CN104459614A - Trajectory detection method based on metastable state of radio-frequency tags - Google Patents

Abstract

The invention provides a trajectory detection method based on the metastable state of radio-frequency tags. According to the method, the movement of objects is detected through the change of the metastable state of tag pairs. The observation result shows that the influence on the state of the tag pairs from the movement of the objects is obvious. An RFID detection system is realized, and the experiment proves that the detection error of the RFID detection system is influenced by the experimental environment; when people move within 1 m away from the tag pairs, the maximum detection rate can reach 95.17%, which shows that the system can be applied to most occasions. With the advantages of low tag cost and unbinding, and the RFID technology will be widely applied to the trajectory detection field for a long time.

Description

A kind of track-detecting method based on radio-frequency (RF) tag metastable condition

Technical field

The invention belongs to radio RF recognition technology field, relate to a kind of track-detecting method, especially based on a track-detecting method for radio-frequency (RF) tag metastable condition, for detecting the moving target occurred in radio frequency identification (RFID) system in real time.

Background technology

The more typical indoor locating system utilizing RFID indoor positioning technologies to research and develop at present has SpotON and LANDMARC [4,5].Wherein SpotON system researched and developed by University of Washington, and it adopts aggregating algorithm, carries out data analysis to the signal intensity collected, thus realizes the location to the three physical dimensions residing for target object.This system signal intensity of using by oneself positions, but due to the instability of signal intensity, positioning precision is limited.

LANDMARC system researched and developed by Michigan State University, this positioning system adopts k arest neighbors (KNN) sorting algorithm, by disposing the reference label of its positional information known in physical space, relative signal intensity is utilized to calculate the location algorithm of target object location.This system proposes the concept of reference label for the first time.But the reference label that this system is disposed belongs to active tag, active tag restricted lifetime, not Portable belt, and can increase cost.

Above-mentioned is indoor positioning technologies popular at present, some other indoor positioning technologies, as super-broadband tech, the technology such as analyzing and processing technology and cellular localization technology based on image, is also applied in the research of indoor positioning.But because RFID has that the volume of its uniqueness is little, cost is low, the life-span is long, penetrability is good, reusing is good, is not afraid of and pollutes and adapt to the plurality of advantages such as various environment, become the important implementation of indoor positioning technologies.

Summary of the invention

The object of the invention is to the shortcoming overcoming above-mentioned prior art, a kind of track-detecting method based on radio-frequency (RF) tag metastable condition is provided, it utilizes label to carry out track detection to metastable condition, testing result accuracy is high, and can in real time for label a large amount of in rfid system to carrying out mobile object track detection.

The object of the invention is to be achieved through the following technical solutions:

This track-detecting method based on radio-frequency (RF) tag metastable condition, comprises the following steps:

1) label is to the sub-firm power training stage:

First based on the Partition Theory of antenna place, specify between reader and label and energy transferring mode between label pair; Next utilizes Fu Lisi equation and Biot-Savart law to carry out formalized description to the mutual interference between the energy transferring between reader and label and label respectively, finally sets up the mutual interference model between label pair;

Corresponding performance number when extremely just activating label that rises and falls causing receiving antenna place signal level is defined as the sub-firm power of label;

The difference of each label own causes it, and metastable to determine performance number different, by label to being arranged in RFID reader read range, fixed by label to position, to detect the reading state of the label in Reader coverage in real time;

(2) the Unified Power stage is adjusted

By regulating the distance of two labels, regulating and metastablely determining watt level;

The power training stage obtains the metastable of each label and determines performance number; The power of label is adjusted to unified value, so that Reader works under same power, with one of them label for benchmark, adjusts other labels and adjust the distance; For convenience of regulating, the label getting middle power value is benchmark, and the label centering after adjustment has a label to obtain approximate baseline performance number; Represent label centering two label interval with d, as 6mm<d<26mm, label can produce the corresponding metastable change determining performance number; Regulate each label pair in the same fashion, make all label centerings have one to reach approximate baseline performance number; When label be less than metastable determine performance number 0.5dbm time, require that after reunification metastable is determined performance number and differed with reference power and be less than or equal to 0.5dbm, adjustable range completes;

