Positioning method based on RFID and phase calibration
阅读说明：本技术 一种基于rfid与相位校准的定位方法 (Positioning method based on RFID and phase calibration ) 是由 马永涛 刘涵凯 于 2019-11-14 设计创作，主要内容包括：本发明公开了一种基于RFID与相位校准的定位方法,包括标签数据采集阶段、像素数据库建立阶段和匹配定位阶段,其中,匹配定位阶段阶段,包括以下步骤：建立相位中心偏移库；将相位校准技术加入定位过程中,建立匹配函数,定位问题转化为寻找使<Image he="61" wi="90" file="DDA0002273572280000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>最大的网格点<Image he="66" wi="66" file="DDA0002273572280000012.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>(The invention discloses a positioning method based on RFID and phase calibration, which comprises a label data acquisition stage, a pixel database establishment stage and a matching positioning stage, wherein the matching positioning stage comprises the following steps: establishing a phase center offset library; the phase calibration technology is added into the positioning process, a matching function is established, and the positioning problem is converted into a search result Maximum grid point)
1. a positioning method based on RFID and phase calibration comprises a label data acquisition stage, a pixel database establishment stage and a matching positioning stage, wherein,
the label data acquisition stage comprises the following steps:
1) carrying out data acquisition on an area to be positioned where the tag is located through a mobile reader antenna: the reader antenna moves along a known track and collects the backscatter signal data of the tags for multiple times, the tag data of N positions are collected in total, and when the reader antenna moves to the nth position, N is more than or equal to 1 and less than or equal to N, and the position is determined, the phase of the backscatter signal of the tags collected by the reader antenna is deltanThen, the acquired phase sequence Θ is:
Θ＝{δ1，...，δN}
simultaneously acquiring time sequences corresponding to the phase sequences one by one
The pixel database establishing stage comprises the following steps:
1) dividing the location area into equally spaced grids, for each grid pointUsing time series
Wherein
2) Let the position of the antenna be paCalculating a sequence of positionsThe distance between each position and the antenna is obtained to obtain a virtual distance sequence
Wherein the content of the first and second substances,
wherein | | · | | is a norm symbol;
3) by virtual distance sequences
wherein the content of the first and second substances,
where f is the signal dominant frequency and c is the speed of light.
A matching positioning stage, comprising the following steps:
1) establishing a phase center offset library: calculating each virtual position p and antenna position pa，mAngle of arrival of signals therebetween
2) Adding a phase calibration technology into a positioning process, establishing a matching function:
where M is the number of antennas, Σ is the sum sign, exp is a power function of the natural logarithm, and where
The positioning problem is converted into a search
Technical Field
The invention belongs to the technical field of RFID positioning, and aims to solve the problem of positioning a label by using a label phase and phase calibration technology obtained by a reader antenna moving along a known track.
Background
With the popularization of mobile internet and smart phones, Location Based Service (LBS) has gained wide attention, driving the development of various modern navigation and positioning technologies. The well-known outdoor positioning technology GPS cannot be applied to indoor positioning due to occlusion of buildings and the like. In recent years, many indoor positioning technologies based on wireless networks, such as WiFi positioning, bluetooth positioning, ZigBee positioning, RFID positioning, and the like, have appeared. The rapid development of the internet of things technology enables the RFID technology to be widely applied to positioning, tracking and backtracking of production, logistics, medicines and the like. In the aspect of indoor positioning, compared with other positioning methods, the RFID has the characteristics of low cost, high positioning accuracy, high identification speed, strong anti-interference performance and the like, and has the advantages of non-contact, non-line-of-sight and capability of identifying and tracking multiple targets simultaneously, so that the RFID gradually becomes the first choice for indoor positioning.
