Modulator, demodulator, and transmission system for use in OFDM transmission

An OFDM demodulator for receiving an OFDM signal generated from a plurality of subcarriers modulated with transmitted data for each given-length symbol, said OFDM demodulator comprising:

• Fourier transform means for separating the OFDM signal into the plurality of subcarriers by Fourier transform to generate a first subcarrier signal;
• carrier phase error detecting means for obtaining an amount of phase correction for each of the plurality of subcarriers in the first subcarrier signal based on subcarriers of known phase assigned as pilot carriers to provide phase reference in the first subcarrier signal;
• and
• phase correcting means for correcting a phase of the first subcarrier signal based on the amounts of phase correction to generate a second subcarrier signal,
• wherein the plurality of subcarriers in the OFDM signal are subjected to differential modulation between subcarriers adjacent in frequency direction with reference to the pilot carriers,
• wherein said carrier phase error detecting means comprises:
• pilot carrier extracting means for extracting a pilot carrier from the first subcarrier signal;
• phase calculating means for calculating a phase of the pilot carrier based on the extracted pilot carrier;
• phase change amount calculating means for calculating an amount of phase change from the calculated phase of the pilot carrier;
• and
• phase correction amount calculating means for calculating an amount of phase correction between the plurality of subcarriers based on the calculated amount of phase change, and
• wherein said phase correcting means corrects the phase of the first subcarrier signal based on the calculated amount of phase correction.

An OFDM demodulation method for demodulating an OFDM signal generated from a plurality of subcarriers modulated with transmitted data for each given-length symbol, said OFDM demodulation method comprising:

• separating the OFDM signal into the plurality of subcarriers by Fourier transform to generate a first subcarrier signal;
• obtaining an amount of phase correction for each of the plurality of subcarriers in the first subcarrier signal based on subcarriers of known phase assigned as pilot carriers to provide phase reference in the first subcarrier signal;
• and
• correcting a phase of the first subcarrier signal based on the amounts of phase correction to generate a second subcarrier signal,
• wherein said obtaining of the amount of phase correction comprises:
• detecting locations of the pilot carriers in the first subcarrier signal to generate a pilot carrier location signal;
• extracting a first pilot carrier from the first subcarrier signal based on the pilot carrier location signal;
• holding known pilot carriers and reading a second pilot carrier corresponding to the detected location among the known pilot carriers based on the pilot carrier location signal;
• calculating a phase difference between the first and second pilot carriers to generate a phase difference signal indicating the phase difference;
• calculating an amount of change of phase rotation between transmitting and receiving ends with respect to a carrier frequency based on the phase difference signal and generating a phase difference change signal indicating the amount of change;
• and
• calculating an amount of phase correction for each of the plurality of subcarriers based on the phase difference signal and the phase difference change signal and generating a phase error correcting signal.

An OFDM demodulation method for demodulating an OFDM signal generated from a plurality of subcarriers modulated with transmitted data for each given-length symbol, said OFDM demodulation method comprising:

• separating the OFDM signal into the plurality of subcarriers by Fourier transform to generate a first subcarrier signal;
• obtaining an amount of phase correction for each of the plurality of subcarriers in the first subcarrier signal based on subcarriers of known phase assigned as pilot carriers to provide phase reference in the first subcarrier signal;
• and
• correcting a phase of the first subcarrier signal based on the amounts of phase correction to generate a second subcarrier signal,
• wherein the plurality of subcarriers in the OFDM signal are subjected to differential modulation between subcarriers adjacent in frequency direction with reference to the pilot carriers,
• wherein said obtaining of the amount of the phase correction comprises:
• extracting a pilot carrier from the first subcarrier signal;
• calculating a phase of the pilot carrier based on the extracted pilot carrier;
• calculating an amount of phase change from the calculated phase of the pilot carrier;
• and
• calculating an amount of phase correction between the plurality of subcarriers based on the calculated amount of phase change, and
• wherein the phase of the first subcarrier signal is corrected based on the calculated amount of phase correction in said correcting of the phase.

