Method and apparatus for calculating the predistortion function from a power amplifier model

• US 6,462,617 B1
• Filed: 06/08/2001
• Issued: 10/08/2002
• Est. Priority Date: 06/08/2001
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Kim, Jaehyeong
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, PATRICIA T
• Application Number:
  US09/878,037
• Time in Patent Office: 487 Days
• Field of Search: 330/2, 330/149, 375/297
• US Class Current: 330/2
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence

Abstract

Disclosed is an apparatus and method for calculating a predistortion function from power amplifier characteristics. A predistortion module generates a predistorted signal in response to an input signal and predistortion coefficients received from a predistortion function calculating module. The predistortion function calculating module generates the predistortion coefficients in response to the given amplifier characteristics. Polynomial fitting is used to obtain the predistortion coefficients. In particular, the input signal is represented by single or multiple sectors having multiple points and then predistortion coefficients are calculated for each sector.

Claims

1. An apparatus for calculating a predistortion function from power amplifier characteristics, said apparatus comprising:

a predistortion module responsive to predistortion coefficients and an input signal by generating a predistorted signal, said predistortion coefficients being of a complex polynomial of order q (q is an integer greater than one);

an amplifier responsive to said predistorted signal by generating an output signal; and

a predistortion function calculating module responsive to said amplifier characteristics by generating said predistortion coefficients, said predistortion function calculating module having a polynomial fitting module, said polynomial fitting module including,

means for uniformly dividing said signal range at q points; and

means for calculating said predistortion coefficients, wherein

said predistortion coefficients are represented by the equation;

$\left[\begin{array}{c}\mathrm{\Re <br><br>}<br><br>\left[a^t\right]\\ \mathrm{\Im <br><br>}<br><br>\left[a^t\right]\end{array}\right]={\left[\begin{array}{cc}\mathrm{\Re <br><br>}<br><br>\left[D\right]& -\mathrm{\Im <br><br>}<br><br>\left[D\right]\\ \mathrm{\Im <br><br>}<br><br>\left[D\right]& \mathrm{\Re <br><br>}<br><br>\left[D\right]\end{array}\right]}^{-1}·<br><br>\left[\begin{array}{c}\mathrm{\Re <br><br>}<br><br>\left[v^t\right]\\ \mathrm{\Im <br><br>}<br><br>\left[v^t\right]\end{array}\right]$

 

wherein a^t is a transpose of a size q vector of said predistortion coefficients, wherein v^t is a transpose of a size q vector of said uniformly divided signal range, and wherein D is a q×

q matrix representation of said output signal.

2. An apparatus for calculating a predistortion function from power amplifier characteristics, said apparatus comprising:

a predistortion module responsive to predistortion coefficients and an input signal by generating a predistorted signal, said predistortion coefficients being of a complex polynomial of order q (q is an integer greater than one);

an amplifier responsive to said predistorted signal by generating an output signal; and

a predistortion function calculating module responsive to said amplifier characteristics by generating said predistortion coefficients, said predistortion function calculating module having a polynomial fitting module, said polynomial fitting module including,

means for uniformly dividing said signal range at q points;

means for calculating said predistortion coefficients;

means for dividing a signal range of said predistorted signal into a given number of sectors;

means for uniformly dividing each of said sectors at a given number of points; and

means for calculating said predistortion coefficients for each of said sectors.

3. A wireless radio frequency communications system including apparatus for calculating a predistortion function from power amplifier characteristics, said system comprising:

a predistortion module responsive to predistortion coefficients and an input signal by generating a predistorted signal, said predistortion coefficients being of a complex polynomial of order q (q is an integer greater than one);

an amplifier responsive to said predistorted signal by generating an output signal; and

a predistortion function calculating module responsive to said amplifier characteristics by generating said predistortion coefficients, said predistortion function calculating module having a polynomial fitting module, said polynomial fitting module including,

means for uniformly dividing said signal range at q points; and

means for calculating said predistortion coefficients, wherein

said predistortion coefficients are represented by the equation;

