RFID indoor positioning system and method based on multi-feature information

Abstract

The invention provides an RFID indoor positioning system and method based on multi-feature information, and relates to the field of RFID and indoor positioning. In order to solve the technical problems of weak anti-interference capability and large positioning error of a single signal in indoor positioning, high-precision indoor positioning is realized by combining multidimensional feature information such as antenna readability, phase difference and RSSI (Received Signal Strength Indicator) signal strength and adopting a two-stage positioning strategy. In the coarse positioning stage, regions are divided according to antenna readability, and region subdivision is carried out by combining an RSSI difference value; in the fine positioning stage, a positioning algorithm is dynamically selected according to the readability parameter of the antenna: when the readability is greater than 2, a hyperbolic equation is constructed based on the phase difference, and a candidate position is optimized by using an RSSI (Received Signal Strength Indicator) difference value; and when the readability is 2, establishing a positioning equation set through the combination of the phase and the RSSI to solve a target coordinate. The method effectively solves the problems of weak anti-interference capability and large error of a traditional single signal feature positioning method, has the advantages of low deployment cost, high positioning precision, high environmental adaptability and the like, and can be widely applied to indoor positioning scenes such as warehouse logistics, intelligent shopping malls, medical navigation and the like.

Description

Technical Field

[0001] This invention belongs to the field of RFID indoor positioning, and in particular relates to an RFID indoor positioning system and method based on multi-feature information. Background Technology

[0002] Radio Frequency Identification (RFID) is an automatic identification technology that uses wireless radio frequency for non-contact, two-way data communication. Its principle involves data communication between an RFID reader and a passive tag to identify the target. Passive RFID technology offers advantages such as low cost, fast reading speed, wide range, no need for additional equipment, and high positioning accuracy. It has been widely applied in various fields including supply chain management, logistics management, access control, production line automation, and warehouse management. RFID-based positioning technology has also become a research hotspot and is one of the most promising information technologies.

[0003] RFID indoor positioning systems require the deployment of numerous RFID readers and tags within the target area, especially in large-scale scenarios such as shopping malls, warehouses, or hospitals, necessitating significant equipment investment to cover the entire area, thus increasing deployment costs. In existing positioning systems based on single signal features, phase is a precise feature parameter that can provide high positioning accuracy, but it is also affected by multipath effects, signal interference, and clock errors, introducing positioning errors. Positioning methods based on Received Signal Strength Indication (RSSI) are significantly affected by signal strength, which is also influenced by antenna gain, antenna and tag orientation, and complex indoor environments, often resulting in poor positioning performance and generally low accuracy. Therefore, researching RFID indoor positioning algorithms based on multiple feature information rather than relying on a single signal feature has become an urgent need. Summary of the Invention

[0004] Based on this, and addressing the technical shortcomings of existing positioning technologies that rely solely on a single signal feature, resulting in weak anti-interference capabilities and large positioning errors, this invention proposes an RFID indoor positioning system and method based on multi-feature information, combining antenna readability, phase, and RSSI signal characteristics. This system can provide the location coordinates of the target, thereby providing a low-cost, robust, and high-precision positioning solution for large-scale indoor scenarios such as warehouses, shopping malls, and hospitals.

[0005] This invention first provides an RFID indoor positioning system based on multi-feature information:

[0006] An RFID indoor positioning system based on multi-feature information comprises an RFID reader, a tag, four directional antennas, several network cables and several radio frequency cables, and a data processing terminal.

[0007] The RFID reader and directional antenna are used to collect the phase information required for positioning. The directional antenna is distributed in a rectangular pattern on the XOY plane. The data processing terminal is responsible for data processing and positioning calculation.

[0008] Optionally, the RFID reader / writer is an Impinj R420.

[0009] Optionally, the label model is the commercial label Alien-9630;

[0010] Optionally, the commercial directional antenna is the VIKITEK VA094;

[0011] Optionally, the data processing terminal is configured with an i5-13500H processor, 16GB of RAM, and a storage device containing the hardware control and positioning capabilities.

[0012] To address the technical problem, this invention also provides an RFID indoor positioning method based on multi-feature information, specifically including the following steps:

[0013] Step S1: Determine the readability range of the system through experiments, and divide the area into q1 to q7: During the experiment, the experimental scenario is 6m×6m, and the Impinj Speedway revolution R420 reader, which is compatible with the EPC Gen 2 protocol, is used and operates at a working frequency of 923.625MHz.

