Data transfer method for a scanning identification system

Translation of description of equivalent WO 9811496 A1

description

method for transmitting data in a Radiofreαuenz identification svsfem

The invention relates to a method for transmitting data in a radio frequency identification system from a transponder to a reading device by load modulation of a transmitted interrogation signal from the reader

When identifying persons, animals and objects, a system has in recent years proved, in which a (stationary or portable) reader (Reader) provides an output connected to the object to be identified transponder via an alternating field with energy, whereupon the transponder responds by sending the data stored in it. Due to the frequency range used is also called radio frequency, id-systems, RFID for short.

An RFID-transponder is generally comprised of an antenna coil and an integrated circuit, all the necessary electronic circuit blocks, such as. For example, for power supply, clock generation, for flow control and for storing the necessary data for identification data includes. The parallel to the antenna coil capacity is also often part of the integrated circuit. However, it can also be formed by a discrete component.

The RFID reader consists of a resonant circuit having a transmitting coil and a capacitor, which is driven by a driver stage with a signal having a generally fixed frequency (for. Example 125 kHz) to continue the reading device contains electronic circuitry blocks to by the to detect absorption modulation from the transponder data transmitted and to data and commands, for. example, by modulation of the field to be transmitted to the transponder.

Reader and transponder form a loosely coupled transformer in the data or in the transmission of energy. Therefore, the power transmission is relatively small.

For most applications, id transponder reader systems, it is desirable and advantageous for the identification expires ie the data exchange between the transponder and reader without delay. So when applying in immobilizer occurs, for example, the problem that the start of a vehicle, the user a period of more than 150 ms, by turning the ignition key to start the engine, as a time delay perceives. It follows that the entire transmission protocol must be passed in this very short period.

When the field the reader takes about two milliseconds before the high coil voltage has built up of about 100 V and evaluated the resultant from the modulation of the transponder low useful signal amounting to a few millivolts and therefore the data can be correctly decoded. The first sent by the transponder ID code is therefore only recognized in the second sequence, which means a delay of the data protocol. A similar problem occurs when changing from one undamped in the damped state, such. As at the end of a write sequence or programming sequence on.

The object of the invention, a method for transmitting data in a radio frequency identification system of a transponder, it is therefore to indicate to a reader by load modulation of a transmitted by the reader interrogation signal, which provides a one-time data transfer the correct result.

This object is achieved by a method having the features of claim 1. In a method for transmitting data in a radio frequency identification system from a transponder to a reader by load modulation of a transmitted by the reader interrogation signal, the transponder is initialized at the beginning of the reception of the interrogation signal and the sending of the response signal, the responses are first a predetermined transmitted number of non-response signal associated with data bits, and then while in a recurring sequence, a terminator sequence followed by the answer signal to the interrogation signal is interrupted.

By the predetermined number of non-response signal associated with data bits, the period of time is bridged, which requires the reader to construct the interrogation field. At the same time the reader is synchronized with the clock of the response signal. Due to the terminator sequence, indicating the beginning of a valid response signal, this is correctly recognized by the reading device already in the first transmission.

The terminator sequence is advantageously composed of a bit string that can not occur in the actual response signal, for example, the interrogation signal is sending the terminator sequence is not modulated for a duration of 1.5 bit. Such a sequence may not occur in the actual response signal and is therefore reliably detected by the reader. It is also possible sending the terminator sequence, the interrogation signal for a duration of 1.5 bit periods belastungszumodulierien. Important for reliable detection is the time duration of 1.5 bit periods that are reliably detected by the reader as a terminator sequence.

a sequence of 3 to 10 logical ones is sent as the predetermined number of non-response signal associated data bits. Within this time the interrogation signal has so far constructed such that the load-modulated response signal can be reliably decoded by the reader in general.

Brief Description of the Figures:

Figure 1 flow chart of the process; Figure 2 shows a terminator in data flow;

Figure 3 shows a table with the operating conditions that lead to the sending of the terminator.

To work around the problem mentioned, the transponder B. sends at the beginning of the data transmission, such as. during initialization, some irrelevant bits, followed by a special data atypical pattern (Terminator), the example of sequences of 1.5 bit periods composed. Thereby, the reader is synchronized, and in addition is indicated by the terminator sequence is the beginning of a valid data word, so that it is correctly detected already at the first transmission.

in the Figure 1 is a flow chart of the method is illustrated. After the reception of the interrogation signal generated by the reader, the transponder is initialized. The initialization includes the one setting the communication Para Menter and the transfer of the transponder in a defined initial state. Subsequently, the transponder by load modulation of the interrogation signal starts to send data to the reader to provide enough time to enable the reader to generate a constant within a certain frame interrogation signal which is necessary for reliable decoding of the data transmitted by the transponder to the reading device, are from the transponder first sent a predetermined number of non-response signal associated with data bits, during which time the reading device is also synchronized to the response signal.

Then, a terminator sequence is sent, which is characterized in that it can not appear in the actual data flow. Particularly advantageous is a 3-bit sequence has been found, in which the interrogation signal for a duration of 1.5 bit unmodulated. 2 shows a terminator in data flow. In addition to the property that this sequence in the actual flow of data can not occur, it is characterized by the duration very short. After the terminator sequence, the response signal is transmitted to the reader. the reader has recognized the terminator sequence, so the response signal is immediately decoded correctly with a very high probability. Nevertheless, the response signal is followed by a terminator sequence as long as repeatedly sent from the transponder to the Abfragesignai is interrupted. Then, either the communication between the reader and the transponder is completed or the reader transmits data or commands to the transponder.

in the table of Figure 3 shows a number of operating states are described in which it is useful to send a terminator sequence to increase the efficiency of data transfer, so it is an addition to the initialization as the transition from write access to the readers access to write error, the response signal to be completed when random access and sending a crypto answer advantageous to the terminator sequence.

advantage: The data can be correctly recognized immediately in the first transmission. This leads to a shortening of the duration of the data transmission.