Chaotic communication system and method using modulation of nonreactive circuit elements

• US 20060072754A1
• Filed: 11/10/2005
• Published: 04/06/2006
• Est. Priority Date: 07/17/1998
• Status: Active Grant

• Current Assignee: Leidos, Inc. (Leidos Holdings, Inc.)
• Original Assignee: Science Applications International Corporation
• Inventors: Martin, Shannon W., Hinton, Daniel E. Sr., Berkley, Antwong L., Edwards, Michael C., Longtin, Laurance P., Bowser, Steven M., Dew, Nelson R., Gardner, Charles P.
• Granted Patent: US 7,245,723 B2
• Time in Patent Office: Days
• US Class Current: 380/263
• CPC Class Codes: H04L 27/001 using chaotic signals for secret or secure communication H04L9/001

Abstract

A chaotic communication system employs transmitting and receiving chaotic oscillating circuits. One improvement to first-generation systems is the ability to modulate a nonreactive element in the transmitting circuit, thus increasing modulation bandwidth. Other features include insertion of a gain control amplifier in a chaotic receiver; signal filtering in chaotic transmitters and receivers; use of chaotic modulation techniques for cellular telephony applications; dual-transmitter and receiver systems; a dual receiver synchronization detector; interfaces to communication systems; analog chaotic signal modulation; use of multiple chaotic transmitters and receivers; digital algorithm improvement using a cube-law nonlinear component; a Gb-only receiver; a Gb-only transmitter; and positive slope transmitter and receiver systems.

Claims

1. A chaotic receiver comprising:

an input terminal that receives a modulated chaotic signal;

an oscillator coupled to the input terminal;

a chaotic circuit comprising a capacitor and a negative resistance circuit;

a gain control amplifier coupled between the oscillator and the chaotic circuit, wherein the gain control amplifier amplifies a voltage present at the oscillator before it reaches the chaotic circuit;

a synchronizing resistor coupled between the input terminal and the chaotic circuit; and

a detection circuit, coupled to the synchronizing resistor, wherein the detection circuit detects periods of synchronization and non-synchronization between the modulated chaotic signal and the chaotic circuit and generates an output corresponding to periods of synchronization and non-synchronization.

2. A chaotic receiver, comprising:

an input terminal that receives a modulated chaotic signal;

an oscillator circuit coupled to the input terminal;

a first chaotic circuit coupled to the oscillator circuit and tuned to a first strange attractor;

a second chaotic circuit coupled to the oscillator circuit and tuned to a second strange attractor; and

means for detecting a difference between the modulated chaotic signal received at the input terminal and respective signals generated by the first and second chaotic circuits.

3. The chaotic receiver of claim 2, further comprising means for generating an absolute value of the difference signal.

4. A method of demodulating a signal modulated according to a chaotic trajectory shift-keying technique, comprising the steps of:

(1) receiving a modulated chaotic signal modulated according to a chaotic trajectory shift-keying technique;

(2) using the modulated chaotic signal to drive an oscillator;

(3) using the modulated chaotic signal and an output of the oscillator to drive a first chaotic circuit tuned to a first strange attractor;

(4) using the modulated chaotic signal and an output of the oscillator circuit to drive a second chaotic circuit tuned to a second strange attractor; and

(5) detecting a difference between the modulated chaotic signal and respective signals generated by the first and second chaotic circuits.

5. The method of claim 4, further comprising the step of:

(6) generating an absolute value signal from the difference detected in step (5).

6. A chaotic receiver, comprising:

an input terminal that receives a modulated chaotic signal;

an oscillator coupled to the input terminal;

a first chaotic circuit coupled to the oscillator and tuned to a first strange attractor;

a second chaotic circuit coupled to the oscillator circuit and tuned to a second strange attractor; and

a detector circuit coupled to the first and second chaotic circuits, wherein the detector circuit subtracts signals present at the first and second chaotic circuits and generates an absolute value signal based on the subtracted signal.

