RFID tag positioning method and system

Abstract

The present invention relates to a RFID tag positioning method and system, and belongs to the field of wireless positioning technology. The method comprises: collecting the phase of the RFID tag through an RFID reader to obtain the phase sequence of the RFID tag; processing the phase sequence of the RFID tag, calculating the coordinates of the RFID tag based on the processed phase sequence, and obtaining the positioning result of the RFID tag; and outputting the positioning result of the RFID tag. The method can obtain a higher positioning accuracy and achieve an anti-interference effect in actual environment applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless positioning, and in particular relates to an RFID tag positioning method and system. Background Art

[0002] With the rise of the Internet of Things industry, people use various electronic tags to connect various entities in production and life to the network, which greatly promotes the improvement of work efficiency. Among them, services based on object location information will greatly improve the efficiency of industrial automation. RFID (Radio Frequency Identification), or radio frequency identification technology, has been widely used in warehousing, logistics and other fields due to its advantages such as passive, small size and fast recognition speed. Some RFID-based object positioning methods have also been proposed.

[0003] Most existing solutions use two RFID tag radio frequency characteristics: received signal power (RSSI) and phase. The RFID radio frequency signal power attenuates as the distance increases during the propagation process, while the signal phase records the signal propagation delay information. Therefore, existing solutions usually refer to these two indicators to analyze the distance information of the tag and then perform positioning.

[0004] In the actual environment, wireless signals are interfered by multipath effects and the label stickers absorb radio frequency signals. Tag signals usually suffer from signal loss and signal distortion, which makes the mapping between signal characteristics and distance unreliable, greatly reducing the applicability of positioning methods in actual scenarios. Highly reliable positioning methods usually require complex hardware equipment deployment or a large number of reference tags, which have high computational complexity and cannot guarantee real-time and universality. Summary of the invention

[0005] The main purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide an RFID tag positioning method and system that can obtain higher positioning accuracy and achieve an anti-interference effect in actual environmental applications.

[0006] According to one aspect of the present invention, the present invention provides an RFID tag positioning method, the method comprising:

[0007] S1: collecting the phase of the RFID tag through an RFID reader to obtain a phase sequence of the RFID tag;

[0008] S2: Processing the phase sequence of the RFID tag, calculating the coordinates of the RFID tag based on the processed phase sequence, and obtaining a positioning result of the RFID tag;

[0009] S3: Output the positioning result of the RFID tag.

[0010] Preferably, collecting the phase of the RFID tag by using an RFID reader to obtain the phase sequence of the RFID tag comprises:

[0011] The RFID reader continuously samples the phase of the RFID tag while moving and records the sampling timestamp. The phase θ of the RFID tag and the sampling time t conform to the following model:

[0012]

[0013] Among them, (X, Y) represents the coordinates of the tag, μ represents the phase shift treated as a fixed constant, λ represents the RF wavelength, and v is the speed at which the reader moves.

[0014] Preferably, the processing of the phase sequence of the RFID tag comprises:

[0015] Abnormal sample points are screened out by first-order difference and singular value filtering, where the first-order difference sequence θ′ of the phase is: θ′=θ(i+1)-θ(i); i is the index of the difference sequence.

[0016] Preferably, the filtering out abnormal sample points by singular value filtering includes:

[0017] For the first-order difference sequence θ′, set the sliding window length to N and the initial index to i. Take the subsequence θ′[i,i+N], calculate the lower quartile Q1, upper quartile Q3, and interquartile range IQR of the subsequence, and verify whether each value x in the subsequence belongs to [Q1-1.5IQR, Q3+1.5IQR]. If not, determine the sample point as an outlier point and set the sample value x to (Q1+Q3) / 2.

