OFDM receiver using polar coordinate system and method thereof
A received signal is converted into a digital signal through an A/D converter and then converted into the polar coordinate system. A synchronizer removes a frequency offset from the digital signal, the digital signal is again converted into an orthogonal coordinate system and a fast fourier transform is performed with a FFT. The digital signal is again converted into the polar coordinate system. An equalizer and a phase compensator compensate respectively a channel distortion and a phase error to the digital signal. Thus, the OFDM receiver using polar coordinate system and method thereof of the present invention can reduce the number of adders and multipliers required in a frequency synchronization, a compensation for channel influence, and a removal of remaining phase error by processing the signal in the polar coordinate system, thereby simplifying the calculation process and the receiver.
1. An orthogonal frequency division multiplexing (OFDM) receiver comprising:
an A/D converter for converting an input analog signal into a digital signal;
a first converter for converting the digital signal input from the A/D converter into a polar coordinate system;
a synchronizer for compensating a frequency offset of the digital signal input from the first converter;
a second converter for converting the digital signal input from the synchronizer into an orthogonal coordinate system;
a FFT for carrying out a fast fourier transform on the digital signal input from the second converter;
an equalizer for compensating a channel distortion of the digital signal input from the FFT; and
a phase compensator for compensating a phase error remaining in the digital signal input from the equalizer.
2. The OFDM receiver according to claim 1 , wherein the synchronizer comprises:
a frequency offset estimator for estimating the frequency offset from the phases of a plurality of phase estimation signals and converting the estimated frequency offset into a phase value; and
a frequency offset corrector for compensating a frequency offset of the digital signal input from the first converter according to the estimated frequency offset.
3. The OFDM receiver according to claim 2 , further comprising a memory for storing a lookup table in which a phase for each frequency offset is recorded,
wherein the frequency offset estimator reads out a phase corresponding to the estimated frequency offset from the lookup table to convert it into the phase read out.
4. The OFDM receiver according to claim 1 , further comprising:
a guard interval remover for removing a guard interval from the digital signal input from the synchronizer.
5. The OFDM receiver according to claim 4 , further comprising a third converter for converting the digital signal input from the FFT into the polar coordinate system and outputting the converted digital signal to the equalizer.
6. The OFDM receiver according to claim 5 , further comprising a fourth converter for converting the digital signal input from the phase compensator into the orthogonal coordinate system.
7. The OFDM receiver according to claim 5 , wherein the equalizer comprises:
a channel distortion estimator for estimating a channel distortion value from magnitudes and phases of the digital signal input from the FFT and outputting the estimated channel distortion value in a magnitude and a phase; and
a channel distortion corrector for compensating a channel distortion of the digital signal input in the polar coordinate system according to the estimated channel distortion value.
8. The OFDM receiver according to claim 7 , further comprising a memory for storing a lookup table in which a phase for each channel distortion value is recorded,
wherein the channel distortion estimator reads out a phase corresponding to the estimated channel distortion value from the lookup table to convert it into the phase read out.
9. The OFDM receiver according to claim 7 , wherein the channel distortion corrector comprises:
a channel distortion magnitude correcting portion for correcting a magnitude of the digital signal according to the channel distortion of the digital signal by multiplying the magnitude of the digital signal input in the polar coordinate system by the magnitude of the estimated channel distortion value; and
a channel distortion phase correcting portion for correcting a phase of the digital signal according to the channel distortion of the digital signal by adding the phase of the estimated channel distortion value to the phase of the digital signal input in the polar coordinate system.
10. The OFDM receiver according to claim 5 , wherein the phase compensator comprises:
a phase error estimator for estimating a phase error remaining in the digital signal by phases of a plurality of phase estimation signals; and
a phase error corrector for compensating a phase error remaining in the digital signal input in the polar coordinate system according to the estimated phase error.
11. The OFDM receiver according to claim 10 , further comprising a memory for storing a lookup table in which a phase for each phase error is recorded,
wherein the phase error estimator reads out a phase corresponding to the estimated phase error from the lookup table to convert it into a phase read out.
