signal and the received signal on which the first frequency shift procedure has been performed, and (iii) decodes the first control symbol to obtain first control information;

a second demodulator that, in operation, (i) performs a second frequency shift procedure on the received signal using a fourth non-zero frequency-shift amount, the fourth non-zero frequency-shift amount having an identical absolute value as the second non-zero frequency-shift amount, the fourth non-zero frequency-shift amount having a different sign from the second non-zero frequency-shift amount, and the fourth non-zero frequency-shift amount being different from the third non-zero frequency-shift amount, (ii) detects the second control symbol using the received signal and the received signal on which the second frequency shift procedure has been performed, and (iii) decodes the second control symbol to obtain second control information, the second control information being different from the first control information; and

a third demodulator that, in operation, demodulates the plurality of other symbols by using the obtained first control information and the obtained second control information.

2. An OFDM reception method executed by an OFDM receiver for receiving a signal transmitted from an OFDM transmitter, the OFDM reception method comprising:

receiving the signal, the signal carrying a frame including a plurality of control symbols transmitted successively and a plurality of other symbols following the plurality of control symbols, the plurality of control symbols including a first control symbol allocated at the beginning of the frame and a second control symbol allocated immediately after the first control symbol, a time-domain signal of the first control symbol including a first useful symbol part and a first guard interval part, the first guard interval part being identical to at least a portion of the first useful symbol part which has been frequency-shifted by a first non-zero frequency-shift amount and a time-domain signal of the second control symbol including a second useful symbol part and a second guard interval part, the second guard interval part being identical to at least a portion of the second useful symbol part which has been frequency-shifted by a second non-zero frequency-shift amount, the first non-zero frequency-shift amount being different from the second non-zero frequency-shift amount;

performing a first frequency shift procedure on the received signal using a third non-zero frequency-shift amount, the third non-zero frequency-shift amount having an identical absolute value as the first non-zero frequency-shift amount, and the third non-zero frequency-shift amount having a different sign from the first non-zero frequency-shift amount;

detecting the first control symbol as the head of the frame using the received signal and the received signal on which the first frequency shift procedure has been performed;

decoding the first control symbol to obtain first control information;

performing a second frequency shift procedure on the received signal using a fourth non-zero frequency-shift amount, the fourth non-zero frequency-shift amount having an identical absolute value as the second non-zero frequency-shift amount, the fourth non-zero frequency-shift amount having a different sign from the second non-zero frequency-shift amount, and the fourth non-zero frequency-shift amount being different from the third non-zero frequency-shift amount;

detecting the second control symbol using the received signal and the received signal on which the second frequency shift procedure has been performed;

decoding the second control symbol to obtain second control information, the second control information being different from the first control information; and

demodulating the plurality of other symbols by using the obtained first control information and the obtained second control information.