METHODS AND SYSTEMS FOR TRANSMISSION MODE SELECTION IN A MULTI CHANNEL COMMUNICATION SYSTEM

• US 20100067401A1
• Filed: 09/16/2008
• Published: 03/18/2010
• Est. Priority Date: 09/16/2008
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Medvedev, Irina, Ketchum, John W., Walton, J. Rodney
• Granted Patent: US 8,619,620 B2
• Time in Patent Office: Days
• US Class Current: 370/253
• CPC Class Codes: H04L 1/0002 by adapting the transmission rate
• CPC Class Codes: H04L 1/0016 involving special memory structures, e.g. look-up tables
• CPC Class Codes: H04L 1/0019 in which mode-switching is based on a statistical approach
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04W 24/02 Arrangements for optimising operational condition

Abstract

Techniques to select a suitable transmission mode for a data transmission in a multi channel communication system with multiple spatial channels having varying SNRs are presented in this disclosure. For certain embodiments, a closed-loop technique may be applied, in which back-off factors used to calculate an effective SNR value fed back to a transmitter are adjusted. An open-loop rate control scheme is also presented in which a transmitter may select a data rate and number of streams based on whether transmitted packets are received in error at a receiver.

Claims

1. A method for open-loop rate control for transmissions between a transmitting terminal and a receiving terminal in a multi-channel wireless communications system, comprising:

transmitting one or more data packets using a plurality of spatial streams at a transmission rate; and

adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error.

2. The method of claim 1, wherein adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error comprises:

increasing the transmission rate for transmitting subsequent packets if a plurality of consecutive packets are successfully received.

3. The method of claim 1, wherein adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error comprises:

decreasing the transmission rate for transmitting subsequent packets if one or more packets are not successfully received.

4. The method of claim 1, further comprising:

monitoring a packet error rate for packets transmitted at a given transmission rate; and

wherein adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error comprises increasing the transmission rate if the packet error rate falls below a first threshold and decreasing the transmission rate if the packet error rate exceeds a second threshold.

5. The method of claim 4, wherein the first and second thresholds are different values.

6. The method of claim 1, wherein adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error comprises:

selecting a combination of modulation and coding schemes and number of spatial streams from a plurality of combinations of modulation and coding schemes and numbers of spatial streams that achieve the same transmission rate.

7. The method of claim 1, wherein adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error comprises:

selecting a combination of modulation and coding schemes and number of spatial streams that achieves a next available higher transmission rate or a next available lower transmission rate relative to a current transmission rate.

8. The method of claim 1, wherein adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error comprises:

adjusting the transmission rate according to a first algorithm during an initialization stage; and

adjusting the transmission rate according to a second algorithm during a steady state.

9. The method of claim 8, wherein:

the initialization stage begins by selecting a highest allowable transmission rate; and

the transmission rate is iteratively reduced until no or few packet errors are detected.

10. The method of claim 8, wherein:

the initialization stage begins by selecting a lowest allowable transmission rate; and

the transmission rate is iteratively increased until packet errors are detected.

11. The method of claim 1, further comprising:

determining an initial transmission rate based on a selected rate fed back from the receiving terminal;

transmitting one or more data packets using the determined initial transmission rate; and

adjusting the determined initial transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets was received in error.

12. A method of selecting transmission modes in multi-channel communications system, comprising:

calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams;

calculating an effective SNR metric as a function of, at least, the SNR metric and one or more back-off parameters;

monitoring packets errors;

adjusting one or more of the back-off parameters based on the monitored packet errors;

selecting a data rate based on the effective SNR metric; and

generating rate feedback based on the selected data rate.

13. The method of claim 12, wherein selecting a data rate based on the effective SNR metric comprises:

selecting, from a lookup table, a highest data rate with a required SNR that is less than or equal to the effective SNR metric.

14. The method of claim 12, wherein calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams comprises:

calculating an average SNR value and standard deviation for the plurality of streams.

