AIRCRAFT COLLISION WARNING SYSTEM

• US 3,691,559 A
• Filed: 03/28/1969
• Issued: 09/12/1972
• Est. Priority Date: 03/28/1969
• Status: Expired due to Term

• Current Assignee: Homer E. Jackson
• Original Assignee: Homer E. Jackson
• Inventors: Homer, E. Jackson
• Primary Examiner(s): Samuel Feinberg
• Assistant Examiner(s): Richard E. Berger
• Application Number:
  US04/811,287
• Time in Patent Office: 1,264 Days
• Field of Search: 343/100SAT,112,112.3,6.5 325/4
• US Class Current: 342/458
• CPC Class Codes: G01S 11/08 using synchronised clocks
• CPC Class Codes: G01S 11/10 using Doppler effect

Abstract

An aircraft collision avoidance system and method involves transmitting a stable reference frequency from a synchronous satellite to aircraft in a region being monitored. Each aircraft in the region receives the reference frequency and transmits a carrier, modulated with the received reference frequency, to other aircraft in a collision avoidance zone. At the other aircraft, an indication of impending collision is provided by measuring the rate of change of the carrier Doppler frequency shift received thereby from the first named aircraft. Sync pulses periodically modulate the reference frequency transmitted from the satellite for aircraft ranging and data control purposes. To limit the collision warning zone relative to each aircraft, the receiver thereof is deactivated at a predetermined time after each sync pulse is received from the satellite.

Claims

1. A method of detecting if vehicles are on a collision course comprising the steps of transmitting a first r.f. carrier having a fixed predetermined frequency from a synchronous satellite to the vehicles, said satellite being fixedly positioned above a subsatellite point on earth, receiving the carrier on vehicles within a predetermined radius from the subsatellite position, said radius defining an area such that the Doppler frequency shift of the first r.f. carrier as received on the vehicles is substantially negligible, retransmitting from the vehicles in the area a replica of at least a portion of the received first r.f. carrier on a second r.f. carrier, receiving the second r.f. carrier on a vehicle in saId area, extracting the Doppler frequency shift imposed on the received second r.f. carrier due to the velocity difference between the vehicle transmitting the second r.f. carrier and the vehicle receiving the second r.f. carrier, and detecting if a change in the Doppler frequency shift in the received second r.f. carrier occurs to determine if a collision course exists between the vehicle transmitting the second carrier and the vehicle receiving the second carrier.

2. The method of claim 1 wherein several vehicles are in the area, and the second carrier transmitted from each of the vehicles is the same, except for Doppler frequency shifts imposed thereon.

3. The method of claim 2 wherein the second carrier transmitted from each vehicle is pulse code modulated for vehicle identification.

4. In a system for determining if first and second vehicles within a predetermined radius of a subsatellite point for a synchronous satellite are on a collision course, said satellite transmitting a first r.f. carrier having a fixed predetermined frequency to said vehicles, the Doppler frequency shift of the first carrier as coupled to said vehicles within said radius being negligible, the first of said vehicles receiving the first carrier and transmitting a replica of a least a portion thereof as modulation on a second r.f. carrier to the second vehicle, the second vehicle including means for receiving the first and second carriers, and means responsive to the received first and second carriers for extracting the Doppler shift frequency on the second carrier due to the relative velocity between the first and second vehicles.

5. The system of claim 4 wherein timing pulses repetitively modulate the first r.f. carrier and the second vehicle further includes means for deactivating said extracting means a selected time interval after reception of each timing pulse until the following timing pulse.

6. A method of determining the range between first and second objects comprising the steps of transmitting a pulse of a first r.f. carrier frequency from a synchronous satellite to said objects, the preparation time of said carrier frequency from said satellite to said objects being substantially the same, receiving the first carrier frequency pulse on both said objects, transmitting from the first object a replica of the pulse received by the first object to the second object, receiving the pulse replica on the second object, and measuring the arrival time of the pulse replica received on the second object relative to the arrival time of the first r.f. carrier frequency pulse received on the second object.

7. The method of claim 6 wherein the pulse replica is transmitted from the first object on a second r.f. carrier frequency.

8. The method of claim 6 wherein the measuring step is performed for only a predetermined time after receipt of the first carrier frequency pulse.

