Abstract: The disclosed subject-matter relates to a method for calibrating an onboard unit of a vehicle identification system, the method comprising: emitting at least one polling message from a first radio beacon; in the first radio beacon, determining a link margin of a communication with a first onboard unit by evaluating a response message of the first onboard unit to the polling message(s); and sending a configuration message from the first radio beacon or a second radio beacon to the first onboard unit or to a second onboard unit with a same characteristic as the first onboard unit to adjust a receive sensitivity or a transmit power of the first or the second onboard unit, respectively, to a level derived from the determined link margin. Alternative embodiments relate to a system and to an onboard unit used in the method.

Abstract: The disclosed subject matter relates to a method for obtaining a backscatter modulated receive signal in an radio-frequency identification (RFID) system, comprising the steps: providing a carrier wave by a local oscillator; generating a transmit signal based on the carrier wave and an input signal; transmitting said transmit signal; receiving a backscatter modulated receive signal; and combining the receive signal with a cancel signal; wherein the method further comprises the step of determining a phase shift and an amplitude adjust from the corrected receive signal; wherein the determined phase shift is applied as a phase rotation when generating the transmit signal; and wherein the cancel signal is based on the un-shifted carrier wave and the determined amplitude adjust. The disclosed subject matter further relates to an RFID reader configured to perform said method.

Abstract: The disclosed subject matter relates to a method for obtaining a backscatter modulated receive signal in an radio-frequency identification (RFID) system, comprising the steps: providing a carrier wave by a local oscillator; generating a transmit signal based on the carrier wave and an input signal; transmitting said transmit signal; receiving a backscatter modulated receive signal; and combining the receive signal with a cancel signal; wherein the method further comprises the step of determining a phase shift and an amplitude adjust from the corrected receive signal; wherein the determined phase shift is applied as a phase rotation when generating the transmit signal; and wherein the cancel signal is based on the un-shifted carrier wave and the determined amplitude adjust. The disclosed subject matter further relates to an RFID reader configured to perform said method.

Abstract: The disclosed subject matter relates to a vehicle identification system comprising a central station, a roadside reader for wirelessly communicating with radio tags carried by vehicles, a mapping unit connected to the reader, and a correlation unit connected to the mapping unit, wherein the correlation unit is configured to correlate second-protocol tag identifications to first-protocol tag identifications from a reserved subset of first-protocol tag identifications, wherein the mapping unit is configured to generate a new first-protocol message upon receiving a second-protocol message from the reader, and wherein the central station is configured to receive and store first-protocol messages from the reader as well as new first-protocol messages from the mapping unit and to identify a vehicle. The disclosed subject matter further relates to a method for identifying vehicles by means of this system.

Abstract: The disclosed subject matter relates to a vehicle identification system comprising a central station, a roadside reader for wirelessly communicating with radio tags carried by vehicles, a mapping unit connected to the reader, and a correlation unit connected to the mapping unit, wherein the correlation unit is configured to correlate second-protocol tag identifications to first-protocol tag identifications from a reserved subset of first-protocol tag identifications, wherein the mapping unit is configured to generate a new first-protocol message upon receiving a second-protocol message from the reader, and wherein the central station is configured to receive and store first-protocol messages from the reader as well as new first-protocol messages from the mapping unit and to identify a vehicle. The disclosed subject matter further relates to a method for identifying vehicles by means of this system.

Abstract: The disclosed subject-matter relates to a method for calibrating an onboard unit of a vehicle identification system, the method comprising: emitting at least one polling message from a first radio beacon; in the first radio beacon, determining a link margin of a communication with a first onboard unit by evaluating a response message of the first onboard unit to the polling message(s); and sending a configuration message from the first radio beacon or a second radio beacon to the first onboard unit or to a second onboard unit with a same characteristic as the first onboard unit to adjust a receive sensitivity or a transmit power of the first or the second onboard unit, respectively, to a level derived from the determined link margin. Alternative embodiments relate to a system and to an onboard unit used in the method.

Abstract: A transponder, such as an electronic toll transponder, is configured to recognize when it is being subjected to consistent and repeated trigger signals over an extended period of time and, in response, the transponder enters a reduced-responsiveness state. In the reduced-responsiveness state, the transponder may only intermittently respond to detected trigger signals. The transponder may recognize when the repeated trigger signal situation has been resolved and then return to normal responsiveness.

Abstract: A radio-frequency identification (RFID) reader having fast-adaptive echo cancellation for backscatter-modulated signals is described. The echo cancellation includes subtracting an RF-level cancel signal from the received signal, where the cancel signal is generated based upon an error measured in the receive signal after down-conversion to baseband and low-pass filtering. The cancel signal is based upon a cumulative sum or integral of error signals and an estimated complex-valued transfer function of the scaling circuit. Methods of quick calibration of the reader are described, including accounting for circuit offsets and determining the estimated complex-valued transfer function.

Abstract: Methods of estimating vehicle location in a roadway using an automatic vehicle identification system are described. The methods involve receiving a set of response signals from a vehicle-mounted transponder at points in time and determining a range rate of the transponder relative to the antenna at each point in time; identifying a minima in the magnitude of the range rate; estimating a first position of the transponder at a first time corresponding to the occurrence of the minima; estimating a velocity of the vehicle based upon one or more of the determined range rates; and estimating a second position of the transponder based upon the first position and the velocity.

