KR100860048B1 - A method of anti-collision in multiple rfid using capture phenomena - Google Patents

Abstract

A method for anti-collision in a multiple RFID(Radio Frequency Identification) using capture is provided to group tags according to a size of a received signal corresponding to a reference signal transmitted from a reader, and induce only groups where capture can be generated well to participate in completion, thereby improving recognition performance. A reader transmits a beacon signal to all tags within a recognition region, and groups tags according to reception strength of the tags(S210). A group pair which will participate in competition of a recognition process so as to generate capture is selected(S220). Tag numbers are identified based on a group having a small tag number by comparing tag numbers according to the selected group pairs(S230). Tags by selected group pairs are recognized through the reader(S240). After that, tags of the rest groups except the group pair are recognized(S260).

Description

A method of anti-collision in multiple RFID using capture phenomena}

1 is a block diagram of a general RFID system.

2 is a diagram illustrating a tag recognition method using a capture phenomenon in an RFID system according to an embodiment of the present invention.

3 is a diagram illustrating signal strengths of tags based on a position of a reader according to an exemplary embodiment of the present invention.

4 is a diagram illustrating a tag group classified according to signal strength based on a position of a reader according to an embodiment of the present invention.

The present invention relates to a RFID tag recognition method using a capture phenomenon that can occur in wireless data transmission, and more particularly, grouping according to the size of the received signal corresponding to the reference signal sent from the reader (reader) In addition, the present invention relates to a RFID tag recognition method using a capture phenomenon to improve the recognition performance by inducing only the corresponding groups that can most likely capture the competition.

Radio Frequency Identification (RFID) systems are commonly used in many applications, including personal identification, item identification, utility line indicators, object tracking, and the like.

The RFID system refers to a state-of-the-art technology for wirelessly recognizing data stored in a microchip using microwave or long wave as an area of automatic recognition such as barcode, magnetic sensor and IC-CARD. RFID is increasingly used in the industry to be recognized as a technology to replace bar codes currently used in logistics, distribution and financial services. In addition, RFID does not require a separate process of directly contacting the reader to the microchip or scanning with the reader at a visible distance to obtain data stored in the microchip, and has the advantage of transmitting a large amount of data.

In general, a process of recognizing a tag by a reader of an RFID system is performed as shown in FIG. 1. The reader broadcasts the request message to all tags. The tags receiving the request message transmit data to the reader. In this case, multiple tags (Mulit-Access) are made in which many tags transmit data to one reader.

In this case of multiple accesses, many tags within a certain distance from the reader transmit data, which inevitably results in data collision, and a process such as retransmission is required to recognize the data in which the collision occurs. In general, repeated retransmission of data causes an increase and a decrease in tag recognition time, thereby reducing the efficiency of the RFID system.

However, due to natural disordered and irregular fading, capture occurs as the signal is divided into several different power levels. The capture phenomenon refers to a phenomenon in which when a tag responds to one channel at the same time, the tag having the strongest signal among the tags is much stronger than the signals of other tags, so that the reader can read it successfully.

As such, the capture phenomenon has the effect of increasing the throughput of the system and reducing the communication delay, but it has not been attempted to accept it as a phenomenon that cannot be technically controlled and to actively induce and utilize it.

The present invention is to solve the problem of the RFID tag recognition method according to the prior art. That is, an object of the present invention is to improve the recognition performance by grouping the tags according to the size of the received signal of the reference signal sent from the reader, and inducing only the corresponding groups that can best capture the competition to participate in the competition. An RFID tag recognition method using a capture phenomenon is provided.

The present invention as a technical concept for achieving the above object, the reader transmits a beacon signal to all the tags in the recognition area, grouping the tag according to the received strength of the tag, and the capture phenomenon can occur Selecting a group pair to participate in the recognition process, comparing the number of tags by the selected group pairs, equalizing the number of tags based on a group having a small number of tags, and recognizing the tags of the selected group pairs through a reader. It provides a multi-RFID tag collision prevention method using a capture phenomenon characterized in that the step consisting of, and the step of recognizing the tag of the remaining group, not the group pair.

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

2 is a diagram illustrating a tag recognition method using a capture phenomenon in an RFID system according to an embodiment of the present invention.

