IQ-imbalance compensation in presence of carrier offset

1. A method implemented in a communication receiver for processing a received Orthogonal Frequency Division Multiplexing (OFDM) wireless communication signal, the method comprising:

applying frequency offset compensation to produce a frequency offset compensated received signal, wherein the frequency offset compensation comprises digital rotation;

determining one or more adjustment values associated with the frequency offset compensation, wherein each of the one or more adjustment values is a complex number associated with an OFDM-symbol of the received OFDM signal, wherein the complex number is a doubling of the phase of the digital rotation corresponding to a particular sample of the OFDM-symbol;

transforming the frequency offset compensated received signal to a frequency domain, wherein the frequency domain comprises a plurality of sub-carrier frequencies;

estimating an in-phase/quadrature imbalance (IQ-imbalance) based on at least the one or more adjustment values, one or more pieces of information related to a first symbol of a first sub-carrier frequency, and one or more pieces of information related to a second symbol of a second sub-carrier frequency, wherein the second sub-carrier frequency is a mirror sub-carrier frequency to the first sub-carrier frequency, said estimating comprising multiplication with a conjugate function of the complex number; and

performing IQ-imbalance compensation of the received OFDM signal based on the estimated IQ-imbalance.

2. The method of claim 1 , wherein performing IQ-imbalance compensation comprises:

adjusting the estimated IQ-imbalance based on the one or more adjustment values; and

performing the IQ-imbalance compensation based on the adjusted estimated IQ-imbalance.

3. The method of claim 1 , wherein estimating the IQ-imbalance comprises:

determining estimated channel values for at least the first sub-carrier frequency, the first sub-carrier frequency having a pilot symbol; and

estimating the IQ-imbalance based on at least:

the one or more pieces of information related to the first symbol, the one or more pieces of information comprising: the pilot symbol, and the at least one determined estimated channel value,

the one or more pieces of information related to the second symbol, and

at least one of the one or more adjustment values.

4. The method of claim 1 , wherein estimating the IQ-imbalance comprises estimating the IQ-imbalance based on one or more pieces of information related to a number of symbols of sub-carrier frequencies that are neighboring sub-carrier frequencies to the mirror sub-carrier frequency.

5. The method of claim 1 , wherein estimating the IQ-imbalance comprises estimating the IQ-imbalance based on a plurality of pilot symbols and one or more pieces of information related to symbols of corresponding mirror sub-carrier frequencies.

6. The method of claim 1 , wherein determining the one or more adjustment values comprises using a digital rotator to generate the complex number during a cyclic prefix of the associated OFDM-symbol or of an adjacent OFDM-symbol.

7. A computer program product stored on a non-transitory computer readable medium and comprising program instructions that, when executed by a data-processing unit associated with a communication receiver, cause the communication receiver to process a received Orthogonal Frequency Division Multiplexing (OFDM) wireless communication signal, the program instructions causing the communication receiver to:

apply frequency offset compensation to produce a frequency offset compensated received signal, wherein the frequency offset compensation comprises digital rotation;

determine one or more adjustment values associated with the frequency offset compensation, wherein each of the one or more adjustment values is a complex number associated with an OFDM-symbol of the received OFDM signal, wherein the complex number is a doubling of the phase of the digital rotation corresponding to a particular sample of the OFDM-symbol;

transform the frequency offset compensated received signal to a frequency domain, wherein the frequency domain comprises a plurality of sub-carrier frequencies;

estimate an in-phase/quadrature imbalance (IQ-imbalance) based on at least the one or more adjustment values, one or more pieces of information related to a first symbol of a first sub-carrier frequency, and one or more pieces of information related to a second symbol of a second sub-carrier frequency, wherein the second sub-carrier frequency is a mirror sub-carrier frequency to the first sub-carrier frequency, said estimating comprising multiplication with a conjugate function of the complex number; and

perform IQ-imbalance compensation of the received OFDM signal based on the estimated IQ-imbalance.