12. An OFDM receiver comprising:
a FFT for carrying out a fast fourier transform on a digital signal;
a first converter for converting the digital signal input from the FFT into a polar coordinate system;
an equalizer for compensating a channel distortion to the digital signal in the polar coordinate system; and
a phase compensator for compensating a phase error remaining in the digital signal input from the equalizer.
13. The OFDM receiver according to claim 12 , further comprising a second converter for converting the digital signal input from the phase compensator into an orthogonal coordinate system.
14. The OFDM receiver according to claim 12 , wherein the equalizer comprises:
a channel distortion estimator for estimating a channel distortion value from magnitudes and phases of the digital signal and outputting the estimated channel distortion value in a magnitude and a phase; and
a channel distortion corrector for compensating a channel distortion of the digital signal input in the polar coordinate system according to the estimated channel distortion value.
15. The OFDM receiver according to claim 14 , further comprising a memory for storing a lookup table in which a phase for each channel distortion value is recorded,
wherein the channel distortion estimator reads out a phase corresponding to the estimated channel distortion value from the lookup table to convert it into the phase read out.
16. The OFDM receiver according to claim 14 , wherein the channel distortion corrector comprises:
a channel distortion magnitude correcting portion for correcting a magnitude of the digital signal according to the channel distortion of the digital signal by multiplying the magnitude of the digital signal input in the polar coordinate system by the magnitude of the estimated channel distortion value; and
a channel distortion phase correcting portion for correcting a phase of the digital signal according to the channel distortion of the digital signal by adding the phase of the estimated channel distortion value to the phase of the digital signal input in the polar coordinate system.
17. The OFDM receiver according to claim 12 , wherein the phase compensator comprises:
a phase error estimator for estimating a phase error remaining in the digital signal by phases of a plurality of phase estimation signals; and
a phase error corrector for compensating a phase error remaining in the digital signal input in the polar coordinate system according to the estimated phase error.
18. The OFDM receiver according to claim 17 , further comprising a memory for storing a lookup table in which a phase for each phase error is recorded,
wherein the phase error estimator reads out a phase corresponding to the estimated phase error from the lookup table to convert it into a phase read out.
19. An OFDM receiving method, comprising the steps of:
converting a received analog signal into a digital signal;
converting the digital signal from an orthogonal coordinate system to a polar coordinate system;
compensating a frequency offset of the digital signal having the polar coordinate system;
converting the digital signal, in which the frequency offset is compensated, from the polar coordinate system to the orthogonal coordinate system;
carrying out a fourier transform to the digital signal converted to the orthogonal system; and
correcting a signal error remaining in the fourier transformed digital signal.
20. The OFDM receiving method according to claim 19 , wherein the compensating step comprises the sub-steps of:
(a) receiving estimation signals to estimate a frequency offset;
(b) converting the estimated frequency offset into a phase; and
(c) correcting a frequency offset of the digital signal by adding the frequency offset converted into a phase to a phase of the digital signal having the polar coordinate system.
21. The OFDM receiving method according to claim 20 , wherein the step (b) reads out a phase corresponding to the estimated frequency offset from a lookup table in which a phase for each frequency offset is recorded, and converts the estimated frequency offset into a phase.
22. The OFDM receiving method according to claim 19 , further comprising the steps of:
converting the digital signal from the orthogonal coordinate system to the polar coordinate system after carrying out the fourier transform;
compensating a channel distortion of the digital signal in the polar coordinate system; and
compensating a phase error remaining in the digital signal in the polar coordinate system.
23. An OFDM receiving method, comprising the steps of:
carrying out a fourier transform on a digital signal in an orthogonal coordinate system;
converting the fourier transformed digital signal into a polar coordinates system;
compensating a channel distortion of the digital signal in the polar coordinate system; and
compensating a phase error remaining in the digital signal in the polar coordinate system.