Method and apparatus for automatically monitoring objects

• US 4,112,421 A
• Filed: 04/16/1975
• Issued: 09/05/1978
• Est. Priority Date: 04/16/1975
• Status: Expired due to Term

• Current Assignee: Information Identification Company Incorporated
• Original Assignee: Information Identification Company Incorporated
• Inventors: Freeny, Charles C. Jr.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Blum, T. M.
• Application Number:
  US05/568,671
• Time in Patent Office: 1,238 Days
• Field of Search: 340/22, 340/23, 340/24, 340/346, 325/4, 325/53, 325/55, 325/64, 325/117, 325/185, 325/186, 325/39, 325/67, 325/113, 325/158, 343/112 D
• US Class Current: 342/457
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

An improved method and apparatus for automatically monitoring objects, such as vehicles, for example, wherein signpost units are positioned at predetermined locations and each signpost unit transmits a binary signpost code for reception via units installed in the objects being monitored and the objects being monitored receive the signpost codes and store object location information. In one aspect, the present invention contemplates a method and an apparatus which has a multi-mode operation capability wherein the location of the monitored objects is reported when the monitored object enters a different coverage region in an automatic reporting mode, wherein only those monitored objects within a predetermined region or on a predetermined route report to the base station in a region or route reporting mode, and wherein only the locations of predetermined monitored objects are reported to the base station in a polling mode. In another aspect, the present invention contemplates an improved method and an apparatus for locating and operating the signpost units to reduce the total number of signpost units required to cover a given number of locations wherein each signpost unit establishes a uniquely identifiable near-field region and a uniquely identifiable far-field region, the signpost units being located to establish uniquely identifiable overlap regions wherein a portion of the far-field region of at least one of the signpost units overlaps a portion of the far-field region on another signpost unit. The method and apparatus of the present invention also provides a non-polling location technique eliminating the necessity of interrogating the monitored objects at regular intervals and reducing the radio channel time required for reporting object location. Further, the method and apparatus of the present invention contemplates signpost units constructed and operating to intermittently transmit the signpost codes in a manner allowing the use of relatively long life battery type electrical power sources reducing the installation expense, the equipment costs and the maintenance expense.

Claims

1. Apparatus for use in monitoring objects within a predetermined monitored area comprising:

at least two signpost units, each signpost unit being positioned within the monitored area and each signpost unit having a predetermined signpost code encoded therein identifying the signpost unit and providing an output signal encoded with the signpost code, each signpost unit outut signal establishing a far-field region extending a distance generally from the signpost unit, each signpost unit being positioned with respect to at least one other signpost unit so a portion of the far-field region of each signpost unit overlaps a portion of the far-field region of at least one other signpost unit, thereby forming an overlap region encompassing a predetermined coverage region with the monitored area;

means in the monitored object receiving the signpost unit output signals having a portion detecting the signpost code encoded in the received signpost unit output signal and providing an output signal in response to the received signpost unit output signal for indicating the location of the monitored object as being within the far-field region of the signpost unit identified via the signpost code corresponding to the signpost code encoded in the received signpost unit output signal; and

means in the monitored object for determining and indicating the location of the monitored object as being within one of the overlap regions.

2. The apparatus of claim 1 wherein the means in the monitored object for determining and indicating the location of the monitored object within one of the overlap regions is defined further to include a portion comparing each received signpost code with the previously received signpost code for determining the reception of at least two different signpost codes and for indicating the location of the monitored object within the overlap region formed via the overlapping portions of the far-field regions of the two signpost units identified via the two different received signpost codes.

3. The apparatus of claim 1 wherein each signpost unit is defined further as providing the output signal with the signpost code encoded therein establishing a near-field region extending a distance from the signpost unit, the far-field region extending a distance from the signpost unit greater than the distance of the near-field region from the signpost unit, and the strength of the signpost unit output signal within the near-field region being greater than the strength of the signpost unit output signal in the far-field region;

and wherein the means in the monitored object for indicating the location of the monitored object within the far-field region is defined further as having a portion detecting the strength of the received signpost unit output signal and providing one output signal in response to a received signpost unit output signal having a signal strength less than a predetermined signal strength level thereby indicating the location of the monitored object within the near-field region of the signpost unit identified via the signpost code encoded in the received signpost unit output signal, and providing another output signal in response to a received signpost unit output signal having a signal strength level greater than the predetermined signal strength level thereby indicating the location of the monitored object within the far-field region of the signpost unit identified via the signpost code encoded in the received signpost unit output signal.

4. The apparatus of claim 3 defined further to include a plurality of signpost units positioned within the monitored area, the far-field region and the near-field region of each signpost unit encompassing predetermined coverage regions within the monitored area, the coverage regions encompassing some of the space within the monitored area and the remaining space within the coverage region defining open regions, the signpost units being spaced within the monitored area to substantially assure the passing of the monitored object from at least one of the coverage regions upon entering one of the open regions and to substantially assure the passing of the monitored object into at least one of the coverage regions upon leaving one of the open regions during the movement of the monitored object within the monitored area.