8. An arrangement for processing a received Orthogonal Frequency Division Multiplexing (OFDM) wireless communication signal, the arrangement comprising:

a frequency offset compensation circuit comprising a digital rotator, the frequency offset compensation unit configured to apply a frequency offset compensation to the received OFDM signal to produce a frequency offset compensated received signal;

determination circuitry configured to determine one or more adjustment values associated with the frequency offset compensation, by determining each of the one or more adjustment values as a complex number associated with an OFDM-symbol of the received OFDM signal, wherein the complex number is a doubling of the phase of the digital rotation corresponding to a particular sample of the OFDM-symbol;

a fast Fourier transform circuit configured to transform the frequency offset compensated received signal to a frequency domain, wherein the frequency domain comprises a plurality of sub-carrier frequencies;

an in-phase/quadrature imbalance (IQ-imbalance) estimator circuit configured to estimate an IQ-imbalance based on at least the one or more adjustment values, one or more pieces of information related to a first symbol of a first sub-carrier frequency, and one or more pieces of information related to a second symbol of a second sub-carrier frequency, wherein the second sub-carrier frequency is a mirror sub-carrier frequency to the first sub-carrier frequency, said estimating comprising multiplication with a conjugate function of the complex number; and

an IQ-imbalance compensation circuit configured to perform IQ-imbalance compensation of the received OFDM signal based on the estimated IQ-imbalance.

9. The arrangement of claim 8 , wherein the IQ-imbalance compensation circuit is configured to:

adjust the estimated IQ-imbalance based on the one or more adjustment values; and

perform the IQ-imbalance compensation based on the adjusted estimated IQ-imbalance.

10. The arrangement of claim 8 ,

further comprising a channel estimator circuit configured to determine estimated channel values for at least the first sub-carrier frequency, the first sub-carrier frequency having a pilot symbol; and

wherein the IQ-imbalance estimator circuit is configured to estimate the IQ-imbalance based on at least:

the one or more pieces of information related to the first symbol, the one or more pieces of information comprising: the pilot symbol, and the at least one determined estimated channel value,

the one or more pieces of information related to the second symbol, and

at least one of the one or more adjustment values.

11. The arrangement of claim 8 , wherein the IQ-imbalance estimator circuit is further configured to estimate the IQ-imbalance based on one or more pieces of information related to a number of symbols of sub-carrier frequencies that are neighboring sub-carrier frequencies to the mirror sub-carrier frequency.

12. The arrangement of claim 8 , wherein the IQ-imbalance estimator circuit is configured to estimate the IQ-imbalance based on a plurality of pilot symbols and one or more pieces of information related to symbols of corresponding mirror sub-carrier frequencies.

13. An electronic communication device comprising a wireless communication receiver that includes an arrangement for processing a received Orthogonal Frequency Division Multiplexing (OFDM) wireless communication signal, the arrangement comprising:

a frequency offset compensation circuit comprising a digital rotator, the frequency offset compensation circuit configured to apply a frequency offset compensation to the received OFDM signal to produce a frequency offset compensated received signal;

determination circuitry configured to determine one or more adjustment values associated with the frequency offset compensation, by determining each of the one or more adjustment values as a complex number associated with an OFDM-symbol of the received OFDM-signal, wherein the complex number is a doubling of the phase of the digital rotation corresponding to a particular sample of the OFDM-symbol;

a fast Fourier transform circuit configured to transform the frequency offset compensated received signal to a frequency domain, wherein the frequency domain comprises a plurality of sub-carrier frequencies;

an in-phase/quadrature imbalance (IQ-imbalance) estimator circuit configured to estimate an IQ-imbalance based on at least the one or more adjustment values, one or more pieces of information related to a first symbol of a first sub-carrier frequency, and one or more pieces of information related to a second symbol of a second sub-carrier frequency, wherein the second sub-carrier frequency is a mirror sub-carrier frequency to the first sub-carrier frequency, said estimating comprising multiplication with a conjugate function of the complex number; and

an IQ-imbalance compensation circuit configured to perform IQ-imbalance compensation of the received OFDM signal based on the estimated IQ-imbalance.