15. The method of claim 14, wherein calculating the effective SNR comprises:

multiplying the standard deviation by a first one of the back-off parameters to obtain a product; and

subtracting the product from, and adding a second back-off parameter to, the average SNR value to obtain an adjusted SNR value.

16. The method of claim 15, wherein calculating the effective SNR further comprises:

using a third back-off parameter as an exponent applied to the adjusted SNR value; and

adding a fourth back-off parameter to the value generated by applying the third back-off parameter as an exponent to the adjusted SNR value.

17. The method of claim 14, wherein calculating an average signal to noise ratio (SNR) value comprises calculating an average SNR value for multiple subcarriers of one or more of the spatial streams.

18. The method of claim 14, wherein calculating an average signal to noise ratio (SNR) value comprises calculating an average SNR value for multiple subcarriers of one or more of the spatial streams.

19. The method of claim 12, wherein one or more of the back-off parameters vary based on the number of spatial streams.

20. The method of claim 12, wherein adjusting one or more of the back-off parameters based on the monitored packet errors comprises:

adjusting at least one of the first back-off parameter in a manner that reduces the calculated effective SNR if N packet errors are observed, wherein N is a positive integer; and

adjusting at least one of the first back-off parameter in a manner that increases the calculated effective SNR if M consecutive packets are observed without errors, wherein M is a positive integer.

21. The method of claim 12, further comprising:

setting the back-off parameters to initial values.

22. The method of claim 21, wherein setting the back-off parameters to initial values comprises:

setting the back-off parameters to initial values if the rate feedback has not been updated for a given amount of time, T.

23. An apparatus for open-loop rate control for transmissions between a transmitting terminal and a receiving terminal in a multi-channel wireless communications system, comprising:

logic for transmitting one or more data packets using a plurality of spatial streams at a transmission rate; and

logic for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error.

24. The apparatus of claim 23, wherein the logic for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to:

increase the transmission rate for transmitting subsequent packets if a plurality of consecutive packets are successfully received.

25. The apparatus of claim 23, wherein the logic for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to:

decrease the transmission rate for transmitting subsequent packets if one or more packets are not successfully received.

26. The apparatus of claim 23, further comprising:

logic for monitoring a packet error rate for packets transmitted at a given transmission rate; and

wherein the logic for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to increase the transmission rate if the packet error rate falls below a first threshold and decrease the transmission rate if the packet error rate exceeds a second threshold.

27. The apparatus of claim 26, wherein the first and second thresholds are different values.

28. The apparatus of claim 23, wherein the logic for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to:

select a combination of modulation and coding schemes and number of spatial streams from a plurality of combinations of modulation and coding schemes and numbers of spatial streams that achieve the same transmission rate.

29. The apparatus of claim 23, wherein the logic for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to:

select a combination of modulation and coding schemes and number of spatial streams that achieves a next available higher transmission rate or a next available lower transmission rate relative to a current transmission rate.

30. The apparatus of claim 23, wherein the logic for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to:

adjust the transmission rate according to a first algorithm during an initialization stage; and

adjust the transmission rate according to a second algorithm during a steady state.

31. The apparatus of claim 30, wherein:

the initialization stage begins by selecting a highest allowable transmission rate; and

the transmission rate is iteratively reduced until no or few packet errors are detected.

32. The apparatus of claim 30, wherein:

the initialization stage begins by selecting a lowest allowable transmission rate; and

the transmission rate is iteratively increased until packet errors are detected.

33. The apparatus of claim 23, further comprising:

logic for determining an initial transmission rate based on a selected rate fed back from the receiving terminal;

logic for transmitting one or more data packets using the determined initial transmission rate; and

logic for adjusting the determined initial transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets was received in error.

34. An apparatus for selecting transmission modes in multi-channel communications system, comprising:

logic for calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams;

logic for calculating an effective SNR metric as a function of, at least, the SNR metric and one or more back-off parameters;

logic for monitoring packets errors;

logic for adjusting one or more of the back-off parameters based on the monitored packet errors;

logic for selecting a data rate based on the effective SNR metric; and

logic for generating rate feedback based on the selected data rate.

