Generation of pre-distortion coefficients
There is disclosed a method for generating pre-emphasis coefficients for a pre-emphasis stage of a non-linear distorting device, the method comprising the steps of: capturing, for a given time period, samples of an input signal and samples of an output signal; determining the direction of an error between the captured samples; adjusting the input signal in a direction to reduce the error to generate an estimate of the pre-distorted input signal; generating updated pre-distortion coefficients in dependence on the estimate of the pre-distorted input signal and generated pre-distortion coefficients for one or more previous time periods.
1. A method for generating pre-emphasis coefficients for a pre-emphasis stage of a non-linear distorting device, the method comprising the steps of:
capturing, for a given time period, samples of an input signal and samples of an output signal;
determining the direction of an error between the captured samples;
adjusting the input signal in a direction to reduce the error to generate an estimate of the pre-distorted input signal; and
generating updated pre-distortion coefficients in dependence on the estimate of the pre-distorted input signal and generated pre-distortion coefficients for one or more previous time periods.
2. The method of claim 1 wherein the step of adjusting the input signal to generate the estimate comprises applying a pointwise function to the captured samples.
3. The method of claim 2 wherein the pointwise function is a least mean squares function.
4. The method of claim 1 wherein the step of generating the pre-emphasis coefficients comprises applying least mean squares Kalman filtering function.
5. The method of claim 1 further comprising the step of determining a magnitude of the error between the captured samples, wherein the adjusting step is adapted to determine the size of the adjustment in dependence on the magnitude of the error.
6. The method of claim 5 wherein the size of the adjustment is reduced as the error is reduced.
7. The method of claim 1 further comprising storing the generated pre-emphasis coefficients.
8. The method of claim 1 wherein the steps are iterative.
9. The method of claim 8 wherein in a first iteration the step of generating the pre-emphasis coefficients is dependent only on the generated estimate.
10. The method of claim 1 wherein the non-linear distorting device is a power amplifier.
11. The method of claim 1 wherein the pre-emphasis coefficients are Volterra coefficients.
12. A computer program product embodied on a non-transitory medium and adapted to perform, when executed, the method of claim 1 .
13. A non-transitory computer-readable storage medium for storing computer program code for performing, when executed, the method of claim 1 .
14. An arrangement for generating pre-emphasis coefficients for a pre-emphasis stage of a non-linear distorting device, comprising:
means for capturing, for a given time period, samples of an input signal and samples of an output signal;
means for generating an intermediate estimate of pre-emphasis coefficients in dependence on the captured samples;
means for determining the direction of an error between the captured samples;
means for adjusting the intermediate estimate of the pre-emphasis coefficients in a direction to reduce the error; and
means for generating the pre-emphasis coefficients in dependence on the adjusted intermediate estimate of the pre-emphasis coefficients and the generated pre-emphasis coefficients for one or more previous time periods.
15. The arrangement of claim 14 wherein the non-linear distorting device is a power amplifier.