Multi-stage rake combining methods and apparatus

• US 6,801,565 B1
• Filed: 06/25/1999
• Issued: 10/05/2004
• Est. Priority Date: 06/25/1999
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Wang, Yi-Pin Eric, Bottomley, Gregory Edward, Ottosson, Tony
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US09/344,898
• Time in Patent Office: 1,929 Days
• Field of Search: 375/142, 375/144, 375/148, 375/150, 375/347, 375/349
• US Class Current: 375/148
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop

Abstract

Information encoded in a spread spectrum signal transmitted in a communications medium is recovered. A composite signal including a spread spectrum signal is received from the communications medium, and correlated with a spreading sequence to generate time-offset correlations. Respective first and second groups of the correlations are combined, e.g., according to estimated channel coefficients, to produce respective first and second combined values. The first and second combined values are then combined in a manner that compensates for correlated impairment in the composite signal to generate an estimate information in the transmitted spread spectrum signal, e.g., using weighting factors generated from an estimated composite channel response and an estimated impairment correlation, or adaptively generated weighting factors. Related apparatus are also described.

Claims

1. A method of recovering information encoded in a spread spectrum signal transmitted in a communications medium, the method comprising the steps of:

receiving a composite signal including a spread spectrum signal from the communications medium;

correlating the received composite signal with a spreading sequence to generate time-offset correlations;

combining a first group of the correlations to produce a first combined value;

combining a second group of the correlations to produce a second combined value; and

combining the first and second combined values in a manner that compensates for correlated impairment in the composite signal to generate an estimate of information in the transmitted spread spectrum signal,

wherein said step of combining the first and second combined values comprises the step of combining the first and second values based on an estimated impairment correlation and on a composite channel response that reflects said step of combining the first group correlations and said step of combining the second group of correlations.

2. A method according to claim 1:

wherein said step of combining a first group of the correlations comprises the step of combining the first group of correlations in a manner that compensates for effect of a channel over which the spread spectrum signal is received; and

wherein said step of combining a second group of the correlations comprises the step of combining the second group of correlations in a manner that compensates for effect of a channel over which the spread spectrum signal is received.

3. A method according to claim 2:

wherein said step of combining a first group of the correlations comprises the step of combining the first group of correlations according to estimated channel coefficients; and

wherein said step of combining a second group of the correlations comprises the step of combining the second group of correlations according to estimated channel coefficients.

4. A method according to claim 3, wherein said step of combining a first group and said step of combining a second group are preceded by the step of generating the channel coefficient estimates.

5. A method according to claim 4, wherein said step of generating the channel coefficient estimates comprises the step of generating the channel coefficient estimates from at least one of a pilot channel, a pilot symbol or a decoded symbol.

6. A method according to claim 1:

wherein said step of combining the first and second combined values is preceded by the steps of;

estimating the composite channel response;

estimating the impairment correlation; and

generating weighting factors from the estimated composite channel response and the estimated impairment correlation; and

wherein said step of combining the first and second combined values comprises the step of combining the first and second combined values according to the generated weighting factors.

7. A method according to claim 6, herein said step of generating weighting factors comprises the step of iteratively generating weighting factors from the estimated composite channel response, the estimated impairment correlation, and previously determined weighting factors.

9. A method according to claim 1, wherein said step of correlating comprises the step of correlating using at least one of a plurality of integrate and dump correlators, a sliding correlator, or a selectively inhibited sliding correlator.

10. A method according to claim 1, wherein said step of correlating comprises the step of correlating using a set of time delays that optimizes a metric that is proportional to a product of the weighting factors and the composite channel response.

8. A method of recovering information encoded in a spread spectrum signal transmitted in a communications medium, the method comprising the steps of:

receiving a composite signal including a spread spectrum signal from the communications medium;

correlating the received composite signal with a spreading sequence to generate time-offset correlations;

combining a first group of the correlations to produce a first combined value;

combining a second group of the correlations to produce a second combined value, and

combining the first and second combined values in a manner that compensates for correlated impairment in the composite signal to generate an estimate of information in the transmitted spread spectrum signal,

wherein said step of combining the first and second combined values comprises the step of combining the first and second values according to weighting factors to generate a third combined value, wherein the weighting factors are adaptively estimated based on comparison of the third combined value to a reference value.