[0018] Preferably, calculating the coordinates of the RFID tag based on the processed phase sequence to obtain the positioning result of the RFID tag includes:

[0019] Use the sliding window to find the target data near the zero point, perform a least squares fit of the function y=aT+b on the data in the sliding window, and obtain the parameters a, b, the zero point value T=(-b / a), and the horizontal coordinate X=v*T of the RFID tag; solve the vertical coordinate Y of the RFID tag according to the optimization objective function to obtain the positioning result (X, Y) of the RFID tag;

[0020] Among them, the optimization objective function is:

[0021]

[0022]

[0023] x i is the horizontal coordinate of the reader's antenna, k = 4π / λ.

[0024] According to another aspect of the present invention, the present invention also provides an RFID tag positioning system, the system comprising:

[0025] An acquisition module, used for acquiring the phase of the RFID tag through an RFID reader to obtain a phase sequence of the RFID tag;

[0026] A calculation module, used to process the phase sequence of the RFID tag, calculate the coordinates of the RFID tag based on the processed phase sequence, and obtain the positioning result of the RFID tag;

[0027] The output module is used to output the positioning result of the RFID tag.

[0028] Preferably, the acquisition module acquires the phase of the RFID tag through an RFID reader, and obtaining the phase sequence of the RFID tag includes:

[0029] The RFID reader continuously samples the phase of the RFID tag while moving and records the sampling timestamp. The phase θ of the RFID tag and the sampling time t conform to the following model:

[0030]

[0031] Among them, (X, Y) represents the coordinates of the tag, μ represents the phase shift treated as a fixed constant, λ represents the RF wavelength, and v is the speed at which the reader moves.

[0032] Preferably, the calculation module processes the phase sequence of the RFID tag including:

[0033] Abnormal sample points are screened out by first-order difference and singular value filtering, where the first-order difference sequence θ′ of the phase is: θ′=θ(i+1)-θ(i).

[0034] Preferably, the calculation module screens out abnormal sample points through singular value filtering, including:

[0035] For the first-order difference sequence θ′, set the sliding window length to N and the initial index to i; take the subsequence θ′[i,i+N], calculate the lower quartile Q1, upper quartile Q3, and interquartile range IQR of the subsequence, and verify for each value x in the subsequence whether it belongs to [Q1-1.5IQR,Q3+1.5IQR]. If not, determine the sample point as an outlier point and set the sample value x to (Q1+Q3) / 2.

[0036] Preferably, the calculation module calculates the coordinates of the RFID tag based on the processed phase sequence, and obtaining the positioning result of the RFID tag includes:

[0037] Use the sliding window to find the target data near the zero point, perform a least squares fit of the function y=aT+b on the data in the sliding window, and obtain the parameters a, b, the zero point value T=(-b / a), and the horizontal coordinate X=v*T of the RFID tag; solve the vertical coordinate Y of the RFID tag according to the optimization objective function to obtain the positioning result (X, Y) of the RFID tag;

[0038] Among them, the optimization objective function is:

[0039]

[0040]

[0041] x i is the horizontal coordinate of the reader's antenna, k = 4π / λ.

[0042] Beneficial effects:

[0043] 1. The present invention observes and samples tag signals from different locations through a mobile reader, and with the help of high-resolution phase information, can obtain higher positioning accuracy.

[0044] 2. The present invention can effectively eliminate erroneous signals through a first-order differential phase filtering algorithm, allow signal loss and distortion, have no restrictions on adjacent sampling intervals, and have a good anti-interference effect in practical environmental applications.

[0045] 3. The present invention can effectively find the zero point of the first-order phase difference sequence through the sliding window fitting algorithm, eliminate erroneous positioning, and improve positioning accuracy and algorithm reliability.

