Systems and methods for frequency-isolated self-interference cancellation

1. A system for frequency-isolated self-interference cancellation comprising:

a transmit coupler, communicatively coupled to a Radio Frequency (RF) transmit signal of a wireless communication system, that samples the RF transmit signal to create a sampled RF transmit signal having a first RF carrier frequency;

a frequency downconverter that converts the sampled RF transmit signal to an Intermediate Frequency (IF) transmit signal having an IF carrier frequency, wherein the IF carrier frequency is less than the first RF carrier frequency;

an RF self-interference canceller that transforms the sampled RF transmit signal to an RF self-interference cancellation signal;

an IF self-interference canceller that transforms the IF transmit signal to an IF self-interference cancellation signal;

a frequency upconverter that converts the IF self-interference cancellation signal to an IF-sourced RF self-interference cancellation signal;

a receive coupler, communicatively coupled to an RF receive signal of the wireless communication system, that combines the RF self-interference cancellation signal and the IF-sourced RF self-interference cancellation signal with the RF receive signal to form a reduced-interference receive signal; and

a frequency shifter.

2. The system of claim 1 , further comprising a delayer, located in a signal path between the RF self-interference canceller and the receive coupler, that delays the RF self-interference cancellation signal.

3. The system of claim 1 , wherein the frequency shifter is coupled to the reduced-interference receive signal and shifts the carrier frequency of the reduced-interference receive signal.

4. The system of claim 3 , further comprising a digital self-interference canceller.

5. The system of claim 4 , wherein the digital self-interference canceller transforms a digital transmit signal of the wireless communication system to a digital self-interference cancellation signal.

6. The system of claim 5 , further comprising a digital-to-analog converter; wherein the digital-to-analog converter converts the digital self-interference cancellation signal to a digitally-sourced RF self-interference cancellation signal; wherein the receive coupler combines the RF self-interference cancellation signal, and the digitally-sourced RF self-interference cancellation signal with the RF receive signal.

7. The system of claim 4 , further comprising an analog-to-digital converter; wherein the analog-to-digital converter converts the sampled RF transmit signal to a digitized RF transmit signal; wherein the digital self-interference canceller transforms a combination of a digital transmit signal and the digitized RF transmit signal to a digital self-interference cancellation signal.

8. The system of claim 4 , further comprising an analog-to-digital converter; wherein the analog-to-digital converter converts the sampled RF transmit signal to a digitized RF transmit signal; wherein the digital self-interference canceller transforms the digitized RF transmit signal to a digital self-interference cancellation signal.

9. The system of claim 8 , further comprising a digital-to-analog converter; wherein the digital-to-analog converter converts the digital self-interference cancellation signal to a digitally-sourced RF self-interference cancellation signal; wherein the receive coupler combines the RF self-interference cancellation signal and the digitally-sourced RF self-interference cancellation signal with the RF receive signal.

10. The system of claim 4 , wherein the carrier frequency shift is tunable and is set by a tuning circuit.

11. The system of claim 1 , wherein the frequency shifter is coupled to the RF receive signal and shifts the carrier frequency of the RF receive signal.

12. The system of claim 1 , wherein the frequency shifter is coupled to the RF transmit signal and shifts the carrier frequency of the RF transmit signal.

13. A method for frequency-isolated self-interference cancellation comprising:

receiving a Radio Frequency (RF) transmit signal of a wireless communications system;

transforming the RF transmit signal into an RF self-interference cancellation signal using an RF self-interference canceller;

frequency downconverting the RF transmit signal to an Intermediate Frequency (IF) transmit signal;

transforming the IF transmit signal into an IF self-interference cancellation signal using an IF self-interference canceller;

frequency upconverting the IF self-interference cancellation signal to an IF-sourced RF self-interference cancellation signal;

combining the RF self-interference cancellation signal and the IF-sourced RF self-interference cancellation signal with an RF receive signal of the wireless communications system to form a reduced-interference receive signal; and

shifting a carrier frequency of the reduced-interference receive signal.

14. The method of claim 13 further comprising:

receiving a digital transmit signal;

transforming the digital transmit signal into a digital self-interference cancellation signal;

converting the digital self-interference cancellation signal to a digitally-sourced RF self-interference cancellation signal; and

combining the digitally-sourced RF self-interference cancellation signal with the RF receive signal.

15. The method of claim 14 further comprising:

converting the RF transmit signal into a digitized RF transmit signal;

transforming the digitized RF transmit signal into a digital self-interference cancellation signal;

converting the digital self-interference cancellation signal to a digitally-sourced RF self-interference cancellation signal; and

combining the digitally-sourced RF self-interference cancellation signal with the RF receive signal.