CN114742082A - Passive ultrahigh frequency RFID relative positioning method based on phased array reader antenna - Google Patents
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Abstract
The invention belongs to the technical field of mobile communication, and relates to a passive UHF RFID relative positioning method based on a phased array reader antenna. The method comprises the following steps: establishing an ultrahigh frequency RFID relative positioning scene based on a phased array antenna, deducing and solving a gain expression of the phased array antenna, obtaining a receiving field intensity ideal profile under a simulation condition, correcting an actually measured field intensity profile by using the ideal profile, and evaluating the corrected profile to realize relative positioning of the tag by adopting a relatively high degree of steepness. The method has the characteristics that the phased array antenna is utilized to carry out relative positioning, the requirements of the system on the environment and the field are reduced, the sequencing error problem caused by the fact that a single-point timestamp is used as a positioning basis can be solved by the position distinguishing method based on the profile abruptness, and the requirement of a user on carrying out relative positioning on the tag array under a passive ultrahigh frequency RFID system can be met.
Description
Technical Field
The invention belongs to the technical field of mobile wireless communication, and relates to a passive ultrahigh frequency RFID relative positioning method based on a phased array reader antenna.
Background
Ultra High Frequency Radio Frequency Identification (UHF RFID) technology is one of the key technologies in the internet of things industry, and has been widely applied to various fields such as industrial automation, commercial automation, transportation control and management, and the like. In production and life, a plurality of scenes such as book management, warehouse logistics, indoor navigation and the like need to identify and position targets. A typical passive UHF RFID positioning system mainly measures the spatial position of an article based on the reception intensity of radio frequency communication between a reader/writer and a tag mounted on an object by using the unique identification characteristic of an electronic tag, and is mainly applied to the field of indoor positioning in which a global positioning system is difficult to perform. In application scenarios (such as luggage conveyer belt, book management, etc.) with densely distributed targets, the relative location of an individual in a dense group is more concerned by the RFID system than the absolute location information of the target, and the relative positioning method based on the RFID technology has become a research hotspot of the industry and academia.
The PinIt system proposed by Dina Katabi et al of the massachusetts institute of technology, utilizes a synthetic aperture radar to extract multipath information in the environment, and obtains position information of the tag based on a multipath profile and a dynamic time warping technique. The OTrack and STPP algorithms proposed by shang guan longfei et al, the university of qing, to solve the problem of positioning in pipeline scenes and book scenes. The OTrack algorithm establishes a probability model for identifying the transient critical area, and monitors the critical area of the reading rate by using the OTrack protocol to acquire the relative sequence of the tags. The STPP algorithm acquires a tag phase profile by moving a reader antenna, and acquires the spatial sequence of the tag by using timestamp information of a peak position. Although the above relative positioning method achieves good results, the following challenges still remain: 1) The PinIt system needs to utilize general software radio equipment, higher requirements are put on equipment functions, and a reference label needs to be laid in the actual use process, so that the application limitation is aggravated; 2) both OTrack and STPP employ microstrip antennas with fixed radiation patterns as reader antennas. In order to obtain the profile information of the phase or the receiving field intensity, the reader antenna is usually required to be mounted on a movable device, so that the dependence degree of the system on the environment and the field is further increased; 3) OTrack and STPP use the highest point time stamp information of the receiving field intensity outline and the phase outline as the positioning basis, but the single point time stamp data has poor robustness relative to noise and is easy to cause sequencing deviation.
Aiming at the problems and the defects, the invention designs an ultrahigh frequency RFID relative positioning method based on a phased array antenna, which realizes the high-precision relative positioning of a tag array by constructing a relative positioning scene of an RFID system based on a phased array antenna reader and a dipole antenna tag, simulates a gain expression of the phased array antenna to obtain a receiving outline of the tag array, corrects the actually measured receiving outline by using the simulated receiving outline, calculates the steepness of each tag according to the corrected outline, sorts the tags according to the timestamp and the steepness of the receiving outline, and further relatively positions all the tags.
Disclosure of Invention
The invention aims to provide a passive ultrahigh frequency RFID relative positioning method based on a phased array reader antenna.
