Radio position determination method and apparatus

Claims

We claim:

1. A method of radio position determination of an unknown position transmitter using a mobile-reference transceiver and a plurality of base repeater generating a slave grid synchronization pulse for time reference, located at known geographic locations in a geographic area and coupled to a central monitoring station generating a master grid synchronization pulse for time reference, comprising the steps of:

emitting by the unknown position transmitter located within the geographical area, a radio wave having modulation compensation for multipath which also serves as a coarse ranging modulation, and a modulated carrier with an identification code;

receiving by at least three base repeaters the radio wave emitted by the unknown position transmitter and measuring at the base repeaters the relative times-of-arrival of the radio wave with respect to the master grid synchronization pulse for deriving ranging times and therefore ranges from said base repeaters to said unknown position transmitter;

computing from the locations of said base repeaters and the measured times-of-arrival, hyperbolic lines of position for the unknown position transmitter;

computing a coarse-position fix of the unknown position transmitter from the hyperbolic lines of position using a least means squares algorithm;

dispatching a search team having a mobile reference transceiver to the coarse-position fix of said unknown-position transmitter;

transmitting from said mobile reference transceiver located within the coarse-position fix a reference signal having modulation compensation for multipath which also serves as a coarse ranging modulation;

receiving by the base repeaters the reference signal emitted by said mobile reference transceiver and computing a difference between the reference signal and the radio wave, for deriving a differential position vector from said mobile reference transceiver to said unknown position transmitter;

guiding the mobile reference transceiver to said unknown position transmitter using the differential position vector;

emitting a polling message by said mobile reference transceiver;

emitting, in response to receiving the polling message, a reply message by said unknown position transmitter;

independently computing from the polling message and the reply message a local-time-of-flight and therefore the local range from the mobile reference transceiver to the unknown position transmitter; and

emitting an audible sound by said unknown position transmitter for assisting in locating the unknown position transmitter.

2. A method of radio position determination of an unknown position transmitter using a mobile-reference transceiver and a plurality of base repeaters having a slave grid synchronization pulse for time reference, located at known geographic locations in a geographic area and coupled to a central monitoring station having a master grid synchronization pulse, comprising the steps of:

emitting by the unknown position transmitter located within the geographical area, a radio wave;

receiving by at least three base repeaters the radio wave emitted by the unknown position transmitter and measuring the relative times-of-arrival of the radio wave with respect to the slave grid synchronization pulse;

computing from the locations of said base repeaters and from the measured relative times-of-arrival a coarse-position fix of the unknown-position transmitter;

transmitting from a mobile reference transceiver located in the geographical area a reference signal;

calculating a differential position vector between said mobile reference transceiver and said unknown position transmitter from the reference signal and the radio wave;

guiding the mobile reference transceiver to said unknown position transmitter using the differential position vector;

emitting a polling message by said mobile reference transceiver;

emitting, in response to receiving the polling message

3. The method as set forth in claim 2 further comprising the step of emitting an audible sound by said unknown position transmitter for assisting in locating the unknown position transmitter.

4. The method as set forth in claim 2 further comprising the step of:

modulating the radio wave with compensation for multipath.

5. The method as set forth in claim 2 further comprising the step of:

modulating the reference signal with compensation for multipath.

6. The method as set forth in claim 1 or 2 further comprising the steps of:

synchronizing the unknown position transmitter to the synchronized pulse.

7. The method as set forth in claim 1 or 2 further comprising the steps of:

synchronizing the mobile reference transceiver to the synchronized pulse.

8. The method as set forth in claim 1 or 2 further comprising the steps of:

transmitting an identification code from the unknown position transmitter to the central monitoring station.

