Two stage radio frequency interference cancellation system and method

• US 8,249,540 B1
• Filed: 08/05/2009
• Issued: 08/21/2012
• 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:
  US12/535,843
• Time in Patent Office: 1,112 Days
• Field of Search: 455/295, 455/296, 455/304, 455/305, 455310-312
• US Class Current: 455/296
• 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 fine cancellation signals, 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 method to detect a radio frequency signal-of-interest in an input signal, that also includes at least one interference signal, comprising:

(a) generating a digital reference signal corresponding to the at least one interference signal in at least a waveform, a magnitude and a delay;

(b) converting the digital reference signal to a corresponding analog coarse cancellation signal;

(c) combining the input signal with the analog coarse cancellation signal in a coarse combiner to generate a coarse residue signal, wherein the interference signal is substantially cancelled and the signal-of-interest is substantially maintained;

(d) generating a fine cancellation signal, corresponding to a residual interference signal in the coarse residue in at least a waveform, a magnitude and a delay;

(e) combining the coarse residue signal with the fine cancellation signal in a fine combiner, to generate a fine residue signal, wherein the residual interference signal is substantially cancelled and the signal of interest is substantially maintained; and

(f) digitizing the fine residue signal and detecting the signal-of-interest.

2. The method according to claim 1, wherein the fine cancellation signal is an analog signal generated based on a second digital reference signal.

3. The method of claim 2, further comprising:

(a) digitally correlating the digitized fine residue signal with the second digital reference signal; and

(b) using the time-averaged digital correlation output to provide an adaptive feedback control of at least one of the magnitude and delay of the fine cancellation signal.

4. The method of claim 3, further comprising applying an iterative algorithm to adjust at least one of the magnitude and delay of the fine cancellation signal, in order to reduce the time-averaged digital correlation output toward zero.

5. The method of claim 1, wherein the digital reference signal is provided by the source signal of an interference signal transmitter.

6. The method of claim 5, wherein at least one of the analog coarse cancellation signal and the fine cancellation signal comprises a linear combination of plurality of representations of a signal having respectively different magnitudes and delays.

7. The method according to claim 1, wherein the at least one interference signal comprises multipath interference, and wherein the analog coarse cancellation signal comprises a plurality of representations of the digital reference signal differing in respective magnitude and delay.

8. The method of claim 1, wherein the fine residue signal is digitized using a superconducting analog to digital converter.

9. The method of claim 1, wherein the fine cancellation signal is generated based on a digital lookup table which is adaptively updated.

10. The method of claim 1, wherein at least a portion of a power of the coarse residue signal is restricted from the fine combiner when the power of the coarse residue signal exceeds a threshold.

11. The method of claim 1, wherein the fine residue signal is digitized with a digitizer having a dynamic range, the dynamic range being insufficient to detect the signal of interest in the input signal, wherein the magnitude and delay of the digital reference signal and the fine cancellation signal are adjusted such that the dynamic range of the digitizer is sufficient to detect the signal-of-interest remaining in the fine residue signal.

12. The method of claim 1, wherein the fine combiner comprises a transformer with at least three coils.

13. The method of claim 12, wherein the transformer comprises a superconducting component.

14. The method of claim 1, wherein the converting comprises analog filtering an oversampled digital pulse train.

15. The method of claim 1, wherein at least one of the coarse cancellation signal and the fine cancellation signal is selectively delayed using a discrete digital time delay.

16. A system adapted to detect a radio frequency signal-of-interest in an input signal, that also includes at least one interference signal, comprising:

(a) a coarse cancellation signal generator, producing a digital reference signal corresponding to the at least one interference signal in at least a waveform, a magnitude and a delay, which is converted to a corresponding analog coarse cancellation signal;

(b) a coarse combiner, adapted to combine the input signal with the analog coarse cancellation signal to generate a coarse residue signal, wherein the interference signal is substantially cancelled and the signal-of-interest is substantially maintained;

(d) a fine cancellation signal generator, producing a fine cancellation signal corresponding to a residual interference signal in the coarse residue in at least a waveform, a magnitude and a delay;

(e) a fine combiner, adapted to combine the coarse residue signal with the fine cancellation signal, to generate a fine residue signal, wherein the residual interference signal is substantially cancelled and the signal of interest is substantially maintained; and

(f) a digitizer adapted to digitize the fine residue signal from which the signal-of-interest is detectable.

17. The system according to claim 16, wherein the fine cancellation signal is an analog signal generated based on a second digital reference signal.

18. The system of claim 17, further comprising:

(a) a digital correlator adapted to correlate the digitized fine residue signal with the second digital reference signal; and

(b) an adaptive feedback control, using the time-averaged digital correlation output, to adjust at least one of the magnitude and delay of the fine cancellation signal.

19. The system of claim 18, further comprising a processor adapted to apply an iterative algorithm to adjust at least one of the magnitude and delay of the fine cancellation signal, in order to reduce the time-averaged digital correlation output toward zero.

20. The system of claim 16, wherein the digital reference signal is provided by the source signal of an interference signal transmitter.

21. The system of claim 20, wherein at least one of the analog coarse cancellation signal and the fine cancellation signal comprises a linear combination of plurality of representations of a signal having respectively different magnitudes and delays.

22. The system according to claim 16, wherein the at least one interference signal comprises multipath interference, and wherein the analog coarse cancellation signal comprises a plurality of representations of the digital reference signal differing in respective magnitude and delay.

23. The system of claim 16, wherein the digitizer comprises a superconducting analog to digital converter.

24. The system of claim 16, further comprising an adaptively updated a digital lookup table for generation of the fine cancellation signal.

25. The system of claim 16, further comprising a limited adapted to restrict at least a portion of a power of the coarse residue signal from the fine combiner when the power of the coarse residue signal exceeds a threshold.

26. The system of claim 16, wherein the digitizer has a dynamic range, the dynamic range being insufficient to detect the signal of interest in the input signal, wherein the magnitude and delay of the digital reference signal and the fine cancellation signal are adjusted such that the dynamic range of the digitizer is sufficient to detect the signal-of-interest remaining in the fine residue signal.

27. The system of claim 16, wherein the fine combiner comprises a transformer with at least three coils.

28. The system of claim 27, wherein the transformer comprises a superconducting component.

29. The system of claim 16, wherein the analog coarse cancellation signal generator comprises an analog filter adapted to filter an oversampled digital pulse train.

30. The system of claim 16, further comprising a discrete digital time delay adapted to selectively delay at least one of the coarse cancellation signal and the fine cancellation signal.

31. A receiver, comprising:

(a) an input adapted to receive an analog signal;

(b) a first combiner adapted to combine the analog signal with a first signal to produce a first combined signal with a reduced power of at least one interferor present in the analog signal;

(c) an overload protection device adapted to selectively block the first combined signal if it represents an overload condition, to produce an overload protected signal;

(d) a second combiner adapted to combine the overload protected signal, received by the second combiner substantially without introduction of intermodulation product of the analog signal and the first signal, with a second signal to produce a second combined signal; and

(e) a saturable detector, adapted to detect information within the second combined signal.

32. The receiver of claim 31, further comprising at least one of an analog amplifier, a digital amplifier, an analog filter, a digitizer, and a transformer.

33. The receiver of claim 32, wherein at least one of the analog amplifier, digital amplifier, analog filter, digitizer, transformer, overload protection device, and saturable detector operate at a cryogenic temperature below about 100 K.