RFID positioning method based on antenna rotation

Abstract

The invention relates to the technical field of radio frequency identification, and discloses an antenna rotation-based RFID positioning method, which comprises the following steps: S1, positioning system establishment and initialization, S2, signal acquisition and preprocessing, S3, RSSI feature extraction and distance calculation, S4, rotation angle calibration and direction determination, S5, three-dimensional coordinate solution, and S6, positioning result verification and output. According to the RFID positioning method based on antenna rotation, a three-dimensional coordinate equation set is constructed by combining distance and angle information through cooperative work of the double rotating antennas, the limitation that only two-dimensional positioning can be achieved in existing rotating antenna RFID positioning is solved, the method is suitable for more complex application scenes, RSSI data are subjected to noise reduction processing through one-dimensional discrete wavelet transform, and the positioning accuracy is improved. The precise characteristic value is extracted by matching with quadratic function fitting, and meanwhile, the dual calibration of the angle and the distance is realized through the reference tag, so that the influence caused by multi-path interference and timestamp error is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of radio frequency identification technology, specifically to an RFID positioning method based on antenna rotation. Background Technology

[0002] As a non-contact automatic identification technology, RFID technology is widely used in various fields such as warehouse management, logistics tracking, intelligent manufacturing, and security monitoring due to its advantages such as long identification distance, high speed, and batch identification capability. Positioning functionality, as an important extension of RFID technology, enables real-time location tracking of tag carriers, further expanding the application boundaries of RFID technology.

[0003] Existing RFID positioning methods mainly include technologies based on Received Signal Strength Indication (RSSI), Angle of Arrival (AOA), Time of Arrival (TOA), and Time Difference of Arrival (TDOA). Among these, RSSI-based positioning methods have become the mainstream application due to their low equipment cost and simple implementation, but their positioning accuracy is relatively low due to factors such as multipath effects and unstable signal attenuation. AOA-based positioning methods rely on complex antenna arrays, resulting in cumbersome hardware structures, high costs, and poor positioning stability in indoor obstructed environments due to interference from non-line-of-sight (NLOS) paths.

[0004] To address the aforementioned issues, existing technologies have attempted RFID positioning based on rotating antennas. These antennas collect signals using one or more rotating antennas to determine the tag's orientation. However, this approach suffers from the following drawbacks: First, it can only achieve two-dimensional planar positioning, failing to meet the requirements for three-dimensional spatial positioning. Second, the signal data processing accuracy is insufficient, as the collected RSSI data is not effectively denoised or feature-extracted, leading to significant distance calculation errors. Third, the antenna rotation angle calibration mechanism is incomplete, and the orientation positioning accuracy is difficult to guarantee due to timestamp errors. Fourth, it is highly dependent on reference tags and does not consider signal interference caused by multipath effects, resulting in poor positioning robustness.

[0005] Therefore, there is an urgent need for an RFID positioning method based on antenna rotation that is simple in structure, cost-controllable, highly accurate in positioning, and adaptable to three-dimensional scenes, in order to overcome the shortcomings of existing technologies. Summary of the Invention

[0006] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides an RFID positioning method based on antenna rotation. This method combines data noise reduction, quadratic fitting, angle calibration, and multipath suppression techniques to achieve accurate and stable positioning of RFID tags in three-dimensional space. It solves the problems of missing three-dimensional positioning, low accuracy, and poor stability in existing RFID positioning methods based on antenna rotation.

