JP2024056261A - RF tag movement direction estimation system - Google Patents

Abstract

To provide an RF tag moving direction estimation system that can more accurately estimate a moving direction of an RF tag.SOLUTION: An RF tag moving direction estimation system 2 can acquire RSSI time-series data that is time-series data of reception signal intensity for a response signal from an RF tag, and PAV time-series data that is time-series data of a predetermined phase value related to the RF tag. The RF tag moving direction estimation system 2 generates characteristics of a radio wave environment according to the place at least within a target area through which the RF tag is assumed to pass so as to generate a time difference between peak timing of a phase value based on the PAV time-series data and peak timing of the reception signal intensity based on the RSSI time-series data. A moving direction of the RF tag is estimated by using the time difference between both of the pieces of peak timing.SELECTED DRAWING: Figure 3

Description

Application for application of Article 30, Paragraph 2 of the Patent Act has been filed. Presented at the 16th IEEE International Conference on RFID (IEEE RFID 2022) from May 17th to 19th, 2022. [Publications, etc.] Presented at the 191st Multimedia Communications and Distributed Processing, 103rd Mobile Computing and New Social Systems, and 89th Intelligent Transportation Systems and Smart Community Joint Research Symposium from May 26th to 27th, 2022.

The present invention relates to a system for estimating the direction of movement of an RF tag.

Traditionally, the logistics and apparel industries have used RFID (Radio Frequency Identification) that uses radio waves in the UHF (Ultra High Frequency) band to manage inventory and product checkout. RFID is a technology that enables individual identification of RF tags by wirelessly communicating between a reader and RF tag.

In recent years, the accuracy with which readers can read RF tags has improved, making it possible to estimate the state of an RF tag, such as whether it is moving or stationary.

As a system for estimating the movement direction of an RF tag, for example, a technology has been proposed in which multiple antennas are arranged in a plane, RF tags are read sequentially via these multiple antennas, and the movement direction of the RF tag is detected based on the position of the antenna that read the RF tag (see, for example, Patent Document 1, etc.).

JP 2014-69659 A

However, in systems that estimate the movement direction of RF tags, there is a demand for improved estimation accuracy of the movement direction.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide an RF tag movement direction estimation system that can estimate the movement direction of an RF tag with greater accuracy.

Below, each means suitable for achieving the above objective will be explained item by item. In addition, the specific effects of the corresponding means will be noted as necessary.

Means 1. An RF tag movement direction estimation system for estimating the movement direction of an RF tag, comprising:
a directional antenna arranged facing a predetermined target area and configured to be capable of transmitting a signal toward the target area and receiving a response signal transmitted from the RF tag in response to receiving the signal;
an RSSI acquisition means for acquiring RSSI time series data, which is time series data of the received signal strength by acquiring a received signal strength of the response signal received by the directional antenna;
a PAV acquisition means for acquiring a phase value that is a value corresponding to a phase difference between a signal transmitted by the directional antenna toward the target area and the response signal received by the directional antenna, thereby acquiring PAV time series data that is time series data of the phase value;
a non-uniformity generating means for generating non-uniformity in a radio wave environment related to communication between an RF tag located within the target area and the directional antenna, so as to generate a time difference between a peak timing of the phase value based on the PAV time series data and a peak timing of the received signal strength based on the RSSI time series data, thereby generating location-dependent characteristics of the radio wave environment at least within the target area;
An RF tag movement direction estimation system comprising: a movement direction estimation means for estimating the movement direction of an RF tag in the target area using the time difference between the peak timing of the phase value based on the PAV time series data and the peak timing of the received signal strength based on the RSSI time series data.

According to the above-mentioned means 1, the non-uniformity generating means generates non-uniformity in the radio wave environment related to the communication between the RF tag located within the target area and the directional antenna, thereby generating location-dependent characteristics of the radio wave environment at least within the target area. This makes it possible to more reliably generate a time difference between the peak timing of the phase value and the peak timing of the received signal strength. Then, the movement direction of the RF tag is estimated using the time difference between the peak timing of the phase value and the peak timing of the received signal strength. Therefore, the movement direction of the RF tag can be estimated with greater accuracy.

Furthermore, according to the above-mentioned means 1, it is not necessary to perform troublesome settings according to each environment, and it is possible to improve the ease of introducing the system. That is, even if the position of the RF tag in the target area is the same, the received signal strength and phase value may vary due to the influence of the material of the objects in the surrounding environment and the radio wave environment. Therefore, if it is possible to accurately estimate the movement direction of the RF tag using only one of the received signal strength and the phase value, it is necessary to perform detailed settings according to each environment. In contrast, the time difference between the peak timings of the phase value and the received signal strength hardly varies depending on the surrounding environment. Therefore, according to the above-mentioned means 1, it is not necessary to perform troublesome settings according to each environment, and it is possible to improve the ease of introducing the system.

The non-uniformity generating means may be configured with a directional antenna, as in Means 2 described below. Therefore, the non-uniformity generating means and the directional antenna do not necessarily need to be separate.

Means 2. The directional antenna is provided in such a manner that only one antenna is provided corresponding to the target area;
The RF tag movement direction estimation system described in means 1, characterized in that the non-uniformity generating means is composed of the directional antenna installed at an angle with respect to the expected movement direction of the RF tag in the target area.