5. The apparatus of claim 3 defined further to include a plurality of signpost units positioned within the monitored area, the far-field region and the near-field region of each signpost unit encompassing predetermined coverage regions within the monitored area and the signpost units being spaced within the monitored area to substantially assure the passing through at least one of the coverage regions by a monitored object entering and leaving the monitored area.

6. The apparatus of claim 3 wherein the means in the monitored object for providing the output signals indicating the location of the monitored object within the near-field and the far-field regions is defined further to include:

a receiver for receiving the signpost unit output signals and providing a receiver output signal encoded with the signpost code encoded in the received signpost unit output signal; and

a power level detector receiving the receiver output signal and providing a power level signal in one state in response to a received receiver output signal having a signal strength less than the predetermined signal strength level thereby indicating the location of the monitored object within the far-field region of the singpost unit identified via the signpost code encoded in the received signpost unit output signal and providing a power level signal in anothr state in response to a received receiver output signal having a signal strength greater than the predetermined signal strength level thereby indicating the location of the monitored object within the near-field region of the signpost unit identified via the signpost code encoded in the received signpost unit output signal.

7. The apparatus of claim 6 wherein the means in the monitored object for providing the output signals indicating the location of the monitored object within the near-field and the far-field regions is defined further to include:

a decoder receiving the receiver output signal and providing the signpost code encoded in the received receiver output signal via a decoder output signal, the decoder receiving the power level signal provided via the power level detector and providing the received power level signal along with the signpost code via the decoder output signal, the state of the power level signal indicating the location of the monitored objection within the near-field region of the signpost unit identified via the signpost code encoded in the receiver output signal in one state of the power level signal and indicating the location of the monitored object within the far-field region of the signpost unit identified via the signpost code encoded in the receiver output in one other state of the power level signal.

8. The apparatus of claim 7 wherein the decoder is defined further as providing a valid data signal in response to receiving a signpost code via the receiver output signal having a predetermined code format.

9. The apparatus of claim 7 wherein each signpost unit is defined further as repeatably providing a time division binary signpost code uniquely identifying the signpost unit;

and wherein the decoder is defined further as providing a valid data signal in response to receiving a signpost code via the receiver output signal having the predetermined code format and repeatable a predtermined number of times.

10. The apparatus of claim 7 defined further to include a plurality of signpost units positioned within the monitored area, the far-field region and the near-field region of each signpost unit encompassing predetermined coverage regions and a portion of the far-field of some of the signpost units overlapping a portion of the far-field region of at least one other signpost unit, the overlapping portions of the far-field regions defining predetermined overlap regions encompassing predetermined coverage regions within the monitored area and the signpost units having the far-field regions forming each overlap region providing the signpost codes in an alternating manner for reception within each overlap region.

11. The apparatus of claim 10 wherein the means in the monitored object for indicating the location of the monitored object within one of the overlap regions is defined further to include:

means receiving the signpost codes and accompanying power level signals via the decoder output signal, storing the received signpost codes and accompanying power level signal, and comparing each of the received signpost codes and accompanying power level signals with the last received signpost code and accompanying power level signal for determining the reception of at least two different signpost codes in an alternating manner each having an accompanying power level signal indicating the location of the monitored object within a far-field region, said means providing an output signal indicating the location of the monitored object in the overlap region formed via the overlapping portions of the far-field regions of the signpost units identified via the received signpost codes.

12. The apparatus of claim 11 wherein the decoder is defined further as providing the signpost code and accompanying power level signal via a plurality of parallel signal paths, each bit of the signpost code being provided on one of the parallel signal paths and the power level signal being provided on one of the parallel signal paths, other than the parallel signal paths having the signpost code bits provided thereon;

and wherein the means storing and comparing the received signpost codes and accompanying power level signals is defined further to include;

a storage unit receiving the signpost codes and accompanying power level signal provided by the decoder on the parallel signal paths, the storage unit storing each received signpost code and accompanying power level signal in one condition of the storage unit, the storage unit providing the signpost code and accompanying power level signal stored therein via a plurality of parallel signal paths in one other condition of the storage unit, each bit of the signpost code and the accompanying power level signal being provided on one of the parallel signal paths; and

a comparison logic network receiving the signpost code provided by the decoder on the parallel signal paths and the signpost code and accompanying power level signal provided by the storage unit on the parallel signal paths, the comparison logic network comparing the signpost code and accompanying power level signal from the decoder with the signpost code and accompanying power level signal from the storage unit, and providing an output signal in response to the signpost code and accompanying power level signal received in the decoder being identical to the signpost code and accompanying power level signal provided via the storage unit, and another output signal in response to the signpost code and accompanying power level signal received in the decoder being different than the signpost code and accompanying power level signal in the storage unit.