35. The apparatus of claim 34, wherein the logic for selecting a data rate based on the effective SNR metric is configured to:

select, from a lookup table, a highest data rate with a required SNR that is less than or equal to the effective SNR metric.

36. The apparatus of claim 34, wherein the logic for calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams is configured to:

calculate an average SNR value and standard deviation for the plurality of streams.

37. The apparatus of claim 36, wherein the logic for calculating the effective SNR is configured to:

multiply the standard deviation by a first one of the back-off parameters to obtain a product; and

subtract the product from, and adding a second back-off parameter to, the average SNR value to obtain an adjusted SNR value.

38. The apparatus of claim 37, wherein the logic for calculating the effective SNR is further configured to:

use a third back-off parameter as an exponent applied to the adjusted SNR value; and

add a fourth back-off parameter to the value generated by applying the third back-off parameter as an exponent to the adjusted SNR value.

39. The apparatus of claim 36, wherein the logic for calculating an average signal to noise ratio (SNR) value is configured to calculate an average SNR value for multiple subcarriers of one or more of the spatial streams.

40. The apparatus of claim 36, wherein the logic for calculating an average signal to noise ratio (SNR) value is configured to calculate an average SNR value for multiple subcarriers of one or more of the spatial streams.

41. The apparatus of claim 34, wherein one or more of the back-off parameters vary based on the number of spatial streams.

42. The apparatus of claim 34, wherein the logic for adjusting one or more of the back-off parameters based on the monitored packet errors is configured to:

adjust at least one of the first back-off parameter in a manner that reduces the calculated effective SNR if N packet errors are observed, wherein N is a positive integer; and

adjust at least one of the first back-off parameter in a manner that increases the calculated effective SNR if M consecutive packets are observed without errors, wherein M is a positive integer.

43. The apparatus of claim 34, further comprising:

logic for setting the back-off parameters to initial values.

44. The apparatus of claim 43, wherein the logic for setting the back-off parameters to initial values is configured to:

set the back-off parameters to initial values if the rate feedback has not been updated for a given amount of time, T.

45. An apparatus for open-loop rate control for transmissions between a transmitting terminal and a receiving terminal in a multi-channel wireless communications system, comprising:

means for transmitting one or more data packets using a plurality of spatial streams at a transmission rate; and

means for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error.

46. The apparatus of claim 45, wherein the means for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to:

increase the transmission rate for transmitting subsequent packets if a plurality of consecutive packets are successfully received.

47. The apparatus of claim 45, wherein the means for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to:

decrease the transmission rate for transmitting subsequent packets if one or more packets are not successfully received.

48. The apparatus of claim 45, further comprising:

means for monitoring a packet error rate for packets transmitted at a given transmission rate; and

wherein the means for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to increase the transmission rate if the packet error rate falls below a first threshold and decrease the transmission rate if the packet error rate exceeds a second threshold.

49. The apparatus of claim 48, wherein the first and second thresholds are different values.

50. The apparatus of claim 45, wherein the means for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to:

select a combination of modulation and coding schemes and number of spatial streams from a plurality of combinations of modulation and coding schemes and numbers of spatial streams that achieve the same transmission rate.

51. The apparatus of claim 45, wherein the means for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to:

select a combination of modulation and coding schemes and number of spatial streams that achieves a next available higher transmission rate or a next available lower transmission rate relative to a current transmission rate.

52. The apparatus of claim 45, wherein the means for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error is configured to:

adjust the transmission rate according to a first algorithm during an initialization stage; and

adjust the transmission rate according to a second algorithm during a steady state.

53. The apparatus of claim 52, wherein:

the initialization stage begins by selecting a highest allowable transmission rate; and

the transmission rate is iteratively reduced until no or few packet errors are detected.

54. The apparatus of claim 52, wherein:

the initialization stage begins by selecting a lowest allowable transmission rate; and

the transmission rate is iteratively increased until packet errors are detected.

