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

• US 20070147329A1
• Filed: 08/09/2006
• Published: 06/28/2007
• Est. Priority Date: 12/06/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Smee, John Edward, Bhushan, Naga, Soriaga, Joseph B., Hou, Jilei, Chen, Jinghu
• Granted Patent: US 8,385,388 B2
• Time in Patent Office: Days
• US Class Current: 370/342
• 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 reconstructing a user'"'"'s 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;

calculating the spatial correlation of the desired user'"'"'s signal; and

computing a reconstructed user'"'"'s signal.

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 user'"'"'s signal is represented by

ĝ

=Wy,

where the vector g is represented by

g=[g_(l)[1], . . . , g_(l)[N], . . . , g_(M)[1], . . . , g_(M)[N]]^T, the vector y is represented by

y=[y₍₁₎[1], . . . , y₍₁₎[N], . . . . . . , y_(M)[1], . . . y_(M)[N]]^T, and the reconstruction matrix W is solved from WR(y,y)=R(g,y).

9. The method of claim 1, wherein in a scenario of a single-path multiple antenna channel at per-chip resolution, the received signal with respect to a desired user'"'"'s 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.

10. The method of claim 9, wherein |s[k]|=1 and s[k] is known at the receiver.

11. The method of claim 9, wherein the additive noise z_(m)[k] is further modeled as an independently, identically distributed zero-mean signal, for all k=1, . . . ,N.

12. The method of claim 11, wherein the additive noise z_(m)[k] is uncorrelated with g_(m)[k].

13. The method of claim 9, wherein the reconstructed user'"'"'s signal is represented by

14. The method of claim 2, wherein in a scenario of a single-antenna multipath channel at sub-chip resolution, the received signal with respect to a desired user'"'"'s signal may be represented by

15. The method of claim 14, 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.

16. The method of claim 15, wherein for closely spaced paths with τ

_l-τ

<sub>l−

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

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

17. The method of claim 15, wherein the closely spaced paths are referred to as fat-paths.

18. The method of claim 17, 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

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 reconstructing a user'"'"'s 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;

means for calculating the spatial correlation of the desired user'"'"'s signal; and

means for computing a reconstructed user'"'"'s signal.

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 with respect to a desired user 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 user'"'"'s signal is represented by

ĝ

=Wy,

where the vector g is represented by

g=[g_(l)[1], . . . ,g_(l)[N], . . . , g_(M)[1], . . . ,g_(M)[N]]^T, the vector y is represented by

y=[y₍₁₎[1], . . . ,y_(M)[N],. . . . . . ,y_(M)[1], . . . ,y_(M)[N]]^T, and the reconstruction matrix W is solved from WR(y,y)=R(g,y).

28. The apparatus of claim 20, wherein in a scenario of a single-path multiple antenna channel at per-chip resolution, the received signal with respect to a desired user'"'"'s 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.

29. The apparatus of claim 28, wherein |s[k]|=1 and s[k] is known at the receiver.

30. The apparatus of claim 28, wherein the additive noise z_(m)[k] is further modeled as an independently, identically distributed zero-mean signal, for all k=1, . . . ,N.

31. The apparatus of claim 30, wherein the additive noise z_(m)[k] is uncorrelated with g_(m)[k].

32. The apparatus of claim 28, wherein the reconstructed user'"'"'s signal is represented b

33. The apparatus of claim 21, wherein in a scenario of a single-antenna multipath channel at sub-chip resolution, the received signal with respect to a desired user'"'"'s signal may be represented by

34. The apparatus of claim 33, 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.

35. The apparatus of claim 34, 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.

36. The apparatus of claim 34, wherein the closely spaced paths are referred to as fat-paths.

37. The apparatus of claim 36, 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

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 user'"'"'s signal; and

a module configured to perform interference cancellation and to reconstruct the user'"'"'s signal from spatially and temporally correlated received samples of the signal.

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 a plurality of channel coefficients of the signal;

means for calculating spatial and temporal correlation of a desired user'"'"'s signal; and

means for computing the reconstructed user'"'"'s signal.

41. The apparatus of claim 40, further comprising:

means for obtaining a reconstruction matrix.