KR20060115689A - Scanning-based tag identification method in rfid systems - Google Patents

Abstract

A scanning-based tag identification method in an RFID(SRadio Frequency IDentification) system is provided to reduce latency caused from bits not generating collision in an anti-collision protocol by performing scanning-based preprocessing before an identification process applying the anti-collision protocol. A reader requests the tags to transmit an ID(S101). The tags transmit the ID to the reader by responding to an ID transmission request of the reader(S103). The reader discriminates the bits having a different value from the same bits by scanning the received IDs(S105). The reader informs the tags of the collision bit and the non-collision bit discriminated by scanning through an informing signal(S107). The tags store a temporary ID formed by only the collision bits among the tag IDs by using the informing bit received from the reader(S109). An identification process is advanced by applying the stored temporary ID to the anti-collision protocol(S111).

Description

Scanning-based tag recognition method of RFID system {SCANNING-BASED TAG IDENTIFICATION METHOD IN RFID SYSTEMS}

1 is a configuration diagram of an RFID system capable of implementing a scanning-based tag recognition method according to the present invention;

2 is a flowchart illustrating a scanning-based tag recognition method according to the present invention;

3 and 4 are graphs showing the change in the number of bits and the number of query-responses required on average for recognition per tag of the binary tree walking algorithm to which the scanning-based tag recognition method according to the present invention is applied;

5 and 6 are graphs showing the change in the number of bits and the number of query-responses required on average for recognition per tag in the query tree algorithm to which the scanning-based tag recognition method according to the present invention is applied;

7 and 8 are graphs showing the change in the number of bits and the number of query-responses required on average for recognition per tag in the collision tracking algorithm applying the scanning-based tag recognition method according to the present invention;

9 is a graph illustrating the number of recognizable tags per unit time of a tree-based algorithm to which the scanning-based tag recognition method according to the present invention is applied.

The present invention relates to a scanning-based tag recognition method of a radio frequency identification (RFID) system. More particularly, the present invention relates to a scanning-based tag recognition method in which an RFID tag anti-collision protocol is applied in an RFID system. The present invention relates to a scanning-based tag recognition method of an RFID system having improved performance to recognize a tag at a high speed by performing a preprocessing process.

RFID is a field of automatic recognition, such as barcode, magnetic sensor, IC-CARD, etc., and is a state-of-the-art technology that wirelessly recognizes data stored in a microchip of a tag using microwave or long wave. RFID is being recognized and recognized as a technology to replace the bar codes currently used in logistics, distribution and financial services. In addition, the RFID does not require a separate process of scanning with the reader at the contact or line of sight required in the conventional method to obtain the information of the tag, and has the advantage of transmitting a large amount of data. However, RFID has problems such as reliability of recognized data and delay of standardization of technology, and research on anti-collision protocol is also needed to improve read rate and identification speed. Do.

Collision is largely due to Reader Collision, which causes multiple readers to query a tag at the same time, which makes the tag confusing to recognize the reader's query. There is a Tag Collision that makes a tag unrecognizable by a tag responding at the same time. In the case of a reader collision, the reader's capability is easily solved because the capability of the reader in the RFID system is sufficient to apply a collision prevention protocol in the existing MAC layer through communication between the readers and the readers. However, in the case of tag collisions, there are many restrictions on the available collision avoidance protocols as the tags currently in use or used for large-scale logistics are low-cost passive tags. The complexity of the calculation, the absence of a battery, and the increase in price according to the memory size are the limitations. Accordingly, the research on the RFID tag collision prevention protocol to solve the tag collision has emerged as a problem to be solved.

The RFID tag collision prevention protocol for resolving tag collisions is largely divided into a deterministic method and a probabilistic method.

The deterministic method is a tree based protocol that guarantees 100% recognition rate and consumes low power. It has a feature that the tag recognition process is predictable by constructing a binary tree using the bits of Tag ID represented by binary bits and then traversing the nodes of the tree to recognize the tags. In the tree-based protocol, tags are synchronized and transmitted simultaneously, and the reader differentiates the tree by recognizing it as a collision when '0' and '1' coexist in the received value. Deterministic methods can be broadly classified into memory based algorithms and memoryless based algorithms. Memory type algorithms include splitting tree algorithm and bit arbitration algorithm. In recognition process, implementation cost increases as reader's query and tag's response should be stored and managed in tag's memory. Bring it. The memoryless algorithm minimizes the cost burden on the tag because the response of the tag is determined not by the consideration of the past reader's query and the response of the tag and by the query of the current reader, but only by the query of the current reader. . Examples include the binary tree working algorithm, the query tree algorithm, and the collision tracking tree algorithm.

