SELF-INTERFERENCE CANCELLATION

• US 20140348018A1
• Filed: 08/11/2014
• Published: 11/27/2014
• Est. Priority Date: 02/03/2011
• Status: Active Grant

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Inventors: BHARADIA, Dinesh, KATTI, Sachin, McMILIN, Emily
• Granted Patent: US 10,284,356 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: H04B 1/126 having multiple inputs, e.g. auxiliary antenna for receiving interfering signal aerials in general H01Q
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver
• CPC Class Codes: H04B 1/56 with provision for simultaneous communication in two directions
• CPC Class Codes: H04L 5/1423 for simultaneous baseband signals
• CPC Class Codes: H04L 5/1461 Suppression of signals in the return path, i.e. bidirectional control circuits

Abstract

A wireless communication device includes, in part, an analog interference cancellation circuit and a controller. The analog cancellation circuit includes a multitude of delay paths each including a delay element and a variable attenuator. The controller dynamically varies the attenuation level of each of the variable attenuators in accordance with the frequency response characteristic of that attenuator to remove a portion of a self-interference signal present in a signal received by the device. The device measures the frequency response characteristic of the communication channel, used in determining the attenuation levels, via one or more preamble symbols. A second portion of the self-interference signal is removed by the device using a multitude of samples of a transmitted signal and a multitude of samples of a signal to be transmitted.

Claims

1. A wireless communication system comprising:

a transmit path adapted to transmit a transmit signal;

a receive path adapted to receive a receive signal;

an analog interference cancellation circuit coupled to the transmit path and adapted to remove a first portion of a self-interference signal from the receive signal, the analog cancellation circuit comprising a plurality of delay paths each including a delay element and a variable attenuator; and

a controller adapted to dynamically vary an attenuation value applied to each of the plurality of variable attenuators in accordance with a frequency response characteristics of the attenuator.

2. The wireless communication system of claim 1 further comprising:

a memory adapted to store at least one frequency response characteristic associated with at least one attenuation value of each of the plurality of the variable attenuators.

3. The wireless communication system of claim 2 wherein said controller is adapted to generate a plurality of attenuation values for each of the plurality of variable attenuators in accordance with an S parameter associated with the variable attenuator.

4. The wireless communication system of claim 1 wherein said wireless communication system is further adapted to measure a frequency response characteristic of a channel through which the transmit signal is transmitted using at least a first preamble symbol, said controller being further adapted to dynamically vary the attenuation value of each of the plurality of variable attenuators in accordance with the frequency response characteristics of the channel.

5. The wireless communication system of claim 4 wherein said first preamble symbol is a WiFi preamble symbol.

6. The wireless communication system of claim 4 wherein said wireless communication system is further adapted to measure the frequency response characteristics of the transmit channel using at least a second preamble symbol.

7. The wireless communication system of claim 4 wherein said wireless communication system is further adapted to measure a frequency response characteristic of each of the plurality of attenuators while setting an attenuation value of each of a remaining ones of the plurality of attenuators to a maximum value.

8. The wireless communication system of claim 7 wherein said wireless communication system is further adapted to apply a least square fit to the plurality of measured frequency response characteristics of the plurality of attenuators.

9. The wireless communication system of claim 7 wherein said controller is adapted to dynamically vary an attenuation value applied to each of the plurality of variable attenuators by minimizing a difference between a first matrix defined by the frequency response characteristics of the channel and a second matrix defined by the frequency response characteristics of the plurality of the delay paths.

10. The wireless communication system of claim 1 further comprising:

a digital interference cancellation circuit coupled to the transmit path and adapted to remove a second portion of the self-interference signal from the receive signal.

11. The wireless communication system of claim 10 wherein said digital interference cancellation circuit is disposed in the controller.

12. The wireless communication system of claim 11 wherein said controller is a processor or a computer.

13. The wireless communication system of claim 1 wherein said wireless communication system is a full-duplex wireless communication system.

