Peak-to-average power reduction for FM OFDM transmission
View Patent ↗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.
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;
averaging the constrained data symbol vectors and the distorted input symbol vectors to produce averaged constrained data symbol vectors; and
remodulating the averaged constrained data symbol vectors.
2. The method of claim 1 , wherein all of 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. 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;
remodulating the constrained data symbol vectors;
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 steps 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 , wherein the step of constraining out-of-band spectral components to lie within a predetermined mask limits the magnitude of the out-of-band components to a non-zero magnitude.
15. The method of claim 1 , wherein the average is a weighted average.
16. 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;
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, for constraining out-of-band spectral components to lie within a predetermined mask, and for averaging the constrained data symbol vectors and the distorted input symbol vectors to produce averaged constrained data symbol vectors; and
a remodulator for remodulating the averaged 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, for constraining out-of-band spectral components by limiting the magnitude of the out-of-band components to a non-zero magnitude of a predetermined mask, and averaging the constrained data symbol vectors and the distorted input symbol vectors to produce averaged constrained data symbol vectors; and
means for remodulating the averaged constrained data symbol vectors.