Method for selecting one or more transponders

p0001The invention relates to a method for selecting one or more transponders from a plurality of transponders by a base station according to the preamble of claim 1.

p0002Such procedures, which are also referred to as anti-collision method, see, for example, in contactless identification systems or so-called Radio Frequency Identification (RFID) systems use. Such a system usually consists of a base station or a reader and a plurality of transponders or remote sensors are located at the same time in the response of the base station. When the data transfer is to take place only between one or a group of transponders and the base station, such a selection procedure must be performed before the corresponding data transmission.

p0003Basically, this distinction between stochastic and deterministic selection. A detailed description of both deterministic selection procedure as well as to stochastic selection process can be found for example in the textbook Klaus Finkenzeller, RFID Handbook, 3rd Ed., Hanser, 2002, see in particular section 7.2 multiple access methods.

p0004Stochastic methods presuppose unlike deterministic process no unique, so-called Unique Identification (U-ID), the construction of which is described for example in ISO 15,963th An award of such U-IDs is carried out, among others, various manufacturer-independent organizations, such as the EAN / UCC or the IATA. The award may be allowed by a manufacturer. Overall, therefore, in open systems, in which the transponder from any manufacturer can be located within the response range of a base station, the uniqueness of the U-ID is not always guaranteed. Stochastic methods permit selection in these cases. Examples of such processes are the so-called stochastic ALOHA method, the slot-based or slotted ALOHA method, and the dynamic slot-based ALOHA method.

p0005The ALOHA method is a transponder controlled stochastic method in which a time offset their transmit the transponder data to be transmitted. The time delay is usually set based on a random number generated in the transponder. If multiple transponders transmit an identification within the same time slot, there occurs a so-called collision. This prevents usually that the base station can receive the transmitted data without errors.

p0006When slotted ALOHA method, the collision probability is significantly reduced in comparison to the simple ALOHA method. It is a controlled from the base station, stochastic process in which the transponder just defined, are synchronous timings active, ie begin transmission of data. For this purpose, the base station front-numbered time slots or slots and the transponder each generate a random number, each transponder corresponds to the random number to the number of a time slot, transmits data or an identifier in this time slot to the base station. To initiate the selection process, the base station sends a command usually to the transponders, is indicated by the start of a selection procedure. Upon receipt of the commands, the respective random numbers to be stored in the transponders that have been, for example, previously calculated in the transponder. If only one transponder transmits an identification within a time slot, this transponder is selected within the time slot or can be selected by the base station by transmitting an acknowledgment signal. The base station may then perform, for example, write and / or read operations on this transponder. If multiple transponders transmit an identification within the same time slot, a collision occurs. Depending on the bit coding, the base station can detect such a collision directly or with delay and skip the corresponding time slot and try work through time slots in which no collision occurs, or launch a new selection procedure by sending a corresponding command to the transponder. Since the transponder typically generate or store a new random number, there is a possibility that now occurs no collision.

p0007The probability of collision depends on the number of transponders in the response range of the base station and the number of time slots provided. Since the number of transponders can vary greatly, a static definition of the number of time slots cause problems. If the number of time slots too small, the collision probability increases greatly. Is the number of time slots is too large, there is a corresponding number of time slots in which no transponder transmits data. The time required for the selection process thus increases sharply in both cases. In order to achieve optimal throughput, should the number of time slots in which the transponders transmit data, be chosen approximately equal to the number of transponders.

p0008To solve this problem, the dynamic slot-based ALOHA method, in which the number of available time slots can be controlled by the base station exists. For example, the base station may initiate a selection process with a small number of time slots. If this often collisions occur, the base station can initiate a new selection process in which the number of time slots is increased, whereby the collision probability decreases. However, the time required for such a dynamic process is relatively large because the adjustment of the optimum number of time slots may take a long time to complete. It requires due to its complexity a correspondingly high circuit complexity.

p0009To generate a random number for the stochastic process, different methods are known. For example, the time between a reset of the transponder and the time at which a first character is received, serve as the basis for calculating the random number. Other methods combine numbers from two different memory areas of the transponder with each other to determine the random number, wherein additionally a received date can be included in the calculation for refining. Other methods use a linear feedback shift register for random number generation, which can be operated for example with an inaccurate clock supply.