According to the above-mentioned means 2, only one directional antenna is provided corresponding to the target area, and this one directional antenna is tilted with respect to the expected direction of movement of the RF tag to generate non-uniformity in the radio wave environment. Therefore, it is possible to generate non-uniformity in the radio wave environment by a relatively simple method, at a relatively low cost, and without requiring a large amount of space for installing the directional antenna. This reduces the workload and costs involved in introducing the system, and improves the flexibility of installation.

Means 3. The RF tag movement direction estimation system described in means 2, characterized in that the directional antenna is installed with an inclination of 30° to 50° with respect to the expected movement direction.

By using the above-mentioned method 3, it is possible to more easily obtain the peak timings of the phase value and the received signal strength, and to more reliably generate a large time difference between the peak timings. This makes it possible to further improve the accuracy of estimating the movement direction of the RF tag.

Means 4. The phase value that can be acquired by the PAV acquisition means is in a range from a predetermined minimum value to a predetermined maximum value,
A PAV correction means for correcting the phase value to generate corrected PAV time series data when one of the phase values included in the PAV time series data varies by a predetermined threshold value or more with respect to the phase value acquired immediately before the phase value,
The RF tag movement direction estimation system according to Means 1, characterized in that the peak timing of the phase value is obtained based on the corrected PAV time series data.

According to the above-mentioned means 4, the phase value that can be acquired by the PAV acquisition means is in the range from a predetermined minimum value to a predetermined maximum value. Therefore, when the RF tag is moving, if the phase value actually falls below the minimum value or exceeds the maximum value, the phase value acquired by the PAV acquisition means will vary significantly from the phase value acquired immediately before that phase value. Therefore, it may be relatively difficult to determine the peak timing of the phase value by using the acquired phase value as it is.

In this regard, according to the above-mentioned means 4, when obtaining the peak timing of the phase value, the corrected PAV time series data obtained by correcting the phase value is used. Therefore, the peak timing of the phase value can be obtained more easily and accurately. As a result, the moving direction of the RF tag can be estimated with even greater accuracy.

Means 5. An approximation equation calculation means for generating a quadratic approximation equation that approximates the change in the received signal strength in the RSSI time series data based on the RSSI time series data,
the approximation formula calculation means generates the quadratic approximation formula using a least squares method;
The RF tag movement direction estimation system according to Means 1, characterized in that the peak timing of the received signal strength is obtained based on the quadratic approximation formula.

When trying to determine the peak timing of the received signal strength based on actual measurement values, it can be difficult to obtain the accurate peak timing when the same value of the received signal strength is continuously measured at or near the peak timing.

In this regard, according to the above-mentioned means 5, the peak timing of the received signal strength is obtained based on a quadratic approximation equation generated using the least squares method. Therefore, the peak timing of the received signal strength can be obtained more accurately. As a result, the moving direction of the RF tag can be estimated with even greater accuracy.

The technical matters related to each of the above means may be combined as appropriate. Therefore, for example, the technical matters related to the above means 2 or 3 may be combined with the technical matters related to the above means 4 or 5.

FIG. 1 is a schematic perspective view illustrating a store and merchandise and the like in the store. FIG. 1 is a schematic plan view illustrating a store and merchandise within the store. FIG. 2 is a block diagram showing a functional configuration of the anti-theft system. FIG. 2 is a schematic perspective view showing the position of a directional antenna, etc. FIG. 2 is a schematic plan view showing the position of a directional antenna, etc. FIG. 1 is a schematic diagram showing a general configuration of an RF tag. 1 is a graph showing the gain of a directional antenna. 1 is a graph showing an example of PAV time-series data. 1 is a graph showing an example of RSSI time-series data. 11 is a graph for explaining correction of a phase value. 11 is a graph for explaining correction of a phase value. 11 is a graph showing an example of corrected PAV time series data, etc. 11 is a graph showing an example of a quadratic approximation equation corresponding to RSSI time series data. 13 is a graph showing simplified corrected PAV time series data and a quadratic approximation equation when an RF tag moves to the left. 13 is a graph showing simplified corrected PAV time series data and a quadratic approximation equation when an RF tag moves to the right. FIG. 2 is a schematic perspective view showing a schematic configuration of a test device. FIG. 2 is a schematic plan view for explaining the inclination angle and the like. FIG. FIG. 11 is a schematic perspective view for explaining a directional antenna constituting the nonuniformity generating means in another embodiment. FIG. 11 is a schematic plan view for explaining a directional antenna constituting the nonuniformity generating means in another embodiment. FIG. 11 is a schematic plan view for explaining the arrangement position of a directional antenna in another embodiment. FIG. 11 is a schematic perspective view for explaining the arrangement position of a directional antenna in another embodiment. FIG. 11 is a schematic perspective view for explaining the arrangement position of a directional antenna in another embodiment. FIG. 11 is a schematic perspective view for explaining the arrangement position of a directional antenna in another embodiment.

One embodiment will be described below with reference to the drawings. As shown in Figs. 1 and 2, the theft prevention system 1 is applied to a store 100, such as an apparel shop, and is a system for preventing various products 101, such as clothes, from being taken out of the store 100 and stolen. Each product 101 is pre-attached with a specific RF tag 102 (see Fig. 6). First, prior to describing the theft prevention system 1, the RF tag 102 will be described.

As shown in FIG. 6, the RF tag 102 has an integrated circuit 102a for storing information and an antenna 102b connected to the integrated circuit 102a. The integrated circuit 102a stores tag identification information for identifying the RF tag 102 (e.g., Electronic Production Code (EPC) etc.) and product identification information for identifying the product 101 to which the RF tag 102 is attached.

