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    • 专利摘要:
    Anti-collision procedure for identification of transponders in an rfid system. The invention solves the problem of the arbitration of responses of the tags by using a controller based on fuzzy rules to determine the variation of the size of the frame, using the information received from the current frame, using the number of collided or empty slots in what is going of received frame, in addition to the size of the frame itself, to readjust to a new size and continue the process until the set of tags is identified. The procedure dynamically adjusts the size of the frame in which these devices host their responses to prevent them from colliding with each other. This adjustment is made using a strategy based on fuzzy logic and the information obtained from the responses of the current frame received in the reader. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2613268A1
    申请号:ES201531673
    申请日:2015-11-19
    公开日:2017-05-23
    发明作者:Laura ARJONA AGUILERA；Hugo LANDALUCE SIMÓN；Asier Perallos Ruiz；Enrique ONIEVA CARACUEL；Alfonso BAHILLO MARTINEZ
    申请人:Fund Deusto；Fundacion Deusto；
    IPC主号:
    专利说明:

    OBJECT OF THE INVENTION
    The object of the present invention is an anti-collision procedure based on fuzzy logic for identification of transponders in an RFID system, which seeks to reduce the identification time of transponders or tags.
    The procedure is characterized by being based on fuzzy logic and takes into account the information contained in the slots already received from the current frame. In addition, it is accompanied by a methodology for reducing the complexity of the protocol that helps reduce identification time.
    The invention is included within the radiocommunication sector and more specifically within the radiofrequency identification (RFID) sector, that is, within the technologies used for the detection and identification of passive devices (tags) using an RFID reader in bands equal to or greater than UHF.
    BACKGROUND OF THE INVENTION
    A radio frequency identification (RFID) system consists of at least one reading device and one transponder device, hereinafter tag. The reader takes the initiative in communication and tries to identify the set of tags that are in the range of their antenna using radio frequency waves (see Figure 1). The tags contain a unique identifier (ID) that they send to the reader to be recognized. In the case of passive tags, contemplated in this invention, the tags feed on the actual signal received from the reader and do not have the ability to communicate with each other.
    The coexistence of tags sharing the same communications channel can cause interference between the transmitted signals making them incomprehensible to said reader. This causes an increase in the identification time of all the tags and the decrease in their bandwidth. This phenomenon is known as the problem of tag collisions. To solve it, an anti-collision protocol is required.
    Currently, RFID systems include various anti-collision protocols, especially those working in bands such as HF, UHF or higher. There are mainly two types of anti-collision protocols: tree-based and Aloha-based. Tree-based protocols subdivide the set of tags every time the reader detects a collision in their responses, until there is only one tag left in that subset and is finally identified [1] [2]. In this way the identification process forms a virtual tree where each node represents a collision. On the other hand, Aloha-based protocols divide time into frames, composed of slots or time slots. The tags choose a single slot within each frame in which they transmit their ID [3], [4], [5].
    Within the Aloha type protocols, there is the protocol currently used in commercial RFID systems, which is also part of the ISO 18000-3C standard. This protocol is known as EPCglobal Class 1 Generation 2 (EPC C1G2) [6]. Its anti-collision procedure arbitrates tag responses sequentially in a temporary size frame
    (L) variable (see Figure 2). Each slot consists of a reader command followed by one, none or several responses of the tags (see Figure 3). Therefore, three types of slots can occur: (1) a collision if two or more tags choose the same slot, (2) an empty slot if no tag responds to the reader's command; or (3) a slot identified if a single tag responds to the reader's command. According to the EPC C1G2 standard, tags initially respond with a 16-bit random number (RN16). If it is correctly received by the reader, then it asks for the full ID. The parameter L defines the number of slots of which the frame is composed, that is, the number of slots where each tag will send its response. So the higher the L, the greater the probability that a tag will choose a different slot from the rest of the tags; in the same way the greater the probability of finding an empty slot. On the contrary, the probability that two tags collide in a slot increases the smaller L. This standard modifies the value of L through parameter Q with the following equivalence L = 2Q. The reader only transmits the value of Q to inform the tags of the frame size. By restricting L to powers of two, the reader sends fewer bits, and the tag calculates the frame size by executing the aforementioned equivalence. The value of Q is updated by the reader in each slot; however, it is not clearly specified how to modify it, beyond increasing or decreasing its value with intervals between 0.1 to 0.5 units. This uncertainty that arises when determining Q accurately has given rise to various works in the literature [7], [8], [9].
