FREQUENCY DEPENDENT I/Q IMPAIRMENT COMPENSATION

• US 20140307768A1
• Filed: 03/26/2014
• Published: 10/16/2014
• Est. Priority Date: 04/10/2013
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Gotman, Maxim, Oved, Tal
• Granted Patent: US 9,130,626 B2
• Time in Patent Office: Days
• US Class Current: 375/232
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04L 27/01 Equalisers baseband equalizers at the transmitter end H04L25/03343; in analogue transmission systems H04B3/04, H04B7/005
• CPC Class Codes: H04L 27/2636 with FFT or DFT modulators, e.g. standard single-carrier frequency-division multiple access [SC-FDMA] transmitter or DFT spread orthogonal frequency division multiplexing [DFT-SOFDM]
• CPC Class Codes: H04L 27/364 Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels
• CPC Class Codes: H04L 27/3863 Compensation for quadrature error in the received signal

Abstract

Methods, systems, and devices are described for compensating for transmit I/Q impairments in a digital signal. A frequency domain version of a first one of the components may be scaled at a wireless modem according to a frequency dependent I/Q impairment compensation function to obtain a compensated frequency domain version of the first one of the components. The compensated frequency domain version of the first one of the components may be combined with a frequency domain version of a second one of the components at the wireless modem to produce a compensated frequency domain version of the digital signal. The compensated frequency domain version of the digital signal may be transformed to the time domain at the wireless modem to produce a compensated time domain version of the digital signal.

Claims

1. A method of compensating for I/Q impairments in a digital signal, comprising:

decomposing the digital signal into a plurality of components;

scaling a frequency domain version of a first component from the plurality of components according to a frequency dependent I/Q impairment compensation function to obtain a compensated frequency domain version of the first component; and

combining the compensated frequency domain version of the first component with a frequency domain version of a second component from the plurality of components to produce a compensated frequency domain version of the digital signal.

2. The method of claim 1, wherein the digital signal comprises an in-phase component and a quadrature component in a time domain, and wherein each of the frequency domain version of the first component and the frequency domain version of the second component corresponds to one of the in-phase component or the quadrature component.

3. The method of claim 1, further comprising:

equalizing the compensated frequency domain version of the digital signal in a frequency domain prior to transforming the compensated frequency domain version of the digital signal to a time domain, wherein the equalizing comprises equalizing in the frequency domain at least one or more of an in-band amplitude ripple associated with an analog low-pass filter or an in-band phase ripple associated with the analog low-pass filter.

4. The method of claim 1, wherein the frequency dependent I/Q impairment compensation function comprises a precompensation function, and wherein the compensated frequency domain version of the digital signal comprises a precompensated frequency domain version of the digital signal produced prior to transmitting the digital signal.

5. The method of claim 4, further comprising:

transforming the precompensated frequency domain version of the digital signal to a time domain at a wireless modem to produce a precompensated time domain version of the digital signal; and

transmitting the precompensated time domain version of the digital signal from the wireless modem over a wireless channel.

6. The method of claim 1, further comprising:

performing a discrete Fourier transform separately on a time domain version of the first component and a time domain version of the second component of the digital signal to obtain the frequency domain version of the first component and the frequency domain version of the second component, respectively.

7. The method of claim 6, wherein the digital signal comprises a single carrier signal, the method further comprising:

performing an inverse discrete Fourier transform on the compensated frequency domain version of the digital signal; and

performing baseband demodulation on an output of the inverse discrete Fourier transform or on the compensated frequency domain version of the digital signal.

8. The method of claim 1, further comprising:

selecting a gain imbalance coefficient and a phase imbalance coefficient of the digital signal with respect to a frequency of the first component;

wherein the frequency dependent I/Q impairment compensation function is based on the gain imbalance coefficient and the phase imbalance coefficient.

9. The method of claim 8, further comprising:

receiving at least one measurement of an I/Q impairment associated with a wireless channel; and

determining one or both of the gain imbalance coefficient and the phase imbalance coefficient based on the received at least one measurement.

