Apparatus and methods for reducing channel estimation noise in a wireless transceiver

• US 7,835,460 B2
• Filed: 12/15/2005
• Issued: 11/16/2010
• Est. Priority Date: 10/27/2005
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Wang, Michael Mao
• Primary Examiner(s): Liu; Shuwang
• Assistant Examiner(s): Joseph; Jaison
• Application Number:
  US11/303,485
• Publication Number:
  US 20070098120A1
• Time in Patent Office: 1,797 Days
• Field of Search: 375/260, 375/278, 375/346, 375/349, 369/94
• US Class Current: 375/278
• CPC Class Codes: H04L 25/0216 with estimation of channel length
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

Apparatus and methods for use in a wireless communication system are disclosed for reducing channel estimation noise in a device such as a wireless transceiver. A disclosed apparatus includes a processor that determines a channel activity portion and a noise portion of a channel estimation. The processor also determines a threshold noise level based on channel estimate values in the noise portion of the channel estimation. The processor compares channel estimate energy values in the channel estimation to the threshold noise level and sets each of the channel estimate energy values being less than the threshold noise level to a predetermined value such as zero in order to reduce or eliminate the noise. Similar methods are also disclosed.

Claims

1. A method for reducing noise in channel estimation of a communication signal comprising:

a) determining a channel activity portion and a noise portion of a P-point time-domain channel estimation;

b) determining a noise energy density value ŵ

of channel estimates occurring during the noise portion of the channel estimation by adjusting the noise energy density value by a predetermined constant λ

;

c) comparing energy values of channel estimates for at least a portion of the channel estimation to the noise energy density value; and

d) setting channel estimate values below a threshold to a predetermined value for each channel estimate having an energy value less than the noise energy density value,

wherein ŵ

is determined as;

2. The method as defined in claim 1, further comprising:

comparing energy values of all channel estimates in the channel estimation to the noise energy density value.

3. The method as defined in claim 1, wherein the at least a portion of the channel estimation includes the noise portion of the channel estimation.

4. The method as defined in claim 1, wherein the predetermined constant λ

is set to account for over estimation of the determined noise energy density value ŵ

resulting from overlap between the channel activity portion of the channel estimation and the noise portion of the channel estimation.

5. The method as defined in claim 1, wherein the predetermined value is zero.

6. The method as defined in claim 1, wherein determining the noise energy density value of channel estimates occurring during the noise portion of the channel estimation further includes utilizing channel estimates occurring in at least the noise portion of at least one previous channel estimation.

7. The method as defined in claim 1, further comprising:

setting channel estimate values to the channel estimate value for each channel estimate having an energy density value greater than the noise energy density value.

8. The method as defined in claim 1, wherein the method is used for reducing noise of channel estimations for orthogonal frequency division multiplexed signals.

9. A method for reducing noise in a communications channel estimation comprising:

a) determining a channel activity portion and a noise portion of a P-point time-domain channel estimation;

b) determining a threshold noise level based on channel estimate values in the noise portion of the channel estimation;

c) comparing at least a portion of channel estimate values in the channel estimation to the threshold noise level;

d) setting each of the at least a portion of channel estimate energy values being less than the threshold noise level to a predetermined value.;

wherein determining the noise threshold value includes determining noise energy density value ŵ

of channel estimates occurring during the noise portion of the channel estimation,

wherein ŵ

is determined as;

10. The method as defined in claim 9, further comprising:

comparing energy values of all channel estimates in the channel estimation to the threshold noise level.

11. The method as defined in claim 9, wherein the at least a portion of the channel estimation includes the noise portion of the channel estimation.

12. The method as defined in claim 9, wherein the energy density value of channel estimates occurring during the noise portion of the channel estimation further . includes adjusting the noise energy density value by a predetermined constant λ

.

13. The method as defined in claim 12, wherein the predetermined constant λ

is set to account for over estimation of the determined noise energy density value resulting from overlap between the channel activity portion of the channel estimation and the noise portion of the channel estimation.

14. The method as defined in claim 9, wherein the predetermined value is zero.

15. The method as defined in claim 9, wherein determining the noise threshold value based on channel estimates occurring during the noise portion of the channel estimation further includes utilizing channel estimates occurring in at least the noise portion of at least one previous channel estimation.

