Multicarrier transmitter and methods for generating multicarrier communication signals with power amplifier predistortion and linearization

• US 20060067426A1
• Filed: 09/28/2004
• Published: 03/30/2006
• Est. Priority Date: 09/28/2004
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Maltsev, Alexander A., Sadri, Ali S., Poldin, Oleg V., Maltsev, Alexander A. Jr.
• Granted Patent: US 7,463,697 B2
• Time in Patent Office: Days
• US Class Current: 375/297
• CPC Class Codes: H04L 25/49 using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems spectral shaping H04L25/03828
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/26035 Maintenance of orthogonality, e.g. for signals exchanged between cells or users, or by using covering codes or sequences using different training sequence per antenna H04B7/0684; code allocation H04J13/16

Abstract

A multicarrier signal is generated by pre-compensating frequency-domain subcarrier symbols for substantially linear distortion subsequently introduced by a time-domain baseband filter.

Claims

1. A multicarrier transmitter comprising:

a frequency-domain predistorter to multiply complex amplitudes of a multicarrier symbol by complex coefficients;

clipping circuitry to clip a time-domain baseband signal transformed from a frequency-domain output of the frequency-domain predistorter; and

a time-domain predistorter to perform low-pass filtering on the clipped time-domain baseband signal.

2. The transmitter of claim 1 wherein the frequency-domain predistorter performs a substantially linear transformation by multiplying a complex amplitude of each of a plurality of subcarrier symbols by an associated one of the complex coefficients, and

wherein the time-domain predistorter performs a substantially linear transformation on the clipped time-domain baseband signal providing a frequency transfer function approximately inverse to a frequency transfer function of the frequency-domain predistorter.

3. The transmitter of claim 2 wherein the complex coefficients are selected to provide a frequency transfer function of the frequency-domain predistorter approximately inverse to a frequency transfer function of the time-domain predistorter for in-band signal components.

4. The transmitter of claim 2 further comprising an adaptation and control unit to provide a clipping level input to the clipping circuitry for selection of a clipping level,

wherein the time-domain predistorter performs the substantially linear transformation based on a set of complex coefficients, and

wherein the adaptation and control unit selects different sets of complex coefficients for both the frequency-domain predistorter and the time-domain predistorter for different modulation types and coding rates associated with the subcarrier symbols.

5. The transmitter of claim 4 further comprising a coefficient storage element to store the different sets of complex coefficients for use by the time-domain predistorter and for use by the frequency-domain predistorter,

wherein at least some of the complex coefficients are different for at least some of the subcarriers.

6. The transmitter of claim 2 wherein the multicarrier symbol comprises the plurality of subcarrier symbols, each subcarrier symbol being associated with one of a plurality of subcarriers of a multicarrier communication channel, and

wherein one of the complex coefficients is provided for each subcarrier of the multicarrier channel.

7. The transmitter of claim 6 wherein the transmitter comprises circuitry to generate an orthogonal frequency division multiplexed signal comprising a plurality of substantially orthogonal symbol-modulated subcarriers,

wherein each subcarrier symbol is associated with one of the orthogonal symbol-modulated subcarriers of the orthogonal frequency division multiplexed signal.

8. The transmitter of claim 2 further comprising a non-linear predistorter to pre-distort a digital signal output from the time-domain predistorter to, at least in part, compensate for non-linear distortion introduced subsequently by a power amplifier,

the non-linear predistorter to provide a predistorted output signal for subsequent amplification by the power amplifier.

9. The transmitter of claim 8 wherein the non-linear predistorter adjusts a predistorted signal maximum of the predistorted output signal to achieve an output level of the power amplifier which is predetermined percentage of a saturation level of the power amplifier.

10. The transmitter of claim 9 further comprising an adaptation and control unit to provide a predistortion control signal to the non-linear predistorter to adjust the predistorted signal maximum of the predistorted output signal to achieve an output level of the power amplifier which is the predetermined percentage of the saturation level of the power amplifier.

11. The transmitter of claim 10 wherein the adaptation and control unit is to generate the predistortion control signal by a comparison of a sampled output from the power amplifier with the digital signal output of the time-domain predistorter.

12. The transmitter of claim 10 wherein the adaptation and control unit is to generate the predistortion control signal by a comparison of a sampled output from the power amplifier with the digital signal output of the time-domain predistorter.

13. The transmitter of claim 10 wherein the non-linear predistorter performs a non-linear transformation based on predistortion coefficients to pre-distort the digital signal output from the time-domain predistorter, and

wherein the adaptation and control unit is to adjust the predistortion coefficients used by the non-linear predistorter in response to changes in a transfer function of the power amplifier including changes in a saturation level of power amplifier.

