Self-interference cancellation in frequency division duplexing system

1. A communication device comprising:

an antenna configured to receive a receive signal in a receive frequency band and transmit a transmit signal in a transmit frequency band;

transmit path circuitry configured to generate the transmit signal, the transmit path circuitry comprising a digital pre-distorter (DPD), a digital to analog converter (DAC), and a power amplifier (PA);

receive path circuitry configured to process the receive signal, the receive path circuitry including a first analog to digital converter (ADC) configured to convert the receive signal from an analog receive signal to a digital receive signal;

coupled path circuitry comprising a coupler, a band rejection filter, a second ADC, a first switch, a second switch, and a third switch; and

self-interference cancellation circuitry,

wherein the coupler is configured to couple a sample of the transmit signal to the first switch, the first switch is configured to connect the coupler switchably to an input of the band rejection filter and the second switch, the second switch is configured to connect an input of the second ADC switchably to the first switch and an output of the band rejection filter, the third switch is configured to connect an output of the second ADC switchably to the self-interference cancellation circuitry and the DPD, the band rejection filter is configured to reject frequencies in the transmit frequency band from the sample of the transmit signal to generate a filtered sample of the transmit signal, the second ADC is configured to convert the filtered sample of the transmit signal from an analog sample of the transmit signal to a digital sample of the transmit signal based on the second ADC being connected to the output of the band rejection filter and to the self-interference cancellation circuitry, and the second ADC is further configured to convert the sample of the transmit signal from an analog sample of the transmit signal to the digital sample of the transmit signal based on being connected to the first switch and to the DPD,

wherein the self-interference cancellation circuitry is configured to:

process the digital sample of the transmit signal that is output by the second ADC by equalizing the digital sample of the transmit signal to the digital receive signal to generate a self-interference cancellation signal; and

apply the self-interference cancellation signal to the digital receive signal that is output by the first ADC to cancel an amount of interference induced in the receive signal by the transmit signal, and

wherein the DPD is configured to generate a pre-distorted digital transmit signal based on the digital sample of the transmit signal, the DAC is configured to convert the pre-distorted digital transmit signal into a pre-distorted analog transmit signal, and the PA is configured to amplify the pre-distorted analog transmit signal to generate the transmit signal.

2. The communication device of claim 1 , wherein the self-interference cancellation circuitry is configured to equalize the digital sample of the transmit signal to the digital receive signal by determining time domain equalizer coefficients based on a first channel response of the receive path circuitry and a second channel response of the coupled path circuitry, and applying the time domain equalizer coefficients to the digital sample of the transmit signal to generate the self-interference cancellation signal.

3. The communication device of claim 1 , further comprising a duplexer operably connected to the antenna and configured to provide isolation between the receive frequency band and the transmit frequency band to reduce a first amount of the interference induced in the receive signal by the transmit signal, the duplexer further configured to receive the transmit signal from the transmit path circuitry and to output the receive signal to the receive path circuitry.

4. The communication device of claim 3 , wherein:

the duplexer is operably connected to the transmit path circuitry and the receive path circuitry, the duplexer further configured to reduce a total amount of power going into the receive path circuitry to guarantee that the receive path circuitry is working in a linear range of the receive path circuitry, and

applying the self-interference cancellation signal to the digital receive signal cancels the interference induced in the receive signal to a noise floor in case that a nonlinearity component generated in the receive path circuitry is less than the noise floor.

5. The communication device of claim 1 , wherein the receive path circuitry further comprises a bandpass filter configured to reject frequencies outside of the receive frequency band from the analog receive signal before input to the first ADC.

6. The communication device of claim 5 , wherein:

based on the receive path circuitry being equipped with intermediate frequency (IF) sampling receiver architecture, the receive path circuitry further comprises a first downconverter configured to downconvert the analog receive signal from a radio frequency (RF) band to an IF band or a baseband before input to the bandpass filter,

the bandpass filter is an IF or baseband bandpass filter configured to reject frequencies outside of a target downconversion bandwidth from the downconverted analog receive signal, and

the coupled path circuitry further comprises a second downconverter and a second IF or baseband bandpass filter, the second downconverter configured to downconvert the analog sample of the transmit signal from the RF band to the IF band or the baseband, the second IF or baseband bandpass filter configured to reject frequencies outside of a second target downconversion bandwidth from the downconverted analog sample of the transmit signal before input to the second ADC.