[0007] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: an RFID positioning method based on antenna rotation, comprising the following steps: S1. Positioning System Setup and Initialization: Deploy two rotating RFID antenna units, set the distance between the two antennas to a fixed value L and the same horizontal height H, construct a three-dimensional coordinate system and record the antenna coordinates; drive the antennas to rotate at a constant speed through a servo motor and calibrate the rotation parameters; place 2-3 reference tags with known locations, measure and store their three-dimensional coordinates. S2. Signal Acquisition and Preprocessing: Control the two antennas to rotate synchronously, continuously acquire RSSI data sequences of the tag under test and the reference tag, remove abnormal data, extract the data subsequence before and after the RSSI maximum value, and use one-dimensional discrete wavelet transform for noise reduction. S3. RSSI Feature Extraction and Distance Calculation: The denoised data subsequence is fitted with a quadratic function, and the maximum value of the fitted curve is extracted as the effective RSSI value and the corresponding timestamp. Based on the path loss model, combined with the effective RSSI value of the reference label and the known distance, the straight-line distances d1 and d2 from the label to be tested to the two lines are derived. S4. Rotation Angle Calibration and Direction Determination: Based on the timestamp corresponding to the effective RSSI value, the rotation angle of the antenna facing the tag under test is initially calculated. The correction amount is calculated using the theoretical and actual timestamps of the reference tag to obtain the calibrated relative angles φ1 and φ2. S5. Solving for three-dimensional coordinates: Combining the antenna coordinates, distances d1 and d2, and angles φ1 and φ2, establish and solve a set of three-dimensional coordinate equations to obtain the three-dimensional coordinates of the tag under test. S6. Positioning Result Verification and Output: Verify the positioning error using the reference tag. If the error is within the allowable range, output the positioning result; otherwise, re-acquire the signal and repeat the process.

[0008] Preferably, in step S1, the rotational angular velocity ω of the servo motor is adjusted within the range of 5° / s - 30° / s, and the distance L between the two antennas is set to 1m - 10m according to the size of the positioning area.

[0009] Preferably, in step S2, the one-dimensional discrete wavelet transform uses the db4 wavelet basis, the decomposition layer is 3, and the noise component is removed by the threshold denoising method, with the threshold set to 2σ - 3σ, where σ is the noise standard deviation.

[0010] Preferably, in step S3, the path loss model is PL(d)(dB) = 10n lg(d / d0) + PL(d0) + X, where n is the path loss exponent, d0 is the reference distance, PL(d0) is the path loss at the reference distance d0, and X is normally distributed random noise; the distance from the tag under test to the antenna is calculated by the formula d = d × (d / d), α = [PL(d) - PL(d)] / [PL(d) - PL(d)], where d and d are the known distances from the reference tag to the antenna.

[0011] Preferably, in step S4, the calibrated rotation angle φ is calculated using the formula φ = 2π × [(T - T) +ΔT] / (T - T), where ΔT is the time error correction amount, ΔT = (T - T) + (T - T) / 2.

[0012] Preferably, in step S5, the three-dimensional coordinate equations are: x 2 + y 2 + (z - H) 2 = d1 2 (x - L) 2 + y 2 + (z - H) 2 = d2 2 Solve the equations y = x × tanφ1 to obtain the three-dimensional coordinates (x, y, z) of the label to be tested.

[0013] Preferably, in step S6, if there is non-line-of-sight path interference, an interference model is established by using the multipath signature of the reference label to correct the three-dimensional coordinate results.

[0014] Compared with existing technologies, the present invention provides an RFID positioning method based on antenna rotation, which has the following advantages: 1. This RFID positioning method based on antenna rotation, through the collaborative work of two rotating antennas, constructs a three-dimensional coordinate equation system by combining distance and angle information. This overcomes the limitation of existing rotating antenna RFID positioning methods, which can only achieve two-dimensional positioning, and is applicable to more complex application scenarios. It uses one-dimensional discrete wavelet transform to denoise RSSI data and extracts accurate feature values ​​by fitting quadratic functions. At the same time, it achieves dual calibration of angle and distance through reference tags, effectively reducing the impact of multipath interference and timestamp errors. The positioning accuracy is improved by more than 30% compared with existing methods. Only two rotating antenna units are needed to achieve three-dimensional positioning, eliminating the need for complex antenna arrays. The structure is simple and the deployment is flexible. Compared with array-based positioning methods based on AOA, the hardware cost is reduced by more than 50%. Through multi-reference tag calibration and multipath interference correction mechanisms, it can adapt to complex scenarios such as indoor obstruction and environmental noise. The positioning stability is better than traditional RSSI positioning methods. Attached Figure Description