9. A method of determining the range between first and second objects comprising the steps of transmitting a pulse of a first r.f. carrier frequency from a synchronous satellite to said objects, the propagation time of said carrier frequency from said satellite to said objects being substantially the same, except as modified by differences in the relative altitude of the objects, receiving the first carrier frequency pulse on both said objects, changing the effective reception time of the first r.f. carrier pulse at each object as a function of object altitude so that the effective reception time of the first r.f. carrier pulse at each object regard less of altitude is substantially the same, transmitting a replica of the pulse effectively received by the first object to the second object, receiving the pulse replica on the second object, and measuring the arrival time of the pulse replica received on the second object relative to the arrival time of the r.f. carrier frequency pulse effectively received on the second object.

10. The method of claim 9 wherein the pulse replica is transmitted from tHe first object on a second r.f. carrier frequency.

11. The method of claim 9 wherein the measuring step is performed for only a predetermined time after receipt of the first carrier frequency pulse.

12. In a system for determining the range between first and second objects wherein a pulse of a first r.f. carrier frequency is transmitted from a synchronous satellite to said objects, said objects being positioned relative to each other and the satellite so that the propagation time of said carrier frequency from said satellite to said objects is substantially the same, the carrier frequency pulse being received and a replica thereof transmitted by the first object to the second object, the second object including means for receiving the pulse replica transmitted from the first object, means for receiving the first r.f. carrier frequency pulse, and means responsive to said receiving means for measuring the arrival time of the pulse replica received on the second object relative to the arrival time of the r.f. carrier frequency pulse at the second object.

13. The system of claim 12 wherein the pulses repetitively modulate the first r.f. carrier and the second object further includes means for deactivating said extracting means a selected time interval after reception of each timing pulse until the following timing pulse.

14. In a system for determining the range between first and second objects, wherein a pulse of a first r.f. carrier frequency is transmitted from a synchronous satellite to said objects, said objects being positioned relative to each other and said satellite so that the propagation time of said carrier frequency from said satellite to said objects is substantially the same except as modified by differences in the relative altitude of the objects;

said first and second objects including;

means for receiving the first carrier frequency pulse, and means for changing the effective reception time of the first r.f. carrier pulse as a function of object altitude so that the effective reception time of the first r.f. carrier pulse at each object is substantially the same;

said first object including;

means for transmitting a replica of the pulse received thereby;

said second object including;

means for receiving the pulse replica transmitted from the first object, and means responsive to the received pulse replica and the received first carrier frequency pulse for measuring the arrival time of the pulse replica relative to the arrival time of the r.f. carrier frequency pulse.

15. The system of claim 14 wherein the pulses repetitively modulate the first r.f. carrier and the second object further includes means for deactivating said extracting means a selected time interval after reception of each timing pulse until the following timing pulse.

16. A system adapted to be included on vehicles in a cooperative collision avoidance system responsive to a fixed predetermined first r.f. carrier transmitted from a synchronous satellite comprising a transceiver responsive to the first r.f. carrier for transmitting a second r.f. carrier modulated with a replica of at least a portion of the first r.f. carrier received thereby and for receiving the second r.f. carrier from other vehicles, and means responsive to the received first r.f. carrier and the received second r.f. carrier for enabling changes to be detected in the relative velocity of a vehicle transmitting the received second r.f. carrier and the vehicle including the transceiver.

17. The system of claim 16 wherein the first r.f. carrier is amplitude modulated with relatively short duration synchronizing pulses between which said carrier has a finite value, and means for amplitude modulating the second carrier with vehicle identification pulses, said last named means being responsive to the received synchronizing pulses so that the synchronizing pulses modulated on the second carrier are not amplitude modulated by the identification pulses.

18. The system of claim 16 wherein timing pulses repetitivelY modulate the first r.f. carrier and further including means for deactivating said enabling means a selected time interval after reception of each timing pulse until the following timing pulse.

19. A system adapted to be included on objects responsive to a fixed predetermined first r.f. carrier transmitted from a synchronous satellite comprising a transceiver responsive to the first r.f. carrier for transmitting a second r.f. carrier modulated with a replica of at least a portion of the first r.f. carrier from other objects, and means responsive to the received first r.f. carrier and the received second r.f. carrier for indicating the relative range between an object transmitting the received second r.f. carrier and the object including the transceiver.

20. The system of claim 19 wherein the first r.f. carrier is amplitude modulated with relatively short duration synchronizing pulses between which said carrier has a finite value, and means for amplitude modulating the second carrier with object identification pulses, said last named means being responsive to the received synchronizing pulses so that the synchronizing pulses modulated on the second carrier are not amplitude modulated by the identification pulses.

21. The system of claim 19 wherein timing pulses repetitively modulate the first r.f. carrier and further including means for deactivating said indicating means a selected time interval after reception of each timing pulse until the following timing pulse.