The method comprises the following specific steps:
step 1; establishing a relative positioning scene suitable for passive ultrahigh Frequency RFID (radio Frequency identification) by taking a dipole antenna selected as a passive tag antenna and a phased array antenna selected as a reader antenna as modeling conditions;
step 2: the method comprises the following steps of selecting a space rectangular coordinate system for the purpose of accurately evaluating tag field intensity information received by a reader, and establishing a reader phased array antenna gain expression model according to an electromagnetic field theory: gR(θR，φR)＝eD(θR，φR) Wherein G isR(θR，φR) Expressed in the radial direction (theta)R，φR) Gain of reader antenna, D (theta)R，φR) Is a directivity coefficient and can be expressed as
Wherein S (theta)R，φR) Is an array factor and can be expressed as
In the phased array antenna gain model, the phased array antenna is positioned on a YOZ plane, the center of mass of the antenna is positioned on an origin O, the normal direction is coincided with the positive direction of the X axis, and the O point and a point A in the space form a ray vector
Is the direction of radiation, θRRepresents from
To
Angle of inclination of phiRRepresents from
To
The rotation angle between the projections of the XOY plane, e denotes the efficiency factor, ImAnd InRepresenting the excitation amplitude along the Y-axis and Z-axis, respectively, M and N representing the array element index, M and N representing the total number of array elements along the Y-axis and Z-axis, respectively, YmAnd znRepresenting the coordinates of the array elements along the Y-axis and Z-axis, dyAnd dzRepresenting the distance difference between adjacent array elements, and respectively representing excitation phase difference along a Y axis and a Z axis by beta and gamma;
and step 3: determining a gain expression according to the structural characteristics of the array antenna, selecting a microstrip antenna with a common 2 × 2 array structure for illustration, and setting e as 1, Im＝In＝1，k＝2π/λ， dz＝dyWhen the array element coordinates are (0, -0.25 λ, 0.25 λ), (0, -0.25 λ, 0.25 λ), (0, 0.25 λ, -0.25 λ), (0, -0.25 λ, and-0.25 λ), respectively, at 0.5 λ, the array element coordinates can be obtained as (0, -0.25 λ, and-0.25 λ), respectively)
Further, the gain expression of the reader antenna may be expressed as
In the formula
And 4, step 4: let the integrand in the reader antenna expression in step 3 be Q, i.e.
Expanding Q, i.e. Q ═ e1+e2+e3+e4+e5+e6+e7+e8+e9Using mathematical tools to pair expanded e1～e9Respectively at thetaR∈[0，π]And phiR∈[0，π]The integral interval of (a) is subjected to constant integral operation, and the calculation result is substituted into the antenna gain expression in the step (3), so that G (theta) can be obtainedR，φR) Is shown as
In the formula
According to the expression, the gain division and the directivity coefficient theta of the phased array antennaRAnd phiRIn addition to this, the phase difference between the excitation phases β and γ of the phased array antenna is also related, i.e. by adjusting θR、φRβ and γ may change the gain of the antenna;
and 5: a simulation model is built for the passive ultrahigh frequency RFID relative positioning scene in the step 1, phased array antennas and tag arrays are placed in the same space rectangular coordinate system, tags face the phased array antennas and are placed perpendicular to an XOY plane and are arranged along the Y-axis direction, the phased array antennas are placed in the tag distribution center, and the centers of all tags in the system and the centers of the phased array antennas are placed at the same height;
step 6: the system changes the main lobe radiation direction of the antenna by adjusting the excitation phase differences beta and gamma, defines the main lobe radiation rotation angle of the antenna as theta, the theta represents the included angle between the radiation direction of the main lobe of the antenna and the positive half shaft of the Y axis, and the main lobe of the array antenna sequentially scans each label to obtain the receiving outline of each label in the process that the theta is increased from 0 degree to 180 degrees;
and 7: according to the theory of the array antenna, as the excitation changes, the antenna directional diagram will change continuously, so that the difference of the receiving field intensity profiles obtained by different tags is large, when the radiation rotation angle θ of the main lobe is 90 °, the steepness of the receiving profile of each tag is increased significantly, when the radiation rotation angle θ of the main lobe is 0 ° and θ is 180 °, the steepness of the receiving profile of each tag is decreased significantly, when a tag approaches the array antenna, the highest point of the receiving profile is likely to appear near θ 90 °, the tags are divided into two groups according to the timestamp information of the highest point of the receiving profile, one group is located on the left side of the array antenna, and the other group is located on the right side of the array antenna according to the formula
