Radio apparatus having distortion compensating function

• US 20020085647A1
• Filed: 11/07/2001
• Published: 07/04/2002
• Est. Priority Date: 07/28/1999
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Nagatani, Kazuo, Takano, Takeshi, Ode, Takayoshi, Oishi, Yasuyuki, Kubo, Tokuro
• Granted Patent: US 6,567,478 B2
• Time in Patent Office: Days
• US Class Current: 375/297
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04B 2001/0433 with linearisation using feedback
• CPC Class Codes: H04J 1/00 Frequency-division multiplex systems H04J14/00 takes precedence
• CPC Class Codes: H04L 27/367 using predistortion
• CPC Class Codes: H04W 52/52 using AGC [Automatic Gain Control] circuits or amplifiers

Abstract

In a radio apparatus which compensates for non-linear distortion of a transmission power amplifier, a distributor feeds back the output signal of the transmission power amplifier, an error-signal estimating arithmetic unit digitally estimates an error signal, which is ascribable to non-linear distortion of the power amplifier, using a transmit signal and feedback signal, the transmit signal and the error signal are DA-converted by separate DA converters, and a combiner combines the output signals of the DA converters and inputs the combined signal to the transmission power amplifier to perform distortion compensation.

Claims

1. A radio apparatus for compensating for non-linear distortion of a transmission power amplifier, characterized by having:

a first DA converter for converting a transmit signal to an analog signal and outputting the analog transmit signal;

a transmission power amplifier for amplifying and transmitting the transmit signal;

branching means for branching part of an output signal of said transmission power amplifier;

an AD converter for converting, to a digital signal, the output signal of the transmission power amplifier branched by the branching means or a signal obtained by subjecting this output signal to predetermined processing, and outputting the digital signal as a feedback signal;

an error estimating arithmetic unit for estimating and outputting an error signal, which is ascribable to non-linear distortion of the amplifier, using the feedback signal and a reference signal, which is the transmit signal;

a second DA converter for converting said error signal to an analog signal and outputting the analog signal; and

a combiner for combining, and outputting to the transmission power amplifier, the transmit signal converted to the analog signal by the first DA converter and the error signal converted to the analog signal by the second DA converter.

3. A radio apparatus according to claim 1 or 2, characterized in that said error estimating arithmetic unit obtains error signals by a digital Cartesian scheme in such a manner that a difference between said reference signal and said feedback signal becomes zero, stores said error signals in a memory in correspondence with transmit-signal values, reads an error signal that corresponds to a present transmit signal out of the memory and outputs the error signal.

4. A radio apparatus according to claim 1 or 2, characterized in that said error estimating arithmetic unit transforms said reference signal and said feedback signal from a rectangular coordinate system to a polar coordinate system, obtains error signals in such a manner that a difference between said reference signal and said feedback signal becomes zero in the polar coordinate system, stores the error signals in memory in correspondence with transmit-signal values, reads an error signal that corresponds to a present transmit signal out of the memory, transforms said error signal from the polar coordinate system to the rectangular coordinate system and outputs the error signal.

5. A radio apparatus according to claim 1 or 2, characterized in that said error estimating arithmetic unit obtains distortion compensation coefficients by adaptive signal processing using said reference signal and said feedback signal, stores said distortion compensation coefficients in a memory in correspondence with transmit-signal power values, reads a distortion compensation coefficient corresponding to a power value of a present transmit signal out of the memory, multiplies said transmit value by the distortion compensation coefficient and outputs, as an error signal, a difference between a transmit signal before multiplication by said distortion compensation coefficient and the transmit signal after multiplication by the distortion compensation coefficient.

6. A radio apparatus according to claim 1 or 2, characterized in that said error estimating arithmetic unit obtains, and stores in a memory, distortion compensation coefficients by adaptive signal processing using said reference signal and said feedback signal, reads a distortion compensation coefficient corresponding to a present transmission power value and a past transmit-signal value out of the memory, multiplies the present transmit value by the distortion compensation coefficient and outputs, as an error signal, a difference between a transmit signal before multiplication by said distortion compensation coefficient and the transmit signal after multiplication by the distortion compensation coefficient.

