Abstract: The invention concerns a modulator (M) for data transmission between a transponder and a base station, which amplitude modulates and/or phase modulates a received electromagnetic carrier signal as a function of data to be transmitted, having a control input at which a modulation control signal is present, having a rectifier (GL) circuit for rectifying the received electromagnetic carrier signal which has at least one rectifier stage (S1-S3), having at least one switching device (SE) which is controllable through the modulation control signal and whose output side intervenes in at least one rectifier stage of the rectifier circuit, and by means of which a reference voltage can be applied to at least one node (H1-H3) of said rectifier stage. The invention further concerns a transponder with such a modulator and a modulation method for operating such [a modulator].

Abstract: A method and apparatus for locating a transponder is provided. A carrier signal is transmitted by a base station and a transponder transmits a locating signal that is generated through phase modulation and backscattering of the carrier signal sent by the base station when the transponder is within a transmission range of the base station, whereby the transponder is located on the basis of the locating signal.

Abstract: A method and device for selecting one or more transponders, in particular backscatter-based transponders, from a plurality of transponders by a base station, which method is based on a slotted ALOHA method, in which the base station defines numbered time slots and a random number generated in a given transponder determines a time slot when the transponder transmits its transponder-specific identification to the base station.

Abstract: A method and system is provided for selecting one or more transponders from a plurality of transponders by a base station, in which a random number generated in a given transponder determines a point in time when the transponder in question transmits an identification to the base station. The base station transmits a selection command, then, in order to determine whether at least one transponder is addressed by the selection command, all addressed transponders substantially simultaneously transmit an identification to the base station at a first point in time, and if more than one transponder is addressed, each addressed transponder transmits its identification to the base station at least once more at an additional point in time. The additional point in time being determined by the value of the random number generated or to be generated in the relevant transponder.