Apparatus and method for measuring signal quality of a wireless communications link

• US 7,016,651 B1
• Filed: 12/17/2002
• Issued: 03/21/2006
• Est. Priority Date: 12/17/2002
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Narasimhan, Ravi
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): Gantt, Alan T.
• Application Number:
  US10/322,130
• Time in Patent Office: 1,190 Days
• Field of Search: 455/67.1, 455/127.1, 455/226.1, 455/226.2, 455/226.3, 455/226.4, 455/423, 375/347, 375/261, 370/210
• US Class Current: 455/67.11
• CPC Class Codes: H04L 1/0001 Systems modifying transmission characteristics according to link quality, e.g. power backoff adaptive data allocation for multicarrier modulation H04L5/0044; controlling transmission power for radio systems H04W52/04
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 25/067 providing soft decisions, i.e. decisions together with an estimate of reliability H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

Techniques for measuring signal quality in a communications link supporting OFDM symbol transfer across plural sub-carriers are disclosed. These techniques employ a link interface receiving OFDM symbol(s) from the link, and a signal-to-noise ratio (SNR) estimation unit generating an estimate of a geometric SNR (SNR_geo) for the received symbols based on an average of the logrithmic difference between soft decision and hard decisions for the received symbol. SNR_geo here defines a scalar measure of the link signal quality, which results in a computationally efficient yet accurate link signal quality assessment, and thereby permit selective link characteristic alteration. Only sub-carrier subsets need be used to derive a relatively an accurate SNR_geo estimate. Sharing calculation resources between SNR estimation and soft decision units further reduce implementation complexity. Hard decision generation may use a relatively quick slicer or more accurate viterbi decoder/OFDM re-coder combination, as design goals dictate.

Claims

1. An apparatus for measuring signal quality in a communications link, the communications link capable of supporting transfer of OFDM symbols modulating data across a plurality of sub-carriers, the apparatus comprising:

a link interface to receive an OFDM symbol from the communications link; and

a signal-to-noise ratio estimation unit to generate an estimate of a geometric signal-to-noise ratio for the OFDM symbol based on an average of a logarithmic difference between a soft decision and a hard decision for the OFDM symbol, the geometric signal-to-noise ratio estimate defining a scalar value of the communications link signal quality.

2. The apparatus of claim 1, wherein

the soft decision defines soft decision information for each of the plurality of sub-carriers;

wherein the hard decision defines hard decision information for each of the plurality of sub-carriers; and

wherein said signal-to-noise ratio estimation unit comprises;

a sub-carrier selection unit to select a subset of the plurality of sub-carriers for the OFDM symbol; and

an estimate calculator to generate the geometric signal-to-noise ratio estimate using soft and hard decision information for the subset of the plurality of sub-carriers selected by said sub-carrier selection unit as the soft and hard decision respectively.

3. The apparatus of claim 2, wherein the subset of the plurality of sub-carriers are regularly spaced within a sub-carrier constellation defined by the plurality of sub-carriers.

4. The apparatus of claim 3, wherein the sub-carrier selection unit selects first and second subsets of the plurality of sub-carriers for first and second symbols respectively, the first and second symbols successively transferred across the communications link, the first and second subsets being at least partially distinct.

5. The apparatus of claim 1, wherein

the communications link comprises a wireless communications link;

and

wherein the OFDM symbol is formatted in compliance with at least one of IEEE 802.11a and IEEE 802.11g standards.

6. The apparatus of claim 1, wherein

the hard decision is provided by a slicer communicatively coupled to said link interface and said signal-to-noise estimation unit;

and

wherein the soft decision is provided by a demodulation/FEQ unit communicatively coupled to said link interface and said signal-to-noise estimation unit.

7. The apparatus of claim 1, wherein

the hard decision is provided by a Viterbi decoder and symbol re-coder communicatively coupled to said link interface and said signal-to-noise estimation unit;

and

wherein the soft decision is provided by a demodulation/FEQ unit communicatively coupled to said link interface and said signal-to-noise estimation unit.