(3) the mobile object detection phase

The target object of motion mainly comprises shadow effect and multipath effect two kinds to the impact of population of tags.Both is by causing different channel fadings to radiowave, thus changes the right astable equilibrium state of label, reaches the object to target object detection; In rfid system, when target object moves to a certain specific position, due to the blocking of transmission path of target object radio frequency signal, and half blind area of electric wave can be formed at the rear of target object, thus form electromagnetic field shade; In this region, signal strength is more weak; Along with the continuous movement of target object, the field intensity at reference point place can occur to change slowly, the decline of the receiving antenna place field intensity that it causes.

Further, the operation of the sub-firm power of above training is increased with fixed step size power the emissive power of Reader, and tag reader situation is just read from not reading, and finally arrives stable reading; Performance number corresponding when just being read by label is decided to be the sub-firm power of this label; Each label reads repeatedly with Reader in the same fashion, until can obtain one stable metastablely determine performance number.

Compared with prior art, the present invention has following beneficial effect:

The present invention does not increase extra equipment, only need use existing commercial RFID read-write equipment, burden can not be produced to the normal operation of system, the invention belongs to unbundling formula detection system, because RFID label tag used in native system belongs to passive label, cost is very low, therefore, it is possible to provide the task that low-cost high-efficiency detects in actual deployment system for a long time.Simultaneously according to carrying out great many of experiments to label metastable condition, show that the present invention is the very practical and effective detection means of one.In addition at secure context, come in and go out to prevent unauthorized person and deposit product area, unbundling formula detection means proposed by the invention provides and detects in real time the invader not carrying any receiver in article surveillance district.With layout a large amount of sensing system compare, the mobility detect mode based on RFID label tag enters has two advantages intrusion detection: low cost and support have radio-frequency apparatus again.

Accompanying drawing explanation

Fig. 1 is the reference label schematic diagram after neighborhood graph is filtered;

Fig. 2 is the reference label schematic diagram after effective reference set filters.

Fig. 3 is the energy transferring between reader and label and the mutual interference E41C label schematic diagram between label

Embodiment

The method of the track detection of RFID under unbundling state is utilized mainly to be divided into several step:

(1) label is to the sub-firm power training stage:

First, what detect based on the mobile object of state transition is the foundation of label to mutual interference model at all.Therefore the present invention is first based on the Partition Theory of antenna place, specify that between reader and label and energy transferring mode between label pair, this basis that to be label set up mutual interference model and basic.Next utilizes Fu Lisi (Friis) equation

And Biot-Savart law

As shown in Figure 3, E41C label can be equivalent to an electric dipole and a magnetic dipole, so the antenna of label can be equivalent to the form of two long straight conductors and square coil, if two long straight conductors respectively belt current be I ₁and I ₂, I ₁=I ₂=I ₀e ^jwt, the area of square coil is a × b, and the distance of it and long straight conductor is D (D is very little), gets I ₁and I ₂along Z-direction.Then the interaction of four conductors is analyzed.

1) .I ₁and S ₁mutual inductance effect

Electric current I ₁magnetic induction density be closed circle line of vector around it, consider I separately ₁the B produced ₁there is column symmetry, so utilize Ampère circuital theorem integrated form or Biot-Savart law, try to achieve I ₁the magnetic induction density produced is

With coil current the magnetic flux of interlinkage is:

By the known coil directed area in illustrating current direction with B ₁direction consistent, coil is got rectangle differential bin dS=ad ρ, and from D to D+b, integration obtains:

Obtaining mutual inductance is thus:

Because I ₁and S ₁the mutual flux direction through coil produced is inconsistent, and resultant flux reduces because of partial offset, M ₁₁be negative, I ₁at S ₁the induction electromotive force of middle generation is:

If S ₁equivalent resistance is R, I ₁at S ₁in induction current:

$I_{11}=\frac{E}{R}=\frac{{\mathrm{\&mu;}}_0\mathrm{ajw}{I}_0{e}^{\mathrm{jwt}}}{2\mathrm{\&pi;R}}\ln \left(\frac{D+b}{D}\right)$

