KR100776532B1 - Method for identifying rf tags in a radio frequency identification system by advanced query tree based anti-collision algorithm - Google Patents

Abstract

A method for identifying an RF tag in an RFID system by using an advanced query tree based anti-collision algorithm is provided to solve problems related to production cost, weight and power consumption of the RF tag caused by other special hardware and software which can sense and process a transmission stop instruction of a reader while receiving a prefix B from each RF tag and transmitting ID matched with the prefix B bit by bit when there occurs a collision. A method for identifying an RF tag in an RFID system by using an advanced query tree based anti-collision algorithm comprises the following several steps. A reader queries a prefix B composed of binary codes with k bits to all the RF tags which embed ID composed of binary codes with n bits(S10). The reader receives k+1 bit to the final bit among the n bits from all the RF tag and detects whether there occurs a collision(S20,S30). If only one RF tag makes response, the reader identifies the RF tag composed of the k bit binary codes of the prefix B and the binary codes of the k+1-th bit to the final bit among the n bits(S40). If plural RF tags make response and there occur collisions, the reader identifies the RF tag by repeating a step of querying a prefix B' and a prefix B'' to all the RF tags wherein the prefix B' is made by adding bits of the k+1-th bit to the c-1-th bit and one bit with a value of zero to the binary codes of the prefix B, the prefix B'' is made by adding one bit with a value of one to the binary codes of the prefix B and the collision occurs at the c-th bit(S50).

Description

RF Tag Identification Method using Enhanced Query Tree-based Collision Avoidance Algorithm of the Radio Frequency Identification System

1 is a tree structure illustrating an RF tag identification method using a tree walking algorithm of a conventional radio frequency identification system.

2 is a tree structure illustrating an RF tag identification method using a query tree algorithm of a conventional radio frequency identification system.

3 is a flowchart illustrating an RF tag identification method using an advanced query tree based anti-collision algorithm of a radio wave identification system according to the present invention.

4 is a tree structure illustrating an RF tag identification method using an advanced query tree based anti-collision algorithm of a radio wave identification system according to the present invention.

5 is a table showing the difference between the RF tag identification method and the conventional RF tag identification method using the advanced query tree-based anti-collision algorithm of the radio wave identification system according to the present invention.

6 is a graph comparing the number of questions / responses between the RF tag identification method and the conventional RF tag identification methods using the improved query tree based anti-collision algorithm of the radio wave identification system according to the present invention.

7 is a graph comparing the number of questions / responses between an RF tag identification method using an improved query tree-based anti-collision algorithm and an RF tag identification method using a conventional query tree algorithm according to the present invention.

8 is a graph comparing the average number of questions / responses per tag between the RF tag identification method and the conventional RF tag identification methods using the improved query tree based collision avoidance algorithm of the radio frequency identification system according to the present invention.

9 is a graph comparing the total number of query / response bits between readers and tags with the RF tag identification method and the conventional RF tag identification methods using the advanced query tree based anti-collision algorithm of the radio frequency identification system according to the present invention. .

10 is a table showing the results of the performance experiment between the RF tag identification method and the conventional RF tag identification method using an advanced query tree-based anti-collision algorithm of the radio wave identification system according to the present invention.

The present invention relates to a radio frequency identification (RFID) system, and more particularly to an RF using an advanced query tree based anti-collision algorithm (AQT) of the radio identification system. Tag identification method.

The radio wave identification system is composed of a plurality of RF tags incorporating unique information (ID) for object identification and a reader having the RF tag identification function, and unique information of the RF tag attached to the object by using the RF signal. A contactless object identification device that identifies an object to which the corresponding RF tag is attached by reading an ID.

The radio frequency identification system is distinguished from a plurality of RF tag identification methods according to the software installed in the reader. Typically, there is an RF tag identification method using a tree-based algorithm that traverses a binary tree and identifies all RF tags. The base algorithms include a tree walking (TW) algorithm that traverses a binary tree in a bit-by-bit manner and identifies RF tags, and an RF tag that traverses a binary tree in a bit-by-variable bit manner. Query Tree (QT) algorithms and Improved Query Tree (IQT) algorithms that traverse binary trees in a variable bit-by-variable bit fashion and identify RF tags.

