Secure communication and ranging system

• US 4,206,462 A
• Filed: 02/08/1961
• Issued: 06/03/1980
• Est. Priority Date: 02/08/1961
• Status: Expired due to Term

• Current Assignee: ITT Corporation (ITT, Inc.)
• Original Assignee: International Telephone and Telegraph Corporation
• Inventors: Nashman, Alvin E., Rabow, Gerald
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Berger, Richard E.
• Application Number:
  US04/087,961
• Time in Patent Office: 7,055 Days
• Field of Search: 343/6.5, 343/6.8, 343/18, 343/12, 343/17.1, 343/11, 343/7.6, 250/6.6, 179/1.5, 178/22, 178/5.1, 325/32, 325/34
• US Class Current: 342/60
• CPC Class Codes: G01S 13/84 for distance determination by phase measurement
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04K 1/00 Secret communication

Abstract

15. In a secure communication system a transmitter comprising first means to modulate a carrier wave with a sub-carrier wave and a desired signal, a code generator synchronized to said sub-carrier wave, second means to modulate the output of said first modulating means with the output of said code generator, and means to transmit the output of said second modulating means to a distant receiver.

Claims

1. In a secure communication and ranging system having a transmitter and receiver at a first location and a transponder at a different location, comprising for said transmitter first means to modulate a first signal with a second signal and a desired signal, means responsive to said second signal to produce an encoding signal, second means to encode the output of said first modulating means with said encoding signal and means to transmit the output of said modulating encoding means, said transponder comprising means to receive the transmitted signals and means to transmit signals in response to the received signals from said transmitter, said receiver at said first location being responsive to said transmitted signals from said transponder and comprising means to decode said received signals with a decoding signal, means to derive said second signal from the decoded signal, means responsive to said derived second signal to produce said decoding signal identical to said encoding signal but displaced in time relative to the distance between said transmitter and said transponder and means responsive to said time displacement between said encoding signal and said decoding signal to determine the range of said transponder from said first location.

2. In a secure communication and ranging system having a transmitter and receiver at a first location and a transponder at a different location comprising for said transmitter first means to modulate a first signal with a second signal and a desired signal, means responsive to said second signal to produce an encoding signal, second means to encode the output of said first modulating means with said encoding signal, means to transmit the output of said encoding means, said transponder comprising means to receive the transmitted signals, and means to transmit signals in response to the received signals from said transmitter, said receiver at said first location being responsive to said transmitted signals from said transponder and comprising means to decode said received signals with a decoding signal, means to derive said second signal from the decoded signal, means responsive to said derived second signal to produce said decoding signal identical to said encoding signal but displaced in time relative to the distance between said transmitter and said transponder and means responsive to said time displacement between said encoding signal and said decoding signal and the phase differencce between said transmitted second signal and said derived second signal to determine the range of said transponder from said first location.

3. In a secure communication and ranging system having a transmitter and receiver at a first location and a transponder at a different location comprising for said transmitter first means to modulate a first signal with a second signal and a desired signal, means responsive to said second signal to produce an encoding signal, second means to encode the output of said first modulating means with said encoding signal and means to transmit the output of said encoding means, said transponder comprising means to receive the transmitted signals and means to transmit signals in response to the received signals from said transmitter, said receiver at said first location being responsive to said transmitted signals from said transponder and comprising means to decode said received signals with a decoding signal, means to derive said second siganl from the decoded signal, means responsive to said derived second signal to produce said decoding signal identical to said encoding signal but displaced in time relative to the distance between said transmitter and said transponder and means responsive to said time displacement between said encoding signal and said decoding signal and the phase difference between said transmitted second signal and said derived second signal to produce a coarse and fine indication respectively of the range of said transponder from said first location.

