Methods and systems for reducing co-channel interference using multiple timings for a received signal

• US 6,304,618 B1
• Filed: 08/31/1998
• Issued: 10/16/2001
• Est. Priority Date: 08/31/1998
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Hafeez, Abdulrauf, Bottomley, Gregory E., Molnar, Karl J.
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): PHU, PHUONG M
• Application Number:
  US09/143,821
• Time in Patent Office: 1,142 Days
• Field of Search: 375/341, 375/265, 375/262, 714/792, 714/793, 714/794, 714/795, 714/796, 714/786
• US Class Current: 375/341
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/03337 Arrangements involving per-survivor processing

Abstract

A plurality of timings are estimated for a received signal wherein the plurality of timings correspond to a plurality of transmitted signals. The received signal is then sampled in accordance with the plurality of timings, to produce a plurality of sample streams from the received signal. Channel estimates are produced for the plurality of transmitted signals and metrics are computed using the sample streams and the channel estimates. Information symbols corresponding to the transmitted signals are detected by using the metrics. Accordingly, by using multiple timings for a received signal, rather than using a common timing, the number of channel taps that are used may be reduced and the accuracy of symbol detection may be increased. The channel estimates may be produced by generating pulse-shape information and producing channel estimates for the multiple transmitted signals using the received signal and the pulse-shape information. Channel estimates may be produced that correspond to a plurality of symbol sequence hypotheses. Channel estimates may be updated using an error signal.

Claims

1. A receiver comprising:

means for estimating a plurality of timings for at least one received signal, the plurality of timings corresponding to a plurality of different transmitted signals having different symbol sequences;

means for sampling the at least one received signal in accordance with the plurality of timings corresponding to a plurality of different transmitted signals having different symbol sequences, to produce a plurality of sample streams;

means for producing channel estimates for the plurality of transmitted signals;

means for computing metrics using the sample streams and the channel estimates; and

means for detecting information symbols corresponding to the plurality of transmitted signals, using the metrics.

2. A receiver according to claim 1 wherein the means for estimating comprises means for correlating the at least one received signal to at least one symbol sequence.

3. A receiver according to claim 1:

wherein the means for estimating comprises means for hypothesizing a timing; and

wherein means for computing comprises means for computing metrics that are associated with the hypothesized timing.

4. A receiver according to claim 1 wherein the means for sampling comprises means for obtaining a single sample per symbol period of the at least one received signal in accordance with the plurality of timings to produce the plurality of sample streams.

5. A receiver according to claim 1 wherein the means for sampling comprises means for obtaining a plurality of samples per symbol period of the at least one received signal in accordance with the plurality of timings to produce the plurality of sample streams.

6. A receiver according to claim 1 wherein the means for producing channel estimates comprises:

means for generating pulse-shape information; and

means for producing channel estimates for the plurality of transmitted signals using the at least one received signal and the pulse-shape information.

7. A receiver according to claim 1 wherein the means for producing channel estimates comprises means for producing channel estimates that are associated with a plurality of symbol sequence hypotheses.

8. A receiver according to claim 1 wherein the means for producing channel estimates comprises means for updating channel estimates using an error signal.

9. A receiver according to claim 1 wherein the means for computing metrics comprises:

means for filtering the sample streams with the channel estimates to produce a plurality of filter outputs; and

means for computing metrics using the filter outputs.

10. A receiver according to claim 1 wherein the means for computing metrics comprises:

means for estimating received values using the channel estimates and hypothesized symbols; and

means for computing metrics using the estimated received values.

11. A receiver according to claim 1 wherein the means for detecting comprises:

means for storing path information that is associated with a plurality of paths;

means for extending the paths by hypothesizing symbol values and computing metrics; and

means for discarding paths based on the metrics.

12. A receiver according to claim 11 wherein the means for discarding paths comprises means for discarding paths based on the metrics and a state space.

13. A receiver according to claim 1 wherein the means for computing metrics comprises:

means for estimating impairment correlation among receive antennas to produce an impairment correlation estimate; and

means for computing metrics using the sample streams, the channel estimates, and the impairment correlation estimate.

14. A receiver according to claim 13 wherein the means for producing channel estimates comprises means for producing channel estimates using the impairment correlation estimate.

78. A received according to claim 1 in combination with a plurality of transmitters, a respective one of which transmits a different one of the plurality of different transmitted signals having different symbol sequences.

