A method for measuring speed in a ultra-high frequency RFID system

Abstract

The present invention relates to a method for measuring the speed of a ultra-high frequency RFID system, belonging to the field of radio frequency identification. In the present invention, the antenna of the RFID reading device is deployed beside or directly above the channel to be monitored, and is directed towards the channel to be monitored; the ultra-high frequency RFID reader is used to collect the tag data and phase information of the RFID tags attached to the object to be measured for speed, and record them together with the timestamp information when the data is collected; the collected tag data information is sorted by tag to obtain the phase and timestamp information of each tag; the tag data and phase information of the collected RFID tags are processed to calculate the moving speed of the object attached with the RFID tags. The method proposed by the present invention has the characteristics of small computational amount, high real-time performance and being easy to be integrated into the existing ultra-high frequency RFID system, and has high practical value in occasions with speed measurement requirements such as motor vehicle electronic identification and intelligent warehousing.

Description

Technical Field

[0001] The present invention belongs to the field of radio frequency identification, and particularly relates to a method for measuring the speed of a ultra-high frequency RFID system. Background Art

[0002] In the application scenarios of RFID, there is sometimes a need for speed measurement. For example, in the scheduling management systems of roads or parking lots, in order to evaluate the congestion situation of roads, it is necessary for the already deployed motor vehicle electronic identification system to be able to collect the movement speeds of various vehicles; the scheduling system of an intelligent warehouse needs to obtain the movement conditions of goods attached with RFID electronic tags carried by assembly lines or robots through various RFID reading devices, etc.

[0003] In response to this demand, RFID reading devices capable of measuring Doppler frequency shift and speed calculation methods have emerged. However, this solution has a high cost and a relatively complex method, which is not conducive to integration into the RFID application system; there are also some methods for estimating speed based on the signal strength and reading rate of RFID tags. These methods have poor accuracy, high algorithm complexity, and poor practicability.

[0004] Therefore, there is an urgent need for an RFID speed measurement method with higher accuracy and lower cost to expand the application scenarios of RFID. The present invention is precisely generated based on this actual demand. Summary of the Invention

[0005] (1) Technical Problems to be Solved

[0006] The technical problem to be solved by the present invention is how to provide a method for measuring the speed of a ultra-high frequency RFID system to solve the problems of poor accuracy, high algorithm complexity, and poor practicability of the existing methods.

[0007] (2) Technical Solutions

[0008] To solve the above technical problems, the present invention proposes a method for measuring the speed of a ultra-high frequency RFID system, which includes the following steps:

[0009] S1. Equipment Deployment Step: Deploy the antenna of the RFID reading device beside or directly above the channel to be monitored and make it face the channel to be monitored directly;

[0010] S2. Data Acquisition Step: During the monitoring process, the RFID reading device identifies the RFID tags within its reading range and records the tag information, the phase of the tag signal, and the time stamp of each identification, that is, the data combination [EPC n , θ n , t n , where n represents the serial number of the data combination sorted in the order of acquisition;

[0011] S3. Data sorting step: Sort the data combinations obtained within a specific time period according to the EPC code to obtain the phase and timestamp combinations [θ i , t i of each tag within the reading range of the RFID reading device during this time period;

[0012] S4. Speed calculation step: Process the phase and timestamp information of the collected RFID tags to obtain the moving speed of the object attached with the RFID tag.

[0013] Further, in the step S1, the vertical distance from the RFID antenna to the channel is h, the distance between the RFID antenna and the RFID tag is s, and the distance from the RFID tag to the projection point of the RFID antenna center on the channel is d. The change amount of d per unit time is the moving speed of the object we are concerned about. The relationship between the phase of the tag response signal and d is: where λ is the wavelength of the ultra-high frequency RFID signal.

[0014] Further, the step S4 specifically includes: an edge detection step, an operation condition judgment step, and an operation step.

[0015] Further, the edge detection step includes: starting from when the RFID tag first enters the reading range, if θ i -θ i-1 > Th, it is determined that a sudden rising edge appears in the RFID tag response signal; if θ i -θ i-1 < -Th, it is determined that a sudden falling edge appears in the phase of the RFID tag response signal. The detected rising edges are counted as R, and the falling edges are counted as N.

[0016] Further, the threshold Th is π / 4.