11. A method of recovering information encoded in a spread spectrum signal transmitted in a communications medium, the method comprising the steps of:

receiving a composite signal including a spread spectrum signal from the communications medium;

correlating the received composite signal with a spreading sequence to generate a plurality of time-offset correlations;

combining a first group of the correlations according to a channel estimate to produce a first combined value;

combining a second group of the correlations according to a channel estimate to produce a second combined value; and

combining the first and second combined values according to weighting factors that compensate for correlated impairment in the composite signal to generate an estimate information in the transmitted spread spectrum signal,

wherein said step of combining the first and second combined values comprises the step of combining the first and second combined values based on an estimated impairment correlation and on a composite channel response that reflects said step of combining the first group of correlations and said step of combining the second group of correlations.

12. A method according to claim 11:

wherein said step of combining the first and second combined values is preceded by the steps of;

estimating the composite channel response;

estimating the impairment correlation; and

generating weighting factors from the estimated composite channel response and the estimated impairment correlation; and

wherein said step of combining the first and second combined values comprises the step of combining the first and second combined values according to the generated weighting factors.

13. A method according to claim 12, wherein said step of generating weighting factors comprises the step of iteratively generating weighting factors from the estimated composite channel response, the estimated impairment correlations, and previously determined weighting factors.

15. A method according to claim 11, wherein said steps of combining a first group and said step of combining a second group are preceded by the step of generating the channel estimate.

16. A method according to claim 11, wherein said step of generating a channel estimate comprises the step of generating the channel estimate from at least one of a pilot channel, a pilot symbol or a decoded symbol.

17. A method according to claim 16, wherein said step of correlating comprises the step of correlating using at least one of a plurality of integrate and dump correlators, a sliding correlator, or a selectively inhibited sliding correlator.

18. A method according to claim 11, wherein said step of correlating comprises the step of correlating using a set of time delays that optimizes a metric that is proportional to a product of the weighting factors and the composite channel response.

14. A method of recovering information encoded in a spread spectrum signal transmitted in a communications medium, the method comprising the steps of:

receiving a composite signal including a spread spectrum signal from the communications medium;

correlating the received composite signal with a spreading sequence to generate a plurality of time-offset correlations;

combining a first group of the correlations according to a channel estimate to produce a first combined value;

combining a second group of the correlations according to a channel estimate to produce a second combined value; and

combining the first and second combined values according to weighting factors that compensate for correlated impairment in the composite signal to generate an estimate information in the transmitted spread spectrum signal,

wherein said step of combining the first and second combined values comprises the step of combining the first and second values to generate a third combined value, wherein the weighting factors are adaptively estimated based on comparison of the third combined value to a reference value.

19. An apparatus for recovering information encoded in a spread spectrum signal included in a composite signal, the apparatus comprising:

a correlation unit operative to correlate the composite signal with a spreading sequence to generate time-offset correlations; and

a multistage combiner responsive to said correlation unit and operative to combine respective groups of the correlations to provide respective intermediate combined values, and to combine the intermediate combined values in a manner that compensates for correlated impairment in the composite signal to estimate information in the transmitted spread spectrum signal,

wherein said multistage combiner comprises;

a first combiner responsive to said correlation unit and operative to combine a first group of the correlations to produce a first combined value;

a second combiner responsive to said correlation unit and operative to combine a second group of the correlations to produce a second combined value; and

a third combiner responsive to said first combiner and to said second combiner and operative to combine the first and second combined values in a manner that compensates for correlated impairment in the composite signal to generate an estimate information in the transmitted spread spectrum signal, wherein said third combiner is operative to combine the first and second combined values based on an estimated impairment correlation and on a composite channel response that reflects effects of said first and second combiners.

20. An apparatus according to claim 19:

wherein said first combiner is operative to combine the first group of correlations in a manner that compensates for effect of a channel over which the spread spectrum signal is received; and

wherein said second combiner is operative to combine the second group of correlations in a manner that compensates for effect of a channel over which the spread spectrum signal is received.