$\left[\begin{array}{c}\mathrm{\Re <br><br>}<br><br>\left[a^t\right]\\ \mathrm{\Im <br><br>}<br><br>\left[a^t\right]\end{array}\right]={\left[\begin{array}{cc}\mathrm{\Re <br><br>}<br><br>\left[D\right]& -\mathrm{\Im <br><br>}<br><br>\left[D\right]\\ \mathrm{\Im <br><br>}<br><br>\left[D\right]& \mathrm{\Re <br><br>}<br><br>\left[D\right]\end{array}\right]}^{-1}·<br><br>\left[\begin{array}{c}\mathrm{\Re <br><br>}<br><br>\left[v^t\right]\\ \mathrm{\Im <br><br>}<br><br>\left[v^t\right]\end{array}\right]$

wherein a^t is a transpose of a size q vector of said predistortion coefficients, wherein v^t is a transpose of a size q vector of said uniformly divided signal range, and wherein D is a q×

q matrix representation of said output signal.

4. A wireless radio frequency communications system including apparatus for calculating a predistortion function from power amplifier characteristics, said system comprising:

a predistortion module responsive to predistortion coefficients and an input signal by generating a predistorted signal, said predistortion coefficients being of a complex polynomial of order q (q is an integer greater than one);

an amplifier responsive to said predistorted signal by generating an output signal; and

a predistortion function calculating module responsive to said amplifier characteristics by generating said predistortion coefficients, said predistortion function calculating module having a polynomial fitting module, said polynomial fitting module including,

means for uniformly dividing said signal range at q points;

means for calculating said predistortion coefficients;

means for dividing a signal range of said predistorted signal into a given number of sectors;

means for uniformly dividing each of said vectors at a given number of points; and

means for calculating said predistortion coefficients for each of said sectors.

5. A method for calculating a predistortion function from power amplifier characteristics, comprising the steps of:

generating a predistorted signal in response to predistortion coefficients and an input signal, said predistortion coefficients being of a complex polynomial of order q (q is an integer greater than one);

amplifying said predistorted signal to generate an output signal; and

generating predistortion coefficients in response to said amplifier characteristics by generating said predistortion coefficients using polynomial fitting, said step of generating said predistortion coefficients further including the steps of,

uniformly dividing said signal at range q points; and

calculating said predistortion coefficients, wherein

said predistortion coefficients are represented by the equation;

$\left[\begin{array}{c}\mathrm{\Re <br><br>}<br><br>\left[a^t\right]\\ \mathrm{\Im <br><br>}<br><br>\left[a^t\right]\end{array}\right]={\left[\begin{array}{cc}\mathrm{\Re <br><br>}<br><br>\left[D\right]& -\mathrm{\Im <br><br>}<br><br>\left[D\right]\\ \mathrm{\Im <br><br>}<br><br>\left[D\right]& \mathrm{\Re <br><br>}<br><br>\left[D\right]\end{array}\right]}^{-1}·<br><br>\left[\begin{array}{c}\mathrm{\Re <br><br>}<br><br>\left[v^t\right]\\ \mathrm{\Im <br><br>}<br><br>\left[v^t\right]\end{array}\right]$

wherein a^t is a transpose of a size q vector of said predistortion coefficients, wherein v^t is a transpose of a size q vector of said uniformly divided signal range, and wherein D is a q×

q matrix representation of said output signal.

6. A method for calculating a predistortion function from power amplifier characteristics, comprising the steps of:

generating a predistorted signal in response to predistortion coefficients and an input signal, said predistortion coefficients being of a complex polynomial of order q (q is an integer greater than one);

amplifying said predistorted signal to generate an output signal; and

generating predistortion coefficients in response to said amplifier characteristics by generating said predistortion coefficients using polynomial fitting, said step of generating said predistortion coefficients further including the steps of,

uniformly dividing said signal at range q points;

calculating said predistortion coefficients;

dividing a signal range of said predistorted signal into a given number of sectors;

uniformly dividing each of said sectors at a given number of points; and

calculating said predistortion coefficients for each of said sectors.

7. An apparatus for calculating a predistortion function from power amplifier characteristics, said apparatus comprising:

a first module that utilizes q points of information from a curve of said amplifier characteristics to obtain predistortion coefficients of a complex polynomial of order q (q is an integer greater than one); and

a second module responsive to said first module by generating a complex polynomial function based on said predistortion coefficients, wherein

said first module utilizes q points of information from a predistortion function curve to obtain said predistortion coefficients, said predistortion function curve obtained by switching axes of said amplifier characteristics curve.