Method for selecting one or more transponders

0001The 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.

0002Such procedures, which also referred to as anti-collision method be found, for example, in contactless identification systems or so-called Radio Frequency Identification (RFID) systems Use. Such a system is usually from a base station or a reader and a plurality of Transponders or remote sensors simultaneously within the response the base station are. When the data transfer only between one or a group of transponders and base station is to take place, must precede the corresponding data transmission such competitions are organized.

0003Is basically made between stochastic and deterministic Selection process differed. A detailed description both deterministic selection procedure as well as to stochastic Selection can be found for example in the textbook Klaus Finkenzeller, RFID Handbook, 3rd Ed., Hanser, 2002, see especially Section 7.2 multiple access methods.

0004Stochastic processes put in contrast to deterministic methods no unique, so-called Unique Identification (U-ID) advance whose structure is described for example in ISO 15,963th An award of such U-IDs is among other things, various multi-vendor made organizations, for example, the EAN / UCC or the IATA. However, the assignment can also be a Manufacturers themselves are made. Overall, therefore, in open Systems in which the transponder of any manufacturer in the operating distance can find a base station, the uniqueness of the U-ID is not always guaranteed. Stochastic methods permit a choice in these cases. Examples of such stochastic Processes are the so-called ALOHA method, the slot-based or slotted ALOHA method, and the dynamic slot based ALOHA method.

0005The ALOHA method is a transponder-controlled, stochastic Method in which a time lag, the transponders to be transmitted their Send data. The time offset is typically based on an in Transponder generated random number set. If more Transponders transmit an identification within the same time slot, occurs a so-called collision. This prevents usually that the base station can receive the transmitted data without errors.

0006In slotted ALOHA method, the probability of collision reduced significantly compared to simple ALOHA method. It is a controlled from the base station, stochastic process in which the transponders are active only at defined, synchronous points in time, ie begin transmission of data. For this purpose, the base station numbered time slots or slots in front and produce the transponder each a random number, each transponder whose random number corresponds to the number of a time slot, data or an identifier transmits in this time slot to the base station. To initiate the Selection process the base station transmits typically a command , Indicated to the transponder by the beginning of a selection procedure becomes. Upon receipt of the commands are in the transponders the respective random numbers stored, for example, previously were calculated in the transponder. If only one transponder a Sends identifier within a time slot, this transponder selected within the time slot or can be obtained by the base station be selected by sending an acknowledgment signal. The base station then, for example, write and / or read operations on this transponder run. If multiple transponders an identification send within the same time slot, a collision occurs. Depending on the coding information, the base station such a collision recognize directly or with delay and the corresponding Skip timeslot and execute trying time slots in which no collision occurs, or a new selection procedure by sending initiate a corresponding command to the transponder. Since the transponders typically generate new random numbers or store, there is a possibility that now occurs no collision.

0007The probability of collision depends on the number of transponders the response range of the base station and the number of available identified timeslots from. Since the number of transponders vary widely can, a static setting of the number of time slots Problems. Is the number of time slots too small, the collision probability strongly. Is the number of time slots is too large, there is a corresponding number of time slots in which no transponder data transfers. The time required for the selection procedure thus takes in both cases, sharply. In order to achieve optimal throughput, If the number of time slots in which the transponders transmit data, equal to the number of transponders are chosen approximately.

0008To solve this problem, the dynamic slot based there ALOHA method, in which the number of data available Time slots can be controlled by the base station. For example the base station a selection procedure with a small number Initiate of time slots. If this often collisions occur may initiate a new selection procedure, the base station, at the number of time slots is increased, whereby the collision probability decreases. The dynamic of such a method However, time required is relatively large because the adjustment of the optimum Number of time slots may take a long time to complete. furthermore requires it due to its complexity a correspondingly high Circuitry.

0009are to produce a random number for the stochastic process known different methods. For example, the time between a reset of the transponder and the time at which a first character is received, as the basis for calculating the random number serve. Other methods combine numbers from two different Memory areas of the transponder together to the to determine random number, wherein additionally to refine a received data can be included in the calculation. Other methods use a linear feedback shift register for random number generation, the example with an inaccurate Clock supply can be operated.

