CN110133584B - High-precision real-time handwriting track tracking method based on passive reflection signals - Google Patents
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Abstract
The invention discloses a high-precision real-time handwriting track tracking method based on a passive reflection signal, which is used in a first deployment passive reflection tracking scene comprising a passive backscatter tag, a signal transmitting end and two signal receiving ends and a second deployment passive reflection tracking scene comprising a passive backscatter tag, a signal transmitting end and three signal receiving ends, and comprises the following steps: step a, confirming whether the passive reflection tracking scene is a first deployment passive reflection tracking scene or a second deployment passive reflection tracking scene, if the passive reflection tracking scene is the first deployment passive reflection tracking scene, performing step b, and if the passive reflection tracking scene is the second deployment passive reflection tracking scene, performing step c; step b, processing and tracking the real-time handwriting track through a first tracking model; and c, processing and tracking the real-time handwriting track through a second tracking model. The tracking method can realize millimeter-level high-precision track tracking with a low cost and a simple system.
Description
Technical Field
The invention relates to the field of track tracking of wireless perception, in particular to a high-precision real-time handwriting track tracking method based on passive reflection signals.
Background
Video-based methods, such as Kinect and Leap Motiont schemes often require specialized equipment and are susceptible to relational conditions and indoor layout. Electronic blackboards or other similar technologies are often very expensive and maintenance overhead is high. Inertial sensor based systems, while low cost and easy to deploy, are quite error-prone, e.g., their cumulative error over 6s may be as high as 60cm, and obviously not available for accurate tracking positioning. Recently, some sound-based systems have been proposed, such as the Vernier approach to track-following accuracy, but unfortunately, there are many practical problems with using sound signals, such as: the low-frequency sound signal is easy to be interfered by environmental noise, high precision cannot be achieved in a practical application scene, the high-frequency ultrasonic signal has stronger directivity and can be harmful to animals (the hearing range of dogs is 15-50000 Hz, and the hearing range of cats is 60-65000 Hz).
As more and more wireless devices are deployed in homes and work environments, a recent trend is to track movement tracks with Radio Frequency (Radio Frequency) signals. RFID-based systems, such as those proposed by Tagoram, tadar, RF-finger, are often limited by the sampling rate and cannot track high-speed moving objects with high accuracy. Even with tag arrays, the error is on the order of centimeters. Meanwhile, existing WiFi-based trajectory tracking systems typically require multiple antennas and the error is on the order of decimeters, for example: the scheme of WiDraw uses 25 antenna Angle-of-Arrival (AOA) technology to implement a 5cm error tracking system, whereas the scheme of WiTag uses only 2 APs but the error may exceed 1m. Other systems based on radio frequency signals, such as those using 60GHz wireless technology, suffer from rapid signal attenuation, high overhead, and limitations of hardware platforms. The solution proposed by WiTrack uses a dedicated FMCW (Frequency-Modulated Continuous-Wave) 1.79GHz bandwidth radar to track human body movements behind the wall, but the error is also up to 20cm. Therefore, the existing handwriting track tracking scheme has the problems that special equipment is needed, the system is complex, or errors are large.
Disclosure of Invention
Based on the problems existing in the prior art, the invention aims to provide a high-precision real-time handwriting track tracking method based on passive reflection signals, which can realize rapid and accurate handwriting track tracking with lower cost.
The invention aims at realizing the following technical scheme:
the embodiment of the invention provides a high-precision real-time handwriting track tracking method based on a passive reflection signal, which is used in a first deployment passive reflection tracking scene comprising a passive backscatter tag, a signal transmitting end and two signal receiving ends and a second deployment passive reflection tracking scene comprising a passive backscatter tag, a signal transmitting end and three signal receiving ends, and comprises the following steps:
step a, confirming whether the passive reflection tracking scene is a first deployment passive reflection tracking scene or a second deployment passive reflection tracking scene, if the passive reflection tracking scene is the first deployment passive reflection tracking scene, performing step b, and if the passive reflection tracking scene is the second deployment passive reflection tracking scene, performing step c;
step b, in the first deployment passive reflection tracking scene, the transmitting end of the signal is positioned on the connecting line of the receiving ends of the two signals, and after the two receiving ends receive the reflected signals of the transmitting end reflected by the passive backscatter tag, the real-time handwriting track is processed and tracked through a first tracking model;
and c, in the second deployment passive reflection tracking scene, the transmitting end of the signal is positioned at any position in the connecting line area of the receiving ends of the three signals, and after the three signal receiving devices receive the reflected signals of the passive reflection tags, the real-time handwriting track is processed and tracked through a second tracking model.