4. In a secure communication and ranging system having a transmitter and receiver at a first location and a transponder at a different location comprising for said transmitter first means to modulate a carrier signal with a subcarrier signal and a desired signal, a first code generator synchronized to said subcarrier signal, second means to encode the output of said first modulating means with the output of said code generator and means to transmit the output of said encoding, said transponder means to receive the transmitted signal and means to transmit a signal in response to the received signal from said transmitter, said receiver at said first location being responsive to said transmitted signal from said transponder and comprising means to decode said received signal, means to derive said subcarrier signal from said decoded signal, a second code generator, means coupling the output of said second code generator to said decoding means, means synchronizing said second code generator to said derived subcarrier whereby the output of said second code generator is made identical to the output of said first code generator but displaced in time relative to the distance between said transmitter and said transponder and means responsive to said time displacement between the output of said first code generator and the output of said second code generator and the phase difference between said transmitted subcarrier signal and said derived subcarrier signal to determine the range of said transponder from said first location.

5. In a secure communication system, a transmitter comprising first means to modulate a first signal with a second signal and a desired signal, means responsive to said second signal to produce an encoding signal, means to encode the output of said first modulating means with said modulating signal, means to transmit the output of said encoding means, a receiver responsive to the transmitted signal and comprising means to decode the received signal with a decoding signal, means to derive said second signal from the decoded signal and means responsive to said derived second signal to produce said decoding signal identical to said encoding signal but displaced in time relative to the distance between said transmitter and said receiver.

6. In a secure communication system, a transmitter comprising first means to modulate a carrier wave with a subcarrier wave and a desired signal, means responsive to said subcarrier wave to produce an encoding signal, means to encode the output of said first modulating means with the encoding signal, means to transmit the output of said encoding means, a receiver responsive to the transmitted signal and comprising means to decode said transmitted signal with a decoding signal, means to derive said subcarrier wave from the decoded signal and means responsive to said derived subcarrier wave to produce said decoding signal identical to said encoding signal of said transmitter but displaced in time relative to the distance between said transmitter and said receiver.

7. In a secure communication system a transmitter comprising first means to modulate a carrier wave with a subcarrier wave and a desired signal, a first code generator synchronized to said subcarrier wave, second means to encode the output of said first modulating means with the output of said code generator, means to transmit the output of said encoding means, a receiver responsive to said transmitted signal and comprising means to demodulate the transmitted signal, means to derive said subcarrier wave from the decoded signal, a second code generator, means coupling the output of said second code generator to said decoding means, and means synchronizing said second code generator to said derived subcarrier signal whereby the output of said second code generator is made identical and phase to the output of said first code generator but displaced in time relative to the distance between said transmitter and said receiver.

8. In a secure communication system, a transmitter comprising means to modulate a carrier wave with a subcarrier wave and a desired signal, means responsive to said subcarrier wave to spread the spectrum of the output of said modulating means, means to transmit the spectrum spreaded signal, a receiver responsive to said transmitted signal and comprising means to reduce the spectrum of said received signal, means to derive said subcarrier wave from said reduced signal, and means synchronizing said spectrum reducing means to said derived subcarrier wave whereby the output of said spectrum reducing means is identical to the output of said modulating means but displaced in time relative to the distance between said transmitter and said receiver.

9. In a secure communication system a transmitter comprising first means to modulate a carrier wave with a subcarrier wave and a desired signal, a first code generator synchronized to said subcarrier wave, means responsive to said first code generator to spread the spectrum of the output of said first modulating means, means to transmit said spectrum spreaded signal, a receiver responsive to the transmitted signal, and comprising means to decode the transmitted signal, means to derive said subcarrier wave from said decoded signal, a second code generator coupled to said decoding means and means synchronizing said second code generator to said derived subcarrier wave whereby the output of said second code generator is made identical to the output of said first code generator but displaced in time relative to the distance between said transmitter and said receiver and the spectrum of said received signal is reduced and made equal to the spectrum of said output of said first modulation means.

10. In a secure communication system a transmitter comprising first means to modulate a carrier wave with a subcarrier wave and a desired signal to produce a narrow bandwidth radio frequency signal, a first code generator synchronized to said subcarrier wave, a first balanced modulator, means coupling the output of said first modulating means and said code generator to said first balanced modulator whereby the output of said balanced modulator is a signal having a spread frequency spectrum greater than said narrow bandwidth signal, means to transmit the output of said first balanced modulator, a receiver responsive to said transmitted signal and comprising a second code generator, decoding means responsive to the output of said second code generator and to the received signal to derive said narrow bandwidth signal, first detection means to derive said desired signal and said subcarrier wave, a second detection means coupled to the output of said first detection means to produce as the output of said second detection means a signal equal in frequency and phase with said received subcarrier wave, means coupling the output of said second detection means to the input of said second code generator whereby said second code generator is synchronized to said subcarrier wave output of said second detection means, and the output of said second code generator is made identical to the output of said first code generator but displaced in time relative to the distance between said transmitter and said receiver and the spectrum of said received signal is reduced and made equal to the spectrum of said narrow bandwidth radio frequency signal.