The stochastic method is a slotted aloha based protocol, which does not guarantee 100% recognition rate and reduces the probability of collision. To improve performance, the frame slotted aloha based anti-collision protocol was devised, which uses a frame consisting of N slots for communication between the reader and the tag. Select a slot to transmit tag information and load the ID. In this algorithm, when multiple tags are selected by one tag and transmitted with ID in one slot at the same time, it is regarded as a collision, and the rate of duplicate selection can be reduced by increasing the number of slots in the frame. However, increasing the number of slots in a frame increases the transmission time of the frame. Despite the conflict, it is difficult to accurately calculate the number of tags to be recognized. Therefore, the calculation of the appropriate number of slots and end points per frame is inevitably dependent on the probabilistic method. Therefore, Aloha-based anti-collision algorithm does not provide the completeness of tag recognition, and it is difficult to expect high efficiency in tag recognition due to retransmission of a slot in which collision occurs.

Probabilistic methods are classified into ID-slot algorithms and bit-slot algorithms. The ID-slot algorithm loads the ID of a tag in each slot and transmits it, whereas the bit-slot algorithm loads information consisting of specific bits for each tag in the slot and transmits the information to the reader, and responds sequentially according to the calling of the reader. That's the way. Representative algorithms of ID-slot algorithms include I-code algorithms and anti-collision algorithms that use bit-slot mechanisms as bit-slot algorithms.

Current proposals from EPC Global include the Binary Tree Working Algorithm in Class 0, the Query Tree Algorithm in Class 1, and the Class 1 Gen. Proposed in ISO / ICE 18000-6C of the International Standard Organization. Deterministic frame slotted aloha algorithm is adopted in Fig. 2, which adds the advantages of the bit-slot algorithm to the frame slot Aloha-based anti-collision algorithm.

However, conventional tag recognition methods employing the collision avoidance protocols as described above include non-collision bits included in the reader-tag query and response for tag ID recognition (for tree-based protocols), There is a problem in that performance is degraded by loading all IDs in the selected slot (for the slot Aloha protocol).

The present invention has been proposed to solve such a conventional problem, and is intended to reduce the time delay caused by bits that do not occur in the collision avoidance protocol.

The key is how quickly an RFID system can collect tag IDs. As a result of various studies, tree-based and Aloha-based anti-collision protocols show some performance, but in actual application, there is a time delay due to the processing time in the tag and reader (especially due to limited tag performance). Therefore, it is necessary to improve the performance of the collision avoidance protocol for faster tag recognition.

There are three ways to improve the performance of the collision avoidance protocol for fast tag recognition. The first is to improve the performance by adjusting the response of the tag. The second is to improve the performance by adjusting the query of the reader. The third is to reduce the burden of the tag ID.

In the present invention, in order to reduce the inherent burden of the tag ID, which is the third performance improvement method, a scanning-based preprocessing process is performed prior to the recognition process using the RFID tag anti-collision protocol in the RFID system, so The purpose of the present invention is to improve the performance of RFID tag anti-collision protocols by eliminating the time delay burden caused by the tag.

The scanning-based tag recognition method of the RFID system according to the present invention for realizing the above object comprises the steps of: (a) requesting the reader to transmit tags to the tags; In response to sending the ID to the reader, and (c) the reader scanning the IDs received from the tags to distinguish bits having the same value (collision bits) and bits having a different value (non-collision bits). And (d) the reader notifying the tags of the collision bits and the non-collision bits, which have been separated through scanning, and (e) the notification signals received after the tags have received the notification signals sent from the reader. Storing a temporary ID consisting of only collision bits in the tag ID using the tag ID; and (f) applying the stored temporary ID to the RFID tag collision prevention protocol. A and a step of proceeding.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

The scanning-based tag recognition method according to the present invention utilizes the same pattern partially in the ID of the tag, so that bits having the same pattern are included in the query and the response in the tag recognition process, resulting in deterioration in performance. Accordingly, this is eliminated in the recognition process to enable high speed tag recognition in the RFID system. To do this, in the scanning-based preprocessing process, the reader first checks the same pattern in the ID of the tag, and informs the tag, and the tag stores only the bits in which the collision occurred in the memory of the tag, and then uses it in the recognition process. Therefore, non-collision bits having the same pattern are no longer included in the tag response in the recognition process, and are not included in the reader's query constructed using the tag's response. Therefore, by using the scanning-based preprocessing process according to the present invention, it is possible to reduce the unnecessary burden on the recognition process, thereby enabling high speed tag recognition.

1 is a block diagram of an RFID system capable of implementing a scanning-based tag recognition method according to the present invention.

As illustrated in FIG. 1, an RFID system in which a tag recognition method according to the present invention is implemented includes a reader 10 and at least one tag 20.