According to the technical scheme provided by the invention, the passive reflection signal-based high-precision real-time handwriting track tracking method provided by the embodiment of the invention has the beneficial effects that:
the tracking method utilizes the working mode of wireless reflection, removes the constraint of a communication protocol and communication overhead, can effectively improve the sampling rate and realizes millimeter-level high-precision track tracking; moreover, no learning or training process is required; the tracking of the object moving at a high speed is supported, and the tracking of any track is supported; if the method can be widely deployed, the application prospect in the Internet of things can be effectively expanded.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for tracking a handwriting track in real time based on a passive reflection signal with high precision, which is provided by an embodiment of the invention;
fig. 2 is a schematic diagram of an application scenario of a track tracking method according to an embodiment of the present invention;
fig. 3 is a schematic diagram of an application scenario of a track tracking method according to an embodiment of the present invention;
fig. 4 is an application scenario schematic diagram of a track tracking method according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will clearly and fully describe the technical solutions of the embodiments of the present invention in conjunction with the specific contents of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to fall within the scope of the invention. What is not described in detail in the embodiments of the present invention belongs to the prior art known to those skilled in the art.
As shown in fig. 1, an embodiment of the present invention provides a high-precision real-time handwriting track tracking method based on a passive reflection signal, which is used in a first deployment passive reflection tracking scene including a passive backscatter tag, a signal transmitting end and two signal receiving ends, and a second deployment passive reflection tracking scene including a passive backscatter tag, a signal transmitting end and three signal receiving ends, and includes the following steps:
step a, confirming whether the passive reflection tracking scene is a first deployment passive reflection tracking scene or a second deployment passive reflection tracking scene, if the passive reflection tracking scene is the first deployment passive reflection tracking scene, performing step b, and if the passive reflection tracking scene is the second deployment passive reflection tracking scene, performing step c;
step b, in the first deployment passive reflection tracking scene, the transmitting end of the signal is positioned on the connecting line of the receiving ends of the two signals, and after the two receiving ends receive the reflected signals of the transmitting end reflected by the passive backscatter tag, the real-time handwriting track is processed and tracked through a first tracking model;
and c, in the second deployment passive reflection tracking scene, the transmitting end of the signal is positioned at any position in the connecting line area of the receiving ends of the three signals, and after the three signal receiving devices receive the reflected signals of the passive reflection tags, the real-time handwriting track is processed and tracked through a second tracking model.
