Transmitter with limited spectral regrowth and method therefor

• US 20040017859A1
• Filed: 11/12/2002
• Published: 01/29/2004
• Est. Priority Date: 07/25/2002
• Status: Active Grant

• Current Assignee: Tamiras Per Pte Ltd LLC (Intellectual Ventures LLC)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Sills, James A., Sperlich, Roland Jr.
• Granted Patent: US 7,113,551 B2
• Time in Patent Office: Days
• US Class Current: 375/296
• CPC Class Codes: H04L 27/368 adaptive predistortion

Abstract

A transmitter (20) for a digital transmission signal (26) includes a pre-distorter (22) to improve linearity of a power amplifier (44). An amplified transmission signal (46) is conditioned into a narrowband feedback signal (58) that is responsive to a logarithm of the power appearing in out-of-band components (42) of the amplified transmission signal (46). The feedback signal (58) is processed in a pre-distortion processor (80) that implements a genetic algorithm (82) to adapt pre-distortion functions implemented in the pre-distorter (22) and improve linearity over time. The genetic algorithm (82) tests a population of randomly-generated pre-distortion functions for fitness (100). A baseline component of the coefficients from pre-distortion functions used in a subsequent population tracks the best-fit pre-distortion function from the current population (126), allowing the use of a limited search space. New populations are generated from old populations using an elitism process (144), and randomized crossover (152), and mutation (154) processes.

Claims

1. A method of processing a transmission signal occupying a predetermined frequency band to reduce spectral regrowth outside said predetermined frequency band, said method comprising:

transforming a modulated form of said transmission signal in accordance with a pre-distortion function to generate a pre-distorted form of said transmission signal;

amplifying said pre-distorted form of said transmission signal in a power amplifier to generate an amplified form of said transmission signal having an in-band component within said predetermined frequency band and an out-of-band component outside said predetermined frequency band;

conditioning said out-of-band component of said amplified form of said transmission signal to generate a feedback signal; and

applying a genetic algorithm to said feedback signal to modify said pre-distortion function.

2. A method as claimed in claim 1 wherein said conditioning activity substantially excludes said in-band component.

3. A method as claimed in claim 1 wherein said conditioning activity is configured so that said feedback signal is responsive to a logarithm of the power exhibited by said out-of-band component of said amplified form of said transmission signal.

4. A method as claimed in claim 1 wherein:

said transforming activity transforms said modulated form of said transmission signal in accordance with a pre-distortion function configured substantially as a polynomial in the form of a sum of a plurality of terms, wherein each of said terms includes a coefficient having a baseline component and an offset component; and

said applying activity comprises;

generating new offset components, and

altering said baseline components in response to said new offset components.

5. A method as claimed in claim 4 additionally comprising:

combining, after said generating activity, said new offset components and said baseline components to form new coefficients; and

programming a pre-distorter in response to said new coefficients to implement said new pre-distortion function.

6. A method as claimed in claim 5 additionally comprising scaling said new offset components to reside within a predetermined search space prior to said combining activity.

7. A method as claimed in claim 4 wherein said applying activity additionally comprises:

generating a population of pre-distortion functions;

identifying a best-fit member from said population of pre-distortion functions, said best-fit member producing the least out-of-band power of all of said pre-distortion functions; and

moving said baseline components toward said coefficients for said best-fit member of said population of pre-distortion functions.

8. A method as claimed in claim 7 wherein said moving activity moves said baseline components toward said coefficients for said best-fit member by a movement amount, said movement amount being defined by a tracking rate.

9. A method as claimed in claim 7 wherein said applying activity further comprises:

moving said baseline components toward said coefficients for said best-fit member by a movement amount; and

adjusting all offset components of all pre-distortion function members of said population in response to said movement amount.

10. A method as claimed in claim 1 wherein said applying activity comprises:

generating a population of pre-distortion functions, wherein each pre-distortion function is a member of said population;

repeating said transforming, amplifying, and conditioning activities for each member of said population; and

identifying a best-fit member from said population, said best-fit member producing less out-of-band power than others of said members.

11. A method as claimed in claim 10 wherein said generating activity generates said population in response to an old population of pre-distortion functions by including elite members from said old population in said population and combining pairs of members from said old population in accordance with a randomized crossover algorithm to generate additional population members.

12. A method as claimed in claim 11 wherein said generating activity additionally applies a randomized mutation algorithm to said additional population members to afford said population an opportunity to identify alternate local minima.