7. The communication device of claim 1 , wherein the coupled path circuitry further includes an amplifier configured to amplify the filtered sample of the transmit signal before input to the second ADC.

8. A method of self-interference cancellation in a communication device, comprising:

generating, by transmit path circuitry, a transmit signal to be transmitted through an antenna in a transmit frequency band;

receiving, via the antenna, a receive signal in a receive frequency band;

converting, by a first analog to digital converter (ADC) in a receive path circuitry, the receive signal from an analog receive signal to a digital receive signal;

connecting, using a first switch, a band rejection filter in a coupled path circuitry to the transmit path circuitry, connecting, using a second switch, the band rejection filter to a second ADC in the coupled path circuitry, connecting, using a third switch, the second ADC to a self- interference cancellation circuitry, rejecting, by the band rejection filter, frequencies in the transmit frequency band from a sample of the transmit signal to generate a filtered sample of the transmit signal, and converting, by the second ADC, the filtered sample of the transmit signal from an analog sample of the transmit signal to a digital sample of the transmit signal based on the second ADC being connected to the band rejection filter and the self-interference cancellation circuitry;

processing, by the self-interference cancellation circuitry, the digital sample of the transmit signal by equalizing the digital sample of the transmit signal to the digital receive signal to generate a self-interference cancellation signal; and

applying, by the self-interference cancellation circuitry, the self-interference cancellation signal to the digital receive signal to cancel an amount of interference induced in the receive signal by the transmit signal,

wherein the method further comprises:

generating, by a digital pre-distorter (DPD), a pre-distorted digital transmit signal based on the digital sample of the transmit signal;

converting, by a digital to analog converter (DAC), the pre-distorted digital transmit signal into a pre-distorted analog transmit signal;

amplifying, by a power amplifier (PA), the pre-distorted analog transmit signal to generate the transmit signal; and

bypassing, using the first switch and the second switch, the band rejection filter such that the sample of the transmit signal is provided to the second ADC, connecting, using the third switch, the second ADC to the DPD, and converting, by the second ADC, the sample of the transmit signal from an analog sample of the transmit signal to the digital sample of the transmit signal based on the band rejection filter being bypassed and the second ADC being connected to the DPD.

9. The method of claim 8 , further comprising:

equalizing, by the self-interference cancellation circuitry, the digital sample of the transmit signal to the digital receive signal by determining time domain equalizer coefficients based on a first channel response of the receive path circuitry and a second channel response of the coupled path circuitry; and

applying by the self-interference cancellation circuitry, the time domain equalizer coefficients to the digital sample of the transmit signal to generate the self-interference cancellation signal.

10. The method of claim 8 , further comprising:

providing, by a duplexer operably connected to the antenna, isolation between the receive frequency band and the transmit frequency band to reduce a second amount of the interference induced in the receive signal by the transmit signal;

receiving, by the duplexer, the transmit signal from the transmit path circuitry; and

outputting, by the duplexer, the receive signal to the receive path circuitry.

11. The method of claim 10 ,

wherein the duplexer is operably connected to the transmit path circuitry and the receive path circuitry,

the method further comprising reducing, by the duplexer, a total amount of power going into the receive path circuitry to guarantee that the receive path circuitry is working in a linear range of the receive path circuitry, and

wherein applying the self-interference cancellation signal to the digital receive signal cancels the interference induced in the receive signal to a noise floor in case that a nonlinearity component generated in the receive path circuitry is less than the noise floor.

12. The method of claim 8 , further comprising rejecting, by a bandpass filter, frequencies outside of the receive frequency band from the analog receive signal before input to the first ADC.

13. The method of claim 12 , further comprising:

based on the receive path circuitry being equipped with intermediate frequency (IF) sampling receiver architecture, downconverting, by a first downconverter, the analog receive signal from a radio frequency (RF) band to an IF band or a baseband before input to the bandpass filter;

rejecting, by the bandpass filter, frequencies outside of a target downconversion bandwidth from the downconverted analog receive signal, wherein the bandpass filter is an IF or baseband bandpass filter;

downconverting, by a second downconverter, the analog sample of the transmit signal from the RF band to the IF band or the baseband; and

rejecting, by a second IF or baseband bandpass filter, frequencies outside of a second target downconversion bandwidth from the downconverted analog sample of the transmit signal before input to the second ADC.

14. The method of claim 8 , further comprising amplifying, by an amplifier, the filtered sample of the transmit signal before the converting.