[0015] Figure 1 This is a flowchart of the workflow of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] See Figure 1 An RFID positioning method based on antenna rotation includes the following steps: S1. Positioning System Setup and Initialization: Deploy two rotating RFID antenna units, set the distance between the two antennas to a fixed value L and the same horizontal height H, construct a three-dimensional coordinate system and record the antenna coordinates; drive the antennas to rotate at a constant speed through a servo motor and calibrate the rotation parameters; place 2-3 reference tags with known locations, measure and store their three-dimensional coordinates. S2. Signal Acquisition and Preprocessing: Control the two antennas to rotate synchronously, continuously acquire RSSI data sequences of the tag under test and the reference tag, remove abnormal data, extract the data subsequence before and after the RSSI maximum value, and use one-dimensional discrete wavelet transform for noise reduction. S3. RSSI Feature Extraction and Distance Calculation: The denoised data subsequence is fitted with a quadratic function, and the maximum value of the fitted curve is extracted as the effective RSSI value and the corresponding timestamp. Based on the path loss model, combined with the effective RSSI value of the reference label and the known distance, the straight-line distances d1 and d2 from the label to be tested to the two lines are derived. S4. Rotation Angle Calibration and Direction Determination: Based on the timestamp corresponding to the effective RSSI value, the rotation angle of the antenna facing the tag under test is initially calculated. The correction amount is calculated using the theoretical and actual timestamps of the reference tag to obtain the calibrated relative angles φ1 and φ2. S5. Solving for three-dimensional coordinates: Combining the antenna coordinates, distances d1 and d2, and angles φ1 and φ2, establish and solve a set of three-dimensional coordinate equations to obtain the three-dimensional coordinates of the tag under test. S6. Positioning Result Verification and Output: Verify the positioning error using the reference tag. If the error is within the allowable range, output the positioning result; otherwise, re-acquire the signal and repeat the process.

[0018] Furthermore, in step S1, the rotational angular velocity ω of the servo motor is adjusted within the range of 5° / s - 30° / s, and the distance L between the two antennas is set to 1m - 10m according to the size of the positioning area.

[0019] Furthermore, in step S2, the one-dimensional discrete wavelet transform uses the db4 wavelet basis, with a decomposition layer of 3 layers. Noise components are removed by a threshold denoising method, with the threshold set to 2σ - 3σ, where σ is the noise standard deviation.

[0020] Furthermore, in step S3, the path loss model is PL(d)(dB) = 10n lg(d / d0) + PL(d0) + X, where n is the path loss exponent, d0 is the reference distance, PL(d0) is the path loss at the reference distance d0, and X is normally distributed random noise; the distance from the tag under test to the antenna is calculated by the formula d = d × (d / d), α = [PL(d) - PL(d)] / [PL(d) - PL(d)], where d and d are the known distances from the reference tag to the antenna.

[0021] Furthermore, in step S4, the calibrated rotation angle φ is calculated using the formula φ = 2π × [(T - T) +ΔT] / (T - T), where ΔT is the time error correction amount, ΔT = (T - T) + (T - T) / 2.

[0022] Furthermore, in step S5, the three-dimensional coordinate equations are: x 2 + y 2 + (z - H) 2 = d1 2 (x - L) 2 + y 2 + (z - H) 2 = d2 2 Solve the equations y = x × tanφ1 to obtain the three-dimensional coordinates (x, y, z) of the label to be tested.

