Method for locating a backscatter-based transponder

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.

Description

[0001] This nonprovisional application claims priority under 35 U.S.C. § 119(a) on German Patent Application No. DE 102004062365.1, which was filed in Germany on Dec. 13, 2004, and which is herein incorporated by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a method for locating a backscatter-based transponder. [0004] 2. Description of the Background Art [0005] Transponders are used in radio frequency identification (RFID) systems. In these systems, unidirectional or bidirectional wireless transmission of data takes place between one or more base stations, or readers, and one or more transponders. Sensors, for example for temperature measurement, may also be integrated in the transponders. Such transponders are also referred to as remote sensors. [0006] The transponders and their transmitting and receiving devices customarily do not have an active transmitter for data transmission to the base station. Such non-active...

AI Technical Summary

Benefits of technology

[0020] It is therefore an object of the present invention to provide a simple and economical method for locating backscatter-based transponders with a comparatively small interference spectrum and a short detection time, in which the transponders transmit a locating signal and in which it is possible for the transponders to receive data while they are continuously transmitting the locating signal.

[0029] In a further embodiment, the locating signal can be generated by modulating the carrier signal transmitted from the base station with a subcarrier. The modulation of the carrier signal with a subcarrier is described, for example, in the textbook by Klaus Finkenzeller, RFID-Handbuch, 3rd edition, HANSER, 2002, see especially Chapter 3.2.1.2.2, (load modulation with subcarriers). Modulation of the carrier signal with a subcarrier permits simplified evaluation of the backscattered signal in the base station, since the backscattered signal, which is significantly weaker in comparison to the carrier signal, is shifted in the frequency range into sidebands, and thus can be separated from the carrier signal in the base station by appropriate filters.

[0030] In a further embodiment of the invention, a memory internal to the transponder can contain one or more parameters for setting the locating signal, in particular a frequency. The parameters can also be transferred to the transponder through a command, for example, in the form of command parameters. In the case that a selection process is needed, the parameter locating command can be the locating command. This makes it possible, for example, to keep the spectra produced by the locating signal or signals from colliding with the spectra of other RFID applications. When the locating signal is set with the aid of the locating command, the base station can dynamically set the spectrum of the locating signal as a function of the ambient conditions encountered. In an advantageous embodiment, the parameter or parameters are used to set a frequency and / or a duty cycle of a modulation signal with which the carrier signal is modulated. In this way, almost any desired spectra of the locating signal can be set. The frequency and / or the duty cycle can be derived from an oscillator clock internal to the transponder. To this end, for example, a counter can be driven by the oscillator clock internal to the transponder, with a modulation state being switched when the counter state reaches the value of a parameter that serves to set the locating signal. Through the use of two parameter values, through which the pulse duty ratios is set, different spectra can be set.

[0031] In a further embodiment of the invention, the transponder can terminate the transmission of the locating signal when a predefinable maximum time has elapsed and / or the transponder receives a command, to make it possible to detect additional transponders in the TTF-operating mode. After a certain time period, the probability that the transponder has been located is high. Consequently, it makes sense for the transponder to terminate transmission of the signal so that other transponders can be located. After locating has been completed, the transponder can also be muted with the aid of a command provided specially for this purpose, in order to allow additional transponders to be located.

Problems solved by technology

In these systems, unidirectional or bidirectional wireless transmission of data takes place between one or more base stations, or readers, and one or more transponders.

This so-called polling causes an interference spectrum.

Thereby, the self caused fluctuations of the input amplitude of the received carrier signal that are caused by the transponder itself, an that arise during the generation of the locating signal through amplitude modulation and backscattering of the received carrier signal, can only be distinguished with great effort from the notch signals generated by the base station, which likewise result in a change in the amplitude of the received carrier signal.

This is often impossible to achieve, since applicable standards and / or regulations would otherwise be violated.

However, such a permanent transmission of information by the base station generates an interference spectrum, which is frequently undesirable.

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