The antenna 102b is provided for reading information stored in the integrated circuit 102a and writing information to the integrated circuit 102a from outside without contact. The antenna 102b has the function of receiving a signal (radio wave) transmitted from the directional antenna 22 described below, and transmitting (transmitting) a predetermined response signal in response to the signal. The response signal includes at least the tag identification information.

Next, we will explain the theft prevention system 1. As shown in FIG. 3, the theft prevention system 1 includes an RF tag movement direction estimation system 2 and a management system 3.

The RF tag movement direction estimation system 2 is a system for estimating the movement direction of an RF tag 102 attached to a product 101, in particular the movement direction of the RF tag 102 passing through a gate 100a described below. The RF tag movement direction estimation system 2 comprises a reader/writer 21, a directional antenna 22, and a data processing system 23. In this embodiment, the reader/writer 21 constitutes the "RSSI acquisition means" and the "PAV acquisition means".

The reader/writer 21 is a device for writing information to the integrated circuit 102a of the RF tag 102 and reading information stored in the integrated circuit 102a. For example, a Speedway Revolution R420 manufactured by Impinj can be used as the reader/writer 21. The reader/writer 21 is controlled by a control module 231 described later, and controls the directional antenna 22 to transmit a signal (Query command) for acquiring information stored in the RF tag 102 (integrated circuit 102a) at predetermined short intervals (for example, every several ms to several tens of ms). A response signal transmitted from the RF tag 102 in response to the transmission of the signal (Query command) is received by the directional antenna 22. As described above, the response signal transmitted from the RF tag 102 includes tag identification information (EPC) and the like.

The reader/writer 21 also acquires the received signal strength (Received Signal Strength Indicator (RSSI)) and phase angle values for the response signal. The phase value is a value corresponding to the phase difference between the signal transmitted from the directional antenna 22 toward the target area 100b described below, and the response signal transmitted from the RF tag 102 in response to this signal and received by the directional antenna 22. The received signal strength and phase values acquired by the reader/writer 21 are associated with tag identification information and sequentially stored in the read information storage device 232 described below via the control module 231.

In this embodiment, the phase value acquired by the reader/writer 21 corresponds to an inverted phase difference. Of course, the reader/writer 21 may be configured to acquire a value corresponding to a non-inverted phase difference. In this embodiment, the phase value that can be acquired by the reader/writer 21 ranges from a predetermined minimum value (e.g., 0) to a predetermined maximum value (e.g., 2π).

The directional antenna 22 is a planar antenna that transmits a signal (radio wave) toward the target area 100b and receives a response signal transmitted from the RF tag 102 in response to receiving the signal. For example, the Yap-101P manufactured by Yeon Corporation can be used as the directional antenna 22. The reason for using the directional antenna 22 is to ensure that the received signal strength acquired by the reader/writer 21 is sufficiently large. The received signal strength is a parameter related to the received power from the directional antenna 22, and therefore varies depending on the gain of the directional antenna 22.

As shown in Figures 1, 4, 5, etc., the directional antenna 22 is arranged on the side of the gate 100a that constitutes the entrance/exit of the store 100, facing a specified target area 100b. In this embodiment, the target area 100b is an area located between a pair of fences that constitute the gate 100a, and is an area through which the RF tag 102 attached to the product 101 is expected to pass. Note that Figure 4 etc. shows the target area 100b in a rough manner. Also, in this embodiment, only one directional antenna 22 is provided corresponding to the target area 100b.

The directional antenna 22 has a maximum gain in the directional front direction (0° direction), and the gain is nearly symmetrical on the left and right sides with respect to the directional front direction (see Figure 7). The directional antenna 22 is installed tilted with respect to the expected movement direction AD of the RF tag 102 in the target area 100b (the direction indicated by the black arrow in Figures 4 and 5, etc.). In this embodiment, the tilt angle α of the directional antenna 22 with respect to the expected movement direction AD is set to be 30° or more and 50° or less.

By tilting the directional antenna 22 as described above, an imbalance in gain occurs between the left and right sides of the directional antenna 22 at least in the target area 100b, generating non-uniformity in the radio wave environment related to communication between the directional antenna 22 and the RF tags 102 located within the target area 100b. As a result, location-dependent characteristics of the radio wave environment (particularly received signal strength) occur at least within the target area 100b. In this embodiment, the "non-uniformity generating means" is constituted by the directional antenna 22 that is installed at an angle with respect to the expected movement direction AD.

The above-mentioned location-dependent characteristics of the radio wave environment result in different characteristics in the way the received signal strength changes depending on the position of the RF tag 102 and in the way the phase value changes depending on the position of the RF tag 102. As a result, a time difference can be created between the peak timing of the phase value and the peak timing of the received signal strength, and this time difference can be made relatively large.

More specifically, since the phase value is a parameter related to the wavelength of the signal and the distance between the directional antenna 22 and the RF tag 102, it is strongly affected by the relative positional relationship between the directional antenna 22 and the RF tag 102. Therefore, when the RF tag 102 passes through the target area 100b, the timing at which the phase value peaks in the corrected PAV time series data (see FIG. 12) described below, which corresponds to the change in the phase value, is when the directional antenna 22 and the RF tag 102 are closest to each other. In this embodiment, since the phase value corresponds to an inverted phase difference, the phase value peaks upward, but if the phase value corresponds to a non-inverted phase difference, the phase value peaks downward. However, regardless of the type of peak, the timing at which the peak occurs remains the same.

