KR20090049346A - Anti collision system and method for rfid tag - Google Patents

Abstract

The present invention relates to an RFID collision detection system and method for detecting a collision between a plurality of RFID tags that may occur in a radio frequency identification (RFID) system and restoring data lost due to the collision. By incorporating a binary tree technology to improve the disadvantages of each of the two technologies it can reduce the time required to recognize the RFID tag when the RFID tag collides.

Radio Frequency IDentification (RFID), RFID Tag, Collision, Anti-collision, ALOHA, Binary Tree

Description

Collision detection system and method of RFID tag {ANTI COLLISION SYSTEM AND METHOD FOR RFID TAG}

The present invention relates to a collision detection system and method of an RFID tag, and more particularly to a collision detection system and method of an RFID tag that can shorten the time required to recognize an RFID tag.

RFID (Radio Frequency IDentification) technology is referred to as "RFID" (RFID) technology, by attaching an RFID tag to a thing to wirelessly identify the information of the thing (identification), the surrounding information of the RFID tag (tag), that is, It is a contactless recognition technology that senses surrounding situation information of an object with an RFID tag. The RFID technology recognizes the information of the object and surrounding environment information from the RFID tag attached to the object, collects, stores, processes, and tracks the information of the object, thereby positioning, remotely processing / managing and exchanging information between the objects, It is possible to provide a variety of services. RFID technology is expected to lead innovation in security, safety and environmental management as well as distribution and goods management by replacing existing bar codes with network and intelligent product management.

In general, an RFID system may be configured to include an RFID tag embedded with information, an RFID reader having a function of reading and decrypting information embedded in the RFID tag, middleware and application service platform for operating them, and the like. The RFID system configured as described above may be used in conjunction with a wired or wireless communication network.

As described above, the RFID system is a recognition system for identifying information through radio signal exchange between an RFID tag and an RFID reader. That is, the RFID reader identifies the information embedded in the RFID tag through wireless communication with the RFID tag located in its area. However, a plurality of RFID tags may be located in an area of an RFID reader. In this case, information recognition from a plurality of RFID tags may be simultaneously performed. As described above, when information recognition from a plurality of RFID tags is simultaneously performed, a delay of a recognition time occurs when a bit of each tag has the same value is referred to as a "collision." Collision of the RFID tag lowers the recognition rate of the RFID tag by losing the data, and incurs power and resource waste due to the transmission of wrong information, the inability to transfer information due to the recognition failure, and the delay of the RFID tag recognition time.

Therefore, collision detection technology for detecting collision between RFID tags and restoring the loss of data according to them is one of the important research areas in RFID technology. The RFID technical standard proposes two protocols, Aloha (ALOHA) and Binary Search / Tree, as a protocol for mediating collision of RFID tags.

However, these protocols take a method of re-transmitting a query from the beginning by retransmitting a query when a collision is detected while the RFID reader recognizes the data of the RFID tag. This has the disadvantage that these protocols require a long time for the recognition of RFID tags. In order to solve this drawback, some advanced technologies such as slotted ALOHA and dynamic slotted ALOHA have been proposed, but these techniques have not been a fundamental solution.

Accordingly, an object of the present invention is to improve the recognition performance of the ALOHA-based collision prevention protocol used in the event of a collision of an RFID tag, thereby reducing the time required to recognize the RFID tag and reducing the carrier power required when the RFID tag is recognized. The present invention provides a collision detection system and method for saving RFID tags.

In one aspect of the present invention for achieving the above object, an RFID tag collision prevention device used to prevent a collision occurring in the identification process for a plurality of RFID tags located in the area of the RFID reader, Detects the collision caused by the radio unit performing radio signal exchange with the RFID tag and the RFID tags located within its area, calculates the collision rate accordingly, and compares the collision rate with the preset reference value. If the collision rate is lower than the reference value, collision prevention is performed on the RFID tags using an Aloha based Additive Links On-line Hawaii Area protocol, and if the collision rate is higher than the reference value, a binary based protocol is used. It may include a control unit for performing a collision avoidance for the RFID tags.