[0014] Step S2, Coarse Positioning Stage: Based on the criteria of antenna readability and Received Signal Strength Index (RSSI), the approximate location information of the tag is obtained. Specifically, the tag's region is determined according to the reading conditions of different antennas: when the antenna readability is 2 or 3, the region is directly determined; while when the antenna readability is 4, a more detailed division is required based on the positive or negative value of the difference in Received Signal Strength Index (RSSI), further subdividing region q7 into region q. a Region q b Region q c and region q d ;

[0015] Step S3, Fine Positioning Stage: A suitable positioning method is selected by determining the antenna readability parameters; specifically,

[0016] Step S31: When the number of readable antennas is greater than 2, construct a hyperbola based on the phase difference, and obtain a small number of candidate intersection points by combining the received signal strength RSSI difference. The target coordinates are obtained by assigning weights according to the received signal strength RSSI difference.

[0017] Step S32: When the number of readable antennas is equal to 2, a set of positioning equations is constructed using phase and received signal strength RSSI. Solving the set of equations yields the target coordinates.

[0018] The beneficial effects of this invention are:

[0019] (1) This invention uses commercial RFID readers and directional antennas. The system design is simple and elegant, which significantly reduces the overall implementation cost and enables efficient deployment with limited budget.

[0020] (2) By combining antenna readability, phase and received signal strength RSSI, this invention can provide reliable location information in both coarse and fine positioning stages, ensuring high-precision positioning in complex indoor environments and improving user experience and positioning effect.

[0021] (3) The positioning system of the present invention can be conveniently applied to a variety of typical indoor environments. It can quickly achieve positioning through simple settings. It is more flexible and has a wider range of applications than traditional positioning systems, which promotes the practical application of indoor positioning technology. Attached Figure Description

[0022] Figure 1 This is a flowchart of the algorithm of the present invention.

[0023] Figure 2 This is a diagram showing the antenna readability test results of the present invention.

[0024] Figure 3 This is a subdivision diagram of region q7 of the present invention.

[0025] Figure 4 This is a schematic diagram of the hyperbola-based four-antenna construction of the present invention.

[0026] Figure 5 This is a schematic diagram of the hyperbola-constructed three-antenna system of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The embodiments described are only one example of the present invention and not all examples.

[0028] This invention provides an RFID indoor positioning system and method based on multi-feature information. In this embodiment, the RFID reader in the figure uses Impinj R420, the passive tag in the tag array is Alien-9746, four commercial VIKITEK VA094 directional antennas are used, and the data processing terminal is configured with an i5-13500H processor, 16G of RAM, and storage devices containing the hardware control and positioning requirements.

[0029] The algorithm flow of this invention is as follows: Figure 1 As shown, the detailed steps of the algorithm implementation are as follows:

[0030] Step S1: Divide the positioning area according to the readability of each antenna:

[0031] An Impinj Speedway revolution R420 reader / writer, compatible with the EPC Gen 2 protocol, was used, operating at a frequency of 923.625MHz. Four directional antennas were designated T1, T2, T3, and T4, with coordinates T1(x1,y1), T2(x2,y2), T3(x3,y3), and T4(x4,y4), respectively, in cm. The distance between two closely spaced adjacent antennas was set to 2λ, where λ is the wavelength. Figure 2 As shown, the region division principle is as follows: a region that is only readable by T1, T2, and T3 is denoted as q1; a region that is only readable by T1, T2, and T4 is denoted as q2; a region that is only readable by T2, T3, and T4 is denoted as q3; a region that is only readable by T1, T3, and T4 is denoted as q4; a region that is only readable by T1 and T2 is denoted as q5; a region that is only readable by T3 and T4 is denoted as q7; and a region that is readable by all of T1, T2, T3, and T4 is denoted as q7.

[0032] Step S2, Coarse Positioning Stage: Based on the criteria of antenna readability and RSSI for determining the area division, the approximate location information of the tag is obtained;

[0033] First, according to Figure 2 The readability experiment results can be categorized according to the following principles:

[0034]

[0035] Here, Area represents the location region of the label.

[0036] Secondly, region q7 was divided into four regions using the RSSI difference between different antenna pairs, namely region q a Region q b Region q c and region q d ,like Figure 3As shown. Let Δ1 be the RSSI difference between the received signal strength of directional antenna T1 and directional antenna T2, Δ2 be the RSSI difference between the received signal strength of directional antenna T2 and directional antenna T4, Δ3 be the RSSI difference between the received signal strength of directional antenna T1 and directional antenna T3, and Δ4 be the RSSI difference between the received signal strength of directional antenna T3 and directional antenna T4. The division rule for region q7 is as follows: First, region 1 and region 2 are determined by Δ1 and Δ2, and Δ2 and Δ3 respectively. If region 1 and region 2 are consistent, region 1 is directly output; if they are inconsistent, region 3 is determined by Δ3 and Δ4. When region 3 matches any result of region 1 or region 2, the consistent result is used as the final output.