14. The transmitter of claim 1 further comprising inverse fast Fourier transform circuitry (IFFT) to generate a time-domain baseband signal from the frequency-domain output of the frequency-domain predistorter, and

wherein the clipping circuitry is to reduce signal peak-to-average power ratio of the time-domain baseband signal.

15. The transmitter of claim 14 wherein the IFFT circuitry further performs an interpolation by adding zeros to frequency-domain output when an IFFT size is greater than a number of subcarriers.

16. The transmitter of claim 1 further comprising:

an adaptation and control unit to provide a clipping level input for the clipping circuitry for selection of a clipping level,

wherein the an adaptation and control unit is to select different sets of the complex coefficients for both the frequency-domain predistorter and the time-domain predistorter for different modulation types and coding rates associated with the subcarrier symbols; and

a modulator to modulate groups of bits of a bit stream to generate the plurality of subcarrier symbols, the modulator to generate one subcarrier symbol for each of the plurality of subcarriers, the modulator to receive a modulation type input from the adaptation and control unit to select a modulation type.

17. The transmitter of claim 16 wherein the adaptation and control unit selects the clipping level input and the sets of the complex coefficients for both the frequency-domain predistorter and the time-domain predistorter based on at least some of a saturation level of the power amplifier, a desired transmit power level, a ripple of a step response function of the time-domain predistorter, and a selected modulation type and coding rate.

18. The multicarrier transmitter comprising:

a frequency-domain predistorter to perform a substantially linear transformation on frequency-domain samples comprising a multicarrier symbol;

clipping circuitry to perform a non-linear transformation on a time-domain baseband signal generated from linearly transformed frequency domain samples provided by the frequency-domain predistorter;

a time-domain predistorter to perform a substantially linear transformation on a clipped time-domain baseband signal provided by the clipping circuitry; and

a non-linear predistorter to perform a non-linear transformation on linearly transformed clipped time-domain signals provided by the time-domain predistorter.

19. The transmitter of claim 18 further comprising a power amplifier to perform a non-linear transformation by amplifying an upconverted analog version of output signals provided by the non-linear predistorter,

wherein the transformation performed by the frequency-domain predistorter is approximately inverse to the transformation performed by the time-domain predistorter.

20. The transmitter of claim 19 wherein the non-linear predistorter is to pre-distort a digital signal output from the time-domain predistorter to, at least in part, compensate for non-linear distortion introduced subsequently by a power amplifier, and

wherein the non-linear predistorter is to provide a predistorted output signal for subsequent amplification by the power amplifier.

21. The transmitter of claim 20 wherein the non-linear predistorter adjusts a predistorted signal maximum of the predistorted output signal to achieve a maximum output level of the power amplifier which is a predetermined percentage of a saturation level of the power amplifier, and

wherein the transmitter further comprises an adaptation and control unit to provide a predistortion control signal to the non-linear predistorter to adjust the predistorted signal maximum of the predistorted output signal to achieve the maximum output level of the power amplifier which is the predetermined percentage of the saturation level of the power amplifier.

22. The transmitter of claim 21 wherein the adaptation and control unit is to generate the predistortion control signal by comparing a sampled output from the power amplifier with the digital signal output of the time-domain predistorter.

23. The transmitter of claim 21 wherein the adaptation and control unit is to generate the predistortion control signal by a comparison of a sampled output from the power amplifier with the digital signal output of the time domain non-linear predistorter.

24. The transmitter of claim 21 wherein the non-linear predistorter performs a non-linear transformation based on predistortion coefficients to pre-distort the digital signal output from the time-domain predistorter, and

wherein the adaptation and control unit is to adjust the predistortion coefficients used by the non-linear predistorter in response to changes in a transfer function of the power amplifier including changes in a saturation level of power amplifier.

25. A method for generating a multicarrier communication signal comprising:

performing a substantially linear transformation on frequency-domain samples comprising a multicarrier symbol with a frequency-domain predistorter;

transforming frequency domain samples provided by the frequency-domain predistorter to generate a time-domain baseband signal;

performing a non-linear transformation on the time-domain baseband signal with clipping circuitry;

performing a substantially linear transformation with a time-domain predistorter on a clipped time-domain baseband signal provided by the clipping circuitry; and

performing a non-linear transformation with a non-linear predistorter on linearly transformed clipped time-domain signals provided by the time-domain predistorter.

26. The method of claim 25 further comprising performing a non-linear transformation with a power amplifier by amplifying an upconverted analog version of output signals provided by the non-linear predistorter,

wherein the transformation performed by the frequency-domain predistorter is approximately inverse to the transformation performed by the time-domain predistorter.

