Vehicle tracking system employing global positioning system (GPS) satellites

• US 5,225,842 A
• Filed: 05/09/1991
• Issued: 07/06/1993
• Est. Priority Date: 05/09/1991
• Status: Expired due to Term

• Current Assignee: Navsys Corporation
• Original Assignee: Navsys Corporation
• Inventors: Sturza, Mark A., Brown, Alison K.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US07/697,754
• Time in Patent Office: 789 Days
• Field of Search: 342/457, 342/357, 342/352, 342/356, 364/449
• US Class Current: 342/357.46
• CPC Class Codes: G01S 19/51 Relative positioning
• CPC Class Codes: G01S 5/0009 Transmission of position information to remote stations involving assistance data G01S5/0236

Abstract

A tracking system employing global positioning system (GPS) satellites provides extremely accurate position, velocity, and time information for vehicles or any other animate or inanimate object within any mobile radio communication system or information system, including those operating in high rise urban areas. The tracking system includes a sensor mounted on each object, a communication link, a workstation, and a GPS reference receiver. The sensor operates autonomously following initialization by an external network management facility to sequence through the visible GPS satellites, making pseudo range and delta range or time difference and frequency difference measurements. No navigation functions are performed by the sensor, thereby permitting significant reductions in the cost thereof. The raw satellite measurements, with relevant timing and status information, are provided to the communication link to be relayed periodically back to the workstation. Differential corrections may also be provided at the workstation to increase the accuracy of the object location determination. In normal operation, three satellite measurements are required to compute the location of the object, but for a short time period a minimum of two satellite measurements are acceptable with time, altitude, and map aiding information being provided by the workstation.

Claims

1. A tracking system employing global positioning system (GPS) satellites for determining the position of one or more objects to be tracked, the tracking system comprising:

sensor means, mounted on each object, the sensor means being operative for receiving signals provided by a plurality of visible GPS satellites and for computing sensor data comprising selected raw satellites measurements;

workstation means, positioned at a central location that is remotely located with respect to said one or more objects, for periodically receiving and storing the raw satellite measurements computed by said sensor means, for computing therefrom position information relative to the one or more objects, and for displaying the computed position information to an operator at said central location, said workstation means being further operative for periodically providing initialization data in the form of sensor commands to said sensor means to enable said sensor means to acquire and track the plurality of visible GPS satellites, said workstation means being operative for storing a digital map containing route and altitude aiding information regarding each of the one or more objects, thereby facilitating computation of said position information using only high elevation satellites and when the one or more objects are operating in a high rise urban environment; and

a communication link coupling said sensor means and said workstation means to facilitate the transfer of sensor data and sensor commands between said sensor means and said workstation means.

4. A tracking system as in claim 1 wherein said workstation means is further operative for transmitting, over said communication link, said computed position information to a corresponding one of the one or more objects.

2. A tracking system employing global positioning system (GPS) satellites for determining the position of one or more objects to be tracked, the tracking system comprising:

sensor means, mounted on each object, the sensor means being operative for receiving signals provided by a plurality of visible GPS satellites and for computing sensor data comprising selected raw satellite measurements;

workstation means, positioned at a central location that is remotely located with respect to said one or more objects, for periodically receiving and storing the raw satellite measurements computed by said sensor means, for computing therefrom position information relative to the one or more objects, and for displaying the computed position information to an operator at said central location, said workstation means being further operative for periodically providing initialization data in the form of sensor commands to said sensor means to enable said sensor means to acquire and track the plurality of visible GPS satellites, said initialization data comprising initial estimates of the position of each of the one or more objects and a satellite selection table; and

a communication link coupling said sensor means and said workstation means to facilitate the transfer of sensor data and sensor commands between said sensor means and said workstation means.

3. A tracking system as in claim 2 wherein said workstation means is further operative for transmitting, over said communication link, said computed position information to a corresponding one of the one or more objects.

