Method and system for signal reconstruction from spatially and temporally correlated received samples

• US 8,385,388 B2
• Filed: 08/09/2006
• Issued: 02/26/2013
• Est. Priority Date: 12/06/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Soriaga, Joseph B., Bhushan, Naga, Hou, Jilei, Chen, Jinghu, Smee, John Edward
• Primary Examiner(s): Payne, David C.
• Assistant Examiner(s): Perez, James M
• Application Number:
  US11/501,972
• Publication Number:
  US 20070147329A1
• Time in Patent Office: 2,393 Days
• Field of Search: 375/130, 375140-142, 375/144, 375147-148, 375/150
• US Class Current: 375/148
• CPC Class Codes: H04B 1/71072 Successive interference cancellation
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/1607 Details of the supervisory signal
• CPC Class Codes: H04L 1/1812 Hybrid protocols; Hybrid automatic repeat request [HARQ]
• CPC Class Codes: H04L 1/1858 Transmission or retransmission of more than one copy of acknowledgement message
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 1/208 involving signal re-encoding
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/03254 Operation with other circuitry for removing intersymbol interference

Abstract

A method and system for reconstructing a user'"'"'s received signal based on knowledge of the user'"'"'s transmitted signal to yield efficient interference cancellation when there is spatial and/or temporal correlation in the received signal. The invention may be applied to the cancellation of pilot, decoded data and overhead signals. The method may involve a linear combination of the received samples across time, e.g., at a per-chip or sub-chip resolution, and across antennas, and build upon previous work in that the tap weights need not be the sole functions of the de-spreader outputs in the RAKE receiver.

Claims

1. A method for computing a reconstructed desired user'"'"'s signal contribution from a received signal, comprising:

estimating spatial correlation of a plurality of received samples of the received signal;

estimating spatial correlation of a plurality of channel coefficients of the received signal, the plurality of channel coefficients comprising signal amplitudes of various paths, including delay, received at multiple antennas;

calculating the spatial correlation of a desired user'"'"'s signal based on the estimated spatial correlation of the plurality of channel coefficients of the received signal; and

computing the reconstructed desired user'"'"'s signal contribution based on the calculated spatial correlation of the desired user'"'"'s signal and the estimated spatial correlation of the plurality of received samples.

2. The method of claim 1, further comprising:

estimating temporal correlation of the plurality of received samples of the received signal;

estimating temporal correlation of the plurality of channel coefficients of the received signal; and

calculating the temporal correlation of the desired user'"'"'s signal.

3. The method of claim 2, further comprising:

obtaining a reconstruction matrix.

4. The method of claim 2, wherein the received signal with respect to a desired user may be represented by

5. The method of claim 4, wherein the additive noise z_(m)[k] is uncorrelated with g_(m)[k].

6. The method of claim 4, wherein s[k] is a transmitted sequence and comprises at least one of data-, pilot- or overhead-sequence followed by a spreading sequence.

7. The method of claim 4, wherein if k corresponds to a sub-chip resolution, then s[k] further includes a convolution with the transmit and receive filters.

8. The method of claim 2, wherein the reconstructed desired user'"'"'s signal contribution is represented by

ĝ

=Wy,

where the vector g is represented by

g=[g_(l)[l], . . . , g_(l)[N], . . . , g_(M)[l], . . . , g_(M)[N]]^T, the vector y is represented by

y=[y_(l)[l], . . . , y_(l)[N], . . . , y_(M)[l], . . . , y_(M)[N]]^T, and the reconstruction matrix W is solved from WR(y,y)=R(g,y).

9. The method of claim 2, wherein in a scenario of a single-antenna multipath channel at sub-chip resolution, the received signal may be represented by

10. The method of claim 9, wherein if the transmit-receive pulse is φ

[k], where k reflects sampling at d times a chip frequency, then the known user'"'"'s signal equals s[k]=x[k]{circle around (x)}φ

[k], where x[k] is an upsampled coded-sequence.

11. The method of claim 10, wherein for closely spaced paths with τ

_l-τ

<sub>l−

1</sub> near one chip interval, the presence of φ

[k] may cause conventional de-spreading techniques to give bad channel path estimates.

12. The method of claim 10, wherein the closely spaced paths are referred to as fat-paths.

13. The method of claim 12, wherein in a moderate-to-high signal-to-noise ratio regime, the spatial and temporal correlation calculating of the desired user'"'"'s signal may be further simplified to compensate for fat-paths and represented by

14. The method of claim 1, wherein in a scenario of a single-path multiple antenna channel at per-chip resolution, the received signal may be represented by

g_(m)[k]=h_(m)s[k], for k=1, . . . , N and m=1, . . . , M ,

where k is the time index in chips, h_(m) is the static over the duration N fade coefficient, s[k] is the spread data, pilot, or overhead signal, and z_(m)[k] may represent received signals from at least other users, other-cell interference, and thermal noise.

15. The method of claim 14, wherein |s[k]|=1 and s[k] is known at a receiver.

16. The method of claim 14, wherein additive noise z_(m)[k] is further modeled as an independently, identically distributed zero-mean signal, for all k=1, . . . , N .

17. The method of claim 16, wherein the additive noise z_(m)[k] is uncorrelated with g_(m)[k].

18. The method of claim 14, wherein the reconstructed desired user'"'"'s signal contribution is represented by

19. The method of claim 1, wherein the signal comprises a Code Division Multiple Access (CDMA) or a Wideband CDMA (W-CDMA) signal.

