Patent ID: 7385950

Claim:
A method of transmitting date between a base station and a passive transponder, one of which may operate as a transmitter and another of which may operate as a receiver at a given time, said method comprising the following steps: transmitting an electromagnetic carrier wave from said transmitter to said receiver; in said transmitter, encoding and modulating a succession of information packets onto said electromagnetic carrier wave, wherein said information rackets include at least a selected information packet and one or more subsequent information packets after said selected information packet, wherein each one of said information packets comprises a header section, a middle section, and an end section, wherein said middle section of at least one of said information rackets includes said data that is encoded by a set of information symbols including at least one variable information symbol and that is modulated onto said carrier wave, wherein said header section of said selected information packet includes identifications which identify respective time durations that are respectively allocated to and that respectively define said information symbols, wherein said time durations include at least one variable time duration that defines said at least one variable information symbol; in said receiver, receiving said electromagnetic carrier wave with said information packets modulated thereon; evaluating said header section of said selected information packet in said receiver to determine therefrom said identifications which identify said time durations that respectively define said information symbols; decoding said data in said receiver based on said identifications of said information symbols; extracting, from said carrier wave, electrical energy needed to operate said passive transponder; and changing a time value of said variable time duration from a first time value in said selected information packet to a second time value different from said first time value in at least one of said one or more subsequent information packets.