0010The deterministic selection process are generally based on a binary search method or a so-called binary search algorithm and require that each transponder in the response the base station assigns a unique identification bit is. The identification bit is usually the Unique Identification (U-ID) formed, for example, with the transponders is assigned to the production thereof. The uniqueness of the U-ID can, however, because of the plurality of U-ID specification in open systems not always be guaranteed.

0011A selection process in which the transponder based on a bitwise Comparison of their unique, statically assigned identification bit are selected with a selection bit, is described in US 5,856,788 described. The selection is made here in a half duplex mode, wherein the transponder one bit of their identification bit transmitted and the base station then transmitted on the basis of Bit values ​​a select transfers. 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 the DC-operator, that is, transponder which corresponding bit of their identification bit with the selection bit matches, remain activated. Due to the half-duplex method is a relatively long time is required until a transponder is selected.

0012In the ISO WD 18000-6 Mode 3 from 01.02.2002 is a selection described, in which the selection is also based on a unique Identification bit done. The selection process operates in Full duplex method whereby the selection time decreases. The Transponders are also by their unique, statically allocated Identification bit selected.

0013The invention is based on the technical problem to provide a method of the type described above, which one to choose or more transponders from a plurality of transponders by a base station, the presence of a clear, static assigned U-ID is not mandatory for the transponders and the time-saving choice of one or more transponders also at a fluctuating number of transponders in the operating distance the base station allows.

0014The invention solves this problem by providing a method with the features of claim 1.

0015According to the invention, when more than one transponder in the same time slot send an identifier for selection within this time slot in a second selection level further, stochastic and / or deterministic, performed by the base station controlled selection procedure. This allows for address assignment example based a slotted ALOHA method within a first selection level, wherein the number of time slots in comparison to a conventional slotted ALOHA method be kept relatively small can. It is possible, the number of time slots in the to choose first selection level constant or dynamically to the number which located in the response area of ​​the base station transponder adapt. Due to the stochastic nature of the first selection level is the existence of a unique, statically allocated Identification bit and a U-ID is not in the transponders necessarily supposes.

0016The second selection plane allows the selection of one or more Transponder even when a fluctuating number of transponders the response range of the base station. When compared to Number of time slots bit transponder in the response of the base station are, that is, if no collisions within a time slot occur or be detected by the base station, is in the first selection level, only one slot based ALOHA method with a relatively small number of time slots carried out. this makes possible timesaving selection of transponder. However, when collisions occur within a time slot, that is, when compared the number of time slots in the operating distance of many transponders Base station are, the second selection plane allows a choice by using another, first from the selection level independent stochastic, deterministic or mixed deterministic-stochastic Selection procedure.

0017In a development of the method according to claim 2 is the stochastic Selection procedure of the second selection level an ALOHA method, in particular this can be a slot-based ALOHA method be. The active in the corresponding timeslot transponder, ie those transponder whose random number the number of the current Time slot corresponds, generate or save this another Random number and take on another slotted ALOHA method part, which nested within the first selection procedure or nested within the corresponding time slot is carried out.

0018In a development of the method according to claim 3 is the deterministic Selection procedure of the second selection level a binary Search process. This allows a quick selection of one or a Group of transponders in the second selection level.

0019In a development of the method according to claim 4 is the deterministic Selection procedure in the transponders respective identification bit provided, a selection bit by the base station bit transmitted to the transponder in the respective Transponder a bitwise comparison of the corresponding bits the identification bit and the selection bit based on a predetermined Comparative criterion carried out and based on the comparison result assigned to a selection bit has a weight and the respective Transponder depending on the valence of his selection bits selected. This allows a time-saving choice, since the selection bit takes place and not the complete sequence of bits transmitted must, to a selection can take place. Advantageously, according to claim 5 generates a Zufallszahlbitfolge in each transponder and as such identification bit provided that the Zufallszahlbitfolge contains. This allows the selection of transponders within the second selection level, even if this through their U-ID no different.

0020In a development of the method according to claim 6 is to check, whether within the same time slot more than one transponder sends an identifier, received from the base station identifier as an acknowledgment signal at least partially on by the base station the transponders transmit back and checked in the transponders, whether the transmitted identifier from the base station with the respective Transponder transmitted ID matches. When mismatch takes the corresponding transponder within the time slot no further part in the selection procedure. When the base station falsely detects no collision is prevented in this way, that transponders are incorrectly selected.

