Systems and methods for cancelling interference using multiple attenuation delays

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;

a subtractor;

N paths, each path 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; wherein a delay element disposed in a first one of the N paths generates a delay shorter than a self-interference arrival time, and wherein a delay element disposed in a second one of the N paths generates a delay longer than the self-interference arrival time; wherein the self-interference arrival time is a delay between arrival of a second sample of a transmit signal at the cancellation circuitry and arrival of a corresponding self-interference signal at the subtractor; wherein the corresponding self-interference signal comprises self-interference resulting from transmission of the second 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;

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

2. 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 corresponding self-interference signal arrives at the subtractor.

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

4. The wireless communication device of claim 2 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.

5. The wireless communication device of claim 4 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.

6. 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.

7. The wireless communication device of claim 6 wherein said subtractor is a balun.

8. The wireless communication device of claim 7 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.

9. The wireless communication device of claim 8 wherein said isolator is a circulator.

10. The wireless communication device of claim 1 further a 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.

11. The wireless communication device of claim 10 further

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

12. The wireless communication device of claim 11 wherein said processing engine comprises a plurality of programmable filters.

13. The wireless communication device of claim 10 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.

14. 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;

subtracting the combined signal from a received signal;

setting a first delay, corresponding to a first one of the N delayed versions of the first sample of the transmit signal, to a value less than a self-interference arrival time; and

setting a second delay, corresponding to a second one of the N delayed versions of the first sample of the transmit signal, to a value greater than the self-interference arrival time;

wherein the self-interference arrival time is a delay between arrival of a second sample of a transmit signal at the cancellation circuitry and arrival of a corresponding self-interference signal at the subtractor; wherein the corresponding self-interference signal comprises self-interference resulting from transmission of the second sample of the transmit signal.

15. The method of claim 14 further comprising:

forming M time windows;

selecting the N delays such that the self-interference arrival time falls within each of the M time windows.

16. The method of claim 15 wherein N is equal to 2M.

17. The method of claim 15 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.

18. The method of claim 17 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.

19. The method of claim 14 further comprising:

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

20. The method of claim 19 further comprising:

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

21. The method of claim 20 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.

22. The method of claim 21 wherein said isolator is a circulator.

23. The method of claim 14 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.

24. The method of claim 23 further comprising:

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

25. The method of claim 24 further comprising:

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

26. The method of claim 23 further comprising:

upconverting a transmit signal;

filtering out unselected portions of the upconverted signal; and

converting the filtered signal to an analog signal.