On the other hand, as described above, the received signal strength varies depending on the gain of the directional antenna 22. Therefore, when the RF tag 102 passes through the target area 100b, in the quadratic approximation equation (see FIG. 13) described below that corresponds to the change in the received signal strength, the timing at which the received signal strength peaks is when the RF tag 102 passes in front of the directional antenna 22.

By creating location-dependent characteristics in the radio wave environment in this way, it is possible to create different characteristics in the way the received signal strength changes depending on the position of the RF tag 102 and in the way the phase value changes depending on the position of the RF tag 102, and thus it is possible to more reliably create a time difference between the peak timing of the phase value and the peak timing of the received signal strength.

The data processing system 23 is composed of a computer including a CPU (Central Processing Unit) that executes a predetermined arithmetic process, a ROM (Read Only Memory) that stores various programs and fixed value data, a RAM (Random Access Memory) that temporarily stores various data when executing various arithmetic processes, a storage device for storing information, and peripheral circuits thereof, an input/output device, and a display device. The data processing system 23 includes a control module 231, a read information storage device 232, a PAV correction unit 233, an approximate expression calculation unit 234, and a moving direction estimation unit 235. In this embodiment, the PAV correction unit 233 constitutes the "PAV correction means", the approximate expression calculation unit 234 constitutes the "approximate expression calculation means", and the moving direction estimation unit 235 constitutes the "moving direction estimation means". The various functions of the control module 231, the PAV correction unit 233, the approximate expression calculation unit 234, and the moving direction estimation unit 235 are realized by the cooperation of various hardware such as the CPU, ROM, and RAM with software previously stored in the storage device.

The control module 231 controls the operation of the reader/writer 21, and stores the received signal strength and phase value acquired by the reader/writer 21 in the read information storage device 232 in association with tag identification information also acquired by the reader/writer 21. This makes it possible to grasp the transition over time of the received signal strength and phase value for the RF tag 102 passing through the target area 100b.

The read information storage device 232 is composed of a HDD (Hard Disk Drive) or SSD (Solid State Drive), and sequentially stores received signal strength and phase values. As a result, the read information storage device 232 stores PAV time series data (see FIG. 8), which is time series data of phase values (Phase Angle Values), and RSSI time series data (see FIG. 9), which is time series data of received signal strength (RSSI). The RSSI time series data and PAV time series data are managed for each individual RF tag 102.

As mentioned above, the phase values that can be obtained by the reader/writer 21 range from a predetermined minimum value to a predetermined maximum value, so if the actual phase value falls below the minimum value or exceeds the maximum value, the phase value in the PAV time series data will fluctuate significantly. Also, in the RSSI time series data, the received signal strength measured continuously at or near the peak timing may have the same value.

In addition, the read information storage device 232 can store the corrected PAV time series data (described below) generated by the PAV correction unit 233 and the quadratic approximation equation (described below) generated by the approximation equation calculation unit 234.

The PAV correction unit 233 corrects the PAV time series data stored in the read information storage device 232 to generate corrected PAV time series data. More specifically, when a phase value of 1 included in the PAV time series data is increased by a predetermined threshold value P(th) (e.g., 0.55π) or more from the phase value acquired immediately before the phase value (the immediately preceding phase value), the PAV correction unit 233 performs a correction to subtract a predetermined correction value (e.g., 2π) from each phase value acquired after the phase value of 1. In other words, when a value P(diff) obtained by subtracting the immediately preceding phase value from the phase value of 1 is equal to or greater than a threshold value+P(th), the PAV correction unit 233 performs a correction to subtract a predetermined correction value from each phase value acquired after the phase value of 1 (see FIG. 10).

On the other hand, when a phase value of 1 included in the PAV time series data is decreased by the threshold value P(th) (e.g., 0.55π) or more from the immediately preceding phase value, the PAV correction unit 233 performs a correction by adding a predetermined correction value (e.g., 2π) to each phase value acquired after the phase value of 1. In other words, when a value P(diff) obtained by subtracting the immediately preceding phase value from the phase value of 1 is equal to or less than -P(th), the PAV correction unit 233 performs a correction by adding a predetermined correction value to each phase value acquired after the phase value of 1 (see FIG. 11).

By correcting the phase values as described above, it is possible to generate corrected PAV time series data (see FIG. 12) in which the phase values vary smoothly. In FIG. 12, an example of the corrected PAV time series data is shown by a thick line. Note that in FIG. 12, for reference, an example of the PAV time series data before correction is shown by a thin line.

The approximation calculation unit 234 generates a quadratic approximation equation that approximates the change in the received signal strength in the RSSI time series data based on the RSSI time series data stored in the read information storage device 232. More specifically, the approximation calculation unit 234 generates the quadratic approximation equation using the least squares method. The least squares method is a technique for finding f(x) that minimizes the following equation (1) when the model function is f(x).

The approximation calculation unit 234 uses the multiple received signal strengths that make up the RSSI time series data as yi in formula (1) to generate a quadratic approximation formula (see FIG. 13). FIG. 13 shows an example of the quadratic approximation formula.

