Method of wireless communication between a base station and a transponder

The invention relates to a method for wireless data transmission between a base station and a, in particular passive, A transponder according to the preamble of claim 1. Such transfer process between one or more base stations or readers and one or more transponders are used for example in contactless identification systems or so-called Radio Frequency Identification (RFID) systems Use. On the transponder can also sensors, for example for temperature measurement, be integrated. Such transponders are also called remote sensors designated.

feature The transponders or their transmitting and receiving devices typically do not have an active transmitter for data transmission to the base station. Such non-active systems are called passive Systems referred to when they do not have their own power supply, and semipassive systems if they own have power. Passive transponders take to their supply needed energy emitted from the base station electromagnetic field.

For data transmission with UHF or microwaves in the far field of the base station Usually the so-called backscatter coupling used. For this purpose, electromagnetic from the base station Carrier waves emitted by the transmitting and receiving device of the transponder according to the to the base station transmitting data modulated by a modulation method and reflected will. The typical modulation methods for this are Amplitude modulation, phase modulation and amplitude shift Keying (ASK) subcarrier, wherein the frequency or the phase position the sub-carrier is changed.

The earlier German patent application 102 04 347 and DE 101 38 217 A1, methods for wireless data transmission between a base station and a transponder described in which to transmitting data packets a head portion, a data portion include with data to be transmitted and an end. The data to be transmitted are encoded using symbols and transmitted, located in the head portion of the data packet. On Symbol is used here to define or interpret the value of a Character. Such a symbol is usually by means of a time between two successive field gaps, so-called "Notches", shown in the header section. Such field gap can at an amplitude modulation, for example, by suppressing or attenuation of the carrier signal or at a double-sideband modulation generated by switching the phase angle of the carrier signal will. The transponder decodes received data packets based the symbols contained in the header section, or on the basis of the symbols associated time periods by determining the value a character whose time duration is compared with the durations of the symbols.

When transmitting data from the transponder to the base station is in some Cases provided, each to be transmitted characters or bit synchronously to be transmitted to a predetermined by the base station clock, wherein the modulation state established at the beginning of the time interval or is known and a change in the modulation state by the time period of the mark in the header portion associated symbol takes place. Typically, the data transmission is alternatively asynchronous.

By choosing the time interval or associated with the symbols Time periods it is possible, the transmission rate within a certain range adapt to the transmission conditions. The range of Transmission rate is limited, inter alia, that the Transponder or a transponder in this competent encoding / decoding unit different to the symbols or signs time no longer resolve related periods, ie indistinguishable can. A higher temporal resolution usually goes with a higher power consumption of the transponder associated as example the clock frequency of a used for durations determination Counter or the charging current of a functionally corresponding analog RC level must be increased in the encoding / decoding unit. Since in the far field of the radiation emitted from the base station electromagnetic Waves prevails a low power density to power can serve the transponder, the attainable range decreases with increasing Power consumption. The encoding or decoding determining Parameter or the encoding / decoding unit is consequently conventionally statically configured such that a sufficient Compromise between high temporal resolution and the achievement of high achievable transfer rate on the one hand and results in low power consumption on the other.

The invention is the technical problem of providing a Method for data transmission of the type described above, the data transfer between the base station and the Transponder having a relatively large range over a wide area transmission rates away allows for optimized power requirements and at relatively low cost can be realized.

The invention solves this problem by providing a method with the features of claim 1.

According to the invention in the transponder the period of at least a symbol determined in the head portion and the function of determined amount of time the encoding and / or decoding mode determining parameter set. This measure can dynamically adapt the encoding or decoding capability the transponder to prevailing transmission conditions will be realized. For example, in a large Distance between the base station and the transponder by suitable choice of the time duration of one symbol in the head section of the Encoding and / or decoding mode determining parameter be set such that the through encoding / decoding unit Power consumption caused is low, thereby a large transmission range can be achieved. In contrast, if sufficient Power in the transponder is available, the parameter can and thereby set the encoding / decoding unit so be that a high data rate can be achieved. The transmission rates range therefore, compared to a method in which the encoding or decoding with constant settings is carried out, clearly increased.

In a development of the method according to claim 2 provides the Parameters, the temporal resolution of the encoding and / or decoding. By such adjustment of the temporal resolution is a effective control of the power consumption of the transponder possible. Also possible a determination of the frequency and / or amplitude resolution the transponder by the parameter or Switching between different encoding or decoding process.