In step b of the above method, the processing method of the first tracking model (which may be called as a PDI-C model, and performing the tag position estimation method using a phase difference iterative model (PDI-C) with limited transmitting end position) includes:
a is used for transmitting a single-tone sinusoidal signal in the air by a transmitting end 0 sin(ω 0 t+θ 0 ) Indicating that its phase is
Establishing a plane rectangular coordinate system, wherein A, B and 0 are used for respectively representing the position of the first receiving end, the position of the second receiving end and the position of the transmitting end; setting the position 0 of the transmitting end as an origin of coordinates, wherein coordinates of A and B are (-R, 0) and (R, 0), and R represents a linear distance from the transmitting end to one of the receiving ends;
in the plane rectangular coordinate system, P is used t (x t ，y t) and Pt+1 (x t+1 ，y t+1 ) To represent the positions of the passive reflection tags at two adjacent times t and t+1, respectively;
by d A 、d B and do Respectively represent P t Distance from point A, B, O, d' A 、d′ B and d′o Respectively represent P t+1 Distance from point A, B, 0;
by using
Respectively represent passive backscatter tags from P t Move to P t+1 Distance moved to A, B, 0;
the following equations are listed according to the above parameters:
let +.P t+1 AO is alpha, at delta P t+1 The AO is obtained by calculation according to the cosine theorem:
at DeltaP tAB and ΔPt+1 In AB, calculated using the median theorem:
the following equations (2) and (3) are combined to obtain the following equation (4):
by the ith receiving end Rx i Acquired phase value formula
The phase of equation (5) above is spread out to eliminate the effect of the 2pi radian period, where Δt represents the time interval between two adjacent sampling points, and the difference in angular frequency, ω, is eliminated by synchronizing all the receiving ends 1 ＝ω 2 ＝ω′；
Subtracting the upper and lower equations in equation (5) to obtain a phase difference
Eliminating equipment difference term theta after differential processing c ；
Calculating the phases of the received signals of other receiving ends according to the same steps;
if it is specified that
And the result of the difference is rewritten as follows in combination with the result of the above equation (2):
wherein 
Combining equations (4) and (6) above, one can obtain a quadratic equation as follows:
wherein ,dA 、d B and do Defined in equation (2) above, all of known quantities, can be solved for
Finally, d 'is calculated by the above equations (2) and (6)' A The position of the passive backscatter tag at time t+1 is obtained as follows:
wherein ,
setting y to be less than or equal to 0; under the condition that the initial position p (0) is known, the position of the passive backscatter tag is obtained through iterative calculation according to p (t+1))=f (p (t), namely, the real-time tracking of the handwriting track is completed.
Among the above methods, the initial position of the passive backscatter tag can be calculated using DAH (see Lei Yang, yekui Chen, xiang-Yangli, chaowei Xiao, mo Li, and Yunhao Liu.2014.Tagoram: real-time tracking of mobile RFID tags to high precision using COTS devices in Proceedings of the 20th annual international conference on Mobile computing and networking.ACM,237-248) or MOWI (see Yunning Zhang, jiliang Wang, weiyi Wang, zhao Wang, and Yunhao Liu.2018.Vernier: accurate and Fast Acoustic Motion Tracking Using Mobile devices in IEEE INFOCOM2018-IEEE Conference on Computer communications IEEE, 1709-1717) and the like, and the angular frequency ω' is estimated using Fast Fourier Transform (FFT).
In step C of the above method, the processing method of the second tracking model (which may be called as a PDI-a model, and the tag position estimating method using a phase difference iterative model (PDI-C) with an arbitrary transmitting end position) includes:
a is used for transmitting a single-tone sinusoidal signal in the air by a transmitting end 0 sin(ω 0 t+θ 0 ) Indicating that its phase is
Establishing a plane rectangular coordinate system, wherein A, B and 0 are used for respectively representing the position of the first receiving end, the position of the second receiving end and the position of the third receiving end; setting the position of a transmitting end as an origin of coordinates, wherein coordinates of A and B are (-R, 0) and (R, 0), R represents the linear distance from a third receiving end to other two receiving ends, and the position of the transmitting end is arbitrarily arranged in the plane rectangular coordinate system;
in the plane rectangular coordinate system, P is used t (x t ，y t) and Pt+1 (x t+1， y t+1 ) Respectively representing the positions of the passive reflection tag at two adjacent moments t and t+1;
by d A 、d B and do Respectively represent P t Distance from point A, B, O, d' A 、d′ B and d′O Respectively represent P t+1 Distance from point A, B, O; wherein d o Representing the distance between the passive backscatter tag and the third receiving end;
by using
Respectively represent passive backscatter tags from P t Move to P t+1 Distance moved to A, B, 0;
by d T Representing the distance from the location of the transmitting end to the passive backscatter tag;
the following equations are listed according to the above parameters:
wherein ,θc1， θ c2 θ c3 Representing equipment difference items, and calculating to obtain:
wherein 
Expressed by the third expression of the above equation (9)
The method comprises the following steps:
the following equations (9) and (10) are combined to obtain the following equation (11):
the equations (11) and (10) are combined to obtain
Linear form solution of (c):
d 'is calculated by the above equations (8) and (9)' A The position of the passive backscatter tag at time t+1 is obtained as follows:
wherein ,
setting y to be less than or equal to 0; under the condition of knowing the initial position p (0), the position of the passive backscatter tag is obtained through iterative calculation according to p (t+1) =f (p (t)), namely, the handwriting track is tracked in real time.