[0017] Further, the operation condition judgment step includes: judging whether the obtained rising edge and falling edge conditions meet the operation conditions. Condition 1 is: a certain number of rising edges and the first falling edge are captured, that is, R > 1, N >= 1; Condition 2 is: the last rising edge and a certain number of falling edges are captured, that is, R >= 1, N > 1; If one of Condition 1 or Condition 2 is met, an operation is performed once; if both Condition 1 and Condition 2 are met, two operations are performed; if neither condition is met, the operation cannot be performed, and this calculation fails. Collect data for a period of time and then make a judgment again.

[0018] Further, the operation step includes: for the data that meets the operation conditions, calculate the speed according to the following formula:

[0019]

[0020] Wherein R is the number of rising edges detected, N is the number of falling edges detected, λ is the wavelength of the ultra-high frequency RFID signal, h is the distance from the antenna of the RFID reading device to the channel, t1 is the average value of the timestamps of two points of the first detected rising edge, t2 is the average value of the timestamps of two points of the last detected rising edge, t3 is the average value of the timestamps of two points of the first detected falling edge, and t4 is the average value of the timestamps of two points of the last detected falling edge.

[0021] Furthermore, for a tag that meets one of Condition 1 and Condition 2, the operation result is directly used as the speed calculation value; for a tag that meets both Condition 1 and Condition 2, the average value of the two operation results is used as the speed calculation value.

[0022] Furthermore, this method is applied to the scheduling management system of a highway or a parking lot, and the channel is the road of the highway or the parking lot.

[0023] Furthermore, this method is applied to the scheduling system of an intelligent warehouse, and the channel is an assembly line.

[0024] (III) Beneficial Effects

[0025] The present invention provides a method for measuring the speed of an ultra-high frequency RFID system. The present invention discloses a method for measuring the speed of an ultra-high frequency RFID system. The method includes: (1) Equipment deployment. Deploy the antenna of the RFID reading device beside or directly above the channel to be monitored, and make it face the channel to be monitored directly. (2) Data acquisition. Use the ultra-high frequency RFID reader to collect the tag data and phase information of the RFID tags attached to the object to be speed-measured, and record them together with the timestamp information when the data is collected; (3) Data sorting. Sort the collected tag data information by tag to obtain the phase and timestamp information of each tag. (4) Speed calculation. Process the tag data and phase information of the collected RFID tags to obtain the moving speed of the object attached with the RFID tags.

[0026] The method proposed by the present invention has the characteristics of small calculation amount, high real-time performance, and being easy to integrate into the existing ultra-high frequency RFID system, and has high practical value in occasions with speed measurement requirements such as vehicle electronic identification and intelligent warehousing. Description of the Drawings

[0027] Figure 1 It is a schematic diagram of the scenario for measuring the speed of the ultra-high frequency RFID system of the present invention;

[0028] Figure 2 It is a schematic diagram of the method flow of the present invention. Detailed Embodiments

[0029] To make the objectives, contents, and advantages of the present invention clearer, the following further describes the specific implementation manners of the present invention in detail with reference to the accompanying drawings and embodiments.

[0030] The present invention discloses a method for measuring the speed of a UHF RFID system. The method includes: (1) Equipment deployment. Deploy the antenna of the RFID reader device beside or directly above the channel to be monitored, and make it face the channel to be monitored directly. (2) Data acquisition. Use a UHF RFID reader to collect the tag data and phase information of the RFID tags attached to the object whose speed is to be measured, and record them together with the timestamp information when the data is collected; (3) Data arrangement. Arrange the collected tag data information by tag to obtain the phase and timestamp information of each tag. (4) Speed calculation. Process the tag data and phase information of the collected RFID tags to obtain the moving speed of the object attached with the RFID tag.

[0031] The method proposed by the present invention has the characteristics of small computational complexity, high real-time performance, and being easy to integrate into existing UHF RFID systems. It has high practical value in occasions such as vehicle electronic identification and intelligent warehousing where speed measurement is required.

[0032] The objective of the present invention is to propose a method for measuring the speed of a UHF RFID system to calculate the moving speed of an object attached with an RFID electronic tag.

[0033] This method makes full use of the linear relationship between the phase information of the RFID tag response signal collected by the UHF RFID reader device and the distance between the RFID tag and the antenna of the RFID reader device when the RFID tag sends a response, as well as the periodicity of the phase change of the RFID tag response signal, and uses the problem of 180° phase ambiguity existing in the RFID tag response phase obtained by the RFID reader device to realize the calculation of the object moving speed.