p0010The deterministic selection is based usually preceded on a binary search method or a so-called binary search algorithm and set that each transponder in the response of the base station is assigned a unique identification bit. The identification bit is usually formed by the Unique Identification (U-ID) that is assigned to the transponders, for example, in their production. The uniqueness of the U-ID can, however, be due to the large number of U-ID specifications are not always guaranteed in open systems.

p0011A selection process in which the transponders are based on a bit by bit comparison of their unique, statically assigned identification bit selected with a selection bit, is in the <patcit id="pcit0001" dnum="US5856788A"><text>US 5856788</text></patcit> described. The selection is made in this case in a half-duplex method in which the transponders each transmitting a bit of its identification bit sequence and the base station then uses the transmitted bit values ​​transmits a select bit. Compare transponder the corresponding bit of their identification bit to the associated selection bit based on a comparison criterion. The comparison criterion in this case is the same operator, ie transponder matches the corresponding bit of their identification bit with the selection bit, remain activated. Due to the half-duplex method, relatively much time is needed until a transponder is selected.

p0012In the ISO WD 18000-6 Mode 3 from 01.02.2002 a selection process is described in which the selection is also carried out based on a unique identification bit. The selection process operates in full duplex mode, whereby the selection time decreases. The transponders are selected also by their unique, statically assigned identification bit.

p0013The <patcit id="pcit0002" dnum="EP1321889A2"><text>EP 1321889 A2</text></patcit> shows an identification method with two selection levels.

p0014The <patcit id="pcit0003" dnum="EP0709803A2"><text>EP 0709803 A2</text></patcit> shows a selection process for a non-contact IC card system.

p0015The <patcit id="pcit0004" dnum="US20030179078A1"><text>US 2003/0179078 A1</text></patcit> shows a transponder, in which a random number using a linear feedback shift register is generated.

p0016The invention is the technical problem of providing a method of the type mentioned above, which does not necessarily contain a condition for selecting one or more transponders from a plurality of transponders by a base station, the presence of a unique, statically allocated U-ID in the transponders and the time-saving allows selection of one or more transponders even with a fluctuating number of transponders in the operating distance of the base station.

p0017The invention solves this problem by providing a method having the features of claim 1.

p0018According to the invention, if more than one transponder in the same time slot to send an identifier for selection within this time slot in a second selection level further, stochastic and / or deterministic, controlled by the base station selection procedure performed. This allows for address assignment, for example based on a slotted ALOHA method within a first selection plane, the number of time slots as compared to a conventional slotted ALOHA method can be kept relatively small. It is possible to select the number of time slots in the first selection level constant or dynamically adjust the number of be located within the response range of the base station transponder. Due to the stochastic nature of the first selection level, the presence of a unique, statically assigned identification bit and a U-ID in the transponders is not mandatory for.

p0019The second selection plane allows the selection of one or more transponders even with a fluctuating number of transponders in the operating distance of the base station. When little transponder in the response of the base station are compared to the number of time slots, that is, if no collisions occur within a time slot or be recognized by the base station, in the first selection level, only one slot based ALOHA method with a relatively small number of time slots performed. This allows a time-saving choice of transponders. However, when collisions within a timeslot occur, ie when compared to the number of time slots are many transponders in the operating distance of the base station, the second selection plane allows a selection by using a further, independent of the first selection level stochastic, deterministic or mixed deterministic-stochastic selection procedure ,

p0020For the deterministic selection procedure in the transponders respective identification bit a selection bit is provided, transmitted by the base station bit to the transponder, in each transponder a bitwise comparison of the corresponding bits of the identification bit sequence and the selection bit carried out based on a predetermined comparison criterion and based on the comparison result assigned selection bit has a weight and the respective transponder selected depends on the quality of his selection bits. This allows a time-saving choice, since the selection bit takes place and not the complete sequence of bits to be transmitted, to a selection can take place.

