Automatic vehicle identification system capable of vehicle lane discrimination

• US 5,701,127 A
• Filed: 02/23/1993
• Issued: 12/23/1997
• Est. Priority Date: 02/23/1993
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Sharpe, Claude Andrew
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/021,123
• Time in Patent Office: 1,764 Days
• Field of Search: 342/42, 342/44, 342/51, 342/454, 342/455, 342/456, 342/457, 340/825.34, 340/825.54, 340/928
• US Class Current: 340/10.2
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G07B 15/063 using wireless information transmission between the vehicle and a fixed station identification of vehicles G08G
• CPC Class Codes: G08G 1/017 identifying vehicles G08G1/015, G08G1/054 take precedence

Abstract

A method of identifying an object and determining in which of at least two areas the object is located is disclosed. The method includes the steps of: focusing a first directional antenna (18) on a first area (28a), focusing a second directional antenna on a second area (28b), transmitting a first field strength pulse (44) from said first directional antenna (18), transmitting a second field strength pulse (46) from said second directional antenna (18), and comparing in a transponder (14) the first field strength pulse (44) to the second field strength pulse (46) to determine in which of the two areas (28a,28b) the transponder (14) is located. Other devices, systems and methods are also disclosed.

Claims

1. An automatic vehicle identification system capable of vehicle lane discrimination, the system comprising:

a) a first directional antenna focused on a first vehicle lane;

b) a first interrogator unit in electrical communication with said first directional antenna, said interrogator unit being operable to transmit a first downlink message to, and to receive a first uplink message from, said first directional antenna;

c) a second directional antenna focused on a second vehicle lane;

d) a second interrogator unit in electrical communication with said second directional antenna, said interrogator unit being operable to transmit a second downlink message to, and to receive a second uplink message from, said second directional antenna;

e) a remote transponder carried on a vehicle in one of said vehicle lanes, said transponder having a transponder antenna operable to receive RF transmissions and having a field strength comparator operable to receive signals from said transponder antenna and to compare a first field strength pulse received from said first directional antenna to a second field strength pulse received from said second directional antenna.

2. The automatic vehicle identification system of claim 1 and further comprising a toll plaza in which said first and second interrogator units and said first and second directional antennas are located, said toll plaza further comprising a reference oscillator which generates a reference carrier wave which is received by said first and second interrogator units such that said first and second interrogator units are coordinated in frequency.

3. The automatic vehicle identification system of claim 1 wherein said transponder further comprises a field strength detector which converts a signal supplied by one of said directional antennas to a voltage which upon exceeding a threshold activates said transponder.

4. The automatic vehicle identification system of claim 1 wherein said transponder further comprises a field demodulator which is operable to demodulate one of said downlink messages.

5. The automatic vehicle identification system of claim 1 wherein said transponder further comprises a control circuit, a modulated reflector, and a backscatter modulator electrically connected therebetween, said control circuit being operable to control said modulator and said reflector to backscatter modulate information onto said continuous wave illumination signal thereby generating an uplink message.

6. The automatic vehicle identification system of claim 5 wherein said first interrogator unit further comprises a first receiver electrically interposed between said first directional antenna and said first control circuit, said receiver being operable to receive said uplink message and to transmit this uplink message to said first control circuit.

7. The automatic vehicle identification system of claim 5 wherein said modulated reflector and said transponder antenna are an integrated transponder antenna.

8. An automatic vehicle identification system capable of vehicle lane discrimination, the system comprising:

a) a first directional antenna focused on a first vehicle lane;

b) a second directional antenna focused on a second vehicle lane;

c) a first remote transponder carried on a first vehicle in said first vehicle lane, said transponder comprising a first transponder antenna operable to receive RF transmissions, a first field strength detector which converts a signal supplied by said first transponder antenna to a voltage which upon exceeding a threshold activates said first transponder, a first field strength comparator which compares a first field strength pulse received from said first directional antenna by said first transponder antenna to a second field strength pulse received from said second directional antenna by said first transponder antenna, a first field demodulator which is operable to demodulate an amplitude modulated first downlink message from the signal supplied by said first transponder antenna, a first transponder control circuit which receives said first demodulated downlink message from said first field demodulator and a signal from said first field strength comparator indicating whether the first vehicle is travelling in said first lane or said second lane, and a first backscatter modulator which, upon reception by said first transponder control circuit said first downlink message, is operable to backscatter modulate a first continuous wave signal applied to said first transponder antenna to generate a first uplink message, said first backscatter modulator operating under control of said first transponder control circuit;

