Apparatus and method for synchronizing nonlinear systems using filtered signals

• US 5,655,022 A
• Filed: 09/29/1995
• Issued: 08/05/1997
• Est. Priority Date: 09/29/1995
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Carroll, Thomas L.
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US08/536,027
• Time in Patent Office: 676 Days
• Field of Search: 380/28, 380/46, 380/48
• US Class Current: 380/263
• CPC Class Codes: H04L 27/001 using chaotic signals for secret or secure communication H04L9/001
• CPC Class Codes: H04L 7/027 extracting the synchronising or clock signal from the received signal spectrum, e.g. by using a resonant or bandpass circuit

Abstract

A filtered cascaded synchronized nonlinear system includes a nonlinear transmitter having stable first and second subsystems. The first subsystem produces a first transmitter signal for driving the second subsystem, and the second subsystem produces a second transmitter signal for driving the first subsystem. A first filter filters the second transmitter signal to produce a filter output signal. A subtractor subtracts the filter output signal from the second transmitter signal to produce a transmitter output signal which is transmitted to a nonlinear cascaded receiver. The receiver includes an adder for summing the received transmitter output signal with a receiver filter output signal to restore frequencies that were subtracted from the second transmitter signal in order to produce a first receiver drive signal. The receiver includes cascaded third and fourth subsystems that are respective duplicates of the first and second subsystems. The third subsystem is driven by the first receiver drive signal to produce a first receiver signal in synchronization with the first transmitter signal. The fourth subsystem is driven by the first receiver signal to produce a second receiver signal in synchronization with the second transmitter signal. A second filter filters the second receiver signal to produce the receiver filter output signal.

Claims

1. A filtered cascaded synchronized nonlinear system comprising:

a nonlinear transmitter comprising;

stable first and second subsystems, said first subsystem producing a first transmitter signal for driving said second subsystem, and said second subsystem producing a second transmitter signal for driving said first subsystem;

first means for filtering the second transmitter signal to produce a filter output signal; and

second means responsive to the second transmitter signal and the filter output signal for producing a transmitter output signal; and

a nonlinear cascaded receiver comprising;

third and fourth cascaded subsystems being respective duplicates of said first and second subsystems;

third means responsive to the transmitter output signal from said second means and to a receiver filter output signal for producing a first receiver drive signal to drive said third subsystem to produce a first receiver signal in synchronization with the first transmitter signal to drive said fourth subsystem;

said fourth subsystem being responsive to the first receiver signal for producing a second receiver signal in synchronization with the second transmitter signal; and

fourth means responsive to said second receiver signal for producing the receiver filter output signal.

2. The filtered cascaded synchronized nonlinear system of claim 1 wherein:

at least part of said first subsystem is external to said second subsystem, and at least part of said second subsystem is external to said first subsystem.

3. The filtered cascaded synchronized nonlinear system of claim 1 wherein:

said second means is a subtractor for subtracting the filter output signal from the second transmitter signal to produce the transmitter output signal;

said third means is an adder for summing the receiver filter output signal with the transmitter output signal to produce the first receiver drive signal; and

each of said first and fourth means is a filter.

4. The filtered cascaded synchronized nonlinear system of claim 1 wherein:

said nonlinear transmitter further includes;

first periodic forcing means for respectively providing phase coherent, periodic first and second forcing signals to said first and second subsystems to force said first and second subsystems to oscillate, at least one of the first and second forcing signals having a non-zero value; and

said nonlinear receiver further includes;

second periodic forcing means for respectively providing phase coherent, periodic third and fourth forcing signals to said third and fourth subsystems to force said third and fourth subsystems to oscillate, all of said first, second, third and fourth forcing signals being phase coherent with each other; and

phase control means being responsive to the first receiver drive signal and the second receiver signal for producing and applying an error signal to said second periodic forcing means, the error signal being proportional to the phase difference between said second periodic forcing means and said first periodic forcing means, said second periodic forcing means being responsive to the error signal for matching the phase of the second periodic forcing means to the phase of said first periodic forcing means, said nonlinear receiver becoming synchronized to the nonlinear transmitter when the phase of the second periodic forcing means in said nonlinear receiver matches the phase of the first periodic forcing means in said nonlinear transmitter.

5. The filtered cascaded synchronized nonlinear system of claim 4 wherein:

said nonlinear receiver is synchronized to said nonlinear transmitter when the second receiver signal matches the first receiver drive signal.

6. A filtered cascaded synchronized nonlinear system comprising:

a nonlinear transmitter comprising;

stable first and second subsystems, said first subsystem producing a first transmitter signal for driving said second subsystem, and said second subsystem producing a second transmitter signal for driving said first subsystem;

first means for removing undesired frequencies from the second transmitter signal to produce a transmitter output signal;

a nonlinear cascaded receiver comprising;

third and fourth cascaded subsystems being respective duplicates of said first and second subsystems;

second means responsive to the transmitter output signal from said first means and to a receiver filter output signal for producing a first receiver drive signal to drive said third subsystem to produce a first receiver signal in synchronization with the first transmitter signal to drive said fourth subsystem;

said fourth subsystem being responsive to the first receiver signal for producing a second receiver signal in synchronization with the second transmitter signal; and

third means responsive to said second receiver signal for producing the receiver filter output signal, the receiver filter output signal corresponding to the undesired frequencies removed from the second transmitter signal.

7. The filtered cascaded synchronized nonlinear system of claim 6 wherein said first means comprises:

fourth means for filtering the second transmitter signal to produce a filter output signal; and

fifth means responsive to the second transmitter signal and the filter output signal for producing the transmitter output signal.

8. The filtered cascaded synchronized nonlinear system of claim 6 wherein said first means comprises:

a communications channel for removing undesired frequencies from the second transmitter signal to produce and transmit the transmitter output signal to said second means.

9. The filtered cascaded synchronized nonlinear system of claim 6 wherein:

at least part of said first subsystem is external to said second subsystem, and at least part of said second subsystem is external to said first subsystem.

10. The filtered cascaded synchronized nonlinear system of claim 7 wherein:

said fifth means is a subtractor for subtracting the filter output signal from the second transmitter signal to produce the transmitter output signal;

said second means is an adder for summing the receiver filter output signal with the transmitter output signal to produce the first receiver drive signal; and

each of said third and fourth means is a filter.