7. A radio apparatus according to claim 1, characterized by further having:

means for converting a transmit signal to a quadrature signal having an in-phase component and a quadrature component;

DA converters, which construct said first DA converter, for converting the signal components of the quadrature signal to respective ones of analog signals;

a first quadrature modulator, to which the analog signal components output from respective ones of the DA converters are input, for subjecting the transmit signal to quadrature modulation;

a quadrature demodulator for subjecting an output signal of the transmission power amplifier to quadrature demodulation processing;

AD converters, which construct said AD converter, for converting an in-phase component and a quadrature component of a quadrature-demodulated signal output from the quadrature modulator to respective ones of digital signals;

DA converters, which construct said second DA converter, for converting an in-phase component and a quadrature component of an error signal output from said error-signal estimating arithmetic unit to respective ones of analog signals; and

a second quadrature modulator, to which the analog signal components output from respective ones of the DA converters are input, for subjecting the error signal to quadrature modulation;

said error-signal estimating arithmetic unit outputting an error signal in such a manner that a difference between the in-phase components and a difference between the quadrature components of the quadrature signal before distortion compensation and the quadrature demodulated signal will become zero, and said combiner combines output signals of the first and second quadrature modulators and inputs the combined signal to the transmission power amplifier.

8. A radio apparatus according to claim 7, characterized by further having sample-and-hold circuits provided on an input side of respective ones of the AD converters;

sampling rate of AD conversion and sampling band being set independently.

9. A radio apparatus according to claim 1, characterized by further having:

means for converting a transmit signal to a quadrature signal having an in-phase component and a quadrature component;

a first digital quadrature modulator, to which the input signal components are input, for subjecting the transmit signal to quadrature modulation and inputting the resulting signal to said first DA converter;

a digital quadrature demodulator for subjecting an output signal of said AD converter to quadrature demodulation processing; and

a second digital quadrature modulator, to which an in-phase component and a quadrature component of an error signal output from said error-signal estimating arithmetic unit are input, for subjecting said error signal to quadrature modulation and inputting the resulting signal to said second DA converter;

said error-signal estimating arithmetic unit outputting an error signal in such a manner that a difference between the in-phase components and a difference between the quadrature components of the quadrature signal before distortion compensation and the quadrature demodulated signal will become zero.

10. A radio apparatus according to claim 9, characterized by further having a sample-and-hold circuit provided on an input side of the AD converter;

sampling rate of AD conversion and sampling band being set independently.

14. A radio apparatus according to claim 9, characterized by further having a sample-and-hold circuit provided on an input side of said AD converter;

sampling rate of AD conversion and sampling band being set independently.

2. A radio apparatus for compensating for non-linear distortion of a transmission power amplifier which amplifies and transmits a multicarrier signal for carrying multiple transmit signals, characterized by having:

a first DA converter for converting each digital transmit signal to an analog transmit baseband signal and outputting the analog baseband signal;

an analog frequency multiplexer for subjecting each transmit baseband signal to a frequency-shift operation decided by carrier spacing and frequency-multiplexing the frequency-shifted signals;

a transmission power amplifier for amplifying and transmitting the frequency-multiplexed signal;

branching means for branching part of an output signal of said transmission power amplifier;

an AD converter for converting, to a digital signal, the output signal of the transmission power amplifier branched by the branching means or a signal obtained by subjecting this output signal to predetermined processing, and outputting the digital signal as a feedback signal;

a digital frequency multiplexer for subjecting each digital transmit signal digitally to a frequency-shift operation decided by carrier spacing, frequency-multiplexing the frequency-shifted signals and outputting the frequency-multiplexed signal as a reference signal;

an error estimating arithmetic unit for estimating and outputting an error signal, which is ascribable to non-linear distortion of the amplifier, using the reference signal and the feedback signal;

a second DA converter for converting said error signal to an analog signal and outputting the analog signal; and

a combiner for combining, and outputting to the transmission power amplifier, the error signal converted to the analog signal by said DA converter and an output signal of said analog frequency multiplexer.