5. A sensor mounted on each of a multiplicity of objects to be tracked in a tracking system employing global positioning system (GPS) satellites, the sensor comprising:

antenna means for receiving signals from one or more GPS satellites;

RF/IF means for receiving signals from said antenna means and for converting those signals to digital samples, said RF/IF means comprising preamplifier means for receiving and amplifying an L1 radio frequency signal having a nominal carrier frequency of 1575.42 MHz, a reference oscillator operating at a frequency F0, phase locked loop means for generating a single local oscillator signal at a frequency 256F0, mixer means for receiving said L1 radio frequency signal from the preamplifier means, said mixer means being responsive to the local oscillator signal for reducing the signal output of the preamplifier means to an intermediate frequency signal having a frequency of 1575.42-256*F0 MHz, low pass filter means for filtering the intermediate frequency signal provided by said mixer means, and digitizer means for digitizing the filtered intermediate frequency signal provided by said low pass filter means;

digital signal processing (DSP) means coupled to said RF/IF means for converting those digital samples to processed digital signals;

a crystal oscillator coupled to said RF/IF means and to said DSP means for generating a local oscillator signal and providing that local oscillator signal to said RF/IF means and to said DSP means; and

microcomputer means coupled to said DSP means for computing, from said signals received from one or more GPS satellites, sensor data comprising selected raw satellite measurements to be transmitted to a remotely located workstation for computation of the position and velocity of the object on which the sensor is mounted.

6. A sensor as in claim 5 wherein said crystal oscillator comprises a temperature compensated crystal oscillator.

7. A sensor as in claim 5 wherein said crystal oscillator comprises a temperature controlled crystal oscillator.

8. A sensor as in claim 5 wherein said digitizer comprises a limiter.

9. A sensor as in claim 5 wherein said DSP means comprises a plurality of individual DSP circuits on a single semiconductor chip, each of said plurality of individual circuits comprising:

a pair of exclusive OR gates for performing code correlation on a signal received from said RF/IF input means and for performing carrier demodulation employed in generating in phase and quadrature signals I and Q;

a pair of up/down counters coupled to said pair of exclusive OR gates for accumulating the in phase and quadrature signals I and Q;

a C/A coder coupled to said pair of exclusive OR gates for generating a coarse acquisition code from a signal indicative of a satellite being tracked;

a code phase numerically controlled oscillator coupled to said C/A coder for indexing said C/A coder;

a carrier numerically controlled oscillator coupled to said pair of exclusive OR gates, for receiving a divided DSP clock signal, and for generating the in phase and quadrature signals I and Q; and

memory map interface means coupled to said microcomputer means for receiving the in phase and quadrature signals I and Q and for generating a plurality of control signals therefrom.

10. A sensor as in claim 5 wherein the frequency F0 at which said reference oscillator operates is 6.1539 MHz.

11. A sensor mounted on each of a multiplicity of objects to be tracked in a tracking system employing global positioning system (GPS) satellites, the sensor comprising:

antenna means for receiving signals from one or more GPS satellites;

RF/IF means for receiving signals from said antenna means and for converting those signals to digital samples;

digital signal processing (DSP) means coupled to said RF/IF means for converting those digital samples to processed digital signals, said DSP means comprising a pair of exclusive OR gates for performing code correlation on a signal received from said RF/IF input means and for performing carrier demodulation employed in generating in phase and quadrature signals I and Q, a pair of up/down counters coupled to said pair of exclusive OR gates for accumulating the in phase and quadrature signals I and Q, a C/A coder coupled to said pair of exclusive OR gates for generating a coarse acquisition code from a signal indicative of a satellite being tracked, a code phase numerically controlled oscillator coupled to said C/A coder for indexing said C/A coder, a carrier numerically controlled oscillator coupled to said pair of exclusive OR gates, for receiving a DSP clock signal derived by dividing reference oscillator frequency F0, and for generating the in phase and quadrature signals I and Q, and memory map interface means coupled to said microcomputer means for receiving the in phase and quadrature signals I and Q and for generating a plurality of control signals therefrom;

a crystal oscillator coupled to said RF/IF means and to said DSP means for generating a local oscillator signal and providing that local oscillator signal to said RF/IF means and to said DSP means; and

microcomputer means coupled to said DSP means for computing, from said signals received from one or more GPS satellites, sensor data comprising selected raw satellite measurements to be transmitted to a remotely located workstation for computation of the position and velocity of the object on which the sensor is mounted.