7. A method of demodulating a signal modulated according to a trajectory shift-keying technique, comprising the steps of:

(1) receiving a modulated chaotic signal;

(2) using the modulated chaotic signal to drive an oscillator circuit;

(3) using the modulated chaotic signal and an output of the oscillator circuit to drive a first chaotic circuit comprising a first nonlinear circuit element and tuned to a first strange attractor;

(4) using the modulated chaotic signal and an output of the oscillator circuit to drive a second chaotic circuit comprising a second nonlinear circuit element and tuned to a second strange attractor; and

(5) detecting a difference between first and second signals present at the first and second chaotic circuits, respectively, by subtracting the first and second signals and generating an absolute value thereof.

8. A chaotic receiver comprising:

an input terminal that receives a modulated chaotic signal;

an oscillator circuit coupled to the input terminal and driven by the modulated chaotic signal;

a chaotic circuit comprising an upper slope circuit that implements a first current-voltage function in an upper quadrant of a current-voltage response plane and a lower slope circuit that implements a second current-voltage function in a lower quadrant of the current-voltage response plane, wherein the first and second current-voltage functions have a different voltage offset, and wherein the upper and lower slope circuits cooperate with the oscillator circuit to generate a local chaotic signal;

a synchronizing circuit, coupled to the oscillator circuit and the chaotic circuit, wherein the synchronizing circuit detects differences between the modulated chaotic signal at the input terminal and the local chaotic signal; and

a detector coupled to the synchronizing circuit which detects periods of synchronization and non-synchronization.

9. The chaotic receiver of claim 8, wherein the upper and lower slope circuits each comprise a voltage source coupled to a negative resistance circuit.

10. The chaotic receiver of claim 8, wherein the upper and lower slope circuits each implement current-voltage functions having the same positive slope.

11. The chaotic receiver of claim 10, wherein each of the upper and lower slope circuits define asymptotically stable intersection points with a negative resistive load line.

12. A method of demodulating a chaotically modulated signal, comprising the steps of:

(1) receiving the chaotically modulated signal;

(2) applying the signal received in step (1) to an oscillator through a resistor that defines a load line;

(3) applying the signal applied to the oscillator in step (2) to first and second slope detector circuits each of which defines a linear current-voltage function that intercepts the load line in a different quadrant of a current-voltage plane;

(4) applying respective outputs of the first and second slope detector circuits to a synchronizing resistor circuit that generates voltage differences corresponding to differences between each respective slope detector circuit and the chaotically modulated signal received in step (1); and

(5) detecting an output from the synchronizing resistor circuit to provide a demodulated signal.

13. The method of claim 12, wherein step (4) comprises the step of using at least one slope detector circuit that satisfies the relation I=GbV−

GaVbp+GbVb, where I is the current through the slope detector circuit, Gb is a first slope constant, V is the voltage across the slope detector circuit, Ga is a second slope constant, and Vbp is a breakpoint voltage.

14. A method of demodulating a chaotically modulated signal, comprising the steps of:

(1) receiving the chaotically modulated signal;

(2) applying the signal received in step (1) to an oscillator through a resistor that defines a current-voltage load line;

(3) applying the signal applied to the oscillator in step (2) to a slope detector circuit that exhibits a current slope function opposite in polarity to that of the load line and which intersects the load line at an equilibrium point corresponding to an equilibrium point of a transmitter;

(4) generating a difference signal representing a difference between the chaotically modulated signal received in step (1) and the output of the slope detector circuit; and

(5) recovering an information signal on the basis of the difference signal generated in step (4).

15. The method of claim 14, wherein step (3) comprises the step of applying the signal applied to the oscillator in step (2) to a second slope detector circuit that exhibits a second current slope function opposite in polarity to that of the load line but which intersects the load line at a different equilibrium point;

and wherein step (4) comprises the step of generating a second difference signal representing a difference between the chaotically modulated signal received in step (1) and the output of the second slope detector circuit.