15. A receiver comprising:

means for generating pulse-shape information for at least one received signal;

means for producing channel estimates for a plurality of different transmitted signals having different symbol sequences, using the at least one received signal and the pulse-shape information;

means for computing metrics using the at least one received signal and the channel estimates; and

means for detecting information symbols corresponding to the plurality of transmitted signals having different symbol sequences, using the metrics.

16. A receiver according to claim 15 wherein the means for producing channel estimates comprises means for producing channel estimates that are associated with a plurality of symbol sequence hypotheses.

17. A receiver according to claim 15 wherein the means for producing channel estimates comprises means for updating channel estimates using an error signal.

18. A receiver according to claim 15 wherein the means for computing metrics comprises:

means for filtering the at least one received signal with the channel estimates to produce a plurality of filter outputs; and

means for computing metrics using the filter outputs.

19. A receiver according to claim 15 wherein the means for computing metrics comprises:

means for estimating received values using the channel estimates and hypothesized symbols; and

means for computing metrics using the estimated received values.

20. A receiver according to claim 15 wherein the means for detecting comprises:

means for storing path information that is associated with a plurality of paths;

means for extending the paths by hypothesizing symbol values and computing metrics; and

means for discarding paths based on the metrics.

21. A receiver according to claim 20 wherein the means for discarding paths comprises means for discarding paths based on the metrics and a state space.

22. A receiver according to claim 15 wherein the means for computing metrics comprises:

means for estimating impairment correlation among receive antennas to produce an impairment correlation estimate; and

means for computing metrics using each received signal, the channel estimates, and the impairment correlation estimate.

23. A receiver according to claim 22 wherein the means for producing channel estimates comprises means for producing channel estimates using received signal, the pulse-shape information, and the impairment correlation estimate.

79. A received according to claim 15 in combination with a plurality of transmitters, a respective one of which transmits a different one of the plurality of different transmitted signals having different symbol sequences.

24. A receiver comprising:

means for estimating a plurality of timings for at least one received signal, the plurality of timings corresponding to a plurality of different transmitted signals having different symbol sequences;

means for sampling the at least one received signal in accordance with the plurality of timings corresponding to a plurality of different transmitted signals having different symbol sequences, to produce a plurality of sample streams;

means for initializing channel estimates for the plurality of transmitted channels and for initializing metrics;

means for computing updated metrics using the sample streams the initialized channel estimates and the initialized metrics;

means for detecting information symbols corresponding to at least one of the transmitted signals, using the updated metrics; and

means for updating the channel estimates using the updated metrics.

25. A receiver according to claim 24 wherein the means for estimating comprises means for correlating the at least one received signal to at least one symbol sequence.

26. A receiver according to claim 24:

wherein the means for estimating comprises means for hypothesizing a timing; and

wherein the means for computing comprises means for computing updated metrics that are associated with the hypothesized timing.

27. A receiver according to claim 24 wherein the means for sampling comprises means for obtaining a single sample per symbol period of the at least one received signal in accordance with the plurality of timings to produce a plurality of sample streams.

28. A receiver according to claim 24 wherein the means for sampling comprises means for obtaining a plurality of samples per symbol period of the at least one received signal in accordance with the plurality of timings to produce a plurality of sample streams.

29. A receiver according to claim 24 wherein the means for initializing channel estimates comprises:

means for generating pulse-shape information; and

means for initializing channel estimates using the pulse-shape information.

30. A receiver according to claim 24 wherein the means for initializing channel estimates comprises means for initializing channel estimates for a plurality of symbol sequence hypotheses.

31. A receiver according to claim 24 wherein the means for updating channel estimates comprises means for updating channel estimates using an error signal.

32. A receiver according to claim 24 wherein the means for computing metrics comprises:

means for filtering the sample streams with the channel estimates to produce a plurality of filter outputs; and

means for computing metrics using the filter outputs.

33. A receiver according to claim 24 wherein the means for computing updated metrics comprises:

means for estimating received values using the channel estimates, hypothesized symbols and known symbol values; and

means for computing metrics using the estimated received values.

34. A receiver according to claim 24 wherein the means for detecting comprises:

means for storing path information that is associated with a plurality of paths;

means for extending the paths by hypothesizing symbol values and computing metrics; and

means for discarding paths based on the metrics.