The controller may calculate the collision rate by comparing the collision bit number with the total number of bits.

The anti-collision apparatus of the RFID tag may further include a memory for displaying and storing a collision bit with respect to the data in which a collision occurs among data received from the tag when a binary protocol is applied.

In another aspect of the present invention for achieving the above object, the collision prevention system of the RFID tag for preventing the collision of the RFID tag generated when a plurality of RFID tags are located in the region of the same RFID reader, its own area If the collision rate is less than the reference value by calculating the collision rate due to RFID tags located in the inside, and comparing the collision rate with a predetermined reference value, collision prevention for the RFID tags is performed using an Aloha-based protocol. When the collision rate is greater than or equal to the reference value, an RFID reader for performing collision prevention on the RFID tags using a binary based protocol, and when the RFID reader transmits an identification signal according to the selected collision prevention protocol, In response to the identification signal may include an RFID tag for performing a wireless signal transmission and reception with the RFID reader. .

In another aspect of the present invention for achieving the above object, a collision prevention method of the RFID tag for preventing a collision occurring in the identification process for a plurality of RFID tags, RFID reader is present in the area of the RFID Calculating a collision rate for tags, comparing the calculated collision rate with a preset reference value, and if the collision rate is less than the reference value, selecting an Aloha-based program and the collision If the rate is greater than or equal to the reference value, the method may include selecting a binary based protocol and performing collision prevention for the RFID tags using the selected protocol.

As mentioned above, the present invention improves the performance of the ALOHA algorithm used in the collision of RFID tags. Through this, the present invention can shorten the RFID tag recognition time and stably maintain the carrier of the RFID tag, thereby saving the carrier power. Through this, the present invention can improve the quality of the RFID service and stably perform the information transmission of the RFID tag.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that detailed descriptions of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a diagram illustrating an example of an RFID environment to which the present invention can be applied.

As shown in FIG. 1, the RFID system may be configured to include at least one tag 100 and at least one reader 110-1 and 110-2. Of course, this is a simplified diagram to aid in understanding the RFID system and can be configured to include multiple readers.

Here, the tag 100 stores information about the object and is attached to the object to be identified. The readers 110-1 and 110-2 identify information about tags existing in their area. Among the information items of the tag 100 which can be identified by the readers 110-1 and 110-2, the time when the tag 100 enters the reader's area, and the tag existing in the reader's area is the corresponding reader. The time of departure within the area of, may include the unique information assigned to the tag existing in the area of the reader. The above-described information items are presented to aid the understanding of the present invention, which is not intended to limit the present invention, and various information items may be used for practicing the present invention as necessary. Each reader 110-1 and 110-2 has a transmitting function and a receiving function for identifying information of a tag and transmitting the identified information.

In FIG. 1, circles drawn by dotted lines around each of the leaders 110-1 and 110-2 indicate an interrogation area of the leader. Ideally, the area of an arbitrary leader will be drawn concentrically with the leader's position as the center point and with the radius of propagation distance from that leader. Of course, in reality, due to various factors such as terrain and radio wave interference, the actual leader area often takes a form different from the ideal area. The shape of the area of the leader is not a limitation of the present invention. Meanwhile, in the RFID system, collisions may occur between the plurality of tags because the plurality of tags exist in one reader (eg, 110-1) area.

In the present invention, in order to mediate collisions occurring between a plurality of tags existing in one reader area and to correctly identify information on each tag, collisions that are differentially performed according to the collision rate at the corresponding readers. Prevention algorithms are used. The collision avoidance algorithm used in the present invention is, in particular, an algorithm in which a binary algorithm is mixed with an Aloha algorithm. In the following, to help understand the present invention, a binary algorithm and an Aloha algorithm will be described first.