2) .I ₁with S ₂mutual inductance effect

The same manner is utilized to obtain:

$I_{12}=\frac{{\mathrm{\&mu;}}_0\mathrm{ajw}{I}_0{e}^{\mathrm{jwt}}}{2\mathrm{\&pi;R}}\ln \left(\frac{2D+2b+L}{2D+b+L}\right)$

3) .I ₂with S ₂mutual inductance effect and I ₁with S ₁mutual inductance effect identical, so:

$I_{22}=\frac{{\mathrm{\&mu;}}_0\mathrm{ajw}{I}_0{e}^{\mathrm{jwt}}}{2\mathrm{\&pi;R}}\ln \left(\frac{D+b}{D}\right)$

4) .I ₂with S ₁mutual inductance effect:

The symmetry of circular cylindrical coordinate is utilized to obtain

I ₂with S ₂the mutual flux direction through coil produced is consistent, and resultant flux increases, M ₂₁for just:

$I_{21}=\frac{{\mathrm{\&mu;}}_0\mathrm{ajw}{I}_0{e}^{\mathrm{jwt}}}{2\mathrm{\&pi;R}}\ln \left(\frac{L+b}{L}\right)$

S ₁with S ₂between Mutual Inductance Coupling effect be symmetrical, and faradic direction is always contrary with the direction of exciting current, if induction current is-I _h;

If I ₀₁and I ₀₂represent S respectively ₁and S ₂receive the electromagnetic energy of reader and the electric current produced, then in the mutual interference model of two label, S ₁and S ₂in induction current can be expressed as

$I_{S_1}=I_{01}+I_{11}+I_{21}+I_H=I_{01}-I_H+\frac{{\mathrm{\&mu;}}_0\mathrm{ajw}{I}_0{e}^{\mathrm{jwt}}}{2\mathrm{\&pi;R}}\ln \left(\frac{D+b}{D}\right)-\frac{{\mathrm{\&mu;}}_0\mathrm{ajw}{I}_0{e}^{\mathrm{jwt}}}{2\mathrm{\&pi;R}}\ln \left(\frac{L+b}{L}\right)$

$I_{S_2}=I_{02}+I_{12}+I_{22}+I_H=I_{02}-I_H+\frac{{\mathrm{\&mu;}}_0\mathrm{ajw}{I}_0{e}^{\mathrm{jwt}}}{2\mathrm{\&pi;R}}\ln \left(\frac{2D+2b+L}{2D+b+L}\right)-\frac{{\mathrm{\&mu;}}_0\mathrm{ajw}{I}_0{e}^{\mathrm{jwt}}}{2\mathrm{\&pi;R}}\ln \left(\frac{D+b}{D}\right)$ Work as I ₀₁with I ₀₂time equal,

Finally establish the mutual interference model between label pair.The mutual interference model that the present invention sets up, the analysis that can theorize to the mutual interference between the label pair being in optional position and derivation.

Due to the fluctuating of receiving antenna place signal level.Cause the fluctuating of tag read state from face, namely just read from not reading, or read to stable.Corresponding performance number when extremely just activating label that rises and falls causing receiving antenna place signal level is defined as the sub-firm power of label.

The difference of each label own causes it, and metastable to determine performance number different, by label to being arranged in RFID reader (Reader) read range, label is fixed position, for subordinate phase Unified Power provides condition, to detect the reading state of the label in Reader coverage in real time.Train the main operation of sub-firm power to be the emissive power of Reader increased with a fixed step size power, tag reader situation is just read from not reading, and finally arrives stable reading.Performance number corresponding when just being read by label is decided to be the sub-firm power of this label.Each label reads repeatedly with Reader in the same fashion, until can obtain one stable metastablely determine performance number.

(2) the Unified Power stage is adjusted

Label causes the difference of label receiving antenna signal level to different distance between mutual interference model care label pair, also the sub-firm power of label is caused to change, a label can make the sub-firm power of another label become large, by regulating the distance of two labels, can regulate and metastablely determine watt level.