p0021In a development of the method according to claim 2, the stochastic selection procedure of the second selection plane is an ALOHA method, in particular, this can be a slot-based ALOHA method. The active in the time slot corresponding transponder, ie those transponders corresponding to the random number the number of the current time slot generate, or this store another random number and take part in a further slotted ALOHA method which nested within the first selection procedure or nested inside the corresponding time slot is carried out.

p0022In a development of the method according to claim 3, the deterministic selection procedure of the second selection level is a binary search process. This enables quick selection of one or a group of transponders in the second selection level.

p0023Advantageously, a Zufallszahlbitfolge is generated and as identification bit sequence such provided, which contains the Zufallszahlbitfolge according to claim 4 in the respective transponder. This allows the selection of transponders within the second selection level, even if they do not differ in their U-ID.

p0024In a development of the method according to claim 5 is to check whether within the same time slot more than one transponder transmits an identifier, transmitted the information received from the base station identifier as an acknowledgment signal at least partially through the base station to the transponder back and checked in the transponders, whether sent from the base station ID matches the identifier transmitted by the respective transponder. Not match the corresponding transponder within the time slot does not participate in the selection procedure. When the base station wrongly recognized no collision is prevented in this way that transponders are incorrectly selected.

p0025In a development of the method according to claim 6 encoding from 3phase1 type is used for transmitting the identifier from a transponder to the base station, as 18000-6 Mode 3 described for example in ISO WD. This allows the base station to detect the bit position of a collision.

p0026In a development of the method according to claim 7, the random number of the first selection level and / or a random number or Zufallszahlbitfolge the second selection level by means of a clocked linear feedback shift register is generated, disable the clock supply during periods with increased compared to an average power consumption of the transponder becomes. This enables a reduction of a peak value of the power consumption of the transponder and thus increasing the coverage area between a base station and a transponder. Advantageously, the clock supply is deactivated during a data transmission between the base station and the transponder in accordance with claim eighth This increases the communication range.

p0027In a development of the method according to claim 9, the clock supply is disabled by means of a controllable logic gate, which is connected between a clock supply unit and the shift register. This enables a simple to implement activation or deactivation of the clock supply.

p0028In a development of the method according to claim 10 the random number of the first selection level and a random number or Zufallszahlbitfolge the second selection level by means of a clocked linear feedback shift register is generated. This reduces the chip area required and thus reduces the production costs compared to a realization, wherein each random number is assigned to a shift register. Furthermore, the power consumption is reduced, thereby to distances between the base station and the transponder increases.

p0029In a development of the method according to claim 11, a first part of a number of bits of the shift register of the random number of the first selection plane and the remaining part of bits of the shift register of the second random number or Zufallszahlbitfolge be assigned. This enables simultaneous production of both random numbers.

p0030In a development of the method according to claim 12 the random number of the first selection level is generated and stored by means of the shift register. Then, the random number of the second selection plane is made by means of the shift register and stored separately from the random number of the first selection level. The readout of the shift register contents for obtaining the random numbers will each be triggered upon entering the respective selection plane. This respectively represents the entire width of the shift register for the random numbers available.

p0031In a development of the method according to claim 13, the shift register is operated by generating the random number of the first selection level with reduced stroke. This reduces power consumption and thus increases the range.

p0032In a development of the method according to claim 14 further random number is generated by logically combining the random number or Zufallszahlbitfolge the second selection level with transponder-specific data when the value range of the random number or Zufallszahlbitfolge the second selection level for the second selection level is insufficient. The further random number may then be used for the second selection plane.

p0033Advantageous embodiments of the invention are illustrated in the drawings and will be described below. This is shown schematically:<dl id="dl0001"><dt>Fig. 1</dt><dd>a flowchart of a competition with two selection levels,</dd><dt>FIG. 2</dt><dd>a diagram of a timing of the selection process of <figref idrefs="f0001">Fig. 1</figref> in an exemplary selection situation and</dd><dt>Fig. 3</dt><dd>a block diagram of a basic arrangement for generating random numbers using a linear feedback shift register.</dd></dl>

p0034<figref idrefs="f0001">Fig. 1</figref> shows a flowchart of a selection process for selecting one or more backscatter-based transponder from a plurality of transponders by a base station with two selection levels. <figref idrefs="f0002">FIG. 2</figref> shows a diagram of a corresponding time sequence of the selection process of <figref idrefs="f0001">Fig. 1</figref> in an exemplary choice situation in which three transponders TR1 to TR3 are in the operating distance of the base station BS, which are successively selected.