[0034] The method includes:

[0035] S1. Equipment deployment step: Deploy the antenna of the RFID reader device beside or directly above the channel to be monitored and make it face the channel to be monitored directly.

[0036] S2. Data acquisition step: During the monitoring process, the RFID reader device identifies the RFID tags within its reading range and records the tag information, the phase of the tag signal, and the timestamp of each identification, that is, the data combination [EPC n , θ n , t n , where n represents the serial number of the data combination sorted in the order of acquisition.

[0037] S3. Data Arrangement Step: Arrange the acquired data combinations within a specific time period according to the EPC code to obtain the phase and timestamp combinations [θ i , t i of each tag within the reading range of the RFID reading device during this time period.

[0038] S4. Speed Calculation Step: Process the phase and timestamp information of the acquired RFID tags to obtain the movement speed of the object attached with the RFID tag.

[0039] Using the relationship between the phase of the RFID tag signal and the distance s from the RFID tag to the antenna, starting from when the RFID tag first enters the reading range, if θ i -θ i-1 > Th, it is determined that there is a sudden rising edge in the response signal of the RFID tag; if θ i -θ i-1 < -Th, it is determined that there is a sudden falling edge in the phase of the response signal of the RFID tag. The threshold Th can be selected as π / 4. Count the detected rising edges as R, count the detected falling edges as N. Denote the time average value in the two phase-time combinations of the first detected rising edge as t1, the time average value in the two phase-time combinations of the last detected rising edge as t2, the time average value in the two phase-time combinations of the first detected falling edge as t3, and the time average value in the two phase-time combinations of the last detected falling edge as t4. Then the time when the object attached with the RFID tag is first detected with a phase rising edge is approximately t1, the time when the object reaches the position directly opposite the antenna is approximately (t3 + t2) / 2, and the time it takes for the object to move from the first detected phase rising edge to the position directly opposite the antenna is:

[0040] t = (t3 + t2) / 2 - t1

[0041] The s when the object is first detected with a phase rising edge is approximately λ(R - 1) + h, where λ is the wavelength of the ultra-high frequency RFID signal, and the corresponding d is approximately:

[0042]

[0043] Then the movement speed of the object can be approximately obtained by the following formula:

[0044]

[0045] Similarly, the movement speed of the object can be calculated using the data acquired during the process when the object gradually moves away from the RFID antenna:

[0046]

[0047] On the premise that the collected data is sufficient, two calculations can be performed to obtain the object's movement speeds v1 and v2 respectively. To improve the accuracy, the average value of v1 and v2 can be taken as the calculation result. If the collected data is insufficient and only one speed value can be calculated, then take this speed value as the calculation result; otherwise, the speed measurement fails.

[0048] Embodiment 1:

[0049] The present invention utilizes the characteristic that the phase of the RFID tag response has a linear relationship with the distance between the RFID tag and the RFID antenna, and fully considers the edge jump phenomenon caused by the periodicity of the phase change during the phase acquisition process of the RFID tag response signal in practical applications and the phase ambiguity problem caused by the principle of solving the phase by the RFID reader device. A threshold-based phase information edge detection method is adopted to determine the change amount of the distance s between the RFID tag and the RFID antenna from the start of the stable reading of the tag to the position where it moves directly opposite the RFID antenna. Since h is known, the distance s of the tag from the center of the antenna when it is stably read by the RFID reader device can be determined. Further, the traveling distance d of the object in the channel direction can be obtained, and combined with the operation of the reading time of the RFID tag by the reader to obtain the running time t of the object in the channel direction. Finally, the approximate movement speed v of the object can be obtained.

[0050] The schematic flow diagram of this method is as Figure 2 shown.

[0051] Device deployment step S1: Deploy the antenna of the RFID reader device beside or directly above the channel to be monitored and make it face the channel to be monitored directly. The vertical distance from the RFID antenna to the channel is h, the distance between the RFID antenna and the RFID tag is s, and the distance from the RFID tag to the projection point of the center of the RFID antenna on the channel is d. The change amount of d per unit time is the movement speed of the object we are concerned about. The relationship between the phase of the tag response signal and d is: where λ is the wavelength of the ultra-high frequency RFID signal.

[0052] Data acquisition step S2: The RFID reader device records the data information of each RFID tag, the phase information of the signal, and the timestamp information of the reading moment [EPC n , θ n , t n .

