Method and apparatus for peak-to-average power reduction

• US 6,741,661 B2
• Filed: 05/22/2001
• Issued: 05/25/2004
• Est. Priority Date: 05/22/2001
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Attar, Rashid A., Wheatley, Charles E. III
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US09/863,244
• Publication Number:
  US 20020176480A1
• Time in Patent Office: 1,099 Days
• Field of Search: 375/296, 375/285, 332/159
• US Class Current: 375/296
• 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

A method and system that reduces the peak-to-average power ratio of a reverse link signal is described. A baseband structure implements a peak reduction technique using peak windowing. A non-rectangular window is used to distort the signal. One embodiment of the window is an inverted-raised cosine with the peak reduction a function of the relative difference in the squared-magnitude of the envelope relative to that of the desired peak-to-average power ratio. Multiple passes through the peak-reduction function may be performed until a desired target peak-to-average power ratio is achieved.

Claims

1. An apparatus comprising:

a peak-to-average reduction module, wherein the reduction module is an inverted raised cosine function and wherein the inverted raised cosine is 1−

α

(cos²x), where $a=\left(\frac{E_{\mathrm{current\_max}}-E_{\mathrm{av}}}{E_{\mathrm{current\_max}}}\right),$

 

E_av is average power for a current period, and E<sub>current—

max</sub> is a maximum value of the signal'"'"'s envelope for a current window that is configured to generate a reduced peak-to-average signal, in response to a peak in a signal that exceeds a target threshold value, by applying a reduction function continually to the peak and terminating the application of the reduction function when the peak is reduced to or below the target threshold value; and

a power amplifier that is configured to amplify the reduced peak-to-average signal.

2. The apparatus of claim 1, wherein the application of the reduction function is terminated when the reduction function has been applied a given number of times.

3. The apparatus of claim 1, wherein the apparatus is a subscriber unit.

4. The apparatus of claim 1, wherein the signal is a CDMA signal.

5. The apparatus of claim 1, wherein the period is a half-slot.

6. An apparatus, comprising:

a reverse link modulator configured to provide channel data;

a channel gain calculation module coupled to said reverse link modulator and configured to calculate reverse link channel gain;

an averaging module that is coupled to said channel gain calculation module and configured to calculate average power of channels on the reverse link;

a threshold module coupled to said averaging module and configured to generate envelope thresholds using a target peak-to-average ratio of the signal and said average power;

a window weight module coupled to said threshold module and configured to align a window with a signal peak and generate window weights to be used for multiplying with filtered samples;

a filter coupled to said reverse link modulator and configured to filter an n-chip (where n is an integer) sample of channel data to generate filtered samples; and

a multiply module coupled to said filter and configured to multiply the filtered samples with an aligned peak window using the window weights from the window weight module, to create modified samples with a reduced peak-to-average power ratio.

7. A method of processing a signal, comprising:

comparing a peak of the signal to a target threshold value; and

applying a reduction function, wherein the reduction function is an inverted raised cosine function and wherein the inverted raised cosine is 1−

α

(cos²x), where $a=\left(\frac{E_{\mathrm{current\_max}}-E_{\mathrm{av}}}{E_{\mathrm{current\_max}}}\right),$

 

E_av is average power for a current period, and E<sub>current—

max</sub> is a maximum value of the signal'"'"'s envelope for a current window continually to the peak if the peak is above the target threshold value to generate a reduced peak-to-average signal; and

terminating the application of the reduction function when the peak is at or below the target threshold value.

8. The method of claim 7, further comprising terminating application of the reduction function once the reduction function has been applied a given number of times.

9. The method of claim 7, further comprising amplifying the reduced peak-to-average signal to generate an amplified signal.

10. The method of claim 7, wherein the signal is a CDMA signal.

11. The method of claim 7, wherein the method is performed by a subscriber unit.

12. The method of claim 9, further comprising transmitting the amplified signal.

13. A method of processing a signal, comprising:

calculating a gain value for the signal on a reverse link;

calculating average power levels of channels on the reverse link;

generating envelope thresholds using a target peak-to-average ratio of the signal and the average power levels;

aligning a window with a peak of the signal;

generating window weights for multiplying with filtered samples of the signal;

filtering an n-chip (where n is an integer) sample of channel data to generate the filtered samples; and

multiplying the filtered samples with an aligned peak window using the window weights to create modified samples with a reduced peak-to-average power ratio.