The movement direction estimation unit 235 estimates the movement direction of the RF tag 102 in the target area 100b. In this embodiment, the movement direction estimation unit 235 estimates whether the movement direction of the RF tag 102 is to the left (direction from inside the store 100 toward the outside of the store 100) or to the right (direction from outside the store 100 toward inside the store 100) when viewed from a position sandwiching the target area 100b between itself and the directional antenna 22.

When estimating the movement direction of the RF tag 102, the movement direction estimation unit 235 obtains the peak timing Tp of the phase value based on the corrected PAV time series data, as shown in Figures 14 and 15. In Figures 14 and 15, the simplified corrected PAV time series data is shown with a thin line, and the simplified quadratic approximation formula is shown with a thick line. As described above, the corrected PAV time series data is generated from the PAV time series data, so that it can be said that the movement direction estimation unit 235 obtains the peak timing Tp of the phase value based on the PAV time series data.

The moving direction estimation unit 235 also obtains the peak timing Tr of the received signal strength based on the quadratic approximation formula. As described above, the quadratic approximation formula is generated from the RSSI time series data, so that the moving direction estimation unit 235 can be said to obtain the peak timing Tr of the received signal strength based on the RSSI time series data.

Next, the movement direction estimation unit 235 calculates the time difference T(diff) (=Tp-Tr) between the peak timing Tp of the phase value and the peak timing Tp of the received signal strength.

Here, when the RF tag 102 moves leftward (from inside the store 100 toward the outside of the store 100) in the target area 100b, the RF tag 102 first passes in front of the direction of the directional antenna 22, and then comes closest to the directional antenna 22. Therefore, when the RF tag 102 moves leftward, the peak timing Tp of the phase value appears after the peak timing Tr of the received signal strength, so Tp>Tr is satisfied (see FIG. 14). Therefore, when the calculated time difference T(diff) is a positive number, the movement direction estimation unit 235 estimates that the RF tag 102 has moved leftward.

On the other hand, when the RF tag 102 moves to the right (from outside the store 100 toward inside the store 100) in the target area 100b, the RF tag 102 first comes closest to the directional antenna 22 and then passes in front of the direction of the directional antenna 22. Therefore, when the RF tag 102 moves to the right, the peak timing Tr of the received signal strength appears after the peak timing Tp of the phase value, so Tp<Tr is satisfied (see FIG. 15). Therefore, when the calculated time difference T(diff) is a negative number, the movement direction estimation unit 235 estimates that the RF tag 102 has moved to the right.

The result of the estimation performed by the movement direction estimation unit 235 regarding the movement direction of the RF tag 102 is sent to the management system 3 (particularly the determination unit 33 described later) in association with the tag identification information of the RF tag 102 for which the movement direction was estimated.

The PAV correction unit 233, the approximation calculation unit 234, and the movement direction estimation unit 235 generate the corrected PAV time series data and the quadratic approximation equation, and estimate the movement direction of the RF tag 102 when a predetermined condition is satisfied. Examples of the predetermined condition include the RF tag 102, whose movement direction is to be estimated, going out of the communication range, a predetermined time having passed since the start of signal transmission and reception, the number of pieces of data on the received signal strength or phase value reaching a predetermined number or more, and a predetermined time having passed since the acquired received signal strength or phase value exceeded a predetermined threshold. Of course, conditions other than those mentioned above may be used as the predetermined condition.

Next, the management system 3 and the like will be described. The management system 3 is a system that checks whether the payment process for the product 101 taken from inside the store 100 to outside the store 100 has been properly completed, and performs a predetermined notification process if the payment process for the product 101 has not been properly completed. The management system 3 can be configured as a computer system having a CPU, ROM, RAM, etc. Before going into a detailed description of the management system 3, the product information storage device 4 and the payment device 5 used for payment of the product 101 will first be described.

As shown in FIG. 3, the product information storage device 4 and the settlement device 5 are configured to be able to send and receive various information. The product information storage device 4 stores at least product identification information and product prices in association with each other. When product identification information is sent from the settlement device 5, the product information storage device 4 returns information regarding the product price associated with the product identification information to the settlement device 5. Note that the management system 3 may be configured to include the product information storage device 4.

The settlement device 5 is installed in the store 100 (see FIG. 1, etc.) and is a device used to pay for the product 101 when purchasing the product 101. The settlement device 5 in this embodiment is a so-called self-checkout, and is equipped with a predetermined product storage space, a device for reading information stored in the RF tag 102, an information display device, and a payment receiving device. When the product 101 is stored in the product storage space, the settlement device 5 reads the information of the RF tag 102 attached to the product 101. The settlement device 5 then transmits the product identification information contained in the read information to the product information storage device 4, and receives information on the product price from the product information storage device 4. This product price indicates the price of the product 101 to which the RF tag 102 whose information was read is attached. When the settlement device 5 obtains the product prices for all the products 101 stored in the product storage space, it calculates the payment amount by adding up the obtained product prices, etc. The settlement device 5 also displays the payment amount on the display device.

Then, when the price of the product 101 is paid for by cash, credit card, etc. using the receiving device, the settlement device 5 transmits the tag identification information related to the RF tag 102 attached to the product 101 for which payment has been completed to the settlement information storage device 31 in the management system 3, which will be described below.

Next, the management system 3 will be described in more detail. The management system 3 is configured to be able to transmit and receive various signals between the RF tag movement direction estimation system 2 and the settlement device 5, and includes a settlement information storage device 31, a notification unit 32, and a determination unit 33.

The settlement information storage device 31 stores tag identification information transmitted from the settlement device 5. In other words, the settlement information storage device 31 stores information for identifying the RF tag 102 attached to the product 101 for which payment has been completed.