[0037] This completes the coarse positioning of the label;

[0038] Step S3, Fine Positioning Stage: Select a suitable positioning method by determining the number of readable antennas;

[0039] Step S31: When the number of readable antennas is greater than 2, first construct a hyperbola based on the phase difference to obtain the candidate coordinates of the tag;

[0040] (1) When the number of readable antennas is 4:

[0041] In an RFID system, the phase measured by the reader is represented as:

[0042]

[0043] Where λ is the wavelength, d is the communication distance between the directional antenna and the tag, and θ T The inherent phase shift θ is caused by the transceiver circuit. e It is the multipath phase shift caused by the reflection and diffraction of signals through different paths in an indoor environment.

[0044] Two directional antennas, T1 and T2, have measured phase values ​​θ1 and θ2, respectively. The tag's position is A(x,y), and the distances from the tag to the two directional antennas are d1 and d2, respectively. Then, θ1 and θ2 are expressed as:

[0045]

[0046] By subtracting equation (3) from equation (4), the inherent phase shift θ is eliminated. T When directional antennas T1 and T2 are close to each other, the multipath effect of the two antennas is similar, and the multipath phase shift θ can also be eliminated through the above operation. e Therefore, the relationship between the phase difference Δθ and the distance difference Δd is expressed as:

[0047]

[0048] Where D = |T1T2|, |T1T2| is the distance between directional antennas T1 and T2, and k is the ambiguity parameter. By setting T1 and T2 as the focal points, equation (5) is transformed into:

[0049]

[0050] Where a = Δd / 2, c = D / 2.

[0051] like Figure 4 As shown, when the antenna readability parameter is 4, the four directional antennas can be used for target localization. The distances from tag A(x,y) to the four antennas are d1=|AT1|, d2=|AT2|, d3=|AT3|, d4=|AT4|, respectively. The four antennas are represented as T1(x1,y1), T2(x2,y2), T3(x3,y3), and T4(x4,y4), and the measured phase values ​​are represented as θ1, θ2, θ3, and θ4. Therefore, two sets of hyperbolas will be constructed, resulting in:

[0052]

[0053] in,

[0054]

[0055] Where Δd1=d2-d1, Δd2=d4-d3, Δθ1=θ2-θ1, Δθ2=θ4-θ3, D1=|T1T2|, D2=|T3T4|, and k1 and k2 are ambiguity parameters. Two sets of hyperbolic equations are constructed using four directional antennas, expressed as:

[0056]

[0057] The periodicity of the phase leads to multiple possibilities for k, resulting in multiple hyperbolas between the two antennas. Furthermore, the number of hyperbolas gradually increases with the distance between the directional antennas. The intersections of the hyperbolas generate numerous intersection points, each of which is a candidate location for the tag.

[0058] (2) When the number of readable antennas is 3:

[0059] like Figure 5 As shown, the tag is located within the readable areas of the three antennas, namely T1, T2, and T3, then:

[0060]

[0061] Where Δd′2=d3-d1, Δθ′2=θ3-θ1, D′2=|T1T3|, the constructed hyperbola equation is:

[0062]

[0063] Secondly, after establishing the phase-based hyperbolic equation, the hyperbola still has multiple intersection points, each forming a candidate location set. The Received Signal Strength Indicator (RSSI) is used to filter these candidate location sets. Let N represent the number of intersection points of the hyperbola, and the coordinates of each intersection point be (X, Y, Z). i ,Y i ), It is the distance from the i-th intersection point to the n-th antenna, expressed as:

[0064]

[0065] Where ζ is the number of readable antennas. The theoretical received signal strength (RSSI) at each intersection and for each antenna is:

[0066]

[0067] Where RSSI0 is the received signal strength RSSI value at reference distance d0, and n e It is the environmental channel constant factor, which has different values ​​in different environments. The environmental factor used in this patent is 2.4, as determined by test results.

[0068] Therefore, the RSSI difference between the received signal strength from the i-th intersection point to the n-th directional antenna is:

[0069]

[0070] in, It is the actual received signal strength (RSSI) value received by the tag from the nth directional antenna.