Referring to FIG. 2, a reader first generates a beacon signal and transmits a group classification criterion according to a predetermined tag reception strength to tags. Each tag classifies itself into a corresponding group by the classification criteria (S210). Here, the group classification criteria may be transmitted before the reader starts recognition, or may be recorded and stored in the nonvolatile memory of the tag from the manufacturing stage. When the reader finishes tag group classification by generating beacon signals to all tags in the reader recognition area, the reader selects two groups with the largest received signal difference that can best capture the image, and participates in the recognition process. do. In the recognition process, the reader generally sends a command requesting a response first, and in the case of the slotted Aloha medium access protocol, the tags are random slots (Random Number Generator). slot) to respond to the reader. In this case, the slot is for determining the time of responding to the RFID reader, and the random number is for determining the time of the response signal.

For example, if the classification criteria of the tag reception strength is divided as shown in [Table 1] below, and the tags of FIG. 3 are classified according to the classification criteria of the tag reception strength, they are classified as shown in FIG. 4.

TABLE 1

Receiving strength 10 mW or more 9.9 to 7.1 mW 7.0 ~ 4.1mW 4.0 ~ 1.1mW 1.0 ~ 0.1mW Group name Group A Group B Group C Group D Group E

In the present invention, as shown in Figure 4 is divided into A, B, C group centered on the reader according to the received signal strength, the number of divided groups depends on the tag receiving strength classification criteria, the tag receiving strength classification criteria is It may be appropriately selected according to the field of application of the invention. According to an embodiment of the present invention, the tags of the groups A, B, and C divided into three groups have the following properties according to the difference in reception strength.

In general, if more than one tag responds to a slot, a collision will occur, preventing the reader from receiving the tag's data. However, if a capture occurs, an exception occurs. When one tag of group A and one tag of group C respond at the same time, the reader recognizes the tag of group A which has a stronger reception strength than the tag of group C. Therefore, the larger the difference in the reception strength, the better the capture phenomenon occurs when tag collision occurs. In addition, since the tags of group B have a small difference in reception strength between the tags of group A and the tags of group C, the tags of group B will always cause a collision if they simultaneously respond with the tags of group A and the tags of group C.

Next, the leader selects groups to participate in the competition of the recognition process (S220). In the group selection, a plurality of groups may be appropriately selected based on various criteria, but a group having a large difference in beacon signal reception strength of the reader is selected so that a capture phenomenon may occur. For example, if there are three groups, the first and third groups with a large difference in reception strengths are raced to recognize the remaining second group, and if there are four groups, the first and third groups, which are even groups, are raced, and then the second and fourth odd groups Compete the group. The same principle of mating can be extended and applied to more than five groups.

In the embodiment of the present invention, the tags of the group B, which is the intermediate group, always collide with the tags of the other group because the reception strength difference is small, and thus always collides.

The number of tags of the group participating in the recognition process maximizes the performance when the same or similar number of tags participates in the recognition. Therefore, the number of tags based on the group with few tags is compared by comparing the number of tags in Group A and the number of tags in Group C. The number of tags is limited (S230).

Here, to find out how many tags belong to Group A and Group C, the leader selects only the Group A tag, and then only 10% of all Group A's tags, for example 10%, participate in the competition. The number can be estimated. In the same way, the number of tags in group C can be estimated. The present invention does not propose a specific method for this tag number estimation method.

If there is a large difference between the number of tags in group A and group C, the competition for the tags of the larger group should be restricted. The method of limiting the number of tags is not particularly limited and may be appropriately selected according to the field of application of the present invention. For example, there is a method of matching a specific bit of memory or generating a random number so that only a certain number of tags is executed. In the present invention, a method of performing a matching of a specific bit and using it will be described by way of example.

For example, when comparing the number of tags of group A and group C, if the number of tags of group A is large, the reader compares the code of the group A tags and the tags of group A to limit the number of tags of group A. In the memory information, the start position of the bit to be compared with the comparison bit and the length of the comparison bit are transmitted through the command, and only the tags in which the data value of a specific bit section in the memory data of the tag matches the comparison bit sent by the reader are replied. You will be asked by command. That is, the number of tags in the group is limited by reading the tags by limiting the number of tags in response to the unique number request of the reader.

