Methods and apparatus for reducing peak-to-RMS amplitude ratio in communication signals

1. A pulse amplitude modulated (PAM) signal generator comprising:

a modulator operable to generate a PAM baseband signal; and, a pulse injector operable to form a pulse and add the formed pulse into the PAM baseband signal at a time interval in which an amplitude of the PAM baseband signal exceeds a predetermined threshold to create a modified baseband signal.

2. The generator of claim 1 wherein the formed pulse, when added to the PAM baseband signal, serves to reduce a peak amplitude to RMS amplitude ratio without substantially degrading a power spectral density.

3. The generator of claim 1 wherein said pulse injector comprises:

a signal analyzer configured to analyze the PAM baseband signal to determine if the predetermined threshold has been exceeded and produces an output having an amplitude-scaling and phase-shifting parameter applied to the pulse;

a pulse-shaping filter configured to filter with an impulse response the output having the amplitude-scaling and phase-shifting parameter to output the formed pulse; and,

an adder configured to add the formed pulse of the filter to the PAM baseband signal.

4. The generator of claim 3 wherein the signal analyzer comprises:

a threshold detector configured to detect when the predetermined threshold is exceeded;

a phase angle measurer configured to measure a phase angle θ m of the PAM baseband signal at a point in time when the threshold is exceeded;

an amplitude measurer configured to measure an amplitude c m of the PAM baseband signal; and,

an amplitude-scaling and phase-shifting calculator configured to compute the amplitude-scaling and phase-shifting parameter for the pulse using the phase angle θ m and amplitude c m .

5. The generator of claim 1 wherein the formed pulse, when added to the PAM baseband signal, serves to reduce a peak amplitude to RMS amplitude ratio without substantially degrading a power spectral density of the signal and while substantially maintaining an in-band measure of signal quality.

6. The generator of claim 1 , further comprising

a frequency upconverter and amplifier stage configured to upconvert and amplify the modified baseband signal.

7. The generator of claim 1 wherein a perturbation sequence representing amplitude-scaling and phase-shifting is applied to the pulse so that when the pulse is added to the PAM baseband signal, the amplitude is reduced to a desired peak amplitude during the time interval.

8. A pulse amplitude modulated (PAM) signal generator comprising:

means for modulating a signal into a PAM baseband signal; and,

means for forming a pulse and adding the formed pulse into the PAM baseband signal at a time interval in which an amplitude of the PAM baseband signal exceeds a predetermined threshold to create a modified baseband signal.

9. The generator of claim 8 wherein the formed pulse, when added to the PAM baseband signal, serves to reduce a peak amplitude to RMS amplitude ratio without substantially degrading a power spectral density.

10. The generator of claim 8 wherein the pulse forming and adding means comprises:

means for analyzing the PAM baseband signal to determine if the predetermined threshold has been exceeded and produce an output having an amplitude-scaling and phase-shifting parameter applied to the pulse;

means for filtering with an impulse response the output having the amplitude-scaling and phase-shifting parameter to output the formed pulse; and,

means for adding the formed pulse to the PAM baseband signal.

11. The generator of claim 10 wherein the analyzing means comprises:

means for detecting when the predetermined threshold is exceeded;

means for measuring a phase angle θm of the PAM baseband signal at a point in time when the threshold is exceeded;

means for measuring an amplitude c m of the PAM baseband signal; and,

means for computing the amplitude-scaling and phase-shifting parameter for the pulse using the phase angle θ m and amplitude c m .

12. The generator of claim 8 wherein the formed pulse, when added to the PAM baseband signal serves to reduce a peak amplitude to RMS amplitude ratio without substantially degrading a power spectral density of the signal and while substantially maintaining an in-band measure of signal quality.

13. The generator of claim 8 , further comprising means for frequency upconverting and amplifying the modified baseband signal.

14. A method for generating a pulse amplitude modulated (PAM) signal comprising:

modulating a signal into a PAM baseband signal;

forming a pulse that is a copy of a pulse in the PAM baseband signal; and,

adding the formed pulse into the PAM baseband signal at a time interval in which an amplitude of the PAM baseband signal exceeds a predetermined threshold to create a modified baseband signal.

15. The method of claim 14 wherein forming a copy of a pulse in the PAM baseband signal comprises:

forming the pulse to reduce a peak amplitude to RMS amplitude ratio without substantially degrading a power spectral density.

16. The method of claim 14 wherein forming the pulse comprises:

analyzing the PAM baseband signal to determine if the predetermined threshold has been exceeded;

producing and applying an amplitude-scaling and phase-shifting parameter to the pulse and forming an output; and,

filtering with an impulse response the output having the amplitude-scaling and phase-shifting parameter to output the formed pulse.

17. The method of claim 16 wherein analyzing the PAM baseband signal comprises:

detecting when the predetermined threshold is exceeded;

measuring a phase angle θ m of the PAM baseband signal at a point in time when the threshold is exceeded;

measuring an amplitude c m of the PAM baseband signal; and

computing the amplitude-scaling and phase-shifting parameter for the pulse using the phase angle θ m and amplitude c m .

18. The method of claim 14 wherein forming a copy of a pulse in the PAM baseband signal comprises:

forming the pulse so that when added to the PAM baseband signal, said pulse serves to reduce a peak amplitude to RMS amplitude ratio without substantially degrading a power spectral density and substantially maintaining an in-band measure of signal quality.

19. The method of claim 14 , further comprising:

frequency upconverting the modified baseband signal; and

amplifying the frequency upconverted signal.

20. The method of claim 14 wherein adding the formed pulse into the PAM baseband signal comprises applying a perturbation sequence representing amplitude-scaling and phase-shifting to the pulse so that when the pulse is added to the PAM baseband signal, the amplitude is reduced to a desired peak amplitude during the time interval.