In the above method, the initial position of the passive backscatter tag can be calculated using a DAH or MOWI method or the like.
Embodiments of the present invention are described in detail below.
The embodiment of the invention provides a track tracking method, which is used for tracking the track of the positioning of a tag by capturing the existing signal in the passive tag reflection space. The system to which the method is applied is deployed with mainly 3 parts, as shown in figure 2,
among them, TX represents a transmitting end, that is, a signal transmitter as a signal source, which is an energy source, and may be a WiFi signal, a bluetooth signal, a TV broadcast signal, etc., which are widely present in the space. Tx transmits a single-tone sinusoidal signal over the air, using A 0 sin(ω 0 t+θ 0 ) Indicating that its phase is
The Tag is a passive backscatter Tag (hereinafter referred to as a passive Tag for convenience of description) and may be composed of an antenna and a microcontroller, etc., where the microcontroller can control an on (absorp) off (reflection) state of the antenna, so that the antenna of the Tag switches back and forth between a reflective state and a non-reflective state, thereby generating reflected signals of two frequency bands (spectrum shifting process).
The energy of the passive tag reflected signal described above may be expressed as follows:
wherein Ptx and Gtx Represents the transmission energy and antenna gain of the transmitting end, d represents the distance between Tx and Tag, and delta Γ A change in RCS (Radar Cross Section) is represented as follows:
wherein λ represents the wavelength of the signal, G tag Antenna gain, Γ, representing tag * The reflection coefficient is represented as follows:
wherein Za ＝R a +jX a The complex impedance of the antenna is generated by controlling the on-off state of the antenna to enable the impedance to jump between two values, so that a reflected signal is generated, and the frequency of the jump of the impedance determines the cheap frequency of the reflected signal.
RX represents the receiving end, if Deltaf represents the frequency of the on-off jump of the antenna, the frequency of the reflected signal is f+Deltaf and f-Deltaf (frequency spectrum shifting). The receiving end can select one of the two frequencies for reception.
The generation of the signal utilizes the existing signal in the space, only a low-cost passive reflection device is needed to generate a new signal, the energy of the reflected signal is very weak, the working range is short, but the interference between systems can be reduced in the space domain, and the offset frequency can be controlled by controllable delta f in the spectrum domain to avoid or reduce the interference of other channels.
The signal propagation model of this system is shown in FIG. 2, when a signal arrives at Tag (distance d 0 Representation) of the phase of the signal will occur
Wherein lambda is c Representing the carrier wavelength. Then, the signal is backscattered by Tag to reach the receiving end Rx i (distance d) i A representation); due to the spectral shifting, the phase offset is denoted +.>
In addition to the phase shift of the RF signal due to propagation, the hardware circuitry (including all Tx, tag and Rx) also introduces additional phase shifts, denoted as θ Tx ，θ Tag and θRx The method comprises the steps of carrying out a first treatment on the surface of the Thus the final receiving end Rx i The phase value obtained is +.>
wherein />
Furthermore, if the clocks of the transmitting end and the receiving end cannot be synchronized, a shift in frequency will be inevitably introduced; thus, at the receiving end Rx i It is necessary to use omega i To replace omega 0 . Finally, the following->
Is represented by the expression:
wherein θci Representing a device difference term, which relates to hardware characteristics. Where phase is a function of the period of 2pi. The phase value is provided with different receiving endsDevice diversity constant
In addition, the initial phase θ 0 Phase offset θ caused by the transmitting end Tx Tag-induced phase offset θ Tag Is an unknown parameter, the unknown parameter has great influence on the tracking and positioning result, and how to eliminate the influence is the key for ensuring the tracking accuracy and precision.