13. The apparatus of claim 12 wherein each signpost unit repeatably provides the time division binary signpost code identifying the signpost unit;

and wherein the decoder provides a valid data signal in response to receiving a signpost code via the receiver output signal having the predetermined code format; and

wherein the comparison logic network is defined further to include;

a plurality of exclusive OR gates, each exclusive OR gate receiving the signal on one of the parallel signal paths provided via the decoder and the signal on one of the parallel signal paths provided via the storage unit, each exclusive OR gate providing an output signal in the "low" state in response to indentical received signals and an output signal in the "high" state in response to different received signals; and

a NAND gate receiving each of the output signals from exclusive OR gates, and providing an output signal in the "high" state in response to receiving a signal in the "high" state from any of the exclusive OR gates thereby indicating a signpost code and accompanying power level signal in the decoder different from the signpost code and accompanying power level signal in the storage unit, and providing an output signal in the "low" state in response to receiving a signal in the "low" state from each of the exclusive OR gates thereby indicating a signpost code and accompanying power level signal in the decoder identical with the signpost code and accompanying power level signal in the storage unit.

14. The apparatus of claim 13 wherein the decoder provides the valid data signal in the "high" state in response to receiving a signpost code having a predetermined code format and the valid data signal in the "low" state in response to receiving a signpost code having a code format other than the predetermined code format;

and wherein the comparison logic network is defined further to include;

an inverter receiving the NAND gate output signal, and providing an output signal in the "high" state in response to receiving a NAND gate output signal in the "low" state, and providing an output signal in the "low" state in response to receiving a NAND gate output signal in the "high" state;

a first NAND gate receiving the valid data signal and the inverter output signal, and providing an output signal in the "high" state in response to receiving a valid data signal in the "high" state and an inverter output signal in the "high" state, and providing an output signal in the "low" state in response to receiving a valid data signal in the "low" state, and providing an output signal in the "low" state in response to receiving an inverter output signal in the "low" state, the first AND gate providing the comparison logic network output signal in the "high" state indicating a signpost code and accompanying power level signal in the decoder identical with the signpost code and accompanying power level signal in the storage unit; and

a second AND gate receiving the valid data signal and the NAND gate output signal, and providing an output signal in the "high" state in response to receiving a valid data signal in the "high" state and a NAND gate output signal in the "high" state, and providing an output signal in the "low" state in response to receiving a valid data signal in the "low" state, and providing and output signal in the "low" state in response to receiving a NAND gate output signal in the "low" state, the second AND gate output signal providing the comparison logic network output signal in the "high" state indicating a signpost code and accompanying power level signal in the decoder different from the signpost code and accompanying power level signal in the storage unit.

15. The apparatus of claim 12 defined further to include:

a vehicle region logic network in the monitored object receiving the output signals from the comparison logic network, and providing an output signal in response to received output signals from the comparison logic network for indicating a signpost code and accompanying power level signal different from the signpost code and accompanying power level signal in the storage unit being consecutively received a predetermined number of times via the decoder, the vehicle region logic network providing another output signal in response to received output signals from comparison logic network for indicating two diferent signpost codes and accompanying power level signals being received via the decoder in an alternating manner a predetermined number of times.

16. The apparatus of claim 15 wherein the vehicle region logic network is defined further as providing a reset signal in response to received output signals from the vehicle region logic network for indicating the same signpost code and accompanying power level signal being received via the decoder;

and wherein the decoder is defined further as receiving the reset signal provided via the vehicle region logic network, the decoder receiving a signpost code and accompanying power level signal in one condition and the decoder being conditioned for receiving a signpost code and accompanying power level signal in response to receiving the reset signal provided via the vehicle region logic network.

17. The apparatus of claim 16 wherein the comparison logic network is defined further as providing an output signal in the "high" state for indicating a signpost code and accompanying power level signal received in the decoder identical with the signpost code and accompanying power level signal in the storage unit, and an output signal in the "high" state indicating a signpost code and accompanying power level signal in the decoder different from the signpost code and accompanying power level signal in the storage unit.

