Hybrid modulus blind equalization for quadrature amplitude modulation (QAM) receivers

1. A Quadrature Amplitude Modulation (QAM) signal receiver, comprising:

a filter to reduce error in equalization, the filter to output a QAM signal;

a decision engine coupled to the filter to determine a symbol based on the QAM signal;

a first error generator coupled to the filter to compute a first error signal based on the QAM signal and a constant;

a second error generator coupled to the filter and the decision engine to compute a second error signal based on the QAM signal and the determined symbol;

an error combinator coupled to the first and second error generators to generate a combined error signal from the first and second error signals; and

an adaptation engine coupled with the error combinator and the filter to reduce a equalization error according to the combined error signal.

2. The receiver of claim 1 , wherein the first error generator comprises a constant modulus algorithm (CMA) error generator.

3. The receiver of claim 2 , wherein the second error generator comprises a decision modulus algorithm (DMA) error generator.

4. The receiver of claim 1 , wherein the error combinator combines the first and second error signals according to a difference between the QAM signal and the determined symbol.

5. The receiver of claim 4 , wherein the error combinator applies a first weight on the first error signal and a second weight on the second error signal to generate the combined error signal; and the first and second weights are determined based on the difference between the QAM signal and the determined symbol.

6. The receiver of claim 5 , wherein the first weight decreases relative to the second weight to zero as the difference between the QAM signal and the determined symbol decreases; and the second weight decreases relative to the first weight to zero as the difference between the QAM signal and the determined symbol increases to above a threshold.

7. The receiver of claim 1 , wherein the combined error signal is a weighted average of the first and second error signals; and the combined error signal is different from each of the first and second error signals.

8. A method, comprising:

receiving a Quadrature Amplitude Modulation (QAM) signal;

determining a symbol corresponding to the received QAM signal;

computing a first error in equalization based on a constant modulus and a second error in equalization based on the determined symbol;

combining the first error and the second error to generate a third error different from each of the first error and the second error; and

adjusting a filter to reduce error in equalization according to the third error.

9. The method of claim 8 , wherein the first error is based on a constant modulus algorithm (CMA) error.

10. The method of claim 9 , wherein the second error is based on a difference between the determined symbol and the received QAM signal.

11. The method of claim 8 , wherein said combining the first error and the second error comprises:

weighting the first error against the second error according to a difference between the determined symbol and the received QAM signal.

12. The method of claim 11 , wherein a weight for the first error decreases relative to a weight for the second error when the difference between the determined symbol and the received QAM signal decreases.

13. The method of claim 8 , wherein said combining the first error and the second error comprises:

determining a weighted average of the first error and the second error according to a difference between the determined symbol and the received QAM signal.

14. The method of claim 13 , wherein a weight for the first error decreases towards zero when the difference between the determined symbol and the received QAM signal decreases towards a threshold.

15. The method of claim 14 , wherein the weight for the second error decreases towards zero when the difference between the determined symbol and the received QAM signal increases towards a threshold.

16. A circuit, comprising:

means for receiving a Quadrature Amplitude Modulation (QAM) signal;

means for determining a symbol corresponding to the received QAM signal;

means for computing a first error in equalization based on a constant modulus and a second error in equalization based on the determined symbols;

means for combining the first error and the second error to generate a third error different from each of the first error and the second error; and

means for adjusting a filter to reduce error in equalization according to the third error.

17. The circuit of claim 16 , wherein the first error is based on a constant modulus algorithm (CMA) error; and the second error is based on a difference between a modulus of the determined symbol and a modulus of the received QAM signal.

18. The circuit of claim 16 , wherein said means for combining comprises:

means for weighting the first error against the second error according to a confidence level in the determined symbol.

19. The circuit of claim 18 , wherein a weight for the first error decreases relative to a weight for the second error when the confidence level increases.

20. The circuit of claim 19 , wherein the weight for the first error decreases towards zero when the confidence level increases towards a first threshold; and the weight for the second error decreases towards zero when the confidence level decreases towards a second threshold.