Binarytrees ensure that all tags are in sync with the reader and begin sending their serial numbers at the right time, and can pinpoint the exact bit of collision when the data in tags collide. The binary tree algorithm checks the collision from the MSB (Most Signification Bit) side and has a rule to reduce the search for the most significant bit of the collision. At this time, for the bit in which the collision has occurred, the bit that was "1" is converted to "0", and the bit that was "0" is converted to "1" and requested again. The process of recognizing a tag through the repetition request for such a collision bit is shown in FIG. 2.

2 illustrates an example of applying a binary algorithm, and illustrates a process of recognizing one tag by performing a repetition request for collision bits.

A transmission request signal for a tag having an identification number of 11111111 or less is transmitted from the reader to the tag through the downlink. Correspondingly, all tags having an identification number of 11111111 or lower, which receive a signal from the corresponding reader, transmit a signal through the uplink. 2, four tags, tag 1, tag 2, tag 3, and tag 4, satisfy the condition. That is, four tags transmit data at the same time, which causes data collision. The collision causes the reader to receive 1X1X001X data. The data received by the reader can be a processing time because the 2nd, 4th, and 8th bits collide with the bits of other tags. The data 1X1X001X in which collision has occurred means that at least one tag exists in the range of 10111111 or more and 11000000 or less.

Receiving the collision data 1X1X001X, the reader requests a retransmission by converting the second bit, which is the most significant bit of the collision, from "1" to "0". To this retransmission request, three tags, tag1, tag2, and tag3, that satisfy the request, respond. The reader can then receive data from tag 3 without conflicting data through the retransmission request for the second bit and the retransmission request for the third tag. That is, the reader receives the data from the tag by specifying the tag through the retransmission request of the repeated data without delay of data transmission due to the collision.

3 is a diagram illustrating a binary tree structure used in a data comparison procedure, and FIG. 4 is a diagram showing a query tree structure used in a data comparison procedure.

These tree structures are also used for specifying data through sequential comparisons.

Next, the algorithm of the Aloha protocol will be described.

In the case of the slotted ALOHA protocol, when the reader broadcasts tags about frame size and slot selection, each tag selects a slot to use in its frame. In this case, if only one tag transmits data in one slot, the data transmitted by the corresponding tag may be received by the reader and may be normally identified. However, when a plurality of tags transmit data in one slot, collisions occur between these tags. If a collision occurs between tags, the reader sends new information again, allowing the tag to select a slot.

FIG. 5 is a diagram illustrating an example of frame allocation when applying a slot Aloha protocol in which a frame size is fixed, and FIG. 6 is a diagram illustrating an example of frame allocation when applying a dynamic slot Aloha protocol in which a frame size is changed. Drawing.

When a plurality of tags transmit data in one slot, a collision occurs. When one tag transmits data in one slot, data transmitted by the tag is received and identified by the reader without collision.

As shown in FIG. 5 and FIG. 6, in the case of the slot Aloha protocol, the number of slots included in one frame is the same, but in the case of the dynamic slot Aloha protocol, the case of the slots included in one frame is variable. .

In the slot Aloha protocol, a fixed size frame is set to deliver the same size frame every time a collision occurs. In this case, the number of slots in one frame

However, the dynamic slot Aloha protocol changes the size of the frame every cycle, taking into account data collisions. The dynamic slot Aloha protocol increases the frame size when the number of slots in which collision occurs is greater than the reference number, and reduces the frame size when the number of empty slots increases. That is, the dynamic slot Aloha protocol increases the number of slots included in one frame if the number of slots in which collision occurs is greater than the reference number, and decreases the number of slots included in one frame when the number of empty slots increases.

Adjustment of the frame size in the dynamic slot Aloha protocol may be performed as follows.

