Fractionally-spaced equalizers for spread spectrum wireless communication

• US 20070127557A1
• Filed: 08/09/2006
• Published: 06/07/2007
• Est. Priority Date: 09/15/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Kang, Inyup, Subrahmanya, Parvathanathan, Sundaresan, Rajesh, Fei, Jia
• Granted Patent: US 8,064,556 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: H04B 1/71057 using maximum-likelihood sequence estimation [MLSE]
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0673 using feedback from receiving side
• CPC Class Codes: H04B 7/0845 per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch rake receivers as such H04B1/7115
• CPC Class Codes: H04L 2025/03509 fractionally spaced H04L2025/03515 takes precedence
• CPC Class Codes: H04L 25/03044 using fractionally spaced delay lines or combinations of fractionally integrally spaced taps
• CPC Class Codes: H04L 25/03292 with channel estimation circuitry

Abstract

This disclosure describes equalization techniques for spread spectrum wireless communication. The techniques may involve estimating a channel impulse response, estimating channel variance, and selecting filter coefficients for an equalizer based on the estimated channel impulse response and the estimated channel variance. Moreover, in accordance with this disclosure, the channel variance estimation involves estimation of two or more co-variances for different received samples. Importantly, the equalizer is “fractionally spaced,” which means that the equalizer defines fractional filtering coefficients (filter taps), unlike conventional equalizers that presume that filter coefficients are defined at integer chip spacing. The techniques can allow the equalizer to account for antenna diversity, such as receive diversity, transmit diversity, or possibly both.

Claims

1. A method of equalization in a spread spectrum wireless communication system comprising:

estimating a channel impulse response;

estimating channel variance by computing two or more co-variances for different received samples; and

selecting filter coefficients for an equalizer based on the estimated channel impulse response and the estimated channel variance.

2. The method of claim 1, wherein the equalizer is a fractionally spaced equalizer having filter taps spaced a fraction of a chip apart.

3. The method of claim 1, wherein the equalizer includes two or more equalization filters, the method further comprising combining outputs of the two or more equalization filters based on antenna diversity.

4. The method of claim 3, further comprising:

combining the output of the two or more equalization filters in a first manner for no diversity;

combining the output of the two or more equalization filters in a second manner for transmit diversity; and

combining the output of the two or more equalization filters in a third manner for receive diversity.

5. The method of claim 4, further comprising combining the output of the two or more equalization filters in a fourth manner for transmit and receive diversity.

6. The method of claim 1, wherein computing the two or more co-variances for different received samples comprise computing co-variances for odd and even samples.

7. The method of claim 1, further comprising:

generating an equalizer output; and

generating a common pilot channel (CPICH) signal based on the equalizer output and antenna diversity.

12. The method of claim 11, wherein the equalizer is a fractionally spaced equalizer having filter taps spaced a fraction of a chip apart.

8. A method of equalization for spread spectrum wireless communication comprising:

selecting filtering coefficients for two or more equalization filters based on an estimated channel impulse response and an estimated channel variance; and

combining output of the two or more equalization filters based on antenna diversity.

9. The method of claim 8, further comprising:

combining the output of the two or more equalization filters in a first manner for no diversity;

combining the output of the two or more equalization filters in a second manner for transmit diversity; and

combining the output of the two or more equalization filters in a third manner for receive diversity.

10. The method of claim 9, further comprising combining the output of the two or more equalization filters in a fourth manner for transmit and receive diversity.

11. The method of claim 8, further comprising:

estimating the channel impulse response; and

estimating the channel variance by computing two or more co-variances for different received samples.

13. A spread spectrum wireless communication device comprising:

a receiver that receives a wireless signal; and

an equalizer that estimates a channel impulse response, estimate channel variance by computing two or more co-variances for different received samples of the signal, and selects filter coefficients for the equalizer based on the estimated channel impulse response and the estimated channel variance.

14. The wireless communication device of claim 13, wherein the equalizer is a fractionally spaced equalizer having filter taps spaced a fraction of a chip apart.

15. The wireless communication device of claim 13, wherein the equalizer includes two or more equalization filters and wherein the equalizer is configured to combine the output of the two or more equalization filters based on antenna diversity.

16. The wireless communication device of claim 15, wherein the equalizer is configured to:

combine the output of the two or more equalization filters in a first manner for no diversity;

combine the output of the two or more equalization filters in a second manner for transmit diversity in which a sending device that sends the signals to the wireless communication device includes multiple transmit antennas; and

combine the output of the two or more equalization filters in a third manner for receive diversity in which the wireless communication device includes multiple receive antennas.

17. The wireless communication device of claim 16, wherein the equalizer is configured to combine the output of the two or more equalization filters in a fourth manner for transmit and receive diversity.

18. The wireless communication device of claim 13, wherein the equalizer computes the two or more co-variances for different received samples by computing co-variances for odd and even samples.

19. An equalizer for a spread spectrum wireless communication device, the equalizer being configured to:

select filtering coefficients for two or more equalization filters based on an estimated channel impulse response and an estimated channel variance; and

combine output of the two or more equalization filters based on based on antenna diversity.

20. The equalizer of claim 19, wherein the equalizer:

combines the output of the two or more equalization filters in a first manner for no diversity;

combines the output of the two or more equalization filters in a second manner for transmit diversity; and

combines the output of the two or more equalization filters in a third manner for receive diversity.

21. The equalizer of claim 20, wherein the equalizer combines the output of the two or more equalization filters in a fourth manner for transmit and receive diversity.

22. The equalizer of claim 19, wherein the equalizer:

estimates the channel impulse response; and

estimates the channel variance by computing two or more co-variances for different received samples.

23. The equalizer of claim 22, wherein the equalizer is a fractionally spaced equalizer having filter taps spaced one-half chip apart.

24. A computer-readable medium comprising program code that when executed in a spread spectrum wireless communication device cause the device to perform equalization by:

estimating a channel impulse response;

estimating channel variance by computing two or more co-variances for different received samples; and

selecting filter coefficients for an equalizer based on the estimated channel impulse response and the estimated channel variance.

25. The computer readable medium of claim 24, wherein the equalizer is a fractionally spaced equalizer having filter taps spaced one-half chip apart.

26. The computer readable medium of claim 24, wherein the equalizer includes two or more equalization filters, the method further comprising combining output of the two or more equalization filters based on antenna diversity.

27. The computer readable medium of claim 24, wherein computing the two or more co-variances for different received samples comprises computing co-variances for odd and even samples.

28. The computer readable medium of claim 24, further comprising program code that when executed causes the device to:

generate an equalizer output; and

generating a common pilot channel (CPICH) signal based on the equalizer output and antenna diversity.

29. A computer-readable medium comprising program code that when executed in a spread spectrum wireless communication device cause the device to perform equalization by:

selecting filtering coefficients for two or more equalization filters of an equalizer based on an estimated channel impulse response and an estimated channel variance; and

combining output of the two or more equalization filters based on based on antenna diversity.

30. The computer readable medium of claim 29, further comprising program code that when executed in the spread spectrum wireless communication device cause the device to:

estimate the channel impulse response; and

estimate the channel variance by computing two or more co-variances for different received samples.

31. The computer readable medium of claim 29, wherein the equalizer is a fractionally spaced equalizer having filter taps spaced one-half chip apart.