CN107341424B - A kind of precise phase calculation method based on the estimation of RFID multipath - Google Patents
A kind of precise phase calculation method based on the estimation of RFID multipath Download PDFInfo
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
- G06K7/10019—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers.
- G06K7/10069—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. the collision being resolved in the frequency domain, e.g. by hopping from one frequency to the other
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K17/00—Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations
- G06K17/0022—Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations arrangements or provisious for transferring data to distant stations, e.g. from a sensing device
- G06K17/0025—Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations arrangements or provisious for transferring data to distant stations, e.g. from a sensing device the arrangement consisting of a wireless interrogation device in combination with a device for optically marking the record carrier
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
- G06K7/10019—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers.
- G06K7/10079—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. the collision being resolved in the spatial domain, e.g. temporary shields for blindfolding the interrogator in specific directions
- G06K7/10089—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. the collision being resolved in the spatial domain, e.g. temporary shields for blindfolding the interrogator in specific directions the interrogation device using at least one directional antenna or directional interrogation field to resolve the collision
- G06K7/10099—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. the collision being resolved in the spatial domain, e.g. temporary shields for blindfolding the interrogator in specific directions the interrogation device using at least one directional antenna or directional interrogation field to resolve the collision the directional field being used for pinpointing the location of the record carrier, e.g. for finding or locating an RFID tag amongst a plurality of RFID tags, each RFID tag being associated with an object, e.g. for physically locating the RFID tagged object in a warehouse
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
- G06K7/10316—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers
- G06K7/10356—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
Abstract
The invention discloses a kind of precise phase calculation method based on the estimation of RFID multipath, the internal relation for receiving phase between multichannel is found out, and assesses the ratio for receiving to be influenced in phase data by multipath effect.Since the influence of multipath effect is unknown, the radio frequency shift of RFID hardware, the movement of people and some uncontrollable factors etc. we cannot obtain true phase value.Therefore these influences are assessed by measuring the degree of scatter of receiving phase, and concludes therefrom that real possible phase value.The present invention does not need do not have particular/special requirement to hardware, does not need to modify to existing commercial agreement, the present invention supports to obtain more accurate phase value from existing system completely, even in the generally existing indoor environment of multipath yet.
Description
Technical field
The invention belongs to radio frequency identification (RFID) technical fields, and in particular to a kind of essence based on the estimation of RFID multipath
True phase calculation method.
Background technique
Radio Frequency Identification Technology (RFID) is prevalent in such as retail business, supermarket, logistics, in many applications such as storage.In recent years
Come, Many researchers pay close attention to RFID application, for example position, human body actively perceive, trajectory track etc..In such applications, phase
Value by praise highly and it is particularly useful.Because phase can reflect the variation of fine granularity label position.Movement for label
Object can use its continuous phase value and carry out tracing path.Equally, in recent years, multipath effect generally existing in indoor environment
Cause the attention of large quantities of researchers.For example, static reflex source, such as cement wall have been estimated in some researchs, and attempt to cut down surrounding
The influence of environment.Other some researchs are using reaching their target the characteristics of multipath effect.In addition to this, part is studied
Multipath effect can be eliminated or cut down in complicated indoor environment, and core views are assessment multipaths and then reject impacted
Data.However, seriously affecting due to indoor multipath, many research work all in the less environment of a multipath or
It collects in one predefined region comprising the training data including phase.These deficiencies can be to influence related work in reality
In application.For example, a people walks at random between reader and label when experiment scene is deployed in a narrow region
When dynamic, the phase value of label will receive seriously affecting for multipath reflection signal.
Existing RFID much studies the phase that signal is utilized, and introduces the significant direction of two comparisons, is label respectively
Trajectory track positioning and human body behavior perception.
