KR101385639B1 - Methods and apparatuses of identifying rfid tag based on dfsa algorithm for the purpose of reducing missing tags in motion - Google Patents

Abstract

The present invention is to provide a method and apparatus of identifying a radio frequency identification (RFID) tag based on dynamic framed slotted ALOHA (DFSA) capable of reducing the loss of the RFID tag by determining the size of an optimal frame in consideration of the collision from recognizing the RFID tag of an RFID reader and the error of a channel, to improve the recognition rate of the RFID tag in an environment in which the RFID tag moves by the relationship of the size of the frame and the number of the frame. [Reference numerals] (AA) Moving direction of a tag

Description

DFHO-based RFID ID tag recognition method and apparatus for reducing loss of moving RFID tag

The present invention relates to a radio frequency identification (RFID) tag recognition technology, and more particularly, to a technology for recognizing an RFID tag when a RFID tag moves.

RFID is a contactless recognition technology that enables information management of various entities using radio frequency. The RFID system consists of an RFID reader that recognizes an object and an RFID tag that transmits information of an object. In order to recognize the information, the RFID reader sends a query, and the received RFID tags transmit a random 16-bit number generated by the RFID tag as a temporary ID to recognize the RFID system. In this recognition process, if multiple RFID tags transmit data at the same time, a collision occurs and recognition fails, which greatly affects the performance of the system. There are several anti-collision algorithms to solve this collision problem. In general, the ALOHA-based Dynamic Framed Slotted ALOHA (DFSA) algorithm is used.

In the DFSA algorithm, one frame consists of a plurality of slots, and the number may change each time. The DFSA method estimates the number of RFID tags using the frame size of the previous stage and the state of each slot, and determines the size of the next stage frame based on this. Each RFID tag attempts to transmit by selecting a random slot based on the determined frame size, and attempts to transmit by selecting a random slot again in the next frame when a collision occurs.

Since the conventional anti-collision algorithm is proposed in a fixed environment without moving the RFID tag, it is not appropriate to apply to an actual industrial environment such as FIG. 1 in which the RFID tag moves. In an environment in which an RFID tag moves, the DFSA method has a high possibility of losing a loss that is not recognized until the RFID tag passes the recognition radius of the RFID reader. These lost RFID tags have a problem that negatively affect the recognition rate and bring down the performance of the system.

Japanese Unexamined Patent JP 2010-530152 (“How to determine the optimal frame size for collision avoidance of RFID tags in RFID systems”, published by SK TELECOM, 2010.09.02)

Disclosure of Invention An object of the present invention is to provide a method and apparatus for improving the recognition rate of an RFID system by determining a frame size in consideration of a moving environment and a loss probability of an RFID tag.

An RFID tag recognition method for achieving the object of the present invention, RFID tag recognition method using a dynamic framed slotted ALOHA (DFSA) method, the step of introducing an RFID tag; Determining, by the RFID reader, the frame size using the probability of loss of the RFID tag; And recognizing the RFID tag using the frame having the frame size.

In the determining of the frame size using the loss probability of the RFID tag, the RFID reader may calculate the loss probability of the RFID tag by using a probability that the recognition of the RFID tag fails.

The probability that the RFID tag fails to be recognized due to collision in any slot is calculated by subtracting the probability of successful recognition of the RFID tag from the overall probability, and the probability of successful recognition of the RFID tag is one slot in one RFID tag. The remaining RFID tags may be calculated by the probability of selecting a slot other than the slot.

The loss probability of the RFID tag may be calculated using a probability that the response signal of the RFID tag is not transmitted by a channel error and a probability that the RFID tag is not recognized.

The probability that the response signal of the RFID tag is not transmitted by the channel error may be calculated using a packet error rate.

The determining of the frame size by using the probability of loss of the RFID tag by the RFID reader estimates the number of frames to be experienced before the RFID tag leaves the recognition region of the RFID reader, and the RFID tag recognizes the recognition region of the RFID reader. The probability of loss of the RFID tag can be estimated by estimating the probability that it will not be recognized from the RFID reader in every frame to be experienced until it escapes.

The determining of the frame size by using the probability of loss of the RFID tag by the RFID reader may include: recognition region of the RFID reader, moving speed of the RFID tag, and recognition region of the RFID reader using the current frame size. We can estimate the number of frames to experience before going out.

The determining of the frame size by using the loss probability of the RFID tag by the RFID reader may include: a frame to be experienced until the estimated RFID tag of the probability that the RFID tag is not recognized in one frame leaves the recognition region of the RFID reader. By multiplying the number of times, the probability of loss of not being recognized by the RFID reader in every frame to be experienced until the RFID tag leaves the recognition region of the RFID reader can be estimated.

