Communications systems for remote mobile communications are becoming more commonplace. Such systems are used in a variety of applications, including Automatic Vehicle Identification (AVI) for Commercial Vehicle Operations (CVO) and for Electronic Toll and Traffic Management (ETTM). Mobile commerce systems may also be used in other contexts, including automated payment at drive-through lanes for fast food outlets, automated payment at parking facilities, and automated payment at fueling stations. ETTM systems, for example, allow drivers to pay highway tolls without stopping, allowing a toll station to process a higher volume of traffic.
These systems typically provide for two-way communication between a reader and a transponder (or “tag”). The reader is usually at a fixed point, such as a toll plaza, and the transponder is usually mounted to a vehicle. The transponder stores information of interest to the transaction, including the identity of the vehicle, time, vehicle type, etc. In a mobile commerce system, the transponder also stores payment information, which may include pre-paid account identity, account balance details, credit card information, or other financial data.
Such communication systems use radio frequency (RF) signals to communicate between the reader and the transponder. These systems typically provide both “read” and “write” capabilities, permitting a reader to access the information stored in the transponder and permitting the transponder to update its stored data in response to instructions from the reader. For example, the reader at a toll plaza may receive and read the transponder information regarding the vehicle type, the most recent toll plaza or on-ramp used by the transponder, and the user's account details. It may then calculate a toll to be paid and transmit instructions to the transponder causing the transponder to debit the account balance stored in its local memory. The reader may also communicate with a remote central database containing account information for individual users to update the status of the user's account.
In operation, the reader sends an RF signal to the transponder. An antenna at the transponder receives the signal from the reader and responds thereto according to a pre-defined protocol. The transponder produces a series of signals, providing the reader with the data stored in the transponder.
Reader-transponder technologies use two physical modes of operation: active transmission or modulated backscatter. In active systems, the transponder includes an active transmitter which responds to interrogation or trigger signals from the reader with an active modulated RF response signal generated by the transponder. Backscatter systems involve a transponder that responds to a continuous wave (CW) RF signal generated by the reader by modulating the continuous wave, electrically switching the transponder's antenna from a reflective to an absorptive characteristic according to the transponder's modulating signal.
There are a number of pre-defined communication protocols for reader-transponder communications in a mobile commerce system. They include various public TDMA protocols, the State of California Code of Regulation (CAL-TRAN) Title 21 (T21) protocol, and proprietary protocols. An example of the latter may be seen in U.S. Pat. No. 5,196,846 to Brockelsby et al. Various pre-defined protocols are discussed in US Pub. No. US2001/0050922, published Dec. 13, 2001 and owned in common with the present application.
The increased use of mobile commerce systems has lead to an increased risk of disclosure of confidential information and theft. A third party may intercept communications between a reader and a transponder and thereby obtain confidential information regarding the transponder and its user. The illicitly obtained information could include personal data, account information, credit card information, or other sensitive data. In some cases, a third party could make use of this illicitly obtained information to impersonate the user or conduct transactions at the user's expense. Another concern is that a third party could track a user's movements based upon the communications between a transponder and a reader.
Accordingly, it would be advantageous to prevent or discourage the interception of communications in a mobile commerce system.
A problem that arises with altering a mobile communication system to address the problem of intercepted communications is that such a mobile communication system typically has a pre-defined communication protocol and a large number of deployed transponders with existing customers. In larger systems, the number of deployed transponders may reach into the millions, making it impractical to deactivate all existing transponders and deploy new transponders in their place all at once. Changes to the system, in the form of new readers, new transponders, or other equipment, should be backward compatible to ensure that the previously deployed transponders continue to function normally within the system.