Synchronizing system

• US 4,545,061 A
• Filed: 09/28/1962
• Issued: 10/01/1985
• Est. Priority Date: 09/28/1962
• Status: Expired due to Term

• Current Assignee: GTE Government Systems Corporation (General Dynamics Corporation)
• Original Assignee: Sylvania Electric Products Incorporated (Ams-Osram AG)
• Inventors: Hileman, Ronald E.
• Primary Examiner(s): Cangialosi, Salvatore
• Application Number:
  US04/226,945
• Time in Patent Office: 8,404 Days
• Field of Search: 328/133, 328/134, 325/32, 178/5.1, 331/25, 375/1, 375/2.2, 375/96, 375/119
• US Class Current: 375/373
• CPC Class Codes: H04B 1/707 using direct sequence modulation

Abstract

This invention relates generally to electronic communication systems, and more particularly to improved means for maintaining close time synchronism between remote stations in carrier dispersal radio communication systems of the spread spectrum type and other correlation communication systems.

Claims

1. In an electronic signal system utilizing at least two separately generated but identical signals, means for maintaining correlated synchronism between said signals which comprises the combination of:

means for periodically shifting the phase of one of said signals relative to the other, means for comparing said periodically shifted signal with the other;

a phase detector having first and second input terminals, first and second signal paths connected from said comparing means and to respective input terminals of said phase detector, said first signal path including periodically phase-reversing integration means and said second signal path including a reference integration means, and means responsive to the output of said phase detector for adjusting the phase of one of said signals in a direction to maintain correlation.

2. In the receiver of a communication system, means for synchronizing a received coded signal with a locally generated similarly coded second signal which comprises:

a comparison circuit, means for applying said received coded signal to said comparison circuit, means for periodically shifting said second coded signal in phase and applying it to said comparison circuit, a phase detector having first and second input terminals, first and second signal paths connected from said comparison circuit to respective input terminals of said phase detector, said first signal path including means for periodically reversing the phase of the output signal of said comparison circuit and means for subsequently integrating said output signal, and said second signal path including a reference integrating means, and means responsive to the output of said phase detector for adjusting the phase of said second coded signal in a direction to maintain correlation with said received coded signal.

3. In a communication system including means for separately generating at least two independent identical coded signals, a comparison circuit, means for applying said coded signals to said comparison circuit, and time searching means responsive to the output of said comparison circuit to bring one of said coded signals into time synchronism with the other, means for maintaining time synchronism between said two coded signals which comprises the combination of:

means for periodically shifting the phase of one of said coded signals relative to the other, a phase detector having first and second input terminals, first and second signal paths connected from said comparison circuit to respective input terminals of said phase detector, said first signal path including means for reversing the phase of the output signal of said comparison circuit in synchronism with said phase-shifting means and a first resonant integrating circuit tuned to the intermediate frequency of said comparison circuit, said second signal path including a second resonant integrating circuit tuned to the aforesaid intermediate frequency, and means responsive to the output of said phase detector for adjusting the time position of one of said coded signals toward perfect synchronism with the other.

4. In a binary code pulsed carrier communication system receiver including a radio frequency energy reception circuit, a mixer circuit connected to said reception circuit, an intermediate frequency amplifier connected to said mixer, a local oscillator, a local binary code pulse generator, a modulator, means connecting said local oscillator and pulse generator to said modulator, means connecting the output of said modulator to said mixer, and time searching means responsive to the output of said intermediate frequency amplifier for synchronizing said local pulse code with a received pulse code having the same structure as the local pulse code, apparatus for maintaining time synchronism between said two sequences which comprises the combination of:

a phase-shifting circuit arranged periodically to change the phase timing of the output of said local pulse generator, a phase detector having first and second input terminals, first and second signal paths connected between the output of said intermediate frequency amplifier and respective input terminals of said phase detector, said first signal path including a phase-reversing switch synchronized with said periodic phase-shifting circuit and a first matched filter tuned to the intermediate frequency of said mixer, said second signal path including a second matched filter also tuned to said intermediate frequency, and a control circuit operative in response to signals from said phase detector for adjusting the time position of the output of said pulse generator.

5. Apparatus in accordance with claim 4 wherein said first and second matched filters are integrate and dump filters, and means for quenching said filters at the end of each cycle of said phase reversing switch.

6. Apparatus in accordance with claim 5 wherein said phase-reversing switch comprises a transformer having a primary winding and a center-tapped secondary winding, means coupling the output of said local pulse generator to said primary winding, and means for alternately connecting the terminals of said secondary winding to a point of reference potential.

7. Apparatus in accordance with claim 6 wherein said first and second signal paths further include respective first and second saturating amplifiers for respectively amplifying the smaller signals and clipping the larger signals from said first and second integrate and dump filters.

8. Apparatus in accordance with claim 7 wherein said control circuit comprises a clock circuit for driving said pulse generator, and a decision circuit operative in response to output signals from said phase detector to shift the frequency of said clock.

9. Apparatus in accordance with claim 7 wherein said control circuit comprises a source of drive pulses for said pulse generator, and a decision circuit operative in response to output signals from said phase detector to shift the phase of said drive pulses.

10. In a radio communication system including a transmitter for producing a carrier signal modulated with a pulse code sequence, and a receiver including means for intercepting said carrier signal, means for providing a local radio frequency signal, means for modulating said local signal with a pulse code sequence identical in structure to the modulation of the carrier signal, and a common mixer circuit for comparing said intercepted and locally modulated signals, apparatus for maintaining time synchronism between said intercepted and local code sequences which comprises:

means for periodically shifting the phase of said local sequence, a phase detector having first and second input terminals, first and second signal paths connected between said mixer circuit and respective input terminals of said phase detector, said first signal path including a phase-reversing switch synchronized with said means for periodically shifting the phase of said local sequence, and a first resonant filter tuned to the intermediate frequency of said mixer, said second signal path including a second resonant filter also tuned to said intermediate frequency, means for quenching said first and second filters at the end of each cycle of said phase-reversing switch, and a control circuit operative in response to the signal output of said phase detector for adjusting the time position of said local sequence.