Method of enabling two-state operation of electronic toll collection system
First Claim
1. A method for determining a state of a transponder, the transponder having at least a first state of operation and a second state of operation, the transponder including an antenna for propagating RF signals, wherein the RF signals have a first polarization in the first state and the RF signals have a second polarization in the second state, and wherein the first polarization is substantially different from the second polarization, the method comprising the steps of:
- transmitting an RF polling signal from a reader to the transponder, the reader having a plurality of antennas for propagating the RF polling signal;
detecting a response signal from the transponder;
if said response signal has said first polarization, determining that the transponder is in said first state; and
if said response signal has said second polarization, determining that the transponder is in said second state.
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Accused Products
Abstract
A method and system for communicating state information from a transponder to a reader. The transponder outputs linearly polarized RF signals having either a first polarization, such as horizontal, or a second polarization, such as vertical. The polarization is selected so as to indicate a first state or a second state. The reader detects whether received RF signals have the first polarization or the second polarization, and thereby determines the state of the transponder. In some embodiments, the reader may include two linearly polarized antennas, one with the first polarization and one with the second polarization, for receiving the RF signals from the transponder and determining the polarization of the received RF signals. The system may be implemented within an electronic toll collection system, wherein the transponders are affixed to the interior of vehicle windshields using a rotatable mounting mechanism having two selectable positions.
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Citations
23 Claims
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1. A method for determining a state of a transponder, the transponder having at least a first state of operation and a second state of operation, the transponder including an antenna for propagating RF signals, wherein the RF signals have a first polarization in the first state and the RF signals have a second polarization in the second state, and wherein the first polarization is substantially different from the second polarization, the method comprising the steps of:
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transmitting an RF polling signal from a reader to the transponder, the reader having a plurality of antennas for propagating the RF polling signal; detecting a response signal from the transponder; if said response signal has said first polarization, determining that the transponder is in said first state; and if said response signal has said second polarization, determining that the transponder is in said second state. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An electronic toll collection system, comprising:
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a transponder including an antenna for propagating RF signals, the transponder having at least a first state of operation and a second state of operation, wherein in said first state the RF signals have a first polarization, and wherein in the second state the RF signals have a second polarization, and wherein said first polarization is substantially different from said second polarization; and a reader including a plurality of antennas for receiving the RF signals from said transponder, the reader including a detector for determining whether said RF signal have said first polarization or said second polarization, and thereby determining whether said transponder is in said first state or said second state. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. An electronic toll collection system, comprising:
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a transponder including a first antenna and a second antenna, the first antenna having a first polarization and the second antenna having a second polarization, wherein said first polarization is substantially different from said second polarization; and a reader including a plurality of antennas for selectively sending first RF signals or second RF signals to said transponder, wherein said first RF signals have said first polarization and said second RF signals have said second polarization, and wherein said transponder includes a detector for distinguishing between said first RF signals and said second RF signals.
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Specification