[0046] The features and advantages of the present invention will become clear through reference to the following drawings and detailed description of specific embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a flow chart of the RFID tag positioning method;

[0048] Figure 2 It is a schematic diagram of a positioning scenario of the present invention;

[0049] Figure 3 It is the sampling phase sequence under ideal conditions and the sampling phase sequence under actual scenarios;

[0050] Figure 4 It is a schematic diagram of the first-order difference filtering algorithm result of the present invention;

[0051] Figure 5 It is a schematic diagram of the two-dimensional fitting algorithm result of the present invention;

[0052] Figure 6 It is a schematic diagram of the RFID tag positioning system. DETAILED DESCRIPTION

[0053] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] Example 1

[0055] Figure 1 This is a flow chart of the RFID tag positioning method. Figure 1 As shown, the present invention provides an RFID tag positioning method, the method comprising:

[0056] S1: collecting the phase of the RFID tag through an RFID reader to obtain a phase sequence of the RFID tag;

[0057] S2: Processing the phase sequence of the RFID tag, calculating the coordinates of the RFID tag based on the processed phase sequence, and obtaining a positioning result of the RFID tag;

[0058] S3: Output the positioning result of the RFID tag.

[0059] The method provided in this embodiment can obtain higher positioning accuracy and achieve the anti-interference effect in actual environment applications.

[0060] Preferably, collecting the phase of the RFID tag by using an RFID reader to obtain the phase sequence of the RFID tag comprises:

[0061] The RFID reader continuously samples the phase of the RFID tag while moving and records the sampling timestamp. The phase θ of the RFID tag and the sampling time t conform to the following model:

[0062]

[0063] Among them, (X, Y) represents the coordinates of the tag, μ represents the phase shift treated as a fixed constant, λ represents the RF wavelength, and v is the speed at which the reader moves.

[0064] Specifically, refer to Figure 2, the RFID reader is placed on a linear moving track or robot, and a radio frequency loop is constructed with the RFID tag installed on the target. The RFID reader continuously samples the phase of the tag while moving and records the sampling timestamp. The phase θ of the tag and the sampling time t conform to the following model:

[0065]

[0066] Where (X, Y) represents the coordinates of the tag, μ represents the phase shift treated as a fixed constant, λ represents the RF wavelength, and v is the speed at which the reader moves.

[0067] Preferably, the processing of the phase sequence of the RFID tag comprises:

[0068] Abnormal sample points are screened out by first-order difference and singular value filtering, where the first-order difference sequence θ′ of the phase is: θ′=θ(i+1)-θ(i).

[0069] Specifically, the phase sampling sequence will periodically "jump" with a half-wavelength distance, that is, when the reader's antenna moves in front of the tag, the distance between the antenna and the tag first approaches and then moves away, and the phase first increases and then decreases. When the phase increases to 2π or decreases to 0, it will start again from 0 or 2π, eventually forming the following Figure 3 The phase time series pattern shown in the left half of the figure is also called "phase confusion". "Phase confusion" will make the mapping relationship between phase and distance unclear, so that the distance information cannot be inferred from the phase value. In addition, in the actual data collection, due to the interference of multipath interference, material absorption and other factors, the phase sequence often has inevitable sampling errors such as signal distortion and signal loss. Figure 3 As shown in the right half of . Considering the actual problems in these environments, this algorithm eliminates phase jumps and filters out poor quality sample points through two steps: first-order difference and singular value filtering. Whether it is a "phase jump" or a sampling error, a high-frequency characteristic will be generated at the sample point. The first-order difference value of the sample point where the "phase jump" and the signal are missing will be much higher than that of the normal sample point. The first-order difference sequence of the phase θ′ conforms to the following model:

[0070]

[0071] Specifically, θ'=θ(i+1)-θ(i).

[0072] Preferably, the filtering out abnormal sample points by singular value filtering includes:

[0073] For the first-order difference sequence θ′, set the sliding window length to N and the initial index to i. Take the subsequence θ′[i,i+N], calculate the lower quartile Q1, upper quartile Q3, and interquartile range IQR of the subsequence, and verify whether each value x in the subsequence belongs to [Q1-1.5IQR, Q3+1.5IQR]. If not, determine the sample point as an outlier point and set the sample value x to (Q1+Q3) / 2.