The RF tag identification method using the tree walking algorithm of the radio wave identification system includes a prefix B (B = B) in which a reader is a binary code of d bits for a plurality of RF tags in which unique information (ID) of n bits of binary code is embedded. When b ₁ b ₂ ,…, b _d ) is queried for all RF tags, each RF tag compares its own information (ID) and prefix and sends the d + 1th bit of the n bits to the reader when a match is made. do. Here, the initial prefix B means the prefix of an empty string having no binary code value.

In this case, when all the RF tags transmit '0' or '1' to the reader, the reader determines that a collision has not occurred, and thus the new prefix B _{d +1} (B _d) having a binary code of d + 1 bit. ₊₁ = b ₁ b ₂ , ..., b _d b _{d +1} ) is repeated to query all RF tags again to identify the RF tag bit by bit. On the other hand, when each RF tag transmits' 0 'and' 1 'to the reader at the same time, the reader determines that a collision has occurred and sends a new prefix B' of B || 0 and B || 1 to all RF. Repeat querying the tag again to identify the RF tag bit by bit.

Here, the prefix B 'of B || 0 is the prefix' b ₁ b ₂ ,..., With _one bit representing the binary code 0 added to the previous prefix B. a, b _d 0 'and, in the B || 1 prefix B "is added to the dog one bit representing the binary code 1 prior prefixes prefix _{B' b 1 b 2, ...,} b d 1 '.

For example, FIG. 1 is a tree structure illustrating six RF tag identification methods incorporating 8-bit unique information (ID) using the tree walking algorithm of the radio wave identification system.

In FIG. 1, six RF tags each include unique information (ID) of '0001 0001', '0001 0101', '0011 0101', '1000 1010', '1100 1011', and '1101 0010'. The number of edges means the prefix.

Referring to FIG. 1, it can be seen that a total of five collisions occurred in identifying six RF tags in which 8 bits of unique information (ID) are embedded, and all 37 questions / answers were provided. It can be seen that the same number of bits of unique information (ID) of each RF tag.

RF tag identification method using a tree walking algorithm that identifies a plurality of RF tags in units of bits as described above, even if there is only one RF tag in the detection area of the reader, query / request to the last bit of the unique information (ID) of the RF tag. As the number of RF tags existing in the detection area of the reader must be performed, the collision between RF tags occurs more frequently. Therefore, RF tag identification time is required and performance of the radio frequency identification system is degraded.

The RF tag identification method using the query tree algorithm of the radio wave identification system includes a prefix B (B = B) in which the reader is a binary code of d bits for a plurality of RF tags in which unique information (ID) of n bits of binary code is embedded. When b ₁ b ₂ ,…, b _d ) are queried for all RF tags, each RF tag compares its own information (ID) with its prefix and, if a match is made, from the d + 1st bit of the n bits to the last n bits. Is sent to the reader. Here, the initial prefix B means the prefix of an empty string having no binary code value.

In this case, when only one RF tag responds, the reader identifies an RF tag having a d-bit binary code of prefix B and a binary code from the d + 1 th bit to the last n bit of the n bits.

In addition, since a collision occurs when a plurality of RF tags respond simultaneously, the reader stores a new prefix B 'of B || 0 and B || 1 in an internal queue, and retrieves a new prefix B' from the internal queue. The RF tag is identified by repeating the query with the RF tag until the internal queue is empty.

Here, the prefix B 'of B || 0 is the prefix' b ₁ b ₂ ,..., With _one bit representing the binary code 0 added to the previous prefix B. a, b _d 0 'and, in the B || 1 prefix B "is added to the dog one bit representing the binary code 1 prior prefixes prefix _{B' b 1 b 2, ...,} b d 1 '.

On the other hand, if no response occurs while waiting for a predetermined time after transmitting the prefix, the reader determines that there is no RF tag starting with the prefix.

For example, FIG. 2 is a tree structure illustrating six RF tag identification methods incorporating 8-bit unique information (ID) using the query tree algorithm of the radio wave identification system.

In FIG. 2, six RF tags each include unique information (ID) of '0001 0001', '0001 0101', '0011 0101', '1000 1010', '1100 1011', and '1101 0010'. The number of edges means the prefix.

Referring to FIG. 2, it can be seen that a total of nine collisions occurred in identifying six RF tags incorporating 8-bit unique information (ID), and all 18 questions / answers were reported. The depth of the tree is 6, which is smaller than when using the tree walking algorithm.

