Method and apparatus for interference estimation in a Generalized Rake receiver

• US 20080002759A1
• Filed: 06/30/2006
• Published: 01/03/2008
• Est. Priority Date: 06/30/2006
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Cairns, Douglas A., Bottomley, Gregory E.
• Granted Patent: US 7,688,881 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
• CPC Class Codes: H04B 2201/709727 GRAKE type RAKE receivers

Abstract

According to one embodiment taught herein, a method of determining impairment correlations between a plurality of delays of interest for a received CDMA signal comprises generating kernel functions as samples of a net channel response of the received CDMA signal taken at defined chip sampling phases for delay differences between the plurality of delays of interest. In a parametric Generalized Rake (G-Rake) receiver embodiment, the delays of interest represent the delay positions of the fingers being used to characterized received signal. In a chip equalizer receiver embodiment, the delays of interest represent the delay positions of the equalizer taps. The method continues with determining impairment correlations based on convolving the kernel functions. Corresponding receiver circuits, including an impairment correlation estimation circuit configured for parametric G-Rake operation, may be implemented in a variety of communication devices and systems, such as in wireless communication network base stations and mobile stations.

Claims

1. A method of determining impairment correlations between a plurality of delays of interest for a received CDMA signal, the method comprising:

generating kernel functions as samples of a net channel response of the received CDMA signal taken at defined chip sampling phases for delay differences between the plurality of delays of interest; and

determining impairment correlations based on convolving the kernel functions.

2. The method of claim 1, wherein determining impairment correlations based on convolving the kernel functions comprises carrying out kernel function convolutions in the frequency domain using one or more Fast Fourier Transforms (FFTs).

3. The method of claim 2, further comprising configuring a size of the one or more FFTs based on a maximum delay spread associated with the delays of interest.

4. The method of claim 1, wherein determining impairment correlations based on convolving the kernel functions comprises convolving kernel functions of different ones of the defined chip sampling phases to determine sub-chip impairment correlations between respective pairs of the delays of interest.

5. The method of claim 4, wherein convolving kernel functions of different ones of the defined chip sampling phases to determine sub-chip impairment correlations between respective pairs of the delays of interest comprises performing a number of Fast Fourier Transforms (FFTs) corresponding to a series of linear convolutions involving the kernel functions of different sampling phases.

6. The method of claim 4, wherein convolving kernel functions of different ones of the defined chip sampling phases to determine sub-chip impairment correlations between respective pairs of the delays of interest comprises interleaving the kernel functions and performing a Fast Fourier Transform (FFT) of the interleaved kernel functions.

7. The method of claim 1, wherein generating kernel functions as samples of a net channel response of the received CDMA signal taken at defined chip sampling phases for delay differences between the plurality of delays of interest comprises computing a kernel function for each of one or more chip sampling phases, at each of one or more chip-spaced sampling times within a defined time window of the received CDMA signal.

8. The method of claim 7, wherein the defined time window of the received CDMA signal corresponds to a maximum delay spread among the delays of interest for the received CDMA signal.

9. The method of claim 7, wherein determining impairment correlations based on convolving the kernel functions comprises convolving the kernel functions in the frequency domain via Fast Fourier Transforms (FFTs) to obtain frequency-domain convolution results, and generating time-domain impairment correlation values by performing Inverse Fast Fourier Transforms (IFFTs) on the frequency-domain convolution results.

10. The method of claim 1, wherein generating kernel functions as samples of a net channel response of the received CDMA signal taken at defined chip sampling phases for delay differences between the plurality of delays of interest comprises computing a kernel function for each of one or more chip sampling phases, at each of one or more chip-spaced sampling times within a defined time window of the received CDMA signal, and interleaving the kernel functions to obtain interleaved kernel functions.

11. The method of claim 10, wherein determining impairment correlations based on convolving the kernel functions comprises convolving the kernel functions in the frequency domain by performing a Fast Fourier Transform (FFT) on the interleaved kernel functions to obtain frequency-domain convolution results, and generating time-domain impairment correlation values by performing an Inverse Fast Fourier Transform (IFFT) on the frequency-domain convolution results.

12. The method of claim 1, further comprising populating entries in an impairment correlation matrix in a parametric Generalized Rake (G-Rake) receiver using the impairment correlations.

13. The method of claim 12, further comprising determining the plurality of delays of interest based on G-Rake finger locations, such that the delay differences correspond to differences between finger delays.