The notification unit 32 has a function of notifying the outside that an incident that may be theft has occurred. In this embodiment, the notification unit 32 notifies the outside (employees, etc.) of the occurrence of the incident by transmitting information indicating the occurrence of the incident to a terminal device carried by the employee, etc. Note that the notification unit 32 may be any unit capable of notifying the outside of the occurrence of the incident, and may notify the outside of the occurrence of the incident using, for example, audio or visual information.

The determination unit 33 determines whether a suspected theft has occurred based on the information sent from the movement direction estimation unit 235 and the information stored in the payment information storage device 31. More specifically, when the determination unit 33 receives information from the movement direction estimation unit 235 indicating movement to the left (from inside the store 100 toward the outside of the store 100) as the estimation result regarding the movement direction of the RF tag 102, the determination unit 33 executes a predetermined confirmation process. In other words, when the movement direction estimation unit 235 estimates that the product 101 and RF tag 102 are moving as if they are being taken out from inside the store 100 to the outside of the store 100, the determination unit 33 executes a predetermined confirmation process.

In the confirmation process, the tag identification information of the RF tag 102 associated with the estimation result is used to determine whether or not payment for the product 101 to which the RF tag 102 is attached has been completed. That is, the determination unit 33 refers to the tag identification information stored in the settlement information storage device 31 and determines whether or not tag identification information identical to the tag identification information of the RF tag 102 associated with the estimation result is stored in the settlement information storage device 31. Then, if tag identification information identical to the tag identification information of the RF tag 102 associated with the estimation result is stored in the settlement information storage device 31, the determination unit 33 determines that payment for the product 101 to which the RF tag 102 is attached has been completed.

On the other hand, if the same tag identification information as that of the RF tag 102 associated with the estimation result is not stored in the payment information storage device 31, the determination unit 33 determines that payment for the product 101 to which the RF tag 102 is attached has not been completed, and activates the notification unit 32. This causes an external notification to be sent that a suspected theft has occurred.

In addition, in this embodiment, when the determination unit 33 receives information from the movement direction estimation unit 235 indicating that the RF tag 102 is moving to the right (from outside the store 100 toward inside the store 100) as an estimation result regarding the movement direction of the RF tag 102, the determination unit 33 does not execute the confirmation process.

As described above in detail, according to this embodiment, the directional antenna 22 installed at an angle to the expected movement direction AD generates non-uniformity in the radio wave environment related to communication between the directional antenna 22 and the RF tag 102 located in the target area 100b, thereby generating location-dependent characteristics of the radio wave environment at least within the target area 100b. This makes it possible to more reliably generate a time difference between the peak timing of the phase value and the peak timing of the received signal strength. The movement direction estimation unit 235 then estimates the movement direction of the RF tag 102 using the time difference between the peak timing of the phase value and the peak timing of the received signal strength. Therefore, the movement direction of the RF tag 102 can be estimated more accurately.

In addition, according to this embodiment, there is no need to perform troublesome settings according to each environment, and the ease of introducing the RF tag movement direction estimation system 2 can be improved. That is, even if the position of the RF tag 102 in the target area 100b is the same, the received signal strength and phase value may vary due to the influence of the material of the objects in the surrounding environment and the radio wave environment. Therefore, in order to be able to accurately estimate the movement direction of the RF tag 102 using only one of the received signal strength and the phase value, it is necessary to perform detailed settings according to each environment. In contrast, the time difference between the peak timings of the phase value and the received signal strength hardly varies depending on the surrounding environment. Therefore, according to this embodiment, there is no need to perform troublesome settings according to each environment, and it is possible to improve the ease of introducing the RF tag movement direction estimation system 2.

In addition, only one directional antenna 22 is provided corresponding to the target area 100b, and this one directional antenna 22 is tilted with respect to the expected movement direction AD of the RF tag 102 to create non-uniformity in the radio wave environment. Therefore, non-uniformity can be created in the radio wave environment by a relatively simple method, at a relatively low cost, and without requiring a large amount of space for installing the directional antenna 22. This reduces the workload and costs associated with introducing the RF tag movement direction estimation system 2, and improves the freedom of installation.

In addition, since the inclination angle α of the directional antenna 22 with respect to the assumed moving direction AD is set to 30° or more and 50° or less, the phase value and the peak timing of the received signal strength can be obtained more easily, and it is more reliably possible to generate a large time difference between the peak timings. Therefore, the estimation accuracy of the moving direction of the RF tag 102 can be further improved.

In addition, in this embodiment, corrected PAV time series data obtained by correcting the phase value is used to obtain the peak timing of the phase value. Therefore, the peak timing of the phase value can be obtained more easily and accurately. As a result, the movement direction of the RF tag 102 can be estimated with even greater accuracy.

Furthermore, in this embodiment, the peak timing of the received signal strength is obtained based on a quadratic approximation equation generated using the least squares method. Therefore, the peak timing of the received signal strength can be obtained more accurately. As a result, the movement direction of the RF tag 102 can be estimated with even greater accuracy.

