Vehicle location system

Abstract

Signals from a number of NAVSTAR global positioning system (GPS) satellites (11,12,13,14) are received by a receiver (16) in a vehicle (15) and a segment of the signals is stored in a memory (18) prior to retransmission by a transmitter (19). A base station (35) receives these transmissions from the mobile unit using a first receiver (36). The base station also receives signals directly from the NAVSTAR GPS satellites using a second receiver (38). A control and calculating apparatus (37) within the base station can determine the ephemeris (course) information for the satellites and can measure the transmission times or propagation delays of signals between the satellites and the vehicle and with this information the control and calculating apparatus can calculate the position of the vehicle unit.

I claim: 
     
       1. A vehicle location system for use in a global positioning system (GPS), comprising at least one vehicle mounted equipment including means for receiving signals directly from the GFS, a fixedly sited base station including first means for receiving signals directly from the GPS, characterised in that the vehicle mounted equipment includes means for recording the received GPS signals and means for retransmitting the recorded GPS signals to the base station, and in that the fixedly sited base station includes second means for receiving the recorded GPS signals retransmitted by the vehicle mounted equipment, and position determining means coupled to the first and second receiving means for determining the position of the vehicle at the time when the vehicle mounted equipment received the GPS signals. 
     
     
       2. A vehicle location system as claimed in claim 1, wherein the vehicle mounted equipment transmits a time of arrival (TOA) signal in addition to retransmitting the recorded GPS signals. 
     
     
       3. A vehicle location system as claimed in claim 1 wherein the rate at which the vehicle mounted equipment retransmits the GPS signals is lower than that at which the signals were recorded. 
     
     
       4. A vehicle location system as claimed in claim 3, wherein the vehicle mounted equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record the GPS signals at preset intervals. 
     
     
       5. A vehicle location system as claimed in claim 2, wherein the GPS is the satellite-based NAVSTAR GPS, and in that the base station has means for obtaining the GPS ephemeris for the satellites in use. 
     
     
       6. A vehicle location system as claimed in claim 5, wherein the means for obtaining the GPS ephemeris in the base station has means for despreading the NAVSTAR GPS signals without using any locally generated pseudo random noise codes. 
     
     
       7. A vehicle mounted equipment for use .Iadd.in a global positioning system (GPS) .Iaddend.with .[.the system as claimed in claim 1.]. .Iadd.a vehicle location system and .Iaddend.including means for receiving .[.the.]. GPS signals, .[.wherein the equipment also includes.]. .Iadd.the vehicle location system comprising a fixedly sited base station including first means for receiving signals directly from the GPS, second means for receiving recorded GPS signals transmitted by the vehicle mounted equipment, and position determining means coupled to the first and second receiving means for determining the position of the vehicle at the time when the vehicle mounted equipment received the GPS signals, said vehicle mounted equipment including .Iaddend.means for recording the received GPS signals and means for retransmitting the recorded GPS signals. 
     
     
       8. A vehicle mounted equipment for use .Iadd.in a global positioning system (GPS) .Iaddend.with .[.the system as claimed in claim 2.]. .Iadd.a vehicle location system and .Iaddend.including means for receiving .[.the.]. GPS signals, .[.wherein the equipment includes.]. .Iadd.the vehicle location system comprising a fixedly sited base station including first means for receiving signals directly from the GPS, second means for receiving recorded GPS signals transmitted by the vehicle mounted equipment, and position determining means coupled to the first and second receiving means for determining the position of the vehicle at the time when the vehicle mounted equipment received the GPS signals, said vehicle mounted equipment including .Iaddend.means for recording the received GPS signals and means for retransmitting the recorded GPS signals and a time of arrival (TOA) signal. 
     
     
       9. A fixedly sited base station for use .Iadd.in a global positioning system (GPS) .Iaddend.with .[.the system as claimed in claim 1.]. .Iadd.a vehicle location system comprising at least one vehicle mounted equipment including means for receiving signals directly from the GPS, means for recording the received GPS signals, and means for retransmitting the recorded GPS signals to the base station, said fixedly sited base station .Iaddend.including first means for receiving GPS signals directly from the GPS, .[.wherein the base station also includes.]. second means for receiving a retransmission of GPS signals from .[.a.]. .Iadd.the .Iaddend.vehicle mounted equipment and means coupled to said first and second receiving means for determining the position of the vehicle mounted equipment at the time the GPS signals were received. 
     
     
       10. A fixedly sited base station as claimed in claim 9, wherein the means for determining the position of the vehicle mounted equipment calculates the position of the base station using the GPS and then calculates the position of the vehicle mounted equipment using a differential technique. 
     
     
       11. A vehicle location system as claimed in claim 2, wherein the rate at which the vehicle mounted equipment retransmits the GPS signals is lower than that at which the signals were recorded. 
     