    Unlike these procedures, the present invention solves the problem of allocating the frame size composed of L slots using a procedure based on fuzzy logic and taking into account the information contained in the slots already received from the current frame. In addition, it is accompanied by a methodology for reducing the complexity of the protocol that helps reduce identification time. Together, they form a new anti-collision protocol, compatible with the ISO 18000-3C standard, which reduces the identification time of the tags.
    [1] Yuan-Cheng Lai; Ling-Yen Hsiao; Bor-Shen Lin, "Optimal Slot Assignment for Binary Tracking Tree Protocol in RFID Tag Identification," in Networking, IEEE / ACM Transactions on, vol.23, no.1, pp. 255-268, Feb. 2015.
    [2] H. Landaluce, A. Perallos, and I. Zuazola, “A fast RFID identification protocol with low tag complexity,” IEEE Communications Letters, vol. 17, no. 9, pp. 1704–1706, 2013.
    [3] C. Qian, Y. Liu, R. Ngan, and L. Ni, “Asap: Scalable collision arbitration for large RFID systems,” IEEE Transactions on Parallel and Distributed Systems, vol. 24, no. 7, pp. 1277-1288, 2013.
    [4] H. Wu, Y. Zeng, J. Feng, and Y. Gu, “Binary tree slotted aloha for passive RFID tag anticollision,” IEEE Transactions on Parallel and Distributed Systems, vol. 24, no. 1, pp. 19–31, 2013.
    [5] Patent No. US 8,305,194 B2 on Nov. 6, 2012. "Collision Resolution Protocol for Mobile RFID Tag Identification"
    [6] “Radio Frequency Identity Protocols class-1 generation-2 UHF RFID protocol for communications at 860 MHz – 960 MHz,” November 2013.
    [7] I. Joe and J. Lee, “A novel anti-collision algorithm with optimal frame size for RFID system,” in 5th ACIS International Conference on Software Engineering Research, Management Applications, 2007. SERA 2007, pp. 424-428, Aug 2007.
    [8] J. Teng, X. Xuan, and Y. Bai, “A Fast Q algorithm based on EPC Generation-2 RFID protocol,” in 6th International Conference on Wireless Communications Networking and Mobile Computing (WiCOM), 2010, pp. 1–4, Sept 2010.
    [9] M. Daneshmand, C. Wang, and K. Sohraby, “A New Slot-Count Selection algorithm for RFID Protocol,” in Second International Conference on Communications and Networking in China. 2007, pp. 926-930, Aug 2007.
    DESCRIPTION OF THE INVENTION
    The present invention relates to a procedure for the arbitration of the responses of the tags that dynamically adjusts the size of the frame in which these devices host their responses to avoid colliding with each other. This adjustment is made using a strategy based on fuzzy logic and the information obtained from the responses of the current frame received in the reader.
    The RFID reader establishes an initial frame size, tags choose a slot within that frame and transmit when their turn comes. The reader starts each new slot with a command and stores the information of the type of response obtained (collision, empty or identified) (see Figure 3). Additionally, when the reader reaches the slot defined as more suitable for the check, it uses the controller based on fuzzy rules to check if the frame size is adequate or should change.
    The invention solves the problem of tag response arbitration using a controller based on fuzzy rules to determine the variation of the frame size, using the information received from the current frame. That is, it uses the number of collided or empty slots as far as the frame received, in addition to the frame size itself, to readjust to a new size and continue the process until the set of tags is identified.
    Unless otherwise indicated, all technical and scientific elements used herein have the meaning normally understood by the person skilled in the art to which this invention pertains. In the practice of the present invention procedures and materials similar or equivalent to those described herein can be used.
    Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention.
    EXPLANATION OF THE FIGURES
    To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation thereof, a set of drawings is attached as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented.
    Figure 1 shows a general scheme of an RFID system, with a reader and five tags located within the range of the reader. In that figure: T1, T2, T3, T4, T5 refers to each of the five tags of the RFID system, R refers to the reader.
    Figure 2 shows the basic structure of a presented protocol frame, composed of L slots. In that figure: S1, S2 ... SL refers to each of the slots in the frame and L refers to the size of the frame, equal to the total number of slots.