11. In a secure communication system a transmitter comprising first means to modulate a carrier wave with a subcarrier wave and a desired signal to produce a narrow bandwidth radio frequency signal, a first code generator synchronized to said subcarrier wave, a first balanced modulator, means coupling the output of said first modulating means and said code generator to said first balanced modulator whereby the output of said balanced modulator is a signal having a spread frequency spectrum greater than said narrow bandwidth signal, means to transmit the output of said first balanced modulator, a receiver responsive to the transmitted signal and comprising a second code generator, decoding means responsive to the output of said second code generator and to the received signal to derive said narrow bandwidth signal, first detection means, means coupling said narrow bandwidth signal to said first detection means, a first phase locked loop coupled to said first detection means to control said first detection means to produce as the output thereof said desired signal and said subcarrier wave, second detection means coupled to the output of said first detection means, a second phase locked loop coupled to said second detection means to control said second detection means to produce as the output thereof a signal equal in frequency and phase with said received subcarrier wave, means coupling the output of said second detection means to the input of said second code generator whereby said second code generator is synchronized to said subcarrier wave output of said second detection means and the output of said second code generator is made identical to the output of said first code generator but displaced in time relative to the distance between said transmitter and said receiver and the spectrum of said received signal is reduced and made equal to the spectrum of said narrow bandwidth radio frequency signal.

12. In a secure communication system a transmitter comprising first means to modulate a carrier wave with a subcarrier wave and a desired signal to produce a narrow bandwidth radio frequency signal, a first code generator synchronized to said subcarrier wave, a first balanced modulator, means coupling the output of said first modulating means and said code generator to said first balanced modulator whereby the output of said balanced modulator is a signal having a spread frequency spectrum greater than said narrow bandwidth signal, means to transmit the output of said first balanced modulator, a receiver responsive to the transmitted signal and comprising a second code generator, decoding means responsive to the output of said second code generator and to the received signal to derive said narrow bandwidth signal, a first phase detector, means coupling said narrow bandwidth signal to said first phase detector, a first phase locked loop comprising a first voltage controlled oscillator coupled to said first phase detector and a first low pass filter coupling the output of said phase detector to said voltage controlled oscillator whereby the output of said first phase detector is said desired signal and said subcarrier wave, a second phase locked loop coupled to the output of said first phase detector and comprising a second phase detector, a second voltage controlled oscillator, a second low pass filter coupling the output of said second phase detector to said voltage controlled oscillator and an electronic phase shifter coupling the output of said second voltage controlled oscillator to said second phase detector to produce as the output of said second voltage controlled oscillator a signal equal in frequency and phase with said received subcarrier wave, means coupling the output of said second voltage controlled oscillator to the input of said second code generator whereby said second code generator is synchronized to said subcarrier wave output of said second voltage controlled oscillator and the output of said second code generator is made identical to the output of said first code generator but displaced in time relative to the distance between said transmitter and said receiver and the spectrum of said received signal is reduced and made equal to the spectrum of said narrow bandwidth radio frequency signal.