)은

의 수학식으로 표현될 수 있다. 여기서, L은 프레임의 크기이다. 한 프레임에서의 전송확률(

)은

의 수학식으로 표현될 수 있다. 이들 수학식을 근거로 충돌을 반영한 최적의 프레임 크기를 유도하면,

의 수학식으로 표현될 수 있다. 이때, 지연시간 D가 최소일 때 프레임 크기는 최적의 크기가 된다.The size of the frame, i.e., the number of slots, required in each round may be calculated based on a collision occurrence rate and an uplink transmitted from each frame slot in the previous round. The process of calculating the frame size based on the collision occurrence rate in each slot is as follows. First, the delay time D = number of retransmissions * frame size for a tag to transmit its ID to the reader. The frame size is known as one round progresses. The probability that a tag successfully sends an ID during a slot (

)silver

It can be expressed by the following equation. Where L is the size of the frame. Transmission probability in one frame (

)silver

It can be expressed by the following equation. Based on these equations, we derive the optimal frame size that reflects the collision,

It can be expressed by the following equation. In this case, the frame size becomes an optimal size when the delay time D is minimum.

In the present invention, by mixing the Aloha protocol and binary protocol to solve the disadvantages of the two protocols to reduce the collision occurring when the tag recognition and propose a collision avoidance algorithm that can shorten the time required for the tag recognition.

The disadvantage of the Aloha method is that if a collision occurs between tags, the tag with the collision requires retransmission for every bit of data transmitted. That is, not only bits in which collision occurs, but also bits recognized normally are retransmitted. The present invention proposes an anti-collision algorithm in which the Aloha protocol and the binary protocol are mixed in order to reduce retransmission for normally recognized bits occurring in the Aloha protocol. The anti-collision protocol described below may be referred to as a hybrid framed slotted ALOHA anti-collision protocol (HFSA) in the sense that the Aloha protocol and the binary protocol are mixed.

The collision avoidance protocol according to the present invention is characterized by applying different algorithms according to the collision rate of the tag. The collision avoidance protocol according to the present invention calculates a collision rate of a tag and applies an Aloha method when the collision rate of the tag is less than a predetermined reference value, and applies a binary method when the collision rate of the tag is equal to or greater than a predetermined reference value. That is, the collision avoidance protocol according to the present invention, when the collision rate of the tag is less than the preset reference value, performs the retransmission of the data in which the collision occurred in units of slots, and if the collision rate of the tag is more than the predetermined reference value, the collision in the bit unit Perform retransmission of this occurred data. When performing retransmission in units of bits, only bits in which collision has occurred are retransmitted. The reference value for deciding whether to apply the Aloha method or the binary method may be determined in advance by experiment. Processes for performing the collision avoidance algorithm according to the present invention will be described with reference to FIG. 7.

7 is a flow chart illustrating the processes of the RFID anti-collision algorithm according to the present invention.

First, whether a tag collision occurs in the reader is identified, and the frame size is adjusted according to the identification result (step 700). After the frame is resized, a retransmission request (step 702) for a tag in which a collision occurs and a tag response corresponding to the retransmission request are made (step 704). Steps 700 to 704 are performed when the collision rate in the reader is less than the preset reference value. That is, when the collision rate in the reader is less than the preset reference value, the collision prevention algorithm by the dynamic slot Aloha method is applied. The collision rate can be calculated as the ratio of the total number of bits delivered to one slot and the number of collision bits.

In operation 706, the collision rate and the reference value are compared. The comparison of the collision rate and the reference value is performed to determine whether to apply the Aloha method or the binary method. If the collision rate is less than the reference value, steps 700 to 704 described above are repeatedly performed, and if the collision rate is greater than or equal to the reference value, steps 708 and below are performed. Steps 708 and below are steps when the binary method is applied. By applying the binary method, data retransmission is performed in bits rather than slot data retransmission.

In step 708, the calculation of the frame size by the dynamic slot Aloha method is stopped, and in step 710, data in which the collision occurs is stored in the memory. At the time of saving, the bit where a collision occurred is displayed and stored. Thereafter, the reader requests retransmission only for bits having a collision with reference to the contents stored in the memory (step 712), and the tag transmits only the requested bits in response to the request from the reader (step 714).

That is, when the collision avoidance algorithm according to the present invention is applied, the frame size is adjusted before the collision rate reaches the reference value, and retransmission is performed in units of slots, and when the collision rate becomes higher than the reference value, only the bit in which the collision occurs is retransmitted. .