The determining of the frame size by using the loss probability of the RFID tag by the RFID reader may select the size of the frame that minimizes the estimated at least the loss probability to determine the next frame size.

In addition, the RFID tag recognition apparatus for achieving the object of the present invention is a RFID tag recognition apparatus using a DFSA (Dynamic Framed Slotted ALOHA) method; An RFID tag transfer unit for moving the RFID tag; And an RFID reader, wherein the RFID reader determines a frame size using an estimated loss probability of the RFID tag, and recognizes the RFID tag using the frame of the determined size.

The RFID reader may calculate the loss probability using the recognition failure probability of the RFID tag.

The RFID reader may estimate the loss probability of the RFID tag by using the probability that the response signal of the RFID tag is not transmitted due to a channel error.

The RFID reader estimates the number of frames to be experienced before the RFID tag leaves the recognition area of the RFID reader, and the probability that the RFID tag will not be recognized by the RFID reader in every frame to be experienced until the RFID tag leaves the recognition area of the RFID reader. By estimating the loss probability of the RFID tag can be estimated.

The RFID reader may estimate the number of frames to be experienced before the RFID tag leaves the recognition region of the RFID reader using the recognition region of the RFID reader, the moving speed of the RFID tag, and the size of the current frame.

The RFID reader multiplies the number of frames to be experienced before the estimated RFID tag leaves the recognition region of the RFID reader by an estimated probability that the RFID tag is not recognized in one frame and the RFID tag is the RFID reader. It is possible to estimate the probability of loss not being recognized from the RFID reader in every frame to be experienced until it goes out of the recognition range.

The RFID reader may select a size of a frame that minimizes the loss probability among the estimated at least one loss probability and determine the size of the next frame.

RFID tag recognition method and apparatus based on DFSA to minimize the loss of a moving RFID tag according to an embodiment of the present invention RFID tag recognition collision of the RFID reader in the environment in which the RFID tag is moved through the relationship between the frame size and the number of frames By determining the optimal frame size in consideration of the error of the channel and the channel, it is possible to reduce the lost RFID tag by improving the recognition rate of the RFID tag.

1 is a conceptual diagram of an environment in which an RFID tag moves according to an embodiment of the present invention.
2 is a diagram illustrating a process of recognizing a RFID tag based on DFSA.
3 is a flowchart illustrating a method for recognizing an RFID tag based on DFSA for minimizing the loss of a moving RFID tag according to an exemplary embodiment of the present invention.
4 is an RFID tag recognition rate of a DFSA-based RFID tag recognition method and a conventional DFSA algorithm-based RFID tag recognition method to minimize the loss of a moving RFID tag according to an embodiment of the present invention when the moving speed of the RFID tag increases. Is a diagram comparing.
5 is a diagram illustrating a method for recognizing a RFID tag based on a DFSA and a method for recognizing a RFID tag based on a conventional DFSA algorithm for minimizing the loss of a moving RFID tag 200 according to an embodiment of the present invention according to the number of successful RFID tags. A comparison of recognition delay times.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

1 is a conceptual diagram of an environment in which an RFID tag 200 moves according to an embodiment of the present invention.

The DFSA-based RFID tag recognition apparatus according to an embodiment of the present invention includes an RFID reader 100, an RFID tag 200, an RFID tag transfer unit, and a controller.

The RFID reader 100 is spaced apart from the RFID tag 200 and spaced apart from the RFID tag transfer unit. The RFID reader 100 has a recognition area 101 and recognizes an RFID tag 200 located in the recognition area 101. The RFID reader 100 recognizes the RFID tag 200 using the RFID tag recognition method described below.

The RFID tag 200 is recognized by the RFID reader 100 and may be positioned on the upper part of the RFID tag transfer unit. The RFID tag transfer unit moves the RFID tag 200. The RFID tag transfer unit may be a conveyor belt.

The control unit controls the operation of the RFID reader 100 and the RFID tag transfer unit. The control unit may have a separate configuration, or may be provided in the RFID reader 100 and the RFID tag transfer unit, respectively. If each is provided, the user can separately control the provided control unit. Or, if each provided, the RFID reader 100 or the RFID tag transfer unit to control one of the RFID reader 100 and the RFID tag transfer unit is provided with a communication device to control the other one of the two received any control signal You can also pass the signal to another.

2 is a diagram illustrating a process of recognizing a RFID tag based on DFSA.

In an environment in which the RFID tag 200 moves, the recognition process proceeds as shown in FIG. 2. In each frame, the RFID tags 200 enter the recognition radius and attempt to recognize the RFID tag 200 according to the density, speed, and previous frame size of the RFID tag 200. When the RFID reader 100 determines the frame size and transmits the determined frame size as a query command to notify the respective RFID tags 200, each RFID tag 200 selects an arbitrary slot and attempts to transmit. At this time, if a plurality of RFID tags 200 selects the same slot and attempts transmission at the same time, a collision occurs and recognition is not performed. In addition, even if only one RFID tag 200 selects one slot, the corresponding RFID tag 200 is not recognized when transmission is not performed correctly due to a channel error.