35. A receiver according to claim 34 wherein the means for discarding paths comprises means for discarding paths based on the metrics and a state space.

36. A receiver according to claim 24 wherein the means for initializing comprises means for initializing channel estimates for a selected one of the plurality of channels using the received signal and known symbol values.

37. A receiver according to claim 24 wherein the means for initializing comprises means for initializing channel estimates for an interfering signal using the received signal and channel estimates of a desired signal.

38. A receiver according to claim 24 wherein the means for initializing comprises means for initializing metrics for a predetermined symbol value for at least one interfering symbol sequence.

80. A received according to claim 24 in combination with a plurality of transmitters, a respective one of which transmits a different one of the plurality of different transmitted signals having different symbol sequences.

39. A method of receiving at least one signal that corresponds to a plurality of different transmitted signals having different symbol sequences, comprising the steps of:

estimating a plurality of timings for the at least one received signal, the plurality of timings corresponding to the plurality of different transmitted signals having different symbol sequences;

sampling the at least one received signal in accordance with the plurality of timings to produce a plurality of sample streams;

producing channel estimates for the plurality of transmitted signals;

computing metrics using the sample streams and the channel estimates; and

detecting information symbols corresponding to the plurality of transmitted signals, using the metrics.

40. A method according to claim 39 wherein the estimating step comprises the step of correlating the at least one received signal to at least one symbol sequence.

41. A method according to claim 39:

wherein the step of estimating comprises the step of hypothesizing a timing; and

wherein the step of computing comprises the step of computing metrics that are associated with the hypothesized timing.

42. A method according to claim 39 wherein the step of sampling comprises the step of obtaining a single sample per symbol period of the at least one received signal in accordance with the plurality of timings to produce the plurality of sample streams.

43. A method according to claim 39 wherein the step of sampling comprises the step of obtaining a plurality of samples per symbol period of the at least one received signal in accordance with the plurality of timings to produce the plurality of sample streams.

44. A method according to claim 39 wherein the step of producing channel estimates comprises the steps of:

generating pulse-shape information; and

producing channel estimates for the plurality of transmitted signals using the at least one received signal and the pulse-shape information.

45. A method according to claim 39 wherein the step of producing channel estimates comprises the step of producing channel estimates that are associated with a plurality of symbol sequence hypotheses.

46. A method according to claim 39 wherein the step of producing channel estimates comprises the step of updating channel estimates using an error signal.

47. A method according to claim 39 wherein the step of computing metrics comprises the steps of:

filtering the sample streams with the channel estimates to produce a plurality of filter outputs; and

computing metrics using the filter outputs.

48. A method according to claim 39 wherein the step of computing metrics comprises the steps of:

estimating received values using the channel estimates and hypothesized symbols; and

computing metrics using the estimated received values.

49. A method according to claim 39 wherein the step of detecting comprises the steps of:

storing path information that is associated with a plurality of paths;

extending the paths by hypothesizing symbol values and computing metrics; and

discarding paths based on the metrics.

50. A method according to claim 49 wherein the step of discarding paths comprises the step of discarding paths based on the metrics and a state space.

51. A method according to claim 39 wherein the step of computing metrics comprises the steps of:

estimating impairment correlation among receive antennas to produce an impairment correlation estimate; and

computing metrics using the same streams, the channel estimates, and the impairment correlation estimate.

52. A receiver according to claim 51 wherein the step of producing channel estimates uses the impairment correlation estimate.

81. A method according to claim 39 wherein the estimating is preceded by transmitting a different one of the different transmitted signals having different symbol sequences from a respective one of a plurality of transmitters.

53. A method of receiving at least one signal that corresponds to a plurality of different transmitted signals having different symbol sequences, comprising the steps of:

generating pulse-shape information for the at least one received signal;

producing channel estimates for the plurality of different transmitted signals having different symbol sequences, using the at least one received signal and the pulse-shape information;

computing metrics using the at least one received signal and the channel estimates; and

detecting information symbols corresponding to the plurality of transmitted signals, using the metrics.

54. A method according to claim 53 wherein the step of producing channel estimates comprises the step of producing channel estimates that are associated with a plurality of symbol sequence hypotheses.

55. A method according to claim 53 wherein the step of producing channel estimates comprises the step of updating channel estimates using an error signal.

56. A method according to claim 53 wherein the step of computing metrics comprises the steps of:

filtering the at least one received signal with the channel estimates to produce a plurality of filter outputs; and

computing metrics using the filter outputs.