Next, to confirm the effects of the above embodiment, the following test was conducted. That is, as shown in FIG. 16, the inclination angle α (see FIG. 17) of the directional antenna 22 with respect to the assumed moving direction AD was changed by 10° increments within the range of 10° to 70°, and a predetermined slider SL to which the RF tag 102 was attached was moved along the assumed moving direction AD, so that the RF tag 102 was moved from left to right (left to right) and from right to left (right to left) 100 times each. Then, the number of times (number of correct answers) that the moving direction of the RF tag 102 estimated by the moving direction estimation unit 235 matched the actual moving direction of the RF tag 102 was found, and the estimation accuracy of the moving direction (= number of correct answers/100) was calculated based on the number of correct answers.

This test was conducted at a place (Place A) where there were relatively few objects around the directional antenna 22, and at a place (Place B) where there were relatively many objects around the directional antenna 22. The moving speed of the RF tag 102 was set to 0.5 m/s, and the height from the floor to the directional antenna 22 (the center) and the height from the floor to the RF tag 102 were both set to 0.6 m. Furthermore, the position of the slider SL was set so that the shortest distance from the directional antenna 22 to the RF tag 102 was 0.9 m. Figure 18 shows the estimation accuracy when the RF tag 102 was moved from left to right and the estimation accuracy when the RF tag 102 was moved from right to left in each of Place A and Place B.

As shown in Figure 18, the estimation accuracy was 90% or higher for all inclination angles α, confirming that the movement direction of the RF tag 102 can be estimated with high accuracy.

In addition, when the inclination angle α is set to 30° or more and 50° or less, the estimation accuracy is 100%, and it was found that the movement direction of the RF tag 102 can be estimated with extremely high accuracy. This is thought to be because the time difference between the peak timing of the phase value and the peak timing of the received signal strength becomes more likely to appear.

From the above test results, it can be said that in order to be able to accurately estimate the movement direction of the RF tag 102, it is preferable to generate characteristics of the radio wave environment depending on the location by tilting the directional antenna 22, etc., and to estimate the movement direction of the RF tag 102 using the time difference between the peak timings of the phase value and the received signal strength.

In order to further improve the accuracy of estimating the movement direction of the RF tag 102, it is preferable to set the inclination angle α of the directional antenna 22 with respect to the assumed movement direction AD to be greater than or equal to 30° and less than or equal to 50°.

The present invention is not limited to the above embodiment, and may be implemented, for example, as follows. Of course, other applications and modifications not exemplified below are also possible.

(a) In the above embodiment, one directional antenna 22 is disposed to the side of the target area 100b, but it may be disposed above or below the target area 100b.

(b) In the above embodiment, the "non-uniformity generating means" is constituted by the directional antenna 22 that is installed at an angle with respect to the expected moving direction AD, but the "non-uniformity generating means" may be any means that generates location-dependent characteristics of the radio wave environment at least within the target area 100b, and generates a time difference between the peak timing of the phase value and the peak timing of the received signal strength.

Therefore, for example, as shown in Figures 19 and 20, the "non-uniformity generating means" may be configured by a plurality of directional antennas 221, 222 arranged in a positional relationship within the target area 100b such that the transmitted signals interfere with each other and are configured to generate a time difference between the peak timings of the received signal strength and phase value. In this case, the same signal may be transmitted from each of the directional antennas 221, 222 to cause interference between these signals, or signals with different phases and amplitudes may be transmitted from each of the directional antennas 221, 222 to more reliably cause interference between the signals and more reliably (more consciously) generate location-specific characteristics of the radio wave environment at least within the target area 100b.

Furthermore, the "non-uniformity generating means" may be configured with multiple directional antennas configured to dynamically control the phase and amplitude of the signal transmitted from each antenna, thereby sending signals (radio waves) in a beam shape (concentrated) to a specific range within the target area 100b, thereby generating a time difference between the peak timings of the received signal strength and phase value. In this case, a smart array antenna may be used instead of multiple directional antennas.

In addition, the "non-uniformity generating means" may be constituted by a directional antenna that has been processed to generate location-specific characteristics of the radio wave environment at least within the target area 100b and generate a time difference in the peak timing of the received signal strength and phase value. Examples of such directional antennas include those that have different gain trends on the left and right sides of the directional front direction (for example, the gain is relatively high on the right side, while the gain is relatively low on the left side).

When multiple directional antennas 221, 222 are used, the directional antennas 221, 222 may be arranged side by side along the expected movement direction AD as shown in Figures 19 and 20, or the directional antennas 221, 222 may be arranged on either side of the target area 100b as shown in Figure 21.

Furthermore, as shown in FIG. 22, the directional antennas 221, 222 may be arranged at positions sandwiching the target area 100b from above and below. In this case, one directional antenna 222 may be arranged under the floor, etc. Also, as shown in FIG. 23, one directional antenna 221 may be arranged on the side of the target area 100b, and the other directional antenna 222 may be arranged above or below the target area 100b. Furthermore, as shown in FIG. 24, one directional antenna 221 may be arranged on the side of the target area 100b, and the other directional antenna 222 may be arranged in front of or behind the target area 100b along the assumed movement direction AD.

In addition, when multiple directional antennas 221, 222 are used, the reader/writer 21 may acquire the received signal strength and phase value based on a signal received by any of the multiple directional antennas 221, 222, or may acquire the received signal strength and phase value based on a signal obtained by combining the signals received by the multiple directional antennas 221, 222.

Of course, the number of directional antennas is not limited to one or two, but may be three or more.

(c) In the above embodiment, the RF tag movement direction estimation system 2 is applied to an anti-theft system 1, but the application of the RF tag movement direction estimation system is not limited to this.

