Peak power reduction using windowing and filtering

• US 7,013,161 B2
• Filed: 09/24/2002
• Issued: 03/14/2006
• Est. Priority Date: 09/24/2002
• Status: Expired due to Fees

• Current Assignee: Blackberry Limited
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Morris, Bradley John
• Primary Examiner(s): Corsaro, Nick
• Assistant Examiner(s): PHU, SANH D
• Application Number:
  US10/254,499
• Publication Number:
  US 20040203430A1
• Time in Patent Office: 1,267 Days
• Field of Search: 455/522, 455/108, 455/69, 455/571, 455/126, 455/127.1, 375/285, 375/261, 375/296, 375/297, 375/298
• US Class Current: 455/522
• CPC Class Codes: H03G 7/002 in untuned or low-frequency amplifiers, e.g. audio amplifiers H03G7/007, H03G7/001, H03G7/008, H03G7/02, H03G7/06 take precedence
• CPC Class Codes: H03G 7/007 of digital or coded signals
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 2201/70706 with means for reducing the peak-to-average power ratio
• CPC Class Codes: H04L 27/2624 by soft clipping

Abstract

Large signal peaks (for example, peaks 105 and 110) can dramatically increase the cost of a communications device by requiring high grade power amplifiers. Peak reduction can reduce the large peaks at a cost of increasing spurious emissions. A circuit (for example, circuit 500) combining a scaling window peak reducing unit (for example, unit 507) and a filter (for example, filter 509) can effectively reduce the signal peaks without significantly increasing spurious emissions.

Claims

1. A method for peak power reduction comprising:

measuring an input signal;

detecting a signal peak with a magnitude exceeding a specified threshold;

centering a scaling window on the detected signal peak;

adjusting the scaling window based on a magnitude of the detected signal peak, wherein the scaling window is adjusted according to the following expression;

$\mathrm{adjusted\_scaling}<br><br>\mathrm{\_window}=\mathrm{scaling\_window}<br><br>\left(1-\frac{1}{\sqrt{\mathrm{peak\_mag}}}\right)$

wherein peak mag is the magnitude of the detected signal peak; and

multiplying the detected signal peak with the adjusted scaling window to reduce the detected signal peak in the input signal via the scaling window.

2. The method of claim 1, wherein the reducing step further comprises the step of normalizing the specified threshold to 1 prior to the adjusting step.

3. The method of claim 1, wherein the detected signal peak is at or near a local maximum.

4. The method of claim 1, wherein the scaling window has an odd number of samples.

5. The method of claim 4, wherein the scaling window is a Gaussian scaling window.

6. The method of claim 4, wherein the scaling window is a Hanning scaling window.

7. The method of claim 4, wherein the scaling window is a Hamming scaling window.

8. The method of claim 1, further comprising filtering the peak reduced input signal.

9. A circuit comprising:

a peak detector having an input coupled to a signal input line, the peak detector containing circuitry to detect signal peaks exceeding a specified threshold;

a scaling window adjustor circuit having an input coupled to the peak detector, the scaling window adjustor circuit containing circuitry to adjust a scaling window based on a signal peak magnitude provided by the peak detector, wherein the scaling window adjustor circuit comprises;

a window scaling function unit coupled to the peak detector, the window scaling function unit containing circuitry to compute a scaling window adjust factor based on the signal peak magnitude provided by the peak detector;

a counter coupled to a second output of the peak detector, the counter to count a specified interval that is a function of a length of the scaling window;

a memory coupled to the counter, the memory to store the scaling window; and

a multiplier having a first input coupled to the window scaling function unit and a second input coupled to the memory, the multiplier to multiply the scaling window with the window adjust factor; and

an output to provide the adjusted scaling window.

10. The circuit of claim 9, wherein the peak detector detects localized signal peaks that exceed the specified threshold.

11. The circuit of claim 9, further comprising a summing block coupled to the multiplier, the summing block to subtract the output of the multiplier from a fixed value, one.

12. The circuit of claim 9, wherein a scaling window adjust factor is computed using the following mathematical expression:

$1-\frac{1}{\sqrt{\mathrm{peak\_mag}}}$

wherein peak_mag is the signal peak magnitude provided by the peak detector.

13. The circuit of claim 9, wherein the specified interval is an interval specified as [0, Scaling_Window_Length−

1], where Scaling_Window_Length is the length of the scaling window.

14. The circuit of claim 9, wherein the specified interval is an interval specified as [1, Scaling_Window_Length], where Scaling_Window_Length is the length of the scaling window.

15. The circuit of claim 9, wherein the circuit outputs the adjusted scaling window only when the peak detector detects a signal peak exceeding the specified threshold.