0021In a development of the method according to claim 7 is used to transfer the identification from a transponder to the base station, a coding used by 3phase1 type, such as those described in ISO WD 18000-6 Mode is described. 3 This enables the base station, to detect the bit position of a collision.

0022In a development of the method according to claim 8, the random number the first selection level and / or a random number or Zufallszahlbitfolge the second selection level by means of a clocked linear feedback shift register generated, the clock supply during phases with a power consumption compared to an average disabled increased power consumption of the transponder becomes. This enables a reduction of a peak value of the power consumption the transponder and thus increases the coverage area between a base station and a transponder. Advantageous is as defined in claim 9, the clock supply during a data transmission disabled between the base station and the transponder. This increases the communication range.

0023In a development of the method according to claim 10, the clock supply deactivated by means of a controllable logic gate, the connected between a clock supply unit and the shift register becomes. This enables a simple to implement activation or deactivation of the clock supply.

0024In a development of the method according to claim 11, the random number the first selection level and a random number or Zufallszahlbitfolge the second selection level by means of a clocked linear generates feedback shift register. This reduces the required Chip area and thus reduces manufacturing costs in comparison to a realization, wherein each random number, a shift register assigned. Furthermore, the power consumption is reduced, thereby to distances between the base station and the transponder increases.

0025be a In a development of the method according to claim 12 first part of a number of bits of the shift register of the random number the first selection plane and the remaining part of bits of the shift register associated with the second random number or Zufallszahlbitfolge. This enables simultaneous production of both random numbers.

0026In a development of the method according to claim 13, the random number generates the first selection level by means of the shift register and stored. Then, the random number of the second Selection level generated and separated by means of the shift register the random number of the first selection level stored. The reading the shift register contents for obtaining the random numbers each triggered upon entering the respective selection plane. This is in each case the entire width of the shift register for the random numbers to Available.

0027In a development of the method according to claim 14, the Shift register after the generation of the random number of the first selection level operated with reduced stroke. This reduces the power consumption and consequently increases the range.

0028In a development of the method according to claim 15 is another Random number by logically combining the random number or Zufallszahlbitfolge the second selection level with transponder-specific Data generated when the value range of the random number or Zufallszahlbitfolge the second selection level for the second selection level not sufficient. The more random number can then for the second selection level be used.

0029Advantageous embodiments of the invention are in the drawings shown and described below. This is shown schematically:<dl tsize="6"><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 FIG. 1 in an exemplary selection situation and </dd><dt>Fig. 3</dt><dd>a block diagram of a basic arrangement for generating Random number using a linear feedback shift register.</dd></dl>

0030Fig. 1 shows a flow diagram of a selection process for selection one or more backscatter-based transponder from a variety of transponders by a base station with two selection levels. Fig. 2 shows a diagram of a corresponding time sequence of the Selection process of FIG. 1 in an exemplary selection situation, in which three transponders TR1 to TR3 in the operating distance of the base station BS are that are selected consecutively.

0031In a step 10 of FIG. 1, the selection process starts in a first Selection level. Typically, the base station BS sends this, a shown in Fig. 2 command 20 to the transponders TR1 to TR3, is indicated by the start of a selection procedure. After Receiving the command 20 are in the transponders TR1 to TR3 respective random numbers generated or calculated and then stored and an internal time slot number counter to an initial value set.

0032In a step 11 of FIG. 1, the base station BS waits for a feedback the transponders TR1 to TR3 and receives, if a Identifier is sent. In FIG. 2 this is by a Wait / receiving period represented 21st

0033The transponders TR1 to TR3 compare the value of their internal time slot number counter Send with the stored random number and in accordance an identifier in the form of U-ID. When in Fig. 2 shown selection situation has only the transponders TR1 to the first time slot corresponding to the random number. The transponder TR1 transfers hence 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 taken place, that is, no further Transponder its U-ID is transmitted simultaneously with TR1. The Transponders TR2 and TR3 remain passive because their random number not the number of the current time slot matches, and wait to a command from the base station, that the next time slot initiates.

