Peak-to-average power reduction for FM OFDM transmission

• US 20050169411A1
• Filed: 02/02/2004
• Published: 08/04/2005
• Est. Priority Date: 02/02/2004
• Status: Active Grant

• Current Assignee: iBiquity Digital Corporation (Adeia Inc.)
• Original Assignee: iBiquity Digital Corporation (Adeia Inc.)
• Inventors: Kroeger, Brian William
• Granted Patent: US 7,542,517 B2
• Time in Patent Office: Days
• US Class Current: 375/350
• CPC Class Codes: H04L 27/2623 Reduction thereof by clipping
• CPC Class Codes: H04L 27/2624 by soft clipping
• CPC Class Codes: H04L 27/2626 Arrangements specific to the transmitter only

Abstract

A method of reducing peak-to-average power ratio in an OFDM signal comprises the steps of modulating a set of subcarriers with a set of data symbol vectors to produce a first modulated signal, limiting the magnitude of the first modulated signal to produce a first limited modulated signal, demodulating the first limited modulated signal to recover distorted input symbol vectors, constraining the distorted input symbol vectors to values greater than or equal to a minimum threshold value to produce constrained data symbol vectors, constraining out-of-band spectral components to lie within a predetermined mask, and remodulating the constrained data symbol vectors. A transmitter that performs the method is also included.

Claims

1. A method of reducing peak-to-average power ratio in an OFDM signal, the method comprising the steps of:

modulating a set of subcarriers with a set of data symbol vectors to produce a first modulated signal;

limiting the magnitude of the first modulated signal to produce a first limited modulated signal;

demodulating the first limited modulated signal to recover distorted input symbol vectors;

constraining the distorted input symbol vectors to values greater than or equal to a minimum threshold value to produce constrained data symbol vectors;

constraining out-of-band spectral components to lie within a predetermined mask; and

remodulating the constrained data symbol vectors.

2. The method of claim 1, wherein the steps of claim 1 are repeated to further reduce peak to average power ratio of the OFDM signal.

3. The method of claim 1, wherein the step of constraining the distorted input symbol vectors comprises the step of:

assigning the threshold value to bits of the distorted input vector having values less than the threshold value.

4. The method of claim 1, wherein the step of constraining the out-of-band spectral components further comprises the step of:

applying the mask to nonactive subcarriers.

5. The method of claim 1, further comprising the steps of:

equalizing the set of data symbol vectors prior to the modulating step;

removing equalization of the set of data symbol vectors following the demodulating step; and

restoring equalization of the set of data symbol vectors prior to the remodulating step.

6. The method of claim 5, wherein the equalizing step uses a vector containing the reciprocal of the complex output gain for each subcarrier.

7. The method of claim 6, further comprising the step of:

adaptively updating the equalization vector.

8. The method of claim 1, further comprising the step of:

compensating the first modulated signal for amplitude and phase modulation distortion.

9. The method of claim 1, wherein the step of modulating a set of subcarriers with a set of data symbol vectors, comprises the steps of:

passing the data symbol vectors through an inverse fast Fourier transform; and

applying a cyclic prefix, a guard band, and a raised root cosine window to the modulated signal.

10. The method of claim 9, wherein the demodulating step comprises the steps of:

weighting and folding the cyclic prefix; and

computing the fast Fourier transform of the data symbol vectors.

11. The method of claim 1, wherein the limiting step comprises soft clipping or compression modeling.

12. The method of claim 1, wherein the step of constraining the distorted input symbol vectors comprises the step of:

placing a minimum value on real and imaginary components of the symbol vectors.

13. The method of claim 1, wherein the set of subcarriers include data subcarriers and reference subcarriers, and the step of constraining the distorted input symbol vectors comprises the step of:

placing a minimum value on real and imaginary components of the symbol vectors carried on the data subcarriers; and

correcting real and imaginary components of the symbol vectors carried on the reference subcarriers.

14. The method of claim 1, further comprising the step of:

averaging the constrained data symbol vectors and the distorted input symbol vectors.

15. The method of claim 14, wherein the average is a weighted average.

16. The method of claim 1, wherein the OFDM signal includes reference subcarriers and the method further comprises the step of:

restoring reference signals on the reference subcarriers to original values of the reference signals.

17. A transmitter for reducing peak-to-average power ratio in an OFDM signal, the transmitter comprising:

a modulator for modulating a set of subcarriers with a set of data symbol vectors to produce a first modulated signal;

a limiter for limiting the magnitude of the first modulated signal to produce a first limited modulated signal;

a demodulator for demodulating the first limited modulated signal to recover distorted input symbol vectors;

a processor for constraining the distorted input symbol vectors to values greater than or equal to a minimum threshold value to produce constrained data symbol vectors, and for constraining out-of-band spectral components to lie within a predetermined mask; and

a remodulator for remodulating the constrained data symbol vectors.

18. The transmitter of claim 17, further comprising:

an equalizer for equalizing the set of data symbol vectors prior to the modulating step.

19. The transmitter of claim 17, further comprising:

a compensator for compensating the first modulated signal for amplitude and phase modulation distortion.

20. A transmitter for reducing peak-to-average power ratio in an OFDM signal, the transmitter comprising:

means for modulating a set of subcarriers with a set of data symbol vectors to produce a first modulated signal;

means for limiting the magnitude of the first modulated signal to produce a first limited modulated signal;

means for demodulating the first limited modulated signal to recover distorted input symbol vectors;

means for constraining the distorted input symbol vectors to values greater than or equal to a minimum threshold value to produce constrained data symbol vectors, and for constraining out-of-band spectral components to lie within a predetermined mask; and

means for remodulating the constrained data symbol vectors.