Two stage radio frequency interference cancellation system and method

• US 10,097,221 B1
• Filed: 12/04/2017
• Issued: 10/09/2018
• Est. Priority Date: 08/07/2008
• Status: Active Grant

• Current Assignee: Hypres, Inc.
• Original Assignee: Hypres, Inc.
• Inventors: Gupta, Deepnarayan, Inamdar, Amol
• Primary Examiner(s): Nguyen, Duc M
• Application Number:
  US15/831,209
• Time in Patent Office: 309 Days
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04B 1/109 by improving strong signal performance of the receiver when strong unwanted signals are present at the receiver input
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver
• CPC Class Codes: H04B 7/15585 by interference cancellation
• CPC Class Codes: H04L 27/01 Equalisers baseband equalizers at the transmitter end H04L25/03343; in analogue transmission systems H04B3/04, H04B7/005

Abstract

A radio frequency receiver subject to a large in-band interferor employs active cancellation with coarse and at least one fine cancellation signal, each with a respective radio frequency combiner, in order to increase the effective dynamic range of the receiver for weak signals of interest. One or both can be digitally synthesized. This is particularly applicable for co-site interference, whereby the interfering transmit signal is directly accessible. A similar system and method may also be applied to external interferors such as those produced by deliberate or unintentional jamming signals, or by strong multipath signals. An adaptive algorithm may be used for dynamic delay and gain matching. In a preferred embodiment, a hybrid technology hybrid temperature system incorporates both superconducting and semiconducting components to achieve enhanced broadband performance.

Claims

1. A radio frequency interference cancelling system, comprising:

an input port configured to receive a plurality of radio frequency signals within a common radio frequency communication band;

a signal combiner, configured to receive the plurality of radio frequency signals within the common radio frequency communication band, and a cancellation signal, and produce a combined output signal;

a digitizer, configured to generate a digitized stream of data representing an amplitude of the combined output signal;

an adaptive signal cancellation processor, configured to;

generate the cancellation signal according to a set of estimated phase and amplitude characteristics of at least one of the radio frequency signals within the common radio frequency communication band; and

iteratively estimate the phase and amplitude characteristics of at least one of the radio frequency signals within the common radio frequency communication band based on at least a correlation of a signal represented in the digitized stream of data and the estimated phase and amplitude characteristics of the at least one of the radio frequency signals, wherein in subsequent iterations, the estimated phase and amplitude characteristics of at least one of the radio frequency signals within the common radio frequency communication band are modified to minimize a mean correlation; and

a demodulator configured to demodulate information from the digitized stream of data.

2. The system according to claim 1, wherein the adaptive signal cancellation processor comprises a waveform lookup table and a digital to analog converter driven in dependence on a content of the lookup table (LUT).

3. The system according to claim 2, wherein the adaptive signal cancellation processor comprises an upper lookup table (LUT) and a lower lookup table (LUT), each having an associated gain, and is configured to adapt the respective lookup table gains according to an algorithm:

initialize the upper LUT with a positive number corresponding to the maximum possible gain that can be implemented in the LUT;

initialize the lower LUT with a negative number corresponding to the maximum possible attenuation that can be implemented in the LUT;

define a current LUT gain which is an arithmetic mean of the upper LUT gain and the lower LUT gain;

if the correlation mean is positive and lower than any previous positive correlation mean, update the Lower LUT gain to the current LUT gain; and

if the correlation mean is negative and higher than any previous negative correlation mean, update the Upper LUT gain to the current LUT gain,

to thereby iteratively reduce a window between the upper LUT gain and the lower LUT gain, to optimize the current LUT gain such that the mean correlation tends toward zero.

4. The system according to claim 1, wherein the digitizer samples at a rate of at least 16 GHz, and the combined signal output comprises a decimated output.

5. The system according to claim 1, wherein the signal combiner operates substantially without introducing distortion.

6. The system according to claim 1, wherein the signal comprises a magnetic flux subtractor.

7. The system according to claim 1, wherein the cancellation signal is generated based on a model of the interfering radio frequency signal.

8. The system according to claim 7, wherein the model comprises a set of digital parameters in at least one lookup table representing a respective waveform of at least one radio frequency signal.

9. The system according to claim 1, further comprising a limiter between the signal combiner and the digitizer.

10. The system according to claim 1, wherein the digitizer is saturable by the plurality of radio frequency signals within the common radio frequency communication band, and the adaptive signal cancellation processor is configured to initiate production of the cancellation signal in a state where the digitizer is saturated by the plurality of radio frequency signals within the common radio frequency communication band to allow demodulation of the information from the digitized stream of data by the demodulator.

