Method and apparatus for processing a modulated signal using an equalizer and a rake receiver

• US 7,397,844 B2
• Filed: 11/03/2005
• Issued: 07/08/2008
• Est. Priority Date: 07/24/2000
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Jalali, Ahmad, Smee, John E.
• Primary Examiner(s): WANG, TED M
• Application Number:
  US11/267,070
• Publication Number:
  US 20060056496A1
• Time in Patent Office: 978 Days
• Field of Search: 375/148, 375/146, 375/136, 375/147, 375/229, 375/316
• US Class Current: 375/148
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 7/0854 using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
• CPC Class Codes: H04L 2025/03617 Time recursive algorithms H04L2025/03643 takes precedence
• CPC Class Codes: H04L 2025/03662 to a fixed value
• CPC Class Codes: H04L 2025/03777 characterised by the signalling
• CPC Class Codes: H04L 25/03019 adaptive, i.e. capable of adjustment during data reception

Abstract

In a method for achieving higher S/N, one or more signals are received and processed to provide one or more streams of samples. In a first processing scheme, the sample stream(s) are equalized within an equalizer to generate symbol estimates, which may be subsequently processed (e.g., despread and decovered) to provide a first stream of recovered symbols. Each sample stream is filtered with a set of coefficients and may be scaled with a scaling factor. The scaled samples for all streams are then combined to generate the symbol estimates. The sample stream(s) may also be processed by a second processing scheme with one or more rake receivers to provide a second stream of recovered symbols. The signal quality for each processing scheme can be estimated and used to select either the first or second processing scheme.

Claims

1. An apparatus comprising:

an equalizer configured to process signal samples to provide symbol estimates, the equalizer comprising a filter and a coefficient adjustment element, the coefficient adjustment element being configured to adjust coefficients used by the filter to filter the signal samples;

a despreader configured to despread the symbol estimates from the equalizer to generate despread symbols;

a decover element configured to decover the despread symbols to generate a first stream of recovered symbols;

a rake receiver configured to process one or more multipaths of the signal samples to provide a second stream of recovered symbols;

a controller configured to estimate a first signal quality of the first stream of recovered symbols and a second signal quality of the second stream of recovered symbols, the controller comparing the first and second signal qualities; and

a switch configured to select the equalizer or the rake receiver to generate recovered data symbols.

2. The apparatus of claim 1, wherein the equalizer and rake receiver both operate on pilot samples, then based on the first and second signal qualities estimated by the controller, the switch selects either the rake receiver or the equalizer to process data samples.

3. The apparatus of claim 1, wherein the despreader and decover element are configured to selectively despread and decover depending on a data rate of a received signal associated with the signal samples.

4. The apparatus of claim 1, wherein the controller is configured to estimate the first signal quality of the first stream of recovered symbols with a mean square error (MSE) between the symbol estimates and expected symbols.

5. The apparatus of claim 1, wherein the equalizer is configured to use information from the rake receiver.

6. The apparatus of claim 5, wherein the rake receiver is configured to identify a strongest multipath of the signal samples, the coefficient adjustment element being configured to adjust the coefficients according to an information related to the identified strongest multipath.

7. The apparatus of claim 6, wherein the information comprises a time offset of the identified strongest multipath.

8. The apparatus of claim 1, wherein the coefficient adjustment element is configured to minimize a mean square error (MSE) between the symbol estimates and expected symbols.

9. The apparatus of claim 1, wherein the coefficient adjustment element is configured to minimize a mean square error (MSE) between filtered samples from the filter and expected symbols.

10. The apparatus of claim 1, wherein the filter comprises at least one of a finite impulse response (FIR) filter and an infinite impulse response (IIR) filter.

11. The apparatus of claim 1, wherein the coefficient adjustment element is configured to use a received pilot signal and an expected pilot signal to adjust the coefficients.

12. The apparatus of claim 11, wherein the coefficient adjustment element is configured to use at least one of a time division multiplexed (TDM) pilot signal and a code division multiplexed (CDM) pilot signal.

13. The apparatus of claim 1, wherein the coefficient adjustment element is configured to use at least one of a least mean square (LMS) algorithm, a recursive least square (RLS) algorithm, and a direct matrix inversion (DMI) algorithm.

14. The apparatus of claim 1, further comprising a plurality of antennas configured to receive a signal, wherein the equalizer comprises a plurality of filters and a plurality of scaling elements, each filter being configured to filter samples of the signal received by a specific antenna, each scaling element being configured to scale filtered samples from a specific filter, the coefficient adjustment element being configured to provide scaling factors to the plurality of scaling elements.

15. The apparatus of claim 14, wherein the equalizer further comprises a summer configured to combine outputs from the plurality of scaling elements.

16. The apparatus of claim 14, wherein the rake receiver is configured to identify a strongest multipath of the signal samples, the coefficient adjustment element being configured to adjust the scaling factors based on the identified strongest multipath.

17. The apparatus of claim 14, wherein the coefficient adjustment element is configured to (a) adjust the coefficients with the one or more scaling factors fixed, and (b) adjust the scaling factors with the coefficients for one or more filters fixed.