A process of recognizing the RFID tag 200 of the RFID reader 100 will be described with reference to FIG. 2. 2, the RFID tag 200 leaves the recognition area 101 of the RFID reader 100 after a predetermined time elapses. 2 illustrates that when the query time of the RFID reader 100 and the RFID tag recognition time of the slot are the same time unit, the RFID tag 200 recognizes the RFID reader 100 when 16 time units have passed. A situation out of the area 101 is assumed. For example, a process in which the RFID tag 1 becomes a lost RFID tag will be described.

Before starting the first frame, three RFID tags 200 are introduced into the recognition area 101 of the RFID reader 100. The RFID reader 100 recognizes that the three RFID tags 200 are the recognition targets, sets the size of the frame to 3, transmits queries to the RFID tags 200, and sequentially recognizes the RFID tags 200 in each slot. Do this. In the first frame, the slot 1 receives the response signal of the RFID tag 3 to recognize the RFID tag 3. Slot 2 does not have a responding RFID tag 200 and becomes a slot in an unresponsive state. Slot 3 receives the response signals of the RFID tags 1 and 2 and receives a response from two or more RFID tags to cause a collision. Slot 3 does not recognize any RFID tag 200. The RFID tag 4 newly introduced into the recognition area 101 of the RFID reader 100 during the RFID tag recognition process of the first frame becomes a recognition object in the second frame, which is the next RFID tag recognition process of the RFID reader 100. RFID tags 1 and 2 not recognized in the first frame are also subject to recognition in the next frame.

In the second frame, the RFID reader 100 knows that RFID tag recognition should be performed on the remaining three RFID tags 200 except the RFID tag 3, which is a recognized RFID tag. Send a query to. The RFID tags 200 which have been queried transmit a response signal to an arbitrary slot. The RFID tag 1 transmits a response signal to the slot 1, the RFID tag 2 transmits a response signal to the slot 2, and the RFID tag 4 transmits a response signal to the slot 2. The RFID tag 1 transmits a response signal to the slot 1, but a channel error occurs and the response signal is not transmitted to the slot 1. Thus, slot 1 does not recognize RFID tag 1 and becomes a slot without a response. Slot 2 receives the response signals of RFID tags 2 and 4, but receives a response from two or more RFID tags 200 and thus has a collision state and thus does not recognize any RFID tag 200. No RFID tag 200 is recognized in the second frame, and the RFID tags 1,2 and 4 are subject to recognition of the next frame. The newly introduced RFID tag 5 during the progress of the second frame is also the object of recognition of the next frame.

In the third frame, the RFID reader 100 transmits a query to the RFID tags 200 which are not recognized in the same manner. Recognition should be performed on the four RFID tags 200, but it is assumed in the example of FIG. 2 that the maximum frame size is three. The RFID tag 5 transmits a response signal to the slot 1, and the slot 1 receives the response of the RFID tag 5 to recognize the RFID tag 5. The RFID tags 1 and 4 transmit a response signal to the slot 2 so that the slot 2 has a collision state and does not recognize any RFID tag 200. The RFID tag 2 transmits a response signal to the slot 3, and the slot 3 receives the response signal of one RFID tag 200 to effectively recognize the RFID tag 3. The RFID tag 1 is not recognized from the RFID reader 100 for 16 time units, thereby leaving the recognition area 101 of the RFID reader 100. The newly introduced RFID tag 6 in the third frame becomes a recognition target of the next RFID tag recognition frame. The RFID tag 1 leaves the recognition area 101 of the RFID reader 100 and becomes a lost RFID tag that is not recognized and disappears from the RFID reader 100.

In the fourth frame, the RFID reader 100 recognizes that the RFID tag 2 becomes a lost RFID tag and transmits a query to the RFID tag 4 and the RFID tag 6 that are the RFID tag recognition targets. Since the RFID tag recognition is performed on the two RFID tags 200, the size of the frame is two. The RFID reader 100 transmits a query to the RFID tag 200, and the RFID tags 4 and RFID tag 5, which are not recognized RFID tags, receive a query from the RFID reader 100 and respond to the slots of the RFID reader 100. Send a signal. The RFID tag 1 that becomes the lost RFID tag outside the recognition area 101 of the RFID reader 100 does not receive a query. RFID tag 5 transmits a response signal to slot 1, but the response signal is not transmitted to slot 1 due to a channel error, and slot 1 becomes a slot in an unresponsive state without a recognized RFID tag. Slot 2 receives the response signal from RFID tag 4 and recognizes RFID tag 4.

