Receiver-side estimation of and compensation for signal impairments

1. A method, comprising:

in a transceiver:

receiving a repeating or periodic signal;

iteratively estimating a carrier frequency offset for the transceiver based on the signal, estimating an I/Q mismatch for the receiver based on the signal and the estimated carrier frequency offset, and compensating for the estimated I/Q mismatch, while the estimated carrier frequency offset is not less than a threshold and for a number of iterations that does not exceed a specified count;

after iteratively estimating the carrier frequency offset, estimating the I/Q mismatch, and compensating for the estimated I/Q mismatch, compensating for the estimated carrier frequency offset as estimated in a final iteration; and

after compensating for the estimated carrier frequency offset as estimated in the final iteration, estimating channel distortion and transmitter-side I/Q mismatch, and compensating for the estimated channel distortion and transmitter-side I/Q mismatch.

2. The method of claim 1 , wherein estimating the transmitter-side I/Q mismatch comprises:

using received pilot symbols that are symmetric with respect to a zero frequency to make frequency response estimates at specified frequencies.

3. The method of claim 2 , wherein estimating the transmitter-side I/Q mismatch further comprises interpolating between the frequency response estimates at the specified frequencies.

4. The method of claim 2 , wherein the specified frequencies comprise mirror frequencies.

5. The method of claim 1 , wherein compensating for the transmitter-side I/Q mismatch comprises performing frequency-selective compensation.

6. The method of claim 1 , wherein compensating for the estimated carrier frequency offset as estimated in the final iteration comprises performing phase rotation.

7. The method of claim 1 , further comprising determining, in the transceiver, that the estimated carrier frequency offset as estimated in a respective iteration is not less than the threshold, wherein estimating the I/Q mismatch for the transceiver and compensating for the estimated I/Q mismatch are performed in the respective iteration in response to the determining.

8. The method of claim 7 , further comprising, in the transceiver:

in the final iteration, determining that the estimated carrier frequency offset is less than the threshold; and

in response to determining that the estimated carrier frequency offset is less than the threshold:

terminating the final iteration;

estimating channel distortion and transmitter-side I/Q mismatch; and

compensating for the estimated channel distortion and transmitter-side I/Q mismatch.

9. The method of claim 1 , wherein estimating the carrier frequency offset comprises calculating the carrier frequency offset based on autocorrelation of the signal.

10. The method of claim 1 , wherein estimating the carrier frequency offset comprises assuming an absence of I/Q mismatch.

11. The method of claim 1 , wherein:

the signal is a narrowband signal; and

estimating the I/Q mismatch for the transceiver comprises calculating a scalar correction factor.

12. The method of claim 1 , wherein the signal comprises a cyclic prefix of an orthogonal frequency-division multiplexing (OFDM) symbol.

13. The method of claim 1 , wherein the signal is a periodic signal and the I/Q mismatch for the transceiver is estimated using non-consecutive periods of the periodic signal.

14. The method of claim 1 , wherein the signal is a periodic signal and estimating the I/Q mismatch for the transceiver comprises:

making a first estimate of the I/Q mismatch for the transceiver based on a first pair of periods of the periodic signal;

making a second estimate of the I/Q mismatch for the transceiver based on a second pair of periods of the periodic signal; and

averaging the first and second estimates.

15. A communication device, comprising:

a receiver to receive signals including a repeating or periodic signal;

one or more processors; and

memory storing one or more programs to be executed by the one or more processors, the one or more programs comprising instructions for:

iteratively estimating a carrier frequency offset for the receiver based on the signal, estimating an I/Q mismatch for the receiver based on the signal and the estimated carrier frequency offset, and compensating for the estimated I/Q mismatch for the receiver, while the estimated carrier frequency offset is not less than a threshold and for a number of iterations that does not exceed a specified count;

after iteratively estimating the carrier frequency offset, estimating the I/Q mismatch, and compensating for the estimated I/Q mismatch, compensating for the estimated carrier frequency offset as estimated in a final iteration; and

after compensating for the carrier frequency offset as estimated in the final iteration, estimating and compensating for channel distortion and transmitter-side I/Q mismatch.

16. The communication device of claim 15 , wherein the instructions to estimate and compensate for channel distortion and transmitter-side I/Q mismatch comprise instructions to use received pilot symbols that are symmetric with respect to a zero frequency to make frequency response estimates at specified frequencies.

17. The communication device of claim 15 , wherein the one or more programs further comprise:

instructions to determine, in each iteration, whether the estimated carrier frequency offset is less than the threshold, before estimating the I/Q mismatch for the receiver; and

instructions to halt execution of an iteration if the estimated carrier frequency offset is less than the threshold.

18. The communication device of claim 17 , wherein the one or more programs further comprise instructions to estimate and compensate for channel distortion and transmitter-side I/Q mismatch after halting execution of an iteration.

19. The communication device of claim 15 , wherein the one or more processors comprise a baseband processor in the receiver.

20. A communication device, comprising:

a receiver to receive signals including a repeating or periodic signal;

means for iteratively estimating a carrier frequency offset for the receiver based on the signal, estimating an I/Q mismatch for the receiver based on the signal and the estimated carrier frequency offset, and compensating for the estimated I/Q mismatch for the receiver, while the estimated carrier frequency offset is not less than a threshold and for a number of iterations that does not exceed a specified count;

means for compensating for the estimated carrier frequency offset as estimated in a final iteration, after iteratively estimating the carrier frequency offset, estimating the I/Q mismatch, and compensating for the estimated I/Q mismatch; and

means for estimating channel distortion and transmitter-side I/Q mismatch after compensating for the carrier frequency offset as estimated in the final iteration.