57. A method according to claim 53 wherein the step of computing metrics comprises the steps of:

estimating received values using the channel estimates and hypothesized symbols; and

computing metrics using the estimated received values.

58. A method according to claim 53 wherein the step of detecting comprises the steps of:

storing path information that is associated with a plurality of paths;

extending the paths by hypothesizing symbol values and computing metrics; and

discarding paths based on the metrics.

59. A method according to claim 58 wherein the step of discarding paths comprises the step of discarding paths based on the metrics and a state space.

60. A method according to claim 54 wherein the step of computing metrics comprises the steps of:

estimating impairment correlation among receive antennas to produce an impairment correlation estimate; and

computing metrics using each received signal, the channel estimates, and the impairment correlation estimate.

61. A receiver according to claim 60 wherein the step of producing channel estimates uses each received signal, pulse-shape information, and the impairment correlation estimate.

82. A method according to claim 53 wherein the estimating is preceded by transmitting a different one of the different transmitted signals having different symbol sequences from a respective one of a plurality of transmitters.

62. A method of receiving at least one signal that corresponds to a plurality of different transmitted signals having different symbol sequences, comprising the steps of:

estimating a plurality of timings for the at least one received signal, the plurality of timings corresponding to the plurality of different transmitted signals having different symbol sequences;

sampling the at least one received signal in accordance with the plurality of timings to produce a plurality of sample streams;

initializing channel estimates for the plurality of transmitted channels and initializing metrics;

computing updated metrics using the sample streams, the initialized channel estimates and the initialized metrics;

detecting information symbols corresponding to at least one of the transmitted signals, using the updated metrics; and

updating the channel estimates using the updated metrics.

63. A method according to claim 62 wherein the step of estimating comprises the step of correlating the at least one received signal to at least one symbol sequence.

64. A method according to claim 62:

wherein the step of estimating comprises the step of hypothesizing a timing; and

wherein the step of computing comprises the step of computing updated metrics that are associated with the hypothesized timing.

65. A method according to claim 62 wherein the step of sampling comprises the step of obtaining a single sample per symbol period of the at least one received signal in accordance with the plurality of timings to produce a plurality of sample streams.

66. A method according to claim 62 wherein the step of sampling comprises the step of obtaining a plurality of samples per symbol period of the at least one received signal in accordance with the plurality of timings to produce a plurality of sample streams.

67. A method according to claim 62 wherein the step of initializing channel estimates comprises the steps of:

generating pulse-shape information; and

initializing channel estimates using the pulse-shape information.

68. A method according to claim 62 wherein the step of initializing channel estimates comprises the step of initializing channel estimates for a plurality of symbol sequence hypotheses.

69. A method according to claim 62 wherein the step of updating channel estimates comprises the step of updating channel estimates using an error signal.

70. A method according to claim 62 wherein the step of computing metrics comprises the steps of:

filtering the sample streams with the channel estimates to produce a plurality of filter outputs; and

computing metrics using the filter outputs.

71. A method according to claim 62 wherein the step of computing updated metrics comprises the steps of:

estimating received values using the channel estimates, hypothesized symbols and known symbol values; and

computing metrics using the estimated received values.

72. A method according to claim 62 wherein the step of detecting comprises:

storing path information that is associated with a plurality of paths;

extending the paths by hypothesizing symbol values and computing metrics; and

discarding paths based on the metrics.

73. A method according to claim 72 wherein the step of discarding paths comprises the step of discarding paths based on the metrics and a state space.

74. A method according to claim 62 wherein the step of initializing comprises the step of initializing channel estimates for a selected one of the plurality of channels using the at least one received signal and known symbol values.

75. A method according to claim 62 wherein the step of initializing comprises the step of initializing channel estimates for an interfering signal using the at least one received signal and channel estimates of a desired signal.

76. A method according to claim 62 wherein the step of initializing comprises the step of initializing metrics for a predetermined symbol value for at least one interfering symbol sequence.

77. A method according to claim 62 wherein the steps of initializing channel estimates, computing updated metrics, detecting information symbols and updating the channel estimates are repeatedly performed to refine the channel estimates.

83. A method according to claim 62 wherein the estimating is preceded by transmitting a different one of the different transmitted signals having different symbol sequences from a respective one of a plurality of transmitters.