9. A radio position determination system comprising:

an unknown position transmitter for transmitting a radio wave having modulation compensation for multipath which also serves as a coarse ranging modulation, said unknown position transmitter having means responsive to receiving a polling pulse for emitting a reply message;

a plurality of base repeaters having a synchronized pulse for time reference, for receiving the radio wave emitted by said unknown position transmitter and determining the relative times-of-arrival of the radio wave with respect to the synchronized pulse for deriving a set of ranging times and therefore a set of ranges from said base repeaters to said unknown position transmitter;

a central monitoring station coupled to said plurality of base repeaters for computing from the locations of said base repeaters and from the measured relative times-of-arrival, a coarse-position fix of the unknown-position transmitter; and

a mobile reference transceiver located within tee coarse-position fix, for transmitting a reference signal, wherein said central monitoring station computes a differential position vector from the reference signal and the radio wave, between said mobile reference transceiver and said unknown position transmitter for guiding said mobile reference transceiver to said unknown position transmitter, and wherein said mobile reference transceiver includes means for emitting the polling message, and responsive to receiving said reply message for determining a said unknown position transmitter and therefore the local range from said mobile reference transceiver to said unknown position transmitter for assisting in locating said unknown position transmitter.

10. The radio position determination system as set forth in claim 9 wherein said unknown position transmitter further includes means for emitting an audible sound for assisting in locating the unknown position transmitter.

11. The radio position determination system as set forth in claim 9 wherein said mobile reference transceiver and said unknown position transmitter each include modulation means for compensating for multipath.

12. The radio position determination system as set forth in claim 9 wherein said mobile reference transceiver and said unknown position transmitter each include means for generating a spread spectrum signal for compensating for multipath.

13. A method of radio position determination of an unknown position transmitter using mobile-reference transceiver and a plurality of base repeater generating a slave grid synchronization pulse for time reference, located at known geographic locations in a geographic area and coupled to a central monitoring station generating a master grid synchronization pulse for base repeater time reference, comprising the steps of:

transmitting the master grid synchronization pulse by the central monitoring station;

retransmitting the master grid synchronization pulse by the base repeaters as a slave grid synchronization pulse, in response to receiving the master grid synchronization pulse;

receiving by the mobile reference transceiver and the unknown position transmitter, the slave grid synchronization pulse for synchronizing with a system protocol cycle, for acquiring system hop timing, and for referring as a frequency reference for subsequent transmitting;

emitting by the unknown position transmitter located within the geographical area, a radio wave having a demand request during a time slot in the system protocol cycle;

determining the base repeater closest to the unknown position transmitter by comparing measured signal to noise ratio;

polling the unknown position transmitter by the central monitoring station via the closest base repeater to the unknown position transmitter in response to the demand request:

responding to the polling of the central monitoring station by the unknown position transmitter during the same time slot in the system protocol cycle;

receiving by at least three base repeaters the radio wave emitted by the unknown position transmitter and measuring the relative times-of-arrival of the radio wave with respect to the master grid synchronization pulse;

computing from the locations of said base repeaters and from the measured relative times-of-arrival a coarse-position fix of the unknown-position transmitter;

transmitting from a mobile reference transceiver located in the geographical area a reference signal;

calculating a differential position vector between said mobile reference transceiver and said unknown position transmitter from the reference signal and the radio wave; and

guiding the mobile reference transceiver to said unknown position transmitter using the differential position vector.

14. The method set forth in claim 13 further comprising the steps of:

emitting a polling message by said mobile reference transceiver;

emitting, in response to receiving the polling message, a reply message by said unknown position transmitter; and

independently computing from the polling message and the reply message a local-time-of-flight and therefore a local range from the mobile reference transceiver to the unknown position transmitter.

15. The method as set forth in claim 14 further comprising the step of emitting an audible sound by said unknown position transmitter for assisting in locating the unknown position transmitter.

16. The method as set forth in claim 1 wherein the step of measuring at the base repeaters the relative times-of-arrival of the radio wave further includes computing the phase difference between the modulation of the radio wave and the phase of the modulation of the master grid synchronization pulse.

17. The method as set forth in claim 2 wherein the step of measuring at the base repeaters the relative times-of-arrival of the radio wave further includes computing the phase difference between the modulation of the radio wave, and the phase of the modulation of the master grid synchronization pulse.