Calculating the profile steepness degree of each label, wherein K is the profile steepness degree of the label, L is the number of sampling points of the receiving profile, and Pr，TIndicating the receiving field strength value, P, corresponding to the l-th sampling pointr，T(l +1) represents the receiving field intensity value corresponding to the l +1 sampling point;
and step 8: for the left label of the array antenna, the K values are arranged in an ascending order to obtain the position information of the left label, for the right label of the array antenna, the K values are arranged in a descending order to obtain the position information of the right label, and finally, the position information of the labels on the two sides is combined to obtain the position information of all the labels;
and step 9: using the ranking accuracy C as an evaluation standard of a relative positioning system, wherein the expression of the ranking accuracy is C-NT/NTotalWhere C is the rank accuracy, NTTo order the correct number of tags, NTotalIs the total number of labels;
step 10: keeping the interval between adjacent tags in the tag array unchanged, taking the vertical distance between the phased array antenna and the tag array as an optimization variable, performing multiple performance simulations, estimating the receiving field intensity profile of each tag according to the methods in the steps 1 to 6 in each simulation, performing relative positioning on each tag by adopting the methods in the steps 7 to 9, finding out the corresponding optimal vertical distance with the maximum sequencing accuracy C from the multiple simulation results, and storing the field intensity profile of the tag array under the theoretical condition at the moment;
step 11: and (3) building an actual measurement scene according to the simulation model in the step (5), applying the optimal vertical distance in the step (10) to the actual measurement scene, executing the operation in the step (6) to obtain a receiving field intensity profile of the tag array, correcting the actual measurement field intensity profile by using the receiving field intensity profile simulated in the step (10), executing the operations from the step (7) to the step (8), obtaining the relative position information of each tag under the actual measurement condition, and realizing relative positioning.
The invention aims to provide a passive ultrahigh frequency RFID relative positioning method based on a phased array reader antenna. The method comprises the steps of deducing a general expression aiming at the gain of a phased array reader antenna, realizing the positioning of a tag array by constructing a passive ultrahigh frequency RFID relative positioning system based on the phased array antenna, obtaining the corresponding optimal vertical distance and field intensity profile when the sequencing accuracy is maximum in a simulation result by establishing a simulation model the same as that of an actual measurement system, applying the optimal vertical distance to an actual measurement scene, correcting the obtained actual measurement field intensity profile by the simulated field intensity profile, sequencing the tag array by performing abruptness calculation and time stamping on the corrected field intensity profile, further obtaining accurate tag position information, and realizing the passive ultrahigh frequency RFID relative positioning of the phased array reader antenna.
Description of the drawings:
FIG. 1 is a block flow diagram of the present invention;
FIG. 2 is a diagram of a phased array antenna radiation scenario;
FIG. 3 is an ideal profile of the field strength of the tag receiver;
FIG. 4 is a measured scene graph;
fig. 5 is a receiving field strength correction profile.
The specific implementation mode is as follows:
as shown in fig. 2, the reader antenna is a phased array antenna, a radiation scene of the phased array antenna is constructed, a space rectangular coordinate system is selected, and a reader phased array antenna gain expression model is established according to an electromagnetic field theory: gR(θR，φR)＝eD(θR，φR) Wherein G isR(θR，φR) Expressed in the radial direction (theta)R，φR) Antenna gain of reader, D (theta)R，φR) Is a directivity coefficient and can be expressed as
Wherein S (theta)R，φR) Is an array factor and can be expressed as
In the phased array antenna gain model, the phased array antenna is positioned on a YOZ plane, the center of mass of the antenna is positioned on an origin O, the normal direction is coincided with the positive direction of the X axis, and the O point and a point A in the space form a ray vector
Is the direction of radiation, θRRepresents from
To
Angle of inclination of phiRRepresents from
To
The rotation angle between the projections of the XOY plane, e denotes the efficiency factor, ImAnd InRepresenting the excitation amplitude along the Y-axis and Z-axis, respectively, M and N representing the array element index, M and N representing the total number of array elements along the Y-axis and Z-axis, respectively, YmAnd znRepresenting the coordinates of the array elements along the Y-axis and Z-axis, dyAnd dzRepresenting the distance difference between adjacent array elements, and beta and gamma represent the excitation phase difference along the Y-axis and the Z-axis, respectively.
