Piecewise polynomial predistortion method and apparatus for compensating nonlinear distortion of high power amplifier

• US 6,642,786 B1
• Filed: 08/15/2002
• Issued: 11/04/2003
• Est. Priority Date: 08/15/2002
• Status: Expired due to Fees

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Kim, Sooyoung, Jin, Minglu, Oh, Deockgil
• Primary Examiner(s): TON, MY TRANG
• Application Number:
  US10/222,629
• Time in Patent Office: 446 Days
• Field of Search: 330/2, 330/107, 330/149
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3258 based on polynomial terms
• CPC Class Codes: H03F 1/3282 Acting on the phase and the amplitude of the input signal

Abstract

A piecewise polynomial predistortion method and apparatus compensates nonlinear distortion of a high power amplifier by including an amplitude predistortion circuit for predistorting an input amplitude signal based on first polynomial coefficients corresponding to the amplitude of the input amplitude signal to provide a predistorted amplitude signal, a phase predistortion circuit for predistorting an input phase signal based on the predistorted amplitude signal and second polynomial coefficients corresponding to the amplitude of the predistorted amplitude signal to provide a predistorted phase signal, a power amplifier for amplifying the predistorted amplitude and phase signal to output an amplified amplitude and phase signal, a first adaptation circuit for updating the first polynomial coefficients based on the predistorted amplitude signal and the amplified amplitude signal and a second adaptation circuit for updating the second polynomial coefficients based on the predistorted amplitude signal, the predistorted phase signal and the amplified phase signal.

Claims

1. A polynomial predistortion apparatus, comprising:

an amplitude predistortion circuit for predistorting an input amplitude signal based on first polynomial coefficients selected according to the amplitude of the input amplitude signal to thereby provide a predistorted amplitude signal;

a phase predistortion circuit for predistorting an input phase signal based on the predistorted amplitude signal and second polynomial coefficients selected according to the amplitude of the predistorted amplitude signal to thereby provide a predistorted phase signal;

a power amplifier for amplifying the predistorted amplitude signal and the predistorted phase signal to thereby output an amplified amplitude signal and an amplified phase signal;

a first adaptation circuit for updating the first polynomial coefficients based on the predistorted amplitude signal and the amplified amplitude signal; and

a second adaptation circuit for updating the second polynomial coefficients based on the predistorted amplitude signal, the predistorted phase signal and the amplified phase signal.

2. The apparatus of claim 1, wherein the amplitude predistortion circuit includes:

a sub-region determination unit for deciding a sub-region of the input amplitude signal to thereby generate a sub-region indication signal representing the decided sub-region, wherein said sub-region is decided according to the amplitude of the input amplitude signal and a plurality of sub-regions is preset for the input amplitude signal;

a coefficient storage unit for selecting and outputting the first polynomial coefficients corresponding to said sub-region indication signal among polynomial coefficients stored therein, wherein the polynomial coefficients are predetermined for each of the sub-regions; and

an amplitude predistortion unit for predistorting the input amplitude signal to output the predistorted amplitude signal by using the input amplitude sign al and the first polynomial coefficients provided from said coefficient storage unit.

3. The apparatus of claim 2, wherein the predistorted amplitude signal is estimated according to a following polynomial function:

4. The apparatus of claim 2, wherein the first adaptation circuit updates the first polynomial coefficients by employing a recursive least square (RLS) algorithm in a direction of minimizing an amplitude approximation error based on the predistorted amplitude signal and the amplified amplitude signal, the amplitude approximation error representing a difference between the predistorted amplitude signal and the amplified amplitude signal.

5. The apparatus of claim 4, wherein the amplitude approximation error E_A is determined as follows:

6. The apparatus of claim 2, wherein the number of sub-regions, sub-region points and the degree of the polynomial function for estimating the predistorted amplitude signal are decided according to the steps of:

(a) providing a test signal to the power amplifier;

(b) calculating an amplitude-dependent amplitude distortion (AM/AM) transfer function of the power amplifier by measuring input and output of the power amplifier based on the test signal and estimating a probability density function (PDF) of the input amplitude signal;

(c) obtaining an ideal inverse amplitude, distortion transfer function of the power amplifier;

(d) calculating total approximation error values of polynomial functions with all combinations of the sub-region points and all combinations of the degrees of the polynomial function for each sub-region, wherein the number of the sub-regions is resulted from the sub-region points and the coefficients of the polynomial functions for each sub-region are calculated by using internal input signals generated based on said estimated PDF and a least mean square (LMS) algorithm;

(e) storing the total approximation error values, the sub-region points, and the coefficients of the polynomial functions for each sub-region if the calculated total approximation error values are equal to or less than a required approximation error value; and

(f) among the stored values, selecting optimum sub-region points and polynomial coefficients for each sub-region with the minimum polynomial degree and the minimum total approximation error value.

