Frequency domain filtering to improve channel estimation in multicarrier systems

• US 7,616,711 B2
• Filed: 12/22/2004
• Issued: 11/10/2009
• Est. Priority Date: 07/20/2004
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Gore, Dhananjay Ashok, Gorokhov, Alexei, Agrawal, Avneesh, Khandekar, Aamod
• Primary Examiner(s): Corrielus; Jean B
• Application Number:
  US11/022,360
• Publication Number:
  US 20060018393A1
• Time in Patent Office: 1,784 Days
• Field of Search: 375/224, 375/227, 375/285, 375/296, 375/340, 375/346, 375/348, 375/350, 370/241, 370/252, 370/491, 370/500
• US Class Current: 375/340
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 25/023 with extension to other symbols
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/006 Quality of the received signal, e.g. BER, SNR, water filling

Abstract

A channel estimation system comprises a filtering component that selectively scales a plurality of carriers as a function of location of the plurality of carriers within a frequency band, wherein the plurality of carriers comprises at least one data carrier and at least one pilot carrier. A component thereafter extrapolates an observation from the at least one pilot carrier, wherein a channel is estimated as a function of the extrapolated observation. The scaling of the carriers facilitates reducing a flooring effect associated with channel estimation. The filtering component can be employed at a transmitter and/or at a receiver, and can be activated and/or deactivated as a function of a sensed data packet type.

Claims

1. A method for reducing channel estimation error in a wireless communications environment, comprising:

selectively scaling a data carrier and a pilot carrier of a communication device within a frequency band, the data carrier and pilot carrier scaled as a function of a location, determined based on a data type, within the band of the data carrier and pilot carrier so that the data carrier and the pilot carrier have less power when they are proximate to an edge of the band than when they are proximate to a center of the band;

obtaining an observation relating to the scaled pilot carrier; and

estimating a channel as a function of the obtained observation.

2. The method of claim 1, further comprising performing a linear transformation upon the obtained observation.

3. The method of claim 1, further comprising performing an IFFT operation on the obtained observation.

4. The method of claim 3, further comprising performing an FFT operation upon results of the IFFT operation.

5. The method of claim 1, wherein the step of selectively scaling further comprises multiplying the pilot carrier and the data carrier by values that are selected as a function of locations of the pilot carrier and data carrier.

6. The method of claim 1, wherein the step of selectively scaling further comprises

providing a greater weight to one or more of a pilot carrier and a data carrier proximate to a center of the band than a weight provided to one or more of a pilot carrier and data carrier proximate to an edge of the band.

7. The method of claim 6, further comprising assuming that an observation relating to a pilot carrier within a guardband is zero.

8. The method of claim 1, further comprising activating the step of selectively scaling the data carrier and the pilot carrier upon detection of a first packet type.

9. The method of claim 8, wherein the first packet type is a 64 QAM data packet.

10. The method of claim 8, further comprising deactivating the step of selectively scaling the data carrier and the pilot carrier upon detection of a second packet type.

11. The method of claim 10, wherein the second packet type is a 16 QAM data packet.

12. The method of claim 1, wherein the step of selectively scaling further comprises positioning the plurality of pilot carriers equidistantly throughout the frequency band.

13. The method of claim 1, wherein the step of selectively scaling further comprises:

defining a number of the plurality of pilot carriers to be a power of 2.

14. The method of claim 1, wherein the step of selectively scaling further comprises scaling the data carrier and the pilot carrier in the frequency domain at a receiver.

15. The method of claim 14, wherein the receiver is part of a mobile unit.

16. The method of claim 1, wherein the step of selectively scaling further comprises scaling the data carrier and the pilot carrier in the frequency domain at a transmitter.

17. The method of claim 16, further comprising employing a raised-cosine filter to selectively scale the data carrier and the pilot carrier in the frequency domain at the transmitter.

18. The method of claim 1, wherein the step of selectively scaling further comprises:

performing an N_p point Inverse Fast Fourier Transform on observations obtained from the plurality of pilot carriers, where N_p is a number of the plurality of pilot carriers.

19. The method of claim 1, wherein the step of selectively scaling further comprises:

estimating the plurality of pilot carriers in time.

20. The method of claim 1, further comprising:

determining that the pilot carrier resides within a guardband; and

assigning a value to the observation relating to the pilot carrier.

21. The method of claim 20, wherein the step of assigning a value further comprises assigning a value of zero.

22. The method of claim 1, wherein the wireless communications environment is an OFDM, OFDMA, CDMA, TDMA, or GSM environment.

23. The method of claim 1. further comprising:

extrapolating the observation from the scaled pilot carrier when the scaled pilot carrier resides within a guard band; and

assigning a value to the extrapolated observation.