Each tag in the A group that receives the command from the reader compares the comparison bit, bit position, and comparison bit length information in the reader command with its memory data to determine whether the tag meets the reader's command condition. Be prepared to respond.

As such, only tags of group C that meet the command conditions of the reader and tags that meet the conditions of group A are prepared to respond to the reader, and the random number generator determines the random number and slot to respond to the reader.

Subsequently, when a response signal is transmitted to the reader from the tags of the group C and the tags meeting the conditions in the group A (S240), the reader receives and accesses the information of the responded tags and processes the data. At this time, even if there is a collision between the tag of the group A and the tag of the group C, the reader recognizes the tag of the group A, whose signal strength is stronger than the tag of the group C, by the capture phenomenon. There is no conflict in the process.

When all the recognition of the group C tag and the tags matching the conditions in the group A are completed, the reader performs the process of recognizing all the remaining tags in the group A (S250), and then the process of recognizing all the tags of the group B. It is performed (S260).

When the RFID tag is recognized using the capture phenomenon, the transmission success probability of one slot is as follows.

The probability Ps for successful identifier recognition in one slot is a case where successful recognition occurs in one slot. This happens again in two cases: the first is when only one tag is selected for a slot and the second is when more than one tag is selected for a slot, but the capture occurs. The sum of these two cases corresponds to Ps.

Ps = Pr [if successful recognition occurs in one slot]

   = Pr [select only one tag in slot] + Pr [select only one tag in slot A and C group]

= B (N, 1,1 / N) + B (N _A , 1,1 / N) B (N _C , 1,1 / N)

Here, B (n, k, p) is as follows, and N _A , N _B , and N _C represent the number of tags belonging to group A, group B, and group C.

Summarizing the above equation, the probability Ps is

Where N = N _A + N _B + N _C , Pg represents the capture gain.

Therefore, if α, β, and γ represent N _A / N, N _B / N, and N _C / N, respectively, the equation above is summarized as follows.

If α + β + γ = 1 and 0 ≤ α, β, γ ≤ 1, the equation Pg has a maximum value at α = γ = 1/2, β = 0 and the value is 1 / 4e.

Referring to the above equation, if the percentage of participation in the recognition process of group A and group C is 50%: 50%, or if the tag of group A can be successfully recognized even for two or more tags of group C, it is 45%: 55 It can be seen that the recognition rate is highest when the percentage is similar. In addition, it can be seen that it is advantageous to have Group B participate in the cognitive process separately.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

As described above, according to the RFID tag recognition method according to the present invention, the tags are grouped according to the size of the received signal corresponding to the reference signal sent from the reader, and competing only among the corresponding groups where the capturing phenomenon can best occur. By providing an RFID tag recognition method using a capture phenomenon to induce participation to improve the recognition performance, it is possible to implement the best recognition speed and more efficient recognition process.

Claims (4)

In the multiple RFID tag collision prevention method, Transmitting a beacon signal to all tags in the recognition region by the reader, and classifying the tag according to the received strength of the tag; Selecting a group pair to participate in the competition of the recognition process so that a capture phenomenon can occur; Comparing the number of tags for each selected group pair to equalize the number of tags based on a group having a small number of tags; Recognizing the selected group pair tag through a reader; Recognizing the tags of the remaining groups other than the group pair; Multiple RFID tag collision prevention method using a capture phenomenon, characterized in that consisting of. The method of claim 1, Selecting a group pair to participate in the competition, A method for preventing collisions of multiple RFID tags using a capture phenomenon, in which a group having a large difference in beacon signal reception strength of readers is paired with each other to participate in a competition. The method of claim 1, Equalizing the number of tags, Multi-RFID tag collision prevention method using a capture phenomenon characterized in that only a certain number of tags that meet the command conditions of the reader among the tags of the large number of tags based on the group with the smallest number of tags to participate in the recognition of similar number of tags per group pair . The method of claim 1, Recognizing the selected group pair tag through a reader, And recognizing the same number of tags of the selected group pair first, recognizing the remaining tags in the group pair, and sequentially recognizing another group pair.

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