A method for detecting the speed and acceleration of an RFID tag

Abstract

The present application relates to the technical field of RFID tag, in particular to a method for detecting the moving speed and acceleration of RFID tag; the present application uses the reader of RFID tag to collect the backscattering signal caused by movement, filters out the part of Query command; through the analysis of the waveform phase of Query command from the start to the end, the electric wave intensity and the time length used by command reflection, the real-time tag movement speed and acceleration size are obtained; the mobility detection can be realized on the ordinary RFID reader and ordinary single antenna (directional antenna), the calculation of tag movement speed and acceleration does not affect the original data transmission of RFID tag, such as EPC.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of RFID tag, and particularly relates to a method for detecting the moving speed and acceleration of RFID tag. BACKGROUND

[0002] With the development of the Internet of Things technology, information interaction between people and things and things is particularly important, and RFID is one of the communication methods. At present, there are relatively mature RFID tags, which use the backscattering principle to generate relatively stable communication with the reader, but these communications are only in a limited distance and the tags have small motion amplitude. In order to improve the application of RFID backscattering communication, it is inevitable to read the moving tags of the RFID reader.

[0003] At present, several schemes are mainly used to detect the speed and acceleration of the moving tag of RFID:

[0004] (1) CRFID tag is used, and acceleration and speed sensors are mounted on the tag, and the corresponding sensor values are transmitted back through the protocol, the disadvantage is that the power consumption is large compared with the RFID tag, the energy consumption is fast, and therefore a large energy is required and the communication distance is short.

[0005] (2) double-antenna collection is used, multi-directional data collection is performed on the same tag, and the speed and acceleration are analyzed through the waveform characteristics of the back transmission, but the device layout is too large, which is not conducive to large-scale use.

[0006] (3) single-antenna collection is used, data reading is performed on a tag, and the current corresponding speed is inferred through the speed model matching of RSSI or packet loss rate and other indicators, but the accuracy is very low, which is not conducive to the use of data processing. SUMMARY

[0007] The technical problem to be solved by the present application is to provide an algorithm for detecting the speed and acceleration of the moving tag with a single directional antenna, so as to facilitate the reading of the moving tag and the method for detecting the moving speed and acceleration of the RFID tag.

[0008] In order to solve the above technical problems, the technical scheme adopted by the present application is:

[0009] A method for detecting the moving speed and acceleration of RFID tag, comprising

[0010] Data collection, collecting data under the motion state of RFID tag;

[0011] Data preprocessing, filtering out high-frequency noise;

[0012] Extracting data features, extracting the received signal's radio wave intensity variation curve, and leaving the Query command part;

[0013] Calculating the characteristics of a single Query command, according to the formula Deriving the characteristic curve from the radio wave intensity variation curve, and judging whether the tag is in a stationary or moving state through the variation amplitude of the derivative; reading the data of the tag that is absolutely available in motion, obtaining the start point and end point of the Query command, the time span of the start point and end point being Δt1, and obtaining the time span of the next Query command being Δt2; the interval between Δt1 and Δt2 being Δt x ; according to the relationship between the radio frequency carrier frequency and the wavelength: The carrier phase before and after the Query command Δt is θ0, θ1 respectively; according to the formula d is the distance between the reader and the tag, and Δd1 and Δd2 are obtained;

[0014] Calculating the speed and acceleration at that time, according to the formula V1 and V2 are obtained; and according to the formula The acceleration a is obtained.

[0015] Further, during data collection, the RFID tag is used in the state of being read by the reader, first stationary, then moving forward at a non-uniform speed of 12 cm, and then collecting the data of the RFID tag in the moving state.

[0016] Further, during data preprocessing, a Hamming window filter is used to filter high-frequency noise.

[0017] Further, during data feature extraction, a sliding window is used to count the window data to extract the radio wave intensity variation curve of the received signal.

[0018] Further, during data feature extraction, a manually designed signal filter is used to filter out the parts not involved in the Class-1 Generation-2 UHF RFID communication protocol, and only leave the Query command part.

[0019] Further, when calculating the characteristics of a single Query command, the variation amplitude of the derivative is used to judge whether the tag is in a stationary or moving state, and when the variation amplitude is less than a preset value, the tag is considered to be in a stationary state; otherwise, it is considered to be in a moving state.

[0020] Further, when calculating the characteristics of a single Query command, the phase diagram of a single Query signal is used to observe whether the Query signal phase before and after is in a complete phase, to determine whether the signal to be obtained is a complete Query signal, and to judge whether the Query signal to be obtained is available.