7. The apparatus of claim 1, wherein the phase predistortion circuit includes:

a sub-region determination unit for determining a sub-region of the predistorted amplitude signal to thereby generate a sub-region indication signal representing the determined sub-region, wherein said sub-region is determined according to the amplitude of the predistorted amplitude signal and a multiplicity of sub-regions is predetermined for the predistorted amplitude signal;

a coefficient storage unit for selecting and outputting the second polynomial coefficients corresponding to said sub-region indication signal among polynomial coefficients stored therein, wherein the polynomial coefficients are predetermined for each of the sub-regions; and

a phase predistortion unit for predistorting the input phase signal to output the predistorted phase signal by using the input phase signal, the predistorted amplitude signal and the second polynomial coefficients provided from said coefficient storage unit.

8. The apparatus of claim 7, wherein the predistorted phase signal is estimated according to a following polynomial function:

9. The apparatus of claim 7, wherein the second adaptation circuit updates the second polynomial coefficients by employing a recursive least square (RLS) algorithm in a direction of minimizing a phase approximation error based on the predistorted amplitude signal, the predistorted phase signal and the amplified phase signal, the phase approximation error representing a difference between the predistorted phase signal and the amplified phase signal.

10. The apparatus of claim 9, wherein the phase approximation error E_P is determined as follows:

11. The apparatus of claim 7, wherein the number of sub-regions, sub-region points and the degree of the polynomial function for estimating the predistorted phase signal are determined according to the steps of:

(a) providing a test signal to the power amplifier;

(b) calculating an amplitude-dependent phase distortion (AM/PM) transfer function of the power amplifier by measuring input and output of the power amplifier based on the test signal and estimating a probability density function (PDF) of the predistorted amplitude signal;

(c) obtaining an ideal inverse phase distortion transfer function of the power amplifier;

(d) calculating total approximation error values of polynomial functions with all combinations of the sub-region points and all combinations of the degrees of the polynomial function for each sub-region, wherein the number of the sub-regions is resulted from the sub-region points and the coefficients of the polynomial functions for each sub-region are calculated by using internal predistorted signals generated based on said estimated PDF and a least mean square (LMS) algorithm;

(e) storing the total approximation error values, the sub-region points, and the coefficients of the polynomial functions for each sub-region if the calculated total approximation error values are equal to or less than a required approximation error value; and

(f) among the stored values, selecting optimum sub-region points, and polynomial coefficients for each sub-region with the minimum polynomial degree and the minimum total approximation error value.

12. A polynomial predistortion method, comprising the steps of:

(a) receiving an input amplitude signal and an input phase signal;

(b) predistorting the input amplitude signal by using first polynomial coefficients selected according to the amplitude of the input amplitude signal to generate a predistorted amplitude signal;

(c) predistorting the input phase signal by using the predistorted amplitude signal and second polynomial coefficients selected according to the amplitude of the predistorted amplitude signal to produce a predistorted phase signal;

(d) amplifying the predistorted amplitude signal and the predistorted phase signal to provide an amplified amplitude signal and an amplified phase signal;

(e) updating the first polynomial coefficients by using the predistorted amplitude signal and the amplified amplitude signal; and

(f) updating the second polynomial coefficients by using the predistorted amplitude signal, the predistorted phase signal and the amplified phase signal.

13. The method as recited in claim 12, wherein the step (b) includes the steps of:

(b1) deciding a sub-region of the input amplitude signal to thereby generate a sub-region indication signal representing the decided sub-region, wherein said sub-region is decided according to the amplitude of the input amplitude signal and a plurality of sub-regions is preset for the input amplitude signal;

(b2) selecting and outputting the first polynomial coefficients corresponding to said sub-region indication signal among polynomial coefficients predetermined for the plurality of sub-regions; and

(b3) predistorting the input amplitude signal to output the predistorted amplitude signal by using the input amplitude signal, the first polynomial coefficients provided from said coefficient storage unit.