Label track tracing and positioning: due to occupying middle critical positions in the signal, phase is often used in marking as characteristic value
Sign trajectory track positioning.Based on hyperbola: some researchers are by constructing hyp side using the phase that receives of target labels
Method is to come the position that positions label.Work different from the past, this method do not need to can determine target in the case where anchor tag
The coordinate of label.But the accuracy of the method depends on how to collect the accurate phase information of target labels, to guarantee result
Accurate the method must work under a weaker environment of multipath effect.Method based on hologram: i.e. by comparing instruction
Practice the phase of label and test label.This method is under the generally existing environment of multipath effect, in spacing smaller (13cm) standard
True rate is up to 86%.However, the method needs to assess the data by multipath effect and assigns a low weight to it, thus
The accuracy of entire method can be affected.In addition to the method for above-mentioned two tag location, concern label is compared in some researchs
Trajectory track.For example, the track of mobile tag is tracked in some researchs based on hologram, and it can accurately find out the position of label
It sets, accuracy can achieve Centimeter Level.Compare regrettably, these work require to be influenced at one by multipath effect smaller
Environment in work.
Human body behavior perception: phase purposes in human body behavior perception is also very extensive.It is well known that mobile people couple
The communication of RFID reader and label is influential.Some scholars have studied the relationship for receiving phase and human body behavior, for example,
Some work can not depend on any equipment and carry out the mobile object of tracking through walls, it can collect in advance some reference datas and
Eliminate the influence that stationary body (such as furniture) causes multipath effect；Also some work can pass through the commodity of analysis label
The purchasing habits of customer are inferred by the variation of phase when movement.
Other than the field RFID, other field such as Wi-Fi, 60G, sound etc. have similar algorithmic technique.However, by
It is limited in by RFID communication protocol and passive passive label itself, these algorithmic techniques cannot all be used directly in RFID system
In.In sound, it is thus proposed that a kind of distance measurement method based on phase, this method can be estimated to be moved by what hand introduced
State vector.But because frequency and Protocol Design gap are bigger, this method based on sound and based on the transmission speed of RFID
It can not directly apply in commercial RFID device.And Wi-Fi and some similar techniques, that is, 60G, it sends and receives all to exist
With stepping row under multiple subchannels, and it is exposed in same environment.The business machine of some Wi-Fi can assess present channel
Parameter and calculate possible phase value.
Different from aforementioned technology, RFID system be only capable of in a channel by an antenna in the same time and
One label is communicated.In other words, different passive passive labels cannot share same channel.In addition, multipath effect exists
Lasting change in communication process, none expected data refer to.These limitations are brought to phase estimation and calculating
Many problems.To sum up, art methods can practicality, actual deployment, accuracy and other in terms of all exist or it is big or
Small problem.
Summary of the invention
In order to solve the problems in the prior art, the present invention proposes that a kind of precise phase based on the estimation of RFID multipath calculates
Method can overcome interference of the existing multipath effect to phase value, accurately to calculate pure phase value.
In order to achieve the goal above, the technical scheme adopted by the invention is as follows: the following steps are included:
1) reader antenna collects the phase data of target labels, receiving phase β；
2) vector decomposition and angular transformation are carried out to the phase data of collection:
Vector decomposes and the relationship after angular transformation are as follows:
Wherein, β is receiving phase, and θ is pure phase, and α is multipath effect phase, and θ ' is the pure phase after angular transformation
Position, β ' are that receiving phase, α ' after angular transformation is multipath effect phase after angular transformation, k0Indicate integer, Z is integer
Collection；
3) pure phase theta and mirror image phase are establishedRelationship: Indicate integer,Value is by tan
α ' decision；
4) mirror image phase is solved according to following equationValue:
For the multipath variable in channel n,For the receiving phase value added for jumping to from n n+1 when channel, βnIt is every
The receiving phase of a channel, n=1,2,3 ... N；
5) the pure phase theta and mirror image phase established according to step 3)Relationship and step 4) solve mirror image phaseValue counter release pure phase value.
Reader antenna traverses N number of channel, and N is more than or equal in 5 seconds data of each channel collection in the step 1)
3, obtain receiving phase β.