[0074] Specifically, θ′ is a monotonically decreasing bounded sequence, and its upper and lower bounds are ±4πv / λ. Since the first-order differences at the "phase jump" and sampling error are much larger than normal samples, this embodiment selects the singular value filtering algorithm to eliminate abnormal samples caused by phase jumps and sampling errors. Specifically, for the first-order difference sequence θ′, the sliding window length is set to N, and the initial index is i. Take the subsequence θ′[i,i+N], calculate the lower quartile Q1, upper quartile Q3, and interquartile range IQR of the subsequence, and verify whether each value x in the subsequence belongs to [Q1-1.5IQR,Q3+1.5IQR]. If not satisfied, the sample point is determined as an outlier point, and the sample value x is set to (Q1+Q3) / 2. Then move the window backward by half the window step, that is, reassign i to i+N / 2, and repeat the above process until the window reaches the tail of the sequence θ′. The results of the first-order difference filtering algorithm are as follows: Figure 4 shown.

[0075] Preferably, calculating the coordinates of the RFID tag based on the processed phase sequence to obtain the positioning result of the RFID tag includes:

[0076] Use the sliding window to find the target data near the zero point, perform a least squares fit of the function y=aT+b on the data in the sliding window, and obtain the parameters a, b, the zero point value T=(-b / a), and the horizontal coordinate X=v*T of the RFID tag; solve the vertical coordinate Y of the RFID tag according to the optimization objective function to obtain the positioning result (X, Y) of the RFID tag;

[0077] Among them, the optimization objective function is:

[0078]

[0079]

[0080] x i is the horizontal coordinate of the reader's antenna, k = 4π / λ.

[0081] Specifically, the filtered first-order difference sequence of the phase is smoother. In theory, the first-order difference sequence has only one zero point with the X-axis, and this zero point is the abscissa X of the tag. However, due to the existence of sampling errors, there may be multiple pseudo "zero points", and the farther the distance between the antenna and the tag, the more severe the multipath interference, and the worse the quality of the data samples. Generally speaking, the first-order difference sequence of the phase is an odd function symmetric about the zero point, and the quality of the data samples at the zero point is usually higher than that at the non-zero points. Therefore, this method searches for the data near the zero point through a sliding time window, and for the data close to the zero point, the term (X - vt) in the denominator 2 is much smaller than Y 2 , so near the zero point, it can be approximated as a linear function. A linear function can be used for least squares fitting to solve the abscissa X of the tag. Since it is an odd function, when the zero point is more in the center of the sliding window, the sum of the data within the window is closer to 0. By comparing the sum of the data in the sliding window to indicate the moving direction of the sliding window, the data segment where the zero point is located can be quickly detected. Specifically, set the time window length to 1 s, set the initial value of the time window start point to the midpoint of the sequence θ′, set the moving step size step to 1 s, set the initial direction flag to "right", and set the moving step size threshold limitStep and the summation threshold limitSum. Calculate the sum sum of the data in the sliding window. If sum > 0, the sliding window moves to the right; if sum < 0, the sliding window moves to the left. At the same time, when the sliding window moves in the opposite direction twice continuously, the moving step size step needs to be halved for a more refined search. Repeat the above steps until sum < limitSum or step < limitStep. Finally, perform least squares fitting of the data in the sliding window with the linear function y = aT + b to obtain the parameters a and b; then the zero point value T = (-b / a), and the coordinate of the tag on the X-axis is X = v * T. The results of the two-dimensional fitting algorithm are as Figure 5 shown.

[0082] After that, use a general numerical optimization method to solve the ordinate Y of the tag. The optimization objective function is:[[]]

[0083]

[0084] where

[0085]

[0086] There are various choices for the specific numerical optimization algorithm, such as Newton's method, the steepest descent method, the LM algorithm, etc. k is 4π / λ, and after substituting the abscissa X of the tag, x can be obtained by calculating X - vt.