[0053] Data sorting step S3: Sort these information according to the tag EPC data and in chronological order to obtain the combination of the phase and timestamp of each tag [θ i , t i .

[0054] Speed calculation step S4: The speed calculation step includes three sub-steps: an edge detection step, an operation condition judgment step, and an operation step.

[0055] Edge detection sub-step S41: Use a method based on threshold judgment to judge the mutation situation of the phase of the RFID tag response signal during the movement process. Specifically: starting from when the RFID tag first enters the reading range, if θ i -θ i-1 > Th, it is determined that a mutant rising edge appears in the RFID tag response signal; if θ i -θ i-1 < -Th, it is determined that a mutant falling edge appears in the phase of the RFID tag response signal. The threshold Th can be selected as π / 4. The detected rising edges are counted as R, and the falling edges are counted as N.

[0056] Operation condition judgment sub-step S42: Judge whether the obtained rising edge and falling edge situations meet the operation conditions. Specifically: a certain number of rising edges and the first falling edge are captured (condition 1), that is, R > 1, N >= 1; the last rising edge and a certain number of falling edges are captured (condition 2), that is, R >= 1, N > 1. If one of condition 1 or condition 2 is met, an operation can be performed; if both condition 1 and condition 2 are met, two operations can be performed; if neither condition is met, the operation cannot be performed, and this calculation fails. Data can be collected for a period of time and then judged again.

[0057] Operation sub-step S43: For the data that meets the operation conditions, the speed can be calculated according to the following formula:

[0058]

[0059] In the formula, R is the number of detected rising edges, N is the number of detected falling edges, λ is the wavelength of the ultra-high frequency RFID signal, h is the distance from the antenna of the RFID reading device to the channel, t1 is the average value of the timestamps of two points of the first detected rising edge, t2 is the average value of the timestamps of two points of the last detected rising edge, t3 is the average value of the timestamps of two points of the first detected falling edge, and t4 is the average value of the timestamps of two points of the last detected falling edge. For the tags that meet one of condition 1 and condition 2, the operation result is directly used as the speed calculation value; for the tags that meet both condition 1 and condition 2, the average value of the two operation results is used as the speed calculation value.

[0060] Furthermore, this method is applied to the scheduling management system of highways or parking lots, and this channel is the road of highways or parking lots.

[0061] Furthermore, this method is applied to the scheduling system of intelligent warehouses, and this channel is the assembly line.

[0062] Example 2:

[0063] A method for measuring the speed of a ultra-high frequency RFID system, comprising:

[0064] (1) Equipment deployment step: Deploy the antenna of the RFID reader device beside or directly above the channel to be monitored and make it face the channel to be monitored.

[0065] (2) Data acquisition step: The RFID reader device records the data information of each RFID tag, the phase information of the signal, and the timestamp information at the reading moment [EPC n , θ n , t n .

[0066] (3) Data sorting step: Sort the [EPC n , θ n , t n obtained in the data acquisition step according to the EPC code of the tag to obtain the combination of phase information and timestamp [θ i , t i .

[0067] (4) Speed calculation step, specifically including an edge detection step, an operation condition judgment step, and an operation step.

[0068] Furthermore, in the speed calculation step, the edge detection method includes:

[0069] Adopt a threshold-based decision method to judge the mutation of the phase information of the RFID tag in motion. If θ i - θ i-1 > Th, it is determined that a mutant rising edge appears in the RFID tag response signal; if θ i - θ i-1 < - Th, it is determined that a mutant falling edge appears in the phase of the RFID tag response signal. After actual measurement, the threshold Th can be selected as π / 4. Count the detected rising edges as R and the falling edges as N.

[0070] Furthermore, in the speed calculation step, the operation condition judgment method includes:

[0071] Two preconditions for calculating the speed using this method: a certain number of rising edges and the first falling edge are captured (condition 1), that is, R > 1, N >= 1; the last rising edge and a certain number of falling edges are captured (condition 2), that is, R >= 1, N > 1. And judge whether the information of a specific tag that has been collected meets these two conditions.