18. The radio position determination system as set forth in claim 9 wherein said plurality of base repeaters determines the relative times-of-arrival of the radio wave with respect to the synchronized pulse by computing the phase difference between the modulation of the radio wave, and the modulation of the synchronized pulse.

19. The method as set forth in claim 13 wherein the step of measuring at the base repeaters the relative times-of-arrival of the radio wave further includes computing the phase difference between the modulation of the radio wave, and the modulation of the master grid synchronization pulse.

20. A method of radio position determination of an unknown position transmitter using a mobile-reference transceiver and a plurality of base repeaters having a slave grid synchronization pulse for time reference, located at known geographic locations in a geographic area and coupled to a central monitoring station having a master grid synchronization pulse, comprising the steps of:

emitting by the unknown position transmitter located within the geographical area, a radio wave hopping on a plurality of frequencies for overcoming faded reception and for providing a coarse ranging modulation;

receiving by at least three base repeaters the radio wave hopping on each of the plurality of frequencies emitted by the unknown position transmitter and measuring the relative times-of-arrival of the radio wave hopping on each of the plurality of frequencies with respect to the slave grid synchronization pulse;

computing from the locations of said base repeaters and from the measured relative times-of-arrival a coarse-position fix of the unknown-position transmitter, wherein the computing step includes removing the times-of arrival suspect of error due to multipath, thereby resulting in a superior accuracy of location of the unknown transmitter in an urban environment;

transmitting from a mobile reference transceiver located in the geographical area a reference signal;

calculating a differential position vector between said mobile reference transceiver and said unknown position transmitter from the reference signal and the radio wave; and

guiding the mobile reference transceiver to said unknown position transmitter using the differential position vector.

21. A radio position determination system comprising:

an unknown position transmitter for transmitting a radio wave hopping on a plurality of frequencies for overcoming faded reception and providing a coarse ranging modulation;

a plurality of base repeaters having a synchronized pulse for time reference, for receiving the radio wave hopping on the plurality of frequencies emitted by said unknown position transmitter and determining the relative times-of-arrival of the radio wave hopping on the plurality of frequencies with respect to the synchronized pulse for deriving a set of ranging times and therefore a set of ranges from said base repeaters to said unknown position transmitter;

central monitoring station means coupled to said plurality of base repeaters for computing from the locations of said base repeaters and from the measured relative times-of-arrival of the radio wave on each of the plurality of frequencies, a coarse-position fix of the unknown-position transmitter, wherein said central processing station computing means includes means for removing the times-of arrival suspect of error due to multipath, thereby resulting in a superior accuracy of the coarse-position fix of said unknown transmitter in an urban environment; and

a mobile reference transceiver located within the coarse-position fix, for transmitting a reference signal, wherein said central monitoring station computes a differential position vector from the reference signal and the radio wave, between said transmitter for guiding said mobile reference transceiver to said unknown position transmitter.

22. A radio position determination system comprising:

an unknown position transmitter for transmitting a radio wave, said unknown position transmitter having means responsive to receiving a polling pulse for emitting a reply message;

a plurality of base repeaters having a synchronized pulse for time reference, for receiving the radio wave emitted by said unknown position transmitter and determining the relative times-of-arrival of the radio wave with respect to the synchronized pulse for deriving a set of ranging times;

a central monitoring station coupled to said plurality of base repeaters for computing from the locations of said base repeaters and from the measured relative times-of-arrival, a coarse-position fix of the unknown-position transmitter; and

a mobile reference transceiver located within the coarse-position fix, for transmitting a reference signal, wherein said central monitoring station computes a differential position vector from the reference signal and the radio wave, between said mobile reference transceiver and said unknown position transmitter for guiding said mobile reference transceiver to said unknown position transmitter, and wherein said mobile reference transceiver includes means for emitting the polling message, and means, responsive to receiving the reply message, for determining a local-time-of-flight from said mobile reference transceiver to said unknown position transmitter for assisting in locating said unknown position transmitter.