8 illustrates an RFID collision identification process according to the present invention.

8 illustrates a case where the collision rate reaches the reference value in the frame n. A collision occurs in slot 3 of frame n and is identified as 101X0X1X. The data "101X0X1X" in which the collision occurred is stored in the memory. That is, the data in which the collision occurred is displayed in the memory where the bit in which the collision occurred is stored. Thereafter, the collision bits are sequentially retransmitted from the first collision bits on the MSB side of the stored data.

The anti-collision protocol according to the present invention described above may be performed by the anti-collision device of the RFID tag provided in the reader. The apparatus for preventing collision of an RFID tag according to the present invention is to detect a collision caused by a radio unit performing a radio signal exchange with an RFID tag, and RFID tags located within its area, and calculate a collision rate accordingly. If the collision rate is less than the reference value by comparing the collision rate with a predetermined reference value, collision prevention is performed on the RFID tags using an Aloha (Additive Links On-line Hawaii Area) based protocol. If the rate is greater than or equal to the reference value, a collision bit is displayed for a control unit that performs collision prevention for the RFID tags using a binary-based protocol, and data in which a collision occurs among data received from the tag when a binary protocol is applied. It can be configured to include a memory for storing.

The collision avoidance algorithm according to the present invention may be performed when data is transmitted and received between the reader and the tag.

1 is a diagram illustrating an example of an RFID environment to which the present invention can be applied.

2 illustrates a process of recognizing one tag by performing a repetition request for collision bits.

3 shows a binary tree structure used in a data comparison procedure.

4 shows a query tree structure used in a data comparison procedure.

5 shows an example of frame allocation when the slot Aloha protocol is applied.

6 shows an example of frame allocation according to the present invention.

7 is a flow chart illustrating the processes of RFID collision identification in accordance with the present invention.

8 illustrates an RFID collision identification process according to the present invention.

Claims (6)

In the RFID tag collision avoidance device used by the RFID reader to prevent a collision occurring in the identification process for a plurality of RFID tags located in its area, A radio unit for performing radio signal exchange with an RFID tag; Wow Detects collision caused by RFID tags located within its area and calculates the collision rate. If the collision rate is less than the reference value, Aloha (Additive Links On- a control unit that performs collision prevention for the RFID tags using a line Hawaii Area) based protocol, and performs collision prevention for the RFID tags using a binary based protocol when the collision rate is greater than or equal to the reference value. Anti-collision device of an RFID tag, characterized in that it comprises a. The method of claim 1, And the control unit calculates the collision rate by comparing the number of collision bits on a frame with the total number of bits of the frame. The method of claim 1, And a memory for displaying and storing a collision bit with respect to data having a collision among data received from the tag when the protocol of the binary method is applied. In the collision prevention system of the RFID tag for preventing the collision of the RFID tag generated when a plurality of RFID tags are located in the region of the same RFID reader, Calculate the collision rate due to RFID tags located within its area, and if the collision rate is less than the reference value by comparing the collision rate with a preset reference value, an Aloha-based protocol is used for the RFID tags. An RFID reader for performing collision avoidance and performing collision avoidance on the RFID tags using a binary based protocol if the collision rate is greater than or equal to the reference value; Wow And an RFID tag that transmits and receives a radio signal with the RFID reader in response to the identification signal when the RFID reader transmits an identification signal according to the selected collision prevention protocol. In the collision prevention method of an RFID tag for preventing a collision occurring in the identification process of a plurality of RFID tags, Calculating, by the RFID reader, collision rates for RFID tags existing within its area; Comparing the calculated collision rate with a preset reference value; Selecting an Aloha-based program if the collision rate is less than the reference value and selecting a binary based protocol if the collision rate is above the reference value; And And anti-collision for the RFID tags using the selected protocol. The method of claim 5, The collision rate calculation in the step of calculating the collision rate, the collision prevention method of the RFID tag, characterized in that by comparing the total number of bits of the collision bit on the frame.

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