Some conventional methods, such as elliptic-based and hyperbolic-based models, have problems in such systems, such that the influence of the diversity of devices cannot be eliminated, and real-time calculation is difficult to realize. Considering calculation and deployment overhead, the invention provides two efficient phase difference iterative algorithms (Phase Differential Iterative Scheme-PDI scheme) and derives the position of the next moment by using the position and geometric information of the previous moment; the two schemes are called PDI-C (Phase Differential Iterative Scheme with Constrained Locations of Transmitter) and PDI-A (Phase Differential Iterative Scheme with Arbitrary Locations of Transmitter) respectively; the location of the transmitting end Tx in the PDI-C model is constrained, only two Rx are needed, and the location of the transmitting end Tx in the PDI-a model can be arbitrary, but three Rx are needed to realize. The application scenarios of the PDI-C model and the PDI-A model are shown in FIG. 3 and FIG. 4, respectively.
The following processes for the PDI-C model and the PDI-A model are specifically described as follows:
(A) The PDI-C model (Phase Differential Iterative Scheme with Constrained Locations of Transmitter) is specifically (i.e., the first tracking model):
in this model, tx is placed on the connection line (constrained) of two receivers Rx, as shown in fig. 3, where Tx is placed at the midpoint of the two receivers to explain the working principle, and then expands to a more general case.
As shown in FIG. 3, a rectangular planar coordinate system is established, wherein A, B,0 represents the position of the receiving end Rx1, the position of the receiving end Rx2 and the position of the transmitting end Tx, respectively, and the Tx position is designated as the origin of coordinates, and the coordinates of A and B are (-R, 0)And (R, 0), R representing the linear distance of the transmitting end to one of the receiving ends; at the same time, use P t (x t ，y t) and Pt+1 (x t+1 ，y t+1 ) Respectively representing the positions of 'Tag' at two adjacent moments t and t+1; d, d A ，d B ，d O Respectively represent P t And the distance between points A, B,0, d' A ，d′ B ，d′ o Respectively represent P t+1 And the distance between points a, B, O.
Representing the 'Tag' from P t Move to P t+1 Distance moved to A during this time, +.>
And the same is true. Following these definitions, the following equations can be listed:
let DeltaP t+1 AO is alpha, at delta P t+1 The cosine law in AO can be used to obtain:
at DeltaP tAB and ΔPt+1 In AB, using the Apollonius theorem (median theorem) it is possible to obtain:
simultaneous equations (2), (3) can be obtained:
from equation (1), the receiving end' Rx can be obtained 1 ' sThe phase of the received signal is:
the (unwrap) phase is spread out here to eliminate the effect of the 2 pi radian period, Δt represents the time interval between two adjacent sampling points, here the difference in angular frequency is eliminated by synchronizing all the receiving ends, ω 1 ＝ω 2 =ω'. Subtracting the upper and lower equations in equation (5) (i.e., making a phase difference) to obtain
(receiving end' Rx) 2 'same computing theory'). By such a differential method, the device differential term θ can be found c Is well eliminated. If specify->
And in combination with the results of equation (2), the differential results can be rewritten as follows:
wherein 
Equations (4) and (6) are combined to obtain a quadratic equation as follows:
d A ，d B ，d O is defined in equation (2), which are known quantities, because equation (7) is related to
Can easily solve the +.>
Finally, d 'can be calculated' A From equations (2) and (6), the Tag position at time t+1 is obtained as follows:
cos α has been defined above, and here y.ltoreq.0 is assumed. In fact, the process is an iterative process, with p (t+1) =f (p (t)), and the Tag position can be iteratively derived as long as the initial position p (0) is known, and is a linear time complexity. Using DAH or MOWI, etc. to calculate the initial position of the passive backscatter tag, fast Fourier Transform (FFT) is used to estimate the angular frequency omega 0 。
(B) The PDI-a model (Phase Differential Iterative Scheme with Arbitrary Locations of Transmitter) (i.e., the second tracking model) is specifically:
