APPARATUS AND METHODS FOR COMPENSATING FOR SIGNAL IMBALANCE IN A RECEIVER

• US 20080130779A1
• Filed: 11/13/2007
• Published: 06/05/2008
• Est. Priority Date: 11/20/2006
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Shusterman, Eliahu, Levi, Zak
• Granted Patent: US 8,090,043 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H03D 3/009 Compensating quadrature phase or amplitude imbalances
• CPC Class Codes: H04L 27/2649 Demodulators
• CPC Class Codes: H04L 27/266 Fine or fractional frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/3863 Compensation for quadrature error in the received signal

Abstract

Apparatus, methods and systems for compensating for an I/Q imbalance may include compensating for an imbalance between a first component of a data signal and a second component of the data signal. The data signal may be modulated by a carrier signal having a frequency error. The first component may be characterized by at least one parameter. The method may include receiving the data and carrier signals; selecting a value for the parameter such that the frequency domain energy at negative frequencies is reduced; and modifying at least one of the components based on the value.

Claims

1. A method for compensating for an imbalance between a first component of a data signal and a second component of the data signal, the data signal having a positive-valued frequency and being modulated by a carrier signal having a frequency error, the method comprising:

receiving the data and carrier signals;

selecting a value for a time domain parameter such that a frequency domain energy corresponding to a negative-valued frequency is minimized; and

modifying in the time domain at least one of the components based on the value.

2. The method of claim 1 further comprising:

estimating a carrier signal frequency corresponding to the carrier signal;

estimating a residual carrier frequency error; and

modifying an estimate of the carrier frequency based on the residual carrier frequency error.

3. The method of claim 2 wherein the modifying comprises:

identifying a first value corresponding to a signal amplitude multiplier for the component; and

identifying a second value corresponding to a phase shift for the component.

4. The method of claim 1 wherein the selecting includes recording a first frequency domain parameter and a second frequency domain parameter for each of a first tone, a second tone and the carrier signal.

5. The method of claim 4 wherein:

for at least one of the first tone, the second tone and the carrier signal, the first and second frequency domain parameters correspond, respectively to first and second bins in a discrete-valued frequency spectrum; and

the first bin is sequentially adjacent the second bin.

6. The method of claim 4 further comprising transmitting an output signal that depends on the first and second frequency domain parameters.

7. The method of claim 4 wherein:

the receiving comprises receiving an orthogonal frequency division multiplexing (OFDM) symbol; and

in the selecting the value corresponds to the OFDM symbol; and

the modifying is performed with respect to the OFDM symbol.

8. The method of claim 4 wherein:

the receiving comprises receiving a plurality of orthogonal frequency division multiplexing (OFDM) symbols;

the selecting is performed for each of the OFDM symbols; and

the modifying is performed for each of the OFDM symbols.

9. The method of claim 4 wherein:

one of the first and second components is an in-phase signal;

the other of the first and second components is a quadrature signal; and

the imbalance is an in-phase/quadrature imbalance.

10. A system operative to record complex parameters corresponding to frequency components of a received signal, the signal carrying at least one orthogonal frequency division multiplexing (OFDM) symbol, the parameters corresponding to:

a carrier frequency having a frequency error;

a first tone; and

a second tone.

11. The system of claim 10 further configured to estimate a frequency bin corresponding to each of the carrier frequency, the first tone and the second tone.

12. The system of claim 10 wherein, when there are first and second complex parameters corresponding to each of the carrier frequency, the first tone and the second tone, the circuit is further operative to:

estimate a second frequency bin corresponding to each of the carrier frequency, the first tone and the second tone; and

record the first and second complex parameters for each of the carrier frequency, the first tone and the second tone.

13. The system of claim 12 further operative to record both of the complex parameters for each of the carrier frequency, the first tone and the second tone based upon an estimated value for each of the carrier frequency, the first tone and the second tone;

wherein all of the estimated values correspond to a single OFDM symbol.

14. The circuit of claim 13 wherein, when the received signal carries a plurality of OFDM symbols, further operative to estimate values of each of the carrier frequency, the first tone and the second tone for each of the OFDM symbols.

15. A system for compensating for an imbalance between a first signal and a second signal, the system comprising:

a first module operative to record, based on the first and second signals, a first frequency domain parameter and a second frequency domain parameter corresponding to each of a first tone, a second tone and a carrier frequency, the first tone, second tone and carrier frequency; and

a second module operative to compute at least one time domain compensation parameter based on the first and second frequency domain parameters.

16. The system of claim 15 further comprising a third module operative to output a compensated signal based on the time domain compensation parameter.

17. The system of claim 15 wherein the at least one time domain compensation parameter comprises three time domain compensation parameters.

18. The system of claim 15 wherein:

the carrier frequency is a receiver carrier frequency;

the first and second signals are received from a transmitter operative to transmit the signals using a transmitter carrier frequency; and

the receiver and transmitter carrier frequencies differ by a carrier frequency offset.

19. The system of claim 18 wherein, when the first and second frequency domain parameters correspond one of the first and second tones:

the first frequency domain parameter corresponds to a first bin in a discrete-valued frequency spectrum;

the second frequency domain parameter corresponds to a second bin in the spectrum; and

the first bin is contiguous with the second bin.

20. The system of claim 18 wherein the first module is operative to select the second bin based on the location in the spectrum of the first bin.

21. The system of claim 20 wherein the location in the spectrum of the second bin is further based on the offset.

22. The system of claim 21 wherein the location in the spectrum of the second bin is further based on the ratio of the offset, in radians, to Pi radians.

23. The system of claim 18 wherein, when there is a residual carrier frequency offset, the second module is operative to:

compute an estimate of the residual frequency offset; and

compute the time domain compensation parameter based on the estimate.

24. The system of claim 15 wherein, when the first module is operative to record the first and second frequency domain parameters for each of a plurality of symbols that are received serially in time, the second module is operative to compute a first average value for the first frequency domain parameter and a second average value for the second frequency domain parameter, the average values based, respectively, on the first and second frequency domain parameters corresponding to the symbols.

25. The system of claim 15 wherein:

the first module is a hardware module; and

the second module is a software module.

26. The system of claim 25 wherein the third module is a hardware module.

27. The system of claim 15 wherein:

the first module is a hardware module; and

the second module is a hardware module.

28. The system of claim 27 wherein the third module is a hardware module.