24. A channel estimation system, comprising:

a filtering component;

an extrapolating component;

at least one memory; and

at least one processor configured to execute instructions stored in the at least one memory, the executed instructions for controlling the filtering component such that the filtering component selectively scales a plurality of carriers as a function of location, based on a data type, of the plurality of carriers within a frequency band, the plurality of carriers comprising at least one data carrier and at least one pilot carrier,

wherein the extrapolating component extrapolates an observation from the at least one pilot carrier and estimates a channel as a function of the extrapolated observation, and

wherein the plurality of carriers are scaled so that carriers proximate to an edge of the band have less power than carriers proximate to a center of the band.

25. The system of claim 24, wherein the filtering component is configured to facilitate reducing a flooring effect associated with channel estimation.

26. The system of claim 24, wherein the at least one pilot carrier comprises a plurality of pilot carriers, and the pilot carriers (N_p) are scaled to a power of two.

27. The system of claim 26, further comprising a component that is configured to perform an N_p point Inverse Fast Fourier Transform upon N_p observations obtained from the Np pilot carriers to facilitate obtaining a full frequency domain channel.

28. The system of claim 27, further comprising a component that is configured to perform an N_p point Fast Fourier Transform to facilitate obtaining a full frequency domain channel.

29. The system of claim 26, wherein the plurality of pilot carriers is staggered in time.

30. The system of claim 26, wherein the plurality of pilot carriers are equi-spaced.

31. The system of claim 26, wherein the filtering component is configured to provide a greater weight to a carrier proximate to a center of the frequency band when compared to a weight provided to a carrier proximate to an edge of the frequency band.

32. The system of claim 24, wherein the filtering component is part of a receiver.

33. The system of claim 24, wherein the filtering component is part of a transmitter.

34. The system of claim 24, wherein at least one pilot carrier lies within a guardband, and an observation relating to the at least one pilot carrier that lies within the guardband is pre-defined.

35. The system of claim 34, wherein the observation relating to the at least one pilot carrier that lies within the guardband is pre-defined to be zero.

36. The system of claim 24, wherein the carriers exist within an OFDM system.

37. The system of claim 24, further comprising a trigger component that activates the filtering component upon receipt of a data packet modulated by way of 64 QAM.

38. The system of claim 24, wherein the filtering component is configured to operate exclusively in the frequency domain.

39. The system of claim 24, further comprising an analysis component configured to obtain scaled observations relating to a plurality of pilot symbols carried on a plurality of selectively scaled carriers.

40. The system of claim 24, wherein the filtering component comprises a pulse-shaping component that facilitates scaling of the at least one data carrier and the at least one pilot carrier, the pulse-shaping component existent within a transmitter.

41. The system of claim 40, wherein the pulse-shaping component employs a raised cosine filter to facilitate scaling of the at least one data carrier and the at least one pilot carrier.

42. The system of claim 24, further comprising a triggering component that activates the filtering component upon analyzing a data packet type.

43. The system of claim 24, wherein the extrapolating component extrapolates a pilot carrier from the plurality of carriers if the pilot carrier falls within a guardband and assigns a value to observations obtained from the pilot carrier.

44. The system of claim 24, further comprising an artificial intelligence component that analyzes contextual data and makes inferences regarding whether the filtering component should be activated as a function of the analysis.

45. The system of claim 24, wherein the filtering component is deactivated with respect to one or more pilot carriers proximate to a band edge.

46. A system that facilitates estimating a channel, comprising:

a component within a transmitter that receives a plurality of carriers within a band;

a pulse shaping component;

at least one memory; and

at least one processor configured to execute instructions stored in the at least one memory, the executed instructions for controlling the pulse shaping component such that the pulse shaping component facilitates shaping the plurality of carriers within the band in the frequency domain by providing power to the plurality of carriers as a function of position, based on a data type, of each of the carriers within the band in order to estimate the channel,

wherein the plurality of carriers are shaped so that carriers proximate to an edge of the band have less power than carriers proximate to a center of the band.

47. The system of claim 46, wherein the plurality of carriers comprises a plurality of pilot carriers and a plurality of data carriers.

48. The system of claim 46, wherein the pulse shaping component is configured to utilize a raised cosine filter in connection with shaping the plurality of carriers within the band.

49. The system of claim 46, wherein the plurality of carriers comprises a plurality of pilot carriers, and a number of pilot carriers (N_p) are scaled to a power of 2.

50. The system of claim 49, further comprising an IFFT component that performs an N_p point Inverse Fast Fourier Transform upon observations obtained from the N_p pilot carriers.