16. The method as defined in claim 9, further comprising:

setting channel estimate values to the channel estimate value for each channel estimate having an energy greater than the noise threshold level.

17. The method as defined in claim 9, wherein the method is used for reducing noise of channel estimations for orthogonal frequency division multiplexed signals.

18. A non-transitory computer readable medium having instructions stored thereon, the stored instructions, when executed by a processor, cause the processor to perform a method to reduce noise in a communications channel estimation, the method comprising:

a) determining a channel activity portion and a noise portion of a P-point time-domain channel estimation;

b) determining a noise energy density value of channel estimates occurring during the noise portion of the channel estimation by adjusting the noise energy density value by a predetermined constant λ

;

c) comparing energy values of channel estimates for at least a portion of the channel estimation to the noise energy density value; and

d) setting channel estimate values below a threshold to a predetermined value for each channel estimate having an energy value less than the noise energy density value,

wherein ŵ

is determined as;

19. The computer readable medium as defined in claim 18, wherein the method further includes comparing energy values of all channel estimates in the channel estimation to the noise energy density value.

20. The computer readable medium as defined in claim 18, wherein the method further includes the at least a portion of the channel estimation including the noise portion of the channel estimation.

21. The computer readable medium as defined in claim 18, wherein the predetermined constant λ

is set to account for over estimation of the determined noise energy density value resulting from overlap between the channel activity portion of the channel estimation and the noise portion of the channel estimation.

22. The computer readable medium as defined in claim 18, wherein the predetermined value is zero.

23. The computer readable medium as defined in claim 18, wherein determining the noise energy density value of channel estimates occurring during the noise portion of the channel estimation further includes utilizing channel estimates occurring in at least the noise portion of at least one previous channel estimation.

24. The computer readable medium as defined in claim 18, wherein the method further includes setting channel estimate values to the channel estimate value for each channel estimate having an energy density value greater than the noise energy density value.

25. The computer readable medium as defined in claim 18, wherein the computer readable medium is used in a transceiver for reducing noise of channel estimations for orthogonal frequency division multiplexed signals.

26. A non-transitory computer readable medium having instructions stored thereon, the stored instructions, when executed by a processor, cause the processor to perform a method to reduce noise in a communications channel estimation, the method comprising:

determining a channel activity portion and a noise portion of a P-point time-domain channel estimation;

determining a threshold noise level based on channel estimate values in the noise portion of the channel estimation;

comparing at least a portion of channel estimate values in the channel estimation to the threshold noise level; and

setting each of the at least a portion of channel estimate energy values being less than the threshold noise level to a predetermined value;

wherein determining the noise threshold value includes determining noise energy density value ŵ

of channel estimates occurring during the noise portion of the channel estimation,

wherein ŵ

is determined as;

27. The computer readable medium as defined in claim 26, wherein the method further includes comparing energy values of all channel estimates in the channel estimation to the threshold noise level.

28. The computer readable medium as defined in claim 26, wherein the at least a portion of the channel estimation includes the noise portion of the channel estimation.

29. The computer readable medium as defined in claim 28, wherein determining the noise threshold value includes determining a noise energy density value of channel estimates occurring during the noise portion of the channel estimation.

30. The computer readable medium as defined in claim 29, wherein the energy density value of channel estimates occurring during the noise portion of the channel estimation further includes adjusting the noise energy density value by a predetermined constant λ

.

31. The computer readable medium as defined in claim 26, wherein the predetermined constant λ

is set to account for over estimation of the determined noise energy density value resulting from overlap between the channel activity portion of the channel estimation and the noise portion of the channel estimation.

32. The computer readable medium as defined in claim 26, wherein the predetermined value is zero.

33. The computer readable medium as defined in claim 26, wherein determining the noise threshold value based on channel estimates occurring during the noise portion of the channel estimation further includes utilizing channel estimates occurring in at least the noise portion of at least one previous channel estimation.

34. The computer readable medium as defined in claim 26, further comprising:

setting channel estimate values to the channel estimate value for each channel estimate having an energy greater than the noise threshold level.

35. The computer readable medium as defined in claim 26, wherein the computer readable medium is used in a transceiver for reducing noise of channel estimations for orthogonal frequency division multiplexed signals.