16. The circuit of claim 15, wherein the circuit outputs a one (1) value at all other times.

17. A peak reduction circuit comprising:

a signal power calculator coupled to a signal input, the signal power calculator containing circuitry to determine a signal power from an input signal;

a window clipper unit coupled to the signal power calculator, the window clipper unit containing circuitry to detect signal peaks with magnitudes exceeding a specified threshold and to provide an adjusted scaling window based on the magnitudes;

a multiplier coupled to the signal input and the window clipper unit, the multiplier to produce a peak reduced signal by multiplying the signal input with the adjusted scaling window;

a second window clipper unit, the second window clipper unit coupled to the signal power calculator and the enable input coupled to the first window clipper unit, wherein the second window clipper unit is turned on after the first window clipper unit detects a signal peak exceeding the specified threshold;

a second multiplier having a first input coupled to the window clipper unit and a second input coupled to the second window clipper unit, the second multiplier to produce a composite adjusted scaling window by multiplying the outputs of the window clipper units; and

a filter unit coupled to the second multiplier.

18. The peak reduction circuit of claim 17 further comprising a normalizer having an input coupled to the signal power calculator and an output coupled to the window clipper unit, the normalizer containing circuitry to adjust a power level in the input signal equal to the specified threshold equal to one.

19. The peak reduction circuit of claim 17 further comprising a delay unit having an input coupled to the signal input and an output coupled to the multiplier, the delay unit to insert a delay that is a function of a duration of a scaling window.

20. The peak reduction circuit of claim 17 wherein the filter unit is configured to-filter the peak reduced signal to eliminate spurious emissions.

21. The peak reduction circuit of claim 19, wherein the delay is a function of the duration of the scaling window plus a function of additional mathematical computations.

22. The peak reduction circuit of claim 21, wherein the additional mathematical computations include an instantaneous power and a threshold scaling computations.

23. The peak reduction circuit of claim 19, wherein the delay is approximately equal to one half the duration of the scaling window.

24. The peak reduction circuit of claim 19, wherein the window clipper unit further comprises an enable input, the enable input turns the window clipper unit on and off.

25. The peak reduction circuit of claim 24, wherein the enable input of the window clipper unit is always on.

26. The peak reduction circuit of claim 17, wherein when the window clipper unit completes its task of providing an adjusted scaling window, the window clipper unit turns off the second window clipper unit, unless the second window clipper unit is actively providing an adjusted scaling window of its own.

27. A peak reduction circuit comprising:

a signal power calculator coupled to a signal input, the signal power calculator containing circuitry to determine a signal power from an input signal;

a window clipper unit coupled to the signal power calculator, the window clipper unit containing circuitry to detect signal peaks with magnitudes exceeding a specified threshold and to provide an adjusted scaling window based on the magnitudes;

a multiplier coupled to the signal input and the window clipper unit, the multiplier to produce a peak reduced signal by multiplying the signal input with the adjusted scaling window; and

a clipping unit having an input coupled to the output of the multiplier and an output coupled to the filter unit, the clipping unit comprising;

a second signal power calculator coupled to the output of the multiplier, the second signal power calculator containing circuitry to determine a second signal power from the output of the multiplier;

a second window clipper unit coupled to the second signal power calculator, the second window clipper unit containing circuitry to detect signal peaks with magnitudes exceeding a specified threshold and to provide a second adjusted scaling window based on the magnitudes;

a second multiplier coupled to the output of the multiplier and the second window clipper unit, the second multiplier to produce a peak reduced signal by multiplying the output of the multiplier with the second adjusted scaling window.

28. The peak reduction circuit of claim 27 further comprising a second delay unit having an input coupled to the output of the multiplier and an output coupled to the second multiplier, the second delay unit to insert a delay equal to one half a duration of a scaling window.

29. The peak reduction circuit of claim 27, further comprising a filter unit coupled to the multiplier, the filter unit to filter the peak reduced signal to eliminate spurious emissions.

30. The peak reduction circuit of claim 27, wherein the window clipper unit further comprises an enable input, the enable input turns the window clipper unit on and off.

31. The method of claim 29, wherein after the filtering step, the method further comprises the steps of:

measuring the peak reduced input signal;

detecting a signal peak with a magnitude exceeding a specified threshold;

reducing the detected signal peak in the input signal via a scaling window; and

filtering the peak reduced input signal to eliminate spurious out-of-band emissions.

32. The method of claim 29, wherein the input signal is a baseband signal and the filtering step is performed by a low-pass filter.

33. The method of claim 29, wherein the input signal is a baseband signal and the filtering step is performed by a band-pass filter.

34. The method of claim 29, wherein the input signal is an intermediate frequency signal and the filtering is performed by a band-pass filter.