27. The method of claim 26 further comprising:

pre-distorting, with the non-linear predistorter, a digital signal output from the time-domain predistorter to, at least in part, compensate for non-linear distortion introduced subsequently by a power amplifier; and

providing a predistorted output signal for subsequent amplification by the power amplifier.

28. The method of claim 27 further comprising:

adjusting, by the non-linear predistorter, a predistorted signal maximum of the predistorted output signal to achieve a maximum output level of the power amplifier which is a predetermined percentage of a saturation level of the power amplifier; and

providing a predistortion control signal to the non-linear predistorter to adjust the predistorted signal maximum of the predistorted output signal to achieve the maximum output level of the power amplifier which is the predetermined percentage of the saturation level of the power amplifier.

29. The method of claim 28 further comprising generating the predistortion control signal by comparing a sampled output from the power amplifier with the digital signal output of the time-domain predistorter.

30. The method of claim 28 further comprising generating the predistortion control signal by comparing a sampled output from the power amplifier with the digital signal output of the non-linear predistorter.

31. The method of claim 28 further comprising:

performing a non-linear transformation, by the non-linear predistorter, based on predistortion coefficients to pre-distort the digital signal output from the time-domain predistorter, and

adjusting the predistortion coefficients used by the non-linear predistorter in response to changes in a transfer function of the power amplifier including changes in a saturation level of power amplifier.

32. A wireless communication device comprising:

a substantially omnidirectional antenna; and

a multicarrier transmitter to transmit a multicarrier communication signal with the antenna, wherein the multicarrier transmitter comprises;

a frequency-domain predistorter to multiply complex amplitudes of a multicarrier symbol by complex coefficients;

clipping circuitry to clip a time-domain baseband signal transformed from a frequency-domain output of the frequency-domain predistorter; and

a time-domain predistorter to perform low-pass filtering on the clipped time-domain baseband signal.

33. The device of claim 32 wherein the frequency-domain predistorter performs a substantially linear transformation by multiplying a complex amplitude of each of a plurality of subcarrier symbols by an associated one of the complex coefficients, and

wherein the time-domain predistorter performs a substantially linear transformation on the clipped time-domain baseband signal providing a frequency transfer function approximately inverse to a frequency transfer function of the frequency-domain predistorter.

34. The device of claim 33 further comprising a non-linear predistorter to pre-distort a digital signal output from the time-domain predistorter to, at least in part, compensate for non-linear distortion introduced subsequently by a power amplifier,

the non-linear predistorter to provide a predistorted output signal for subsequent amplification by the power amplifier.

wherein the non-linear predistorter adjusts a predistorted signal maximum of the predistorted output signal to achieve a maximum output level of the power amplifier which is a predetermined percentage of a saturation level of the power amplifier.

35. A machine-readable medium that provides instructions, which when executed by one or more processors, cause the processors to perform operations comprising:

performing a substantially linear transformation on frequency-domain samples comprising a multicarrier symbol with a frequency-domain predistorter;

transforming frequency domain samples provided by the frequency-domain predistorter to generate a time-domain baseband signal;

performing a non-linear transformation on the time-domain baseband signal with clipping circuitry;

performing a substantially linear transformation with a time-domain predistorter on a clipped time-domain baseband signal provided by the clipping circuitry; and

performing a non-linear transformation with a non-linear predistorter on linearly transformed clipped time-domain signals provided by the time-domain predistorter.

36. The machine-readable medium of claim 35 wherein the instructions, when further executed by one or more of the processors cause the processors to perform operations further comprising:

performing a non-linear transformation with a power amplifier by amplifying an upconverted analog version of output signals provided by the non-linear predistorter,

wherein the transformation performed by the frequency-domain predistorter is approximately inverse to the transformation performed by the time-domain predistorter.

37. The machine-readable medium of claim 36 wherein the instructions, when further executed by one or more of the processors cause the processors to perform operations further comprising:

pre-distorting, with the non-linear predistorter, a digital signal output from the time-domain predistorter to, at least in part, compensate for non-linear distortion introduced subsequently by a power amplifier; and

providing a predistorted output signal for subsequent amplification by the power amplifier.

38. The machine-readable medium of claim 37 wherein the instructions, when further executed by one or more of the processors cause the processors to perform operations further comprising:

adjusting, by the non-linear predistorter, a predistorted signal maximum of the predistorted output signal to achieve a maximum output level of the power amplifier which is a predetermined percentage of a saturation level of the power amplifier; and

providing a predistortion control signal to the non-linear predistorter to adjust the predistorted signal maximum of the predistorted output signal to achieve the maximum output level of the power amplifier which is the predetermined percentage of the saturation level of the power amplifier.