20. An apparatus for computing a reconstructed desired user'"'"'s signal contribution from a received signal, comprising:

means for estimating spatial correlation of a plurality of received samples of the received signal;

means for estimating spatial correlation of a plurality of channel coefficients of the received signal, the plurality of channel coefficients comprising signal amplitudes of various paths, including delay, received at multiple antennas;

means for calculating the spatial correlation of a desired user'"'"'s signal based on estimated spatial correlation of the plurality of channel coefficients of the received signal; and

means for computing the reconstructed desired user'"'"'s signal contribution based on calculated spatial correlation of the desired user'"'"'s signal and estimated spatial correlation of the plurality of received samples.

21. The apparatus of claim 20, further comprising:

means for estimating temporal correlation of the plurality of received samples of the received signal;

means for estimating temporal correlation of the plurality of channel coefficients of the received signal; and

means for calculating the temporal correlation of the desired user'"'"'s signal.

22. The apparatus of claim 21, further comprising:

means for obtaining a reconstruction matrix.

23. The apparatus of claim 21, wherein the received signal may be represented by

24. The apparatus of claim 23, wherein the additive noise z_(m)[k] is uncorrelated with g_(m)[k].

25. The apparatus of claim 23, wherein s[k] is a transmitted sequence and comprises at least one of data-, pilot- or overhead-sequence followed by a spreading sequence.

26. The apparatus of claim 23, wherein if k corresponds to a sub-chip resolution, then s[k] further includes a convolution with the transmit and receive filters.

27. The apparatus of claim 21, wherein the reconstructed desired user'"'"'s signal contribution is represented by

ĝ

=Wy,

where the vector g is represented by

g=[g_(l)[l], . . . , g_(l)[N], . . . , g_(M)[l], . . . , g_(M)[N]]^T, the vector y is represented by

y=[y_(l)[l], . . . , y_(l)[N], . . . , y_(M)[l], . . . , y_(M)[N]]^T, and the reconstruction matrix W is solved from WR(y,y)=R(g,y).

28. The apparatus of claim 21, wherein in a scenario of a single-antenna multipath channel at sub-chip resolution, the received signal may be represented by

29. The apparatus of claim 28, wherein if the transmit-receive pulse is φ

[k] , where k reflects sampling at d times a chip frequency, then the known user'"'"'s signal equals s[k]=x[k]{circle around (x)}φ

[k], where x[k] is an upsampled coded-sequence.

30. The apparatus of claim 29, wherein for closely spaced paths with τ

_l-τ

<sub>l−

1</sub> near one chip interval, the presence of φ

[k] may cause conventional de-spreading techniques to give bad channel path estimates.

31. The apparatus of claim 29, wherein the closely spaced paths are referred to as fat-paths.

32. The apparatus of claim 31, wherein in a moderate-to-high signal-to-noise ratio regime, the calculating means of the spatial and temporal correlation of the desired user'"'"'s signal may be further simplified to compensate for fat-paths and represented by

33. The apparatus of claim 20, wherein in a scenario of a single-path multiple antenna channel at per-chip resolution, the received signal may be represented by

g_(m)[k]=h_(m)s[k], for k=1, . . . , N and m=1, . . . , M,

where k is the time index in chips, h_(m) is the static over the duration N fade coefficient, s[k] is the spread data, pilot, or overhead signal, and z_(m)[k] may represent received signals from at least other users, other-cell interference, and thermal noise.

34. The apparatus of claim 33, wherein |s[k]|=1 and s[k] is known at a receiver.

35. The apparatus of claim 33, wherein additive noise z_(m)[k] is further modeled as an independently, identically distributed zero-mean signal, for all k=1, . . . , N.

36. The apparatus of claim 35, wherein the additive noise z_(m)[k] is uncorrelated with g_(m)[k].

37. The apparatus of claim 33, wherein the reconstructed desired user'"'"'s signal contribution is represented by

38. The apparatus of claim 20, wherein the signal comprises a Code Division Multiple Access (CDMA) or a Wideband CDMA (W-CDMA) signal.

39. An interference cancellation (IC) apparatus comprising:

a receiver configured to receive a received signal; and

a module configured to perform interference cancellation and to compute a reconstructed desired user'"'"'s signal contribution from spatially and temporally correlated received samples of the received signal and spatially and temporally correlated channel coefficients of the received signal, the channel coefficients comprising signal amplitudes of various paths, including delay, received at multiple antennas;

wherein the module is further configured to calculate spatial and temporal correlation of a desired user'"'"'s signal based on the spatially and temporally correlated channel coefficients, and further wherein computation of the reconstructed desired user'"'"'s signal contribution is based on calculated spatial and temporal correlation of the desired user'"'"'s signal and the spatially and temporally correlated received samples.

40. The apparatus of claim 39, wherein the module comprises:

means for estimating spatial and temporal correlation of the received samples;

means for estimating spatial and temporal correlation of the plurality of channel coefficients of the received signal;

means for calculating spatial and temporal correlation of a desired user'"'"'s signal based on estimated spatial correlation of the plurality of channel coefficients of the received signal; and

means for computing the reconstructed desired user'"'"'s signal contribution based on calculated spatial and temporal correlation of the desired user'"'"'s signal and estimated spatial and temporal correlation of the plurality of received samples.

41. The apparatus of claim 40, further comprising:

means for obtaining a reconstruction matrix.

42. A non-transitory computer readable medium embodying a method of computing a reconstructed desired user'"'"'s signal contribution from a received signal, the method comprising:

estimating spatial correlation of a plurality of received samples of the received signal;

estimating spatial correlation of a plurality of channel coefficients of the received signal, the plurality of channel coefficients comprising signal amplitudes of various paths, including delay, received at multiple antennas;

calculating the spatial correlation of a desired user'"'"'s signal based on the estimated spatial correlation of the plurality of channel coefficients of the received signal; and

computing the reconstructed desired user'"'"'s signal contribution based on the calculated spatial correlation of the desired user'"'"'s signal and the estimated spatial correlation of the plurality of received samples.