As described above, RFID tags 200 and non-recognized RFID tags 200 are generated during one frame. Unrecognized RFID tags 200 attempt to transmit in the next frame. At this time, the existing frame size determination method is determined as the number of RFID tags 200 for estimating the size of the next frame, but DFSA-based RFID tag recognition for minimizing the loss of the moving RFID tag 200 according to an embodiment of the present invention. The method determines the frame size to minimize the estimated probability of loss.

As the size of the frame increases, the number of RFID tags 200 recognized in the frame increases, but the number of slots increases, so that the recognition time of the frame increases, and the number of incoming RFID tags 200 increases according to the frame size. The number of tags 200 also increases. As the size of the frame increases, the number of frames experienced by the moving RFID tag 200 decreases, so that the number of times that a response signal can be transmitted to the slot decreases, thereby increasing the probability of loss of the RFID tag 200. . In addition, as the size of the frame decreases, the number of frames that can be experienced by the moving RFID tag 200 increases, but the probability that the slot has a collision state by transmitting a response signal by a plurality of RFID tags 200 in a small number of slots. Since this becomes large, the number of RFID tags 200 that succeeds in recognition in one frame is reduced. Accordingly, the probability that the RFID tag 200 deviates from the recognition radius without experiencing the continuous collision and is not recognized by the RFID reader 100 increases.

3 is a flowchart illustrating a method for recognizing a RFID tag based on a DFSA for minimizing the loss of a moving RFID tag 200 according to an embodiment of the present invention. Hereinafter, a DFSA-based RFID tag recognition method for minimizing the loss of a moving RFID tag 200 according to an embodiment of the present invention will be described with reference to the flowchart of FIG. 3.

는 i번째 프레임에서 인식되지 못한 RFID 태그(200)의 수

와 새로 인식 반경에 들어오는 RFID 태그(200)의 수

의 합으로 계산된다.

은 i번째 프레임에서 RFID 태그(200)의 인식이 성공하지 못하는 확률

로 계산할 수 있다. i번째 프레임에서 새로 유입된 RFID 태그(200)의 수

는 i 번째 프레임의 크기인

, 슬롯 시간인

, RFID 태그(200)의 속도인

및 RFID 태그(200)의 밀도인

의 곱으로 계산할 수 있다. 아래의 수학식 1은 다음 프레임에서 인식을 시도하는 RFID 태그(200)의 수를 나타낸다.First, the RFID tag 200 flows into the recognition area 101 of the RFID reader 100 (S101). There are RFID tags 200 that flow into the recognition area 101 of the RFID reader 100 and attempt to recognize each frame for the first time. The number of RFID tags 200 that enters the recognition radius is determined by the size of the previous frame, and the number of RFID tags 200 that attempt to recognize in the next frame is the number of RFID tags 200 that enter the recognition radius in the previous frame. And the number of RFID tags 200 which failed to recognize in the previous frame. The number of RFID tags 200 that attempt to transmit in the next i + 1 th frame in an environment in which the RFID tag 200 moves at constant speed.

Is the number of RFID tags 200 not recognized in the i-th frame.

And the number of RFID tags 200 coming into the newly recognized radius

Is calculated as the sum of.

Is the probability that the recognition of the RFID tag 200 is not successful in the i-th frame

Can be calculated as Number of newly introduced RFID tags 200 in the i th frame

Is the size of the i th frame

, Slot time

, The speed of the RFID tag 200

And the density of the RFID tag 200

Can be calculated as the product of. Equation 1 below represents the number of RFID tags 200 that attempt to recognize in the next frame.

Next, the RFID reader 100 performs recognition of the RFID tag 200 (S102). The RFID reader 100 calculates the frame size and informs each RFID tag 200 of the determined frame size. The RFID tag 200 recognizes the RFID tag 200 by calculating the number of the RFID tags 200 and setting the size of the frame to transmit a query to each RFID tag 200. The size of the frame used in this step is the size of the frame calculated in the previous frame. If the size of the previous frame is not calculated, the default value can be used.

Next, the RFID reader 100 measures the recognition probability of the RFID tag 200 (S103). Each RFID tag 200 selects a random slot and attempts to transmit. At this time, if a plurality of RFID tags 200 selects the same slot and attempts transmission at the same time, a collision occurs and recognition is not performed. In this case, only one random RFID tag 200 may select one slot to measure a probability of successful transmission.