[0021] Further, the method for detecting the RFID tag moving speed and acceleration size is executed multiple times, and the results obtained multiple times are averaged.

[0022] The present application has the beneficial effect that: the reader of the RFID tag collects the backscattering signal caused by the movement, establishes a communication channel through the Class-1 Generation-2 UHF RFID communication protocol, filters out only the part of the Query command through the waveform received by the reader; through the analysis of the waveform phase from the beginning to the end of the Query command, the electric wave intensity (amplitude), and the time length used for command reflection, the real-time tag movement speed and acceleration size are obtained; the algorithm (method) for detecting the RFID tag speed and acceleration size of the present application is named as Query signal characteristic analysis algorithm (Query signal characteristic analysis algorithm), hereinafter referred to as QSCA algorithm, which can realize the mobility detection on the ordinary RFID reader and the ordinary single antenna (directional antenna), and calculate the tag movement speed and acceleration without affecting the original data transmission of the RFID tag, such as EPC. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 (a) is the original signal diagram of the method for detecting the RFID tag speed and acceleration size of the embodiment of the present application;

[0024] Figure 1 (b) is the signal amplitude characteristic diagram of the method for detecting the RFID tag speed and acceleration size of the embodiment of the present application;

[0025] Figure 1 (c) is the useful information diagram of the method for detecting the RFID tag speed and acceleration size of the embodiment of the present application;

[0026] Figure 1 (d) is the Query signal local amplification diagram of the method for detecting the RFID tag speed and acceleration size of the embodiment of the present application;

[0027] Figure 2 is the amplitude and phase diagram of a single Query of the method for detecting the RFID tag speed and acceleration size of the embodiment of the present application;

[0028] Figure 3 is the Δt1, Δt2, Δt3 diagram of the method for detecting the RFID tag speed and acceleration size of the embodiment of the present application; x relationship diagram;

[0029] Figure 4 Figure 1 is a flow chart of a method for detecting the speed and acceleration of an RFID tag according to an embodiment of the present application. DETAILED DESCRIPTION

[0030] To make the technical contents, purposes and effects of the present application clear, the following will be described in conjunction with the embodiments and the accompanying drawings.

[0031] Embodiment 1

[0032] Please refer to Figures 1 to 4 A method for detecting the speed and acceleration of an RFID tag,

[0033] Hardware requirements: USRP reader directional antenna and common commercial RFID tag

[0034] Due to the characteristics of the directional antenna, there are few points with the same magnetic field in the same horizontal plane, so the speed relative to the antenna has little effect on reading the tag, and therefore the method only considers the algorithm for the mirror speed and acceleration.

[0035] 1. Data collection

[0036] In this experiment, the tag was first stationary, then moved forward at an uneven speed of 12 cm, and then the data in the moving state was collected using a common commercial RFID tag, such as Figure 1 (a) (the horizontal axis is time, in us).

[0037] 2. Data preprocessing

[0038] Hamming window filter is used to filter high-frequency noise.

[0039] 3. Extracting data characteristic values

[0040] (1) The sliding window statistical window data is used to extract the electric wave intensity change curve of the received signal, as shown in Figure 1 (b).

[0041] (2) The artificially designed signal filter is used to filter out the parts not involved in the Class-1 Generation-2 UHF RFID communication protocol, and only leave the Query command part, as shown in Figure 1 (c), Figure 1 (d) is Figure 1 (c) local enlarged view.

[0042] 4. Calculate the characteristics of a single Query command

[0043] From Figure 1 (b) electric wave intensity characteristic curve and formula The derivative of the characteristic curve can be obtained, and if the variation range is not large, the tag can be considered to be in a static state. If the variation range is large, the tag is considered to be in motion. Since incomplete transmission may occur during communication, the phase diagram of a single Query signal is also needed to observe whether the Query signal phase before and after is in a complete phase, to see whether the signal to be obtained is a complete Query signal, and to determine whether the Query signal to be obtained is acceptable. Figure 2 The data of the tag in motion and absolutely acceptable are read from Figure 1 1.457 x 10 6 to 1.4598 x 10 6 , Figure 2 The amplitude and phase diagrams of a single Query command are obtained, and the starting point of the true Query command is node 1 and the ending point is node 2. The horizontal axis is time, and the unit is us. The time span between node 1 and node 2 can be easily obtained as Δt1 = 1774 us. In the same way, the time interval of the next Query command is Δt2 = 1800 us, and the interval time between the two commands is Δt x = 13259 us. The relationship can be seen from Figure 3 .