p0035In a step 10 of <figref idrefs="f0001">Fig. 1</figref> start the selection process in a first selection level. Typically, the base station BS sends an thereto in<figref idrefs="f0002">FIG. 2</figref> shown command 20 to the transponders TR1 to TR3, by the beginning of a selection procedure is displayed. After receiving the command 20 TR1 to TR3 respective random numbers are in the transponders created or computed and then stored and set an internal time slot number counter to an initial value.

p0036In a step 11 of <figref idrefs="f0001">Fig. 1</figref> waiting for the base station BS on a feedback of the transponders TR1 to TR3, and receives this, if an identifier is sent. In<figref idrefs="f0002">FIG. 2</figref> this is represented by a waiting / receiving period 21st

p0037The transponders TR1 to TR3 compare the value of their internal time slot number counter with the stored random number and send in accordance an identifier in the form of U-ID. When in<figref idrefs="f0002">FIG. 2</figref> shown selection situation has only the transponder TR1 the associated for the first time slot random number. The transponder TR1 thus transmits its U-ID with a code from 3phase1 type in a backscatter period 22 within the first time slot to the base station. The base station receives the U-ID and detect with the help of coding that no collision has occurred, ie no further transponder has its U-ID transmitted simultaneously with TR1. The transponders TR2 and TR3 remain passive because their random number does not match the number of the current time slot, and waiting for a command from the base station that leads to the next time slot.

p0038The transponder TR1 is now considered selected, said further steps may be performed on the final selection, for example, the transmission of an acknowledgment signal from the base station to the transponder. In a step 12 of<figref idrefs="f0001">Fig. 1</figref> communicates the base station BS bidirectionally with the transponder TR1 and can, for example, write and / or read operations on the selected transponder TR1 run. In<figref idrefs="f0002">FIG. 2</figref> This is represented by a communication period 23rd

p0039Because of phase shifts and widely different levels can occur, particularly at large distances between the transponders TR1 to TR3, and the base station BS, despite the appropriate coding happen that a collision occurs, which is not recognized by the base station BS. For collision detection is in addition to a suitable coding in the<figref idrefs="f0002">FIG. 2</figref> possibility not shown, that the signal received by the base station BS U-ID is transmitted by this to the transponders TR1 to TR3 as an acknowledgment signal back. In the respective transponders TR1 to TR3 is then checked whether the transmitted identifier from the base station BS or U-ID matches the identifier transmitted from the respective transponders TR1 to TR3. If it is determined in a transponder that is no match, he takes no further part in the current selection procedure in this time slot. If they match the corresponding transponder is selected.

p0040After completion of the communication with the transponders TR1 in step 12, the base station BS transmits a next slot command to the transponders TR1 to TR3, in a step 13 of <figref idrefs="f0001">Fig. 1</figref>Whereupon this increment its internal time slot number counter. In<figref idrefs="f0002">FIG. 2</figref> this corresponds to a period 24 Alternatively, transfer the number of the current time slot to the transponders TR1 to TR3, the base station BS. The previously selected transponder TR1 takes no further part in the selection process. If the base station BS wants to end the selection process, it sends in step 13 instead of the next slot commands a command to the transponders TR1 to TR3 that this indicates the selection process end. then switch to a corresponding operating state.