8. A baseband processor capable of processing a baseband signal borne across a communications link, comprising:

an FFT unit to recover a received symbol from the baseband signal, the received symbol modulating data across a plurality of sub-carriers;

a soft decision unit responsive to said FFT unit to recover a soft decision of a transmitted symbol corresponding to the received symbol;

a hard decision unit responsive to said soft decision unit to recover a hard decision of the transmitted symbol based on the soft decision; and

a signal-to-noise ratio estimation unit to generate an estimate of a geometric signal-to-noise ratio for the received symbol based on an average of a logarithmic difference between the soft and hard decisions, the geometric signal-to-noise ratio estimate defining a scalar measure of signal quality for the communications link.

9. The baseband processor of claim 8, further comprising a channel estimator responsive to said FFT unit to provide a plurality of channel estimates for the received symbol corresponding to the plurality of sub-carriers;

and

wherein said soft decision unit responds to said channel estimator to recover the soft decision using the plurality of channel estimates.

10. The baseband processor of claim 8, wherein

the soft decision defines soft decision information for each of the plurality of sub-carriers;

wherein the hard decision defines hard decision information for each of the plurality of sub-carriers; and

wherein said signal-to-noise ratio estimation unit comprises;

a sub-carrier selection unit to select a subset of the plurality of sub-carriers for the received symbol; and

an estimate calculator to generate the geometric signal-to-noise ratio estimate using soft and hard decision information for the subset of the plurality of sub-carriers selected by said sub-carrier selection unit, as the soft and hard decision respectively.

11. The baseband processor of claim 10, wherein said estimate calculator and said soft decision unit share common calculation circuitry.

12. The baseband processor of claim 10, wherein the subset of the plurality of sub-carriers are regularly spaced within a sub-carrier constellation defined by the plurality of sub-carriers.

13. The baseband processor of claim 12, wherein

said FFT unit successively recovers first and second received symbols from the baseband signal, each of the first and second received symbols modulating data across the plurality of sub-carriers;

and

wherein said sub-carrier selection unit selects first and second subsets of the plurality of sub-carriers, the first and second subsets being at least partially distinct.

14. The baseband processor of claim 8, wherein

the communications link comprises a wireless communications link;

and

wherein the received symbol comprises an OFDM symbol compliant with at least one of IEEE 802.11a and IEEE 802.11g standards.

15. The baseband processor of claim 8, wherein:

said soft decision unit comprises a demodulation/FEQ unit; and

wherein said hard decision unit comprises one of a slicer and a combination of a Viterbi decoder and a symbol re-coder.

16. A transceiver, comprising:

a receiver capable of receiving a baseband signal borne across a wireless communications link; and

a baseband processor responsive to said receiver and comprising;

an FFT unit to recover a received symbol from the baseband signal, the received symbol modulating data across a plurality of sub-carriers;

a soft decision unit responsive to said FFT unit to recover a soft decision of a transmitted symbol corresponding to the received symbol;

a hard decision unit responsive to said soft decision unit to recover a hard decision of the transmitted symbol based on the soft decision; and

a signal-to-noise ratio estimation unit to generate an estimate of a geometric signal-to-noise ratio for the received symbol based on an average of a logarithmic difference between the soft and hard decisions, the geometric signal-to-noise ratio estimate defining a scalar measure of signal quality for the communications link.

17. The transceiver of claim 16, further comprising a channel estimator responsive to said FFT unit to provide a plurality of channel estimates for the received symbol corresponding to the plurality of sub-carriers;

and

wherein said soft decision unit responds to said channel estimator to recover the soft decision using the plurality of channel estimates.

18. The transceiver of claim 16, wherein

the soft decision defines soft decision information for each of the plurality of sub-carriers;

wherein the hard decision defines hard decision information for each of the plurality of sub-carriers; and

wherein said signal-to-noise ratio estimation unit comprises;

a sub-carrier selection unit to select a subset of the plurality of sub-carriers for the at least one symbol; and

an estimate calculator to generate the geometric signal-to-noise ratio estimate using soft and hard decision information for the subset of the plurality of sub-carriers selected by said sub-carrier selection unit as the soft and hard decision respectively.