Determining gain expression according to structural characteristics of array antenna, and selecting common 2 × 2 arrayThe microstrip antenna with a column structure is exemplified, and each parameter of the 2 × 2 phased array antenna is e-1, Im＝In＝1，k＝2π/λ，dz＝dyThe matrix element coordinates were (0, -0.25 λ, 0.25 λ), (0, -0.25 λ, 0.25 λ), (0, 0.25 λ, -0.25 λ), (0, -0.25 λ, and-0.25 λ), respectively, and the values were obtained
The gain expression of the reader antenna can be expressed as
In the formula
Making the integrand of the array antenna gain expression equal to Q, i.e.
Expanding Q, i.e. Q ═ e1+e2+e3+e4+e5+e6+e7+e8+e9Using mathematical tools to pair expanded e1～e9Respectively at thetaR∈[0，π]And phiR∈[0，π]The integral interval of (a) is subjected to constant integral operation, and the calculation result is substituted into the antenna gain expression in the step (3), so that G (theta) can be obtainedR，φR) Is shown as
In the formula
A passive ultrahigh frequency RFID relative positioning scene simulation model is built, a phased array antenna and a tag array are placed in the same space rectangular coordinate system, tags face the phased array antenna and are placed perpendicular to an XOY plane and are arranged along the Y-axis direction, the phased array antenna is placed in a tag distribution center, and the centers of all tags in the system and the centers of the phased array antenna are placed at the same height. The system changes the main lobe radiation direction of the antenna by adjusting the excitation phase differences beta and gamma, defines the main lobe radiation rotation angle of the antenna as theta, the theta represents the included angle between the radiation direction of the main lobe of the antenna and the positive half shaft of the Y axis, the theta rotates from 0 degree to 180 degrees, the main lobe of the array antenna sequentially scans each label, and the receiving outline of each label is obtained.
Dividing the tags into two groups according to the timestamp information of the highest point of the receiving outline, wherein one group is positioned on the left side of the array antenna, the other group is positioned on the right side of the array antenna, and the tags are divided into two groups according to a formula
Calculating the profile steepness of each label, wherein K is the profile steepness of the label, L is the number of sampling points of the receiving profile, and Pr，TIndicating the receiving field strength value, P, corresponding to the l-th sampling pointr，T(l +1) represents the receiving field intensity value corresponding to the l +1 th sampling point, for the left label of the array antenna, the K values are arranged in an ascending order to obtain the position information of the left label, for the right label of the array antenna, the K values are arranged in a descending order to obtain the position information of the right label, and finally, the position information of the labels on the two sides is combined to obtain the position information of all the labels.
Using the ranking accuracy C as an evaluation standard of a relative positioning system, wherein the expression of the ranking accuracy is C-NT/NTotalWhere C is the rank accuracy, NTTo order the correct number of tags, NTotalKeeping the interval between adjacent tags in the tag array unchanged for the total number of tags, changing the vertical distance between the phased array antenna and the tag array, and performing multiple performance simulations, wherein in each simulation, each tag is subjected toAnd (3) relative positioning, finding out the optimal vertical distance corresponding to the maximum sequencing accuracy C from the results of multiple simulations, and storing the field intensity profile of the tag array under the theoretical condition at the moment, as shown in fig. 3.
The method comprises the steps of building an actual measurement scene according to a simulation model, applying an optimal vertical distance obtained through simulation to the actual measurement scene, obtaining a field intensity profile of a label array from actual measurement, correcting the actual measurement field intensity profile by using the simulated field intensity profile under the condition of the optimal vertical distance, dividing the labels into two groups according to timestamp information of the highest point of a receiving profile, calculating the abruptness of each label profile by using an abruptness formula, arranging K values in an ascending order for the left labels of the array antenna to obtain the position information of the left labels, arranging the K values in a descending order for the right labels of the array antenna to obtain the position information of the right labels, obtaining the relative position information of each label under the actual measurement condition, and realizing relative positioning.