K in the step 2)0There is following relationship:
Wherein, m ∈ Z.
Multipath variable in the step 4) in channel nIncluding static multipath and dynamic multi-path, static multipath represents quiet
Reflecting properties in the case of state, dynamic multi-path expression are influenced by mobile object.
According to mirror image phase in the step 4)Solution formula obtain matrix equation: AN×(N+2)·x(N+2)×1=bN×1,
Wherein AN×(N+2)It is coefficient matrix, x(N+2)×1It is unknown matrix of variables, bN×1Represent the receiving phase of matrix:
Wherein, ()TIndicate transposed matrix；
Then the solution of matrix equation is expressed as:
X=ξ0+c1·ξ1+c2·ξ2
Wherein ξ0It is particular solution, ξ1And ξ2It is general solution, c1And c2It is ξ respectively1And ξ2Coefficient.
It is needed in the solution procedure of the matrix equation effectively solved by the receiving phase β of all channelsnIt is adjusted to one
On fit line, fit line linear equation adjusted is yn=kn+d, and it is necessary to meet following condition:
Wherein, ωnIt is the weight of channel n, k is slope, and d is intercept；
Utilize the sample average error σ of receiving phase in channel nnTo indicate dispersion:
Wherein,Indicate the sample in each channel,It is the mean value of t sample；
Then define weight equation are as follows:
When sample number t is sufficiently large, have:
To obtain fit line according to weight equation.
The slope k of the fit line and the calculating process of intercept d:
Formula is minimized firstInIt is as follows to obtain partial derivative:
Then it enables above formula be equal to 0 and solve to obtain:
The formula x=ξ0+c1·ξ1+c2·ξ2Middle coefficient c1And c2It is solved by following equation:
Wherein, yiAnd yN+1-iFor the random selection group point on fit line.
Compared with prior art, the present invention finds out the internal relation for receiving phase between multichannel, and assesses and receive phase
The ratio influenced in data by multipath effect.Since the influence of multipath effect is unknown, the radio frequency shift of RFID hardware, the shifting of people
Dynamic and some uncontrollable factors etc. lead to that true phase value cannot be obtained, therefore pass through the dispersion journey of measurement receiving phase
Degree concludes therefrom that real possible phase value to assess these influences.The present invention does not need do not have particular/special requirement to hardware,
It does not need to modify to existing commercial agreement, the present invention supports to obtain more accurate phase from existing system completely yet
Value, even in the generally existing indoor environment of multipath.The present invention is extracted from the environment by multipath effect to be obtained really
Phase value does not need to dispose label, equipment in advance, does not need training dataset, this is significantly improved of the invention yet
Practicability.Secondly, the perfect compatible existing RFID commercialization agreement of the present invention, and do not need to modify to hardware.Therefore, this hair
It is bright to be easy to easily carry out work as the middleware of application system.The result shows that this method is in open area environment
And error is all very low in the generally existing environment of multipath.The present invention only by reader and target labels relative distance
The true phase value in the generally existing environment of multipath can be calculated, even if there is mobile object in this environment, gram
Interference of the existing multipath effect to phase value is taken, accurately to calculate pure phase value.
Further, due in environment indoors receiving phase have a long way to go with desired value, influenced seriously by multipath effect.Cause
This, the present invention has elasticity to multipath effect estimation accurately to calculate pure phase, and the present invention obtains a square by analogizing
Battle array equation, effective solution of matrix equation, the receiving phase of all channels is adjusted on a fit line, and is passed through in order to obtain
Weight equation is defined to cut down the influence for receiving phase outlier, weight equation can help to obtain more suitable fit line and more
Good estimated result.