An OFDM transmission system for transmitting an OFDM signal generated from a plurality of subcarriers modulated with transmitted data for each given-length symbol from a transmitting end to a receiving end through a wired or radio transmission path,

• wherein said transmitting end comprises an OFDM modulator comprising:
• data modulation means for assigning subcarriers of known phase from among a plurality of subcarriers among transmission subcarriers used in the transmission of the OFDM signal as pilot carriers to provide phase reference, and modulating data carriers which are the subcarriers other than the pilot carriers among the transmission subcarriers with the transmitted data;
• and
• OFDM signal generating means for generating the OFDM signal from the transmission subcarriers including the pilot carriers and the data carriers after modulation,
• wherein said receiving end comprises an OFDM demodulator comprising:
• Fourier transform means for separating the OFDM signal into the plurality of subcarriers by Fourier transform to generate a first subcarrier signal;
• phase error calculating means for obtaining an amount of phase correction for each of the plurality of subcarriers in the first subcarrier signal based on subcarriers of known phase assigned as pilot carriers in the first subcarrier signal, and
• phase correcting means for correcting a phase of the first subcarrier signal based on the amounts of phase correction to generate a second subcarrier signal, and
• wherein said phase error calculating means comprises:
• pilot carrier location detecting means for detecting locations of the pilot carriers in the first subcarrier signal to generate a pilot carrier location signal;
• pilot carrier extracting means for extracting a first pilot carrier from the first subcarrier signal based on the pilot carrier location signal;
• a pilot carrier memory operable to hold known pilot carriers and read a second pilot carrier corresponding to the detected location among the known pilot carriers based on the pilot carrier location signal;
• phase difference calculating means for calculating a phase difference between the first and second pilot carriers to generate a phase difference signal indicating the phase difference;
• phase change amount calculating means for calculating an amount of change of phase rotation between transmitting and receiving ends with respect to a carrier frequency based on the phase difference signal and generating a phase difference change signal indicating the amount of change;
• and
• phase correction amount calculating means for calculating an amount of phase correction for each of the plurality of subcarriers based on the phase difference signal and the phase difference change signal and generating a phase error correcting signal.

An OFDM transmission system for transmitting an OFDM signal generated from a plurality of subcarriers modulated with transmitted data for each given-length symbol from a transmitting end to a receiving end through a wired or radio transmission path,

• wherein said transmitting end comprises an OFDM modulator comprising:
• differential modulation means for assigning subcarriers of known phase from among a plurality of subcarriers among transmission subcarriers used in the transmission of the OFDM signal as pilot carriers to provide phase reference, and subjecting the transmission subcarriers to differential modulation between subcarriers adjacent in frequency direction with the transmitted data with reference to the pilot carriers;
• and
• OFDM signal generating means for generating the OFDM signal from the transmission subcarriers after the differential modulation,
• wherein said receiving end comprises an OFDM demodulator comprising:
• Fourier transform means for separating the OFDM signal into the plurality of subcarriers by Fourier transform to generate a first subcarrier signal;
• phase error calculating means for obtaining an amount of phase correction for each of the plurality of subcarriers in the first subcarrier signal based on subcarriers of known phase assigned as pilot carriers in the first subcarrier signal;
• phase correcting means for correcting a phase of the first subcarrier signal based on the amounts of phase correction to generate a second subcarrier signal, and
• differential demodulation means for subjecting the second subcarrier signal to differential demodulation with reference to the pilot carriers to reproduce the transmitted data, and
• wherein said phase error calculating means comprises:
• pilot carrier extracting means for extracting a pilot carrier from the first subcarrier signal;
• phase calculating means for calculating a phase of the pilot carrier based on the extracted pilot carrier;
• phase change amount calculating means for calculating an amount of phase change from the calculated phase of the pilot carrier, and
• phase correction amount calculating means for calculating an amount of phase correction between the plurality of subcarriers based on the calculated amount of phase change, and
• wherein said phase correcting means corrects the phase of the first subcarrier signal based on the calculated amount of phase correction.