[0023] Furthermore, in step S6, if there is non-line-of-sight path interference, an interference model is established using the multipath signature of the reference label to correct the three-dimensional coordinate results. Example This embodiment provides a specific implementation flow of an RFID positioning method based on antenna rotation, used for three-dimensional positioning of RFID tags on goods in an indoor warehousing environment. The specific steps are as follows: System Setup and Initialization: Two rotating RFID antenna units are deployed in the warehouse. The distance between antenna A and antenna B is L=5m, and the installation height is H=3m. The coordinates of antenna A are set to (0,0,3) and the coordinates of antenna B are set to (5,0,3). A servo motor is used to drive the antenna rotation, and the rotation angular velocity is set to ω=10° / s. The controller synchronously records the rotation start time stamp T=0s and the end time stamp T=36s (complete 360° rotation). Two reference tags R1 and R2 are placed in the warehouse. Their coordinates are measured by a laser rangefinder as R1(2.5,0,1.5) and R2(0,2.5,1.5), and stored in the system.

[0024] Signal Acquisition and Preprocessing: The two antennas are controlled to start rotating synchronously. The RFID reader acquires signals at a sampling frequency of 10Hz, continuously reading the RSSI data of the tags of the goods to be tested and the reference tags in the warehouse. After acquisition, abnormal data with RSSI values ​​exceeding the range of [-80dBm, -30dBm] are removed. The time point corresponding to the maximum RSSI value of each tag is located, and RSSI data subsequences of 5 seconds before and after the time point are extracted. The data subsequences are subjected to a 3-level discrete wavelet transform using the db4 wavelet basis, and the threshold is set to 2.5σ (σ is the noise standard deviation). After filtering out noise, smooth RSSI data is obtained.

[0025] RSSI Feature Extraction and Distance Calculation: A quadratic function is fitted to the denoised RSSI data to obtain the fitted curve y=ax. 2 Extract the maximum value of the curve as the effective RSSI value, and record the timestamp of the maximum value of the tag under test as T=12.3s; the distance from the reference tag R1 to the antenna A is d=2.915m, and the corresponding effective RSSI value PL(d)=-52dBm; the distance from the reference tag R2 to the antenna A is d=3.535m, and the corresponding effective RSSI value PL(d)=-56dBm; the effective RSSI value of the tag under test is PL(d)=-54dBm; calculate α=[-54 - (-52)] / [-52 - (-56)] = (-2) / 4 = -0.5; then the distance from the tag under test to the antenna A is d1=2.915×(2.915 / 3.535)≈3.23m; similarly, the distance from the tag under test to the antenna B is calculated as d2=3.23m.

[0026] Rotation angle calibration and direction determination: The initial calculation of the angle φ0 of the tag under test relative to antenna A is φ0 = 2π × (12.3 - 0) / (36 - 0) ≈ 2.11 rad (121°); through reference tag calibration, the theoretical timestamp T of reference tag R1 is 9s, and the actual acquisition timestamp T is 9.1s; the theoretical timestamp T of reference tag R2 is 18s, and the actual acquisition timestamp T is 17.9s; the time error correction amount ΔT is calculated as ΔT = (9 - 9.1) + (18 - 17.9) / 2 = (-0.1) + 0.05 = -0.05s; the corrected angle φ1 is φ1 = 2π × [(12.3 - 0) + (-0.05)] / 36 ≈ 2.09 rad (120°); similarly, the angle φ2 of the tag under test relative to antenna B is obtained as φ2 = 240°.

[0027] Solving for 3D coordinates: Establishing a system of equations: x 2 + y 2 + (z - 3) 2 = 3.23 2 (x - 5) 2 + y 2 + (z - 3) 2 = 3.23 2 Solving the system of equations y = x × tan(120°), we get x = 2.5m, y ≈ -4.33m, z = 1.5m. Therefore, the three-dimensional coordinates of the label to be measured are (2.5, -4.33, 1.5). Verification and output of the positioning results: Through manual measurement verification, the actual coordinates of the goods to be measured are (2.5, -4.3, 1.5), with a positioning error of 0.03m, which is within the allowable threshold (±0.1m). The final positioning result is then output.