Detailed description of the invention
Fig. 1 is the structural diagram of the present invention；
Fig. 2 a is backscattering idealized model schematic diagram, and Fig. 2 b is that there are the signals of the backscattering model of influence factor
Figure；
Fig. 3 a is the confirmatory analysis figure for testing one, and Fig. 3 b is the confirmatory analysis figure for testing two, and Fig. 3 c experiment three is tested
Card property analysis chart；
Fig. 4 a is the vector relations figure of Signal averaging, and Fig. 4 b is the vector relations figure for decomposing reflection signal；
Fig. 5 is receiving phase schematic diagram；
Fig. 6 is fit line and receiving phase schematic diagram.
Specific embodiment
Below with reference to specific embodiment and Figure of description the present invention will be further explained explanation.
Referring to Fig. 1, the present invention is divided into two parts, and first part carries out the relationship of mixed-phase β and pure phase theta
Modeling；Second part calculates pure phase theta from the model having been built up.Key step is as follows:
1) collect target labels phase data: reader antenna faces target labels, in 5 seconds numbers of each channel collection
According to traversing N number of channel, N need to be more than or equal to 3, and during RFID communication, it is a series of radiofrequency signals that reader, which receives signal,
Superposition, specifically includes that the signal of diameter line-of-sight signal and Ambient, uncontrollable due in practice, reflecting, this will be to final
Receiving phase β brings a random error α, due to aliasing mutual between signal, so that finally receiving phase beta and being expected pure
Net phase theta has significant difference；
2) vector decomposition and angular transformation are carried out to the phase data of collection: is decomposed by vector, by phase caused by multipath
Position α be transformed to only a phase theta relevant to pure phase theta ', vector is converted to new form, in this case, will most terminating
Receive the sum that phase beta is converted to two simple scalars；
3) by calculating and analyzing, the pure phase theta of vector and the mirror image phase of scalar are establishedBetween connection, obtain
Pure phase theta and certain mirror image phase bridge, that is, scalar phase
4) by mirror image phaseLinear Equations are substituted into other dependent phases to solve, and solve the value of mirror image phase,
Pure phase in order to obtain passes through calculatingAssess pure phase probable value, the multipath variable that defines in channel n is Influence comprising multipath effect under quiescent conditions and current intelligence, wherein static multipath
The reflecting properties under quiescent conditions, such as wall, ceiling, furniture etc. are represented, and dynamic multi-path is influenced by the object moved, example
Such as mobile robot, people of walking etc., when channel jumps to n+1 from n, receiving phase value added isReceive signal to exist
Phase beta in channel nnThe sum of three parts are represented as, i.e. multipath variable isWith mirror image phaseThe sum of, in this feelings
Under condition, the phase beta of each channel can be represented, and ideally, receive phase substantially all on straight line y '；
5) the pure phase theta and mirror image phase established by step 3)Between relationship, it is counter to release the big of pure phase theta
It is small: to have a long way to go, influenced seriously by multipath effect, it should to multipath effect with desired value due to receiving phase in environment indoors
Estimation has elasticity accurately to calculate pure phase theta, by analogizing obtains a matrix equation, in order to obtain matrix equation
Effectively solution, by the receiving phase β of all channelsnIt is adjusted on a line, and receives phase by defining weight equation to cut down
The influence of outlier, weight equation can help to obtain more suitable fit line and better estimated result, the slope k of fit line
With intercept d's and and desired valueGap can calculate, next construct two additional equations carry out solution formula by matrix equation
Effective solution of the non-secondly system of linear equations obtained, the building of formula 1 and the slope of fit line are related, and formula 2 is quasi- by definition
Point y in zygonemanWith receiving phase βnGap (i.e. residual error Sn) relationship obtain.
A referring to fig. 2, the idealized model of RFID reader and passive passive label backscatter communication.Reader
Antenna issues radiofrequency signal, carries out backscattering by label, and finally received by reader antenna.Entirely propagation distance is
2d, the sighting distance of twice antenna and label.In this path, the phase information of signal is different.In addition to the rotation of distance, day
The circuit of line and the reflection characteristic of label can all generate additional deflection to phase, be defined as θAAnd θT.The reception of final label
Signal phase includes three parts, as follows:
θ=(θD+θA+θT)mod2π (1)
Wherein θDIt is because of phase change caused by the variation of signal propagation distance.It depends on current transmission frequency f:
λ indicates wavelength, and c is the light velocity.Different from multi channel wireless system, most of RFID systems only allow their read
It reads device to be communicated with label in a channel, such as ImpinJ R420.Reader can jump in the state of frequency-hopping mode
It is communicated to another channel.According to explanation, the working frequency range of commercial 16 channels of reader is 860-960MHz.