RFID is a technology that reads tag information using radio waves after attaching a tag to an object. It can be applied to various fields such as logistics management, security, and distribution of things. By replacing the existing contact bar code with RF, information can be read at a faster speed than the bar code, and in addition to the advantage that the distance limitation of the operating environment is alleviated, a separate benefit of intelligence of the object can be obtained.

In a ubiquitous computing environment, a number of tags 20 belong to one reader 10, and information from multiple tags 20 inevitably collides due to its concurrency and density. Therefore, when there are several tags 20 within the reading range of one reader 10, the several tags 20 respond at the same time by request of the reader 10. At this time, the signals of the various tags 20 interfere with each other to cause a collision.

There is a need for a method of resolving the interference between the response signals of the tags 20 so as to recognize the responses of each tag 20 without collision. This is a collision avoidance protocol (or an algorithm).

2 is a flowchart illustrating a scanning-based tag recognition method according to the present invention.

The tag recognition method proposed in the present invention undergoes a preprocessing process including a Request-Scanning-Informing (RSI) step.

A process of recognizing a tag through the implementation of another scanning-based tag recognition method will now be described with reference to FIGS. 1 and 2.

First step (S101): Request

The reader 10 requests the plurality of tags 20 to transmit all of their IDs.

Second Step (S103): Response

The tags 20 transmit the ID to the reader 10 in synchronization with the ID transmission request of the reader 10.

Third Step (S105): Scanning

The reader 10 scans the IDs received from the multiple tags 20 to distinguish bits with the same value (collision bits) and bits with different values (non-collision bits).

Fourth Step (S107): Informing

The reader 10 informs the tags 20 of the collision bits and the non-collision bits which are separated through the scanning.

In detail, the reader 10 transmits an informing sequence to distinguish the collision bits from the non-collision bits to the tags 20. For example, the notification signal is composed of '0' and '1', the collision bit is represented by '0' and the non-collision bit is represented by '1'. The reader 10 transmits a notification signal of a tag ID length consisting of '0' and '1' to the tags 20 so that the tags 20 may know the location of the bit where the collision occurs on the ID.

5th Step (S109): Save

After receiving the notification signal transmitted from the reader 10, the tags 20 store the temporary ID including only the collision bits in the tag ID in the memory (not shown) by using the received notification signal. Use it as ID in the process.

Sixth Step (S111): Identification

The recognition process is performed by applying the temporary ID stored in the memory of the tags 20 to the RFID tag collision prevention protocol.

Seventh Step (S113): Restoration

The reader 10 reconstructs the ID by applying the values of the non-collision bits obtained in the scanning process and the value of each tag ID of the collision bits obtained in the recognition process to the location information about the collision-non-collision obtained through the scanning process. Do this.

As described above, the reader 10 recognizes all the tags 20 through the preprocessing process of steps S101 to S109, and reduces the burden of non-collision bits in the RFID tag collision prevention protocol, thereby indicating an indication of a time delay in the recognition process. The tree depth of the tree-based protocol and the slot size of the slot Aloha-based protocol can be reduced. Therefore, the scanning-based preprocessing process according to the present invention enables RFID tag anti-collision protocols to enable high speed tag recognition.

The performance of the tag recognition method including the scanning-based preprocessing procedure proposed in the present invention exists between the best case and the worst case. The optimal case here is when n collisions occur in a k-bit tag ID and 2 ⁿ tags exist in the reader's recognition area. For example, if there is an RFID system with a slot-based collision prevention protocol, h is the average number of query-response required to recognize a tag. ^The anti-collision protocol with the scanning-based preprocessing process requires a total of (2xk + 1) + n × h × 2 ⁿ bits, whereas ⁿ bits are required. It can be seen. On the other hand, the worst case is when a collision occurs randomly and happens to the entire tag ID regardless of the number of tags in the reader's recognition area. In this case, the anti-collision protocol incorporating a scanning-based preprocessing process requires a total of (2 × k + 1) + k × h × 2 ⁿ bits for tag recognition, resulting in performance degradation as much as the scanning burden.

The tag recognition method of the present invention including the scanning-based preprocessing process can be efficiently used in supply chain management of logistics distribution. Class 1 Gen. EPC Global's proposal to ISO / ICE 18000-6C of the International standard organization. According to 2, the ID of the tag includes 8 bits of version information, 28 bits of EPC manager information, 24 bits of object number, and 36 bits of serial number. It consists of 96 bits in total. In this case, if the product is made at the factory and packed by item, only the serial number is different. If a company makes the product in a short time and loads it on a container, it is only the item number and the serial number are different. Therefore, the tag IDs attached to the commodity will have a positive effect on the recognition performance of the scanning based preprocessing method as the collision partially occurs in the supply chain.

3 and 4 illustrate examples of changing the number of bits and the number of query-responses required on an average for recognition per tag of a binary tree walking algorithm to which a scanning-based preprocessing process is applied to help understand the present invention.