[0071] make Indicates the difference in antenna n The minimum corresponding intersection index is represented as:

[0072]

[0073] Therefore, when the number of readable antennas ζ is 4, four intersection points i1, i2, i3 and i4 are obtained from the four antennas respectively, and the coordinates of the intersection point corresponding to each i are (X i ,Y i When each intersection point i is correctly identified, the four coordinates are consistent, and any one of them can be chosen as the final target position. When at least two i are equal, the coordinates of the corresponding i are directly selected as the final target position. However, if each i is different (i.e., i1≠i2≠i3≠i4), the weight of each candidate position is first calculated based on the received signal strength RSSI, expressed as:

[0074]

[0075] in, This represents the theoretical distance between a given candidate location and the nth antenna. Under these conditions, the actual received signal strength was observed. The likelihood probability is then normalized to the weights as follows:

[0076]

[0077] The final positioning coordinates of the tag are:

[0078]

[0079] When the number of readable antennas ζ is 3, three intersection points i1, i2, and i3 are obtained from the three antennas respectively, and the coordinates of the intersection point corresponding to each i are (X... i ,Y i The process of solving the coordinates is the same as when the number of readable antennas ζ is 4.

[0080] Step S32: When the number of readable antennas is 2, the tag is located in the area readable by both antennas. When it is in area q6, only directional antennas T3 and T4 can detect the tag. Therefore, the phase difference caused by the arrival signals from the tag to the two directional antennas is:

[0081]

[0082] Where d3 and d4 represent the distances from the target to directional antennas T3 and T4, respectively, and k′ is the ambiguity parameter.

[0083] The relationship between RSSI and distance is expressed as follows:

[0084] d = 10^(abs(RSSI) - RSSI0) / 10n e (twenty four)

[0085] Then d3 and d4 are represented as follows:

[0086]

[0087] Therefore, the final coordinates (x, y) of the label are obtained by solving this system of equations. The solution process for region q5 is the same as that for region q6.

[0088] At this point, the precise positioning of the label is complete.

[0089] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, all equivalent substitutions, modifications, alterations, etc., made according to the disclosure of the present invention should be included within the scope of protection of the present invention.

Claims

1. An RFID indoor positioning system based on multi-feature information, characterized in that, Includes an RFID reader / writer, The system includes a passive tag, four directional antennas, several network cables and several radio frequency cables, and a data processing terminal. The RFID reader and directional antennas are used to collect the phase information required for positioning. The directional antennas are distributed in a rectangular pattern on the XOY plane. The data processing terminal is responsible for data processing and location calculation.