The wireless positioning technology of the RFID is mainly divided into two types: one is based on a non-ranging method, usually without a determined signal propagation model, a large number of reference tags are arranged in a positioning area in advance, the reference tags with similar positions are screened out after certain operation, and the final positioning coordinates are determined by using the reference tags; the other method is a distance measurement-based method, the distances between a person and a plurality of wireless point devices are determined according to a signal propagation model, and the position of the person is determined through geometric relation transformation. The method based on the distance measurement mainly comprises the following steps: the aoa (angle of arrival) signal angle of arrival method, the toa (time of arrival) signal time of arrival method, the tdoa (time Difference of arrival) signal time Difference of arrival method, and the rssi (received signal strength indication) received signal strength method. The RSSI positioning method estimates the received label by establishing a propagation model through signal strength and distance, has low power and low cost, does not need additional equipment function support, and is limited in positioning precision because signal energy information is influenced by various factors such as non-line-of-sight, multipath and the like besides distance factors in the propagation process. TOA and TDOA location methods compute distance primarily by measuring the time of flight of electromagnetic waves, which requires or requires precise reference times for clock synchronization of hardware facilities. The AOA positioning method mainly measures the arrival direction of the label signal through an antenna array of a reader, and the method needs the antenna array with special functions, so that the accuracy is limited by the performance of equipment, and the cost is relatively high.
In a scene that the tag and the reader move relatively, the synthetic aperture technology can form a virtual antenna array by using the relative movement between the antenna and the target, and the position of the target is determined by coherent superposition of a plurality of sampling phase values, so that the synthetic aperture technology has good anti-noise and multi-path interference capabilities, and can improve the positioning accuracy. And the method is suitable for unique dynamic application scenes such as handheld devices and the like, and does not need to additionally arrange a reference label and a time-consuming calibration stage. Meanwhile, the cost is relatively low, and the positioning can be realized only by commercial equipment.
Existing RFID location methods typically consider the antenna phase center to be constant. This is possible when the antenna and tag are stationary. However, in SARRFID, relative movement of the reader antenna and tag changes the angle of arrival of the signal, resulting in a change in the antenna phase center, which we call Phase Center Shift (PCS). The PCS will affect the observed phase and cause positioning errors. Therefore, the invention provides a positioning method based on RFID and phase calibration.
Disclosure of Invention
The invention relates to a positioning method based on RFID and phase calibration, which utilizes a synthetic aperture technology to assist in collecting label information data and adopts a method based on phase and amplitude data to perform matching positioning. The invention obtains the phase and amplitude data of the corresponding label at different antenna positions through the reader antenna moving along the known track, establishes a pixel database through a phase and amplitude data model, and carries out high-precision matching positioning on the label by calculating the similarity of a label measurement vector and a pixel point data vector. The invention does not depend on additional equipment and a reference label, can acquire the position of the label in the area to be positioned only by one mobile reader antenna, and can realize millimeter-level positioning accuracy. The technical scheme of the invention is as follows:
a positioning method based on RFID and phase calibration comprises a label data acquisition stage, a pixel database establishment stage and a matching positioning stage, wherein,
the label data acquisition stage comprises the following steps:
1) carrying out data acquisition on an area to be positioned where the tag is located through a mobile reader antenna: the reader antenna moves along a known track and collects the backscatter signal data of the tags for multiple times, the tag data of N positions are collected in total, and when the reader antenna moves to the nth position, N is more than or equal to 1 and less than or equal to N, and the position is determined, the phase of the backscatter signal of the tags collected by the reader antenna is deltanThe phase sequence of the acquisitionColumn Θ is:
Θ＝{δ1，...，δN}
simultaneously acquiring time sequences corresponding to the phase sequences one by one
The pixel database establishing stage comprises the following steps:
1) dividing the location area into equally spaced grids, for each grid pointUsing time series
Wherein
2) let the position of the antenna be paCalculating a sequence of positionsThe distance between each position and the antenna is obtained to obtain a virtual distance sequence