12. A sensor as in claim 11 wherein the frequency of said reference oscillator signal F0 is 6.1539 MHz and wherein said DSP clock signal is derived by dividing said reference oscillator signal F0 by 3 to obtain a DSP clock signal whose frequency is 2.01513 MHz.

13. A sensor as in claim 11 wherein said DSP means comprises a plurality of individual DSP circuits on a single semiconductor chip.

14. A sensor as in claim 11 wherein said crystal oscillator comprises a temperature compensated crystal oscillator.

15. A sensor as in claim 11 wherein said crystal oscillator comprises a temperature controlled crystal oscillator.

16. A tracking process employing global positioning system (GPS) satellites for determining the position of each of one or more objects to be tracked, the process comprising:

mounting a sensor on each object;

receiving signals at the sensor provided by a plurality of visible GPS satellites;

computing, in the sensor, sensor data comprising selected raw satellite measurements, from the signals received at the sensor;

providing a workstation at a central location;

periodically receiving and storing, at the workstation, the raw satellite measurements computed by the sensor;

storing a digital map in the workstation, the digital map containing route and altitude aiding information regarding each of the one or more objects, thereby facilitating computation of the position information using only high elevation satellites and when the one or more objects are operating in a high rise urban environment;

computing, in the workstation, position information relative to each of the one or more objects from the received and stored raw satellite measurements;

displaying the computed position information to an operator at said central location; and

periodically transferring initialization data, in the form of sensor commands, from the workstation to the sensor over a communication link to enable the sensor means to acquire and track the plurality of visible GPS satellites.

17. A tracking process as in claim 16, further comprising the step of transmitting, over the communication link, the computed position information to a corresponding one of the one or more objects.

18. A tracking process as in claim 16 wherein the step of displaying comprises displaying the computed position information relative to each of the one or more objects overlayed on a map of a region in which the one or more objects are located.

19. A tracking process as in claim 16 further comprising the step of broadcasting the computed position information of each of the one or more objects to a corresponding one of the one or more objects.

20. A tracking process as in claim 16 wherein the step of computing position information comprises computation of position information in terms of an offset coordinate.

21. A tracking process as in claim 16 wherein the step of computing position information comprises computation of position information with a reference to a point on the digital map.

22. A tracking process as in claim 16 wherein the step of computing position information comprises:

providing a GPS reference receiver for receiving signals provided by the plurality of visible GPS satellites;

deriving a satellite visibility table using the GPS reference receiver;

storing the satellite visibility table in the workstation;

computing, in the workstation, the position of each visible GPS satellite;

computing, in the workstation, an estimated pseudo range and corresponding line-of-sight vector to a median position for the plurality of visible satellites in an area of operation of the one or more objects;

deriving differential corrections from the GPS reference receiver;

adding the differential corrections to the computed estimated pseudo range to correct for atmospheric effects and errors in the computed position of each visible GPS satellite;

computing, in the workstation, a least squares transformation matrix, using the computed line-of-sight vectors, for all of the visible GPS satellites;

computing, in the workstation, one or more measurement residual vectors, including an estimated altitude offset from a median position in the area of operation of the one or more objects; and

multiplying, in the workstation, the one or more computed measurement residual vectors by the computed least square transformation matrix.

23. A tracking process employing global positioning system (GPS) satellites for determining the position of each of one or more objects to be tracked, the process comprising:

mounting a sensor on each object;

receiving signals at the sensor provided by a plurality of visible GPS satellites;

computing, in the sensor, sensor data comprising selected raw satellite measurements, from the signals received at the sensor;

providing a workstation at a central location;

periodically receiving and storing, at the workstation, the raw satellite measurements computed by the sensor;

computing, in the workstation, position information relative to each of the one or more objects from the received and stored raw satellite measurements;

displaying the computed position information to an operator at said central location; and

periodically transferring initialization data, in the form of sensor commands, including initial estimates of the position of each of the one or more objects and a satellite selection table, from the workstation to the sensor over a communication link to enable the sensor means to acquire and track the plurality of visible GPS satellites.