d) a second remote transponder carried on a second vehicle in said second vehicle lane, said transponder comprising a second transponder antenna operable to receive RF transmissions, a second field strength detector which converts a signal supplied by said second transponder antenna to a voltage which upon exceeding a threshold activates said second transponder, a second field strength comparator which compares a first field strength pulse received from said first directional antenna by said second transponder antenna to a second field strength pulse received from said second directional antenna by said second transponder antenna, a second field demodulator which is operable to demodulate an amplitude modulated second downlink message from the signal supplied by said second transponder antenna, a second transponder control circuit which receives said second demodulated downlink message from said second field demodulator and a signal from said second field strength comparator indicating whether the second vehicle is travelling in said first second lane or said second lane, and a second backscatter modulator which, upon reception by said second transponder control circuit said second downlink message, is operable to backscatter modulate a second continuous wave signal applied to said second transponder antenna to generate a second uplink message, said second backscatter modulator operating under control of said second transponder control circuit; and

e) a toll plaza comprising

i) a reference oscillator generating a reference carrier wave,

ii) a first interrogator unit in electrical communication with said first directional antenna and with said reference oscillator, said interrogator unit having

(1) a first transmitter which transmits a first wake-up burst which is of sufficient field strength at a first pre-selected distance to trigger said first field strength detector to activate said first transponder, transmits a downlink message to said first remote transponder, said downlink message being transmitted using On-OffKeying, and said transmitter further transmitting a first continuous wave illumination signal onto said first transponder so said first transponder may backscatter modulate said first continuous wave illumination signal to generate said first uplink message,

(2) a first receiver for reception of said first uplink message and for separation of said first uplink message from spurious non-modulated reflections, and

(3) a first control circuit for control of said first transmitter and said first receiver, said first control circuit operable to direct said first transmitter to send said first wake-up burst, followed by said first downlink message, said downlink message having periods of RF energy transmission including a first field strength pulse and periods during which no RF energy is transmitted including a first field strength pause, and said first control circuit still further operable to direct said first transmitter to send said first continuous wave illumination signal following said first downlink message and coincident with said first continuous wave illumination signal to direct said first receiver to receive said first uplink message; and

(iii) a second interrogator unit in electrical communication with said second directional antenna and with said reference oscillator, said second interrogator unit coordinated by said reference oscillator to said first interrogator unit and having

(1) a second transmitter which transmits a second wake-up burst which is of sufficient field strength at a second pre-selected distance to trigger said second field strength detector to activate said second transponder, transmits a downlink message to said second remote transponder, said downlink message being transmitted using On-OffKeying, and said transmitter further transmitting a second continuous wave illumination signal onto said second transponder so said second transponder may backscatter modulate said second continuous wave illumination signal to generate said second uplink message,

(2) a second receiver for reception of said second uplink message and for separation of said second uplink message from spurious non-modulated reflections, and

(3) a second control circuit for control of said second transmitter and said second receiver, said second control circuit operable to direct said second transmitter to send said second wake-up burst, followed by said second downlink message, said downlink message having periods of RF energy transmission including a second field strength pulse during said first field strength pause and periods during which no RF energy is transmitted including the time during which said first field strength pulse is transmitted, and said second control circuit still further operable to direct said second transmitter to send said second continuous wave illumination signal following said second downlink message and coincident with said sending of said second continuous wave illumination signal to direct said second receiver to receive said second uplink message.

9. A method of identifying an object and determining in which of at least two areas the object is located, the method comprising:

a) focusing a first directional antenna on a first area;

b) focusing a second directional antenna on a second area;

c) transmitting a first field strength pulse by a first interrogator unit in electrical communication with said first directional antenna;

d) transmitting a second field strength pulse by a second interrogator unit in electrical communication with said second directional antenna; and

e) comparing in a transponder the first field strength pulse received from said first directional antenna to the second field strength pulse received from said second directional antenna whereby the transponder can determine in which of the two areas it is located by the relative magnitude of the received first and second field strength pulses.