The power training stage obtains the metastable of each label and determines performance number.In experimental situation, need the power of label to be adjusted to unified value, so that Reader works under same power, with one of them label for benchmark, adjust other labels and adjust the distance.For convenience of regulating, the label getting middle power value is benchmark.Label centering after adjustment has a label can obtain approximate baseline performance number.Represent label centering two label interval with d, as 6mm<d<26mm, label can produce the corresponding metastable change determining performance number.Regulate each label pair in experimental situation in the same fashion, make all label centerings have one can reach approximate baseline performance number.Because label is very responsive to mobile object, when label be less than metastable determine performance number 0.5dbm time, the most responsive to mobile object, so require that after reunification metastable is determined performance number and differed with reference power and be less than or equal to 0.5dbm, adjustable range completes.

(3) the mobile object detection phase

Traditional RFID location system based on KNN algorithm utilizes target object to position the rate of change that the RSSI value of reference label affects.But complicated and changeable due to indoor environment, target object is sometimes insecure on the impact of reference label, therefore proposes the probe algorithm based on metastable condition.

The target object of motion mainly comprises shadow effect and multipath effect two kinds to the impact of population of tags.Both is by causing different channel fadings to radiowave, thus changes the right astable equilibrium state of label, reaches the object to target object detection; In rfid system, when target object moves to a certain specific position, due to the blocking of transmission path of target object radio frequency signal, and half blind area of electric wave can be formed at the rear of target object, thus form electromagnetic field shade; In this region, signal strength is more weak; Along with the continuous movement of target object, the field intensity at reference point place can occur to change slowly, the decline of the receiving antenna place field intensity that it causes.

Be specially: the present invention proposes two kinds of methods to improve the detection accuracy of KNN algorithm.

In this probe algorithm, whole locating area is divided into some subregions centered by each reference label, during original state, the different pels that every sub regions is corresponding in areal map, and use identical gray scale to characterize, such figure is called neighborhood graph.When the tag array in subregion monitors object of which movement, the metastable equilibrium state of the reference label in some subregions can be moved, and pel corresponding for this subregion is characterized by different gray scales, as shown in Figure 1.Because target object is sometimes insecure on the impact of metastable equilibrium state, therefore can dispose K reader at the diverse location of locating area, each reader maintains oneself a neighborhood graph.When detect in locating area have object of which movement time, the subregion that the common factor getting this K neighborhood graph affects as target object.Like this, just those insecure nodes that affect have been filtered out.In Fig. 1, have employed the neighborhood graph of 4 readers, occur simultaneously for the neighborhood graph of centre.Can see, by the filtration of neighborhood graph, a lot of insecure subregion has all been filtered.

Owing to there is a large amount of barriers in indoor environment, there is complicated multipath effect, therefore also likely move with the metastable equilibrium state of target object at a distance of distant reference label.This discrete insecure state transition has a great impact for the detection accuracy of RFID location system.Based on above-mentioned consideration, the present invention proposes the choosing method of the reference set disposed based on space.The reference set that the present invention selects should meet such condition: in reference set, have a reference mode and every other reference mode spatial neighbor at least.The present invention calls effective reference set this reference set.In this method, invention introduces the thought of graph theory.Compared with traditional KNN algorithm, the present invention no longer only estimates according to the position of feature to target object of sample value, but is filtered out by non-conterminous for discrete space reference mode, positions according in the clique obtained.If the metastable equilibrium state of a reference label there occurs migration, but its neighbor node does not have the migration of present condition, the state transition of this reference label is insecure, is harmful, is therefore filtered out by this type of label detection accuracy.After the filtration of neighborhood graph in Fig. 2, occurred in final neighborhood graph two discrete with other non-conterminous reference modes in reference mode space, this category node is called harmful reference mode.After the filtration of the reference set disposed based on space, the reference label finally obtained as shown in the figure.Insecure reference label is greatly reduced, and positioning precision is greatly improved.

