Multiple protocol transponder

Abstract

A multi protocol transponder for a communications network having a antenna for receiving a first RF signal transmitted according to a communications protocol and a detector for identifying the communications protocol from the first RF signal. A protocol controller is provided for executing the identified communications protocol to generate a second RF signal. Thereafter an antenna transmits the second RF signal according to the communications protocol either by active transmission or modulated backscatter. The transponder may implement a variety of wide area and localized lane based protocols for Automatic Vehicle Identification systems such as CVO and Toll systems.

1 . A multi-protocol transponder for communicating with a reader using RF communications in accordance with a plurality of possible protocols, the reader using a selected one of the plurality of possible protocols, the transponder comprising: 
 an antenna;    an RF modem connected to the antenna for receiving an RF signal induced in the antenna by radiated RF energy from the reader, the RF modem demodulating the received RF signal and outputting a digital signal; and    a digital controller for receiving the digital signal and controlling the generation of a response signal in accordance with the selected protocol,    the RF modem including a protocol detector for receiving the RF signal and identifying the selected one of the plurality of possible protocols based upon the radiant energy level of the received RF signal.    
   
   
       2 . The multi-protocol transponder claimed in  claim 1 , wherein the plurality of possible protocols includes at least three candidate protocols and wherein said protocol detector includes means for measuring the radiant RF energy against a first threshold and identifying the presence of the RF communications based upon the radiant RF energy exceeding the first threshold.  
   
   
       3 . The multi-protocol transponder claimed in  claim 2 , wherein said protocol detector includes means for testing the RF signal for indicia of one of said candidate protocols and, based on said testing, either selecting said one of said candidate protocols or comparing the radiant RF energy against a second threshold, and means for testing the RF signal for indicia of a second of said candidate protocols if the radiant RF energy exceeds said second threshold.  
   
   
       4 . The multi-protocol transponder claimed in  claim 1 , wherein the plurality of possible protocols includes two or more candidate protocols and wherein said protocol detector includes means for excluding protocols as candidate protocols based upon testing the radiant RF energy against a set of escalating thresholds.  
   
   
       5 . The multi-protocol transponder claimed in  claim 4 , wherein the means for excluding includes means for identifying indicia of a particular protocol within the RF signal based upon finding that the radiant RF energy exceeds one of said escalating thresholds.  
   
   
       6 . The multi-protocol transponder claimed in  claim 1 , wherein the RF modem includes an active transmitter component for sending the response signal by active transmission and a backscatter modulation component for sending the response signal by backscatter modulation, and wherein the digital controller selects between the active transmitter component and the backscatter modulation component based upon the protocol identified by the RF modem.  
   
   
       7 . The multi-protocol transponder claimed in  claim 1 , wherein the plurality of possible protocols include a TDMA protocol, a Title 21 protocol, and an IAG protocol.  
   
   
       8 . The multi-protocol transponder claimed in  claim 1 , wherein the reader operates within an electronic toll collection system, the RF communication relate to a toll transaction, and the multi-protocol transponder is associated with a vehicle.  
   
   
       9 . A method for operating a multi-protocol transponder communicating with a reader using RF communications in accordance with a plurality of possible protocols, the reader using a selected one of the plurality of possible protocols, the transponder including an antenna, the method comprising the steps of: 
 receiving an RF signal induced in the antenna by radiated RF energy from the reader;    identifying the selected one of the plurality of possible protocols based upon the radiant RF energy level of the received RF signal;    demodulating the received RF signal to obtain a digital signal; and    generating a response signal in accordance with the selected protocol.    
   
   
       10 . The method claimed in  claim 9 , wherein the plurality of possible protocols includes at least three candidate protocols and wherein said step of identifying includes measuring the radiant RF energy against a first threshold and identifying the presence of the RF communications based upon the radiant RF energy exceeding the first threshold.  
   
   
       11 . The method claimed in  claim 10 , wherein said step of identifying further includes steps of testing the RF signal for indicia of one of said candidate protocols and, based on said testing, either selecting said one of said candidate protocols or comparing the radiant RF energy against a second threshold, and a step of testing the RF signal for indicia of a second of said candidate protocols if the radiant RF energy exceeds said second threshold.  
   
   
       12 . The method claimed in  claim 9 , wherein the plurality of possible protocols includes two or more candidate protocols and wherein said step of identifying includes a step of excluding protocols as candidate protocols based upon testing the radiant RF energy against a set of escalating thresholds.  
   
   
       13 . The method claimed in  claim 12 , wherein the step of excluding includes a step of identifying indicia of a particular protocol within the RF signal based upon finding that the radiant RF energy exceeds one of said escalating thresholds.  
   
   
       14 . The method claimed in  claim 9 , further including a step of transmitting the response signal, wherein the step of transmitting includes modulating the response signal with an RF carrier signal.  
   
   
       15 . The method claimed in  claim 14 , wherein the transponder includes an active transmitter and a backscatter modulation transmitter and wherein said step of modulating includes selecting between the active transmitter and the backscatter modulation transmitter based upon the protocol identified in said identifying step.  
   
   
       16 . The method claimed in  claim 9 , wherein the plurality of possible protocols include a TDMA protocol, a Title 21 protocol, and an IAG protocol.