[0072] Furthermore, in the speed calculation step, the operation method includes:

[0073] The moving speed of the RFID tag is calculated as follows:

[0074]

[0075] Where R is the number of rising edges detected, N is the number of falling edges detected, λ is the wavelength of the ultra-high frequency RFID signal, h is the distance from the antenna of the RFID reading device to the channel, t1 is the average value of the timestamps of two points of the first detected rising edge, t2 is the average value of the timestamps of two points of the last detected rising edge, t3 is the average value of the timestamps of two points of the first detected falling edge, and t4 is the average value of the timestamps of two points of the last detected falling edge. For a tag that meets one of Condition 1 and Condition 2, the operation result is directly used as the speed calculation value; for a tag that meets both Condition 1 and Condition 2, the average value of the two operation results is used as the speed calculation value.

[0076] The method proposed by the present invention has the characteristics of small computational complexity, high real-time performance, and being easy to integrate into the existing ultra-high frequency RFID system. It has high practical value in occasions such as vehicle electronic identification and intelligent warehousing where speed measurement is required.

[0077] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A method for measuring speed in a ultra-high frequency RFID system, characterized in that, The method comprises the following steps: S1. Equipment deployment step: Deploy the antenna of the RFID reading device beside or directly above the channel to be monitored and make it face the channel to be monitored; S2. Data acquisition step: During the monitoring process, the RFID reader device identifies the RFID tags within its reading range and records the tag information, the phase of the tag signal, and the timestamp of each identification, i.e., the data combination [EPC n , θ n , t n , where n represents the serial number of the data combination sorted in the order of acquisition; S3. Data sorting step: Sort the data combinations obtained within a specific time period according to the EPC code to obtain the phase and timestamp combinations [θ i , t i of each tag within the reading range of the RFID reading device during this time period; S4. Speed calculation step: Process the phase and timestamp information of the collected RFID tags to obtain the moving speed of the object attached with the RFID tags; Wherein, The step S4 specifically includes: an edge detection step, an operation condition judgment step, and an operation step; The edge detection step includes: starting from when the RFID tag first enters the reading range, if θ i -θ i-1 > Th, it is determined that there is a sudden rising edge in the RFID tag response signal; if θ i -θ i-1 < -Th, it is determined that there is a sudden falling edge in the phase of the RFID tag response signal, and the detected rising edge is counted as R, and the falling edge is counted as N; The operation condition judgment step includes: judging whether the obtained rising edge and falling edge conditions meet the operation conditions. Condition 1 is: a certain number of rising edges and the first falling edge are captured, that is, R>1, N>=1; Condition 2 is: the last rising edge and a certain number of falling edges are captured, that is, R>=1, N>1; If one of Condition 1 or Condition 2 is met, an operation is performed once; If both Condition 1 and Condition 2 are met, two operations are performed; If neither of the two conditions is met, the operation cannot be performed, the current calculation fails, and data is collected for a period of time and then judged again; The operation step includes: for the data that meets the operation conditions, calculate the speed according to the following formula: In the formula, R is the number of detected rising edges, N is the number of detected falling edges, λ is the wavelength of the ultra-high frequency RFID signal, h is the distance from the RFID reading device antenna to the channel, t1 is the average value of the timestamps of two points of the first detected rising edge, t2 is the average value of the timestamps of two points of the last detected rising edge, t3 is the average value of the timestamps of two points of the first detected falling edge, and t4 is the average value of the timestamps of two points of the last detected falling edge.

2. The method for measuring speed of an ultra-high frequency RFID system according to claim 1, characterized in that, In the step S1, the vertical distance from the RFID antenna to the channel is h, the distance between the RFID antenna and the RFID tag is s, and the distance from the RFID tag to the projection point of the center of the RFID antenna on the channel is d. The change amount of d per unit time is the movement speed of the object we are concerned about. The relationship between the phase of the tag response signal and d is: where λ is the wavelength of the ultra-high frequency RFID signal.

3. The ultra-high frequency RFID system speed measurement method according to claim 1, characterized in that, The threshold Th is π / 4.

4. The method for measuring the speed of the ultra-high frequency RFID system according to claim 1, wherein For the tags that meet one of Condition 1 and Condition 2, the operation result is directly used as the speed calculation value; for the tags that meet both Condition 1 and Condition 2, the average value of the two operation results is used as the speed calculation value.

5. The ultra-high frequency RFID system speed measurement method according to claim 1, characterized in that This method is applied to the scheduling management system of a road or a parking lot, and the channel is the road of the road or the parking lot.

6. The method for measuring the speed of the ultra-high frequency RFID system according to claim 1, wherein, This method is applied to the scheduling system of an intelligent warehouse, and the channel is an assembly line.

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