System and method for adaptive simultaneous transmit and receive leakage cancellation

• US 10,393,859 B2
• Filed: 10/17/2016
• Issued: 08/27/2019
• Est. Priority Date: 10/17/2016
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Marr, Harry B., Gianvittorio, John P., Caldwell, Jeffrey, Parker, Samuel E., Cangeme, John
• Primary Examiner(s): McGue, Frank J
• Application Number:
  US15/295,084
• Publication Number:
  US 20180106884A1
• Time in Patent Office: 1,044 Days
• Field of Search: 342 89
• CPC Class Codes: G01S 7/023 Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques auxiliary means for detecting or identifying radar signals or the like G01S7/021; means for anti-jamming G01S7/36
• CPC Class Codes: G01S 7/038 Feedthrough nulling circuits
• CPC Class Codes: G01S 7/292 Extracting wanted echo-signals
• CPC Class Codes: G01S 7/352 Receivers
• CPC Class Codes: G01S 7/354 Extracting wanted echo-signals Doppler systems G01S13/50
• CPC Class Codes: G01S 7/358 using I/Q processing

Abstract

Method and apparatus for leakage signal cancellation in a simultaneous transmit and receive RF system includes: generating a digital transmit signal for transmission from the system; receiving a receive signal produced by reflection of the transmit signal from an object or generated by a second RF system; adaptively filtering the transmit signal by an adaptive finite input response (FIR) filter; calculating filter coefficients for the adaptive FIR filter in real-time at a different sampling rate; adaptively inputting the calculated filter coefficients to the adaptive FIR filter to generate a cancellation signal in real-time; and applying the cancellation signal to the receive signal to cancel leakage in the receive signal to generate an optimum receive signal.

Claims

1. A method for leakage signal cancellation in a simultaneous transmit and receive RF system, the method comprising:

generating a digital transmit signal;

delaying the digital transmit signal by a FIFO to control the number of delayed clock cycles of the digital transmit signal;

converting the delayed digital signal to an analog transmit signal and transmitting the analog transmit signal from the system;

receiving a receive signal produced by reflection of the analog transmit signal from an object or generated by a second RF system;

adaptively filtering the digital transmit signal by an adaptive finite input response (FIR) filter;

converting a digital output signal of the adaptive FIR filter to analog domain to generate an analog cancellation signal;

calculating filter coefficients for the adaptive FIR filter in real-time;

adaptively inputting the calculated filter coefficients to the adaptive FIR filter;

adding the analog cancellation signal to the receive signal to generate an analog error signal for cancelling leakage in the receive signal;

converting the analog error signal to a digital error signal; and

using the digital error signal to calculate the filter coefficients for the adaptive FIR filter in real-time.

2. The method of claim 1, wherein said adaptively filtering the digital transmit signal is performed in a time domain.

3. The method of claim 1, wherein said adaptively filtering the digital transmit signal is performed in a frequency domain.

4. The method of claim 1, wherein said calculating the filter coefficients for the adaptive FIR filter comprises calculating a next filter coefficient in real-time as a function of a current filter coefficient, a frequency domain cancellation signal and a complex conjugate of a frequency domain of a down-sampled signal of the digital error signal.

5. The method of claim 4, wherein said next filter coefficient W(m+1) is computed as:

W(m+1)=W(m)+P(m)·

X*(m)·

E(m),

where W(m) is the current filter coefficient, E(m) is the frequency domain cancellation signal, X*(m) is the complex conjugate of the frequency domain of the down-sampled transmit signal, and P(m) is a variable coefficient that controls a convergence rate.

6. The method of claim 4, wherein said calculating the filter coefficients for the adaptive FIR filter comprises using a least squares method for the down-sampled signal to calculate the filter coefficients in real-time.

7. The method of claim 1, further comprising up-sampling the calculated filter coefficients before inputting the calculated filter coefficients to the adaptive FIR filter.

8. The method of claim 1, further comprising increasing a clock rate of an output signal of the adaptive FIR filter by a clock domain crossing circuit and converting the output signal to an analog signal to generate the analog cancellation signal.

9. The method of claim 1, further comprising down-sampling the digital error signal before calculating the filter coefficients for the adaptive FIR filter.

10. An apparatus for leakage signal cancellation in a simultaneous transmit and receive RF system comprising:

a digital waveform generator for generating a digital transmit signal;

a FIFO for delaying the digital transmit signal to control the number of delayed clock cycles of the digital transmit signal;

a first digital-to-analog converter (DAC) for converting the delayed digital signal to an analog transmit signal and transmitting the analog transmit signal from the system;

a receiver for receiving a receive signal produced by reflection of the analog transmit signal from an object or generated by a second RF system;

an adaptive finite input response (FIR) filter for adaptively filtering the digital transmit signal;

a second digital-to-analog converter (DAC) for converting a digital output signal of the adaptive FIR filter to analog domain to generate an analog cancellation signal;

a frequency domain adaptive filter (FDAF) circuit for calculating filter coefficients for the adaptive FIR filter in real-time and adaptively inputting the calculated filter coefficients to the FIR filter;

an adder for adding the analog cancellation signal to the receive signal to generate an analog error signal for cancelling leakage in the receive;

an analog-to-digital converter (ADC) for converting the analog error signal to a digital error signal;

wherein the FDAF circuit uses the digital error signal to calculate the filter coefficients for the adaptive FIR filter in real-time.

11. The apparatus of claim 10, wherein said adaptive FIR filter operates in a time domain, or in a frequency domain.

12. The apparatus of claim 10, wherein the FDAF circuit calculates the filter coefficients for the adaptive FIR filter as a function of a current filter coefficient, a frequency domain cancellation signal and a complex conjugate of a frequency domain of a down-sampled signal of the digital error signal.

13. The apparatus of claim 12, wherein said next filter coefficient W(m+1) is computed by the FDAF circuit as:

W(m+1)=W(m)+P(m)·

X*(m)·

E(m),

where W(m) is the current filter coefficient, E(m) is the frequency domain cancellation signal, X*(m) is the complex conjugate of the frequency domain of the down-sampled transmit signal, and P(m) is a variable coefficient that controls a convergence rate.

14. The apparatus of claim 10, wherein the FDAF circuit uses a least squares method for the down-sampled signals to calculate the filter coefficients in real-time.

15. The apparatus of claim 10, further comprising an up-sampling circuit for up-sampling the calculated filter coefficients before inputting the calculated filter coefficients to the adaptive FIR filter.