24. A tracking process as in claim 23 wherein the step of displaying comprises displaying the computed position information relative to each of the one or more objects overlayed on a map of a region in which the one or more objects are located.

25. A tracking process as in claim 23 further comprising the step of broadcasting the computed position information of each of the one or more objects to a corresponding one of the one or more objects.

26. A tracking process as in claim 23 herein the step of computing position information comprises computation of position information in terms of an offset coordinate.

27. A tracking process as in claim 23, further comprising the step of transmitting, over the communication link, the computed position information to a corresponding one of the one or more objects.

28. A tracking process as in claim 23 wherein the step of computing position information comprises:

providing a GPS reference receiver for receiving signals provided by the plurality of visible GPS satellites;

deriving a satellite visibility table using the GPS reference receiver;

storing the satellite visibility table in the workstation;

computing, in the workstation, the position of each visible GPS satellite;

computing, in the workstation, an estimated pseudo range and corresponding line-of-sight vector to a median position for the plurality of visible satellites in an area of operation of the one or more objects;

deriving differential corrections from the GPS reference receiver;

adding the differential corrections to the computed estimated pseudo range to correct for atmospheric effects and errors in the computed position of each visible GPS satellite;

computing, in the workstation, a least squares transformation matrix, using the computed line-of-sight vectors, for all of the visible GPS satellites;

computing, in the workstation, one or more measurement residual vectors, including an estimated altitude offset from a median position in the area of operation of the one or more objects; and

multiplying, in the workstation, the one or more computed measurement residual vectors by the computed least square transformation matrix.

29. A tracking process employing global positioning system (GPS) satellites for determining the position of each of one or more objects to be tracked, the process comprising:

mounting a sensor on each object;

receiving signals at the sensor provided by a plurality of visible GPS satellites;

computing, in the sensor, sensor data comprising selected raw satellite measurements, from the signals received at the sensor;

providing a workstation at a central location;

periodically receiving and storing, at the workstation, the raw satellite measurements computed by the sensor;

computing, in the workstation, position information relative to each of the one or more objects from the received and stored raw satellite measurements;

displaying the computed position information to an operator at said central location; and

periodically transferring initialization data, in the form of sensor commands, from the workstation to the sensor over a communication link to enable the sensor means to acquire and track the plurality of visible GPS satellites;

wherein the step of computing position information comprises;

providing a GPS reference receiver for receiving signals provided by the plurality of visible GPS satellites;

deriving a satellite visibility table using the GPS reference receiver;

storing the satellite visibility table in the workstation;

computing, in the workstation, the position of each visible GPS satellite;

computing, in the workstation, an estimated pseudo range and corresponding line-of-sight vector to a median position for the plurality of visible satellites in an area of operation of the one or more objects;

deriving differential corrections from the GPS reference receiver;

adding the differential corrections to the computed estimated pseudo range to correct for atmospheric effects and errors in the computed position of each visible GPS satellite;

computing, in the workstation, a least squares transformation matrix, using the computed line-of-sight vectors, for all of the visible GPS satellites;

computing, in the workstation, one or more measurement residual vectors, including an estimated altitude offset from a median position in the area of operation of the one or more objects; and

multiplying, in the workstation, the one or more computed measurement residual vectors by the computed least square transformation matrix.

30. A tracking process as in claim 29 wherein the step of displaying comprises displaying the computed position information relative to each of the one or more objects overlayed on a map of a region in which the one or more objects are located.

31. A tracking process as in claim 29 further comprising the step of broadcasting the computed position information of each of the one or more objects to a corresponding one of the one or more objects.

32. A tracking process as in claim 29 wherein the step of computing position information comprises computation of position information in terms of an offset coordinate.