10. The method of claim 9 and further comprising the step of differentiating by said transponder between a downlink message from said first interrogator unit and a downlink message from a second interrogator unit.

11. The method of claim 10 and further comprising the step of responding by said transponder with an uplink message to the interrogator unit associated with the directional antenna that is focused on the area in which the transponder is located.

20. The method of claim 10 wherein said first downlink message comprises said first field strength pulse and a first field strength pause and said second downlink message comprises a second field strength pause coincident with said first field strength pulse and a second field strength pulse coincident with said first field strength pause.

21. The method of claim 11 wherein said uplink message is formed in said transponder by backscatter modulating a continuous wave illumination signal from said interrogator unit.

12. An automatic vehicle identification system capable of vehicle lane discrimination, the system comprising:

a) a first directional antenna focused on a first vehicle lane;

b) a first interrogator unit in electrical communication with said first directional antenna, said interrogator unit being operable to transmit a first downlink message to, and to receive a first uplink message from, said first directional antenna;

c) a second directional antenna focused on a second vehicle lane;

d) a second interrogator unit in electrical communication with said second directional antenna, said interrogator unit being operable to transmit a second downlink message to, and to receive a second uplink message from, said second directional antenna;

e) a remote transponder carried on a vehicle in one of said vehicle lanes, said transponder having

i. a transponder antenna operable to receive RF transmissions,

ii. a field strength comparator operable to receive signals from said transponder antenna and to compare a first field strength pulse received from said first directional antenna to a second field strength pulse received from said second directional antenna,

iii. a modulator operable to modulate a carrier with information contained within said remote transponder, and

iv. a control circuit for receiving the results of said field strength comparison and for enabling said modulator.

13. The automatic vehicle identification system of claim 12 wherein said modulator is a backscatter modulator that is operable to backscatter modulate a continuous wave illumination signal from said interrogator unit by modifying the radar cross section of a modulated reflector under the direction of said control unit.

14. The automatic vehicle identification system of claim 13 wherein said modulated reflector and said transponder antenna form an integrated transponder antenna.

15. A remote transponder carried on a vehicle for automatic vehicle identification, said transponder comprising:

a) a transponder antenna operable to receive RF transmissions;

b) a field strength comparator operable to receive signals from said transponder antenna and to compare a first field strength pulse received from a first interrogator directional antenna to a second field strength pulse received from a second interrogator directional antenna;

c) a modulator operable to modulate a carrier with information contained within said remote transponder; and

d) a control circuit for receiving the results of said field strength comparison and for enabling said modulator.

16. The remote transponder of claim 15 wherein said modulator is a backscatter modulator that is operable to backscatter modulate a continuous wave illumination signal from said interrogator unit by modifying the radar cross section of a modulated reflector under the direction of said control unit.

17. The remote transponder of claim 16 wherein said modulated reflector and said transponder antenna form an integrated transponder antenna.

18. A toll plaza comprising:

a) a first directional antenna focused on a first vehicle lane;

b) a second directional antenna focused on a second vehicle lane;

c) a reference oscillator generating a reference carrier wave;

d) a first interrogator unit in electrical communication with said first directional antenna and with said reference oscillator;

e) a second interrogator unit in electrical communication with said second directional antenna and with said reference oscillator, said second interrogator unit coordinated by said reference oscillator to said first interrogator unit; and

f) a control circuit for control of said first and second interrogator units, said control circuit operable to direct each of said first and second interrogator units to send selected periods of RF energy transmission wherein each interrogator unit sends an identifying field strength pulse via its respective directional antenna during a period in which no RF energy is transmitted from the other interrogator unit whereby said transponder may compare the first field strength pulse received from said first directional antenna to a second field strength pulse received from said second directional antenna.

19. The toll plaza of claim 18 and further comprising a third directional antenna focused on a third vehicle lane and a third interrogator unit in electrical communication with said third directional antenna and with said reference oscillator.