     
       12. A vehicle location system as claimed in claim 11, wherein the vehicle mounted equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record GPS signals at preset intervals. 
     
     
       13. A vehicle location system as claimed in claim 2, wherein the vehicle mounted equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record GPS signals at preset intervals. 
     
     
       14. A vehicle location system as claimed in claim 1, wherein the vehicle mounted equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record GPS signals at preset intervals. 
     
     
       15. A vehicle location system as claimed in claim 1, wherein the base station includes a means for obtaining the GPS ephemeris for satellites of the GPS. .Iadd. 
     
     
       16.  A vehicle location system as claimed in claim 1, wherein the means for determining the position of the vehicle mounted equipment calculates the position of the base station using the GPS and then calculates the position of the vehicle mounted equipment using a differential technique. .Iaddend..Iadd. 
     
     
       17.  A mobile equipment location system for use in a global positioning system (GPS), comprising at least one mobile equipment including means for receiving signals directly from the GPS, a base station including first means for receiving signals directly from the GPS, characterized in that the mobile equipment includes means for recording the received GPS signals and means for retransmitting the recorded GPS signals to the base station, and in that the base station includes second means for receiving the recorded GPS signals retransmitted by the mobile equipment, and position determining means coupled to the first and second receiving means for determining the position of the mobile equipment at the time when the mobile equipment received the GPS signals. .Iaddend..Iadd.18. A mobile equipment location system for use in a global positioning system (GPS), comprising at least one mobile equipment including means for receiving signals directly from the GPS, a base station at a known, location, including first means for receiving signals directly from the GPS, characterised in that the mobile equipment includes means for recording the received GPS signals and means for retransmitting the recorded GPS signals to the base station, and in that the base station includes second means for receiving the recorded GPS signals retransmitted by the mobile equipment, and position determining means coupled to the first and second receiving means for determining the position of the mobile equipment at the time when the mobile equipment received the GPS signals. 
     
     
        .Iaddend..Iadd.19.  A mobile equipment location system as claimed in claim 17, wherein the mobile equipment transmits a time of arrival (TOA) signal in addition to retransmitting the recorded GPS signals. .Iaddend..Iadd.20. A mobile equipment location system as claimed in claim 17, wherein the rate at which the mobile equipment retransmits the GPS signals is lower than that at which the signals were recorded. .Iaddend..Iadd.21. A mobile equipment location system as claimed in claim 20, wherein the mobile equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record the GPS signals at preset intervals. .Iaddend..Iadd.22. A mobile equipment location system as claimed in claim 19, wherein the GPS is the satellite-based NAVSTAR GPS, and in that the base station has means for obtaining the GPS ephemeris for the satellites in use. .Iaddend..Iadd.23. A mobile equipment location system as claimed in claim 22, wherein the means for obtaining the GPS ephemeris in the base station has means for despreading the NAVSTAR GPS signals without using any locally generated pseudo random noise codes. .Iaddend..Iadd.24. A mobile equipment for use in a global positioning system (GPS) with a mobile equipment location system and including means for receiving GPS signals, the mobile equipment location system comprising a base station including first means for receiving signals directly from the GPS, second means for receiving recorded GPS signals transmitted by the mobile equipment, and position determining means coupled to the first and second receiving means for determining the position of the mobile equipment at the time when the mobile equipment received the GPS signals, said mobile equipment including means for recording the received GPS signals and means for retransmitting the recorded GPS signals. .Iaddend..Iadd.25. A mobile equipment for use in a global positioning system (GPS) with a mobile equipment location system and including means for receiving GPS signals, the mobile equipment location system comprising a base station including first means for receiving signals directly from the GPS, second means for receiving recorded GPS signals transmitted by the mobile equipment, and position determining means coupled to the first and second receiving means for determining the position of the mobile equipment at the time when the mobile equipment received the GPS signals, said mobile equipment including means for recording the received GPS signals and means for retransmitting the recorded GPS signals and a time of arrival (TOA) signal. .Iaddend..Iadd.26. A base station for use in a global positioning system (GPS) with a mobile equipment location system comprising at least one mobile equipment including means for receiving signals directly from the GPS, means for recording the received GPS signals, and means for retransmitting the recorded GPS signals to the base station, said base station including first means for receiving GPS signals directly from the GPS, second means for receiving a retransmission of GPS signals from the mobile equipment and means coupled to said first and second receiving means for determining the position of the mobile equipment at the time the GPS signals were received. .Iaddend..Iadd.27. A base station as claimed in claim 26, wherein the means for determining the position of the mobile equipment calculates the position of the base station using the GPS and then calculates the position of the mobile equipment using a differential technique. .Iaddend..Iadd.28. A mobile equipment location system as claimed in claim 19, wherein the rate at which the mobile equipment retransmits the GPS signals is lower than that at which the signals are recorded. .Iaddend..Iadd.29. A mobile equipment location system as claimed in claim 28, wherein the mobile equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record GPS signals at preset intervals. .Iaddend..Iadd.30. A mobile equipment location system as claimed in claim 19, wherein the mobile equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record GPS signals at preset intervals. .Iaddend..Iadd.31. A mobile equipment location system as claimed in claim 17, wherein the mobile equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record GPS signals at preset intervals. 
     