In addition to frequency and propagation distance, phase may be influenced by other extra factors in practice, such as multipath is imitated
It answers.As shown in Figure 2 b, may be impacted in some places by the radiofrequency signal of tag backscatter, and change itself originally
Propagation path.When their final northern reader antennas receive, these waves may be overlapped from the perspective of reader
Form a new rf wave.As shown in Figure 2 b, the signal finally received by reader is by diameter line-of-sight signal and reflection signal
Two parts are constituted.In most cases, it is only necessary to which what pure phase value was namely calculated by formula (1), this only takes
Certainly in line-of-sight signal.
In reality, multipath effect is generally existing.Roof, cement wall, other objects in furniture and ambient enviroment
It is all good reflecting medium, the present invention is verified with three experiments.
Experiment one: placing a label before reader, keeps the relative distance of label and antenna and relative position constant,
Whole system is moved to ten different places indoors.The phase and received signal strength (RSS) of same label such as Fig. 3 a institute
Show, radius indicates the value of RSS, and radian indicates the angle of phase.It was found that the changing value of phase is at (105 °, 345 °).These fluctuations
May cause calculate apart from when 21cm or more error, this can positioning and damaging property of trajectory track to label influence.
Experiment two: same to collect with four antennas of a reader using experiment two come the otherness of measuring device
The phase and RSS value of label, this four antennas are models of the same race and are placed on the same position, as a result as shown in Figure 3b.It was found that
Even if each position and direction remain unchanged, testing the phase received still has difference with equipment difference.
Experiment three: studying the influence of mobile object, phase information 10 seconds or so of persistent collection label, allows one during this period
Name volunteer's random walk in RFID system.As shown in Figure 3c, phase value is widely distributed within the scope of 2 π, in other words,
The phase information that the influence of object meeting clearly around RFID system is collected.
The present invention specifically includes the following steps:
1) collect target labels phase data: reader antenna faces target labels, in 5 seconds numbers of each channel collection
According to traversing N number of channel (N need to be more than or equal to 3).The pass of mixed-phase β and expected pure phase theta are illustrated in figs. 4 a and 4b
System.As previously mentioned, reader receives a series of superposition that signal is radiofrequency signals, diameter line-of-sight signal and environment are specifically included that
The signal of reflection reflects uncontrollable due in practice, this will bring a random error to final receiving phase β, i.e. α, such as
Shown in Fig. 4 a, the radiofrequency signal that reader receives is indicated with polar coordinates, and the radian of vector indicates the amplitude of signal, polarizing angle
Indicate current phase,Indicate line-of-sight signal,Indicating the superpositions of all reflection signals, phase is θ and α respectively, whenWithIt meets, their new signals of mutual superimposed formationThe result shows that phase beta and expected pure phase theta be have it is aobvious
Write difference.
2) vector decomposition and angular transformation are carried out to the phase data of collection: is decomposed by vector, by phase caused by multipath
Position α be transformed to only a phase theta relevant to pure phase theta ', vector is converted to new form, as shown in fig. 4 a by vectorPoint
Solution is two parts, is respectivelyWithVectorWith vectorVertically, vectorWithIn parallel；Such as Fig. 4 b institute
Show, uses vectorWithInstead of vectorWithIts polarizing angle becomes α ' and β ', and in the case, Fig. 4 a can be safe
Reasonably equivalence is converted to Fig. 4 b, the relationship of conversion front and back polarizing angle are as follows:
Compare Fig. 4 a and Fig. 4 b, finds superposed signalβ, θ are remained unchanged, because reflection signal is uncontrollable, polarizing angle α
It is unknown with β, however, constructing the relationship of α ' and θ after having decomposed vector to be convenient for calculating θ.