In this probe algorithm, when having target object to occur around reference label, the metastable equilibrium state of reference label can change, and the times N i that the present invention changes metastable equilibrium state is as the weights with reference to label.The weights of reference label are normalized, as shown in formula (0-1).What deserves to be explained is, state change frequency is a process variable, and the position of target object is an instantaneous flow, and process variable can not directly be inferred instantaneous flow.Therefore the present invention makes a setting: within the shorter time period, as 200 milliseconds, and the position of target object is almost constant.Using the number of times of state change in the time window that this is smaller as the weights with reference to label.Reader used in an experiment is per second can identify 1100 labels, and recognition speed is efficient.Position simultaneously residing for people is a region, instead of a point, and therefore the setting of this paper can't cause serious interference to positioning error.

${\mathrm{\&omega;}}_i=\frac{N_i}{{\mathrm{\&Sigma;}}_{j=1}^k{N}_i^j}---(0-1)$

By the weights ω of each reference label _iand corresponding coordinate (x _i, y _i), namely can obtain the estimated value of this moment target object present position, as shown in formula (0-2).

$(\hat{x},\hat{y})=\underset{i=1}{\overset{k}{\mathrm{\&Sigma;}}}{\mathrm{\&omega;}}_i(x_i,y_i)---(0-2)$

In the present invention, available data are extremely limited, are only whether whether tag state migration occurs and produces to block to affect two information.The astable equilibrium state that the present invention is utilized in an experiment disturbs generation mutually by two labels.The different label interval recognition success rate of d to its surrounding objects object of label centering is different.Adjust the distance to the height of the position right relative to label with the angle of reader, target object, target object and label height etc. the factor on ground of label all can have an impact to recognition success rate in addition.Good deployment scheme can improve the precision of detection greatly.Therefore the present invention may be researched and analysed every factor that recognition success rate has an impact above-mentioned by great many of experiments, and the deployment scheme then choosing effect optimum is applied in detection system.

Claims (2)

1. based on a track-detecting method for radio-frequency (RF) tag metastable condition, it is characterized in that, comprise the following steps:

1) label is to the sub-firm power training stage:

First based on the Partition Theory of antenna place, specify between reader and label and energy transferring mode between label pair; Next utilizes Fu Lisi equation and Biot-Savart law to carry out formalized description to the mutual interference between the energy transferring between reader and label and label respectively, finally sets up the mutual interference model between label pair;

Corresponding performance number when extremely just activating label that rises and falls causing receiving antenna place signal level is defined as the sub-firm power of label;

The difference of each label own causes it, and metastable to determine performance number different, by label to being arranged in RFID reader read range, fixed by label to position, to detect the reading state of the label in Reader coverage in real time;

(2) the Unified Power stage is adjusted

By regulating the distance of two labels, regulating and metastablely determining watt level;

The power training stage obtains the metastable of each label and determines performance number; The power of label is adjusted to unified value, so that Reader works under same power, with one of them label for benchmark, adjusts other labels and adjust the distance; For convenience of regulating, the label getting middle power value is benchmark, and the label centering after adjustment has a label to obtain approximate baseline performance number; Represent label centering two label interval with d, as 6mm<d<26mm, label can produce the corresponding metastable change determining performance number; Regulate each label pair in the same fashion, make all label centerings have one to reach approximate baseline performance number; When label be less than metastable determine performance number 0.5dbm time, require that after reunification metastable is determined performance number and differed with reference power and be less than or equal to 0.5dbm, adjustable range completes;

(3) the mobile object detection phase

The impact of target object on population of tags of motion comprises shadow effect and multipath effect two kinds, and these two kinds by causing different channel fadings to radiowave, thus changing the right astable equilibrium state of label, reaching the object detected target object.

2. the track-detecting method based on radio-frequency (RF) tag metastable condition according to claim 1, it is characterized in that, train the operation of sub-firm power to be the emissive power of Reader increased with fixed step size power, tag reader situation is just read from not reading, and finally arrives stable reading; Performance number corresponding when just being read by label is decided to be the sub-firm power of this label; Each label reads repeatedly with Reader in the same fashion, until can obtain one stable metastablely determine performance number.