[0087] This embodiment uses a mobile reader to observe and sample tag signals from different locations, and with the help of high-resolution phase information, can obtain higher positioning accuracy. This embodiment uses a first-order differential phase filtering algorithm to effectively eliminate erroneous signals, allow signal loss and distortion, and has no restrictions on adjacent sampling intervals, and has a good anti-interference effect in practical environmental applications. This embodiment uses a sliding window fitting algorithm to effectively find the zero point of the first-order differential sequence of the phase, eliminate erroneous positioning, and improve positioning accuracy and algorithm reliability.

[0088] Example 2

[0089] Figure 6 This is a schematic diagram of the RFID tag positioning system. Figure 6 As shown, the present invention also provides an RFID tag positioning system, the system comprising:

[0090] The acquisition module 601 is used to acquire the phase of the RFID tag through an RFID reader to obtain a phase sequence of the RFID tag;

[0091] A calculation module 602 is used to process the phase sequence of the RFID tag, calculate the coordinates of the RFID tag based on the processed phase sequence, and obtain the positioning result of the RFID tag;

[0092] The output module 603 is used to output the positioning result of the RFID tag.

[0093] Preferably, the acquisition module 601 acquires the phase of the RFID tag through an RFID reader, and obtaining the phase sequence of the RFID tag includes:

[0094] The RFID reader continuously samples the phase of the RFID tag while moving and records the sampling timestamp. The phase θ of the RFID tag and the sampling time t conform to the following model:

[0095]

[0096] Among them, (X, Y) represents the coordinates of the tag, μ represents the phase shift treated as a fixed constant, λ represents the RF wavelength, and v is the speed at which the reader moves.

[0097] Preferably, the calculation module 602 processes the phase sequence of the RFID tag including:

[0098] Abnormal sample points are screened out by first-order difference and singular value filtering, where the first-order difference sequence θ′ of the phase is: θ′=θ(i+1)-θ(i).

[0099] Preferably, the calculation module 602 screens out abnormal sample points through singular value filtering, including:

[0100] For the first-order difference sequence θ′, set the sliding window length to N and the initial index to i. Take the subsequence θ′[i,i+N], calculate the lower quartile Q1, upper quartile Q3, and interquartile range IQR of the subsequence, and verify whether each value x in the subsequence belongs to [Q1-1.5IQR, Q3+1.5IQR]. If not, determine the sample point as an outlier point and set the sample value x to (Q1+Q3) / 2.

[0101] Preferably, the calculation module 602 calculates the coordinates of the RFID tag based on the processed phase sequence, and obtains the positioning result of the RFID tag including:

[0102] Use the sliding window to find the target data near the zero point, perform a least squares fit of the function y=aT+b on the data in the sliding window, and obtain the parameters a, b, the zero point value T=(-b / a), and the horizontal coordinate X=v*T of the RFID tag; solve the vertical coordinate Y of the RFID tag according to the optimization objective function to obtain the positioning result (X, Y) of the RFID tag;

[0103] Among them, the optimization objective function is:

[0104]

[0105]

[0106] x i is the horizontal coordinate of the reader's antenna, k = 4π / λ.

[0107] The specific implementation process of the functions realized by each module in this embodiment 2 is the same as the implementation process of each step in embodiment 1, and will not be repeated here.

[0108] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A RFID tag positioning method, It is characterized in that The method comprises: S1: collecting the phase of the RFID tag through an RFID reader to obtain a phase sequence of the RFID tag; S2: Processing the phase sequence of the RFID tag, calculating the coordinates of the RFID tag based on the processed phase sequence, and obtaining a positioning result of the RFID tag; S3: Output the positioning result of the RFID tag; The step of calculating the coordinates of the RFID tag based on the processed phase sequence to obtain the positioning result of the RFID tag includes: Use the sliding window to find the target data near the zero point, perform a least squares fit of the function y=aT+b on the data in the sliding window, and obtain the parameters a, b, the zero point value T=(-b / a), and the horizontal coordinate X=v*T of the RFID tag; solve the vertical coordinate Y of the RFID tag according to the optimization objective function to obtain the positioning result (X, Y) of the RFID tag; Among them, the optimization objective function E(Y) is: x i is the horizontal coordinate of the reader's antenna at the i-th phase sequence, k = 4π / λ.