18. The apparatus of claim 17 wherein the vehicle region logic network is defined further to include:

a first flip-flop network receiving the comparison logic network output signal indicating different signpost codes and accompanying power level signals in the decoder and the storage unit and providing an output signal in the "low" state in response to a received comparison logic network output signal in the "low" state;

a first inverter receiving the first flip-flop network output signal and providing an output signal in the "low" state in response to a received first flip-flop network output signal in the "high" state, and providing an output signal in the "high" state in response to receiving a first flip-flop network output signal in the "low" state;

an AND gate receiving the comparison logic network output signal indicating the identical signpost codes and accompanying power level signals in the decoder and the storage unit and receiving the first inverter output signal, the first AND gate providing an output signal in the "high" state in response to receiving a comparison logic network output signal in the "high" state and in the "high" state of the first inverter output signal, the first AND gate providing an output signal in the "low" state in response to receiving a comparison logic network output signal in the "low" state and providing an outut signal in the "low" state in response to receiving a first inverter output signal in the "low" state; and

a first OR gate receiving the first AND gate output signal and the comparison logic network output signal indicating different signpost codes and accompanying power level signals in the decoder and storage unit, the first OR gate providing the reset signal in the "high" state in response to receiving a comparison logic network output signal in the "high" state and providing the reset signal in the "high" state in response to receiving a first inverter output signal in the "high" state.

19. The apparatus of claim 15 wherein the comparison logic network is defined further as providing an output signal in the "high" state for indicating a signpost code and accompanying power level signal received in the decoder identical with the signpost code and accompanying power level signal in the storage unit, and an output signal in the "high" state indicating a signpost code and accompanying power level signal in the decoder different from the signpost code and accompanying power level signal in the storage unit;

and wherein the vehicle region logic network is defined further to include;

a first flip-flop network receiving the comparison logic network output signal indicating different signpost codes and accompanying power level signals in the decoder and the storage unit and providing an output signal in the "low" state in response to a received comparison logic network output signal in the "low" state;

a first inverter receiving the first flip-flop network output signal and providing an output signal in the "low" state in response to a received first flip-flop network output signal in the "high" state, and providing an output signal in the "high" state in response to receiving a first flip-flop network output signal in the "low" state;

an AND gate receiving the comparison logic network output signal indicating the identical signpost codes and accompanying power leverl signals in the decoder and the storage unit and receiving the first inverter output signal, the first AND gate providing an output signal in the "high" state in response to receiving a comparison logic network output signal in the "high" state and in the "high" state of the first inverter output signal, the first AND gate providing an output signal in the "low" state in response to receiving a comparison logic network output signal in the "low" state and providing an output signal in the "low" state in response to receiving a first inverter output signal in the "low" state; and

a first counter receiving the comparison logic network output signal indicating different signpost codes and accompanying power level signals and providing the vehicle region logic network output signal in the "high" state in response to receiving a predetermined number of pulses for indicating a signpost code and accompanying power level signal different from the signpost code and accompanying power level signal in the storage unit being consecutively received a predetermined number of times via the decoder, the counter receiving the first AND gate output signal and being reset in response to a received first AND gate output signal in the "high" state.

20. The apparatus of claim 19 wherein the vehicle region logic network is defined further to include:

a second counter receiving the comparison logic network output signal indicating a signpost code and accompanying power level signal received in the decoder identical to the signpost code and accompanying power level signal in the storage unit, and providing an output signal in the "high" state in response to receiving a predetermined number of pulses for providing a vehicle region logic network output signal in the "high" state indicating the moving of a monitored object from one of the coverage regions within the monitored area, the second counter receiving and being reset in response to a "high" state of the comparison logic network output signal indicating different signpost codes and accompanying power level signals in the decoder and the storage unit;

a second OR gate receiving the second counter output signal, the first AND gate output signal and the counter output signal, the second OR gate providing an output signal in the "high" state in response to receiving a signal in the "high" state;

a third OR gate receiving the first counter output signal and the second counter output signal and providing an output signal in the "high" state in response to receiving a signal in the "high" state;

a fourth OR gate receiving each of the comparison logic network output signals and providing an output signal in the "high" state in response to a received comparison logic network output signal in the "high" state;

a third counter receiving the fourth OR gate output signal and providing an output signal in the "high" state in response to receiving a predetermined number of fourth OR gate output signal pulses, the third counter receiving the second OR gate output signal and being reset in response to a received second OR gate output signal;

a second flip-flop network receiving the third counter output signal and providing an output signal in the "high" state in response to a received second flip-flop network output signal in the "high" state, the second flip-flop network receiving the third OR gate output signal and being reset in response to receiving a third OR gate output signal in the "high" state;

a second inverter receiving the first counter output signal, and providing an output signal in the "high" state in response to receiving a first couter output signal in the "low" state and providing an outut signal in the "low" state in response to receiving a first counter output signal in the "high" state; and

a second AND gate receiving the second inverter output signal and the second flip-flop network output signal, and providing an output signal in the "high" state in response to receiving a second inverter output signal in the "high" state and a second flip-flop network output signal in the "high" state, the second AND gate providing the vehicle region logic network output signal indicating two different signpost codes and accompanying power level signals being received via the decoder in an alternating manner a predetermined number of times.