10. The method of claim 8, wherein scaling the frequency domain version of the first component comprises:

use a frequency-dependent scalar for the first component, wherein the frequency-dependent scalar is defined by

11. The method of claim 8, further comprising:

receiving a plurality of versions of the digital signal from a plurality of antenna ports in accordance with a multiple input multiple output (MIMO) transmission of the digital signal, each antenna port associated with a separate gain imbalance coefficient and a separate phase imbalance coefficient;

performing a joint imbalance compensation and spatial equalization operation on the frequency domain version of the first component by multiplying the frequency domain version of the first component by a MIMO spatial equalizer matrix adapted according to the gain imbalance coefficients and the phase imbalance coefficients of the plurality of antenna ports.

12. The method of claim 1, wherein the method further comprises:

computing the frequency domain version of the first component of the digital signal as;

X_e(f)= 1/2[X(f)+x*(−

f)]; and

computing the second component of the digital signal as;

X_o(f)= 1/2[X(f)−

x*(−

f)]

wherein X_e(f) comprises the first component of the digital signal, X_o(f) comprises the second component of the digital signal, X(f) comprises a frequency domain version of the digital signal, and f comprises a frequency.

13. An apparatus for compensating for I/Q impairments in a digital signal, comprising:

means for decomposing the digital signal into a plurality of components;

means for scaling a frequency domain version of a first component from the plurality of components according to a frequency dependent I/Q impairment compensation function to obtain a compensated frequency domain version of the first component; and

means for combining the compensated frequency domain version of the first component with a frequency domain version of a second component from the plurality of components to produce a compensated frequency domain version of the digital signal.

14. The apparatus of claim 13, further comprising:

equalizing the compensated frequency domain version of the digital signal in a frequency domain prior to transforming the compensated frequency domain version of the digital signal to a time domain, wherein the equalizing comprises equalizing in the frequency domain at least one or more of an in-band amplitude ripple associated with an analog low-pass filter or an in-band phase ripple associated with the analog low-pass filter.

15. The apparatus of claim 13, wherein the frequency dependent I/Q impairment compensation function comprises a precompensation function, and wherein the compensated frequency domain version of the digital signal comprises a precompensated frequency domain version of the digital signal produced prior to transmitting the digital signal, the apparatus further comprising:

means for transforming the precompensated frequency domain version of the digital signal to a time domain at a wireless modem to produce a precompensated time domain version of the digital signal; and

means for transmitting the precompensated time domain version of the digital signal from the wireless modem over a wireless channel.

16. The apparatus of claim 13, further comprising:

means for performing a discrete Fourier transform separately on a time domain version of the first component and a time domain version of the second component of the digital signal to obtain the frequency domain version of the first component and the frequency domain version of the second component, respectively.

17. The apparatus of claim 16, wherein the digital signal comprises a single carrier signal, the apparatus further comprising:

means for performing an inverse discrete Fourier transform on the compensated frequency domain version of the digital signal; and

means for performing baseband demodulation on an output of the inverse discrete Fourier transform or on the compensated frequency domain version of the digital signal.

18. The apparatus of claim 13, further comprising:

means for selecting a gain imbalance coefficient and a phase imbalance coefficient of the digital signal with respect to a frequency of the first component;

wherein the frequency dependent I/Q impairment compensation function is based on the gain imbalance coefficient and the phase imbalance coefficient.

19. The apparatus of claim 18, further comprising:

means for receiving at least one measurement of an I/Q impairment associated with a wireless channel; and

means for determining one or both of the gain imbalance coefficient and the phase imbalance coefficient based on the received at least one measurement.