p0041If continuing the selection process is the flow chart of <figref idrefs="f0001">Fig. 1</figref> returning to step 11, ie, the base station BS waits for the feedback of the transponder TR2 and TR3 and receives, if an identifier is sent. In<figref idrefs="f0002">FIG. 2</figref> this is represented by a renewed waiting / receiving period 21st

p0042Since in the in <figref idrefs="f0002">FIG. 2</figref> have shown selection situation the transponders TR2 and TR3 identical random numbers, send them in connection to the next slot command 24 in the accompanying backscatter period 22 at the same time their respective U-ID, whereby a collision at bit positions arises not match their bit values. Due to the bit coding, the base station detects the collision and branches instead to step 12 to step 14 of<figref idrefs="f0001">Fig. 1</figref>,

p0043In step 14 of <figref idrefs="f0001">Fig. 1</figref> sends a base station BS in <figref idrefs="f0002">FIG. 2</figref> shown command 25 is displayed to the transponders TR1 to TR3, by the beginning of a selection procedure of a second selection level.

p0044In a step 15, the second selection procedure is nested carried out within the second time slot, which may be a stochastic, deterministic or mixed deterministic-stochastic selection procedure.

p0045As stochastic process, for example, serve a simple ALOHA method, a slot-based or a dynamic slot based ALOHA method. Upon receipt of the start commands 25 each random numbers are in this case in the transponders TR2 and TR3 again created or computed and then stored and set an internal Subzeitschlitznummernzähler to an initial value. There a nested ALOHA method is performed within a time slot of the parent slotted ALOHA method.

p0046When deterministic methods can be used for example a conventional binary search process. A suitable example is the 18000-6 Mode 3 from 01.02.2002 described selection process in which the selection is made in the above-cited standard ISO WD based on a U-ID.

p0047A mixed deterministic-stochastic selection process, as it is presently used for the second selection level is, in the non-prior <patcit id="pcit0005" dnum="DE10336308A1"><text>German patent application DE 103 36 308 A1</text></patcit> described by the applicant, which is hereby incorporated by reference in the content of the present application. The selection is made here using a identification bit that contains a static component and a U-ID and a dynamic share, based on a generated in the transponder random number. To select each such an identification bit a selection bit is in the transponders provided, transmitted by the base station bit to the transponder, in each transponder a bitwise comparison of the corresponding bits of the identification bit sequence and the selection bit carried out based on a predetermined comparison criterion and based on the comparison result a selection bit assigned a value. The respective transponder is selected depending on the valence of his selection bits.

p0048In the <figref idrefs="f0002">FIG. 2</figref> shown second selection procedure is a deterministic selection procedure and is performed according to ISO 18000-6 WD fashion. 3 The base station BS transmits this, in a period 26, the bit by bit selection bit and the transponder TR2 scatters in full duplex mode in the backscatter period 22 its identification bit sequence to the base station back which coincides with the selection bit. The transponder TR2 is thus selected. Since the identification bit of the transponder TR3 does not coincide with the selection bit, this transmits the backscatter-period 22a only a portion of its identification bit sequence to the base station back. The backscattering is terminated at a time point at which one bit of the selection bit does not match a corresponding bit of its identification bit sequence. The transponder TR3 remains passive. Instead of a single selection, there is the alternative option of selecting groups of transponders, that is, in this case, TR2 and TR3 simultaneously. After the selection of a not shown, bi-directional data transfer between the transponder TR2 and the base station takes place.

p0049For the subsequent selection of the transponder TR3 the base station BS retransmits within the deterministic selection procedure a start command, not shown, which initiates a second deterministic selection process. Since the transponder TR2 was selected in the previous selection process, he no longer takes part in the subsequent selection process.

p0050The base station BS transmits a bit by bit selection bit and now the transponder TR3 scatters in full duplex mode its identification bit sequence to the base station back which coincides with the selection bit. After the selection of a not shown, bi-directional data transfer between the transponder TR3 and the base station takes place.

p0051Subsequently, the base station transmits a next slot command to the transponders TR1 to TR3 in step 13 of <figref idrefs="f0001">Fig. 1</figref>Whereupon this increment its internal time slot number counter. In<figref idrefs="f0002">FIG. 2</figref> this corresponds to the period 24. Since the selection situation shown no further transponder in the response of the base station BS are, it receives in the following time slots no further identifications. After all the time slots have been processed, the base station BS terminates the selection process by sending a corresponding command.