Therefore, for example, the RF tag movement direction estimation system may be applied to inventory management in a warehouse, employee attendance management, and employee presence management.

When applying the RF tag movement direction estimation system to inventory management in a warehouse, for example, a directional antenna is placed corresponding to the entrance/exit of the warehouse, and the movement direction of the RF tag attached to the product at the entrance/exit is estimated based on the phase value and received signal strength acquired via the directional antenna. In this configuration, if it is estimated that the product and therefore the RF tag have moved to the left (from inside the warehouse to outside the warehouse), the inventory quantity for that product is decreased by one, whereas if it is estimated that the product and therefore the RF tag have moved to the right (from outside the warehouse to inside the warehouse), the inventory quantity for that product is increased by one, and other such processes can be performed to manage inventory in the warehouse.

When applying the RF tag movement direction estimation system to the attendance management of employees, for example, a directional antenna is placed corresponding to the entrance/exit gate of the employee, and the movement direction of the RF tag carried by the employee at the entrance/exit gate is estimated based on the phase value and received signal strength acquired through the directional antenna. In this configuration, if it is estimated that the employee or RF tag has moved to the left (e.g., from inside the company to outside the company), the employee is deemed to have left work, whereas if it is estimated that the employee or RF tag has moved to the right (e.g., from outside the company to inside the company), the employee is deemed to have arrived at work. This allows the attendance management of employees, etc.

Furthermore, when the RF tag movement direction estimation system is applied to the presence management of employees, etc., a directional antenna is arranged corresponding to the entrance/exit of a room, and the movement direction of the RF tag carried by the employee, etc. at the entrance/exit is estimated based on the phase value and received signal strength acquired via the directional antenna. In this configuration, if it is estimated that the employee, etc. and the RF tag have moved to the left (e.g., from inside the room to outside the room), it is determined that the employee, etc. has left the room, whereas if it is estimated that the employee, etc. and the RF tag have moved to the right (e.g., from outside the room to inside the room), it is determined that the employee, etc. has entered the room, thereby enabling the presence management of employees, etc.

The RF tag movement direction estimation system may be used to determine whether a purchased item has moved from inside the store to outside the store, thereby making it possible to estimate whether any items have been left behind in the store. For example, the determination unit 33 may compare the tag identification information of an RF tag 102 that is estimated by the movement direction estimation unit 235 to have moved to the left (from inside the store 100 to outside the store 100) at predetermined time intervals with the tag identification information stored in the payment information storage device 31, making it possible to estimate whether any items 101 (i.e., items left behind) have not been taken outside the store 100 despite the fact that payment has been completed.

Of course, the RF tag movement direction estimation system may also be applied to applications other than those mentioned above.

2...RF tag movement direction estimation system, 21...reader/writer (RSSI acquisition means, PAV acquisition means), 22...directional antenna (non-uniformity generation means), 100b...target area, 102...RF tag, 233...PAV correction unit (PAV correction means), 234...approximation equation calculation unit (approximation equation calculation means), 235...movement direction estimation unit (movement direction estimation means).

Claims (5)

An RF tag movement direction estimation system for estimating the movement direction of an RF tag, comprising:
a directional antenna arranged facing a predetermined target area and configured to be capable of transmitting a signal toward the target area and receiving a response signal transmitted from the RF tag in response to receiving the signal;
an RSSI acquisition means for acquiring RSSI time series data, which is time series data of the received signal strength by acquiring a received signal strength of the response signal received by the directional antenna;
a PAV acquisition means for acquiring a phase value that is a value corresponding to a phase difference between a signal transmitted by the directional antenna toward the target area and the response signal received by the directional antenna, thereby acquiring PAV time series data that is time series data of the phase value;
a non-uniformity generating means for generating non-uniformity in a radio wave environment related to communication between an RF tag located within the target area and the directional antenna, so as to generate a time difference between a peak timing of the phase value based on the PAV time series data and a peak timing of the received signal strength based on the RSSI time series data, thereby generating location-dependent characteristics of the radio wave environment at least within the target area;
An RF tag movement direction estimation system comprising: a movement direction estimation means for estimating the movement direction of an RF tag in the target area using the time difference between the peak timing of the phase value based on the PAV time series data and the peak timing of the received signal strength based on the RSSI time series data. the directional antenna is provided in such a manner that only one antenna corresponds to the target area;
The RF tag movement direction estimation system according to claim 1, characterized in that the non-uniformity generating means is composed of the directional antenna installed at an angle with respect to the expected movement direction of the RF tag in the target area. The RF tag movement direction estimation system according to claim 2, characterized in that the directional antenna is installed at an angle of 30° to 50° with respect to the expected movement direction. the phase value that can be acquired by the PAV acquisition means is in a range from a predetermined minimum value to a predetermined maximum value,
A PAV correction means for correcting the phase value to generate corrected PAV time series data when one of the phase values included in the PAV time series data varies by a predetermined threshold value or more with respect to the phase value acquired immediately before the phase value,
2. The RF tag moving direction estimation system according to claim 1, wherein the peak timing of the phase value is obtained based on the corrected PAV time series data. an approximation equation calculation means for generating a quadratic approximation equation approximating a change in the received signal strength in the RSSI time series data based on the RSSI time series data;
the approximation formula calculation means generates the quadratic approximation formula using a least squares method;
2. The RF tag movement direction estimation system according to claim 1, wherein the peak timing of the received signal strength is obtained based on the quadratic approximation formula.

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