55. The apparatus of claim 45, further comprising:

means for determining an initial transmission rate based on a selected rate fed back from the receiving terminal;

means for transmitting one or more data packets using the determined initial transmission rate; and

means for adjusting the determined initial transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets was received in error.

56. An apparatus for selecting transmission modes in multi-channel communications system, comprising:

means for calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams;

means for calculating an effective SNR metric as a function of, at least, the SNR metric and one or more back-off parameters;

means for monitoring packets errors;

means for adjusting one or more of the back-off parameters based on the monitored packet errors;

means for selecting a data rate based on the effective SNR metric; and

means for generating rate feedback based on the selected data rate.

57. The apparatus of claim 56, wherein the means for selecting a data rate based on the effective SNR metric is configured to:

select, from a lookup table, a highest data rate with a required SNR that is less than or equal to the effective SNR metric.

58. The apparatus of claim 56, wherein the means for calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams is configured to:

calculate an average SNR value and standard deviation for the plurality of streams.

59. The apparatus of claim 58, wherein the means for calculating the effective SNR is configured to:

multiply the standard deviation by a first one of the back-off parameters to obtain a product; and

subtract the product from, and adding a second back-off parameter to, the average SNR value to obtain an adjusted SNR value.

60. The apparatus of claim 59, wherein the means for calculating the effective SNR is further configured to:

use a third back-off parameter as an exponent applied to the adjusted SNR value; and

add a fourth back-off parameter to the value generated by applying the third back-off parameter as an exponent to the adjusted SNR value.

61. The apparatus of claim 58, wherein the means for calculating an average signal to noise ratio (SNR) value is configured to calculate an average SNR value for multiple subcarriers of one or more of the spatial streams.

62. The apparatus of claim 58, wherein the means for calculating an average signal to noise ratio (SNR) value is configured to calculate an average SNR value for multiple subcarriers of one or more of the spatial streams.

63. The apparatus of claim 56, wherein one or more of the back-off parameters vary based on the number of spatial streams.

64. The apparatus of claim 56, wherein the means for adjusting one or more of the back-off parameters based on the monitored packet errors is configured to:

adjust at least one of the first back-off parameter in a manner that reduces the calculated effective SNR if N packet errors are observed, wherein N is a positive integer; and

adjust at least one of the first back-off parameter in a manner that increases the calculated effective SNR if M consecutive packets are observed without errors, wherein M is a positive integer.

65. The apparatus of claim 56, further comprising:

means for setting the back-off parameters to initial values.

66. The apparatus of claim 65, wherein the means for setting the back-off parameters to initial values is configured to:

set the back-off parameters to initial values if the rate feedback has not been updated for a given amount of time, T.

67. A computer-program product for open-loop rate control for transmissions between a transmitting terminal and a receiving terminal in a multi-channel wireless communications system, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:

instructions for transmitting one or more data packets using a plurality of spatial streams at a transmission rate; and

instructions for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error.

68. The computer-program product of claim 67, wherein the instructions for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error further comprise:

instructions for increasing the transmission rate for transmitting subsequent packets if a plurality of consecutive packets are successfully received.

69. The computer-program product of claim 67, wherein the instructions for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error further comprise:

instructions for decreasing the transmission rate for transmitting subsequent packets if one or more packets are not successfully received.

70. The computer-program product of claim 67, wherein the instructions further comprise:

instructions for monitoring a packet error rate for packets transmitted at a given transmission rate; and

wherein the instructions for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error further comprise instructions for increasing the transmission rate if the packet error rate falls below a first threshold and instructions for decreasing the transmission rate if the packet error rate exceeds a second threshold.

71. The computer-program product of claim 70, wherein the first and second thresholds are different values.

72. The computer-program product of claim 67, wherein the instructions for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error further comprise:

instructions for selecting a combination of modulation and coding schemes and number of spatial streams from a plurality of combinations of modulation and coding schemes and numbers of spatial streams that achieve the same transmission rate.