은 i번째 프레임에서 한 개의 RFID 태그(200)가 한 슬롯을 선택하고 나머지

개의 RFID 태그(200)들이 특정 슬롯을 제외한 다른 슬롯을 선택하는 이항 확률로 계산할 수 있다. i번째 프레임에서 RFID 태그(200)가 인식 되지 않을 확률은

이 되고, 이를 해당 프레임에 인식대상이 되는 RFID 태그(200)의 수에 곱하여 해당 프레임에서 인식에 실패한 RFID 태그(200)의 수

를 계산할 수 있다.The probability that an arbitrary RFID tag 200 succeeds in transmission in one slot of the i-th frame may be calculated by Equation 2 below. The probability that the RFID tag 200 succeeds in transmission

In the i th frame, one RFID tag 200 selects one slot and the other

RFID tags 200 may be calculated with a binomial probability of selecting a slot other than a specific slot. The probability that the RFID tag 200 is not recognized in the i-th frame is

This is multiplied by the number of RFID tags 200 to be recognized in the corresponding frame and the number of RFID tags 200 that fail to recognize in the corresponding frame.

Can be calculated.

Next, the probability of transmission failure due to channel error is calculated (S104). When only one RFID tag 200 selects one slot, the RFID tag 200 must be recognized successfully, but the transmission of the response signal fails according to the channel environment, so that the RFID tag 200 may not be recognized. If the transmission is not performed correctly due to a channel error, the corresponding RFID tag 200 is not recognized. The channel error can be calculated by calculating the bit error rate and the packet error rate using the signal-to-noise ratio.

The signal-to-noise ratio is generated according to the distance between each RFID tag 200 and the RFID reader 100 at a specific time point, and the bit error rate may be calculated using the generated signal-to-noise ratio. In the case of a packet consisting of M bits, an error does not occur when all bits are successfully transmitted, and the packet error rate can be calculated using the bit error rate.

는

와 잡음 신호의 세기

의 비로 계산할 수 있다. RFID 태그(200)가 수신한 신호의 세기

는 RFID 리더(100)의 신호 송신 파워

, RFID 리더(100)의 안테나 이득

, RFID 태그(200)의 안테나 이득

, 신호의 파장

, 및 RFID 태그(200)와 RFID 리더(100) 사이의 거리

를 이용하여 계산한다. RFID 태그(200)가 수신한 신호의 세기인

는 아래의 수학식 3과 같이 계산할 수 있다.Signal to noise ratio over distance

The

And the strength of the noise signal

It can be calculated as the ratio of. The strength of the signal received by the RFID tag 200

Signal transmission power of the RFID reader 100

Gain of the RFID reader 100

Gain of RFID tag 200

Signal wavelength

, And the distance between the RFID tag 200 and the RFID reader 100

Calculate using The strength of the signal received by the RFID tag 200

May be calculated as in Equation 3 below.

는 RFID 태그(200)가 수신한 신호의 세기

를 잡음 신호의 세기

로 나누어 아래의 수학식 4와 같이 계산할 수 있다.And the signal-to-noise ratio

Is the strength of the signal received by the RFID tag 200

The strength of the noise signal

It can be calculated as shown in Equation 4 below.

In addition, the bit error rate BER (s) for reflecting the channel environment in the RFID system may be calculated using Equation 5 below using the signal-to-noise ratio SNR (s) according to the distance. In the DFSA-based RFID tag recognition method for minimizing the loss of the moving RFID tag 200 according to an embodiment of the present invention, a constant value based on a modulation method is defined as k. The RFID reader 100 and the RFID tag 200 of the RFID system generally use an ASK (Amplitude Shift Keying) method, and k is 1 when the ASK method is used. The bit error rate BER (s) can be calculated using Equation 5 below. Here, Q (x) means Q-Function of Gaussian probability distribution. Q (X) represents the probability that the standard normal random variable is greater than X.

The packet error rate PER (s) may be calculated as Equation 6 below as a probability that an error occurs when the entire packet is transmitted when the RFID reader 100 and the RFID tag 200 communicate in the RFID system. M is the number of bits constituting the packet. Equation 6 calculates the probability of packet error by subtracting the probability that all bits do not cause an error from the overall probability.

을 계산한다. 각각의 RFID 태그(200)와 RFID 리더(100) 사이의 거리 s는 임의의 값을 가지므로, RFID 태그(200)들의 평균 패킷 에러율

을 사용하여 분실확률을 추정한다. RFID 리더(100)와 RFID 태그(200)사이의 거리는 RFID 리더(100)의 인식 영역(101) 지름의 반이 최대가 되고, 거리가 0인 경우가 최소가 되기 때문에 이를 이용하여

을 계산한다. 아래의 수학식 7을 사용하여 평균 패킷 에러율을 계산할 수 있다. 여기서 r은 RFID 리더(100)의 인식 영역(101)의 지름을 의미한다. 각 RFID 태그(200)의 평균 패킷 에러율을 RFID 리더(100)의 인식 영역(101)범위 내에서 RFID 리더(100)와의 거리에 따라 적분하여 구할 수 있다.Average packet error rate of all the RFID tags 200 included in the recognition area 101 of the RFID reader 100 to calculate the probability of loss using the packet error rate.

