Receiver with a decision feedback equalizer and a linear equalizer

• US 20030223489A1
• Filed: 06/04/2002
• Published: 12/04/2003
• Est. Priority Date: 06/04/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Jayaraman, Srikant, Fernandez-Corbaton, Ivan Jesus, Smee, John
• Granted Patent: US 7,027,503 B2
• Time in Patent Office: Days
• US Class Current: 375/233
• CPC Class Codes: H04L 1/188 Time-out mechanisms
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 2025/03573 between recursive and non-recursive
• CPC Class Codes: H04L 2025/03617 Time recursive algorithms H04L2025/03643 takes precedence
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence

Abstract

Techniques for selecting either a DFE or an LE for use to equalize a received signal, and for quickly and efficiently determining the coefficients for the selected equalizer. In an embodiment, a method is provided whereby the DFE is initially adapted based on the received signal and a particular adaptive algorithm (e.g., the LMS algorithm) for an initial time period. A quality metric is then determined for an output of the DFE. The DFE is selected for use if the quality metric is better than a threshold value, and the LE is selected otherwise. If the LE is selected, then the initial values for the coefficients of the LE may be derived based on the coefficients of a feed-forward filter and a feedback filter for the DFE, and the LE coefficients may further be adapted for an additional time period prior to its use to equalize the received signal.

Claims

1. A method for equalizing a received signal in a wireless communication system, comprising:

adapting a decision feedback equalizer (DFE) based on the received signal for an initial time period;

determining a quality metric for an output of the DFE;

selecting the DFE for use to equalize the received signal if the quality metric is better than a threshold value; and

selecting a linear equalizer (LE) for use to equalize the received signal if the quality metric is worse than the threshold value.

2. The method of claim 1, further comprising:

if the LE is selected for use, deriving initial values for coefficients of the LE based on coefficients of a feed-forward filter and a feedback filter for the DFE.

3. The method of claim 2, further comprising:

if the LE is selected for use, adapting the coefficients of the LE for an additional time period prior to using the LE to equalize the received signal.

4. The method of claim 1, further comprising:

if the DEE is selected for use, adapting coefficients of the DEE for an additional time period prior to using the DEE to equalize the received signal.

5. The method of claim 1, wherein the quality metric relates to a mean square error (MSE) between equalized symbols from the DFE and expected symbols for the equalized symbols.

6. The method of claim 1, wherein the quality metric relates to a signal-to-noise-and-interference ratio (SENR).

7. The method of claim 1, wherein the quality metric relates to an error rate of detected symbols provided by a slicer to the DFE.

8. A method for equalizing a received signal in a wireless communication system, comprising:

adapting a decision feedback equalizer (DFE) based on the received signal for an initial time period;

determining a quality metric for an output of the DFE after the initial time period;

selecting either the DFE or a linear equalizer (LE) for use to equalize the received signal based on the quality metric; and

if the LE is selected for use,

deriving initial values for coefficients of the LE based on coefficients of a feed-forward filter and a feedback filter for the DFE, and

adapting the coefficients of the LE for an additional time period prior to using the LE to equalize the received signal.

9. An adaptive equalizer suitable for use in a wireless communication system, comprising:

a filter unit configurable to implement either a decision feedback equalizer (DFE) or a linear equalizer (LE), wherein the DFE or the LE is selected for use to equalize a received signal depending on a quality metric determined for an output of the DFE; and

an adaptation unit operative to derive coefficients for the DFE or the LE depending on whether the DFE or LE is selected for use.

10. The adaptive equalizer of claim 9, wherein the filter unit is initially configured to implement the DFE.

11. The adaptive equalizer of claim 10, wherein the DFE is adapted based on the received signal for an initial time period and the quality metric is determined after the initial time period.

12. The adaptive equalizer of claim 11, wherein if the LE is selected for use, the adaptation unit is further operative to derive initial values for coefficients of the LE based on coefficients of a feed-forward filter and a feedback filter for the DFE.

13. The adaptive equalizer of claim 12, wherein only a subset of the feedback filter coefficients is used to derive the initial coefficient values for the LE.

14. The adaptive equalizer of claim 12, wherein the adaptation unit is further operative to adapt the coefficients of the LE for an additional time period prior to using the LE to equalize the received signal.

15. The adaptive equalizer of claim 9, wherein the DFE is implemented with a feed-forward filter and a feedback filter, and wherein the LE is implemented with the feed-forward filter and by disabling the feedback filter.