0034The transponder TR1 is now regarded as selected, with the final Selection further steps can be carried out, for example, the transmission of an acknowledgment signal from the base station to the transponder. In a step 12 of FIG. 1 communicates the base station BS bidirectionally with the transponder TR1 and can, for example, Write and / or read operations on the selected run transponder TR1. In FIG. 2 this is indicated by a communication period 23 shown.

0035Because of phase shifts and widely varying levels it can, particularly with large distances between Transponders TR1 to TR3, and the base station BS, despite the appropriate Coding happen that a collision occurs, the not from the Base station BS is detected. For collision detection is next an appropriate coding, the possibility is not shown in Fig. 2 that received from the base station BS U-ID by this to the Transponder TR1 is transferred to TR3 as an acknowledgment signal back. In the respective transponders TR1 to TR3 is then checked whether the transmitted from the base station BS identifier or U-ID with the respective Transponders TR1 to TR3 transmitted ID matches. If it is determined in a transponder that consensus present, he does not continue at the current selection procedure part in this time slot. If they match, the appropriate Transponder selected.

0036After completion of communication with the transponder TR1 in Step 12, the base station BS a next slot command to the transponders TR1 to TR3 in a step 13 of FIG. 1, to which this increment its internal time slot number counter. In FIG. 2, this corresponds to a period 24. Alternatively, the Base station BS and the number of the current time slot to the Transponder TR1 transmitted to TR3. 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, the this, the selection process end displays. then switch to a corresponding operating state.

0037If continuing the selection process is in the flowchart of FIG. 1 returned to step 11, ie, the base station BS waits for the Confirmation of the transponders TR2 and TR3 and receives, if an identifier is sent. In FIG. 2 this is by a renewed Wait / receiving period 21 shown.

0038As in the selection of situation shown in Fig. 2, the transponder TR2 and TR3 have identical random numbers, send them in connection to the next slot 24 in the accompanying command Backscatter period 22 at the same time their respective U-ID, whereby a collision formed at bit positions, the bit values ​​do not agree. Due to the bit coding, the base station detects the collision and branches to step 12 instead of to step 14 of FIG. 1,.

0039In step 14 of FIG. 1, the base station BS 2 sends a in Fig. Shown Command 25 to the transponders TR1 to TR3, by the beginning displayed a selection procedure of a second selection level becomes.

0040In a step 15, the second selection procedure is nested within the second time slot carried out, wherein a stochastic order, deterministic or mixed deterministic-stochastic can act selection procedure.

0041As stochastic process, for example, a simple ALOHA method, a slot-based or a dynamic slot-based ALOHA method used. After receiving the start command 25 are again in the transponders TR2 and TR3 in this case each Random numbers generated or calculated and then stored and an internal Subzeitschlitznummernzähler to an initial value set. There is then a nested ALOHA method within a time slot of the parent slotted ALOHA method performed.

0042When deterministic methods, for example, a conventional binary search methods can be used. A suitable Example of this is in the above-cited standard ISO WD 18000-6 Mode 3 described from 01.02.2002 selection process in which the Selection is based on a U-ID.

0043A mixed deterministic-stochastic selection process, as it herein is used for the second selection level, is not in the German patent application DE 103 36 308 A1 of described Applicant, which is incorporated herein by reference is made to the content of the present application. The selection worked out using a identification bit that a static component containing or a U-ID and a dynamic portion, which on a Random number generated in the transponder is based. For selection in the Transponders each provided such identification bit, a selection bit by the base station bit by bit to the transponders transmitted, in each transponder a bitwise comparison between 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 a assigned value. The respective transponder is dependent on the significance of his selection bits selected.

0044The second selection procedure shown in Fig. 2 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 bitwise the selection bit and the transponder TR2 scatters in full-duplex operation in backscatter period 22 to its identification bit, the base station back, which corresponds to the selection bit. Of the Transponder TR2 is thus selected. Since the identification bit TR3 of the transponder does not coincide with the selection bit transfers, this in backscatter period 22a only a portion of its identification bit to the back base station. The backscatter is terminated at a point in time when a 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 is alternatively the possibility to select groups of transponders, that is, at the same time in this case, TR2 and TR3. After selecting finds a not shown, bi-directional data transfer between the transponder TR2 and the base station instead.