     
        .Iaddend..Iadd. 2.  A mobile equipment location system as claimed in claim 17, wherein the base station includes a means for obtaining the GPS ephemeris for satellites of the GPS. .Iaddend..Iadd.33. A mobile equipment location system as claimed in claim 18, wherein the mobile equipment transmits a time of arrival (TOA) signal in addition to retransmitting the recorded GPS signals. .Iaddend..Iadd.34. A mobile equipment location system as claimed in claim 18, wherein the rate at which the mobile equipment retransmits the GPS signals is lower than that at which the signals were recorded. .Iaddend..Iadd.35. A mobile equipment location system as claimed in claim 34, wherein the mobile equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record the GPS signals at preset intervals. .Iaddend..Iadd.36. A mobile equipment location system as claimed in claim 33, wherein the GPS is the satellite-based NAVSTAR GPS, and in that the base station has means for obtaining the GPS ephemeris for the satellites in use. .Iaddend..Iadd.37. A mobile equipment location system as claimed in claim 36, wherein the means for obtaining the GPS ephemeris in the base station has means for despreading the NAVSTAR GPS signals without using any locally generated pseudo random noise codes. .Iaddend..Iadd.38. A mobile equipment for use in a global positioning system (GPS) with a mobile equipment location system and including means for receiving GPS signals, the mobile equipment location system comprising a base station at a known location including first means for receiving signals directly from the GPS, second means for receiving recorded GPS signals transmitted by the mobile equipment, and position determining means coupled to the first and second receiving means for determining the position of the mobile equipment at the time when the mobile equipment received the GPS signals, said mobile equipment including means for recording the received GPS signals and means for retransmitting the recorded GPS signals. .Iaddend..Iadd.39. A mobile equipment for use in a global positioning system (GPS) with a mobile equipment location system and including means for receiving GPS signals, the mobile equipment location system comprising a base station at a known location including first means for receiving signals directly from the GPS, second means for receiving recorded GPS signals transmitted by the mobile equipment, and position determining means coupled to the first and second receiving means for determining the position of the mobile equipment at the time when the mobile equipment received the GPS signals, said mobile equipment including means for recording the received GPS signals and means for retransmitting the recorded GPS signals and a time of arrival (TOA) signal. .Iaddend..Iadd.40. A base station at a known location for use in a qlobal positioning system (GPS) with a mobile equipment location system comprising at least one mobile equipment including means for receiving signals directly from the GPS, means for recording the received GPS signals, and means for retransmitting the recorded GPS signals to the base station, said base station including first means for receiving GPS signals directly from the GPS, second means for receiving a retransmission of GPS signals from the mobile equipment and means coupled to said first and second receiving means for determining the position of the mobile equipment at the time the GPS signals were received. .Iaddend..Iadd.41. A base station as claimed in claim 40, wherein the means for determining the position of the mobile equipment calculates the position of the base station using the GPS and then calculates the position of the mobile equipment using a differential technique. .Iaddend..Iadd.42. A mobile equipment location system as claimed in claim 33, wherein the rate at which the mobile equipment retransmits the GPS signals is lower than that at which the signals are recorded. .Iaddend..Iadd.43. A mobile equipment location system as claimed in claim 42, wherein the mobile equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record GPS signals at preset intervals. .Iaddend..Iadd.44. A mobile equipment location system as claimed in claim 33, wherein the mobile equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record GPS signals at preset intervals. .Iaddend..Iadd.45. A mobile equipment location system as claimed in claim 18, wherein the mobile equipment further comprises control means coupled to the recording means such that signals from the control means cause the recording means to record GPS signals at preset intervals. .Iaddend..Iadd.46. A mobile equipment location system as claimed in claim 18, wherein the base station includes a means for obtaining the GPS ephemeris for satellites of the GPS. .Iaddend..Iadd.47. A mobile equipment location system as claimed in claim 17, wherein the means for determining the position of the mobile equipment calculates the position of the base station using the GPS and then calculates the position of the mobile equipment using a differential technique. .Iaddend..Iadd.48. A mobile equipment location system as claimed in claim 18, wherein the means for determining the position of the mobile equipment calculates the position of the base station using the GPS and then calculates the position of the mobile equipment using a differential technique. .Iaddend.