14. A wireless communication system comprising:

a transmit path adapted to transmit a transmit signal;

a receive path adapted to receive a receive signal;

a digital interference cancellation circuit coupled to the transmit path and adapted to dynamically remove a first portion of a self-interference signal from the receive signal using a plurality of samples of a transmitted signal and a plurality of samples of a signal to be transmitted.

15. The wireless communication system of claim 14 wherein said wireless communication system is further adapted to define a frequency response characteristic of a channel through which the transmit signal is transmitted using at least first and second preamble symbols.

16. The wireless communication system of claim 15 wherein said first and second preamble symbols are WiFi preamble symbols.

17. The wireless communication system of claim 15 wherein said wireless communication system further defines the frequency response characteristic of the channel by forming a first matrix whose elements represent samples of the at least first and second preamble symbols.

18. The wireless communication system of claim 17 wherein said first matrix is a first Toeplitz matrix.

19. The wireless communication system of claim 17 wherein the elements of the first Toeplitz matrix are first order samples of the at least first and second preamble symbols.

20. The wireless communication system of claim 19 wherein said digital interference cancellation circuit is adapted to dynamically remove linear components of the first portion of the self-interference signal from the receive signal by minimizing a difference between a second matrix defined by samples of the receive signal and the first Toeplitz matrix.

21. The wireless communication system of claim 20 wherein said wireless communication system further defines the frequency response characteristic of the channel by forming a third matrix whose elements represent higher than first order samples of the at least first and second preamble symbols.

22. The wireless communication system of claim 21 wherein said higher than first order samples are third, fifth, and seventh order samples of the at least first and second preamble symbols.

23. The wireless communication system of claim 22 wherein said third matrix is a second Toeplitz matrix.

24. The wireless communication system of claim 23 wherein said digital interference cancellation circuit is adapted to dynamically remove nonlinear components of the first portion of the self-interference signal from the receive signal by minimizing a difference between the second matrix and the second Toeplitz matrix.

25. The wireless communication system of claim 24 further comprising:

an analog interference cancellation circuit coupled to the transmit path and adapted to remove a second portion of a self-interference signal from the receive signal, the analog cancellation circuit comprising a plurality of delay paths each including a delay element and a variable attenuator; and

a controller adapted to dynamically vary an attenuation value applied to each of the plurality of variable attenuators.

26. The wireless communication system of claim 25 wherein said digital interference cancellation circuit is disposed in the controller.

27. The wireless communication system of claim 26 wherein said controller is a processor or a computer.

28. The wireless communication system of claim 14 wherein said wireless communication system is a full-duplex wireless communication system.

29. A method of operating a wireless communication system, the method comprising:

transmitting a transmit signal from a transmit path;

receiving a receive signal from a receive path; and

dynamically varying an attenuation value applied to each of a plurality of variable attenuators disposed in the wireless communication system in accordance with a frequency response characteristics of the attenuators thereby to remove a first portion of a self-interference signal from the receive signal.

30. The method of claim 29 further comprising:

storing in a memory at least one frequency response characteristic associated with at least one attenuation value of each of the plurality of the variable attenuators.

31. The method of claim 30 further comprising:

generating a plurality of attenuation values for each of the plurality of variable attenuators in accordance with an S parameter associated with the variable attenuator.

32. The method of claim 29 further comprising:

measuring a frequency response characteristic of a channel through which the transmit signal is transmitted using at least a first preamble symbol; and

dynamically varying the attenuation value of each of the plurality of variable attenuators in accordance with the frequency response characteristics of the channel.

33. The method of claim 32 wherein said first preamble symbol is a WiFi preamble symbol.

34. The method of claim 32 further comprising:

measuring the frequency response characteristic of the transmit channel using at least a second preamble symbol.

35. The method of claim 32 further comprising

measuring a frequency response characteristic of each of the plurality of attenuators while setting an attenuation value of each of a remaining ones of the plurality of attenuators to a maximum value.