21. An apparatus according to claim 20:

wherein said first combiner is operative to combine the first group of correlations according to estimated channel coefficients; and

wherein said second combiner is operative to combine the second group of correlations according to estimated channel coefficients.

22. An apparatus according to claim 21, further comprising a channel estimator operative to generate the channel coefficient estimates.

23. An apparatus according to claim 22, wherein said channel estimator is operative to generate the channel coefficient estimates from at least one of a pilot channel, a pilot symbol or a decoded symbol.

24. An apparatus according to claim 19, further comprising:

a composite channel response estimator operative to estimate the composite channel response;

an impairment correlation estimator operative to estimate the impairment correlation; and

a weighting factor estimator responsive to said composite channel response estimator and to said impairment correlation estimator and operative to generate weighting factors from the estimated composite channel response and the estimated impairment correlation; and

wherein said third combiner is operative to combine the first and second combined values according to the generated weighting factors.

25. An apparatus according to claim 24, wherein said weighting factor estimator is operative to iteratively generate weighting factors from the estimated composite channel response, the estimated impairment correlation, and previously determined weighting factors.

26. An apparatus according to claim 19, wherein said third combiner is operative to combine the first and second values according to weighting factors to generate a third combined value, and further comprising an adaptive weighting factor estimator operative to adaptively estimate weighting factors based on comparison of the third combined value to a reference value.

27. An apparatus according to claim 19, wherein said correlation unit comprises at least one of a plurality of integrate and dump correlators, a sliding correlator, or a selectively inhibited sliding correlator.

28. An apparatus according to claim 19, wherein said correlation unit is operative to correlate the composite signal with the spreading sequence using a set of time delays that optimizes a metric that is proportional to a product of the weighting factors and the composite channel response.

29. An apparatus for recovering information encoded in a spread spectrum signal transmitted in a communications medium, the apparatus comprising:

means for receiving a composite signal including a spread spectrum signal from the communications medium;

means, responsive to said means for receiving, for correlating the composite signal with a spreading sequence to generate time-offset correlations;

means, responsive to said means for correlating, for combining a first group of the correlations to produce a first combined value;

means, responsive to said means for correlating, for combining a second group of the correlations to produce a second combined value; and

means, responsive to said means for combining a first group and to said means for combining a second group, for combining the first and second combined values in a manner that compensates for correlated impairment in the composite signal to generate an estimate information in the transmitted spread spectrum signal,

wherein said means for combining the first and second combined values comprises means for combining the first and second values based on an estimated impairment correlation and on a composite channel response that reflects said means for combining the first group correlations and said means for combining the second group of correlations.

30. An apparatus according to claim 29, further comprising:

means for estimating the composite channel response;

means for estimating the impairment correlation; and

means for generating weighting factors from the estimated composite channel response and the estimated impairment correlation; and

wherein said means for combining the first and second combined values comprises means for combining the first and second combined values according to the generated weighting factors.

31. An apparatus according to claim 30, wherein said means for generating weighting factors comprises means for iteratively generating weighting factors from the estimated composite channel response, the estimated impairment correlation, and previously determined weighting factors.

32. An apparatus according to claim 29:

wherein said means for combining a first group of the correlations comprises means for combining the first group of correlations in a manner that compensates for effect of a channel over which the spread spectrum signal is received; and

wherein said means for combining a second group of the correlations comprises means for combining the second group of correlations in a manner, that compensates for effect of a channel over which the spread spectrum signal is received.

33. An apparatus according to claim 32:

wherein said means for combining a first group of the correlations comprises means for combining the first group of correlations according to estimated channel coefficients; and

wherein said means for combing a second group of the correlations comprises means for combining the second group of correlations according to estimated channel coefficients.

34. An apparatus according to claim 33, further comprising means for generating the channel coefficient estimates.

35. An apparatus according to claim 34, wherein said means for generating the channel coefficient estimates comprises means for generating the channel coefficient estimates from at least one of a pilot channel, a pilot symbol or a decoded symbol.