the above described PDI-C model shows a simple and efficient Tag location tracking method, but if in most practical scenarios the location of Tx may not be controllable, it is expected that it can be arbitrarily placed/deployed, and the present PDI-a model is further presented. In this model, as shown in FIG. 4, a new receiving end Rx is introduced at the origin 3 To release Tx. In this model, most of the definitions in PDI-C, d, can be multiplexed A ，d B Meaning of (d) is unchanged o Expressed are Tag and Rx 2 The distance between R and Rx represents the receiving end Rx 3 To two other receiving ends (Rx 1 /Rx 2 ) Is a distance of (3). At the same time, an additional variable d is introduced T It represents the distance between Tx (at any position) to Tag. The same is true:
wherein ,θc1 ，θ c2 ，θ c3 Representing the device difference term, similar to the analysis of equation (6) above, can be derived:
wherein 
Compared with the PDI-C model, a new variable is added>
It can be expressed by the third equation of equation (9), resulting in:
in PDI-A, equation (4) is still true, and simultaneous equations (4) and (10) can be obtained
Linear form solution of (c):
subsequent procedures are consistent with PDI-C and are not described here again, it being noted that
The two-time difference is used to eliminate the component omega' delta related to the angular frequency of time and the sampling interval t This is significant, in some extreme conditions, the angular frequency ω 0 And sampling interval delta t May not be constant and their effect may be ignored. In addition, the PDI-C moduleThe processing of the model is still linear and lighter than the PDI-C model because +.>
Here a linear solution. The algorithm pseudo code corresponding to the PDI-A model processing process is as follows:
(C) Other treatments:
(C1) Kalman filtering:
so far, the obtained track may still have errors caused by intractable system noise, in order to further remove the noise and improve the track accuracy, the invention adopts a Kalman filtering model based on 2D Continuous Wiener Process Acceleration (CWPA) (see L.Wang, K.Sun, H.Dai, A.X.Liu, and X.Wang, "WiTrace: centimer-Level Passive Gesture Tracking Using WiFi Signals," in IEEE SECON, 2018) and can deal with the condition that the acceleration of an object is disturbed by Gaussian noise. After adding the conventional kalman filtering step, the computational complexity is still linear.
(C2) Doppler effect:
the formula of the Doppler effect can be expressed as
wherein vo Indicating the movement speed of the observer, v s Representing the speed of movement of the signal source, f and f' represent the emission frequency and the observation frequency, respectively. As shown in fig. 2, in the system of the present invention, signal propagation is divided into two parts: tx→tag and tag→Rx. Taking tag→rx as an example (tx→tag is the same), v denotes the propagation velocity of electromagnetic waves in air, and is about c=3×10 9 m/s，v s Represents the velocity of 'Tag' relative to Rx, v o =0 because Rx is stationary in the design of the present invention. Thus, the effect of the Doppler effect can be expressed as +.>
Due to v s C, i.e
So f' ≡f, here the effect of the doppler effect on tracking accuracy is ignored.
(D) Generalizing to more general deployment:
the device in the method application scenario of the present invention supports a more free deployment, in FIG. 3, if Rx 1 and Rx2 The coordinates of (C) are (-R) A 0) and (0, R B ) At DeltaP t+1AO and ΔPt+1 The cosine theorem for alpha in AB can be obtained:
and (3) finishing to obtain:
it can be found that when R A ＝R B When R, the form is identical to equation (3) (another equation can be obtained by taking the value at Δp tAO and ΔPt In AB, P +. t AO uses the cosine theorem). Further, tx is at Rx 1 Left, or Rx 2 The same relationship can be obtained on the right. Therefore, in the PDI-C model, the constraint on the location of Tx is that it needs to be placed on the line of two receivers, which can be considered a semi-free deployment. In the PDI-a, tx may be placed at will (mainly in the signal receiving range), and 3 receiving ends may be placed on one connecting line, without limitation of distance in theory.