p0052The selection process described enables the timesaving selecting one or more transponders from a plurality of transponders by a base station even with a fluctuating number of transponders in the operating distance of the base station, wherein the presence of a unique, statically allocated U-ID is not mandatory for the transponders ,

p0053<figref idrefs="f0003">Fig. 3</figref> shows a block diagram of a basic arrangement for the generation of random numbers, which is integrated in a transponder TR. The arrangement includes a timing generator TG, a controllable logic gate LG, a control unit SE and a clocked linear feedback shift register SR, which provides the random numbers. The shift register is loaded by the control unit SE in the course of an initialization, to a reset signal, so that the shift register takes up a defined initial value.

p0054The clock generator TG is used for clock supply of shift register SR. The logic gates LG is connected between the clock generator TG and the shift register SR and a clock input of the shift register SR. The logic gates LG is supplied with a clock enable signal TF, which is provided from the control unit SE. When the clock enable signal TF performs an enable level, situated on a clock signal of the clock generator TG to the shift register, ie its clock supply is active and generates the beat of the clock supply continuously random numbers. When the clock enable signal TF performs a barrier level, the clock signal is decoupled from the shift register SR, ie its clock supply is disabled and no new random numbers generated. When disabled, the clock supply, the power consumption of the device is greatly reduced.

p0055The control unit SE controls the logic gates LG in such a way that the clock pulse supply of the shift register SR during phases with an increased in comparison with an average power consumption of the transponder TR will be disabled. Phases with increased power consumption occur especially during a data transmission between a base station and the transponder TR.

p0056If a stochastic or mixed deterministic-stochastic selection procedure is used in the second selection level, it may be necessary to generate a second random number or Zufallszahlenbitfolge. Using the in<figref idrefs="f0003">Fig. 3</figref> shown arrangement, it is possible to generate both a random number of the first selection plane and a random number or Zufallszahlbitfolge the second selection plane, to produce them only a single shift register SR is required. This reduces the chip area required and thus reduces the production costs compared to a realization in which each selection level is assigned to a shift register for random number generation. Furthermore, the power consumption is reduced, thereby to distances between the base station and the transponder TR increase.

p0057In a first variant for the production of two different random numbers with only a shift register SR, the number of bits of the shift register is greater than would be necessary for generating the random number of the first selection plane.

p0058If a shift register SR is used with a width of 8 bits, for example, 5 bits of the shift register SR of the random number of the first selection level and 3 bits of the shift register SR of the random number of the second selection level can be assigned. Using the 5 bits of the first selection level can be up to 32 different time slots within the first selection level differ and using the 3 bits of the second selection level can be addressed up to 8 different transponder, bearing in mind that not all bits of the shift register SR simultaneously be zero.

p0059If this range of values ​​of the random number for the second selection level is not enough, another random number may be generated by logically combining the random number of the second selection level with transponder-specific data that is used as a random number for the second selection level. In the transponder-specific data can be data from a memory area of ​​the transponder, which is addressed by using the random number of the second selection level. In the logic operation may be, be any logical operations, such as an AND, OR and / or an XOR operation.

p0060In the method described, the shift register SR is so long exposed to the clock supply until the selection of the first selection plane is initiated by the base station by sending a corresponding command. The binary content of the shift register is read out after receiving the commands and separated into a random number of the first and the second random number in a plane, that the random numbers are generated simultaneously. Then, the shift register SR is turned off, whereby the power consumption is reduced.

p0061In an alternative embodiment, the random number of the first selection plane is produced after receipt of the command from the shift register, read out therefrom and stored, wherein the full width of the shift register is available for the random number. Subsequently, the clock supply of shift register SR will remain active until another random number is needed in the second selection level. The random number of the second selection plane is then removed from the shift register and stored separately from the random number of the first selection level, which is the full width of the shift register is available also for the random number of the second level. Consequently, this procedure increases the available range of values ​​of the random numbers of the first and the second level, but compared to the simultaneous generation of random numbers in terms of absorption unfavorable. In order to reduce the power consumption of the shift register can be operated after the generation of the first random number with reduced clock or the clock supply can be turned off during a communication with the base station.