As described above, the RF tag identification method using the query tree algorithm that identifies a plurality of RF tags in variable bit units is often non-responsive to the reader's query, although the number of questions / responses is reduced than that of the tree walking algorithm. As the number of RF tags occurring and present in the detection area of the reader increases, collisions between RF tags frequently occur frequently, resulting in deterioration of the performance of the radio frequency identification system.

The RF tag identification method using the improved query tree algorithm of the radio wave identification system includes a prefix B having a reader having a d-bit binary code for a plurality of RF tags in which unique information (ID) of n-bit binary code is embedded. When B = b ₁ b ₂ ,…, b _d ) is queried for all RF tags, each RF tag compares its unique information (ID) with its prefix, and if a match is found, the last n from the d + 1th of n bits Send up to bits sequentially to the reader. Here, the initial prefix B means the prefix of an empty string having no binary code value.

At this time, the reader receives the unique information (ID) sequentially transmitted by each RF tag and at the same time checks whether a received bit collision occurs.

If '0' and '1' are received at the same time, a collision occurs. Therefore, the reader sends a 'stop command' to each RF tag to stop transmitting the remaining bits.

The RF tag receiving the 'stop transmission command' immediately stops transmitting the remaining bits and prepares to receive a new prefix B from the reader.

Accordingly, the reader generates a new prefix B '(B) generated by adding a binary code from the previous prefix B of the d bit to the k-1 th bit, which is the bit before the k th bit where the collision occurred in the d + 1 th of n bits. '= b ₁ b ₂ , ..., b _d b _{d +1} , ..., b _{k -1} ) is repeated to query all RF tags again to identify the RF tag.

As described above, the RF tag identification method using the improved query tree algorithm for identifying a plurality of RF tags in a variable bit unit has its own unique information (ID) that matches the prefix B and receives the prefix B when each collision occurs. ) And the additional hardware and software that detects and processes the 'stop transmission command' of the reader during the bit by bit transmission are added, thereby increasing the production cost of the RF tag, There is a disadvantage that makes it difficult to lower the power.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide a reader with a k-bit binary code for a plurality of RF tags embedded with unique information (ID) of n-bit binary code. After querying all RF tags for prefix B (B = b ₁ b ₂ ,…, b _k ), check for collision by receiving all k + 1th bits of the n bits from the n bits to the last n bits from each RF tag. Prefix B with binary code 0 added to the binary code from k + 1th of the n bits to the c-1th bit, the bit before the cth bit where the collision occurred Prefix B "(B" = b ₁ b _{2 with} B '(B' = b ₁ b ₂ , ..., b _k b _{k +1} , ..., b _{c -1} 0) plus one bit representing binary code 1 _{, ..., b k b k +1} , ..., b c -1 1) to repeat the re-query to all the RF tag of the improved radio frequency identification system to identify the RF tags Using a tree-based re-anti-collision algorithm (AQT) to provide an RF tag identification method.

In order to achieve the object of the present invention as described above, RF tag identification method using the advanced query tree-based anti-collision algorithm (AQT) of the radio frequency identification system according to the present invention, the unique information (ID) of n-bit binary code A first step of interrogating a plurality of RF tags having a prefix to all RF tags by prefix B (B = b ₁ b ₂ ,..., B _k ) of k-bit binary codes; A second step of checking whether there is a collision by receiving all k + 1th bits to the last n bits of n bits from each RF tag; As a result of the collision check, if only one RF tag responds, the reader ends the k-bit binary code of prefix B (B = b ₁ b ₂ , ..., b _k ) and the k + 1th bit of the n bits. a third step of identifying an RF tag of up to n bits in binary code; And c-1, a bit before c th bit where the collision occurred at k + 1th of the n bits in the previous prefix B of k bits when the collision occurred as a result of the collision check result. Prefix B '(B' = b ₁ b ₂ , ..., b _k b _{k +1} , ..., b _{c -1} 0) with one bit representing binary code 0 added to the binary code up to the first bit and binary code 1 Repeat querying all RF tags with the prefix B "(B" = b ₁ b ₂ , ..., b _k b _{k +1} , ..., b _{c -1} 1) with one bit indicating A fourth process of identifying; characterized in that consisting of.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail.

3 is a flowchart illustrating an RF tag identification method using an advanced query tree based anti-collision algorithm of a radio wave identification system according to the present invention.