    Figure 3 shows the structure of the three types of slots described in the invention. In that figure: The X axis corresponds to the temporal evolution of the tag arbitration process; the Y axis is composed of two sections, the reader transmissions (upper) and the responses of the tags (lower); "Collision slot" refers to a slot in which two or more tags transmit; "Empty slot" refers to a slot in which no tag transmits; "Identified slot" refers to a slot in which only one tag transmits; RN16 refers to the 16-bit random number sent by the tag in the slot corresponding to SC = 0; T1 and T2 refers to tags 1 and 2 respectively; ACK refers to the command sent by the reader to indicate the correct reception of the response sent by the tag; and Tag ID refers to the Tag Identifier, which uniquely identifies it, differentiating it from the rest of the tags.
    Figure 4 presents the flowchart of the reader executing the anti-collision protocol of the invention. In that figure: Q refers to the parameter that determines the size of the frame L = 2Q; Qc refers to the QUERY command sent by the reader; QR refers to the QUERY_REP command sent by the reader; QA refers to the QUERY_ADJ command sent by the reader; "Empty" refers to the reader's counter nor does it represent the number of slots in which no tag transmits; "Collisions" refers to the counter of the reader nc that represents the number of slots where a collision of the tag responses occurs; ΔQ refers to the increase in the value of Q and CRD refers to the Controller based on fuzzy rules.
    Figure 5 presents the flow chart of the tag executing the anti-collision protocol of the invention. In that figure: QR refers to the QUERY_REP command sent by the reader; QA refers to the QUERY_ADJ command sent by the reader; ACK refers to the command sent by the reader to indicate the correct reception of the response sent by the tag; RN16 refers to the 16-bit random number sent by the tag in the slot corresponding to SC = 0; SC refers to the Tag Slot Counter; and ID refers to the Tag Identifier, which uniquely identifies it by differentiating it from the rest of the tags.
    Figure 6 shows the CRD tags for parameter Q. In that figure: Low, Medium and High refer to the three tags that encode the Q variable; the X axis represents the values of Q; and the Y axis represents the degree of belonging of the value of Q to each of the labels.
    Figure 7 shows the labels for the SW parameter. In that figure: Low and High refer to the three CRD tags that encode the SW variable; The X axis represents the SW values and the Y axis represents the degree of belonging of the SW value to each of the labels.
    Figure 8 represents the structure of the first frame of the operating example. In this figure: T1, T2, T3, T4, T5 and T6 refers to each of the tags that participate in the first frame of the identification process; Q refers to the parameter that determines the size of the frame L = 2Q, "collision" indicates that in the current slot there has been a response of two or more tags; “Empty” indicates that in the present slot no tag has responded; “Identified” indicates that in the current slot only one tag has transmitted its response; check slot refers to the slot in which it is checked whether the current frame size is appropriate.
    Figure 9 shows the execution of the operating example. This figure shows the slot that selects each tag in each frame. The script indicates that the tag has been previously identified and therefore ceases to participate in the identification process and in bold the slot in which the tag has been identified is represented, in the corresponding frame.
    PREFERRED EMBODIMENT OF THE INVENTION
    In view of the figures, a preferred embodiment of the proposed invention is described below.
    Considering an RFID system like the one presented in Figure 1, with a single reader and several passive tags transmitting on the same channel, the invention of the following procedure is proposed. This is a procedure that resolves the existing undefined standard EPC C1G2, in the choice of the size of the frame used in the responses of the tags, forming a new anti-collision protocol that reduces the identification time. The proposed invention uses the same commands as the EPC C1G2 standard:
    - QUERY (Qc): Transmitted at the beginning of the identification process for
    set the initial frame size. Tags randomly choose
    a value for its slot counter (SC) in the range [0.2Q -1].
    - QUERY_ADJ (QA): It is transmitted every time the reader needs
    Readjust frame size. The tags therefore reset
    randomly the SC in the range [0.2Q-1].
    - QUERY_REP (QR): It is transmitted when the reader goes to the next slot
    Of the plot. The tags decrease by 1 their SC.
    Figure 4 and Figure 5 show the methodology followed by the reader and each tag respectively. The protocol establishes an initial frame size with Q = 2, that is, 4. It transmits the first QUERY command and communicates the frame size to the tags. The tags receive the size of the frame and generate a random value for the SC. Those whose value is 0 transmit. According to the responses received, the reader determines what type of slot it is and updates the empty or collision slot counters. Subsequently, check in which position of the frame it is, that is, which has been the last slot checked to check if it is in the most appropriate slot to perform the frame check. If so, the reader executes the controller based on fuzzy rules to calculate the increase or decrease of the ΔQ frame. Finally, the new value of Q is calculated and checked if its value has changed. In the event of a change in its value, the reader sends a QA command to reset the frame size and resets the empty counters and collisions. Otherwise, the reader sends a QR command and goes to the next slot in the frame. The reader takes the initiative at all times in the process by transmitting some of the commands mentioned at the beginning of each slot. The responses of the tags (see Figure 5) occur when the SC counter of any of them is 0. In that case, it transmits a 16-bit random number (RN16). If the reader receives this number correctly, he answers with an ACK command that contains the received RN16. The tag understands that your RN16 has been correctly received and begins to send the ID in full, being identified.