19. The transceiver of claim 18, wherein said estimate calculator and said soft decision unit share common calculation circuitry.

20. The transceiver of claim 18, wherein the subset of the plurality of sub-carriers are regularly spaced within a sub-carrier constellation defined by the plurality of sub-carriers.

21. The transceiver of claim 20, wherein

said FFT unit successively recovers first and second received symbols from the baseband signal, each of the first and second received symbols modulating data across the plurality of sub-carriers;

and

wherein said sub-carrier selection unit selects first and second subsets of the plurality of sub-carriers, the first and second subsets being at least partially distinct.

22. The transceiver of claim 16, wherein the received symbol comprises an OFDM symbol compliant with at least one of IEEE 802.11a and IEEE 802.11g standards.

23. The transceiver of claim 16, wherein:

said soft decision unit comprises a demodulation/FEQ unit; and

wherein said hard decision unit comprises one of a slicer and a combination of a Viterbi decoder and a symbol re-coder.

24. The transceiver of claim 16, further comprising a control unit responsive to said signal-to-noise estimation unit to selectively alter a characteristic of the communications link based on the geometric signal-to-noise ratio estimate generated by said signal-to-noise estimation unit.

25. A network interface apparatus, comprising:

a transceiver, comprising;

a receiver capable of receiving a baseband signal borne across a wireless communications link; and

a baseband processor responsive to said receiver and comprising;

an FFT unit to recover a received symbol from the baseband signal, the received symbol modulating data across a plurality of sub-carriers;

a soft decision unit responsive to said FFT unit to recover a soft decision of a transmitted symbol corresponding to the received symbol;

a hard decision unit responsive to said soft decision unit to recover a hard decision of the transmitted symbol based on the soft decision;

a signal-to-noise ratio estimation unit to generate an estimate of a geometric signal-to-noise ratio for the received symbol based on an average of a logarithmic difference between the soft and hard decisions, the geometric signal-to-noise ratio estimate defining a scalar measure of signal quality for the communications link; and

a decoder responsive to said soft decision unit to recover data corresponding to the soft decision; and

a network interface responsive to said decoder to receive the data, said network interface including a control unit responsive to said signal-to-noise estimation unit to selectively alter a characteristic of the communications link based on the geometric signal-to-noise ratio estimate generated by said signal-to-noise estimation unit.

26. An information processing apparatus, comprising:

an information processor;

a transceiver responsive to said information processor and comprising;

a receiver capable of receiving a baseband signal borne across a wireless communications link; and

a baseband processor responsive to said receiver and comprising;

an FFT unit to recover a received symbol from the baseband signal, the received symbol modulating data across a plurality of sub-carriers;

a soft decision unit responsive to said FFT unit to recover a soft decision of a transmitted symbol corresponding to the received symbol;

a hard decision unit responsive to said soft decision unit to recover a hard decision of the transmitted symbol based on the soft decision;

a signal-to-noise ratio estimation unit to generate an estimate of a geometric signal-to-noise ratio for the received symbol based on an average of a logarithmic difference between the soft and hard decisions, the geometric signal-to-noise ratio estimate defining a scalar measure of signal quality for the communications link; and

a decoder responsive to said soft decision unit to recover data corresponding to the soft decision; and

a network interface responsive to said decoder to receive the data and selectively transmit the data to said information processor, said network interface including a control unit responsive to said signal-to-noise estimation unit to selectively alter a characteristic of the communications link based on the geometric signal-to-noise ratio estimate generated by said signal-to-noise estimation unit.

27. An apparatus for measuring signal quality in a communications link, the communications link capable of supporting transfer of OFDM symbols modulating data across a plurality of sub-carriers, the apparatus comprising:

means for receiving an OFDM symbol from the communications link; and

means for generating an estimate of a geometric signal-to-noise ratio for the OFDM symbol based on an average of a logrithmic difference between a soft decision and a hard decision for the OFDM symbol, the geometric signal-to-noise ratio estimate defining a scalar value of the communications link signal quality.