36. The method of claim 35 further comprising

applying a least square fit to the plurality of measured frequency response characteristics of the plurality of attenuators.

37. The method of claim 35 further comprising:

dynamically varying an attenuation value applied to each of the plurality of variable attenuators by minimizing a difference between a first matrix defined by the frequency response characteristics of the channel and a second matrix defined by the frequency response characteristics of a plurality of the delay paths in which the plurality of the attenuators are disposed.

38. The method of claim 29 further comprising:

removing a second portion of the self-interference signal from the receive signal using a digital interference cancellation circuit.

39. The method of claim 38 further comprising wherein said digital interference cancellation circuit is disposed in a processor configured to execute instructions.

40. The method of claim 29 wherein said wireless communication system is a full-duplex wireless communication system.

41. A method of operating a wireless communication system, the method comprising:

transmitting a transmit signal from a transmit path;

receiving a receive signal from a receive path; and

removing a first portion of a self-interference signal from the receive signal using a plurality of samples of a transmitted signal and a plurality of samples of a signal to be transmitted.

42. The method of claim 41 further comprising:

defining a frequency response characteristic of a channel through which the transmit signal is transmitted using at least first and second preamble symbols.

43. The method of claim 42 wherein said first and second preamble symbols are WiFi preamble symbols.

44. The method of claim 42 further comprising:

defining the frequency response characteristic of the channel by forming a first matrix whose elements represent samples of the at least first and second preamble symbols.

45. The method of claim 44 wherein said first matrix is a first Toeplitz matrix.

46. The method of claim 42 wherein the elements of the first Toeplitz matrix are first order samples of the at least first and second preamble symbols.

47. The method of claim 46 further comprising:

dynamically removing linear components of the first portion of the self-interference signal from the receive signal by minimizing a difference between a second matrix defined by samples of the receive signal and the first Toeplitz matrix.

48. The method of claim 47 further comprising:

defining the frequency response characteristic of the channel by forming a third matrix whose elements represent higher than first order samples of the at least first and second preamble symbols.

49. The method of claim 48 wherein said higher than first order samples are third, fifth, and seventh order samples of the at least first and second preamble symbols.

50. The method of claim 49 wherein said third matrix is a second Toeplitz matrix.

51. The method of claim 50 further comprising:

dynamically removing nonlinear components of the first portion of the self-interference signal from the receive signal by minimizing a difference between the second matrix and the second Toeplitz matrix.

52. The method of claim 51 further comprising:

dynamically varying an attenuation value applied to each of a plurality of variable attenuators thereby to remove a second portion of a self-interference signal from the receive signal.

53. The method of claim 51 further comprising:

dynamically varying the attenuation value applied to each of the plurality of variable attenuators using a processor; and

removing the first portion of a self-interference signal from the receive signal using the processor.

54. The method of claim 41 wherein said wireless communication system is a full-duplex wireless communication system.

55. A system for full-duplex signal shaping for a full-duplex radio comprising:

an analog self-interference cancellation component, coupled to a transmit line and a receive line of the full-duplex radio, that removes a first portion of self-interference from a receive signal of the full-duplex radio;

the analog self-interference cancellation component comprising scaling and delay circuitry; and

a digital filter engine, coupled to the transmit line and the receive line of the full-duplex radio, that removes a second portion of self-interference from the receive signal.

56. The system of claim 55 wherein the scaling and delay circuitry is coupled to the transmit line by a power splitter and coupled to the receive line by a balun;

wherein the scaling and delay circuitry takes a transmit signal as input and outputs a self-interference signal;

wherein the self-interference signal is subtracted from a receive signal by the balun.

57. The system of claim 56 wherein the scaling and delay circuitry comprises a programmable attenuator.

58. The system of claim 55 wherein the digital filter engine includes programmable filters, intermediate frequency converters, and a filter engine API;

wherein the filter engine API configures the programmable filters and intermediate frequency converters to perform full-duplex signal shaping.

