Pre-distortion for a radio frequency power amplifier

1. A method of determining coefficients of a pre-distorter for compensation of distortion of a signal by an amplifier, the method comprising:

sampling an input signal upstream of the amplifier to generate a plurality of input samples;

sampling an output signal downstream of the amplifier to generate a plurality of output samples, each of the plurality of output samples corresponding to a respective input sample;

generating a selected set of samples comprising selected input samples from the plurality of input samples; and

determining coefficients of the pre-distorter based upon at least some of the samples in the selected set of samples and their corresponding output samples.

2. The method of claim 1 , wherein the selected input samples from the plurality of input samples are selected based upon a frequency domain analysis of the selected set of samples.

3. The method of claim 1 , wherein the selected input samples from the plurality of input samples are selected based upon a frequency domain analysis of the selected set of samples and amplitude analysis of the selected input samples.

4. The method of claim 1 , wherein the selected input samples from the plurality of input samples are selected based upon a frequency domain analysis of the selected set of samples and an analysis of time of sampling of the selected input samples.

5. The method of claim 4 , wherein the frequency domain analysis of the selected set of samples comprises comparing a frequency spectrum of the selected set of samples to a frequency spectrum of a previously selected set of samples.

6. The method of claim 4 , wherein the frequency domain analysis of the selected set of samples comprises comparing a flatness of a frequency spectrum of the selected set of samples to a flatness of a frequency spectrum of a previously selected set of samples.

7. The method of claim 1 , wherein the selected set of samples further comprises a previously selected set of samples.

8. The method of claim 1 , wherein:

sampling an input signal upstream of the amplifier to generate a plurality of input samples comprises:

sampling the input signal upstream of the pre-distorter to generate a plurality of first input samples; and

sampling the output signal downstream of the pre-distorter to generate a plurality of second input samples, each of the second input samples corresponding to a respective first input sample;

generating a selected set of samples comprises:

selecting first input samples based upon a frequency domain analysis of a selected set of first samples comprising the selected first input samples and a previously selected set of first samples; and

selecting second input samples corresponding to the selected first input samples; and

wherein determining updated coefficients of the pre-distorter is based upon the selected second input samples and the corresponding output samples.

9. The method of claim 1 , wherein the input signal consists of at least two cellular signals.

10. The method of claim 9 , wherein at least two of the at least two cellular signals are dissimilar.

11. The method of claim 10 , wherein one cellular signal is LTE and another cellular signal is GSM.

12. A transmit chain, comprising:

a pre-distorter;

an amplifier downstream of the pre-distorter;

a first sampler operable to sample an input signal upstream of the amplifier to generate a plurality of input samples;

a second sampler operable to sample an output signal downstream of the amplifier to generate a plurality of output samples, each of the plurality of output samples corresponding to a respective input sample; and

a controller operable to determine updated coefficients of the pre-distorter based upon (a) selected input samples which are selected from the plurality of input samples, and (b) their corresponding output samples.

13. The transmit chain of claim 12 , wherein the controller is operable to select the selected input samples from the plurality of input samples based upon a frequency domain analysis of the selected set of samples.

14. The transmit chain of claim 12 , wherein the controller is operable to select the selected input samples from the plurality of input samples based upon a frequency domain analysis of the selected set of samples and amplitude analysis of the selected input samples.

15. The transmit chain of claim 12 , wherein the controller is operable to select the selected input samples from the plurality of input samples based upon a frequency domain analysis of the selected set of samples and an analysis of time of sampling of the selected input samples.

16. The transmit chain of claim 12 , wherein the input signal consists of at least two cellular signals.

17. The transmit chain of claim 16 , wherein at least two of the at least two cellular signals are dissimilar.

18. A method of determining coefficients of a pre-distorter for compensation of distortion of a signal by an amplifier, the method comprising:

sampling an input signal upstream of the amplifier to generate a plurality of input samples;

sampling an output signal downstream of the amplifier to generate a plurality of output samples, each of the plurality of output samples corresponding to a respective input sample; and

determining coefficients of the pre-distorter based upon (a) input samples selected from the plurality of input samples and (b) their corresponding output samples.

19. The method of claim 18 , wherein the input samples selected from the plurality of input samples are selected based upon frequency domain analysis.

20. The method of claim 18 , wherein the input samples selected from the plurality of input samples are selected based upon frequency domain analysis and amplitude analysis.