2. The RFID indoor positioning system based on multi-feature information according to claim 1, characterized in that... This invention includes an RFID indoor positioning method based on multi-feature information, characterized by comprising the following steps: Step S1: Divide the positioning area according to the readability of each antenna: The four directional antennas are denoted as T1, T2, T3, and T4, with coordinates T1(x1,y1), T2(x2,y2), T3(x3,y3), and T4(x4,y4), respectively. The area division principle is as follows: the area readable only by T1, T2, and T3 is denoted as q1; the area readable only by T1, T2, and T4 is denoted as q2; the area readable only by T2, T3, and T4 is denoted as q3; the area readable only by T1, T3, and T4 is denoted as q4; the area readable only by T1 and T2 is denoted as q5; the area readable only by T3 and T4 is denoted as q7; and the area readable by all three antennas (T1, T2, T3, and T4) is denoted as q7. Step S2, Coarse Positioning Stage: Based on the criteria of antenna readability and received signal strength RSSI, the area division is determined to obtain the approximate location information of the tag; First, the division principle can be expressed as: Here, Area represents the location region of the label; Secondly, region q7 was divided into four regions using the RSSI difference between different antenna pairs, namely region q a Region q b Region q c and region q d Let Δ1 be the RSSI difference between the received signal strength of directional antenna T1 and directional antenna T2, Δ2 be the RSSI difference between the received signal strength of directional antenna T2 and directional antenna T4, Δ3 be the RSSI difference between the received signal strength of directional antenna T1 and directional antenna T3, and Δ4 be the RSSI difference between the received signal strength of directional antenna T3 and directional antenna T4. The division rule of region q7 is as follows: First, region 1 and region 2 are determined by Δ1 and Δ2, and Δ2 and Δ3 respectively. If region 1 and region 2 are consistent, the region is directly output. If they are inconsistent, region 3 is determined by Δ3 and Δ4. When region 3 matches any result of region 1 or region 2, the consistent result is used as the final output. This completes the coarse positioning of the label; Step S3, Fine Positioning Stage: Select a suitable positioning method by determining the number of readable antennas; Step S31: When the number of readable antennas is greater than 2, first construct a hyperbola based on the phase difference to obtain the candidate coordinates of the tag; (1) When the number of readable antennas is 4: In an RFID system, the phase measured by the reader is represented as: Where λ is the wavelength, d is the communication distance between the directional antenna and the tag, and θ T The inherent phase shift θ is caused by the transceiver circuit. e It is the multipath phase shift caused by the reflection and diffraction of signals through different paths in an indoor environment; The directional antennas are T1 and T2, and the measured phase values ​​are θ1 and θ2, respectively. The tag's position is A(x,y), and the distances from the tag to the two directional antennas are d1 and d2, respectively. Then, θ1 and θ2 are expressed as: By subtracting equation (3) from equation (4), the inherent phase shift θ is eliminated. T and multipath phase shift θ e Therefore, the relationship between the phase difference Δθ and the distance difference Δd is expressed as: Where D = |T1T2|, |T1T2| is the distance between directional antenna T1 and directional antenna T2, and k is the ambiguity parameter. By setting T1 and T2 as the focus, equation (5) is transformed into: Where a = Δd / 2, c = D / 2; When the number of readable antennas is 4, four directional antennas are used for target localization; the distances from tag A(x,y) to the four antennas are d1=|AT1|, d2=|AT2|, d3=|AT3|, d4=|AT4|, respectively, where the four antennas are represented as T1(x1,y1), T2(x2,y2), T3(x3,y3), and T4(x4,y4), respectively, and the measured phase values ​​are θ1, θ2, θ3, and θ4, respectively. Two sets of hyperbolas can be constructed to obtain: in, Where Δd1=d2-d1, Δd2=d4-d3, Δθ1=θ2-θ1, Δθ2=θ4-θ3, D1=|T1T2|, D2=|T3T4|, and k1 and k2 are ambiguity parameters; two sets of hyperbolic equations are constructed using four directional antennas, expressed as: in, (2) When the number of readable antennas is 3: The tag is located within the readable areas of three directional antennas, designated T1, T2, and T3. Therefore: Where Δd′2=d3-d1, Δθ′2=θ3-θ1, D′2=|T1T3|, k′2 is the ambiguity parameter, and the constructed hyperbolic equation is: Next, we solve equation (14) to obtain the intersection points of the hyperbola; let N represent the number of intersection points of the hyperbola, and the coordinates of each intersection point be (X... i ,Y i ), i = 1, 2, ..., N, It is the distance from the i-th intersection point to the n-th antenna, expressed as: Where ζ is the number of readable antennas, and the theoretical received signal strength (RSSI) value for each intersection and each directional antenna is: Where RSSI0 is the received signal strength RSSI value at reference distance d0, and n e It is the environmental channel constant factor; Therefore, the RSSI difference between the received signal strength from the i-th intersection point to the n-th directional antenna is: in, It is the actual received signal strength (RSSI) value received by the tag from the nth directional antenna; make Indicates the difference in antenna n The intersection index corresponding to the minimum is represented as: Therefore, when the number of readable antennas ζ is 4, four intersection points i1, i2, i3, and i4 are obtained from the four antennas respectively, and the coordinates of the intersection point corresponding to each i are (X... i ,Y i When each intersection point i is correctly identified, the four coordinates are consistent, and any one of them can be chosen as the final target position. When at least two i are equal, the coordinates of the corresponding i are directly selected as the final target position. However, if each i is different (i.e., i1≠i2≠i3≠i4), the weight of each candidate position is first calculated based on the received signal strength RSSI, expressed as: in, This represents the theoretical distance between a given candidate location and the nth antenna. Under these conditions, the actual received signal strength was observed. The likelihood probability is then normalized to the weights as follows: The final positioning coordinates of the tag can be represented as: When the number of readable antennas ζ is 3, three intersection points i1, i2, and i3 are obtained from the three antennas, and the corresponding intersection point coordinates are (X... i ,Y i The process of solving for its coordinates is the same as when the number of readable antennas ζ is 4. Step S32: When the number of readable antennas is 2, the tag is located in the area readable by both antennas; when in area q6, only directional antennas T3 and T4 can detect the tag, and the phase difference caused by the arrival signals from the tag to the two directional antennas is: Where d3 and d4 represent the distances from the target to directional antennas T3 and T4, respectively, and k′ is the ambiguity parameter; The relationship between received signal strength (RSSI) and distance is expressed as follows: d=10 ^ (abs(RSSI)-RSSI0) / 10n e (24) Then d3 and d4 are represented as follows: Therefore, the final coordinates (x, y) of the label can be obtained by solving this system of equations; The solution process for region q5 is the same as that for region q6; At this point, the precise positioning of the label is complete.

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