The tracking method of the invention utilizes the working mode of wireless reflection, removes the constraint of communication protocol and communication overhead, can effectively improve the sampling rate and can realize millimeter-level high-precision track tracking; moreover, no learning or training process is required; the tracking of the object moving at a high speed is supported, and the tracking of any track is supported; if the method can be widely deployed, the application prospect in the Internet of things can be effectively expanded.
Examples:
the devices used in step a are 1 passive reflective tag, 1 signal generator, and several signal receiving devices. The number of signal receiving apparatuses is 2 or 3 depending on the scene. If the position of the signal generator is controllable, only 2 receiving devices are needed, and if the position of the signal generator is not controllable (arbitrary), 3 receiving devices are used, and the deployment mode is shown in fig. 3 and 4. If the positions of the sending ends are controllable, only one connecting line is required to be deployed between the 1 sending ends and the 2 receiving ends, and if the positions of the sending ends are not controllable, only 3 receiving ends are required to be deployed on one connecting line.
And b, after the signal receiving and transmitting equipment is deployed, the transmitting end generates a constant single-tone sinusoidal signal, the carrier frequency is f, the tag is only required to be attached to an object with tracking (the object can be a hand, a commodity, a goods and the like), the object with the tag is moved, meanwhile, the receiving end receives a signal, the frequency of the received signal is f+deltaf or f-deltaf, deltaf is the antenna impedance change frequency of the tag, and the frequency is controllable and can be set according to actual conditions. Multiple receiving devices require clock synchronization.
And C, after receiving the signal of the receiving end, processing the signal by the corresponding PDI-A model or the corresponding PDI-C model to obtain the motion track of the label, thereby realizing track tracking.
Those of ordinary skill in the art will appreciate that: all or part of the flow of the method implementing the above embodiments may be implemented by a program to instruct related hardware, where the program may be stored in a computer readable storage medium, and the program may include the flow of the embodiment of each method as described above when executed. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a random access Memory (Random Access Memory, RAM), or the like.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the scope of the present invention should be included in the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.
Claims (2)
1. The high-precision real-time handwriting track tracking method based on the passive reflection signals is characterized by comprising the following steps of:
step a, confirming whether the passive reflection tracking scene is a first deployment passive reflection tracking scene or a second deployment passive reflection tracking scene, if the passive reflection tracking scene is the first deployment passive reflection tracking scene, performing step b, and if the passive reflection tracking scene is the second deployment passive reflection tracking scene, performing step c;
step b, in the first deployment passive reflection tracking scene, the transmitting end of the signal is positioned on the connecting line of the receiving ends of the two signals, and after the two receiving ends receive the reflected signals of the transmitting end reflected by the passive backscatter tag, the real-time handwriting track is processed and tracked through a first tracking model; the processing mode of the first tracking model comprises the following steps:
a is used for transmitting a single-tone sinusoidal signal in the air by a transmitting end 0 sin(ω 0 t+θ 0 ) Indicating that its phase is
Establishing a plane rectangular coordinate system, wherein A, B and O are used for respectively representing the position of the first receiving end, the position of the second receiving end and the position of the transmitting end; setting the position O of the transmitting end as an origin of coordinates, wherein coordinates of A and B are (-R, 0) and (R, 0), and R represents a linear distance from the transmitting end to one of the receiving ends;
in the plane rectangular coordinate system, P is used t (x t ，y t) and Pt+1 (x t+1 ，y t+1 ) To represent the positions of the passive reflection tags at two adjacent times t and t+1, respectively;
by d A 、d B and dO Respectively represent P t Distance from point A, B, O, d' A 、d′ B and d′O Respectively represent P t+1 Distance from point A, B, O;
by using
Respectively represent passive backscatter tags from P t Move to P t+1 Distance moved toward A, B, O;
the following equations are listed according to the above parameters:
let +.P t+1 AO is alpha, at delta P t+1 The AO is obtained by calculation according to the cosine theorem:
at DeltaP tAB and ΔPt+1 In AB, calculated using the median theorem:
the following equations (2) and (3) are combined to obtain the following equation (4):
by the ith receiving end Rx i Acquired phase value formula
The phase of the received signal of the first receiving end is obtained as follows: />
The phase of equation (5) above is spread out to eliminate the effect of the 2pi radian period, where Δt represents the time interval between two adjacent sampling points, and the difference in angular frequency, ω, is eliminated by synchronizing all the receiving ends 1 ＝ω 2 ＝ω′；
The ith receiving end Rx i Lambda in the obtained phase value formula c Representing the carrier wavelength; θ ci Representing i device difference items "; θ Tx Representing the phase shift caused by the transmitting end; θ Tag Representing the phase shift caused by the passive tag; θ Rxi A device diversity constant representing a device diversity constant of the phase value at the ith receiving end;
subtracting the upper and lower equations in equation (5) to obtain a phase difference
Eliminating equipment difference term theta after differential processing cl ；
Calculating the phases of the received signals of other receiving ends according to the same steps;
if it is specified that
And the result of the difference is rewritten as follows in combination with the result of the above equation (2):
wherein 
Combining equations (4) and (6) above, one can obtain a quadratic equation as follows:
wherein ,dA 、d B and dO Defined in equation (2) above, all of known quantities, can be solved for
Finally, d 'is calculated by the above equations (2) and (6)' A The position of the passive backscatter tag at time t+1 is obtained as follows:
wherein ,
setting y to be less than or equal to 0; under the condition of knowing an initial position p (0), according to p (t+1) =f (p (t)), the position of the passive backscatter tag is obtained through iterative calculation, namely, the handwriting track is tracked in real time;
step c, in the second deployment passive reflection tracking scene, the transmitting end of the signal is positioned at any position in the connecting line area of the receiving ends of the three signals, and after the three signal receiving devices receive the reflected signals of the passive reflection tags, the real-time handwriting track is processed and tracked through a second tracking model;
the processing mode of the second tracking model comprises the following steps:
a is used for transmitting a single-tone sinusoidal signal in the air by a transmitting end 0 sin(ω 0 t+θ 0 ) Indicating that its phase is
Establishing a plane rectangular coordinate system, wherein A, B and O are used for respectively representing the position of the first receiving end, the position of the second receiving end and the position of the third receiving end; setting the position of a transmitting end as an origin of coordinates, wherein coordinates of A and B are (-R, 0) and (R, 0), R represents the linear distance from a third receiving end to other two receiving ends, and the position of the transmitting end is arbitrarily arranged in the plane rectangular coordinate system;
in the plane rectangular coordinate system, P is used t (x t ，y t) and Pt+1 (x t+1 ，y t+1 ) Respectively representing the positions of the passive reflection tag at two adjacent moments t and t+1;
by d A 、d B and dO Respectively represent P t Distance from point A, B, O, d' A 、d′ B and d′O Respectively represent P t+1 Distance from point A, B, O; wherein d O Representing the distance between the passive backscatter tag and the third receiving end;
by using
Respectively represent passive backscatter tags from P t Move to P t+1 Distance moved toward A, B, O;
by d T Representing the distance from the location of the transmitting end to the passive backscatter tag;
the following equations are listed according to the above parameters:
wherein ,θc1 ，θ c2 ，θ c3 Representing equipment difference items, and calculating to obtain:
wherein 
Expressed by the third expression of the above equation (9)
The method comprises the following steps:
the following equations (9) and (10) are combined to obtain the following equation (11):
the equations (11) and (10) are combined to obtain
Linear form solution of (c):
d 'is calculated by the above equations (8) and (9)' A The position of the passive backscatter tag at time t+1 is obtained as follows:
wherein ,
setting y to be less than or equal to 0; under the condition of knowing the initial position p (0), the position of the passive backscatter tag is obtained through iterative calculation according to p (t+1) =f (p (t)), namely, the handwriting track is tracked in real time.
2. The method for tracking a handwriting trace in real time based on high precision of a passive reflection signal according to claim 1 wherein the initial position of a passive backscatter tag is calculated using a DAH or MOWI method and the angular frequency ω' is estimated using a fast fourier transform.
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