. Since the distance s between each RFID tag 200 and the RFID reader 100 has any value, the average packet error rate of the RFID tags 200

Estimate the probability of loss using. Since the distance between the RFID reader 100 and the RFID tag 200 is half of the diameter of the recognition area 101 of the RFID reader 100 is maximum, and the distance is 0, the minimum is used.

. Equation 7 below can be used to calculate the average packet error rate. Here, r means the diameter of the recognition area 101 of the RFID reader 100. The average packet error rate of each RFID tag 200 can be obtained by integrating according to the distance from the RFID reader 100 within the recognition region 101 of the RFID reader 100.

Next, the RFID reader 100 calculates a loss probability (S105). The probability of loss may be calculated by considering the number of frames to be experienced, the size of each frame, and the probability of not being recognized in each frame until the RFID tag 200 leaves the recognition area 101 of the RFID reader 100.

Since the RFID reader 100 does not know the size of the next frame, it estimates the number of frames that the RFID tag 200 will experience, assuming that all frame sizes are the same as the current frame size. The RFID reader 100 calculates a loss probability by estimating the number of frames that the RFID tags 200 that enter the recognition radius in the corresponding frame will experience.

를 현재의 프레임 크기

에 따라 추정한다. i번째 이후의 프레임 크기

는 현재의 프레임 크기

과 같다고 가정하여 경험하게 될 프레임 수

를 추정한다.The RFID reader 100 may experience the number of frames to be experienced before the RFID tag 200 of the i-th frame leaves the recognition area 101 of the RFID reader 100.

Current frame size

Estimate according to frame size after i

Is the current frame size

The number of frames you will experience assuming

.

는 RFID 리더(100)의 인식 영역(101)의 지름r과 현재의 프레임 크기

, 슬롯 시간인

및 RFID 태그(200)의 속도인

를 사용하여 아래의 수학식 8과 같이 계산될 수 있다. RFID 태그(200)가 경험하는 프레임의 수는 자연수이다. 따라서 버림을 통해 RFID 태그(200)가 경험하는 프레임의 수를 자연수로 생성한다.When the RFID tag 200 is recognized according to the DFSA-based RFID tag recognition method for minimizing the loss of the moving RFID tag 200 according to an embodiment of the present invention, after a predetermined time passes, the RFID tag 200 Is evenly distributed within the recognition radius, and the number of RFID tags 200 entering and leaving the recognition radius becomes a stable state, so that the frame size may also converge to a certain size. The number of frames to be experienced before the RFID tag 200 of the i-th frame leaves the recognition area 101 of the RFID reader 100.

Is the diameter r of the recognition area 101 of the RFID reader 100 and the current frame size.

, Slot time

And the speed of the RFID tag 200

It can be calculated using Equation 8 below. The number of frames experienced by the RFID tag 200 is a natural number. Accordingly, the number of frames experienced by the RFID tag 200 is generated as a natural number through discarding.

는 i번째 프레임에서 인식에 성공할 확률인

과 패킷 에러율인

를 사용하여 계산할 수 있다. RFID 태그(200)의 분실확률은 RFID 태그(200)가 이동하면서 경험하는 프레임마다 인식에 실패할 확률을 모두 곱하여 생성할 수 있다. 각 프레임에서 인식에 실패할 확률은 RFID 태그 인식에 실패할 확률과, RFID 태그 인식에 성공하더라도 채널 오류로 응답 신호가 RFID 리더(100)의 슬롯에 전송되지 않을 확률을 더한 값이다. RFID 태그(200)의 분실확률은 아래의 수학식 9와 같이 계산할 수 있다.The loss probability, which is a probability that the RFID tag 200 is not recognized by the collision or the channel error until the RFID tag 200 exits the recognition radius, may be calculated through Equation 9. If the RFID tag 200 enters the recognition radius in the k-th frame,

Is the probability of successful recognition at the i-th frame

And packet error rate

Can be calculated using. The loss probability of the RFID tag 200 may be generated by multiplying the probability that recognition fails for each frame experienced while the RFID tag 200 moves. The probability that the recognition fails in each frame is the sum of the probability of failing the RFID tag recognition and the probability that the response signal is not transmitted to the slot of the RFID reader 100 due to a channel error even if the RFID tag recognition is successful. The loss probability of the RFID tag 200 may be calculated as in Equation 9 below.

However, there is a problem that it is difficult to accurately estimate the loss probability experienced by the RFID tag 200 because the success probability changes as the frame size changes every frame. Therefore, the DFSA-based RFID tag recognition method for minimizing the loss of the moving RFID tag 200 according to an embodiment of the present invention estimates the loss probability similar to the value of the actual loss probability.