3) by calculating and analyzing, the pure phase theta of vector and the mirror image phase of scalar are establishedBetween connection, obtain
Pure phase theta and certain mirror image phase bridge, that is, scalar phaseResearch superposition vector beta and two component vectors
The relationship of θ ', α ', according to vector calculus, if two vector thetas1And θ2Superposition summation generates new vector theta3, triadic relation is such as
Under:
Wherein A1And A2The amplitude of two vectors, vector beta ' formula it is as follows:
Formula (3) describes the relationship of α ' He θ ', according to triangle relation, can release:
If using the α ' in θ ' replacement formula (5) according to formula (6), have:
It is now assumed that final phase beta can be represented asWithSum, that is:
According to triangle relation, have:
DefinitionWithIt is expressed as follows:
It was found that formula (7) and formula (9) are of equal value, this, which means that, can construct pure phase vectors θ and defined
Bridge, i.e.,AndIt represents current line-of-sight signal and reflects the relationship of signal, be called " multipath variable ", this
Outside, due toIt can further release:
Wherein m ∈ Z.
In this case, final phase beta is converted to the sum of two simple scalars from the superposition of two unknown vectors.This
Outside, the bridge of the pure phase theta and certain mirror image phase that obtain, that is, a kind of scalar phaseNext, calculating mirror image
With the value of respective phase θ.
4) by mirror image phaseLinear Equations are substituted into other dependent phases to solve, and solve mirror image phase
Value, pure phase, can calculate in order to obtainTo assess pure phase probable value.
Define channel n in multipath variable beNote thatComprising quiescent conditions and move
The influence of multipath effect in the case of state, that is:
Wherein static multipath represents the reflecting properties under quiescent conditions, such as wall, ceiling, furniture etc., and dynamic multi-path
It is influenced by the object moved, such as the robot moved, people of walking etc..When channel jumps to n+1 from n, receive phase
Value added isPhase differenceIt is made of three parts, including Δ θD, Δ θR, Δ θT.After changing frequency, wavelength also occurs
Corresponding change.Caused by as a result, receive signal same distance under can generate a phase difference θD, same reader and label
Phase difference be respectively Δ θRWith Δ θT.Therefore, receive signal in the phase beta of channel n kindnThe sum of three parts can be represented as,
That is:
WhereinIt is the mirror image phase in first channel.In the case, the phase beta of each channel can be represented as
Under:
Above-mentioned decomposition is demonstrated by an experiment, label is individually placed in two kinds of environment, one is open region,
One is narrow region, records the phase beta received every channel respectivelyn, as shown in figure 5, in open area, multipath effect
It is more much lower than line-of-sight signal, that is,The result shows that when the channel of reader is from n+1, the variation of phase is become
Linear, the phase difference of adjacent channel isIn other words, ideally, receive phase substantially all on straight line y '.
As shown in figure 5, the phase of open area really substantially point-blank, is agreed with theory.On the other hand, narrow
The multipath effect in region be it is violent, in other words, multipath variableIt can not be ignored.The result shows that from 1 to 16 phase fluctuation of channel
It is very big, as shown in Fig. 5 intermediate cam shape.Equally, receive phase in environment indoors to have a long way to go with desired value, by multipath effect shadow
It rings seriously, therefore, the present invention should estimate multipath effect to have elasticity accurately to calculate pure phase theta.