21. The apparatus of claim 20 wherein the vehicle region logic network is defined further to include:

a fifth OR gate output signal receiving the first counter output signal and the second flip-flop network output signal, and providing an output signal in the "high" state in response to receiving one of the first counter output signals and the second flip-flop network output signal in the "high" state, the fifth OR gate output signal being received via the first flip-flop network and the first flip-flop network output signal being reset in response to receiving a fifth OR gate output signal in the "high" state.

22. The apparatus of claim 15 wherein the storage unit is defined further as receiving a signal for conditioning the storage unit to provide the signpost code and accompanying power level signal via the storage unit parallel signal paths in the "high" state of the received signal;

and wherein the apparatus is defined further to include;

a location encoder in the monitored object receiving the signpost code and accompanying power level signal from the storage unit via the storage unit parallel signal paths in one condition of the storage unit; and

means in the monitored object receiving the vehicle region logic network output signal indicating a signpost code and accompanying power level signal received in the decoder identical with the signpost code and accompanying power level signal in the storage unit in the "high" state and receiving the vehicle region logic network output signal indicating a signpost code and accompanying power level signal in the decoder different from the signpost code and accompanying power level signal in the storage unit in the "high" state, said means providing the output signal in the "high" state for conditioning the storage unit to provide the signpost code and accompanying power level signal via the storage unit parallel signal paths for storin the location encoder in the "high" state of any one of the vehicle region logic network output signals received via said means.

23. The apparatus of claim 22 wherein the encoder is defined further as receiving the vehicle region logic network output signal indicating two different signpost codes and accompanying power level signals being received via the decoder in an alternating manner, the encoder storing the vehicle region logic network output signal indicating two different signpost codes and accompanying power level signals being received via the decoder in an alternating manner and the stored vehicle region logic network output signal along with the signpost codes and accompanying power level signals identifying an overlap region.

24. The apparatus of claim 22 wherein the location encoder is defined further as receiving the vehicle region logic network indicating two different signpost codes and accompanying power level signals being received via the decoder in an alternating manner and the state of predetermined bit positions of the signpost code stored in the location encoder being changed in response to the vehicle region logic network output signal received via the location encoder for providing a pseudo-signpost code uniquely identifying the overlap region formed via the four-field regions identified via the two different signpost codes received in an alternating manner.

25. The apparatus of claim 22 wherein the apparatus is defined further to include:

means in the monitored object connected to the location encoder for receiving and transmitting the codes stored in the location encoder in response to the location encoder receiving a code from the storage unit in an automatic reporting mode, said means having a portion for receiving a code identifying one of the coverage regions within the monitored area and comparing the received code with the code stored in the location encoder identifying one of the coverage regions, and transmitting the codes stored in the location encoder in response to an identical comparison of the received code with the code stored in the location encoder identifying one of the coverage regions in a region reporting mode.

26. The apparatus of claim 22 wherein the location encoder is defined further as having a vehicle code stored therein for identifying the monitored object;

and wherein the apparatus is defined further to include;

means in the monitored object connected to the location encoder for receiving and transmitting the codes stored in the location encoder in response to the location encoder receiving a code from the storage unit in an automatic reporting mode, said means having a portion for receiving a vehicle code identifying one of the monitored objects and comparing the received vehicle code with the vehicle code stored in the location encoder, and transmitting the codes stored in the location encoder in response to an identical comparison of the received vehicle code with the vehicle code stored in the location encoder in a vehicle polling mode.

27. The apparatus of claim 26 wherein the means for transmitting the codes in the location encoder is defined further as having a portion for receiving a code identifying one of the coverage regions within the monitored area and comparing the received code with the code stored in the location encoder identifying one of the coverage regions and transmitting the codes stored in the location encoder in response to an identical comparison of the received code with the code stored in the location encoder identifying one of the coverage regions in a region reporting mode.

28. The apparatus of claim 27 defined further to include:

means in the monitored object for receiving operating mode bits and conditioning the means for transmitting the codes in the location encoder in the automatic reporting mode in response to one received predetermined operating mode bit, and conditioning the means for transmitting the codes in the vehicle reporting mode in response to another received predetermined operating mode bit, and conditioning the means for transmitting the codes in the region reporting mode in response to one other received predetermined operating mode bit.

29. The apparatus of claim 22 defined further to include:

means in the monitored object for transmitting the codes stored in the location encoder in one condition; and

means in the monitored object for conditioning the means for transmitting the codes in the condition for transmitting the codes stored in the location encoder.

30. The apparatus of claim 22 wherein the monitored object includes a vehicle transmitter-receiver for two-way voice communication, the vehicle transmitter-receiver being available for transmitting and receiving codes except when the vehicle transmitter-receiver is being utilized for voice communication;

and wherein the apparatus is defined further to include;

an interface unit in the monitored object connected to the vehicle transmitter-receiver and to the location encoder for connecting the codes in the location encoder to the vehicle transmitter-receiver for transmission via the vehicle transmitter-receiver when the vehicle transmitter-receiver is available for transmitting and receiving codes.