28. The apparatus of claim 27, wherein

the soft decision defines soft decision information for each of the plurality of sub-carriers;

wherein the hard decision defines hard decision information for each of the plurality of sub-carriers; and

wherein said generating means comprises;

means for selecting a subset of the plurality of sub-carriers for the OFDM symbol; and

means for generating the geometric signal-to-noise ratio estimate using soft and hard decision information for the subset of the plurality of sub-carriers selected by said selecting means as the soft and hard decision respectively.

29. The apparatus of claim 28, wherein the subset of the plurality of sub-carriers are regularly spaced within a sub-carrier constellation defined by the plurality of sub-carriers.

30. The apparatus of claim 29, wherein said selecting means selects first and second subsets of the plurality of sub-carriers for first and second symbols respectively, the first and second symbols successively transferred across the communications link, the first and second subsets being at least partially distinct.

31. The apparatus of claim 27, wherein

the communications link comprises a wireless communications link;

and

wherein the OFDM symbol is formatted in compliance with at least one of IEEE 802.11a and IEEE 802.11 g standards.

32. The apparatus of claim 27, wherein

the hard decision is provided by means for slicing the soft decision;

and

wherein the soft decision is provided by means for demodulating and equalizing the OFDM symbol.

33. The apparatus of claim 27, wherein

the hard decision is provided by a means for decoding and symbol re-coding the soft decision;

and

wherein the soft decision is provided by a means for demodulating and equalizing the OFDM symbol.

34. A baseband processor capable of processing a baseband signal borne across a communications link, comprising:

means for recovering a received symbol from the baseband signal, the received symbol modulating data across a plurality of sub-carriers;

means for recovering a soft decision of a transmitted symbol corresponding to the received symbol;

means for recovering a hard decision of the transmitted symbol based on the soft decision; and

means for generating an estimate of a geometric signal-to-noise ratio for the received symbol based on an average of a logarithmic difference between the soft and hard decisions, the geometric signal-to-noise ratio estimate defining a scalar measure of signal quality for the communications link.

35. The baseband processor of claim 34, further comprising means for providing a plurality of channel estimates for the received symbol corresponding to the plurality of sub-carriers;

and

wherein said soft decision recovery means comprises means for recovering the soft decision using the plurality of channel estimates.

36. The baseband processor of claim 34, wherein

the soft decision defines soft decision information for each of the plurality of sub-carriers;

wherein the hard decision defines hard decision information for each of the plurality of sub-carriers; and

wherein said generating means comprises;

means for selecting a subset of the plurality of sub-carriers for the at least one symbol; and

means for generating the geometric signal-to-noise ratio estimate using soft and hard decision information for the subset of the plurality of sub-carriers selected by said selecting means, as the soft and hard decision respectively.

37. The baseband processor of claim 36, wherein said signal-to-noise ratio estimate generating means and said soft decision recovery means share common calculation means.

38. The baseband processor of claim 36, wherein the subset of the plurality of sub-carriers are regularly spaced within a sub-carrier constellation defined by the plurality of sub-carriers.

39. The baseband processor of claim 38, wherein

said received symbol recovery means successively recovers first and second received symbols from the baseband signal, each of the first and second received symbols modulating data across the plurality of sub-carriers;

and

wherein said selecting means selects first and second subsets of the plurality of sub-carriers, the first and second subsets being at least partially distinct.

40. The baseband processor of claim 34, wherein

the communications link comprises a wireless communications link;

and

wherein the received symbol comprises an OFDM symbol compliant with at least one of IEEE 802.11a and IEEE 802.11g standards.

41. The baseband processor of claim 34, wherein:

said soft decision recovery means comprises demodulation/FEQ means; and

wherein said hard decision recovery means comprises one of slicer means and Viterbi decoder and re-coder means.