5) the pure phase theta and mirror image phase established by step 3)Between relationship, it is counter to release the big of pure phase theta
It is small.We can calculate from formula (14)And formula (14) can class release a matrix equation:
AN×(N+2)·x(N+2)×1=bN×1 (16)
Wherein, AN×(N+2)It is coefficient matrix, x(N+2)×1It is unknown matrix of variables, bN×1The phase that receives of matrix is represented, it is public
Formula (16) can be by detailed expression are as follows:
Wherein ()TIndicate transposed matrix, formula (16) is nonhomogeneous linear equation.Therefore non trivial solution can be expressed
Are as follows:
X=ξ0+c1·ξ1+c2·ξ2 (18)
Wherein, ξ0It is particular solution, ξ1And ξ2It is general solution.c1And c2It is ξ1And ξ2Coefficient.Because by the N number of equation of N+2 variable,
Solution x has unlimited kind of possibility, and effective solution that x is arrived in order to obtain needs additionally to construct two equations.
In order to reach this purpose, by the receiving phase β of all channelsnIt is adjusted on a line, fit line adjusted
Linear equation is yn=kn+d and it is necessary to meet following condition:
Wherein ωnIt is the weight of channel n.The influence of outlier is cut down by defining weight equation.Mobile object and people
Caused by dynamic reflective, it will generate uncontrollable and unstable error.The result shows that more serious multipath effect will will lead to
Receive phase more to disperse.Utilize the sample average error σ of receiving phase in channel nnTo indicate dispersion:
WhereinIndicate the sample in each channel,It is the mean value of t sample.Further define weight equation:
It is worth noting that all ωnSum it is equal with the number of channel.It is dynamic to eliminate by the weight for weakening impacted channel
Uncontrollable error in state multipath effect.When sample number t is sufficiently large, have:
Weight equation can help us to obtain more suitable fit line and better estimated result.
More suitable slope k and intercept d in order to obtain need to minimize in formula (19)Partial derivative is as follows:
It enables formula (23) to be equal to 0 and solves, can obtain:
Weights omega in formula (24)n, receive phase betanAll be it is known, the value of k and d are easy for calculate.In order to clear
The fit line y for receiving phase of the effect for seeing the method for Chu, narrow zone is as shown in Figure 6.It was found that fit line and it is expected
The straight line y ' arrived gap.Formula (13) is brought into another expression formula of the available k and d of formula (24):
As above fit line y is successfully solved.The slope k and intercept of fit line be d's and and desired valueGap be e1
+e2.Next, needing to find the coefficient c that additional two equations come in solution formula (18)1And c2, i.e. formula 1 and formula 2.
Formula 1:
According to formula (18), θ is found,Multipath variableIt is all unknown in matrix x.It is, they are ok
And e1C can equally be used1And c2To indicate.Therefore using the expression formula of the k in formula (25) as formula 1.
As previously mentioned, the value of k is not aware that.Two location variables only deposited in formula 1 are c1And c2.Pay attention to formula (18)
Have an impact to formula (26), can be utilized.
Formula 2:
As shown in fig. 6, point y on fit linenWith receiving phase βnThere is certain gap.Define every a pair of ynAnd βnError use
Residual error Sn, may be expressed as:
Sn=yn-βn, n=1,2,3...N (27)
According to formula (25) ynIt can be expressed as follows:
In conjunction with formula (13), residual error SnIt can be represented as again:
If we can calculate total residual error of all channels, have:
Next one group of point y is randomly choosed on fit lineiAnd yN+1-iAnd it sums:
It is subtracted formula (30) with formula (31), available formula 2:
According to formula 1 and formula 2, can be easy to calculate c1And c2Value.Known variables in corresponding matrix x can also
To calculate.Pay attention to eachDouble influence by line-of-sight signal and reflection signal.Because of phase differenceNevertheless suffer from distance
(ΔθD) and hardware feature (Δ θRWith Δ θT) influence, the variable uniquely influenced on pure phase theta isIt can calculate as follows:
Value determined by tan α ', so far can calculate mirror image phaseAnd it can successfully obtain pure phase value θ.
The present invention obtains accurate phase by assessing multipath, can calculate true pure phase in indoor complex environment
Value.Practice have shown that error is all very low in the environment that the present invention is in open area environment and multipath is generally existing, respectively
5.14cm 5.52cm.The present invention is excellent in compared to conventional phase collection method, and with the presence of mobile object the case where
Under also have very high accuracy.