Wherein the content of the first and second substances,
wherein | | · | | is a norm symbol;
3) by virtual distance sequences
wherein the content of the first and second substances,
wherein f is the main frequency of the signal, and c is the speed of light;
in the stage of the matching positioning stage, the method comprises the following steps:
1) establishing a phase center offset library: calculating each virtual position p and antenna position pa，mAngle of arrival of signals therebetween
2) Adding a phase calibration technology into a positioning process, establishing a matching function:
where M is the number of antennas, Σ is the sum sign, exp is a power function of the natural logarithm, and where
3) The positioning problem is converted into a search
The invention relates to a positioning method based on RFID and phase calibration, which comprises the steps of firstly adopting a synthetic aperture technology, carrying out matching positioning by a method of acquiring phase and amplitude data of a label at different positions at certain space intervals through a reader antenna moving along a known track, then establishing a pixel database of an area to be positioned based on a phase and amplitude data model, finally calculating the similarity between a label measurement vector and a pixel point data vector to carry out matching positioning, and selecting a pixel point with the highest similarity, wherein the position of the pixel point corresponds to label information. Compared with the traditional RFID label positioning method, the method can be more suitable for dynamic scenes such as conveyor belts, handheld equipment and the like, and has good anti-multipath interference capability. In addition, the invention can carry out high-precision positioning on the label only by a mobile reader antenna without an additional reference label and a time-consuming calibration stage. Existing RFID location methods typically consider the antenna phase center to be constant. This is possible when the antenna and tag are stationary. However, in SAR RFID, relative movement of the reader antenna and tag changes the angle of arrival of the signal, resulting in a change in the antenna phase center, which we refer to as Phase Center Shift (PCS). The PCS will affect the observed phase and cause positioning errors. Therefore, the invention provides a positioning method based on RFID and phase calibration.
Drawings
FIG. 1 is a positioning scenario.
Fig. 2 shows the phase center shift.
Fig. 3 shows the positioning result.
Detailed Description
The following describes a positioning method based on RFID and phase calibration according to the present invention with reference to the accompanying drawings.
A tag localization scenario based on synthetic aperture technology is shown in fig. 1. In a tag data acquisition stage, a 4m × 4m scene to be positioned is established, a moving track of a reader antenna is a straight line along an X axis, the moving track is located at a boundary of an area to be positioned by 20cm, the total length is 4m, and measurement data of a tag is acquired at a space interval of 4cm every time the reader moves, so that 100(N equals to 100) readings are acquired by the antenna during the moving period when the working frequency of the reader is 867.5MHz and the corresponding wavelength is 34.6 cm. The distance between the pixel points of the region to be positioned in the pixel database establishing stage can be set to be 5cm, and if higher positioning precision is expected, the pixel points can be set more densely.
The positioning method estimates the position of the label measurement data in real time according to the acquired label measurement data, the algorithm flow is shown in figure 2, and the steps are as follows:
1) and carrying out data acquisition on the area to be positioned where the tag is located through the mobile reader antenna. The reader antenna moves along a known track and collects the backscattering signal data of the labels for multiple times, and the label data of N positions are collected in total. When the reader antenna moves to the nth position (N is more than or equal to 1 and less than or equal to N), the phase of the label backscatter signal collected by the reader antenna is deltanThen, the acquired phase sequence Θ is:
Θ＝{δl，...，δN}
meanwhile, the time sequence corresponding to the phase sequence one by one can be collected
2) Dividing the location area into equally spaced grids, for each grid point
Wherein
3) Let the position of the antenna be paCalculating a sequence of positions
Wherein the content of the first and second substances,
where | | · | | is a norm symbol.
4) By virtual distance sequencesThe virtual phase sequence can be calculated:
wherein the content of the first and second substances,
where f is the signal dominant frequency and c is the speed of light.
5) And establishing a phase center offset library. Calculating each virtual position p and antenna position pa，mAngle of arrival of signals therebetween
6) Adding a phase calibration technology into a positioning process, establishing a matching function:
wherein M is the number of antennas. And Σ is the summation sign. exp is a power function of the natural logarithm, and wherein
7) At this point, the positioning problem is converted into a searchMaximum grid point
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