5 and 6 illustrate examples of changing the number of bits and the number of query-responses required on average for recognition per tag of a query tree algorithm to which a scanning-based preprocessing process is applied to help understand the present invention.

7 and 8 illustrate examples of changes in the number of bits and the number of query-responses required on an average for recognition per tag of a collision tracking algorithm to which a scanning-based preprocessing process is applied to help understand the present invention.

In FIGS. 3 to 8, 'BTWA' represents a binary tree walking algorithm, 'QTA' represents a query tree algorithm, 'CTTA' represents a collision tracking algorithm, and each preceding 'S' represents a scanning base according to the present invention. '36' represents the recognition process for products with different serial numbers only, and '60' represents the recognition process for products with different item numbers and serial numbers.

As shown in FIGS. 3 to 8, tree-based RFID tag anti-collision protocols using a scanning-based preprocessing process are generally used in terms of the number of bits required for recognition per tag and the number of query-response responses in comparison with the case without applying the scanning-based preprocessing process. It can be confirmed that this has an advantage. Here, the total number of bits required for the recognition process can be obtained as 'the average number of _bits required for recognition per tag N _bits × number of _tags N _tags '. Since N _tags cannot be adjusted, the total number of _bits required is determined by N _bits . It can be said that it is determined. In addition, N _bits change according to the tree depth and the number of bits of the tag ID. Therefore, since the non-collision bits can be removed through the scanning-based preprocessing process, the recognition process can be processed by reducing the tree depth and the number of bits of the tag ID, thereby improving performance.

In addition, slot-aloha-based RFID tag anti-collision protocols can also be applied to scanning-based preprocessing, and in tree-based RFID tag anti-collision protocols in terms of the number of bits required for recognition per tag. It can be seen deductively that a similar effect as in the case can be obtained. In the case of slot-based collision avoidance protocols, only the number of tags is relative to the number of query-responses (number of slots) that are required for recognition per tag on an average basis. ), The total number of bits required for the recognition process can be calculated as 'tag ID bits IDN _bits × number of questions and answers required for recognition per tag N _ITERATION × number of _tags N _tags ', where N _ITERATION and N _{Since the tags change} according to the number of tags and cannot be adjusted, the total number of _bits required is determined by IDN _bits . Therefore, since the non-collision bits can be removed in the recognition process through the scanning-based preprocessing process, the slot size according to the number of tag ID bits is reduced, resulting in improved performance.

Therefore, if the scanning-based preprocessing process according to the present invention is applied to the RFID tag collision prevention protocol, the time required for tag recognition can be reduced.

FIG. 9 illustrates the number of recognizable tags per second for tree-based algorithms applying a scanning-based preprocessing process.

It has been described so far limited to one embodiment of the present invention, it is obvious that the technology of the present invention can be easily modified by those skilled in the art. Such modified embodiments should be construed as naturally included in the technical spirit described in the claims of the present invention.

As described above, the present invention can develop a tag collision prevention protocol in an RFID system in a manner that enables faster tag recognition. The scanning-based preprocessing process according to the present invention is applicable to all RFID tag anti-collision protocols, thereby improving the performance of RFID tag anti-collision protocols by eliminating the time delay burden caused by non-collision bits. By improving the performance to recognize it as a system, it is possible to operate the RFID system quickly and efficiently.

Claims (4)

A tag recognition method of an RFID system including a reader and a plurality of tags, (a) the reader requesting the tags to send IDs; (b) the tags transmitting the ID to the reader in response to a request for transmitting the ID of the reader; (c) the reader scanning the IDs received from the tags to distinguish bits having the same value (collision bits) and bits having a different value (non-collision bits); (d) the reader notifying the tags of the collision bit and the non-collision bit separated through the scanning through a notification signal; (e) storing a temporary ID consisting of only the collision bits in a tag ID by using the notification signal received after the tags receive the notification signal sent from the reader; (f) performing the recognition process by applying the stored temporary ID to the RFID tag collision prevention protocol Scanning-based tag recognition method of the RFID system comprising a. The method of claim 1, The tag recognition method, (g) ID recovery by applying the value of the non-collision bits obtained through the scanning and the value of each tag ID of the collision bits obtained in the recognition process to the position information about the collision-non-collision obtained by the reader through the scanning. Steps to perform Scanning-based tag recognition method of the RFID system further comprising. The method according to claim 1 or 2, In step (d), the reader configures the notification signals as '0' and '1' and transmits them to the tags. Scanning-based tag recognition method in RFID system. The method of claim 3, wherein In step (d), the reader transmits the notification signal of the tag ID length consisting of '0' and '1' to the tags, so that the tags know the location of the bit where the collision occurs on the ID. Scanning-based tag recognition method in RFID system.

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