20. The apparatus of claim 18, wherein the means for scaling the frequency domain version of the first component comprises:

means for using a frequency-dependent scalar for the first component, wherein the frequency-dependent scalar is defined by

21. The apparatus of claim 18, further comprising:

means for receiving a plurality of versions of the digital signal from a plurality of antenna ports in accordance with a multiple input multiple output (MIMO) transmission of the digital signal, each antenna port associated with a separate gain imbalance coefficient and a separate phase imbalance coefficient;

means for performing a joint imbalance compensation and spatial equalization operation on the frequency domain version of the first component by multiplying the frequency domain version of the first component by a MIMO spatial equalizer matrix adapted according to the gain imbalance coefficients and phase imbalance coefficients of the plurality of antenna ports.

22. The apparatus of claim 13, further comprising:

means for computing the first component of the digital signal as;

X_e(f)= 1/2[X(f)+x*(−

f)]; and

means for computing the second component of the digital signal as;

X_o(f)= 1/2[X(f)−

x*(−

f)]

wherein X_e(f) comprises the first component of the digital signal, X_o(f) comprises the second component of the digital signal, X(f) comprises a frequency domain version of the digital signal, and f comprises a frequency.

23. A wireless modem configured to compensate for transmit I/Q impairments in a digital signal comprising a plurality of components, the wireless modem comprising a processor and:

a scaling circuit configured to scale a frequency domain version of a first component from the plurality of components according to a frequency dependent I/Q impairment compensation function to obtain a compensated frequency domain version of the first component; and

an adder circuit configured to combine the compensated frequency domain version of the first component with a frequency domain version of a second component from the plurality of components to produce a compensated frequency domain version of the digital signal.

24. The wireless modem of claim 23, further comprising:

an equalizer circuit communicatively coupled with the adder circuit and configured to equalize the compensated frequency domain version of the digital signal in a frequency domain prior to transforming the compensated frequency domain version of the digital signal to a time domain, wherein the equalizing comprises equalizing in the frequency domain at least one or more of an in-band amplitude ripple associated with an analog low-pass filter or an in-band phase ripple associated with the analog low-pass filter.

25. The wireless modem of claim 23, further comprising:

a first discrete Fourier transform circuit configured to transform a time domain version of the first component of the digital signal to the frequency domain version of the first component; and

a second discrete Fourier transform circuit configured to transform a time domain version of the second component of the digital signal to the frequency domain version of the second component.

26. The wireless modem of claim 23, wherein the digital signal comprises a single carrier signal, the wireless modem further comprising:

an inverse discrete Fourier transform circuit configured to transform the compensated frequency domain version of the digital signal to a time domain; and

a baseband modulator/demodulator circuit communicatively coupled with an output of the inverse discrete Fourier transform circuit.

27. The wireless modem of claim 23, further comprising:

a selection circuit configured to select a gain imbalance coefficient and a phase imbalance coefficient of the digital signal with respect to a frequency of the first component;

wherein the frequency dependent I/Q impairment compensation function is based on the gain imbalance coefficient and the phase imbalance coefficient.

28. The wireless modem of claim 27, wherein the scaling circuit is further configured to:

use a frequency-dependent scalar for the first component, wherein the frequency-dependent scalar is defined by

29. The wireless modem of claim 23, further comprising:

a multiple input multiple output (MIMO) detector configured to receive a plurality of versions of the digital signal from a plurality of antenna ports in accordance with a MIMO transmission of the digital signal, each antenna port associated with a separate gain imbalance coefficient and a separate phase imbalance coefficient; and

a receiver processor configured to perform a joint imbalance compensation and spatial equalization operation on the frequency domain version of the first component by multiplying the frequency domain version of the first component by a MIMO spatial equalizer matrix adapted according to the gain imbalance coefficients and phase imbalance coefficients of the plurality of antenna ports.

30. A non-transitory computer-readable storage medium storing instructions executable by at least one processor to:

decompose a digital signal into a plurality of components;

scale a frequency domain version of a first component from the plurality of components according to a frequency dependent I/Q impairment compensation function to obtain a compensated frequency domain version of the first component; and

combine the compensated frequency domain version of the first component with a frequency domain version of a second component from the plurality of components to produce a compensated frequency domain version of the digital signal.