22. A system adapted to be included on vehicles in a cooperative collision avoidance system responsive to a fixed predetermined first r.f. carrier transmitted from a synchronous satellite comprising a transceiver responsive to the first r.f. carrier for transmitting a second r.f. carrier modulated with a replica of at least a portion of the first r.f. carrier received thereby and for receiving the second r.f. carrier from other vehicles, and means responsive to the received first r.f. carrier and the received second r.f. carrier for indicating the relative range between a vehicle transmitting the received second r.f. carrier and the vehicle including the transceiver and for enabling changes to be detected in the relative velocity between the transmitting vehicle and the vehicle including the transceiver.

23. The system of claim 22 wherein timing pulses repetitively modulate the first r.f. carrier and further including means for deactivating said indicating and enabling means a selected time interval after reception of each timing pulse until the following timing pulse.

24. A method of determining the range between vehicles and detecting if the vehicles are on a collision course comprising the steps of transmitting a first r.f. carrier having a predetermined, fixed frequency from a synchronous satellite to the vehicles, said carrier being amplitude modulated with relatively short duration synchronizing pulses between which said carrier has a finite value, said satellite being fixedly positioned above a subsatellite point on earth, receiving the carrier on vehicles within a predetermined radius from the subsatellite position, said radius defining an area such that the Doppler frequency shift of the first r.f. carrier as received on the vehicles is substantially negligible, retransmitting from the vehicles in the area a replica of at least a portion of the received first r.f. carrier on a second r.f. carrier, said portion including said synchronizing pulse and at least a segment of the finite value carrier, receiving the second r.f. carrier on a vehicle in said area, extracting the Doppler frequency shift imposed on the received r.f. carrier due to the velocity difference between the vehicle transmitting the second r.f. carrier and the vehicle receiving the second r.f. carrier, detecting if a change in the Doppler frequency shift in the received second r.f. carrier occurs to determine if a collision course exists between the vehicle transmitting the second carrier and the vehicle receiving the second carrier, and detecting the time interval between receipt of the synchronizing pulse modulated on the received second carrier and the synchronizing pulse modulated on the first carrier received at the vehicle to determine the range between the vehicle transmitting the second carrier and the vehicle receiving the second carrier.

25. The method of claim 24 further including the step of limiting the time of the Doppler frequency shift extraction and the relative range detection to a selected time after receiving the synchronizing pulse modulated on the first carrier.

26. A method of determining the range between vehicles and detecting if the vehicles are on a collision course comprising the steps of transmitting a first r.f. carrier having a predetermined, fixed frequency from a synchronous satellite to the vehicles, said carrier being amplitude modulated with relatively short duration synchronizing pulses between which said carrier has a finite value, said satellite being fixedly positioned above a subsatellite point on earth, receiving the carrier on vehicles within a predetermined radius from the subsatellite position, said radius defining an area such that the Doppler frequency shift of the first r.f. carrier as received on the vehicles is substantially negligible, retransmitting from the vehicles in the area a replica of at least a portion of the received first r.f. carrier on a second r.f. carrier, said portion including said synchronizing pulse and at least a segment of the finite value carrier, receiving the second r.f. carrier on a vehicle in said area, extracting the Doppler frequency shift imposed on the received r.f. carrier due to the velocity difference between the vehicle transmitting the second r.f. carrier and the vehicle receiving the second r.f. carrier, detecting if a change in the Doppler frequency shift in the received second r.f. carrier occurs to determine if a collision course exists between the vehicle transmitting the second carrier and the vehicle receiving the second carrier, and limiting the detection time of the Doppler frequency shift to a selected time after receiving the synchronizing pulse modulated on the first carrier.

27. The method of claim 6 further comprising the step of periodically transmitting the pulse.

28. A method of determining the range between first and second objects comprising the steps of transmitting a first r.f. carrier frequency from a synchronous satellite to said objects, at said satellite modulating the first carrier with a reference time signal having a periodically occurring identifiable characteristic, the propagation time of said carrier frequency from said satellite to said objects being substantially the same, receiving the first carrier frequency with the reference time signal modulated thereon on both said objects, transmitting from the first object a replica of the reference time signal identifiable characteristic modulated on the first carrier frequency as received by the first object to the second object, receiving the signal replica on the second object, and measuring the arrival time of the reference time signal identifiable characteristic replica received on the second object relative to the arrival time of the first r.f. carrier frequency reference time signal identifiable characteristic received on the second object.