0045For the subsequent selection of the transponder TR3, the base station BS within the deterministic selection procedure again a start command, not shown, of a second deterministic Selection process initiates. Since the transponder TR2 in the previous Selection process has been selected, it assumes the following Selection process no longer participate.

0046The base station BS transmits a bit now and the selection bit Transponder TR3 scatters in full duplex mode its identification bit back to the base station which corresponds to the selection bit. After selecting a place not shown, bidirectional data transfer between the transponder and the base station instead of TR3.

0047Subsequently, the base station transmits a next slot command to the transponders TR1 to TR3 in step 13 of FIG. 1, whereupon this their internal time slot number counter increment. In FIG. 2 corresponds to the period 24. As shown in the selection situation no further transponder in the response of the base station BS are, it receives in the following time slots no further identifications. After all timeslots processed are, the base station BS terminates the selection process by sending a corresponding commands.

0048The selection process described enables the timesaving selection one or more transponders from a plurality of Transponders by a base station even in a highly 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.

0049Fig. 3 shows a block diagram of a basic arrangement for generating random numbers, which is integrated in a transponder TR. The order includes a clock generator TG, a controllable logic gates LG, a control unit SE and a clocked linear feedback Shift register SR, which provides the random numbers. The shift register is by the control unit SE in the course of an initialization with a Reset signal is applied, whereby the shift register a defined Initial value takes.

0050The clock generator TG is used for clock supply of shift register SR. The logic gate LG is between the clock generator TG and the Shift register SR and a clock input of the shift register SR looped. The logic gate LG is a clock enable signal TF applied, which is provided from the control unit SE. If the clock enable signal TF an enable level results, there is a clock signal 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 rejection level is the clock signal 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 increases the arrangement sharply.

0051The control unit SE controls the logic gates LG in such a way that the Clock supply of shift register SR during phases having a Compared to an average power consumption of increased power consumption the transponder TR is deactivated. Phases with increased Power occur particularly during data transmission between on one base station and the transponder TR.

0052When mixed, a stochastic or in the second selection level deterministic-stochastic selection procedure is used, it may be necessary, a second random number or Zufallszahlenbitfolge to create. With the help of the arrangement shown in Fig. 3, it is possible both a random number of the first selection level and a generate random number or Zufallszahlbitfolge the second selection level, where to produce them only a single shift register SR is required. This reduces the chip area required and reduced Consequently, the manufacturing cost compared to a realization, wherein each selection level, a shift register for random number generation assigned. Furthermore, the power consumption is reduced, thereby to distances between the base station and the transponder TR increase.

0053In a first variant for the production of two different random numbers with only a shift register SR is the number of bits of the shift register is greater than that for generating the random number of first selection level may be necessary.

0054When 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 the first selection level and 3 bits of the shift register SR of the random number the second selection level be assigned. With the help of 5 Bits of the first selection level can be up to 32 different different time slots within the first selection level and with Help the 3 bits of the second selection level can be up to 8 different Transponder address, bearing in mind that not all the bits of the shift register SR can be zero simultaneously.

0055If this range of values ​​of the random number for the second selection level is not sufficient, another random number by logically combining the random number of the second selection level with transponder-specific Data is generated, the random number for the second selection level is used. 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 logical link may be any logical operations, for example, an AND, OR and / or an XOR operation, act.

0056In the method described, the shift register SR as long applied to the clock supply until the selection of the first Selection level by the base station by sending a corresponding Command is initiated. The binary content of the shift register is read out upon receipt of the command and in a Random number of the first and separated into a random number of the second level, that is, the random numbers are generated simultaneously. subsequently the shift register SR is turned off, minimizing power consumption is reduced.

0057In an alternative embodiment, after reception of the Commands the random number of the first selection level from the shift register generated, read out therefrom and stored, wherein the full width of the shift register for the random number available stands. Subsequently, the clock supply of shift register remains SR activated until another random number in the second selection level is required. The random number of the second selection level then removed from the shift register and separated from the random number saved the first selection level, which for the Random number of the second level, the full width of the shift register is available. This approach sweise increases consequently the for Available range of values ​​of the random numbers of the first and However, the second level is, compared to simultaneous production the random numbers in terms of absorption unfavorable. to Reduction of the power consumption of the shift register after the continue to operate generating the first random number with reduced clock are respectively the clock supply can during communication be disabled with the base station.