2. The method according to claim 1, It is characterized in that The step of collecting the phase of the RFID tag by using an RFID reader to obtain the phase sequence of the RFID tag comprises: The RFID reader continuously samples the phase of the RFID tag while moving and records the sampling timestamp. The phase θ of the RFID tag and the sampling time t conform to the following model: Among them, (X, Y) represents the coordinates of the tag, μ represents the phase shift treated as a fixed constant, λ represents the RF wavelength, and v is the speed at which the reader moves.

3. The method according to claim 2, It is characterized in that The processing of the phase sequence of the RFID tag comprises: Through first-order difference and singular value filtering, abnormal sample points are screened out, where the first-order difference sequence of the phase θ ′ is: ′ =θ(i+1)-θ(i); i is the index of the differential sequence, and θ(i) is the i-th phase sequence value.

4. The method according to claim 3, It is characterized in that The method of filtering out abnormal sample points by singular value filtering includes: For the first-order difference sequence θ ′ , set the sliding window length to N; take the subsequence θ ′ [i,i+N], calculate the lower quartile Q1, upper quartile Q3, and interquartile range IQR of the subsequence, and verify whether each value x in the subsequence belongs to [Q1-1.5IQR,Q3+1.5IQR]; if not, determine the sample point as an outlier point and set x to (Q1+Q3) / 2.

5. An RFID tag positioning system, It is characterized in that The system comprises: An acquisition module, used for acquiring the phase of the RFID tag through an RFID reader to obtain a phase sequence of the RFID tag; A calculation module, used to process the phase sequence of the RFID tag, calculate the coordinates of the RFID tag based on the processed phase sequence, and obtain the positioning result of the RFID tag; An output module, used to output the positioning result of the RFID tag; The calculation module calculates the coordinates of the RFID tag based on the processed phase sequence, and obtains the positioning result of the RFID tag, including: Use the sliding window to find the target data near the zero point, perform a least squares fit of the function y=aT+b on the data in the sliding window, and obtain the parameters a, b, the zero point value T=(-b / a), and the horizontal coordinate X=v*T of the RFID tag; solve the vertical coordinate Y of the RFID tag according to the optimization objective function to obtain the positioning result (X, Y) of the RFID tag; Among them, the optimization objective function E(Y) is: x i is the horizontal coordinate of the reader's antenna at the i-th phase sequence, k = 4π / λ.

6. The system according to claim 5, It is characterized in that The acquisition module acquires the phase of the RFID tag through an RFID reader, and obtains the phase sequence of the RFID tag, including: The RFID reader continuously samples the phase of the RFID tag while moving and records the sampling timestamp. The phase θ of the RFID tag and the sampling time t conform to the following model: Among them, (X, Y) represents the coordinates of the tag, μ represents the phase shift treated as a fixed constant, λ represents the RF wavelength, and v is the speed at which the reader moves.

7. The system according to claim 6, It is characterized in that The calculation module processes the phase sequence of the RFID tag including: Abnormal sample points are filtered out by first-order difference and singular value filtering, where the first-order difference sequence of the phase θ ′ is: ′ =θ(i+1)-θ(i), θ(i) is the i-th phase sequence value.

8. The system according to claim 7, It is characterized in that The calculation module screens out abnormal sample points by singular value filtering, including: For the first-order difference sequence θ ′ , set the sliding window length to N, the initial index to i; take the subsequence θ ′ [i,i+N], calculate the lower quartile Q1, upper quartile Q3, and interquartile range IQR of the subsequence, and verify whether each value x in the subsequence belongs to [Q1-1.5IQR,Q3+1.5IQR]. If not, the sample point is determined as an outlier point and x is set to (Q1+Q3) / 2.

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