73. The computer-program product of claim 67, wherein the instructions for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error further comprise:

instructions for selecting a combination of modulation and coding schemes and number of spatial streams that achieves a next available higher transmission rate or a next available lower transmission rate relative to a current transmission rate.

74. The computer-program product of claim 67, wherein the instructions for adjusting the transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets were received in error further comprise:

instructions for adjusting the transmission rate according to a first algorithm during an initialization stage; and

instructions for adjusting the transmission rate according to a second algorithm during a steady state.

75. The computer-program product of claim 74, wherein:

the initialization stage begins by selecting a highest allowable transmission rate; and

the transmission rate is iteratively reduced until no or few packet errors are detected.

76. The computer-program product of claim 74, wherein:

the initialization stage begins by selecting a lowest allowable transmission rate; and

the transmission rate is iteratively increased until packet errors are detected.

77. The computer-program product of claim 67, wherein the instructions further comprise:

instructions for determining an initial transmission rate based on a selected rate fed back from the receiving terminal;

instructions for transmitting one or more data packets using the determined initial transmission rate; and

instructions for adjusting the determined initial transmission rate for transmitting subsequent packets based on whether one or more of the transmitted data packets was received in error.

78. A computer-program product for selecting transmission modes in multi-channel communications system, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:

instructions for calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams;

instructions for calculating an effective SNR metric as a function of, at least, the SNR metric and one or more back-off parameters;

instructions for monitoring packets errors;

instructions for adjusting one or more of the back-off parameters based on the monitored packet errors;

instructions for selecting a data rate based on the effective SNR metric; and

instructions for generating rate feedback based on the selected data rate.

79. The computer-program product of claim 78, wherein the instructions for selecting a data rate based on the effective SNR metric further comprise:

instructions for selecting, from a lookup table, a highest data rate with a required SNR that is less than or equal to the effective SNR metric.

80. The computer-program product of claim 78, wherein the instructions for calculating a signal to noise ratio (SNR) metric based on SNR values for a plurality of spatial streams further comprise:

instructions for calculating an average SNR value and standard deviation for the plurality of streams.

81. The computer-program product of claim 80, wherein the instructions for calculating the effective SNR further comprise:

instructions for multiplying the standard deviation by a first one of the back-off parameters to obtain a product; and

instructions for subtracting the product from, and adding a second back-off parameter to, the average SNR value to obtain an adjusted SNR value.

82. The computer-program product of claim 81, wherein the instructions for calculating the effective SNR further comprise:

instructions for using a third back-off parameter as an exponent applied to the adjusted SNR value; and

instructions for adding a fourth back-off parameter to the value generated by applying the third back-off parameter as an exponent to the adjusted SNR value.

83. The computer-program product of claim 80, wherein the instructions for calculating an average signal to noise ratio (SNR) value further comprise instructions for calculating an average SNR value for multiple subcarriers of one or more of the spatial streams.

84. The computer-program product of claim 80, wherein the instructions for calculating an average signal to noise ratio (SNR) value further comprise instructions for calculating an average SNR value for multiple subcarriers of one or more of the spatial streams.

85. The computer-program product of claim 78, wherein one or more of the back-off parameters vary based on the number of spatial streams.

86. The computer-program product of claim 78, wherein the instructions for adjusting one or more of the back-off parameters based on the monitored packet errors further comprise:

instructions for adjusting at least one of the first back-off parameter in a manner that reduces the calculated effective SNR if N packet errors are observed, wherein N is a positive integer; and

instructions for adjusting at least one of the first back-off parameter in a manner that increases the calculated effective SNR if M consecutive packets are observed without errors, wherein M is a positive integer.

87. The computer-program product of claim 78, wherein the instructions further comprise:

instructions for setting the back-off parameters to initial values.

88. The computer-program product of claim 87, wherein the instructions for setting the back-off parameters to initial values further comprise:

instructions for setting the back-off parameters to initial values if the rate feedback has not been updated for a given amount of time, T.