42. A transceiver, comprising:

means for receiving a baseband signal borne across a wireless communications link; and

baseband processor means, comprising;

means for recovering a received symbol from the baseband signal, the received symbol modulating data across a plurality of sub-carriers;

means for recovering a soft decision of a transmitted symbol corresponding to the received symbol;

means for recovering a hard decision of the transmitted symbol based on the soft decision; and

means for generating an estimate of a geometric signal-to-noise ratio for the received symbol based on an average of a logarithmic difference between the soft and hard decisions, the geometric signal-to-noise ratio estimate defining a scalar measure of signal quality for the communications link.

43. The transceiver of claim 42, further comprising means for providing a plurality of channel estimates for the received symbol corresponding to the plurality of sub-carriers;

and

wherein said soft decision recovery means comprises means for recovering the soft decision using the plurality of channel estimates.

44. The transceiver of claim 42, wherein

the soft decision defines soft decision information for each of the plurality of sub-carriers;

wherein the hard decision defines hard decision information for each of the plurality of sub-carriers; and

wherein said generating means comprises;

means for selecting a subset of the plurality of sub-carriers for the at least one symbol; and

means for generating the geometric signal-to-noise ratio estimate using soft and hard decision information for the subset of the plurality of sub-carriers selected by said selecting means, as the soft and hard decision respectively.

45. The transceiver of claim 44, wherein said signal-to-noise ratio estimate generating means and said soft decision recovery means share common calculation means.

46. The transceiver of claim 44, wherein the subset of the plurality of sub-carriers are regularly spaced within a sub-carrier constellation defined by the plurality of sub-carriers.

47. The transceiver of claim 46, wherein

said received symbol recovery means successively recovers first and second received symbols from the baseband signal, each of the first and second received symbols modulating data across the plurality of sub-carriers;

and

wherein said selecting means selects first and second subsets of the plurality of sub-carriers, the first and second subsets being at least partially distinct.

48. The transceiver of claim 42, wherein the received symbol comprises an OFDM symbol compliant with at least one of IEEE 802.11a and IEEE 802.11g standards.

49. The transceiver of claim 42, wherein:

said soft decision recovery means comprises demodulation/FEQ means; and

wherein said hard decision recovery means comprises one of slicer means and Viterbi decoder and re-coder means.

50. The transceiver of claim 42, further comprising a means for selectively altering a characteristic of the communications link based on the geometric signal-to-noise ratio estimate generated by said generating means.

51. A network interface apparatus, comprising:

transceiver means, comprising;

means for receiving a baseband signal borne across a wireless communications link; and

baseband processor means, comprising;

means for recovering a received symbol from the baseband signal, the received symbol modulating data across a plurality of sub-carriers;

means for recovering a soft decision of a transmitted symbol corresponding to the received symbol;

means for recovering a hard decision of the transmitted symbol based on the soft decision;

means for generating an estimate of a geometric signal-to-noise ratio for the received symbol based on an average of a logarithmic difference between the soft and hard decisions, the geometric signal-to-noise ratio estimate defining a scalar measure of signal quality for the communications link; and

means for recovering data corresponding to the soft decision; and

means for receiving the data, said data receiving means including means for selectively altering a characteristic of the communications link based on the geometric signal-to-noise ratio estimate generated by said generating means.

52. An information processing apparatus, comprising:

information processor means;

transceiver means, comprising;

means for receiving a baseband signal borne across a wireless communications link; and

baseband processor means, comprising;

means for recovering a received symbol from the baseband signal, the received symbol modulating data across a plurality of sub-carriers;

means for recovering a soft decision of a transmitted symbol corresponding to the received symbol;

means for recovering a hard decision of the transmitted symbol based on the soft decision;

means for generating an estimate of a geometric signal-to-noise ratio for the received symbol based on an average of a logarithmic difference between the soft and hard decisions, the geometric signal-to-noise ratio estimate defining a scalar measure of signal quality for the communications link; and

means for recovering data corresponding to the soft decision; and

means for receiving the data and selectively transmitting the data to said information processor means, said data receiving means including means for selectively altering a characteristic of the communications link based on the geometric signal-to-noise ratio estimate generated by said generating means.

