System and method for adaptive predistortion

• US 6,614,854 B1
• Filed: 05/28/1999
• Issued: 09/02/2003
• Est. Priority Date: 05/28/1999
• Status: Expired due to Term

• Current Assignee: CarrierComm, Inc. (Moseley Wireless Solutions Group)
• Original Assignee: CarrierComm, Inc. (Moseley Wireless Solutions Group)
• Inventors: Krizman, Donna M., Babb, Roger A., Chow, Peter El Kwan
• Primary Examiner(s): VO, DON NGUYEN
• Application Number:
  US09/322,243
• Time in Patent Office: 1,558 Days
• Field of Search: 375/296, 375/297, 330/107, 330/149, 330/294, 330/302, 332/159, 332/103, 332/160, 332/161, 332/162, 455/126, 455/114, 455/115, 455/127
• US Class Current: 375/297
• CPC Class Codes: H04L 1/0016 involving special memory structures, e.g. look-up tables
• CPC Class Codes: H04L 1/0023 characterised by the signalling
• CPC Class Codes: H04L 2025/03802 Signalling on the reverse channel
• CPC Class Codes: H04L 27/368 adaptive predistortion

Abstract

Distortion introduced into a multiamplitude signal format or amplitude and phase signal format by a high power microwave amplifier is compensated by a system which adapts itself to non-linearities present in the amplifier and predistorts the input signals before they are subjected to the non-linearities created by the amplifier. The degree of predistortion is non-fixed and varies or is updated as the non-linear conversion characteristics of the amplifier change with time. The distortion can also be compensated by using a power curve look-up table.

Claims

1. A method of transmitting a signal having desired characteristics, comprising the steps of:

storing a set of lookup tables of correction parameters for correcting a baseband signal, wherein lookup tables of said set correspond to different conditions of an operating attribute of an amplifier used in transmitting said signal;

detecting a condition of an attribute of an output signal of said amplifier;

selecting a current lookup table of said set for use in manipulating a modulated signal, wherein selection of a current lookup table by said selecting step is at least in part a function of said condition of said operating attribute of said amplifier;

accepting a data signal to be transmitted;

modulating said accepted data signal to provide said modulated signal;

distorting said modulated signal as a function of said current lookup table; and

amplifying said modulated signal to supply said output signal.

2. The method according to claim 1, further comprising the steps of:

identifying distortion characteristics corresponding to a plurality of conditions of said operating attribute of said output signal; and

inverting said distortion characteristics to form respective ones of said correction parameters.

3. The method according to claim 1, wherein said condition of said output signal is a scalar quantity.

4. The method according to claim 3, wherein said scalar quantity is power output.

5. The method according to claim 1, further comprising the steps of radiating said output signal into space;

receiving the radiated output signal;

detecting in-phase and quadrature components of the received signal; and

updating ones of said distortion characteristics corresponding to said operating attribute.

6. The method according to claim 5, further comprising the step of:

transmitting information as a finction of said detecting in-phase and quadrature components step from a location of said receiving to a location of said radiating.

7. The method according to claim 6, wherein said information includes unrefined data provided by said detecting in-phase and quadrature components step.

8. The method according to claim 6, wherein said information includes update distortion characteristics.

9. The method according to claim 1, further comprising the steps of:

radiating said output signal into space;

receiving the radiated output signal;

detecting a characteristic of the received output signal; and

performing said amplifying step in response to said characteristic of the received output signal.

10. The method according to claim 9, further comprising the step of transmitting said charateristic of said received signal from said receiver location to said transmitter location.

11. The method according to claim 1, further comprising the step of:

adjusting an amplitude of said distorted modulated signal prior to amplification by said amplifying step.

12. The method according to claim 11, where in said attribute of said output signal is a power level, and wherein said adjusting step alters a condition of said attribute sufficiently to cause selection of a different lookup table of said set as said current lookup table by said selecting step.

13. The method according to claim 1, wherein lookup tables of said set are associated with a particular condition of said operating attribute different from a condition of said operating attribute of a next lookup table by a predetermined amount.

14. The method according to claim 13, wherein said predetermined amount is ½

dB.

15. The method according to claim 13, wherein said predetermined amount is an amount less than an accurate resolution of detecting said condition of said attribute according to said detecting step.

16. The method according to claim 15, further comprising the step of:

grouping lookup tables of said set to provide a plurality of groups of lookup tables, wherein selection of any lookup table of a group of lookup tables substantially only results in an amplitude adjustment difference between selection of any other lookup table of said group when implemented.

17. A system for predistorting a signal to be amplified, said system comprising:

means for storing a set of lookup tables of predistortion parameters for correcting an amplified signal, wherein lookup tables of said set correspond to different power levels of said amplified signal;

means for measuring a power level of said amplified signal;

means for selecting a current lookup table of said set for use in predistorting a signal, wherein selection of a current lookup table by said selecting means is at least in part a function of said measured power level;

means for accepting a signal to be amplified;

means for distorting said accepted signal as a function of said current lookup table; and

means for amplifying said distorted signal to supply said amplified signal.