59. The system of claim 58 wherein one of the programmable filters is a finite response filter.

60. The system of claim 55 wherein the scaling and delay circuitry includes an analog self-interference cancellation circuit comprising:

a plurality of signal paths, each signal path including a delay element and a scaling element, wherein each signal path receives a sampled transmit signal and outputs a delayed and weighted transmit signal;

a combiner that combines the delayed and weighted transmit signals of the plurality of signal paths to form a self-interference signal representative; and

a controller that controls parameters of the scaling elements.

61. The system of claim 60 wherein the controller further controls parameters of the delay elements.

62. The system of claim 60 wherein the scaling elements comprise a variable attenuator and parameters of the scaling elements comprise a variable attenuator attenuation value.

63. The system of claim 62 wherein the controller controls parameters of the scaling elements based on sinc function intersections with an estimated self-interference signal;

wherein the controller adapts the parameters of the scaling elements using an iterative optimization algorithm.

64. The system of claim 60 wherein the controller controls parameters of the scaling elements by determining signal path responses, measuring self-interference, and adapting the parameters of the scaling elements based on the signal path responses and the self-interference.

65. The system of claim 60 wherein the controller controls parameters of the scaling elements by receiving signal path response data, generating a first self-interference signal estimate, applying a first set of parameter values based on the first self-interference signal estimate, generating a second self-interference signal estimate using the first set of parameter values, and applying a second set of parameter values based on the second self-interference signal estimate.

76. The system of claim 63 wherein the iterative optimization algorithm includes selecting a subset of coefficients based on a coefficient selection algorithm.

66. A method for full-duplex signal shaping for a full-duplex radio comprising:

receiving a receive signal of a full-duplex radio;

performing analog self-interference cancellation to remove a first portion of self-interference from the receive signal; and

performing digital self-interference removal to remove a second portion of self-interference from the receive signal.

67. The method of claim 66 wherein the receive signal is received on a plurality of wireless spectrum fragments.

68. The method of claim 66 wherein performing analog self-interference cancellation comprises:

receiving a transmit signal of a full-duplex radio;

generating a set of delayed versions of the transmit signal;

scaling the set of delayed versions of the transmit signal to produce a set of delayed and scaled signals;

combining the set of delayed and scaled signals to create a combined signal; and

subtracting the combined signal from the receive signal.

69. The method of claim 68 further comprising:

after subtracting the combined signal from the receive signal, downconverting the receive signal;

filtering the receive signal; and

converting the receive signal from an analog signal to a digital signal before performing digital self-interference removal.

70. The method of claim 69 wherein performing digital self-interference removal comprises digital filtering.

71. The method of claim 69 wherein performing digital self-interference removal comprises cancelling linear digital self-interference and cancelling nonlinear digital self-interference.

72. The method of claim 71 wherein performing digital self-interference removal further comprises correcting gain and phase error.

73. The method of claim 72 wherein performing digital self-interference removal further comprises cancelling a local oscillator leakage.

74. The method of claim 68 further comprising adapting analog self-interference cancellation by determining signal path responses, measuring self-interference, and adapting the parameters of the scaling elements based on the signal path responses and the self-interference.

75. The method of claim 68 further comprising adapting analog self-interference cancellation by receiving signal path response data, generating a first self-interference signal estimate, applying a first set of parameter values based on the first self-interference signal estimate, generating a second self-interference signal estimate using the first set of parameter values, and applying a second set of parameter values based on the second self-interference signal estimate.

77. The method of claim 71 wherein cancelling linear digital self-interference comprises estimating self-interference channel coefficients, wherein estimating self-interference channel coefficients includes selecting a subset of coefficients according to a coefficient selection algorithm.

78. The method of claim 71 wherein cancelling nonlinear digital self-interference comprises estimating nonlinear self-interference model coefficients, wherein estimating nonlinear self-interference model coefficients includes selecting a subset of coefficients according to a coefficient selection algorithm.