13. In a secure communication system a transmitter comprising first means to modulate a carrier wave with a subcarrier wave and a desired signal to produce a narrow bandwidth radio frequency signal, first means to multiply the frequency of said subcarrier wave, a first code generator synchronized to the multiplied frequency of said subcarrier wave, a first balanced modulator, means coupling the output of said first modulating means and said code generator to said first balanced modulator whereby the output of said balanced modulator is a signal having a spread frequency spectrum greater than said narrow bandwidth signal, means to transmit the output of said first balanced modulator, a receiver responsive to the transmitted signal and comprising a second code generator, decoding means responsive to the output of said second code generator and to the received signal to derive said narrow bandwidth signal, a first phase detector, means coupling said narrow bandwidth signal to said first phase detector, a first phase locked loop comprising a first voltage controlled oscillator coupled to said first phase detector and a first low pass filter coupling the output of said phase detector to said voltage controlled oscillator whereby the output of said first phase detector is said desired signal and said subcarrier wave, a second phase locked loop coupled to the output of said first phase detector and comprising a second phase detector, a second voltage controlled oscillator, a second low pass filter coupling the output of said second phase detector to said voltage controlled oscillator and an electronic phase shifter coupling the output of said second voltage controlled oscillator to said second phase detector to produce as the output of said second voltage controlled oscillator a signal equal in frequency and phase with said received subcarrier wave, second means to multiply said subcarrier wave output of said second voltage controlled oscillator coupled to the output of said electronic phase shifter, means coupling the output of said second multiplier to the input of said second code generator whereby said second code generator is synchronized to said subcarrier wave output of said second voltage controlled oscillator and the output of said second code generator is made identical to the output of said first code generator but displaced in time relative to the distance between said transmitter and said receiver and the spectrum of said received signal is reduced and made equal to the spectrum of said narrow bandwidth radio frequency signal.

14. In a secure communication and ranging system having a transmitter and receiver at a first location and a transponder at a different location comprising for said transmitter first means to modulate a carrier wave with a subcarrier wave and a desired signal to produce a narrow bandwidth radio frequency signal, a first code generator synchronized to said subcarrier wave, a first balanced modulator, means coupling the output of said first modulating means and said code generator to said first balanced modulator whereby the output of said balanced modulator is a signal having a spread frequency spectrum greater than said narrow bandwidth signal, and means to transmit the output of said first balanced modulator, said transponder comprising means to receive the transmitted signals and means to transmit signals in response to the received signals from said transmitter, said receiver at said first location being responsive to said transmitted signal from said transponder and comprising a second code generator, decoding means responsive to the output of said second code generator and to said received signal to derive a narrow bandwidth signal, a first phase detector, means coupling said narrow bandwidth signal to said first phase detector, a first phase locked loop comprising a first voltage controlled oscillator coupled to said first phase detector and a first low pass filter coupling the output of said phase detector to said voltage controlled oscillator whereby the output of said first phase detector includes said subcarrier wave, a second phase locked loop coupled to the output of said first phase detector and comprising a second phase detector, a second voltage controlled oscillator, a second low phase filter coupling the output of said second phase detector to said voltage controlled oscillator and an electronic phase shifter coupling the output of said second voltage controlled oscillator to said second phase detector to produce as the output of said second voltage controlled oscillator a signal equal in frequency and phase with said received subcarrier wave, means coupling the output of said second voltage controlled oscillator to the input of said second code generator whereby said second code generator is synchronized to said subcarrier wave output of said second voltage controlled oscillator and the output of said second code generator is made identical to the output of said first code generator but displaced in time relative to the distance between said transmitter and said transponder and the spectrum of said received signal is reduced and made equal to the spectrum of said narrow bandwidth radio frequency signal, means to compare the phase of said transmitted subcarrier wave and said subcarrier wave output of said second voltage controlled oscillator, said phase difference being a fine indication of the range of said transponder from said first location, means to count the number of cycles of said transmitter subcarrier wave in the interval between the start of a code word in said first code generator and the start of a code word in said second code generator, said count representing a coarse indication of the range of said transponder from said first location, the total of said coarse and fine indications representing the total range of said transponder from said first location.

15. In a secure communication system a transmitter comprising first means to modulate a carrier wave with a sub-carrier wave and a desired signal, a code generator synchronized to said sub-carrier wave, second means to modulate the output of said first modulating means with the output of said code generator, and means to transmit the output of said second modulating means to a distant receiver.

16. In a secure communication system a receiver responsive to the transmission of signals from a transmitter, said transmitted signals having desired signals modulated with a sub-carrier wave and the output of a code generator, comprising:

means to decode said transmitted signal, means to derive said sub-carrier wave from the decoded signal, a code generator, means coupling the output of said code generator to said decoding means and means synchronizing said code generator to said derived sub-carrier signal whereby the output of said receiver code generator is made identical to the output of the transmitter code generator but displaced in time relative to the distance between said transmitter and said receiver.