18. The apparatus of claim 1, wherein the apparatus comprises a remote terminal.

19. A system comprising:

a base station configured to transmit a pilot signal and a data signal;

a remote terminal configured to receive the pilot signal and data signal, the remote terminal comprising;

an equalizer configured to process samples of the pilot and data signals to provide symbol estimates, the equalizer comprising a filter and a coefficient adjustment element, the coefficient adjustment element being configured to adjust coefficients used by the filter to filter the samples;

a despreader configured to despread the symbol estimates from the equalizer to generate despread symbols;

a decover element configured to decover the despread symbols to generate a first stream of recovered symbols;

a rake receiver configured to process one or more multipaths of the pilot and data signals samples to provide a second stream of recovered symbols;

a controller configured to estimate a first signal quality of the first stream of recovered symbols and a second signal quality of the second stream of recovered symbols, the controller comparing the first and second signal qualities; and

a switch configured to select the equalizer or the rake receiver to generate recovered data symbols.

20. The system of claim 19, wherein the remote terminal is configured to train the equalizer coefficients using the pilot signal and demodulate the data signal.

21. A method for processing received signal samples, the method comprising;

equalizing the received signal samples to provide symbol estimates, the step of equalizing comprising filtering the signal samples and adjusting coefficients used during the filtering step;

despreading the symbol estimates to generate despread symbols;

decovering the despread symbols to generate a first stream of recovered symbols;

processing one or more multipaths of the signal samples by a rake receiver to provide a second stream of recovered symbols;

estimating a first signal quality of the first stream of recovered symbols and a second signal quality of the second stream of recovered symbols,

comparing the first and second signal qualities; and

selecting one of the first and the second stream of recovered symbols to generate recovered data symbols.

22. The method of claim 21, wherein the equalizing step and the multipath processing step are performed on pilot samples.

23. The method of claim 21, wherein the dispreading step and the decovering step are selectively performed based on a data rate of a received signal associated with the signal samples.

24. The method of claim 21, wherein the estimating the first signal quality of the first stream of recovered symbols is based on a mean square error (MSE) between the symbol estimates and expected symbols.

25. The method of claim 21, further comprising:

identifying a strongest multipath of the signal samples; and

adjusting the filter coefficients according to an information related to the identified strongest multipath.

26. The method of claim 25, wherein the information comprises a time offset of the identified strongest multipath.

27. The method of claim 21, wherein the coefficient adjustment step minimizes a mean square error (MSE) between the symbol estimates and expected symbols.

28. The method of claim 21, wherein the coefficient adjustment step minimizes a mean square error (MSE) between filtered samples generated during the filtering step and expected symbols.

29. The method of claim 21, wherein the filtering step is performed by one of a finite impulse response (FIR) filter and an infinite impulse response (IIR) filter.

30. The method of claim 21, wherein the coefficient adjustment step is performed on a received pilot signal and an expected pilot signal to adjust the coefficients.

31. The method of claim 21, wherein the coefficient adjustment step is performed on one of a time division multiplexed (TDM) pilot signal and a code division multiplexed (CDM) pilot signal.

32. The method of claim 21, wherein the coefficient adjustment step is performed using one of a least mean square (LMS) algorithm, a recursive least square (RLS) algorithm, and a direct matrix inversion (DMI) algorithm.

33. An apparatus for processing received signal samples, the apparatus comprising;

means for equalizing the received signal samples to provide symbol estimates, the step of equalizing comprising filtering the signal samples and adjusting coefficients used during the filtering step;

means for despreading the symbol estimates to generate despread symbols;

means for decovering the despread symbols to generate a first stream of recovered symbols;

means for processing one or more multipaths of the signal samples by a rake receiver to provide a second stream of recovered symbols;

means for estimating a first signal quality of the first stream of recovered symbols and a second signal quality of the second stream of recovered symbols,

means for comparing the first and second signal qualities; and

means for selecting one of the first and the second stream of recovered symbols to generate recovered data symbols.

34. The apparatus of claim 33, wherein the means for equalizing and the means for multipath processing are operate on pilot samples.

35. The apparatus of claim 33, wherein the means for dispreading and the means for decovering selectively operate based on a data rate of a received signal associated with the signal samples.

36. The apparatus of claim 33, wherein the means for estimating the first signal quality of the first stream of recovered symbols operates based on a mean square error (MSE) between the symbol estimates and expected symbols.

37. The apparatus of claim 33, further comprising:

means for identifying a strongest multipath of the signal samples; and

means for adjusting the filter coefficients according to an information related to the identified strongest multipath.

38. The apparatus of claim 37, wherein the information comprises a time offset of the identified strongest multipath.

39. The apparatus of claim 33, wherein the means for adjusting the filter coefficient minimizes a mean square error (MSE) between the symbol estimates and expected symbols.

40. The apparatus of claim 33, wherein the means for adjusting the filter coefficient minimizes a mean square error (MSE) between filtered samples generated during the means for filtering and expected symbols.

41. The apparatus of claim 33, wherein the means for filtering is one of a finite impulse response (FIR) filter and an infinite impulse response (IIR) filter.