OFDM receiving apparatus and method of demodulation in OFDM receiving apparatus
An apparatus for receiving an OFDM modulated signal includes: an A/D converter converting the received signal to a digital signal; a quadrature demodulator performing quadrature detection of the digital signal and converting the digital signal to a base-band signal; an FFT circuit transforming the base-band signal to a signal of a frequency domain by performing a fast Fourier transformation; an equalizer equalizing the signal of the frequency domain and obtaining demodulated data; an error correcting circuit performing error correction and decoding the demodulated data obtained by the equalizer; an interference detector detecting a receiving quality for each predetermined frequency band from the demodulated data; and a synchronous sequencer assigning weights to the base-band signal and the signal of the frequency domain based on the receiving quality data, and reproducing a timing synchronized signal and a clock pulse required for the demodulation.
1. An apparatus for receiving an Orthogonal Frequency Division Multiplex (OFDM) modulated signal, the apparatus comprising:
an A/D converter converting the received signal to a digital signal;
a quadrature demodulator performing a quadrature detection of the digital signal converted by the A/D converter and converting the digital signal to a base-band signal of a time domain;
a fast Fourier transform circuit transforming the base-band signal converted by the quadrature demodulator to a signal of a frequency domain by performing a fast Fourier transformation;
an equalizer equalizing the signal of the frequency domain transformed by the fast Fourier transform circuit and obtaining demodulated data;
an error correcting circuit performing an error correction and decoding the demodulated data obtained by the equalizer;
an interference detector detecting a receiving quality for each predetermined frequency band from the demodulated data obtained by the equalizer; and
a synchronous sequencer assigning weights to the base-band signal of the time domain outputted from the quadrature demodulator and the signal of the frequency domain outputted from the fast Fourier transform circuit, based on the receiving quality detected in the interference detector, and reproducing a timing synchronized signal and a clock pulse required for the demodulation of the receiving signals.
2. The apparatus of claim 1 , wherein the synchronous sequencer detects an error in carrier frequency from the base-band signal of the time domain and the signal of the frequency domain, and supplies a frequency control signal, which cancels the detected frequency error, to the quadrature demodulator.
3. The apparatus of claim 1 , further comprising a common phase error elimination circuit assigning weights to the signal of the frequency domain transformed by the fast Fourier transform circuit for each the predetermined frequency band based on the receiving quality, detecting a common phase error in each sub-carrier, and performing a phase rotation to eliminate the common phase error from the signal of the frequency domain.
4. The apparatus of claim 3 , wherein the common phase error elimination circuit performs delay detection on the signal of the frequency domain, extracts the sub-carrier of a pilot signal from the signal of the frequency domain performed by the delay detection, assigns weights to the sub-carriers of the pilot signal based on the receiving quality detected by the interference detector and determines the average of internal-symbol, detects the common phase error based on the determined average value, and performs the phase rotation to eliminate the common phase error from the signal of the frequency domain.
5. The apparatus of claim 3 , wherein the interference detector detecting the receiving quality for each the predetermined frequency band from the signal of the frequency domain transformed by the fast Fourier transform circuit.
6. The apparatus of claim 5 , further comprising an interference elimination filter modifying a frequency band-pass for outputting the signal of the time domain, outputted from the quadrature demodulator to the synchronous sequencer, based on the receiving quality detected by the interference detector.
7. The apparatus of claim 6 , wherein the interference elimination filter rejects signals in a frequency band in which the interference detected by the interference detector exists.
8. The apparatus of claim 5 , wherein the interference detector detects variance information from a predetermined reference signal point for each sub-carrier and generates a weighting coefficient as the receiving quality based on the variance information.
9. The apparatus of claim 8 , wherein the interference detector includes:
a variance detector detecting the variance information from the predetermined reference signal point for each of the sub-carriers;
an average value detector calculating the average value of the variance information for each of the sub-carriers; and
an interference carrier detector generating the receiving quality from the variance information and the average value for each the sub-carrier.
10. The apparatus of claim 3 , further comprising an interference elimination filter modifying a frequency band-pass for outputting the signal of the time domain, outputted from the quadrature demodulator to the synchronous sequencer, based on the receiving quality detected by the interference detector.
11. The apparatus of claim 10 , wherein the interference elimination filter rejects signals in a frequency band in which the interference detected by the interference detector exists.
12. The apparatus of claim 3 , wherein the interference detector detects variance information from a predetermined reference signal point for each sub-carrier and generates a weighting coefficient as the receiving quality based on the variance information.
13. The apparatus of claim 12 , wherein the interference detector includes:
a variance detector detecting the variance information from the predetermined reference signal point for each of the sub-carriers;
an average value detector calculating the average value of the variance information for each of the sub-carriers; and
an interference carrier detector generating the receiving quality from the variance information and the average value for each the sub-carrier.
14. The apparatus of claim 1 , further comprising an interference elimination filter modifying a frequency band-pass for outputting the signal of the time domain, outputted from the quadrature demodulator to the synchronous sequencer, based on the receiving quality detected by the interference detector.
15. The apparatus of claim 14 , wherein the interference elimination filter rejects signals in a frequency band in which the interference detected by the interference detector exists.
16. The apparatus of claim 14 , wherein the interference detector detects variance information from a predetermined reference signal point for each sub-carrier and generates a weighting coefficient as the receiving quality based on the variance information.
17. The apparatus of claim 16 , wherein the interference detector includes:
a variance detector detecting the variance information from the predetermined reference signal point for each of the sub-carriers;
an average value detector calculating the average value of the variance information for each of the sub-carriers; and
an interference carrier detector generating the receiving quality from the variance information and the average value for each the sub-carrier.
18. The apparatus of claim 1 , wherein the interference detector detects variance information from a predetermined reference signal point for each sub-carrier and generates a weighting coefficient as the receiving quality based on the variance information.
19. The apparatus of claim 18 , wherein the interference detector includes:
a variance detector detecting the variance information from the predetermined reference signal point for each of the sub-carriers;
an average value detector calculating the average value of the variance information for each of the sub-carriers; and
an interference carrier detector generating the receiving quality from the variance information and the average value for each the sub-carrier.
20. A method of demodulation in an apparatus for receiving an Orthogonal Frequency Division Multiplex (OFDM) modulated signal, the method comprising:
converting the received signal to a digital signal;
performing a quadrature detection on the digital signal and converting the digital signal to a base-band signal of a time domain;
transforming the base-band signal to a signal of a frequency domain by performing a fast Fourier transformation;
equalizing the signal of the frequency domain and obtaining demodulated data;
performing an error correction and decoding the demodulated data;
detecting a receiving quality for each predetermined frequency band from the demodulated data; and
assigning weights to the base-band signal of the time domain and the signal of the frequency domain based on the receiving quality, and reproducing a timing synchronized signal and a clock pulse required for the demodulation of the receiving signals.
21. The method of claim 20 , further comprising assigning weights to the signal of the frequency domain for each the predetermined frequency band based on the receiving quality, detecting a common phase error in each sub-carrier, and performing a phase rotation to eliminate the common phase error from the signal of the frequency domain.
22. The method of claim 21 , wherein in the reproduction of the timing synchronized signal and the clock pulse, signals in a frequency band in which the interference exists are eliminated from the base-band signal of the time domain with an interference elimination filter to modify a frequency band-pass based on the receiving quality.
23. The method of claim 20 , wherein in the reproduction of the timing synchronized signal and the clock pulse, signals in a frequency band in which the interference exists are eliminated from the base-band signal of the time domain with an interference elimination filter to modify a frequency band-pass based on the receiving quality.