External indicator for electronic toll communications

1. An external indicator for use in proximity to an on-board unit of an electronic toll collection system, the electronic toll collection system including a roadside unit for communicating with the on-board unit and conducting an electronic toll collection (ETC) transaction, the on-board unit including an on-board antenna and an on-board transceiver for sending and receiving RF transmissions and an on-board processor for controlling the on-board transceiver and conducting the ETC transaction with the roadside unit, the external indicator comprising:

an RF antenna;

an RF detector coupled to said RF antenna for demodulating an RF signal induced in said RF antenna by an RF transmission and for outputting a demodulated signal;

a processor having an input for receiving said demodulated signal and an output for providing an indicator signal, the processor having a component for determining if said demodulated signal is indicative of an ETC transmission between said on-board unit and said roadside unit and, if so, generating said indicator signal, wherein said component is configured to determine that said demodulated signal is indicative of said ETC transmission by identifying that said demodulated signal comprises a transponder response signal from said on-board unit; and

an indicator device coupled to the output of said processor, said indicator device producing a sensory event in response to said indicator signal.

2. The external indicator claimed in claim 1 , wherein said processor includes a signal strength component for comparing a signal strength of said demodulated signal with a first threshold level.

3. The external indicator claimed in claim 2 , wherein said signal strength component outputs a detection signal if said signal strength of said demodulated signal exceeds said first threshold level, and wherein said component for determining operates in response to said detection signal.

4. The external indicator claimed in claim 2 , wherein said signal strength component comprises a first comparator for applying said first threshold level.

5. The external indicator claimed in claim 4 , wherein said signal strength component further includes a second comparator for applying a second threshold level, wherein said second comparator outputs said demodulated signal to said component for determining.

6. The external indicator claimed in claim 1 , wherein said indicator device comprises at least one visual device, sensory device, or kinetic device.

7. The external indicator claimed in claim 1 , wherein said indicator device is selected from the group consisting of a light emitting diode, a speaker, a buzzer, a chime, a vibratory mechanism, an incandescent light, and a display screen.

8. A method of signalling detection of a likely electronic toll collection (ETC) transaction between an on-board unit and a roadside unit, the on-board unit including an on-board antenna and an on-board transceiver for sending and receiving RF transmissions and an on-board processor for controlling the on-board transceiver and conducting the ETC transaction with the roadside unit, the method comprising the steps of:

receiving and demodulating an RF signal to produce a demodulated signal at an external indicator separate from the on-board unit;

determining at the external indicator if the demodulated signal is indicative of an ETC communication between the roadside unit and the on-board unit and, if so, generating an indicator signal, wherein said step of determining includes identifying that said demodulated signal comprises a transponder response signal from said on-board unit; and

outputting said indicator signal to an indicator device for producing an sensory event at the external indicator in response to said indicator signal.

9. The method claimed in claim 8 , including a step of comparing a signal strength of said demodulated signal with a first threshold level.

10. The method claimed in claim 9 , including a step of outputting a detection signal based upon said step of comparing if said signal strength of said demodulated signal exceeds said first threshold level, and wherein said step of determining is performed in response to said detection signal.

11. The method claimed in claim 9 , wherein said step of determining includes a second step of comparing the signal strength of said demodulated signal with a second threshold level.

12. The method claimed in claim 8 , wherein said indicator device comprises at least one visual device, sensory device, or kinetic device.

13. The method claimed in claim 8 , wherein said indicator device is selected from the group consisting of a light emitting diode, a speaker, a buzzer, a chime, a vibratory mechanism, an incandescent light, and a display screen.

14. The external indicator claimed in claim 1 , wherein said external indicator excludes an RF transmitter.

15. The external indicator claimed in claim 1 , wherein said external indicator has no direct connection with the on-board unit.

16. The method claimed in claim 8 , wherein said steps of receiving and determining include (a) receiving a RF signal from the roadside reader, (b) identifying the RF signal from the roadside reader as a reader trigger signal, (c) detecting an RF signal from the on-board reader, and (d) identifying the RF signal from the on-board reader as said transponder response signal.

17. The method claimed in claim 16 , wherein said steps of identifying include demodulating and digitizing said RF signals, and comparing said demodulated RF signals with expected characteristics.

18. The method claimed in claim 8 , wherein said step of receiving comprises receiving said RF signal inductively via an RF antenna.