18. The system according to claim 17, further comprising:

means for radiating said amplified signal;

means for receiving the radiated signal;

means for detecting in-phase and quadrature components of the received signal; and

means for updating ones of said predistortion parameters corresponding to a particular power level as a function of said detected in-phase and quadratic components.

19. The system according to claim 18, further comprising:

means for transmitting update information from said receiving means to a transmitter location associated with said means for distorting.

20. The system according to claim 17, further comprising:

means for adjusting an amplitude of said distorted signal prior to amplification by said amplifying means.

21. The system according to claim 17, wherein lookup tables of said set are associated with a particular power level offset from a power level associated with a next lookup table of said set by a predetermined uniform amount.

22. The system according to claim 21, wherein said predetermined amount is ½

dB.

23. The system according to claim 21, wherein said predetermined amount is an amount less than an accurate power level measuring resolution of said means for measuring.

24. The system according to claim 23, further comprising:

means for grouping lookup tables of said set to provide a plurality of groups of lookup tables, wherein selection of any lookup table of a group of lookup tables substantially only results in an amplitude adjustment difference between selection of any other lookup table of said group when implemented.

25. A system for transmitting a signal having desired characteristics, comprising:

an amplifier accepting an input signal for manipulation and providing a manipulated input signal as an output signal;

a memory having stored therein data including correction parameters for correcting said manipulation of said input signal by said amplifier, wherein said data is identifiable in sets corresponding to different characteristics of said output signal;

a detector coupled to an output signal of said amplifier operable to detect a characteristic of said output signal;

a processor in communication with said memory and said detector, wherein said processor operates under control of an instruction set adapted to select a current set of said data for use in manipulating said modulated signal as a function of said characteristic; and

a predistorter in communication with said processor and said amplifier having a memory for storing at least one set of said data, wherein said predistorter stores said current set of said data and manipulates a signal according to said current set of said data.

26. The system of claim 25, wherein said sets of data are lookup tables.

27. The system of claim 25, wherein said different characteristics are different power levels of said output signal.

28. The system of claim 25, wherein said detector operates to detect a power level of said output signal.

29. The system of claim 25, wherein said data sets comprise:

a plurality of in-phase signal component multipliers; and

a plurality of quadrature signal component multipliers, wherein ones of said in-phase signal component multipliers and said quadrature signal component multipliers are associated with a particular magnitude of said signal manipulated by said predistorter.

30. The system of claim 25, further comprising:

a detector coupled to said output signal detecting at least one component of the output signal, wherein said detector provides information to update said data to reflect changes in operation of said amplifier over time.

31. The system of claim 30, wherein said at least one component detected comprises an in-phase component of said output signal.

32. The system of claim 30, wherein said at least one component detected comprises a quadrature component of said output signal.

33. The system of claim 30, wherein said updating is performed at predefined intervals.

34. The system of claim 30, wherein said updating is performed upon the occurrence of a predetermined condition.

35. The system of claim 34, wherein said predetermined condition is detection of an unacceptable output signal quality.

36. The system of claim 30, further comprising:

a receiver disposed to receive said output signal after wireless transmission of said output signal, wherein said detector is collocated with said receiver.

37. The system of claim 25, further comprising:

an attenuator disposed in a signal path between said predistorter and said amplifier adapted to adjust an amplitude of said output signal.

38. The system of claim 37, wherein said characteristic of said output signal is a power level, and wherein said attenuator alters said characteristic sufficiently to cause selection of a different data set by said processor.

39. The system of claim 25, wherein data sets of said data are associated with a particular characteristic value offset from a characteristic value of a next data set by a predetermined amount.

40. The system of claim 39, wherein said predetermined amount is ½

dB.

41. The system of claim 39, wherein said predetermined amount is an amount less than an accurate resolution of detecting said characteristic by said detector.

42. The system of claim 41, wherein said data sets stored in said memory are grouped to include a plurality of groups of data sets each including a plurality of data sets such that use of any data set of any of said groups by said predistorter substantially only results in an amplitude adjustment difference between use of any other data set of said group.

43. A predistortion amplifier system comprising:

a memory for storing a set of lookup tables of correction parameters for correcting a baseband signal;

a receiver for receiving a data signal;

a modulator for modulating a baseband signal with said data signal to supply a modulated signal;

a predistorter for predistorting said modulated signal using a selected one of said correction parameters;

an amplifier for amplifying said modulated signal to supply an output signal;

a detecting circuit for detecting a characteristic of said output signal; and

a selector for selecting one table from the set of lookup tables in response to said characteristic of said output signal.