을 i번째 프레임에서 프레임 크기가

일 때의 성공확률

,

및 인식영역(101) 내에서 경험하는 프레임 수

을 사용하여 아래의 수학식 10과 같이 계산할 수 있다. 수학식 10은

를 근사하여 계산한다. 본 발명의 일 실시 예에 따른 이동하는 RFID 태그(200)의 분실을 최소화하는 DFSA 기반의 RFID 태그 인식 방법에서는 각 프레임마다 프레임 크기가 변하지만 일정 시간이 흐른 뒤 유입되는 RFID 태그(200)의 수가 일정하고, RFID 리더(100)의 인식 영역(101)에 존재하는 RFID 태그(200)의 수가 일정하게 되어 프레임 크기가 일정하게 된다. 프레임 크기가 일정하게 되면

및

은 일정하게 유지될 수 있으므로, 근사값의 추정은 유효하다.The probability that the RFID tag 200 coming from the i-th frame becomes a lost RFID tag 200 that is not recognized by the RFID reader 100 and exits the recognition radius is

The frame size at the i-th frame

Probability of success when

,

And the number of frames experienced in the recognition area 101

It can be calculated using Equation 10 below. Equation 10 is

Calculate by approximating In the DFSA-based RFID tag recognition method for minimizing the loss of the moving RFID tag 200 according to an embodiment of the present invention, the frame size changes for each frame, but the number of RFID tags 200 introduced after a certain time passes. The number of RFID tags 200 existing in the recognition area 101 of the RFID reader 100 is constant, and the frame size is constant. If the frame size is constant

And

Can be kept constant, so the estimation of the approximation is valid.

는

을 최소로 하는 프레임 크기

을 사용하여 추정될 수 있다. 이는 아래의 수학식 11과 같이 표현될 수 있다.Next, the size of the next frame is determined (S106). Considering the relationship between the frame size and the number of frames experienced by the RFID tag 200, the frame size for minimizing the probability of loss estimated by the RFID reader 100 in order to determine the optimal frame size to reduce the lost RFID tag 200 is determined. Find and determine the frame size as a result. Substituting at least one frame size into Equation 11 below estimates a frame size that minimizes the probability of loss. Size of (i + 1) th frame to minimize the probability of loss

The

Frame size to minimize

Can be estimated using This can be expressed by Equation (11) below.

Finally, the RFID reader 100 determines whether an unrecognized RFID tag 200 exists in the recognition area 101 (S107). If there is no RFID tag 200 recognized in the recognition area 101, the RFID reader 100 terminates the recognition of the RFID tag 200. On the other hand, when the RFID reader 100 determines that the unrecognized RFID tag 200 exists in the recognition area 101, the RFID reader 100 proceeds again from the step S102 of performing the recognition of the RFID tag 200. At this time, if the RFID tag 200 continues to flow into the recognition area 101 of the RFID reader 100, the process proceeds again from step S101. The RFID reader 100 performs recognition of the RFID tag using the determined frame size (S102). The method of performing the RFID tag recognition using the determined frame size may use the method of performing the RFID tag in the conventional RFID tag recognition method of the DFSA method. After the recognition of the RFID tag, the method of determining the size of the next frame uses a DFSA-based RFID tag recognition method for minimizing the loss of the moving RFID tag 200 according to an embodiment of the present invention.

4 is a DFSA-based RFID tag recognition method and a conventional DFSA algorithm-based RFID tag to minimize the loss of the moving RFID tag 200 according to an embodiment of the present invention when the moving speed of the RFID tag 200 increases. It is a figure comparing the RFID tag recognition rate of the recognition method.

When the RFID tag 200 is distributed at a constant density and passes the recognition radius of the RFID reader 100 at a constant speed, the ratio of the number of successful RFID tags 200 to the total number of RFID tags 200 is recognized as a recognition rate. Defined. Simulation parameters according to the EPC global Class 1 Generation 2 standard were set and used as shown in Table 1 below. Referring to the simulation result of FIG. 4, the result of using the DFSA-based RFID tag recognition method for minimizing the loss of the moving RFID tag 200 according to an embodiment of the present invention is AMMT with C-ratio estimation and AMMT with zero estimation. 2 and DFSA with C-ratio estimation and DFSA with zero estimation are shown as a result of using a conventional frame determination method of DFSA. When using the DFSA-based RFID tag recognition method that minimizes the loss of the moving RFID tag 200 according to an embodiment of the present invention, it can be seen that the recognition rate is improved by 10% or more compared to the conventional frame determination method of the DFSA.