The following is a specific embodiment: the actually measured scene is as shown in fig. 4, the tag array is composed of 7 dipole antenna tags, the distance between the phased array antenna and the tag array is set to be the optimal vertical distance according to the simulation result, the phased array antenna collects the receiving field intensity profile of the tag array under the actually measured condition, the ideal profile shown in fig. 3 is used for correction, fig. 5 shows the corrected receiving field intensity profile, the tags are relatively positioned by using a steepness method, and the steepness of the obtained field intensity profiles of the tags 1 to 7 is 3.2550 × 10 respectively-5、4.2222×10-5、 6.6170×10-5、6.9863×10-5、6.9358×10-5、4.7637×10-5、2.9397×10-5The highest point of the field intensity profile of the label 4 appears near the main lobe rotation angle theta of 90 degrees, the labels with the highest points of the profile appearing at the left side of the highest point of the label 4 are divided into a first group, the first group of labels are provided with labels 5, labels 6 and labels 7, the steepness of the first group of labels is arranged in an ascending order, and the relative positions of the first group of labels are obtained as the labels 7, the labels 6 and the labels 5; label with contour highest point appearing to the right of the highest point of label 4And dividing the label array into a second group, wherein the second group of labels comprises a label 1, a label 2 and a label 3, arranging the steepness of the first group of labels in a descending order to obtain the relative positions of the second group of labels as the label 3, the label 2 and the label 1, and finally integrating the position information of the two groups of labels, so that the relative positioning result of the label array is as follows: label 1, label 2, label 3, label 4, label 5, label 6, and label 7 are in this order from left to right, and the accuracy of the sorting is 1.
Claims (1)
1. A passive ultrahigh frequency RFID relative positioning method based on a phased array reader antenna comprises the following specific steps:
step 1; establishing a relative positioning scene suitable for a passive ultrahigh Frequency RFID (radio Frequency identification) by taking a dipole antenna selected as a passive tag antenna and a phased array antenna selected as a reader antenna as a modeling condition;
step 2: the method comprises the following steps of selecting a space rectangular coordinate system for the purpose of accurately evaluating tag field intensity information received by a reader, and establishing a reader phased array antenna gain expression model according to an electromagnetic field theory: gR(θR，φR)＝eD(θR，φR) Wherein G isR(θR，φR) Expressed in the radial direction (theta)R，φR) Gain of reader antenna, D (theta)R，φR) Is a directivity coefficient and can be expressed as
Wherein S (theta)R，φR) Is an array factor and can be expressed as
In the gain model of the phased array antenna, the phased array antenna is positioned on a YOZ surface, the center of mass of the antenna is positioned on an original point O, the normal direction is coincided with the positive direction of an X axis, and the point O and a point A in the space form a ray vector
As a radiation sideTo, thetaRRepresents from
To
Angle of inclination of phiRRepresents from
To
The rotation angle between the projections of the XOY plane, e denotes the efficiency factor, ImAnd InDenote the excitation amplitude along the Y-axis and Z-axis, respectively, M and N denote the array element index, M and N denote the total array element number along the Y-axis and Z-axis, respectively, YmAnd znRepresenting the coordinates of the array elements along the Y-axis and Z-axis, dyAnd dzRepresenting the distance difference between adjacent array elements, and respectively representing excitation phase difference along a Y axis and a Z axis by beta and gamma;
and step 3: determining a gain expression according to the structural characteristics of the array antenna, selecting a microstrip antenna with a common 2 × 2 array structure for illustration, and setting e as 1, Im＝In＝1，k＝2π/λ，dz＝dyWhen the array element coordinates are (0, -0.25 λ, 0.25 λ), (0, -0.25 λ, 0.25 λ), (0, 0.25 λ, -0.25 λ), (0, -0.25 λ, and-0.25 λ), respectively, at 0.5 λ, the array element coordinates can be obtained as (0, -0.25 λ, and-0.25 λ), respectively)
Further, the gain expression of the reader antenna may be expressed as
In the formula
And 4, step 4: let the integrand in the reader antenna expression in step 3 be Q, i.e.