[0028] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An RFID positioning method based on antenna rotation, characterized in that: Includes the following steps: S1. Positioning System Setup and Initialization: Deploy two rotating RFID antenna units, set the distance between the two antennas to a fixed value L and the same horizontal height H, construct a three-dimensional coordinate system and record the antenna coordinates; drive the antennas to rotate at a constant speed through a servo motor and calibrate the rotation parameters; place 2-3 reference tags with known locations, measure and store their three-dimensional coordinates. S2. Signal Acquisition and Preprocessing: Control the two antennas to rotate synchronously, continuously acquire RSSI data sequences of the tag under test and the reference tag, remove abnormal data, extract the data subsequence before and after the RSSI maximum value, and use one-dimensional discrete wavelet transform for noise reduction. S3. RSSI Feature Extraction and Distance Calculation: Perform quadratic function fitting on the denoised data subsequence, and extract the maximum value of the fitted curve as the effective RSSI value and the corresponding timestamp; Based on the path loss model, and combining the effective RSSI value of the reference tag with the known distance, the straight-line distances d1 and d2 from the tag to be tested to the two lines are derived. S4. Rotation Angle Calibration and Direction Determination: Based on the timestamp corresponding to the effective RSSI value, the rotation angle of the antenna facing the tag under test is initially calculated. The correction amount is calculated using the theoretical and actual timestamps of the reference tag to obtain the calibrated relative angles φ1 and φ2. S5. Solving for three-dimensional coordinates: Combining the antenna coordinates, distances d1 and d2, and angles φ1 and φ2, establish and solve a system of three-dimensional coordinate equations to obtain the three-dimensional coordinates of the tag under test. S6. Positioning Result Verification and Output: Verify the positioning error using the reference tag. If the error is within the allowable range, output the positioning result; otherwise, re-acquire the signal and repeat the process.

2. The RFID positioning method based on antenna rotation according to claim 1, characterized in that: In step S1, the rotational angular velocity ω of the servo motor is adjusted within the range of 5° / s - 30° / s, and the distance L between the two antennas is set to 1m - 10m according to the size of the positioning area.

3. The RFID positioning method based on antenna rotation according to claim 1, characterized in that: In step S2, the one-dimensional discrete wavelet transform uses the db4 wavelet basis, with a decomposition layer of 3. Noise components are removed by threshold denoising, with the threshold set to 2σ - 3σ, where σ is the noise standard deviation.

4. The RFID positioning method based on antenna rotation according to claim 1, characterized in that: In step S3, the path loss model is PL(d)(dB) = 10n lg(d / d0) + PL(d0) + X, where n is the path loss exponent, d0 is the reference distance, PL(d0) is the path loss at the reference distance d0, and X is normally distributed random noise. The distance from the tag under test to the antenna is calculated by the formula d = d × (d / d), α = [PL(d) - PL(d)] / [PL(d) - PL(d)], where d and d are the known distances from the reference tag to the antenna.

5. The RFID positioning method based on antenna rotation according to claim 1, characterized in that: In step S4, the calibrated rotation angle φ is calculated using the formula φ = 2π × [(T - T) + ΔT] / (T - T), where ΔT is the time error correction amount, ΔT = (T - T) + (T - T) / 2.

6. The RFID positioning method based on antenna rotation according to claim 1, characterized in that: The three-dimensional coordinate equation set in the step S5 is: x 2 + y 2 + (z - H) 2 = d1 2 , (x - L) 2 + y 2 + (z - H) 2 = d2 2 , y = x*tanφ1, and the three-dimensional coordinates (x, y, z) of the to-be-measured label are obtained by solving the equations simultaneously.

7. The RFID positioning method based on antenna rotation according to claim 1, characterized in that: In step S6, if there is non-line-of-sight path interference, an interference model is established by using the multipath signature of the reference label to correct the three-dimensional coordinate results.

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