KR20080042625A - Frame selection method for the rfid system - Google Patents

Abstract

A method for selecting a frame for an RFID(Radio Frequency IDentification) system is provided to select a frame size adaptively in an anti-collision algorithm presented by an ISO(International Organization for Standardization)/IEC(Internet Electrotechnical Commission) 18000-6 Type C standard. An ISO/IEC 18000-6 Type C standard adaptively provides a C value for an anti-collision algorithm according to a frame size. The frame size is 2^Q and Q is a positive integer, and the C value is 0.5 when the Q is smaller than 6. The C value is 0.5 when the Q is 7. The C value is 0.3 when the Q is smaller than 8. The C value is 0.2 when the Q is 9 or 10. The C value is 0.1 when the Q is bigger than 11.

Description

Frame Selection Method for RFID System

1 is a diagram illustrating a tag identification procedure in the ISO / IEC 18000-6 Type C standard.

FIG. 2 shows a slot count Q algorithm in the ISO / IEC 18000-6 Type C standard. FIG.

3 to 5 are views showing the recognition time of the entire tag according to the change of the C value.

The present invention relates to a frame selection method for an RFID system.

RFID (Radio Frequency IDentification) is a technology that transmits and receives information using a radio frequency from an electronic tag attached to a target object and provides a related service. Currently, the most widely used bar code system has a disadvantage in that the reader and the tag must be in the visible range and the recognition distance is short. However, unlike the barcode system, the RFID system that can read and store the information wirelessly from the electronic tag is able to transmit and receive information over a long distance, and can be transmitted and received in a long distance. Has advantages In particular, the RFID system can identify the product specification, price, distribution route, and deadline automatically by attaching electronic tags to various items without having to read them one by one like a barcode system. Be in the spotlight. In addition, RFID systems are expected to be able to do much more than the role of barcodes as the sensor technology and miniaturization technology of ubiquitous network is further developed.

International standards related to RFID are being developed by the Joint Technical Committee 1 (JTC), which was jointly formed by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). Regarding the standardization of RFID in the UHF band, Type A and Type B standards have been finalized as a standard of 18000-6 (860 ~ 960MHz band radio access standard) in ISO / IEC JTC1 SC31 WG4. Separately, Class 0 and Class 1 specifications were finalized as an EPC (Electronic Product Code) standard around the MIT Auto ID center. Recently, the EPC Class 1 Gen2 standard proposed by EPCglobal has been assumed to ISO, and has been incorporated into ISO / IEC 18000-6 Type C standards following the Type A and B standards. Class 1 Gen2, called UHF Gen2, is expected to outperform any other specification in inter-reader interference resolution, security, and data rate. Class 1 Gen2 is therefore expected to be established as a single unified standard for passive RFID media in the UHF band.

An object of the present invention is to provide a frame selection method for an RFID system that adaptively selects a frame size in the collision avoidance algorithm proposed in the ISO / IEC 18000-6 Type C standard.

According to an aspect of the present invention to achieve the above objects, according to the size of the frame in the ISO / IEC 18000-6 Type C standard, where the frame size is 2 ^Q and the Q value is a positive integer The C value is provided, but the C value is 0.5 when the Q value is 6 or less, 0.4 when the Q value is 7, 0.4 when the Q value is 8, 0.3 when the Q value is 9 and 10, 0.2 when the Q value is 9, and 10 or more. In this case, a frame selection method for an RFID system of 0.1 may be provided.

Hereinafter, with reference to the accompanying drawings, the configuration and operation of the embodiment of the present invention will be described in detail. The drawings and the description of the drawings are examples of the present invention, which does not limit the scope of the present invention.

In general, an RFID system is composed of one reader and a plurality of tags, and multiple accesses are made in which a plurality of tags simultaneously access a reader. Therefore, when multiple tags are in the same processing space, it is important to recognize the tags correctly and without errors. Passive RF tags used in RFID systems are very limited in their ability to communicate with other tags and only with readers. The reader communicates with each tag over a wireless channel, all tags simultaneously receiving signals from the reader and responding to commands from the reader. The problem is that one reader must recognize several tags that have been responded to at the same time. This is called `` tag collision ''. Recently, tag collisions are gradually increasing due to the introduction of multi-readers that can recognize various tags to reduce installation costs. In order to recognize tags at high speed, these problems are anti-collision algorithms and the core technology of RFID systems.

Anti-collision algorithms commonly used today are divided into Aloha and Binary-tree. The Aloha method is a slotted-ALOHA method that divides the response time of a tag into several fixed slots and allows the tags to transmit data to their selected slots. ISO / IEC 18000-6 Type A uses an Adaptive Slotted-ALOHA scheme that handles collisions by dynamically adjusting the number of slots to distinguish multiple tags. The size of the slot is communicated by the reader to the tags dynamically, and the tag responds by randomly selecting its slot. The binary-tree scheme avoids collisions by using the bit position where the collision occurred, by appropriately controlling the number of tags that respond simultaneously. ISO / IEC 18000-6 Type B uses the binary-tree concept by default for collision resolution. The binary-tree method repeats the process of finally finding one tag while dividing the entire tag into detailed subgroup units when a collision occurs. EPCglobal's Class 0 and Class 1 also employ binary-tree algorithms. The performance of these collision avoidance algorithms can be determined by the protocol between the tag and the reader and the reader system. As the reader distinguishes multiple tags and adjusts collisions to exchange data with one specific tag, the tags cause various state changes and process commands broadcast to themselves and other tags according to their current state. do.