13. A method as claimed in claim 1 additionally comprising:

performing said transforming, amplifying, conditioning, and applying activities to allow a first worst-case amount of adjacent channel power; and

after said performing activity, altering said applying activity to form an altered-applying activity that allows a second worst-case amount of adjacent channel power, said second amount being less than said first amount; and

repeating said transforming, amplifying, and conditioning activities with said altered-applying activity.

14. A method of processing a transmission signal to reduce spectral regrowth, said method comprising:

transforming a modulated form of said transmission signal to generate a pre-distorted form of said transmission signal, said modulated form of said transmission signal being transformed in accordance with a pre-distortion function configured substantially as a polynomial in the form of a sum of a plurality of terms, wherein each of said terms includes a coefficient having a baseline component and an offset component;

amplifying said pre-distorted form of said transmission signal in a power amplifier to generate an amplified form of said transmission signal;

conditioning said amplified form of said transmission signal to generate a feedback signal; and

processing said feedback signal to modify said pre-distortion function into a new pre-distortion function by identifying new offset components, then altering said baseline components in response to said new offset components.

15. A method as claimed in claim 14 additionally comprising:

combining said new offset components and said baseline components to generate new coefficients; and

programming a pre-distorter in response to said new coefficients to implement said new pre-distortion function.

16. A method as claimed in claim 15 additionally comprising scaling said new offset components to reside within a predetermined search space prior to said combining activity.

17. A method as claimed in claim 14 wherein:

said processing activity additionally comprises;

generating a population of pre-distortion functions, and

identifying a best-fit member from said population of pre-distortion functions, said best-fit member producing the least out-of-band power of all of said pre-distortion functions; and

moving said baseline components toward said coefficients for said best-fit member of said population of said pre-distortion functions.

18. A method as claimed in claim 17 wherein said moving activity moves said baseline components toward said coefficients for said best-fit member by a movement amount, said movement amount being defined by a tracking rate.

19. A method as claimed in claim 17 wherein said processing activity further comprises:

moving said baseline components toward said coefficients for said best-fit member by a movement amount; and

adjusting all offset components of all pre-distortion function members of said population in response to said movement amount.

20. A method as claimed in claim 14 wherein:

said amplified form of said transmission signal has an in-band component within a predetermined frequency band and an out-of-band component outside said predetermined frequency band; and

said conditioning activity conditions substantially only said out-of-band component.

21. A method as claimed in claim 20 wherein said conditioning activity is configured so that said feedback signal is responsive to a logarithm of the power exhibited by said out-of-band component of said amplified form of said transmission signal.

22. A method as claimed in claim 14 wherein said processing activity additionally applies a genetic algorithm to said feedback signal to modify said pre-distortion function.

23. A digital communication transmitter for transmitting a transmission signal occupying a predetermined frequency band while limiting spectral regrowth outside said predetermined frequency band, said transmitter comprising:

a pre-distorter configured to receive a modulated form of said transmission signal, to transform said modulated form of said transmission signal in accordance with a pre-distortion function, and to generate a pre-distorted form of said transmission signal;

a power amplifier coupled to said pre-distorter and configured to amplify said pre-distorted form of said transmission signal and to generate an amplified form of said transmission signal having an in-band component within said predetermined frequency band and an out-of-band component outside said predetermined frequency band;

a conditioning circuit coupled to said power amplifier to condition said out-of-band component of said amplified form of said transmission signal, said conditioning circuit generating a feedback signal; and

a processor coupled to said conditioning circuit and to said pre-distorter, said processor being configured to apply a genetic algorithm to said feedback signal and to modify said pre-distortion function.

24. A transmitter as claimed in claim 23 wherein said conditioning circuit comprises a filter configured to substantially pass said out-of-band component while substantially blocking said in-band component.

25. A transmitter as claimed in claim 23 wherein said conditioning circuit comprises a logarithmic amplifier configured so that said feedback signal is responsive to a logarithm of the power exhibited by said out-of-band component of said amplified form of said transmission signal.

26. A transmitter as claimed in claim 23 wherein:

said pre-distorter transforms said modulated form of said transmission signal in accordance with a pre-distortion function configured substantially as a polynomial in the form of a sum of a plurality of terms, wherein each of said terms includes a coefficient having a baseline component and an offset component; and

said processor is configured to identify new offset components and to alter said baseline components in response to said new offset components.

27. A transmitter as claimed in claim 23 wherein said processor is configured to generate a population of pre-distortion functions, wherein each pre-distortion function is a member of said population, and to identify a best-fit member from said population, said best-fit member producing less out-of-band power than others of said members.