    Description of the fuzzy rules-based controller (CRD):
    By using a controller based on fuzzy rules (CRD) that uses information collected during the current frame, the increment is calculated
    or adequate decrement for said plot. Two input variables are used for this: the slot expense, called SW and the current value of Q that represents the frame size as an exponent of a power of two.
    - SW: Slot spending is a measure calculated from the information obtained from the plot executed so far. For this, the maximum between the collision and empty counters and the position of the last slot received by the reader is used. The function of belonging to fuzzy sets is shown in Figure 6. Values outside the range covered by the trapezoids correspond to those of the range limit.
    - Q: Determine the size of frame L as 2Q. and ranges from 2 to a reasonable number. Its membership function is shown in Figure 7. As in the previous case, the values outside the range covered by the trapezoids correspond to those of the range limit.
    These parameters are used as input of the CRD, a fuzzy controller based on AND rules. To obtain the output, a set of six rules is proposed that will determine the output of the ΔQ controller in the form of four possible values: Null = 0, Low = 1, Medium = 2 and High = 3. The set of details is detailed below. employee rules:
    - Rule 1: If (Q is Low) AND (SW is Low) Then ΔQ is Low - Rule 2: If (Q is Low) AND (SW is High) Then ΔQ is High - Rule 3: Yes (Q is Medium) AND (SW is Low) Then ΔQ is Null - Rule 4: Yes (Q is Medium) AND (SW is High) Then ΔQ is Medium - Rule 5: If (Q is High) AND (SW is Low) Then ΔQ is Null 35 -Rule 6: If (Q is High) AND (SW is High) Then ΔQ is Low
    This rule is intended, on the one hand, that the larger the frame size, the smaller the increase in Q and on the other hand, the greater the number of collisions and gaps per frame, the greater the increase in Q.
    Description of the CRD launch process:
    Since the QA frame adjustment commands require a higher bit transmission than the QR, it is beneficial for the system that the frame is adjusted in a small number of occasions, but that these are successful. In this invention a methodology is proposed in which the plot is adjusted at a single point during the course of the plot or at the end of the plot if it is determined invariable in the first instance. That is, the reader will launch the CRD after receiving the response of the tags in a certain slot, called check slot. The value of the check slot will vary depending on the size of the frame, adjusting to the most appropriate values to achieve a successful adjustment in a single check. If the CRD launched in the check slot determines that the frame size should not vary, the reader continues in the next slot until the end where the CRD will be launched again. On the other hand, if the variation is not zero, the reader communicates the new frame size to the tags and starts that new frame from the beginning. In this way, if the calculated size is not the right one, it can be cut at a suitable point that establishes a balance between the number of QA needed and the error that may exist in the choice of the frame size.
    Detailed description of an embodiment of the invention: Example of operation for a set of six tags
    In this section we describe the operation of the invention in the case of an example of identifying a set of six tags located within the range of the reader. In order for a passive tag to participate in the identification process, it must be within the range of the reader. Otherwise, the tag cannot be fed or receive commands from the reader.
    Below is the separate identification process in the 4 frames needed to identify the set of tags; accompanied by Figure 9, where the slot chosen randomly by each tag in each of the frames is shown:
     Frame 1: the reader sends the Qc command with the value of Q = 2. The six tags receive this value and randomly select a slot in the frame of L = 22 = 4 slots (see Figure 8). Upon receiving the response of the tags, the reader computes the value of the check slot. For this we define the value of the relative point in the frame (r) with a constant r = 9, and the 5 ℎ� = ⌈ / ⌉ = ⌈4 / 9⌉ = 1 is calculated. The reader, therefore, analyzes the responses received in the first slot of the first frame, collisions = 1, empty = 0 and launches the fuzzy controller to calculate the increase or decrease of the frame, ΔQ. The value of SW is 1 and ΔQ = CRD (1,2) = 3. The updated value of Q is Q 'therefore Q' = Q + ΔQ = 2 + 3 = 5. Since the value of Q has been modified , the reader ends the frame and begins frame 2 with the new size L = 25 = 32.