Referring to FIG. 3, the reader of the radio frequency identification system initially has a prefix B (B = b ₁ b) of k-bit binary code for a plurality of RF tags in which unique information (ID) of n-bit binary code is embedded. ₂ , ..., b _k ) is queried to all RF tags (S10). Here, the initial prefix B means the prefix of an empty string having no binary code value.

Accordingly, when each RF tag compares its own information (ID) with a prefix and transmits all k + 1th bits to the last n bits of the n bits to the reader, when the matching is performed, the reader from each RF tag It receives all k bits from the k + 1th bit to the last n bits of the n bits and checks for collision (S20, S30).

If only one RF tag responds as a result of the collision check, the reader ends the k-bit binary code of the prefix B (B = b ₁ b ₂ , ..., b _k ) and the k + 1th bit of the n bits. An RF tag of up to n bits in binary code is identified (S40).

As a result of collision checking, when a plurality of RF tags simultaneously respond and a collision occurs, the reader c-th bit, which is a bit before the c-th bit where a collision occurred in k + 1th of the n bits, in the previous prefix B of k bits. New prefix B '(B' = b ₁ b ₂ , ..., b _k b _{k +1} , ..., b _{c -1} 0) plus one bit representing binary code 0 to binary code up to bit and binary code 1 Repeatingly querying all RF tags for the new prefix B "(B" = b ₁ b ₂ , ..., b _k b _{k +1} , ..., b _{c -1} 1) with one additional bit indicating Identify (S50).

For example, FIG. 4 is a tree structure illustrating an RF tag identification method using an advanced query tree based anti-collision algorithm of a radio wave identification system according to the present invention.

In FIG. 4, six RF tags each include unique information (ID) of '0001 0001', '0001 0101', '0011 0101', '1000 1010', '1100 1011', and '1101 0010'. The number of edges means the prefix.

Referring to FIG. 4, a total of five collisions occurred in identifying six RF tags in which 8 bits of unique information (ID) are embedded, and it can be seen that all 10 queries / responses were made, and no response did not occur. It can be seen that the tree has a depth of 3, which makes the tree structure simpler than using a conventional tree walking algorithm or a query tree algorithm.

For reference, the difference between the RF tag identification method and the conventional RF tag identification method using the improved query tree-based anti-collision algorithm of the radio wave identification system according to the present invention is shown in FIG.

Referring to FIG. 5, in the radio frequency identification system using the tree walking algorithm, the query tree algorithm, the improved query tree algorithm, and the improved query tree based anti-collision algorithm according to the present invention, the RF tag is transmitted from the reader. There must be a matching circuit for comparing the prefix value and its unique information (ID).

In addition, in the other three methods except for the query tree algorithm, the non-responsive RF tag does not exist, but the non-responsive RF tag exists in the query tree, which causes the reader to wait for a predetermined time. This may affect the RF tag identification time.

The identification time takes much time in the tree walking algorithm, and the query tree algorithm is faster than the tree walking algorithm, but slower than the improved query tree algorithm and the improved query tree based anti-collision algorithm according to the present invention.

The advanced query tree algorithm requires additional hardware and software to handle the collision in the event of an RF tag. This not only increases the cost of producing the RF tag, but also increases the overall overhead for RF tag identification because additional instructions are required.

On the other hand, in the improved query tree based anti-collision algorithm according to the present invention, since collision identification is performed in the reader, all the RF tags can be identified more quickly and faster than the query tree algorithm without any additional functions.

In addition, the result of comparing and evaluating the performance of the radio frequency identification system to which the RF tag identification method using the improved query tree based anti-collision algorithm (AQT) according to the present invention is compared with the radio frequency identification system using the tree working algorithm and the query tree algorithm is described. 6 to 10.

In the performance evaluation, a simulation program was written in C ++ to compare the number of query / response, collision, and transmission bits for the tree walking algorithm, the query tree algorithm, and the improved query tree based collision prevention algorithm according to the present invention. The tag's unique information (ID) was 96 bits, which is the EPC Global standard, and the number of RF tags was 2, 4, 16, 64, 128, 256, 512, 1024, and 2048. The result is the average of the results of five replicates.

6 is a graph comparing the number of questions / responses between the RF tag identification method and the conventional RF tag identification methods using the advanced query tree based collision avoidance algorithm of the radio frequency identification system according to the present invention. Compared to the tree algorithm or the improved query tree based anti-collision algorithm according to the present invention, it can be seen that as the number of RF tags increases, the number of questions / responses increases with the geometrical order.