36. A transceiver apparatus configured to reduce noise in a channel estimation comprising:

a channel estimator processor configured to;

determine a channel activity portion and a noise portion of a P-point time-domain channel estimation;

determine a noise energy density value ŵ

of channel estimates occurring during the noise portion of the channel estimation and adjusting the noise energy density value by a predetermined constant λ

;

compare energy values of channel estimates for at least a portion of the channel estimation to the noise energy density value; and

set channel estimate values below a threshold to a predetermined value for each channel estimate having an energy value less than the noise energy density value,

wherein ŵ

is determined as;

37. The transceiver as defined in claim 36, wherein the processor is further configured to compare energy values of all channel estimates in the channel estimation to the noise energy density value.

38. The transceiver as defined in claim 36, wherein the at least a portion of the channel estimation includes the noise portion of the channel estimation.

39. The transceiver as defined in claim 36, wherein the processor is configured to adjust the noise energy density value by a predetermined constant λ

to determine the noise energy density value of channel estimates occurring during the noise portion of the channel estimation.

40. The transceiver as defined in claim 39, wherein the processor is further configured to set the predetermined constant λ

to account for over estimation of the determined noise energy density value resulting from overlap between the channel activity portion of the channel estimation and the noise portion of the channel estimation.

41. The transceiver as defined in claim 36, wherein the predetermined value is zero.

42. The transceiver as defined in claim 36, wherein the processor is further configured to use channel estimates occurring in at least the noise portion of at least one previous channel estimation to determine the noise energy density value of channel estimates occurring during the noise portion of the channel estimation further includes.

43. The transceiver as defined in claim 36, wherein the processor is further configured to set channel estimate values to the channel estimate value for each channel estimate having an energy density value greater than the noise energy density value.

44. The transceiver as defined in claim 36, wherein the transceiver is configured to receive orthogonal frequency division multiplexed signals.

52. The transceiver as defined in claim 36, wherein the transceiver is configured to receive orthogonal frequency division multiplexed signals.

45. A transceiver apparatus configured to reduce noise in a channel estimation comprising:

a channel estimator processor configured to;

determine a channel activity portion and a noise portion of a P-point time-domain channel estimation;

determine a threshold noise level based on channel estimate values in the noise portion of the channel estimation;

compare at least a portion of channel estimate values in the channel estimation to the threshold noise level;

set each of the at least a portion of channel estimate energy values being less than the threshold noise level to a predetermined value;

wherein the processor is further configured to determine a noise energy density value ŵ

of channel estimates occurring during the noise portion of the channel estimation to determine the threshold value, and further configured to adjust the noise energy density value ŵ

by a predetermined constant λ

to determine the energy density value of channel estimates occurring during the noise portion of the channel estimation,

wherein ŵ

is detetinined as;

46. The transceiver as defined in claim 45, wherein the processor is further configured to compare energy values of all channel estimates in the channel estimation to the threshold noise level.

47. The transceiver as defined in claim 45, wherein the at least a portion of the channel estimation includes the noise portion of the channel estimation.

48. The transceiver as defined in claim 45, wherein the processor is configured to set the predetermined constant λ

to account for over estimation of the determined noise energy density value ŵ

resulting from overlap between the channel activity portion of the channel estimation and the noise portion of the channel estimation.

49. The transceiver as defined in claim 45, wherein the predetermined value is zero.

50. The transceiver as defined in claim 45, wherein the processor is further configured to use channel estimates occurring in at least the noise portion of at least one previous channel estimation in order to determine the noise threshold value based on channel estimates occurring during the noise portion of the channel estimation.

51. The transceiver as defined in claim 45, wherein the processor is further configured to set channel estimate values to the channel estimate value for each channel estimate having an energy greater than the noise threshold level.

53. An apparatus for resolving timing in a wireless communication device comprising:

means for determining a channel activity portion and a noise portion of a P-point time-domain channel estimate;

means for determining a noise energy density ê

of the channel estimate occurring during the noise portion of the channel estimate by adjusting the noise energy density value by a predetermined constant λ

;

means for determining whether the energy of at least a portion of kth channel estimates are less than the value of the noise energy density; and

means for setting the channel estimate to zero when the energy of a channel estimate is less than the value of the noise energy density,

wherein ŵ

is determined as;

54. The apparatus as defined in claim 53, further comprising:

means for setting the channel estimate equal to the actual channel estimate when the energy of a channel estimate is greater than the value of the noise energy density.