[0044] According to the relationship between the radio carrier frequency and the wavelength: c is the speed of light, 3 x 10 8 m / s, f is the carrier frequency 920 MHz, and λ is the carrier wavelength. According to the principle of radio frequency, the carrier signal is a periodic repeating signal, and the phase value repeats in the communication process in the form of an integer multiple of half the carrier wavelength. Since amplitude modulation is used in the communication protocol, the baseband signal basically does not affect the change of the phase, and the phase detection circuit of the reader can obtain the carrier phase before and after the Query command Δt1, which are θ0 and θ1, respectively. Thus, we have: where n is the integer multiple of half the wavelength, and d is the distance between the reader and the tag.

[0045] Since the experiment itself is in motion and does not move more than half a wavelength in a single Query command, the distance traveled by the tag in Δt1 is The distance traveled by the tag in Δt2 is Δd2 using the same method.

[0046] 5. The speed and acceleration at the time are calculated according to the above data

[0047] The data obtained above can be used in the formula The corresponding velocities V1 and V2 are calculated, in the above example about V1 = 0.60 m / s and V2 = 0.62 m / s; then the formula is used to find the acceleration at that time, in the previous example the acceleration is found to be 1.33 m / s 2 .

[0048] The above description is only an example of the present application, and does not limit the patent scope of the present application, any equivalent transformation using the content of the present application specification and drawings, or direct or indirect application in related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for detecting the velocity and acceleration magnitude of an RFID tag movement, characterized by, Comprising Data acquisition, collect the data of RFID tag in motion state; Data preprocessing, filter out high-frequency noise; Extracting data features, extract the received signal strength variation curve and leave the Query command part; The characteristics of a single Query command are calculated according to the formula The derivative of the characteristic curve is obtained from the radio wave intensity change curve, and the variation range of the derivative is used to determine whether the tag is in a stationary or moving state; the data of the tag in absolute motion is read to obtain the start point and end point of the Query command, the time span of the start point and end point is Δt1, and the time span of the next Query command is Δt2; the interval between Δt1 and Δt2 is Δt x ; according to the relationship between the radio frequency carrier frequency and the wavelength: The carrier phase before and after the Query command Δt is θ0 and θ1, respectively; according to the formula d is the distance between the reader and the tag, and Δd1 and Δd2 are obtained; The speed and acceleration magnitude at that time are calculated according to the formula V1 and V2 are obtained; and the acceleration a is obtained according to the formula V1 and V2 are obtained; and the acceleration a is obtained according to the formula 2. The method for detecting the RFED tag moving speed and acceleration magnitude according to claim 1, characterized in that, During data acquisition, use RFID tags in the state of reading by the reader, first static, then move forward at an uneven speed of 12 cm, and then collect the data of RFID tags in motion state.

3. The method for detecting the RFED tag moving velocity and acceleration magnitude according to claim 1, characterized in that, During data preprocessing, use Hamming window filter to filter out high-frequency noise.

4. The method for detecting the RFED tag's moving velocity and acceleration magnitude according to claim 1, wherein, When extracting data features, use sliding window statistics to extract the received signal strength variation curve.

5. The method for detecting the RFED tag's moving velocity and acceleration magnitude according to claim 1, wherein, When extracting data features, use artificial design signal filter to filter out the part not involved in Class-1 Generation-2 UHF RFID communication protocol, and only leave the Query command part.

6. The method for detecting the RFED tag's moving velocity and acceleration magnitude according to claim 1, wherein, When calculating the characteristics of a single Query command, the derivative variation amplitude is used to determine whether the tag is in a static or motion state. When the variation amplitude is less than the preset value, the tag is considered to be in a static state; otherwise, it is considered to be in a motion state.

7. The method for detecting the RFED tag's moving velocity and acceleration magnitude according to claim 1, wherein, When calculating the characteristics of a single Query command, the phase diagram of a single Query signal is used to observe whether the Query signal phase before and after is in a complete phase to determine whether the signal to be obtained is a complete Query signal and whether the Query signal to be obtained is acceptable.

8. The method for detecting the RFED tag's moving velocity and acceleration magnitude according to claim 1, wherein, The method for detecting the moving speed and acceleration of RFID tags is executed multiple times, and the average value of the results obtained multiple times is taken.

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