31. The apparatus of claim 15 defined further to include:

means in the monitored object for providing an output signal pulse in response to the movement of the object a predetermined distance;

a counter in the monitored object receiving the output signal pulses from the means for providing an output signal pulse in response to the movement of the object a predetermined distance, the counter providing an output signal pulse in response to a predetermined number of input signal pulses received from the means for providing an output signal pulse in response to the movement of the object, the counter output signal pulses indicating the movement of the object a predetermined distance, the counter having a portion for receiving a reset signal and the counter being reset in response to a received reset signal;

means in the monitored object receiving the vehicle region logic network output signal indicating identical signpost codes being repeatedly received via the decoder and providing an output signal in the "high" state in response thereto, and receiving the vehicle region logic network output signal indicating different signpost codes received in an alternating manner via the decoder and providing an output signal in the "high" state in response thereto, the counter receiving the output signals from said means and the counter being reset in response to a received output signal from said means in the "high" state, the counter providing an output signal indicating the movement of the object a predetermined distance unless reset via said means output signal in the "high" state;

a location encoder in the monitored object receiving and storing the counter output signal; and

means in the monitored object for transmitting the counter signal stored in the location encoder.

32. The apparatus of claim 15 defined further to include:

a timer in the monitored object providing output signal pulses at a predetermined rate;

a counter in the monitored object receiving the timer output signal pulses and providing an output signal in response to a received predetermined number of timer output signal pulses, the counter output signal indicating a predetermined time lapse, and the counter receiving a signal and being reset in response to a received signal in the "high" state;

means in the monitored object receiving the vehicle region logic network output signal indicating identical signpost codes being repeatedly received via the decoder and providing an output signal in the "high" state in response thereto, and receiving the vehicle region logic network output signal indicating different signpost codes received in an alternating manner via the decoder and providing an output signal in the "high" state in response thereto, the counter receiving the output signal from said means and being reset in response to a received signal from said means in the "high" state, the counter output signal indicating the time lapsed since the object entered one of the coverage regions;

a location encoder in the monitored object receiving and storing the counter output signal; and

means in the monitored object for transmitting the counter signal stored in the location encoder.

33. The apparatus of claim 6 wherein the means in the monitored object for indicating the location of the monitored object within one of the overlap regions is defined further to include:

means storing the received signpost and accompanying power level signals, and comparing each of the received signpost codes and accompanying power level signals with the previously received signpost code and accompanying power level signal for determining the reception of at least two different signpost codes each having an accompanying power level signal indicating the location of the monitored object within a far-field region, thereby indicating the location of the monitored object in the overlap region formed via the overlapping portions of the far-field regions of the signpost units identified via the received signpost codes.

34. The apparatus of claim 33 wherein each signpost unit is defined further to include:

a signpost encoder encoded with a time division binary signpost code, having an "on" condition and an "off" condition, the signpost encoder receiving a signal and being conditioned in the "on" condition in response thereto, the signpost encoder providing the signpost code via an output signal in the "on" condition of the signpost encoder;

means, having an "on" condition, an "off" condition and providing an output signal in the "on" condition, said means being conditioned in the "on" condition for a predetermined "on" period of time and being conditioned in the "off" condition for a predetermined "off" period of time, the output signal of said means being connected to the signpost encoder for conditioning the signpost encoder in the "on" condition, the ratio of the "on" period of time to the sum of the "on" and the "off" periods of time (the cycle period of time) defining the duty cycle and the "off" period of time being greater than the "on" period of time of said means for lowering the duty cycle;

means receiving the signpost encoder output signal for transmitting a signpost unit output signal encoded with the signpost code.

35. The apparatus of claim 34 wherein the means for conditioning the signpost encoder in the "on" condition of some of the signpost units is defined further as conditioning the signpost encoders in the "on" condition for a first period of time sufficient to provide the signpost code a predetermined number of times via the signpost encoder output signal in the "on" condition of the signpost encoder for operating some of the signpost units at a first pulse repetition frequency;

and wherein the means for conditioning the signpost encoder in the "on" condition of the remaining signpost units is defined further as conditioning the signpost encoders in the "on" condition for a second period of time sufficient to provide the signpost code a predetermined number of times via the signpost encoder output signal in the "on" condition of the signpost encoder for operating the remaining signpost units at a second pulse repetition frequency, the second pulse repetition frequency being different than the first pulse repetition frequency.

36. The apparatus of claim 34 wherein the means for conditioning the signpost encoder in the "on" condition of some of the signpost units is defined further as conditioning the signpost units in the "on" condition and the "off" condition for a predetermined first cycle period of time;

and wherein the means for conditioning the signpost encoder in the "on" condition of the remaining signpost units is defined further as conditioning the signpost units in the "on" condition and "off" condition for a predetermined second cycle period of time, the second cycle period of time being greater than the first cycle period of time.

