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

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.

Description

BRIEF DESCRIPTION OF DRAWINGS

The features, nature, and advantages of the present application may be more apparent from the detailed description set forth below with the drawings. Like reference numerals and characters may identify the same or similar objects.

FIG. 1 illustrates a wireless communication system with base stations and access terminals.

FIG. 2 illustrates an example of transmitter structure and/or process, which may be implemented at an access terminal of FIG. 1.

FIG. 3 illustrates an example of a receiver process and/or structure, which may be implemented at a base station of FIG. 1.

FIG. 4 illustrates another embodiment of a base station receiver process or structure.

FIG. 5 illustrates a general example of power distribution of three users in the system of FIG. 1.

FIG. 6 shows an example of a uniform time-offset distribution for frame asynchronous traffic interference cancellation for users with equal transmit power.

FIG. 7 illustrates an interlacing structure used for the reverse link data packets and a forward link automatic repeat request channel.

FIG. 8 illustrates a memory that spans a complete 16-slot packet.

FIG. 9A illustrates a method of traffic interference cancellation for an example of Sequential Interference Cancellation (SIC) with no delayed decoding.

FIG. 9B illustrates an apparatus to perform the method of FIG. 9A.

FIG. 10 illustrates a receiver sample buffer after arrival of successive subpackets of an interlace with Interference Cancellation (IC) of decoded subpackets.

FIG. 11 illustrates an overhead channels structure.

FIG. 12A illustrates a method to first perform Pilot IC (PIC) and then perform Overhead IC (OIC) and Traffic IC (TIC) together.

FIG. 12B illustrates an apparatus to perform the method of FIG. 12A.

FIG. 13A illustrates a variation of the method in FIG. 12A.

FIG. 13B illustrates an apparatus to perform the method of FIG. 13A.

FIG. 14A illustrates a method to perform joint PIC, OIC and TIC.

FIG. 14B illustrates an apparatus to perform the method of FIG. 14A.

FIG. 15A illustrates a variation of the method in FIG. 14A.

FIG. 15B illustrates an apparatus to perform the method of FIG. 15A.

FIG. 16 illustrates a model of transmission system.

FIG. 17 illustrates an example response of combined transmit and receive filtering.

FIGS. 18A and 18B show an example of channel estimation (real and imaginary components) based on the estimated multipath channel at each of three RAKE fingers.

FIGS. 19A and 19B show examples of an improved channel estimate based on RAKE fingers and despreading with the data chips.

FIG. 20A illustrates a method for despreading at RAKE finger delays with regenerated data chips.

FIG. 20B illustrates an apparatus to perform the method of FIG. 20A.

FIGS. 21A and 21B show an example of estimating the composite channel using uniformly spaced samples at chipx2 resolution.

FIG. 22A illustrates a method for estimating composite channel at uniform resolution using regenerated data chips.

FIG. 22B illustrates an apparatus to perform the method of FIG. 22A.

FIG. 23 illustrates a closed loop power control and gain control with fixed overhead subchannel gain.

FIG. 24 is a variation of FIG. 23 power control and gain control with fixed overhead subchannel gain.

FIG. 25 illustrates an example of power control with fixed overhead subchannel gain.

FIG. 26 is similar to FIG. 24 except with overhead gain control.

FIG. 27 illustrates a variation of FIG. 26 with DRC-only overhead gain control.

FIG. 28 illustrates a graph of actual and reconstructed Channel Impulse Responses (CIRs).

FIG. 29A illustrates a method for iterative IC with iterative finger delay adaptation.

FIG. 29B illustrates an apparatus to perform the method of FIG. 29A.

FIG. 30 illustrates a graph of actual, reconstructed and improved CIRs.

FIGS. 31 and 32 illustrate an example and result of channel estimation with fat-paths, respectively.

FIGS. 33 and 34 illustrate an example and result of channel estimation without fat-paths, respectively.

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; andcomputing 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; andcalculating 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,

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,

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 τl-τl−1 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; andmeans 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; andmeans 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,

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,

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 τl-τl−1 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; anda 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; andmeans for computing the reconstructed user's signal.

41. The apparatus of claim 40, further comprising: means for obtaining a reconstruction matrix.