Expanding Q, i.e. Q ═ e1+e2+e3+e4+e5+e6+e7+e8+e9Using mathematical tools to pair expanded e1～e9Respectively at thetaR∈[0，π]And phiR∈[0，π]The integral interval of (a) is subjected to constant integral operation, and the calculation result is substituted into the antenna gain expression in the step (3), so that G (theta) can be obtainedR，φR) Is shown as
In the formula
According to the expression, the gain division and the directivity coefficient theta of the phased array antennaRAnd phiRIn addition to this, the phase difference between the excitation phases β and γ of the phased array antenna is also related, i.e. by adjusting θR、φRβ and γ may change the gain of the antenna;
and 5: a simulation model is built for the passive ultrahigh frequency RFID relative positioning scene in the step 1, phased array antennas and tag arrays are placed in the same space rectangular coordinate system, tags face the phased array antennas and are placed perpendicular to an XOY plane and are arranged along the Y-axis direction, the phased array antennas are placed in the tag distribution center, and the centers of all tags in the system and the centers of the phased array antennas are placed at the same height;
step 6: the system changes the main lobe radiation direction of the antenna by adjusting the excitation phase differences beta and gamma, defines the main lobe radiation rotation angle of the antenna as theta, the theta represents the included angle between the radiation direction of the main lobe of the antenna and the positive half shaft of the Y axis, and the main lobe of the array antenna sequentially scans each label to obtain the receiving outline of each label in the process that the theta is increased from 0 degree to 180 degrees;
and 7: according to the theory of the array antenna, as the excitation changes, the antenna directional diagram will change continuously, so that the difference of the receiving profiles obtained by different tags is large, when the radiation rotation angle θ of the main lobe is 90 °, the steepness of the receiving profile of each tag is increased significantly, when the radiation rotation angle θ of the main lobe is 0 ° and θ is 180 °, the steepness of the receiving profile of each tag is decreased significantly, when a tag approaches the array antenna, the highest point of the receiving profile is likely to appear near θ 90 °, the tags are divided into two groups according to the timestamp information of the highest point of the receiving profile, one group is located on the left side of the array antenna, and the other group is located on the right side of the array antenna according to the formula
Calculating the profile steepness degree of each label, wherein K is the profile steepness degree of the label, L is the number of sampling points of the receiving profile, and Pr，TIndicating the receiving field strength value, P, corresponding to the l-th sampling pointr，T(l +1) representing a receiving field intensity value corresponding to the l +1 th sampling point;
and 8: for the left label of the array antenna, the K values are arranged in an ascending order to obtain the position information of the left label, for the right label of the array antenna, the K values are arranged in a descending order to obtain the position information of the right label, and finally, the position information of the labels on the two sides is combined to obtain the position information of all the labels;
and step 9: using the ranking accuracy C as an evaluation standard of a relative positioning system, wherein the expression of the ranking accuracy is C-NT/NTotalWhere C is the sorting accuracy, NTTo order the correct number of tags, NTotalIs the total label number;
step 10: keeping the interval between adjacent tags in the tag array unchanged, taking the vertical distance between the phased array antenna and the tag array as an optimization variable, performing multiple performance simulations, estimating the receiving field intensity profile of each tag according to the methods in the steps 1 to 6 in each simulation, performing relative positioning on each tag by adopting the methods in the steps 7 to 9, finding out the corresponding optimal vertical distance with the maximum sequencing accuracy C from the multiple simulation results, and storing the field intensity profile of the tag array under the theoretical condition at the moment;
step 11: and (3) building an actual measurement scene according to the simulation model in the step (5), applying the optimal vertical distance in the step (10) to the actual measurement scene, executing the operation in the step (6) to obtain a field intensity profile of the tag array, correcting the actual measurement field intensity profile by using the field intensity profile simulated in the step (10), executing the operations from the step (7) to the step (8), obtaining the relative position information of each tag under the actual measurement condition, and realizing relative positioning.
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