37. The apparatus of claim 36 wherein the means for conditioning the signpost encoder in the "on" condition of some of the signpost units is defined further as conditioning the signpost units in the "on" condition for a predetermined period of time for providing a first duty cycle;

and wherein the means for conditioning the signpost encoder in the "on" condition of the remaining signpost units is defined further as conditioning the signpost units in the "on" condition for a predetermined period of time for providing a second duty cycle, the second duty cycle being approximately equal to the first duty cycle.

38. The apparatus of claim 37 wherein the means for conditioning the signpost encoder in the "on" condition of some of the signpost units and the means for conditioning the signpost encoder in the "on" condition of the remaining signpost units are each defined further as conditioning the signpost encoders in the "on" and the "off" conditions to provide a ratio of the first cycle period of time to the second cycle period of time at least equal to the period of time required to provide the signpost code stored in any of the signpost units via the signpost encoder output signal.

39. The apparatus of claim 38 wherein the period of time required to transmit the signpost code one time via the signpost units having the first cycle period of time is approximately equal to the period of time required to transmit the signpost code one time via the signpost units having the second cycle period of time.

40. The apparatus of claim 34 wherein the means for transmitting the signpost codes is defined further to include:

a transmitter for transmitting the signpost codes provided via the signpost encoder output signal in the relatively high frequency range to produce a radiation pattern establishing a relatively steep radiation field gradient thereby establishing a near-field region extending a predetermined distance from the signpost unit and a far-field region extending a predeterming distance from the near-field region, the strength of the transmitted signal within the near-field region being greater than the strength of the transmitted signal within the far-field region.

41. The apparatus of claim 34 wherein the means for transmitting the signpost codes is defined further to include:

an FSK generator, having an "on" condition and an "off" condition, receiving the signpost encoder output signal and receiving the output signal provided via the means for conditioning the signpost encoder in the "on" condition, the FSK generator being conditioned in the "on" condition in response to receiving the output signal provided via the means for conditioning the signpost encoder in the "on" condition and the FKS generator providing an output signal having one frequency (f_s) in response to receiving a signpost code bit representing a logical "zero" and another frequency (f_m) in response to receiving a signpost code bit representing a logial "one" in the "on" condition of the FSK generator;

a transmitter modulator, having an "on" condition and an "off" condition, receiving the output signal provided via the means for conditioning the signpost encoder in the "on" condition and the transmitter modulator being conditioned in the "on" condition in response thereto providing a transmitter modulator output signal; and

a transmitter receiving the output signal provided via the means for conditioning the signpost encoder in the "on" condition and receiving the transmitter modulator output signal, the transmitter providing an output signal having a predetermined frequency and the transmitter output signal being modulated via the transmitter modulator output signal.

42. The apparatus of claim 6 wherein the signpost units are each defined further as having an "on" and an "off" condition and wherein each signpost unit provides the output signal encoded with the signpost code in the "on" condition, some of the signpost units being conditioned in the "on" condition and the "off" condition for a predetermined first cycle period of time and as being conditioned in the "on" condition for a predetermined first period of time sufficient to provide the signpost code a predetermined number of times via the signpost unit output signal thereby operating the signpost units at a first pulse repetition frequency;

and wherein at least some of the remaining signpost units are each defined further as being conditioned in the "on" condition and the "off" condition for a predetermined second cycle period of time and as being conditioned in the "on" condition for a predetermined second period of time sufficient to provide the signpost code a predetermined number of times via the signpost unit output signal thereby operating the signpost units at a second pulse repetition frequency, the second pulse repetition frequency being greater than the first pulse repetition frequency and at least one more signpost code being provided during the first period of time as compared to the number of times the signpost code is provided during the second period of time.

43. The apparatus of claim 42 wherein each signpost unit is defined further to include:

a signpost encoder encoded with a time division binary signpost code, having an "on" condition and an "off" condition, the signpost encoder receiving a signal and being conditioned in the "on" condition in response thereto, the signpost encoder providing the signpost code via an output signal in the "on" condition of the signpost encoder;

means, having an "on" condition, an "off" condition and providing an output signal in the "on" condition, said means being conditioned in the "on" condition for a predetermined "on" period of time and being conditioned in the "off" condition for a predetermined "off" period of time, the output signal of said means being connected to the signpost encoder for conditioning the signpost encoder in the "on" condition, the ratio of the "on" period of time to the sum of the "on" and the "off" periods of time (the cycle period of time) defining the duty cycle and the "off" period of time being greater than the "on" period of time of said means for lowering the duty cycle;

a battery type electrical operating power supply connected to the means for conditioning the signpost encoder in the "on" condition, the operating life of the battery type electrical operating power supply being increased via the lowering of the duty cycle; and

means receiving the signpost encoder output signal for transmitting a signpost unit output signal encoded with the signpost code.