In a development of the method according to claim 3 is the parameter a charging current of an RC circuit, for determining the time periods the symbols used. In this way, for example, a capacitor of the RC circuit with a defined charging current during the duration of a particular symbol charged via a resistor of the RC circuit and the generated voltage value stored in a memory circuit will.

In a development of the method according to claim 4 is the parameter a clock frequency of a counter circuit for determining the time periods the symbols used. The control of the clock frequency of the counter circuit in dependence on the time duration of one symbol in the head section ensures that on the one hand the clock frequency of the counter circuit is set such that the temporal resolution is sufficient to all characters to encode or decode secure, and on the other hand the clock frequency is minimized so that power consumption of the transponder with respect to the data transmission rate is minimal.

In a development of the method according to claim 5, the parameter in dependence on the determined time duration of the first symbol set in the header section. This leads to a simple implementation the setting of the parameter, as for the first symbol with a symbol For example, maximum or minimum length to be agreed can, thus ensuring that the following symbols are not a Exceeding or falling below of measured values ​​during decoding to lead.

In a development of the method according to claim 6 of the charging current decreases a predeterminable prior to receiving a first data packet A minimum value, which is increased upon receipt of the first data packet, when associated to the determined time duration of the symbol voltage value the RC circuit is less than or equal to an adjustable Limit value, and is maintained when the duration of the time Symbols corresponding voltage value is greater than the adjustable threshold is.

In a development of the method according to claim 7, the clock frequency increases a predeterminable prior to receiving a first data packet A minimum value which increases when receiving the first data packet , when a time period associated to the determined value of the symbol counter the counter circuit is less than or equal to an adjustable Limit value, and is maintained when the duration of the time Symbols corresponding counter value is greater than the adjustable threshold value. In this way it is ensured, in analogy to Claim 6, that a Transponders in the far field of the base station when the supply of the Transponder is little energy available, with minimum clock frequency or minimal charge current, ie, minimal power consumption, operable. When the counter value is less than the adjustable threshold value is, the clock frequency is sufficient for reliable decoding or Encoding not from and is increased. If enough power supply is available to the consequent increased power consumption ensure the data transfer rate can accordingly increase. If the power consumption in this case is too high, can for example be a reset of the transponder, which this not participate in the data transfer. Since the data transmission basically starts with low power consumption, is the base station To address in a position transponder that is far from her are removed. The base station may use the period of the Symbols control whether a transponder in its far-field low Data transmission rate in a communication participates or not.

In a development of the method according to claim 8 is the least another portion, a data portion, the data using encodes at least one other symbol of the head portion and be transmitted.

Advantageous embodiments of the invention are in the drawings shown and described below. In the figures:<dl tsize="6"><dt>Fig. 1</dt><dd>a schematic block diagram of an RFID system with a base station and a transponder,</dd><dt>FIG. 2</dt><dd>a schematic diagram of a data packet with a Head portion, a data portion and an end portion and</dd><dt>Fig. 3</dt><dd>a schematic diagram of the head portion of FIG. 2.</dd></dl>

Fig. 1 shows a schematic block diagram of an RFID system ST with a base station BS and a passive transponder TR. In between the base station BS and the transponder TR wirelessly transmitted bidirectionally data packets DP. emitted, the base station BS electromagnetic carrier waves to transmit data from the transponder TR to the base station BS according to the to the base station BS are modulated to transmit data packets DP and reflected. The transponder TR takes the power needed to supply its P emitted from the base station BS electromagnetic Field.

The transponder TR comprises, among other, not shown circuit parts a modulator / demodulator unit MD, for example, a Receiver Signal Strength Indicator (RSSI) circuit for signal recovery may include, coupled with the encoding / decoding unit KD and the encoding / decoding unit KD coupled control unit ST. In transponder TR received Input signals are in the modulator / demodulator unit MD demodulated, and signals to be transmitted are modulated accordingly. A coding and decoding of data packets DP takes place in the Encoding / decoding unit instead of KD. To this end, this includes a Time acquisition unit ZE for determining the periods of modulation states or time intervals of field gaps, which as a digital counter circuit DZS or alternatively as an analog RC-circuit RCS can be formed.