The anti-collision algorithm used in Type C, a standard adopted by EPC Global, which assumes EPC Class 1 Gen2 in ISO, is an Aloha slot random random collision avoidance algorithm. In the ISO / IEC 18000-6 Type C standard, the tags each independently select a slot with a number between 0 and 2 ^{Q- 1} and have a Q value that is a parameter included in the instruction (Query or QueryAdjust) received from the reader. Send the data. In this case, since slots are randomly selected, if multiple tags select the same slot, a collision occurs and the reader does not receive accurate information.

1 is a diagram illustrating a tag identification procedure in the ISO / IEC 18000-6 Type C standard. Referring to FIG. 1, when a tag is within a valid reader range, the reader determines which tags to participate in the competition through a Select message, and informs the number of slots allocated to the frame through a Query message, and the frame starts. . The leader then gets three results: First, there is no response from the tag. In this case, the reader can advance to the next slot by sending a QueryRep message or send a QueryAdjust message to adjust the frame size through the Q value. Second, when only one tag is responded to and receives correct information from the tag, a QueryRep message is transmitted to indicate the start of the next slot (upper part of FIG. 1). Third, when a collision occurs due to multiple tags responding, as in the case where there is no response, the frame size can be adjusted through the Q value by sending a QueryRep message to the next slot or sending a QueryAdjust message (the lower part of FIG. 1). .

If there is no response as in the first case described above or a collision occurs as in the third case described above, the next slot or the frame size should be adjusted according to the number of tags. The Q algorithm presented in the ISO / IEC 18000-6 Type C standard represents a frame size of 2 ^{Q. As} shown in FIG. 2, the frame size is adjusted by increasing Q by C when there is a collision and decreasing Q by C when there is no response. . Where the C value is set to 0.1 ≦ C ≦ 0.5. However, the ISO / IEC 18000-6 Type C standard does not specify the value C, which is a definitive control parameter. Obviously, if the C value is chosen too large, the frame size will be significantly overshooted, whereas if it is chosen too small, swiftness will fall.

It is important to find the C value based on the frame size (or the number of tags). Here, the C value becomes the rate of change of the frame size, and through experiments, the appropriate C value according to the number of tags is presented.

The experiment assumes that the system consists of one reader and many tags in an ideal channel environment (error-free). First, we use the fixed values in the standard document to calculate the time of tag recognition. Set the Tari value indicating the length of Data-0 to 12.5 ms and taking into account the link timing of FIG. 1, the time from the sending of the Select message to the recognition of all tags (the EPC code of the last recognized tag The result value is calculated by calculating the average time of data transmission between the reader and the tag).

3 to 5 are diagrams illustrating recognition times of all tags according to a change in a C value. 3 to 5, it can be seen that setting a large C value (0.5) when the frame size is small and setting a small C value (0.1) when the frame size is large can reduce the recognition time. . The appropriate C value for each frame size is shown in the table below.

Q value Frame size C value One 2 0.5 2 4 0.5 3 8 0.5 4 16 0.5 5 32 0.5 6 64 0.5 7 128 0.4 8 256 0.3 9 512 0.2 10 1024 0.2 11 2048 0.1 12 4096 0.1 13 8192 0.1 14 16384 0.1 15 32768 0.1

In slotted random collision avoidance algorithm of ISO / IEC 18000-6 Type C, an international standard for RFID systems in the 860MHz to 960MHz band, as described above, the C value is set according to the degree of collision and adaptively Provide a way to resize. In general, Framed Slotted-ALOHA algorithms that adjust the frame size according to the number of tags should speed up the frame size when the frame size is small, and slow down the frame size when the frame size is large. will be. In particular, in ISO / IEC 18000-6 Type C, since the frame size is given as 2 ^Q , the frame size increases rapidly as the Q value increases, so an appropriate C value according to the Q value is an important control parameter. As described above, the recognition speed can be reduced by providing an appropriate C value according to the frame size in ISO / IEC 18000-6 Type C.

The present invention is not limited to the above embodiments, and many variations are possible by those skilled in the art within the spirit of the present invention.

According to the present invention, it is possible to provide a frame selection method for an RFID system that adaptively selects a frame size in an anti-collision algorithm proposed in the ISO / IEC 18000-6 Type C standard.

Claims (1)

According to the ISO / IEC 18000-6 Type C standard, the corresponding C value is provided according to the size of the frame, where the frame size is 2 ^Q and the Q value is a positive integer. The C value is 0.5 when the Q value is 6 or less, 0.4 when the Q value is 7, 0.4 when the Q value is 8, 0.3 when the Q values are 9 and 10, 0.2 when the Q value is 11 or more, and 0.1 when the Q value is 11 or more. Frame Selection Method for RFID System.

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