Method for selecting one or more transponders

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. The random number is generated in a given transponder with the aid of a random number generator, the relevant random number generator is switched into a counter operating mode after reception of a selection command transmitted by the base station, while a count state of the random number generator is decremented or incremented when the base station transmits the start of a time slot, the relevant transponder transmits a transponder-specific identification to the base station if the count state of its random number generator is equal to a predetermined value, and the relevant random number generator is then switched back into the operating mode for random number generation.

Description

[0001] This nonprovisional application claims priority under 35 U.S.C. § 119(a) on German Patent Application No. DE102004041437.8-31, which was filed in Germany on Aug. 27, 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 selecting one or more transponders, in particular backscatter-based transponders, from a plurality of transponders by a base station. [0004] 2. Description of the Background Art [0005] Selection methods, which are also called anticollision methods, are typically used in, for example, contactless identification systems or radio frequency identification (RFID) systems. A system of this nature typically has a base station or a reader and a plurality of transponders or remote sensors, which are located in a response area of the base station at the same time. If the data transmission is to take place only between one transponder or a group of transponder...

AI Technical Summary

Benefits of technology

[0017] It is therefore an object of the present invention to provide a method and a device for a base station to select one or more transponders from a plurality of transponders that permits reliable and time-efficient selection and requires comparatively little chip area for implementation in a transponder.

[0018] In accordance with the invention, the random number can be generated in a given transponder with the aid of a random number generator. The random number generator is switched into a counter operating mode after reception of a selection command transmitted by the base station. In the counter operating mode, the random number generator operates as a normal counter or slot counter. The count state of the random number generator operating as a counter is decremented or incremented when the base station transmits the start of a time slot. If the count state of the random number generator is equal to a predetermined value, the relevant transponder transmits a transponder-specific identification to the base station. The relevant random number generator is then switched back into the operating mode for random number generation. As a result of the fact that the random number generator also serves as a slot counter during certain time intervals, it is possible to eliminate a separate slot counter used only for this purpose. This reduces the chip area needed. Due to the switchover of the random number generator to the operating mode for random number generation after the transmission of the transponder-specific identification, the generation of a new random number begins as early as possible. In the case of random number generation based on a dispersion of the clock source, this ensures optimal utilization of the random number space, since the differences in the clock sources of different transponders have a greater effect as a result of the longer time duration of random number generation. When another selection process is to be performed after the current selection process, for example because collisions have occurred in a slot, usable random numbers are thus available soon in the transponders in question, with the result that no waiting time is necessary between successive selection processes.

[0019] In a further embodiment, the random number can be generated with the aid of a linear feedback shift register. Such shift registers can easily be switched between the operating mode for generating the random number and the counter operating mode. Moreover, it is simple to generate random numbers with the aid of such components in combination with a dispersion or uncertainty of a clock source used to clock the shift register.

[0020] In yet a further embodiment, switchover into the operating mode for generating random numbers can depend on whether the base station transmits a command to the transponder following the transmission of the transponder-specific identification. For example, switchover into the operating mode for generating random numbers can be omitted if the base station sends an acknowledgement command to the transponder in question. The selection of the transponder is indicated by the acknowledgement command, i.e., it need not necessarily participate in a subsequent process. In this case, the immediate switchover into the operating mode for generating random numbers can be omitted, which reduces the power consumption of the transponder and thus increases its transmission range.

[0021] In another embodiment, an initial count state of the random number generator can be the generated random number, and the relevant transponder transmits its transponder-specific identification to the base station when the count state of its random number generator is zero. The random number generator merely switches to the counter operating mode here and then decrements or increments the count state. Consequently, no separate storage element for storing the random number is necessary, thus reducing the chip area needed. Detection that the count state has assumed the value ZERO is simpler to implement in circuit technology than a comparison with an arbitrary value. This in turn reduces the necessary chip area.

Problems solved by technology

As a result, it is not always possible to ensure the uniqueness of U-IDs in open systems in which transponders from arbitrary manufacturers may be located in the response area of a base station.

This generally prevents the base station from being able to receive the transmitted data error-free.

When multiple transponders transmit an identification within the same time slot, a collision occurs.

Since the number of transponders can fluctuate tremendously, a static number of time slots can lead to problems.

If the number of time slots is too small, the probability of collision increases sharply.

Since the random number generator and the slot counter are designed as separate units, such an implementation requires a relatively large chip area.

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