An OFDM transmission system for transmitting an OFDM signal generated from a plurality of subcarriers modulated with transmitted data for each given-length symbol from a transmitting end to a receiving end through a wired or radio transmission path,

• wherein said transmitting end comprises an OFDM modulator comprising:
• differential modulation means for assigning subcarriers of known phase from among a plurality of subcarriers among transmission subcarriers used in the transmission of the OFDM signal as pilot carriers to provide phase reference, and subjecting the transmission subcarriers to differential modulation between subcarriers adjacent in frequency direction with the transmitted data with reference to the pilot carriers;
• and
• OFDM signal generating means for generating the OFDM signal from the transmission subcarriers after the differential modulation;
• wherein said receiving end comprises an OFDM demodulator comprising:
• Fourier transform means for separating the OFDM signal into the plurality of subcarriers by Fourier transform to generate a first subcarrier signal;
• inter-carrier phase difference calculating means for calculating a phase difference between the adjacent subcarriers based on the first subcarrier signal;
• phase error calculating means for calculating an amount of phase difference correction which is an amount of correction to the phase difference between the adjacent subcarriers based on the pilot carriers included in the first subcarrier signal;
• and
• phase correcting means for correcting the phase difference between the adjacent subcarriers in accordance with the amount of phase difference correction,
• wherein said phase error calculating means comprises:
• pilot carrier extracting means for extracting a pilot carrier from the first subcarrier signal;
• phase calculating means for calculating a phase of the pilot carrier based on the extracted pilot carrier;
• phase change amount calculating means for calculating an amount of phase change from the calculated phase of the pilot carrier;
• and
• phase correction amount calculating means for calculating an amount of phase correction between the plurality of subcarriers based on the calculated amount of phase change, and
• wherein said phase correcting means corrects the phase difference indicated by an output of said inter-carrier phase difference calculating means based on the calculated amount of phase correction.

An OFDM demodulator for receiving an OFDM signal generated from a plurality of subcarriers modulated with transmitted data for each given-length symbol, said OFDM demodulator comprising:

• subcarrier separating means for separating the OFDM signal into the plurality of subcarriers to generate a first subcarrier signal;
• carrier phase error detecting means for obtaining an amount of phase correction for each of the plurality of subcarriers in the first subcarrier signal based on subcarriers of known phase assigned as pilot carriers to provide phase reference in the first subcarrier signal;
• and
• phase correcting means for correcting a phase of the first subcarrier signal based on the amounts of phase correction to generate a second subcarrier signal,
• wherein said carrier phase error detecting means comprises:
• pilot carrier location detecting means for detecting locations of the pilot carriers in the first subcarrier signal to generate a pilot carrier location signal;
• pilot carrier extracting means for extracting a first pilot carrier from the first subcarrier signal based on the pilot carrier location signal;
• a pilot carrier memory operable to hold known pilot carriers and read a second pilot carrier corresponding to the detected location among the known pilot carriers based on the pilot carrier location signal;
• phase difference calculating means for calculating a phase difference between the first and second pilot carriers to generate a phase difference signal indicating the phase difference;
• phase change amount calculating means for calculating an amount of change of phase rotation between transmitting and receiving ends with respect to a carrier frequency based on the phase difference signal and generating a phase difference change signal indicating the amount of change;
• and
• phase correction amount calculating means for calculating an amount of phase correction for each of the plurality of the subcarriers based on the phase difference signal and the phase difference change signal and generating a phase error correcting signal.

An OFDM demodulation method for demodulating an OFDM signal generated from a plurality of subcarriers modulated with transmitted data for each given-length symbol, said OFDM demodulation method comprising:

• separating the OFDM signal into the plurality of subcarriers to generate a first subcarrier signal;
• obtaining an amount of phase correction for each of the plurality of subcarriers in the first subcarrier signal based on subcarriers of known phase assigned as pilot carriers to provide phase reference in the first subcarrier signal;
• and
• correcting a phase of the first subcarrier signal based on the amounts of phase correction to generate a second subcarrier signal,
• wherein said obtaining of the amount of phase correction comprises:
• detecting locations of the pilot carriers in the first subcarrier signal to generate a pilot carrier location signal;
• extracting a first pilot carrier from the first subcarrier signal based on the pilot carrier location signal;
• holding known pilot carriers and reading a second pilot carrier corresponding to the detected location among the known pilot carriers based on the pilot carrier location signal;
• calculating a phase difference between the first and second pilot carriers to generate a phase difference signal indicating the phase difference;
• calculating an amount of change of phase rotation between transmitting and receiving ends with respect to a carrier frequency based on the phase difference signal and generating a phase difference change signal indicating the amount of change;
• and
• calculating an amount of phase correction for each of the plurality of subcarriers based on the phase difference signal and the phase difference change signal and generating a phase error correcting signal.