5 is a DFSA-based RFID tag recognition method for minimizing the loss of a moving RFID tag 200 according to an embodiment of the present invention and the conventional DFSA algorithm based RFID according to the number of successful RFID tags 200 A diagram comparing the recognition delay times of the tag recognition methods. The simulation result of FIG. 5 shows AMMT with C-ratio estimation and AMMT with zero estimation as a result of using a DFSA-based RFID tag recognition method for minimizing the loss of a moving RFID tag 200 according to an embodiment of the present invention. As a result of using the conventional frame determination method of DFSA, DFSA with C-ratio estimation and DFSA with zero estimation are shown.

Referring to FIG. 5, when the number of incoming RFID tags 200 increases, the number of slots when using a DFSA-based RFID tag recognition method for minimizing the loss of a moving RFID tag 200 according to an embodiment of the present invention. It can be seen that is reduced to 30% than the number of slots used in the conventional DFSA algorithm-based RFID tag recognition method.

Claims (16)

In the RFID tag recognition method using DFSA (Dynamic Framed Slotted ALOHA) method,
Introducing an RFID tag;
Determining, by the RFID reader, the frame size using the probability of loss of the RFID tag; And
Recognizing an RFID tag using a frame having the frame size,
The determining of the frame size by using the probability of loss of the RFID tag by the RFID reader estimates the number of frames to be experienced before the RFID tag leaves the recognition region of the RFID reader, and the RFID tag recognizes the recognition region of the RFID reader. RFID tag recognition method for estimating the probability of loss of the RFID tag by estimating the probability that it will not be recognized from the RFID reader in every frame to be experienced until the departure. The method according to claim 1,
And determining, by the RFID reader, the frame size using the probability of loss of the RFID tag, calculating the probability of loss of the RFID tag using the probability that the recognition of the RFID tag fails. 3. The method of claim 2,
The probability that the recognition of the RFID tag fails is calculated by subtracting the probability of successful recognition of the RFID tag from the overall probability, and the probability of the recognition of the RFID tag succeeding is that one RFID tag selects one slot and the remaining RFID tags are RFID tag recognition method characterized in that it is calculated by the probability of selecting a slot other than the slot. 3. The method of claim 2,
And a loss probability of the RFID tag is calculated using a probability that the response signal of the RFID tag is not identified by a channel error. 5. The method of claim 4,
And a probability that a response signal of the RFID tag is not transmitted by a channel error is calculated using a packet error rate. delete The method according to claim 1,
The determining of the frame size by using the probability of loss of the RFID tag by the RFID reader may include: recognition area of the RFID reader, moving speed of the RFID tag, and recognition area of the RFID reader using the current frame size. RFID tag recognition method characterized in estimating the number of frames to experience before leaving. The method of claim 7, wherein
The determining of the frame size by using the probability of loss of the RFID tag by the RFID reader may not recognize the RFID tag in one frame in the number of frames to be experienced until the estimated RFID tag leaves the recognition region of the RFID reader. Multiplying the missing probability to estimate the loss probability that the RFID tag will not be recognized by the RFID reader in every frame to be experienced until the RFID tag leaves the recognition region of the RFID reader. The method of claim 8,
The determining of the frame size by using the loss probability of the RFID tag by the RFID reader may select the size of the frame that minimizes the loss probability among the estimated at least one loss probability to determine the next frame size. RFID tag recognition method. In RFID tag recognition device using DFSA (Dynamic Framed Slotted ALOHA) method
A plurality of RFID tags;
An RFID tag transfer unit for moving the RFID tag; And
Includes an RFID reader,
The RFID reader determines the frame size using the estimated loss probability of the RFID tag, recognizes the RFID tag using the frame of the determined size,
The RFID reader estimates the number of frames to be experienced before the RFID tag leaves the recognition area of the RFID reader, and the probability that the RFID tag will not be recognized by the RFID reader in every frame to be experienced until the RFID tag leaves the recognition area of the RFID reader. And estimating a loss probability of the RFID tag by estimating a loss of the RFID tag. 11. The method of claim 10,
And the RFID reader calculates the probability of loss using a probability of failure to recognize an RFID tag. The method of claim 11,
And the RFID reader further estimates a loss probability of the RFID tag by further using a probability that the response signal of the RFID tag is not identified by a channel error. delete 11. The method of claim 10,
The RFID reader estimates the number of frames to be experienced before the RFID tag leaves the recognition region of the RFID reader using the recognition region of the RFID reader, the moving speed of the RFID tag, and the size of the current frame. Tag recognition device. 15. The method of claim 14,
The RFID reader multiplies the number of frames to be experienced until the estimated RFID tag leaves the recognition area of the RFID reader by the probability that the RFID tag is not recognized in one frame so that the RFID tag leaves the recognition area of the RFID reader. RFID tag recognition device, characterized in that for estimating the loss probability that will not be recognized from the RFID reader in every frame to be experienced. The method of claim 15,
And the RFID reader selects a size of a frame that minimizes the loss probability among the estimated at least one loss probability and determines the size of a next frame.

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