53. A method for measuring signal quality in a communications link, the communications link capable of supporting transfer of OFDM symbols modulating data across a plurality of sub-carriers, the method comprising:

receiving an OFDM symbol from the communications link; and

generating an estimate of a geometric signal-to-noise ratio for the OFDM symbol based on an average of a logarithmic difference between a soft decision and a hard decision for the OFDM symbol, the geometric signal-to-noise ratio estimate defining a scalar value of the communications link signal quality.

54. The method of claim 53, wherein

the soft decision defines soft decision information for each of the plurality of sub-carriers;

wherein the hard decision defines hard decision information for each of the plurality of sub-carriers; and

wherein said generating step comprises;

selecting a subset of the plurality of sub-carriers for the OFDM symbol; and

generating the geometric signal-to-noise ratio estimate using soft and hard decision information for the subset of the plurality of sub-carriers selected in said selecting step as the soft and hard decision respectively.

55. The method of claim 54, wherein the subset of the plurality of sub-carriers are regularly spaced within a sub-carrier constellation defined by the plurality of sub-carriers.

56. The method of claim 55, wherein said selecting step comprises selecting first and second subsets of the plurality of sub-carriers for first and second symbols respectively, the first and second symbols successively transferred across the communications link, the first and second subsets being at least partially distinct.

57. The method of claim 53, wherein

the communications link comprises a wireless communications link;

and

wherein the OFDM symbol is formatted in compliance with at least one of IEEE 802.11a and IEEE 802.11g standards.

58. The method of claim 53, further comprising:

slicing the soft decision to provide the hard decision; and

demodulating and equalizing the OFDM symbol to provide the soft decision.

59. The method of claim 53, further comprising:

decoding and symbol re-coding the soft decision to provide the hard decision; and

demodulating and equalizing the OFDM symbol to provide the soft decision.

60. The method of claim 53, further comprising selectively altering a characteristic of the communications link based on the geometric signal-to-noise ratio estimate generated in said generating step.

61. A computer program product, comprising computer readable program code causing an information processor to perform the following steps support of measuring signal quality in a communications link, the communications link capable of supporting transfer of OFDM symbols modulating data across a plurality of sub-carriers, the steps comprising:

receiving an OFDM symbol from the communications link; and

generating an estimate of a geometric signal-to-noise ratio for the OFDM symbol based on an average of a logarithmic difference between a soft decision and a hard decision for the OFDM symbol, the geometric signal-to-noise ratio estimate defining a scalar value of the communications link signal quality.

62. The product of claim 61, wherein

the soft decision defines soft decision information for each of the plurality of sub-carriers;

wherein the hard decision defines hard decision information for each of the plurality of sub-carriers; and

wherein said generating step comprises;

selecting a subset of the plurality of sub-carriers for the OFDM symbol; and

generating the geometric signal-to-noise ratio estimate using soft and hard decision information for the subset of the plurality of sub-carriers selected in said selecting step as the soft and hard decision respectively.

63. The product of claim 62, wherein the subset of the plurality of sub-carriers are regularly spaced within a sub-carrier constellation defined by the plurality of sub-carriers.

64. The product of claim 63, wherein said selecting step comprises selecting first and second subsets of the plurality of sub-carriers for first and second symbols respectively, the first and second symbols successively transferred across the communications link, the first and second subsets being at least partially distinct.

65. The product of claim 61, wherein

the communications link comprises a wireless communications link;

and

wherein the OFDM symbol is formatted in compliance with at least one of IEEE 802.11a and IEEE 802.11g standards.

66. The product of claim 61, the steps further comprising:

slicing the soft decision to provide the hard decision; and

demodulating and equalizing the OFDM symbol to provide the soft decision.

67. The product of claim 61, the steps further comprising:

decoding and symbol re-coding the soft decision to provide the hard decision; and

demodulating and equalizing the OFDM symbol to provide the soft decision.

68. The product of claim 61, the steps further comprising selectively altering a characteristic of the communications link based on the geometric signal-to-noise ratio estimate generated in said generating step.