7 is a graph comparing the number of questions / responses between an RF tag identification method using an improved query tree-based collision avoidance algorithm and an RF tag identification method using a conventional query tree algorithm according to the present invention. In all cases, the number of queries / responses of the improved query tree-based anti-collision algorithm according to the present invention is smaller than the number of queries / responses of the existing query tree algorithm, and the experimental results show an improvement of approximately 28.9%. Can be.

8 is a graph comparing an average number of queries / responses per tag between an RF tag identification method and a conventional RF tag identification method using an advanced query tree based anti-collision algorithm of the radio frequency identification system according to the present invention. Is an average of 122 times, a query tree algorithm is 3 times, and the improved query tree based anti-collision algorithm according to the present invention is also excellent in an average number of queries / responses per RF tag.

9 is a graph comparing the total number of query / response bits between readers and tags with the RF tag identification method and the conventional RF tag identification methods using the advanced query tree based anti-collision algorithm of the radio frequency identification system according to the present invention. As can be seen, the tree walking algorithm is charged a lot of transmission costs. As a result of the experiment, the ratio of the number of query bits and the number of response bits for each algorithm is 987.4% and the rate of response bits is 1.6% for the tree walking algorithm. The query bit rate is increased because the depth of the tree is determined by the length of the ID bits of the RF tag. For the query tree algorithm, the average query bit rate is 1.6% and the response bit rate is 98.4%. This is because in the case of the query tree algorithm, since the prefix is increased by one bit, the ratio of the number of response bits of the RF tags is higher than that of the number of query bits. In addition, in the case of the query tree algorithm, non-response occurs above all, resulting in a waiting time and a long tag discrimination time.

In the improved query tree based anti-collision algorithm according to the present invention, the average query bit rate is 1.2% and the average response bit rate is 98.2%.

FIG. 10 shows the results of a performance experiment between the RF tag identification method and the conventional RF tag identification methods using the enhanced query tree based collision avoidance algorithm of the radio frequency identification system according to the present invention. As a table distinguished by the number and the number of non-responses, it can be seen that the tree walking algorithm has much lower performance than the query tree algorithm and the improved query tree based anti-collision algorithm according to the present invention. Although there is not much difference between the query tree algorithm and the improved query tree based anti-collision algorithm according to the present invention, it can be seen that the improved query tree based anti-collision algorithm according to the present invention shows good performance in most evaluation items.

RF tag identification method using the advanced query tree-based anti-collision algorithm (AQT) of the radio wave identification system according to the present invention described above is not limited to the above-described embodiment, the gist of the present invention claimed in the following claims Without departing from the scope of the present invention to those of ordinary skill in the art to the extent that various modifications can be made to the technical spirit.

RF tag identification method using the advanced query tree-based collision avoidance algorithm (AQT) of the radio frequency identification system according to the present invention as described above, RF using the existing tree walking algorithm, query tree algorithm, improved query tree algorithm Compared with the tag identification method, collisions can be avoided and collision positions can be detected to detect all RF tags existing in the detection area of the reader faster than before.

Claims (1)

For many RF tags that contain unique information (ID) in n-bit binary code, the reader attaches the prefix B (B = b ₁ b ₂ ,…, b _k ) in k-bit binary code to all RF tags. A first process of querying; A second step of checking whether there is a collision by receiving all k + 1th bits to the last n bits of n bits from each RF tag; As a result of the collision check, if only one RF tag responds, the reader ends the k-bit binary code of prefix B (B = b ₁ b ₂ , ..., b _k ) and the k + 1th bit of the n bits. a third step of identifying an RF tag of up to n bits in binary code; And As a result of collision checking, when a plurality of RF tags simultaneously respond and a collision occurs, the reader c-th bit, which is a bit before the c-th bit where the collision occurred in k + 1th of the n bits, in the previous prefix B of k bits. Binary code 1 with the prefix B '(B' = b ₁ b ₂ , ..., b _k b _{k +1} , ..., b _{c -1} 0) with one bit representing binary code 0 added to the binary code up to the bit The RF tag is identified by repeating querying all RF tags with the prefix B "(B" = b ₁ b ₂ , ..., b _k b _{k +1} , ..., b _{c -1} 1) with one additional indicating bit. A fourth process of doing; RF tag identification method using an advanced query tree-based anti-collision algorithm (AQT) of the radio frequency identification system, characterized in that consisting of.

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