SYSTEMS AND METHODS FOR CANCELLING INTERFERENCE USING MULTIPLE ATTENUATION DELAYS

• US 20130301488A1
• Filed: 06/07/2013
• Published: 11/14/2013
• Est. Priority Date: 02/08/2012
• 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: Mehlman, Jeff, Bharadia, Dinesh, Katti, Sachin, HONG, STEVEN
• Granted Patent: US 9,331,737 B2
• Time in Patent Office: Days
• US Class Current: 370/278
• 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

Abstract

A wireless communication device includes, in part, at least one antenna for receiving or transmitting a signal, and a cancelation circuit adapted to cancel or reduce the self-interference signal. The cancelation circuit includes, in part, a control block, N delay and attenuation paths, a combiner, and a subtractor. Each path includes a delay element and a variable attenuator whose attenuation level varies in response to a control signal generated by the control block. Each path receives a sample of the transmit signal and generates a delayed and attenuated (weighted) version of the sample signal. The combiner combines the N delayed and weighted versions of the sample signal to construct a signal representative of the self-interference signal. The subtractor subtracts the constructed signal from the received signal thereby the cancel or reduce the self-interference signal therefrom.

Claims

1. A wireless communication device comprising:

at least one antenna for receiving or transmitting a signal;

a cancellation circuitry adapted to receive a first sample of a transmit signal, said cancellation circuitry comprising;

a control block;

N paths each comprising a delay element and an associated variable attenuator whose attenuation level varies in response to the control block, each path receiving the first sample of the transmit signal and generating a delayed and weighted version of the first sample of the transmit signal;

a combiner adapted to combine the N delayed and weighted versions of first sample of the transmit signal to construct a signal representative of a first portion of a self-interference signal; and

a subtractor adapted to subtract the constructed signal from the received signal, wherein N is an integer greater than or equal to 2.

2. The wireless communication device of claim 1 wherein a delay element disposed in a first one of the paths generates a delay shorter than an arrival time of a second sample of the transmit signal at the subtractor, and wherein a delay element disposed in a second one of the paths associated with the first path generates a delay longer than the arrival time of the second sample of the transmit signal at the subtractor.

3. The wireless communication device of claim 1 wherein said N paths comprise 2M paths forming M associated pairs of delay paths, the delays generated by the delay elements of each associated pair of delay paths forming a window within which the second sample of the transmit signal arrives at the subtractor.

4. The wireless communication device of claim 3 wherein N is equal to 2M.

5. The wireless communication device of claim 3 wherein said controller determines the attenuation levels of the variable attenuators in accordance with values of intersections of an estimate of the self-interference signal and 2M sinc functions centered at boundaries of the M windows.

6. The wireless communication device of claim 5 wherein a peak value of at least a subset of the 2M sinc functions is set substantially equal to an amplitude of the estimate of the self-interference signal.

7. The wireless communication device of claim 1 wherein said cancellation circuitry further comprises:

a splitter adapted to generate the sampled transmit signal in response to the transmit signal.

8. The wireless communication device of claim 7 wherein said subtractor is a balun.

9. The wireless communication device of claim 8 further comprising:

an isolator having a first port coupled to the antenna, a second port coupled to a transmit line of the wireless communication device, and a third port coupled to a receive line of the wireless communication device.

10. The wireless communication device of claim 9 wherein said isolator is a circulator.

11. The wireless communication device of claim 1 further comprising:

a frequency downconverter configured to downconvert an output signal of the subtractor;

a filter adapted to filter out unselected portions of the downconverted signal; and

an analog-to-digital converter adapted to convert an output signal of the filter to a digital signal.

12. The wireless communication device of claim 11 further comprising:

a processing engine configured to remove a second portion of the self-interference signal from the output signal of the analog-to-digital converter.

13. The wireless communication device of claim 12 wherein said processing engine comprises a plurality of programmable filters.

14. The wireless communication device of claim 11 further comprising:

a frequency upconverter configured to upconvert a transmit signal;

a filter adapted to filter out unselected portions of the upconverted signal; and

a digital-to-analog converter adapted to convert an output signal of the filter to an analog signal.

15. A method of canceling or reducing a self-interference signal, the method comprising:

receiving a first sample of a transmit signal at a receiver;

generating N delayed versions of the first sample of the transmit signal;

attenuating the N delayed signals to generate N attenuated and delayed signals;

combining the N attenuated and delayed signals to generate a combined signal representative of a first portion of a self-interference signal; and

subtracting the combined signal from the received signal.

16. The method of claim 15 further comprising:

setting a first delay forming a first one of the N delayed versions of the first sample of the transmit signal to a value less than an arrival time of a second sample of the transmit signal;

setting a second delay forming a second one of the N delayed versions of the first sample of the transmit signal to a value greater than the arrival time of the second sample of the transmit signal.

17. The method of claim 15 further comprising:

forming M time windows;

selecting the N delays such that the arrival time of the second sample of the transmit signal falls within each of the M time windows.

18. The method of claim 17 wherein N is equal to 2M.

19. The method of claim 17 further comprising:

attenuating the N delayed signals in accordance with values of intersections of an estimate of the self-interference signal and 2M sinc functions centered at boundaries of the M windows.

20. The method of claim 19 further comprising:

setting a peak value of at least a subset of the 2M sinc functions substantially equal to an amplitude of the estimate of the self-interference signal.

21. The method of claim 15 further comprising:

receiving the first sample of the transmit signal from a splitter.

22. The method of claim 21 further comprising:

subtracting the combined signal from the received signal via a balun.

23. The method of claim 22 further comprising:

coupling a first port of an isolator to an antenna used by the receiver to receive signals;

coupling a second port of the isolator to the receiver; and

coupling a third port of the isolator to a transmitter causing self-interference at the receiver.

24. The method of claim 23 wherein said isolator is a circulator.

25. The method of claim 15 further comprising:

downconverting the difference between the combined signal and the received signal to generate a downconverted signal;

filtering out unselected portions of the downconverted signal; and

converting the filtered signal to a digital signal.

26. The method of claim 25 further comprising:

removing a second portion of the self-interference signal from the converted digital signal.

27. The method of claim 26 further comprising:

removing a second portion of the self-interference signal from the converted digital signal using a plurality of programmable filters.

28. The method of claim 25 further comprising:

upconverting a transmit signal;

filtering out unselected portions of the upconverted signal; and

converting the filtered signal to an analog signal.