51. The system of claim 50, wherein the IFFT component resides within a receiver.

52. The system of claim 50, further comprising a FFT component that performs an N_p point Fast Fourier Transform upon outputs of the Inverse Fast Fourier Transform.

53. The system of claim 46, wherein the pulse shaping component provides greater power to carriers proximate to a center region of the band when compared to power provided to carriers proximate to an edge of the band.

54. The system of claim 46, wherein the transmitter is configured to transmit signals using an OFDM, OFDMA, CDMA, TDMA, or GSM protocol.

55. A system that improves channel estimation with respect to flooring, comprising:

at least one memory; and

at least one processor configured to execute instructions stored in the at least one memory, the executed instructions controlling;

means for selectively scaling one or more carriers within a communications band in a frequency domain as a function of a position, based on a data type, of the one or more carriers within the communications band, the one or more carriers comprising a pilot carrier;

means for extracting an observation from the pilot carrier; and

means for determining a channel estimate as a function of the extracted observation,

wherein the pilot carrier is scaled to have less power when the pilot carrier is proximate to an edge of the band than when the pilot carrier is proximate to a center of the band.

56. The system of claim 55, wherein the:

means for extracting extracts a plurality of observations from a plurality of selectively scaled pilot carriers within the communications band.

57. The system of claim 56, wherein the executed instructions further control means for uniformly-spacing the plurality of pilot carriers with respect to frequency within the communications band.

58. The system of claim 56, wherein the executed instructions further control means for estimating the plurality of pilot carriers in time.

59. The system of claim 56, wherein the means for selectively scaling one or more carriers is included in a receiver.

60. The system of claim 59, wherein the executed instructions further control means for multiplying the plurality of pilot carriers by values chosen according to position of the pilot carriers within the band.

61. The system of claim 56, wherein the means for selectively scaling one or more carriers is included in a transmitter.

62. The system of claim 61, wherein the executed instructions further control means for utilizing a raised cosine filter to selectively scale the pilot carriers.

63. The system of claim 56, wherein the executed instructions further control means for linearly transforming the extracted observations.

64. The system of claim 56, wherein the executed instructions further control:

means for performing an Inverse Fast Fourier Transform upon the extracted observations; and

means for generating a corresponding output.

65. The system of claim 64, wherein the executed instructions further control means for performing a Fast Fourier Transform upon the output.

66. The system of claim 56, wherein the executed instructions further control:

means for determining that a subset of the plurality of pilot carriers exist within a guardband; and

means for assigning a value to a subset of observations that correspond to the subset of pilot carriers.

67. The system of claim 66, wherein the executed instructions further control means for assigning a value of zero to the subset of observations.

68. The system of claim 56, wherein the executed instructions further control means for more highly weighting a carrier proximate to a center of the band than a carrier proximate to an edge of the band.

69. The system of claim 55, wherein the executed instructions further control:

means for detecting a data packet type associated with the extracted observation; and

means for determining whether to selectively scale the one or more carriers as a function of the detected data packet type.

70. The system of claim 69, wherein the detected data packet type is a 64 QAM data packet type.

71. An apparatus comprising:

a processor; and

a computer-readable medium having code for estimating a channel, the code comprising instructions for;

scaling a plurality of carriers in a frequency domain as a function of location, determined based on a data type, of each of the plurality of carriers within a band, the plurality of carriers comprises a pilot carrier and a data carrier;

determining locations of the pilot carrier within the band; and

extrapolating an observation from the pilot carrier used to estimate a channel,

wherein the data carrier and the pilot carrier are scaled to have less power when they are proximate to an edge of the band than when they are proximate to a center of the band, and the processor is configured to execute the instructions.

72. The apparatus of claim 71, the instructions further comprising:

determining that the pilot carrier exists within a guardband; and

assigning a pre-defined value to the observation.

73. The apparatus of claim 72, the instructions further comprising assigning a value of zero to the observation corresponding to the pilot carrier.

74. The apparatus of claim 71, the instructions further comprising estimating a channel as a function of the extracted observation.

75. The apparatus of claim 71, further comprising:

a receiver, wherein the processor comprises a portion of the receiver.

76. An apparatus for facilitating a channel estimate in a wireless communication system, the apparatus comprising:

at least one memory; and

a microprocessor configured to execute instructions stored in the at least one memory for generating a channel estimate, the instructions comprising the steps of;

selectively weighting carriers in a frequency domain as a function of position, determined based on a data type, of the respective carriers within a frequency band, the carriers comprising a pilot carrier, the pilot carrier being weighted to have less power when the pilot carrier is proximate to an edge of the band than when the pilot carrier is proximate to a center of the band;

extracting an observation from the pilot carrier; and

linearly transforming the observation to facilitate estimating a channel.