Method and system for adaptive peak to average power ratio reduction in orthogonal frequency division multiplexing communication networks

• US 8,331,466 B2
• Filed: 10/03/2008
• Issued: 12/11/2012
• Est. Priority Date: 10/04/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Guo, Ning, McGowan, Neil, Morris, Bradley John
• Primary Examiner(s): Ometz, David
• Assistant Examiner(s): Garcia, Santiago
• Application Number:
  US12/245,047
• Publication Number:
  US 20090092195A1
• Time in Patent Office: 1,530 Days
• Field of Search: 375/260
• US Class Current: 375/260
• CPC Class Codes: H04L 27/2623 Reduction thereof by clipping
• CPC Class Codes: H04L 27/2624 by soft clipping

Abstract

A method and system adaptively reduce a peak-to-average power ratio in a communication system. Energy is clipped from at least one peak of a modulated signal. The modulated signal includes a plurality of sub-carriers. At least one data sub-carrier is adaptively selected for peak-to-average power ratio reduction use based on known scheduling information. The clipped energy is distributed among at least one data sub-carrier.

Claims

1. A method for adaptively reducing a peak-to-average power ratio in a communication system, the method comprising:

clipping energy from at least one peak of a modulated signal, the modulated signal including a plurality of sub-carriers;

adaptively selecting at least one data sub-carrier for peak-to-average power ratio reduction use based on known scheduling information; and

distributing the clipped energy among the at least one data sub-carrier by filtering the clipped energy using a filter having coefficients based at least in part on a re-growth control factor, wherein the re-growth control factor is used to scale the coefficients of the filter, wherein a value of the re-growth control factor is between 0 and 1, wherein the re-growth control factor is used to control re-growth of the at least one peak after said clipping and iteratively repeating the distribution based on the regrowth control factor.

2. The method of claim 1, further comprising:

assigning communication devices to data sub-carriers;

mapping the orthogonal frequency division multiplexing symbol onto the modulated signal; and

determining the at least one data sub-carrier for distributing the clipped energy based on assigning the communication devices.

3. The method of claim 2, further comprising:

transforming the clipped signal for use in a frequency domain;

filtering the transformed signal using the filter;

transforming the filtered signal for use in a time domain; and

combining the transformed filtered signal with the modulated signal to produce an output signal having a peak-to-average power ratio less than the peak-to-average power ratio of the modulated signal.

4. The method of claim 3, wherein:

the filter includes a weighted coefficient for each sub-carrier.

5. The method of claim 4, wherein the coefficient for each sub-carrier is determined based at least in part on assigning the communication devices, a total amount of sub-carriers for the modulated signal, an amount of sub-carriers for each modulation scheme, an amount of reserved sub-carriers and signal quality parameters.

6. The method of claim 5, wherein the signal quality parameters include the peak-to-average power ratio for the output signal and residual constellation error for each sub-carrier.

7. The method of claim 2, further comprising:

filtering the clipped modulated signal using a g-function; and

combining the filtered clipped energy with the clipped modulated signal to produce an output signal having a peak-to-average power ratio less than the peak-to-average power ratio of the modulated signal.

8. The method of claim 7, wherein the g-function is constructed by:

constructing an F-filter in a frequency domain, the F-filter including a weighted coefficient for each sub-carrier; and

transforming the F-filter to a g-function for use in a time domain.

9. The method of claim 8, wherein the coefficient for each sub-carrier is determined based at least in part on assigning the communication devices, a total amount of sub-carriers for the modulated signal, an amount of sub-carriers for each modulation scheme, an amount of reserved sub-carriers and signal quality parameters.

18. The method of claim 1, wherein the re-growth control factor is determined based at least in part on a number of reserved sub-carriers.

10. A system for adaptively reducing a peak-to-average power ratio in a communication system, the system comprising:

a scheduler operating to adaptively select at least one data sub-carrier for peak to average power ratio reduction;

a clipper, operating to clip energy from at least one peak of a modulated signal, the modulated signal including an orthogonal frequency division multiplexing symbol having a plurality of sub-carriers; and

a filter, communicatively coupled to the scheduler and to the clipper, the filter operating to adaptively distribute the clipped energy among the at least one data sub-carrier, the filter having coefficients based at least in part on a re-growth control factor, wherein the re-growth control factor is used to scale the coefficients of the filter, wherein a value of the re-growth control factor is between 0 and 1, wherein the re-growth control factor is used to control re-growth of the at least one peak after said clipping and iteratively repeating the distribution based on the regrowth control factor.

11. The system of claim 10, wherein the filter further operates to adaptively distribute the clipped energy among at least one reserved sub-carrier.

12. The system of claim 11, further comprising a filter generator communicatively coupled to the scheduler, the filter generator operating to create the filter, and wherein the scheduler further operates to:

assign communication devices to data sub-carriers;

map the orthogonal frequency division multiplexing symbol onto the modulated signal; and

determine the at least one data sub-carrier for distributing the clipped energy based on assigning the communication devices.

13. The system of claim 12, wherein the filter is an F-filter, the F-filter including a weighted coefficient for each sub-carrier, the system further comprising:

a fast Fourier transform communicatively coupled to the clipper and to the filter, the fast Fourier transform operating to transform the clipped modulated signal for use in a frequency domain;

an inverse fast Fourier transform communicatively coupled to the filter, the inverse fast Fourier transform operating to transform the filtered clipped signal for use in a time domain; and

a subtracter, communicatively coupled to the inverse fast Fourier transform and to the clipper, the subtracter operating to combine the transformed filtered clipped signal with the modulated signal to produce an output signal having a peak-to-average power ratio less than the peak-to-average power ratio of the modulated signal.

14. The system of claim 13, wherein the filter generator determines the coefficient for each sub-carrier based at least in part on assigning the communication devices, a total amount of sub-carriers for the modulated signal, an amount of sub-carriers for each modulation scheme, an amount of reserved sub-carriers, the peak-to-average power ratio for the output signal and residual constellation error for each sub-carrier.

15. The system of claim 14, further comprising a configuration unit communicatively coupled to the scheduler and to the filter generator, the configuration unit operating to:

determine a number of iterations and a clipping threshold for the clipper;

determine the re-growth control factor; and

define a maximum and a minimum amount of sub-carriers available for peak-to-average power ratio reduction.

16. The system of claim 12, wherein the filter is a g-function, the filter generator operating to construct an F-filter in a frequency domain, the F-filter including a weighted coefficient for each sub-carrier, the system further comprising:

an inverse fast Fourier transform communicatively coupled to the filter generator and to the filter, the inverse fast Fourier transform operating to transform the F-filter to the g-function for use in a time domain; and

a subtracter, communicatively coupled to filter and to the clipper, the subtracter operating to combine the filtered clipped signal with the modulated signal to produce an output signal having a peak-to-average power ratio less than the peak-to-average power ratio of the modulated signal.

17. The system of claim 16, wherein the coefficient for each sub-carrier is determined based at least in part on assigning the communication devices, a total amount of sub-carriers for the modulated signal, an amount of sub-carriers for each modulation scheme, an amount of reserved sub-carriers and signal quality parameters.