36. An apparatus according to claim 29, wherein said means for correlating comprises at least one of a plurality of integrate and dump correlators, a sliding correlator, or a selectively inhibited sliding correlator.

37. An apparatus according to claim 29, wherein said means for correlating comprises means for correlating using a set of time delays that optimizes a metric that is proportional to a product of the weighting factors and the composite channel response.

38. An apparatus for recovering information encoded in a spread spectrum signal transmitted in a communications medium, the apparatus comprising:

means for receiving a composite signal including a spread spectrum signal from the communications medium;

means, responsive to said means for receiving, for correlating the composite signal with a spreading sequence to generate time-offset correlations;

means, responsive to said means for correlating, for combining a first group of the correlations to produce a first combined value;

means, responsive to said means for correlating, for combining a second group of the correlations to produce a second combined value; and

means, responsive to said means for combining a first group and to said means for combining a second group, for combining the first and second combined values in a manner that compensates for correlated impairment in the composite signal to generate an estimate information in the transmitted spread spectrum signal,

wherein said means for combining the first and second combined values comprises means for combining the first and second values according to weighting factors to generate a third combined value, and further comprising means for adaptively estimating weighting factors based on comparison of the third combined value to a reference value.

39. An apparatus for recovering information encoded in a spread spectrum signal transmitted in a communications medium, the apparatus comprising:

means for receiving a composite signal including a spread spectrum signal from the communications medium;

means, responsive to said means for receiving, for correlating the received composite signal with a spreading sequence to generate a plurality of time-offset correlations;

means, responsive to said means for correlating, for combining a first group of the correlations according to a channel estimate to produce a first combined value;

means, responsive to said means for correlating, for combining a second group of the correlations according to a channel estimate to produce a second combined value; and

means, responsive to said means for combining a first group and to said means for combining a second group, for combining the first and second combined values according to weighting factors that compensate for correlated impairment in the composite signal to generate an estimate of information in the transmitted spread spectrum signal,

wherein said means for combining the first and second combined values comprises means for combining the first and second combined values based on an estimated impairment correlation and on a composite channel response that reflects said means for combining the first group of correlations and said means for combining the second group of correlations.

40. An apparatus according to claim 39, further comprising:

means for estimating the composite channel response;

means for estimating the impairment correlation; and

means for generating weighting factors from the estimated composite channel response and the estimated impairment correlation; and

wherein said means for combining the first and second combined values comprises means for combining the first and second combined values according to the generated weighting factors.

41. An apparatus according to claim 40, wherein said means for generating weighting factors comprises means for iteratively generating weighting factors from the estimated composite channel response, the estimated impairment correlation, and previously determined weighting factors.

42. An apparatus according to claim 39, further comprising means for generating the channel estimate.

43. An apparatus according to claim 39, wherein said means for generating a channel estimate comprises means for generating the channel estimate from at least one of a pilot channel, a pilot symbol or a decoded symbol.

44. An apparatus according to claim 43, wherein said means for correlating comprises at least one of a plurality of integrate and dump correlators, a sliding correlator, or a selectively inhibited sliding correlator.

45. An apparatus according to claim 39, wherein said means for correlating comprises means for correlating using a set of time delays that optimizes a metric that is proportional to a product of the weighting factors and the composite channel response.

46. An apparatus for recovering information encoded in a spread spectrum signal transmitted in a communications medium, the apparatus comprising:

means for receiving a composite signal including a spread spectrum signal from the communications medium;

means, responsive to said means for receiving, for correlating the received composite signal with a spreading sequence to generate a plurality of time-offset correlations;

means, responsive to said means for correlating, for combining a first group of the correlations according to a channel estimate to produce a first combined value;

means, responsive to said means for correlating, for combining a second group of the correlations according to a channel estimate to produce a second combined value, and

means, responsive to said means for combining a first group and to said means for combining a second group, for combining the first and second combined values according to weighting factors that compensate for correlated impairment in the composite signal to generate an estimate of information in the transmitted spread spectrum signal,

wherein said means for combining the first and second combined values comprises means for combining the first and second values to generate a third combined value, and further comprising means for adaptively estimating weighting factors based on comparison of the third combined value to a reference value.