     Frame 2: the reader starts the second frame by resetting its size with the QA command and the value of Q = 5. In this frame, the check slot takes the value of ⌈32 / 9⌉ = 4. The reader advances in this second frame, finding slots 1,2 and 4 empty, and an identification in slot 3. Upon receiving the responses from slot 4, the reader launches the fuzzy controller again with the parameters: empty = 3 and collisions = 0 and the value of SW = 0.75. This results in an increase of ΔQ = CRD (0.75.5) = 3. Since the number of gaps is greater than the number of collisions for this second frame, the new value of Q is Q-ΔQ = 5-3 = 2. Again the value of Q has been modified, so the reader ends the current frame.
     Frame 3: the reader begins by adjusting the size of the frame by transmitting the QA command with Q = 2. In this frame the check slot = 1, as in the first one. As can be extracted from Figure 9, there are two successes in slots 1 and 3, a gap in slot 2 and a collision in slot
    4. Following the procedure, in slot 1 the fuzzy controller is executed with SW = 0. The increment obtained is ΔQ = CRD (0.2) = 0. That is, the value of Q is not affected in this check, so the reader advances in the plot by transmitting QRs until finishing it. After receiving the response of the tags in slot 4, the reader must check the frame size again by launching the fuzzy controller with SW =
    0.25. The increase again is null, ΔQ = CRD (0.25.2) = 0.
     Frame 4: the reader starts the fourth frame by transmitting QA with Q = 2. At the beginning of this frame there are still 3 tags to identify. Again the check slot corresponds to the first slot. After receiving the first satisfactory response, the fuzzy controller is used with SW = 0. The controller indicates that the frame remains invariant ΔQ = CRD (0.2) = 0, so the reader continues analyzing the rest of the slots in the frame transmitting QRs.
    As seen in Figure 9, in this frame we have three successes in slots 1,2 and 4 and a gap in slot 3. There are no collisions in this frame. When the reader finishes, since there have been no collisions, the identification process ends.
    As global results, to identify 6 tags the reader has needed 13 slots, of which 2 have been collisions and 5 have been empty.
    Describing sufficiently the nature of the present invention, as well as the way of putting it into practice, it is noted that, within its essentiality, it may be implemented in other embodiments that differ in detail from that indicated by way of example. , and which will also achieve the protection sought, provided that it does not alter, change or modify its fundamental principle.
    权利要求:
    Claims (4)
    [1]
    1. Anti-collision procedure for transponder identification in an RFID system characterized in that it dynamically adjusts the size of the frame in which these devices host their responses to avoid colliding between them, where this adjustment is made using a controller based on fuzzy rules (CRD) that uses the information obtained from the responses of the current frame received in the reader as input and comprises the following steps:
    a) The reader sets a plot size at its beginning and tags
    they choose a slot within said frame to transmit. b) At the end of each slot, the reader checks if it is necessary to launch the CRD. c) If the controller is launched and determines that the current size should
    change, the plot ends and a new one begins with a new size.
    d) If the controller is launched and determines that the size should not vary, the reader continues the current frame to the end, where the CRD will be launched again.
    e) In case of not launching the controller, the reader continues in the next slot again checking whether or not to launch it until the end of the frame, where it will be launched again.
    [2]
    2. Method according to claim 1, characterized in that the CRD will be launched after receiving the responses of the tags in a certain slot of the frame, whose value will vary depending on the size of the frame.
    [3]
    3. Method according to claim 2, characterized in that for the analysis of the responses received in the determined slot and launching the fuzzy controller to calculate the increase or decrease of the frame, the following is taken into account:
    a) The expense in slots (SW), which is calculated taking into account the number ofcollisions and empty slots that have occurred throughout the current plot.b) The current frame size (Q). The last calculated value of the frame
    which has been previously transmitted to tags.
    ΔQ = CRD (SW, Q)
    WhereΔQ is the increase or decrease of the plotCRD, controller based on fuzzy rules
    SW, is the expense in slots
    Q current frame size
    Being the size of the future plot Q ’= Q + ΔQ
    [4]
    4. Computer program characterized in that it comprises program code means adapted to perform the steps of the process according to any of claims 1 to 3, when said program is executed in
    10 a general purpose processor, a digital signal processor, an FPGA, an ASIC, a microprocessor, a microcontroller or any other form of programmable hardware.
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    CN111444733B|2020-03-18|2022-03-22|杭州电子科技大学|Method and system for adaptively adjusting value of receiving window|
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