14. The method as recited in claim 13, wherein the predistorted amplitude signal is estimated according to a following polynomial function:

15. The method as recited in claim 13, wherein the first polynomial coefficients are updated by employing a recursive least square (RLS) algorithm in a direction of minimizing an amplitude approximation error based on the predistorted amplitude signal and the amplified amplitude, signal, the amplitude approximation error representing a difference between the predistorted amplitude signal and the amplified amplitude signal.

16. The method as recited in claim 15, wherein the amplitude approximation error E_A is determined as follows:

17. The method as recited in claim 13, wherein the number of sub-regions, sub-region points and the degree of the polynomial function for estimating the predistorted amplitude signal are decided according to the steps of:

(p) providing a test signal to a power amplifier;

(q) calculating an amplitude-dependent amplitude distortion (AM/AM) transfer function of the power amplifier by measuring input and output of the power amplifier based on the test signal and estimating a probability density function (PDF) of the input amplitude signal;

(r) obtaining an ideal inverse amplitude distortion transfer function of the power amplifier;

(s) calculating total approximation error values of polynomial functions with all combinations of the sub-region points and all combinations of the degrees of the polynomial function for each sub-region, wherein the number of the sub-regions is resulted from the sub-region points and the coefficients of the polynomial functions for each sub-region are calculated by using internal input signals generated based on said estimated PDF and a least mean square (LMS) algorithm;

(t) storing the total approximation error values, the sub-region points, and the coefficients of the polynomial functions for each sub-region if the calculated total approximation error values are equal to or less than a required approximation error value; and

(u) among the stored values, selecting optimum sub-region points and polynomial coefficients for each sub-region with the minimum polynomial degree and the minimum total approximation error value.

18. The method as recited in claim 12, wherein the step (c) includes the steps of:

(c1) determining a sub-region of the predistorted amplitude signal to thereby generate a sub-region indication signal representing the determined sub-region, wherein said sub-region is determined according to the amplitude of the predistorted amplitude signal and a multiplicity of sub-regions is predetermined for the predistorted amplitude signal;

(c2) selecting and outputting the second polynomial coefficients corresponding to said sub-region indication signal among polynomial coefficients are predetermined for the multiplicity of sub-regions; and

(c3) predistorting the input phase signal to output the predistorted phase signal by using the input phase signal, the predistorted amplitude signal and the second polynomial coefficients.

19. The method as recited in claim 18, wherein the predistorted phase signal is estimated according to a following polynomial function:

20. The method as recited in claim 18, wherein the second polynomial coefficients are updated by employing a recursive least square (RLS) algorithm in a direction of minimizing a phase approximation error based on the predistorted amplitude signal, the predistorted phase signal and the amplified phase signal, the phase approximation error representing a difference between the predistorted phase signal and the amplified phase signal.

21. The method as recited in claim 20, wherein the phase approximation error E_P is determined as follows:

22. The method as recited in claim 18, wherein the number of sub-regions, sub-region points and the degree of the polynomial function for estimating the predistorted phase signal are determined according to the steps of:

(p) providing a test signal to a power amplifier;

(q) calculating an amplitude-dependent phase distortion (AM/PM) transfer function of the power amplifier by measuring input and output of the power amplifier based on the test signal and estimating a probability density function (PDF) of the predistorted amplitude signal;

(r) obtaining an ideal inverse phase distortion transfer function of the power amplifier;

(s) calculating total approximation error values of polynomial functions with all combinations of the sub-region points and all combinations of the degrees of the polynomial function for each sub-region, wherein the number of the sub-regions is resulted from the sub-region points and the coefficients of the polynomial functions for each sub-region are calculated by using internal predistorted signals generated based on said estimated PDF and a least mean square (LMS) algorithm;

(t) storing the total approximation error values, the sub-region points, and the coefficients of the polynomial functions for each sub-region if the calculated total approximation error values are equal to or less than a required approximation error value; and

(u) among the stored values, selecting optimum sub-region points, and polynomial coefficients for each sub-region with the minimum polynomial degree and the minimum total approximation error value.