16. The adaptive equalizer of claim 15, wherein the LE is implemented with the feed-forward filter having an extended length.

17. The adaptive equalizer of claim 15, wherein the feed-forward filter and the feedback filter are each implemented with a finite impulse response (FIR) filter.

18. The adaptive equalizer of claim 9, wherein the adaptation unit is operative to derive the coefficients for the DFE or the LE based on a particular adaptive algorithm.

19. The adaptive equalizer of claim 18, wherein the adaptive algorithm is a least mean square (LMS) algorithm.

20. The adaptive equalizer of claim 9, wherein the adaptation unit is operative to adapt the coefficients for the DFE or the LE based on expected symbols.

21. The adaptive equalizer of claim 20, wherein the expected symbols are pilot symbols.

22. The adaptive equalizer of claim 20, wherein the expected symbols are detected symbols provided by a slicer based on a particular signal constellation.

23. The adaptive equalizer of claim 9, wherein the adaptation unit is operative to determine the quality metric for the DFE output.

24. The adaptive equalizer of claim 9, wherein the quality metric relates to a mean square error (MSE) between equalized symbols from the DFE and expected symbols.

25. The adaptive equalizer of claim 9, wherein the quality metric relates to a signal-to-noise-and-interference ratio (SINR).

26. The adaptive equalizer of claim 9, wherein the quality metric relates to an error rate of detected symbols provided by a slicer to the DFE.

27. An adaptive equalizer suitable for use in a wireless communication system, comprising:

a filter unit configurable to implement either a decision feedback equalizer (DFE) or a linear equalizer (LE), wherein the DFE or the LE is selected for use to equalize a received signal depending on a quality metric determined for an output of the DFE; and

an adaptation unit operative to determine the quality metric for the DFE output, derive coefficients for the DFE or the LE depending on whether the DFE or LE is selected for use, and if the LE is selected for use,

derive initial values for coefficients of the LE based on coefficients of a feed-forward filter and a feedback filter for the DFE, and

adapt the coefficients of the LE for an additional time period prior to using the LE to equalize the received signal.

28. A memory communicatively coupled to a digital signal processing device (DSPD) capable of interpreting digital information to:

adapt a decision feedback equalizer (DFE) based on a received signal for an initial time period;

determine a quality metric for an output of the DFE;

select the DFE for use to equalize the received signal if the quality metric is better than a threshold value; and

select a linear equalizer (LE) for use to equalize the received signal if the quality metric is worse than the threshold value.

29. A computer program product for equalizing a received signal in a wireless communication system, comprising:

code for adapting a decision feedback equalizer (DFE) based on a received signal for an initial time period;

code for determining a quality metric for an output of the DFE;

code for selecting the DFE for use to equalize the received signal if the quality metric is better than a threshold value;

code for selecting a linear equalizer (LE) for use to equalize the received signal if the quality metric is worse than the threshold value; and

a computer-usable medium for storing the codes.

30. An integrated circuit, comprising:

a filter unit configurable to implement either a decision feedback equalizer (DFE) or a linear equalizer (LE), wherein the DFE or the LE is selected for use to equalize a received signal depending on a quality metric determined for an output of the DFE; and

an adaptation unit operative to derive coefficients for the DFE or the LE depending on whether the DFE or LE is selected for use.

31. A receiver system in a wireless communication system, comprising:

a receiver unit operative to process a received signal to provide data samples; and

a data processor operative to process the data sample to provide equalized symbols, the data processor including

a filter unit configurable to implement either a decision feedback equalizer (DFE) or a linear equalizer (LE), wherein the DFE or the LE is selected for use to equalize a received signal depending on a quality metric determined for an output of the DFE; and

an adaptation unit operative to derive coefficients for the DFE or the LE depending on whether the DFE or LE is selected for use.

32. An apparatus in a wireless communication system, comprising:

means for implementing a decision feedback equalizer (DFE) or a linear equalizer (LE) at any given moment;

means for adapting the DFE based on a received signal for an initial time period;

means for determining a quality metric for an output of the DFE; and

means for selecting either the DFE or the LE for use to equalize the received signal based on the quality metric.

33. The apparatus of claim 32, further comprising:

means for deriving initial values for coefficients of the LE based on coefficients of a feed-forward filter and a feedback filter for the DFE, if the LE is selected for use.

34. The apparatus of claim 33, further comprising:

means for adapting the coefficients of the LE for an additional time period prior to using the LE to equalize the received signal, if the LE is selected for use.