44. A method for monitoring objects within a predetermined monitored area utilizing signpost units wherein each signpost unit transmits an output signal having a signpost code encoded therein uniquely identifying the signpost unit and establishing a far-field region extending a distance generally from the signpost unit and wherein each monitored object is capable of receiving the signpost unit output signals, the method comprising:

positioning the signpost units in the monitored area;

positioning at least one of the signpost units with respect to at least one of the other signpost units so a portion of the far-field region of at least one signpost units overlaps a portion of the far-field region of at least one of the other signpost units for forming an overlap region encompassing a predetermined coverage region within the monitored area receiving the signpost unit output signals at the monitored objects;

detecting the signpost code encoded in the signpost unit output signals received at the monitored objects;

providing an output signal in response to the signpost unit output signal received at the monitored object for indicating the location of the monitored object as being within the far-field region of the signpost unit identified via the signpost code corresponding to the signpost code encoded in the signpost unit output signal received at the monitored object; and

determining and indicating at the monitored object the location of the monitored object as being within one of the overlap regions.

45. The method of claim 44 wherein the step of determining and indicating the location of the monitored object within one of the overlap regions is defined further to include the step of:

comparing ech received signpost code with the previously received signpost code for determining the reception of at least two different signpost codes and for indicating the location of the monitored object within the overlap region formed via the overlapping portions of the far-field regions of the two signpost units identified via the two different signpost codes received at the monitored object.

46. The method of claim 45 defined further to include the steps of:

providing the output signal of one of the signpost units forming an overlap region at a first pulse repetition frequency; and

providing the output signal of the other signpost unit forming an overlap region at a second pulse repetition frequency, the first pulse rate frequency being different than the second pulse rate frequency for providing the output signal of one of the signpost units in an alternating manner with respect to the output signal of the other signpost unit forming an overlap region.

47. The method of claim 46 wherein the step of comparing each received signpost code with the previously received signpost code is defined further as determining the reception of at least two different signpost codes in an alternating manner for indicating the location of the monitored object within the overlap region formed via the overlapping portions of the far-field regions of the two signpost units identified via the two different signpost codes received in an alternating manner at the monitored object.

48. The method of claim 47 wherein each of the signpost units repeatably provides a time division binary signpost code uniquely identifying the signpost unit encoded in the signpost unit output signal, and wherein the method is defined further to include the steps of:

determining the reception of a signpost code at the monitored object repeatable a predetermined number of times before comparing the received signpost code with the previously received signpost code.

49. The method of claim 45 defined further to include the steps of:

transmitting the signpost code provided via one of the signpost units forming an overlap region for a predetermined period of time during a first cycle period of time; and

transmitting the support code provided via the other signpost unit forming an overlap region for a predetermined period of time during a second cycle period of time, the second cycle period of time being greater than the first cycle period of time.

50. The method of claim 49 wherein the step of transmitting the signpost codes during the first cycle period of time is defined further as transmitting the signpost code repetitively a predetermined number of times during each first cycle period of time;

and wherein the step of transmitting the signpost codes during the second cycle period of time is defined further as transmitting the signpost code repetitively a predetermined number of times during each second cycle period of time, the number of times the signpost code is repetitively transmitted during the second cycle period of time being different than the number of times the signpost code is repetitively transmitted during the first cycle period of time, the ratio of the first cycle period of time to the second cycle period of time being at least equal to the time required to transmit the signpost code one time during the first cycle period of time and at least equal to the time required to transmit the signpost code one time during the second cycle period of time, and the time required to transmit the signpost code one time during the first cycle period of time being approximately equal to the time required to transmit the signpost code one time during the second cycle period of time.

51. The method of claim 49 wherein the step of transmitting the signpost codes during the first cycle period of time is defined further as transmitting the signpost codes for a first period of time during the first cycle period of time;

and wherein the step of transmitting the signpost codes during the second cycle period of time is defined further as transmitting the signpost codes for a second period of time different from the first period of time.

52. The method of claim 51 wherein the step of transmitting the signpost codes during the first cycle period of time is defined further as transmitting the signpost code a predetermined number of times during each first cycle period of time;

and wherein the step of transmitting the signpost codes during the second cycle period of time is defined further as transmitting the signpost code a predetermined number of times during each second cycle period of time different than the number of times the signpost code is transmitted during the first cycle period of time.

53. The method of claim 52 wherein the step of transmitting the signpost codes during the second cycle period of time is defined further as transmitting the signpost codes for the second period of time during the second cycle period of time, the ratio of the second period of time to the second cycle period defining the duty cycle and the duty cycle being approximately equal to the ratio of the first period of time to the first cycle period of time.