11. A radio apparatus according to claim 2, characterized by further having:

means for converting respective ones of transmit signals to quadrature signals each having an in-phase component and a quadrature component;

DA converters, which construct each of said first DA converters, for converting an in-phase component and a quadrature component of a respective quadrature signal to respective ones of analog signals;

a first quadrature modulator, for each quadrature signal, to which the analog in-phase and quadrature components output from corresponding DA converters are input, for subjecting the transmit signal to quadrature modulation;

a quadrature demodulator for subjecting an output signal of the transmission power amplifier, or a signal obtained by subjecting said output signal to predetermined processing, to quadrature demodulation processing;

AD converters, which construct said AD converter, for converting an in-phase component and a quadrature component of the quadrature demodulated signal output from the quadrature demodulator to respective ones of digital signals;

DA converters, which construct said second DA converter, for converting an in-phase component and a quadrature component of an error signal output from said error-signal estimating arithmetic unit to respective ones of analog signals; and

a second quadrature modulator, to which the signal components of the error signal output from said DA converters are input, for subjecting the error signal to quadrature modulation;

said error-signal estimating arithmetic unit outputting an error signal in such a manner that a difference between the in-phase components and a difference between the quadrature components of the quadrature signal before distortion compensation and the quadrature demodulated signal will become zero, and said combiner combines output signals of the first and second quadrature modulators and inputs the combined signal to the transmission power amplifier.

12. A radio apparatus according to claim 11, characterized by further having sample-and-hold circuits provided on an input side of respective ones of the AD converters;

sampling rate of AD conversion and sampling band being set independently.

13. A radio apparatus according to claim 2, characterized by further having:

means for converting respective ones of transmit signals to quadrature signals each having an in-phase component and a quadrature component;

a first digital quadrature modulator, for every quadrature signal, to which digital in-phase and quadrature components are input, for subjecting the transmit signal to quadrature modulation and inputting the resulting signal to said first DA converter;

a digital quadrature demodulator for subjecting an output signal of said AD converter to quadrature demodulation processing; and

a second digital quadrature modulator, to which an in-phase component and a quadrature component of an error signal output from said error-signal estimating arithmetic unit are input, for subjecting said error signal to quadrature modulation and inputting the resulting signal to said second DA converter;

said error-signal estimating arithmetic unit outputting an error signal in such a manner that a difference between the in-phase components and a difference between the quadrature components of the quadrature signal before distortion compensation and the quadrature demodulated signal will become zero.

15. A radio apparatus according to 2, characterized by further having a correction circuit for every transmit signal, said correction circuit having an AD converter for converting, to a digital signal, an analog signal obtained by a frequency shift performed by said analog frequency multiplexer, and means for comparing an output of this AD converter with a signal obtained by digitally subjecting said transmit signal to the frequency-shift operation, and correcting amplitude and phase of the output signal based upon result of the comparison;

said digital frequency multiplexer combining output signals of respective ones of the correction circuits and outputting the combined signal as the reference signal.

16. A radio apparatus according to claim 11, characterized by further having a correction circuit for every transmit signal, said correction circuit having a quadrature demodulator for subjecting an analog signal, which is obtained by a frequency shift performed by said analog frequency multiplexer, to quadrature demodulation processing, AD converters for converting, to respective ones of digital signals, an in-phase component and a quadrature component of a quadrature-demodulated signal from the quadrature demodulator, and means for comparing outputs of these AD converters with signals obtained by digitally subjecting said transmit signal to the frequency-shift operation, and correcting amplitude and phase of the output signal based upon result of the comparison;

said digital frequency multiplexer combining output signals of respective ones of the correction circuits and outputting the combined signal as the reference signal.