The control unit ST is used inter alia for controlling the encoding / decoding unit KD and comprises a memory SP, of for storing determined in the time acquisition unit ZE values and reference values ​​used. When the time acquisition unit ZE as digital Counter circuit DZS is realized, the clock frequency is f Counter circuit DZS provided by the control unit ST. If the time detecting unit ZE is formed as an RC circuit RCS is the charging current I determined by the control unit ST. The clock frequency f or the charging current I is in this case of the encoding or decoding mode determining parameter since it temporal resolution the time acquisition unit ZE sets.

Fig. 2 shows a schematic diagram of one of the base station the transponder transmitted data packet DP of FIG. 1 at the output the modulator / demodulator unit MD with a head portion KA, followed by a data section DA with data to be transmitted and an end portion EA followed.

The head portion KA of Fig. 2 is shown in more detail in Fig. 3. in the illustrated head portion KA are three symbols ZA, 0^* and EOT^* contain. The symbols ZA, 0^* and EOT^* by successive Field gaps or so-called "notches" of the base station BS produced emitted carrier signal that shown in Fig. 3 as short pulses are. The first symbol ZA has a duration t1, the second icon 0^* a time t2 and the third symbol EOT^* a time t3, where the time periods t1 to t3 by the time acquisition unit ZE of Fig. 1 be determined. When the time acquisition unit ZE as a digital counter circuit DZS is realized, will each one the time periods t1 to t3 associated Counter value stored in the memory SP of the control unit ST. When the time acquisition unit ZE realized as an RC circuit RCS is, is in accordance with a voltage value scored in the memory SP stored.

The clock frequency f or the charging current I of the time acquisition unit ZE is determined by the control unit ST after the start of the transponder TR initialized to a minimum value, so that a minimal power consumption the transponder TR results. This enables starting of the Transponder TR in the far field of the base station BS.

Upon receiving a first transmitted from the base station BS the data packet DP, that is, after the time duration t1 of the first symbol ZA determined was, the clock frequency f of the counter circuit DZS or is Charging current I of the RC circuit in the transponder depending on RCS the determined time duration T1 is set. For this purpose, the time period t1 associated counter or the voltage value in the control unit ST a stored in the memory SP reference compared. If the Counter value or the voltage value is less than the stored reference is, the control unit ST increases the clock frequency f and the charging current I. Otherwise, there is no change. The increase can be in one stage or more stages, for example, proportional to the difference between ermitteltem and hinterlegtem value, done. By increasing the clock frequency f or the charging current I, the transponder TR with higher Data Transfer Rate to be operated as the time detecting unit ZE in this operating mode to the symbols ZA, 0 * and EOT * associated Periods t1, t2, t3 or time may differ from each other, although the differences between the time periods t1, t2, t3 due to the are higher data transmission rate is less. Using the dynamic Switching of the clock frequency f and the charging current I can be thus realizing a large transfer rate range, while at the same by the power-saving start-up of the transponder TR high Transmission ranges are realizable.

For the transmission of user data in the data section DA generates the base station successive field gaps, the time interval between the corresponding characters to be transmitted. The transponder or its Time acquisition unit ZE measures with the set based on the time t1 temporal resolution the distance this field gaps and compares the measured times to the times t2 and t3 of the symbols 0^* and EOT^*, The symbol 0^* or its associated time period t2 serves here to Coding and decoding the binary symbol "0" or "1", from which up the data to be transmitted in the data section DA are. The symbol EOT^* is used to signify the end of a data packet DP and is transmitted in the end portion EA of the data packet DP, including any, are used from t3 derived waveforms can. A binary characters in the data portion DA whose duration is smaller than the symbol 0 * corresponding time duration t2, is in the Transponder TR interpreted as a "0". A character whose period greater than t2 and smaller than the symbol EOT^* corresponding period t3 is, is interpreted as a "1". If the interval between two successive field gaps larger than t3, recognizes the transponder TR the end of a data packet.

It is alternatively possible, in addition to the symbol ZA just another symbol 0^* or EOT^* and to transfer the other time periods by previously known divider ratios with respect to this period in calculate transponder.

The data transmission from the transponder to the base station may also with on the basis of the time t1 set temporal resolution, for example, according to the German in Patent Application 102 04 347 Methods described occur.

The decoding decisive parameter in the embodiment shown the temporal resolution of the coding and decoding, However, it is alternatively possible, depending on the character format information further the encoding and / or decoding mode adjust parameters determining, for example, the type switching the coding between different coding variants.