Abstract: Methods for determining a range rate of a backscatter transponder and readers implementing the methods are described. The reader transmits a continuous wave signal and receives a modulated reflected response signal from the transponder, mixes the modulated reflected response signal with the carrier frequency to produce a downconverted signal, bandpass filters the downconverted signal to pass a bandpass filtered signal containing at least the modulation frequency, applies a non-linear amplitude transfer function to produce a modulation-suppressed signal, and measures the frequency of the modulation-suppressed signal and determines the range rate from the measured frequency.

Abstract: Systems, Methods, and Apparatus for enhanced transponder programming in an open road toll system are disclosed. An example method includes transmitting, in a normal mode, a programming signal from one of the antennas over a first coverage area to instruct the transponder to store data in its memory, the data being contained in the programming signal. The example method further includes determining that the transponder did not store the data in its memory. Based on the determination that the transponder did not store the data in its memory the programming signal is transmitted in an enhanced mode, from one antennas over a second coverage area.

Abstract: Methods for determining a range rate of a backscatter transponder and readers implementing the methods are described. The reader transmits a continuous wave signal and receives a modulated reflected response signal from the transponder, mixes the modulated reflected response signal with the carrier frequency to produce a downconverted signal, bandpass filters the downconverted signal to pass a bandpass filtered signal containing at least the modulation frequency, applies a non-linear amplitude transfer function to produce a modulation-suppressed signal, and measures the frequency of the modulation-suppressed signal and determines the range rate from the measured frequency.

Abstract: Methods of estimating vehicle location in a roadway using an automatic vehicle identification system are described. The methods involve receiving a set of response signals from a vehicle-mounted transponder at points in time and determining a range rate of the transponder relative to the antenna at each point in time; identifying a minima in the magnitude of the range rate; estimating a first position of the transponder at a first time corresponding to the occurrence of the minima; estimating a velocity of the vehicle based upon one or more of the determined range rates; and estimating a second position of the transponder based upon the first position and the velocity.

Abstract: A radio-frequency identification (RFID) reader having fast-adaptive echo cancellation for backscatter-modulated signals is described. The echo cancellation includes subtracting an RF-level cancel signal from the received signal, where the cancel signal is generated based upon an error measured in the receive signal after down-conversion to baseband and low-pass filtering. The cancel signal is based upon a cumulative sum or integral of error signals and an estimated complex-valued transfer function of the scaling circuit. Methods of quick calibration of the reader are described, including accounting for circuit offsets and determining the estimated complex-valued transfer function.

Abstract: Systems, Methods, and Apparatus for enhanced transponder programming in an open road toll system are disclosed. An example method includes transmitting, in a normal mode, a programming signal from one of the antennas over a first coverage area to instruct the transponder to store data in its memory, the data being contained in the programming signal. The example method further includes determining that the transponder did not store the data in its memory. Based on the determination that the transponder did not store the data in its memory the programming signal is transmitted in an enhanced mode, from one antennas over a second coverage area.

Abstract: A transponder communication system and method for communicating with a transponder in an electronic toll collection system. A roadside reader attempts to program the transponder in a normal mode in which a programming signal is transmitted to a first coverage area. If the programming attempt in the normal mode is unsuccessful, the reader attempts to program the transponder in an enhanced mode in which a programming signal is transmitted to a second coverage area. The coverage area is adjusted after the programming attempt in the normal mode by using an adjacent antenna to the antenna used to transmit in the normal mode or by increasing the power of the programming signal to a level that is greater than the level used to transmit the programming signal in the normal mode.

Abstract: A system and method for predicting the location of a vehicle in an electronic toll collection system employing a wide area communication protocol. The vehicle includes a transponder that sends reports regarding the position of the vehicle and the time at which the position was determined. The system includes a vehicle position predictor for estimating the future position of the vehicle within a roadway based on two or more reports of past positions and the times at which they were recorded. Speed data or other data impacting likely future position may also be reported and factored into the estimate. The estimate of future position may be used in connection with triggering enforcement measures, timing a toll transaction, integrating wide area toll communications into a legacy toll transaction system, or for other applications.

Abstract: A transponder, such as an electronic toll transponder, is configured to recognize when it is being subjected to consistent and repeated trigger signals over an extended period of time and, in response, the transponder enters a reduced-responsiveness state. In the reduced-responsiveness state, the transponder may only intermittently respond to detected trigger signals. The transponder may recognize when the repeated trigger signal situation has been resolved and then return to normal responsiveness.

Abstract: An adaptive communication system and method for use in an electronic toll collection system utilizing transponders located in vehicles travelling on a toll roadway. A transponder memory stores configuration type data that identifies the type of the vehicle carrying the transponder, the transponder or the transponder's mounting. The transponder transmits the configuration type data to the communication system. The communication system includes a memory which contains a database of predetermined communication parameters for various types of configuration types. The communication system looks up the predetermined communication parameters for the configuration type and adjusts variable communication parameters accordingly. Predetermined communication variables may include the transmit power of an antenna, or the receive sensitivity of the antenna or the position of the vehicle in order to maximize the likelihood of a successful communication.

Abstract: A system and method for predicting the location of a vehicle in an electronic toll collection system employing a wide area communication protocol. The vehicle includes a transponder that sends reports regarding the position of the vehicle and the time at which the position was determined. The system includes a vehicle position predictor for estimating the future position of the vehicle within a roadway based on two or more reports of past positions and the times at which they were recorded. Speed data or other data impacting likely future position may also be reported and factored into the estimate. The estimate of future position may be used in connection with triggering enforcement measures, timing a toll transaction, integrating wide area toll communications into a legacy toll transaction system, or for other applications.