17. A radio apparatus according to 13, characterized by further having a correction circuit for every transmit signal, said correction circuit having an AD converter for converting, to a digital signal, an analog signal obtained by a frequency shift performed by said analog frequency multiplexer, a digital quadrature demodulator for subjecting an output signal of this AD converter to quadrature demodulation processing, and means for comparing the quadrature-demodulated signal with a signal obtained by digitally subjecting said transmit signal to the frequency-shift operation, and correcting amplitude and phase of the output signal based upon result of the comparison;

said digital frequency multiplexer combining output signals of respective ones of the correction circuits and outputting the combined signal as the reference signal.

18. A radio apparatus according to claim 2, characterized by further having PLL circuits, to which are input digital frequency signals used to subject the transmit signals to the frequency-shift operation in the digital frequency multiplexer, for generating carrier frequency signals used in the frequency shift of said analog frequency multiplexer.

19. A radio apparatus according to claim 2, characterized by further having DA converters for DA-converting digital frequency signals used to subject the transmit signals to the frequency-shift operation in the digital frequency multiplexer, and adopting the analog frequency signals, which are obtained by the DA conversion, as carrier frequency signals used in the frequency shift of said analog frequency multiplexer.

20. A radio apparatus for compensating for non-linear distortion of a transmission power amplifier which amplifies and transmits a multicarrier signal for carrying multiple transmit signals, characterized by having:

a frequency shifter for subjecting each digital transmit signal digitally to a frequency-shift operation decided by carrier spacing;

a DA converter for DA-converting each frequency-shifted transmit signal;

an analog frequency multiplexer for frequency-multiplexing outputs of each of the DA converters;

a transmission power amplifier for amplifying and transmitting a transmit signal;

branching means for branching part of an output signal of said transmission power amplifier;

an AD converter for converting, to a digital signal, the output signal of the transmission power amplifier branched by said branching means or a signal obtained by subjecting this output signal to predetermined processing, and outputting the digital signal as a feedback signal;

a digital frequency multiplexer for digitally combining the frequency-shifted transmit signals and outputting a reference signal;

an error estimating arithmetic unit for estimating and outputting an error signal, which is ascribable to non-linear distortion of the amplifier, using the reference signal and said feedback signal;

a DA converter for converting said error signal to an analog signal and outputting the analog signal; and

a combiner for combining, and outputting to the transmission power amplifier, the error signal converted to the analog signal by said DA converter and an output signal of said analog frequency multiplexer.

21. A radio apparatus for compensating for non-linear distortion of a transmission power amplifier which amplifies and transmits a multicarrier signal for carrying multiple transmit signals, characterized by having:

a sampling-rate converter for converting each digital transmit signal to a digital signal having a sampling rate decided by carrier spacing;

a digital quadrature modulator for subjecting an output signal of each sampling-rate converter to quadrature modulation;

a DA converter for converting an output signal of each quadrature modulator to an analog signal;

first combining means for combining outputs of the DA converters;

a transmission power amplifier for amplifying and transmitting a transmit signal;

branching means for branching part of an output signal of said transmission power amplifier;

an AD converter for converting, to a digital signal, the output signal of the transmission power amplifier branched by said branching means or a signal obtained by subjecting this output signal to predetermined processing, and outputting the digital signal as a feedback signal;

a digital frequency multiplexer for performing frequency multiplexing by digitally subjecting each digital transmit signal to a frequency-shift operation decided by carrier spacing, and outputting a reference signal;

an error estimating arithmetic unit for estimating and outputting an error signal, which is ascribable to non-linear distortion of the amplifier, using the reference signal and said feedback signal;

a DA converter for converting said error signal to an analog signal and outputting the analog signal; and

a second combiner for combining, and outputting to the transmission power amplifier, the error signal converted to the analog signal by said DA converter and an output signal of said second combiner.