Abstract: One or more roadside collection stations (RCS) communicate over a short-range, high speed bidirectional microwave communication link with one or more in-vehicle units (IVU) associated with one or more respectively corresponding vehicles in one or more traffic lanes of a highway. At least two up-link (IVU to RCS) communication sessions and at least one downlink (RCS to IVU) communication session are transacted in real time during the limited duration of an RCS communication footprint as the vehicle travels along its lane past a highway toll plaza. Especially efficient data formatting and processing is utilized so as to permit, during this brief interval, computation of the requisite toll amount and a fully verified and cryptographically secured (preferably anonymous) debiting of a smart card containing electronic money. Preferably an untraceable electronic check is communicated in a cryptographically sealed envelope with opener.

Abstract: A system for reading from and for writing data into electronic tags which may be associated with objects which are moving with respect to an interrogator, or may be located in fixed positions in the path of a moving interrogator. The interrogator, which is stationary if the tag is moving, sends a continuous RF signal to the remote tag. The tag backscatter-modulates the received RF signal with data temporarily or permanently stored in the tag, including, for example, data associated with the object to which the tag is attached, for example, its identity or contents. The system of this invention uses a very efficient encoding technique for the data which is backscatter-modulated by the tag and received by the interrogator. The backscatter-modulated signals are made up of signals of first and second frequencies f.sub.1 and 2f.sub.1, respectively, where the second frequency 2f.sub.1 is twice the first frequency f.sub.

Abstract: This invention relates to an improved signal reader for reading signals from transponders placed on moveable objects such as ship containers, automobiles or railroad cars. The reader sends out a continuous signal, which is modified by the information contained in the transponder attached to the moveable object. Multiple antennas, each of which receive separate signals, may be multiplexed at the reader. The improved circuit of the invention provides quick recognition of the receipt of a valid signal from a transponder or, in the alternative, the absence of such a valid signal.