14. The method of claim 1, further comprising populating entries in an impairment correlation matrix in a chip equalizer using the impairment correlations.

15. The method of claim 14, further comprising determining the plurality of delays of interest based on chip equalizer tap locations, such that the delay differences correspond to differences between tap delays.

16. A receiver circuit for determining impairment correlations between a plurality of delays of interest for a received CDMA signal, the receiver circuit comprising one or more processing circuits configured to:

generate kernel functions as samples of a net channel response of the received CDMA signal taken at defined chip sampling phases for delay differences between the plurality of delays of interest; and

determine impairment correlations based on convolving the kernel functions.

17. The receiver circuit of claim 16, wherein the one or more processing circuits are configured to determine impairment correlations based on convolving the kernel functions by carrying out kernel function convolutions in the frequency domain using one or more Fast Fourier Transforms (FFTs).

18. The receiver circuit of claim 17, wherein a size of the one or more FFTs carried out by the one or more processing circuits is based on a maximum delay spread associated with the delays of interest.

19. The receiver circuit of claim 16, wherein the one or more processing circuits are configured to determine impairment correlations based on convolving the kernel functions by convolving kernel functions of different ones of the defined chip sampling phases to determine sub-chip impairment correlations between respective pairs of the delays of interest.

20. The receiver circuit of claim 19, wherein the one or more processing circuits are configured to convolve kernel functions of different ones of the defined chip sampling phases to determine sub-chip impairment correlations between respective pairs of the delays of interest by performing a number of Fast Fourier Transforms (FFTs) corresponding to a series of linear convolutions involving the kernel functions of different sampling phases.

21. The receiver circuit of claim 19, wherein the one or more processing circuits are configured to convolve kernel functions of different ones of the defined chip sampling phases to determine sub-chip impairment correlations between respective pairs of the delays of interest by interleaving the kernel functions and performing a Fast Fourier Transform (FFT) of the interleaved kernel functions.

22. The receiver circuit of claim 16, wherein the one or more processing circuits are configured to generate kernel functions as samples of a net channel response of the received CDMA signal taken at defined chip sampling phases for delay differences between the plurality of delays of interest by computing a kernel function for each of one or more chip sampling phases, at each of one or more chip-spaced sampling times within a defined time window of the received CDMA signal.

23. The receiver circuit of claim 22, wherein the defined time window of the received CDMA signal corresponds to a maximum delay spread among the delays of interest for the received CDMA signal.

24. The receiver circuit of claim 22, wherein the one or more processing circuits are configured to determine impairment correlations based on convolving the kernel functions by convolving the kernel functions in the frequency domain via Fast Fourier Transforms (FFTs) to obtain frequency-domain convolution results, and generating time-domain impairment correlation values by performing Inverse Fast Fourier Transforms (IFFTs) on the frequency-domain convolution results.

25. The receiver circuit of claim 16, wherein the one or more processing circuits are configured to generate kernel functions as samples of a net channel response of the received CDMA signal taken at defined chip sampling phases for delay differences between the plurality of delays of interest by computing a kernel function for each of one or more chip sampling phases, at each of one or more chip-spaced sampling times within a defined time window of the received CDMA signal, and interleaving the kernel functions to obtain interleaved kernel functions.

26. The receiver circuit of claim 25, wherein the one or more processing circuits are configured to determine impairment correlations based on convolving the kernel functions by convolving the kernel functions in the frequency domain by performing a Fast Fourier Transform (FFT) on the interleaved kernel functions to obtain frequency-domain convolution results, and generating time-domain impairment correlation values by performing an Inverse Fast Fourier Transform (IFFT) on the frequency-domain convolution results.

27. The receiver circuit of claim 16, wherein the receiver circuit comprises a parametric Generalized Rake (G-Rake) circuit configured to populate entries in an impairment correlation matrix using the impairment correlations.

28. The receiver circuit of claim 27, wherein the parametric G-Rake circuit is configured to determine the plurality of delays of interest based on G-Rake finger locations, such that the delay differences correspond to differences between finger delays.

29. The receiver circuit of claim 16, wherein the receiver circuit comprises a chip equalizer circuit configured to populate entries in an impairment correlation matrix using the impairment correlations.

30. The receiver circuit of claim 29, wherein the chip equalizer circuit is configured to determine the plurality of delays of interest based on chip equalizer tap locations, such that the delay differences correspond to differences between tap delays.

31. A wireless communication device comprising the receiver circuit of claim 16.