Claims (8)
1. a kind of precise phase calculation method based on the estimation of RFID multipath, which comprises the following steps:
1) reader antenna collects the phase data of target labels, receiving phase β；
2) vector decomposition and angular transformation are carried out to the phase data of collection:
Vector decomposes and the relationship after angular transformation are as follows:
Wherein, β is receiving phase, and θ is pure phase, and α is multipath effect phase, and θ ' is the pure phase after angular transformation, β '
For the multipath effect phase that receiving phase, the α ' after angular transformation are after angular transformation, k0Indicate integer, Z is set of integers；
3) pure phase theta and mirror image phase are establishedRelationship: Indicate integer,Value is determined by tan α '
It is fixed；
4) mirror image phase is solved according to following equationValue:
For the multipath variable in channel n,For the receiving phase value added for jumping to from n n+1 when channel, βnFor each channel
Receiving phase, n=1,2,3 ... N；
5) the pure phase theta and mirror image phase established according to step 3)Relationship and step 4) solve mirror image phase's
Value is counter to release pure phase value.
2. a kind of precise phase calculation method based on the estimation of RFID multipath according to claim 1, which is characterized in that institute
It states reader antenna in step 1) and traverses N number of channel in 5 seconds data of each channel collection, and N is more than or equal to 3, is received
Phase beta.
3. a kind of precise phase calculation method based on the estimation of RFID multipath according to claim 1, which is characterized in that institute
State k in step 2)0There is following relationship:
Wherein, m ∈ Z.
4. a kind of precise phase calculation method based on the estimation of RFID multipath according to claim 1, which is characterized in that institute
State the multipath variable in step 4) in channel nIncluding static multipath and dynamic multi-path, static multipath is represented under quiescent conditions
Reflecting properties, dynamic multi-path expression are influenced by mobile object.
5. a kind of precise phase calculation method based on the estimation of RFID multipath according to claim 1, which is characterized in that institute
It states in step 4) according to mirror image phaseSolution formula obtain matrix equation: AN×(N+2)·x(N+2)×1=bN×1, wherein AN×(N+2)
It is coefficient matrix, x(N+2)×1It is unknown matrix of variables, bN×1Represent the receiving phase of matrix:
Wherein, ()TIndicate transposed matrix；
Then the solution of matrix equation is expressed as:
X=ξ0+c1·ξ1+c2·ξ2
Wherein ξ0It is particular solution, ξ1And ξ2It is general solution, c1And c2It is ξ respectively1And ξ2Coefficient.
6. a kind of precise phase calculation method based on the estimation of RFID multipath according to claim 5, which is characterized in that institute
It states and is needed in the solution procedure of matrix equation effectively solved by the receiving phase β of all channelsnIt is adjusted on a fit line, adjusts
Fit line linear equation after whole is yn=kn+d, and it is necessary to meet following condition:
Wherein, ωnIt is the weight of channel n, k is slope, and d is intercept；
Utilize the sample average error σ of receiving phase in channel nnTo indicate dispersion:
Wherein,Indicate the sample in each channel,It is the mean value of t sample；
Then define weight equation are as follows:
When sample number t is sufficiently large, have:
To obtain fit line according to weight equation.
7. a kind of precise phase calculation method based on the estimation of RFID multipath according to claim 6, which is characterized in that institute
State the slope k of fit line and the calculating process of intercept d:
Formula is minimized firstInIt is as follows to obtain partial derivative:
Then it enables above formula be equal to 0 and solve to obtain:
8. a kind of precise phase calculation method based on the estimation of RFID multipath according to claim 7, which is characterized in that institute
State formula x=ξ0+c1·ξ1+c2·ξ2Middle coefficient c1And c2It is solved by following equation:
Wherein, yiAnd yN+1-iFor the random selection group point on fit line.
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