11. The system according to claim 1, further comprising an antenna, configured to receive the plurality of radio frequency signals within the common radio frequency communication band, and an input from a transmitter representing at least one of the plurality of radio frequency signals.

12. A method of cancelling radio frequency interference, comprising:

receiving a plurality of radio frequency signals within a common radio frequency communication band;

combining the plurality of radio frequency signals within the common radio frequency communication band, and a cancellation signal, and producing a combined output signal;

digitizing an amplitude of the combined output signal to produce a digitized stream of data;

adaptively generating the cancellation signal according to a set of estimated phase and amplitude characteristics of at least one of the radio frequency signals within the common radio frequency communication band, and iteratively estimating the phase and amplitude characteristics of at least one of the radio frequency signals within the common radio frequency communication band based on at least a correlation of a signal represented in the digitized stream of data and the estimated phase and amplitude characteristics of the at least one of the radio frequency signals, wherein in subsequent iterations, the estimated phase and amplitude characteristics of at least one of the radio frequency signals within the common radio frequency communication band are modified to minimize a mean correlation; and

demodulating information from the digitized stream of data.

13. The method according to claim 12, wherein the cancellation signal is generated by a digital to analog converter based on a content of a lookup table (LUT).

14. The method according to claim 13, wherein said adaptively generating employs an upper lookup table (LUT) and a lower lookup table (LUT), each having an associated gain, and comprises:

initializing the upper LUT with a positive number corresponding to the maximum possible gain that can be implemented in the LUT;

initializing the lower LUT with a negative number corresponding to the maximum possible attenuation that can be implemented in the LUT;

defining a current LUT gain which is an arithmetic mean of the upper LUT gain and the lower LUT gain;

if the correlation mean is positive and lower than any previous positive correlation mean, updating the Lower LUT gain to the current LUT gain; and

if the correlation mean is negative and higher than any previous negative correlation mean, updating the Upper LUT gain to the current LUT gain,

to thereby iteratively reduce a window between the upper LUT gain and the lower LUT gain, to optimize the current LUT gain such that the mean correlation tends toward zero.

15. The method according to claim 12, wherein said digitizing comprises decimating, and said combining comprises employing a magnetic flux subtractor which operates substantially without introducing distortion.

16. The method according to claim 12, wherein the cancellation signal is generated based on a model of the interfering radio frequency signal, wherein the model comprises a set of digital parameters in at least one lookup table representing a respective waveform of at least one radio frequency signal.

17. The method according to claim 12, further comprising amplitude limiting a signal between said combining and said digitizing.

18. A method for co-site interference suppression, comprising:

receiving a plurality of radio frequency signals in a radio frequency communication band through an antenna, comprising at least one radio frequency signal which is interfering with at least one other radio frequency signal, and for which concurrent waveform parameters are available;

combining the plurality of radio frequency signals, and a cancellation signal, to produce a combined output signal;

digitizing an amplitude of the combined output signal to produce a digitized stream of data;

adaptively generating the cancellation signal dependent on the concurrent waveform parameters, and iteratively estimating the phase and amplitude characteristics of the at least one radio frequency signal band based on at least a correlation of information represented in the digitized stream of data and the concurrent waveform parameters, wherein in subsequent iterations, the estimated phase and amplitude characteristics of at least one of the radio frequency signals are modified to minimize a mean correlation; and

demodulating information from at least one other radio frequency signal in the digitized stream of data.

19. The method according to claim 18, wherein said adaptively generating employs an upper lookup table (LUT) and a lower lookup table (LUT), each having an associated gain, and comprises:

initializing the upper LUT with a positive number corresponding to the maximum possible gain that can be implemented in the LUT;

initializing the lower LUT with a negative number corresponding to the maximum possible attenuation that can be implemented in the LUT;

defining a current LUT gain which is an arithmetic mean of the upper LUT gain and the lower LUT gain;

if the correlation mean is positive and lower than any previous positive correlation mean, updating the Lower LUT gain to the current LUT gain; and

if the correlation mean is negative and higher than any previous negative correlation mean, updating the Upper LUT gain to the current LUT gain,

to thereby iteratively reduce a window between the upper LUT gain and the lower LUT gain, to optimize the current LUT gain such that the mean correlation tends toward zero.

20. The method according to claim 18, further comprising amplitude limiting a signal between said combining and said digitizing.