CN106446733A - Label reception power prediction method of ultra high frequency (UHF) radio frequency identification (RFID) electronic toll collection (ETC) applications - Google Patents

Abstract

The present invention discloses a label reception power prediction method of UHF RFID ETC applications. The method comprises the steps of setting a reader antenna as a Cartesian coordinate origin, setting the Cartesian coordinate of a label as unknown, and solving a first-order reflection surface equation by the application scene geometrical parameters and the geometrical relationships, namely a plane equation of an automobile engine hood plane, a left temporary road vehicle right side surface and a right temporary road left side surface; by a free space radio wave propagation formula, calculating a visual range electric field intensity vector from the reader antenna to the label; separately calculating the coordinates of the reflection points on the above reflection surface; by a first-order reflection matrix equation of an electromagnetic wave, separately calculating the electric field intensity vectors of an incident wave and a reflection wave arriving at the label at the reflection surface; solving the label electric field vector sum, a label chip antenna port matching coefficient and a polarization matching coefficient, and finally obtaining a label reception power calculation result in the space. The label reception power prediction method of the present invention can obtain a higher prediction precision than the conventional lognormal model and Leslie Model, and obtain the prediction speed more convenient and faster than a commercial electromagnetic calculation software based on Maxwell's equations.

Description

A kind of label receiving power Forecasting Methodology of UHF RFID ETC application

Technical field

The present invention relates to electrical technology field, particularly a kind of label receiving power prediction side of UHF RFID ETC application Method.

Background technology

RF identification (RFID) technology of hyperfrequency (UHF) frequency range has label low cost, identifies that distance is remote, can once read The features such as take multi-tag, in intelligent transportation and intelligence such as the identifications of electric non-stop toll (ETC), electronic license plate and container Logistics field has huge application potential.Reduce label cost for maximizing, UHF rfid system adopts wireless power transmission And back-scattering modulation technique, the electromagnetic wave that labeling requirement radiates from reader obtains energy.Reader is to electric wave between label Random multipath transmisstion, will lead to there is a certain proportion of identification blind spot in identification region, reduce rfid system identification certainty, this Always restrict the one of the main reasons of this technology broader applications.Different from general mobile communication and indoor wireless communication Technology.

At present, the main method of modeling UHF rfid system radio wave propagation includes statistics and Decided modelling method.Statistics Modeling typically point sighting distance and non line of sight situation, by a large amount of scrnario testing data matchings, set up label receiving power and obey one Determine the statistical channel model of statistical distribution functions, can solve well to be normally applied under environment and carry out asking of link power budget Topic, but they adopt be all Ruili or this model modeling multipath fading of Lay, using logarithmic model modeling large scale path damage Consumption, and for application-specific scene, empirical method too vague generalization, Shortcomings in accuracy.

Then, people adopt the numerical computation method of electromagnetic field, make up deficiency in terms of accuracy for the statistical channel model. As using Ansoft company HFSS commercial electromagnet software for calculation, and adopt ray tracing method.Numerical method degree of accuracy is high, but The workload setting up model space geometric and the amount of calculation solving magnetic distribution are too big, for situations such as practical application deployment simultaneously Inapplicable.

The antenna rf parameter of UHF RFID technique typical case's application is respectively provided with certainly with scene reflectivity (scattering) body geometric distribution , there is dependency between field strength distribution and typical application scenarios geometrical characteristic parameter in identification range, but be hidden in body feature In the classical statistic of statistical channel model, in practical application, it is difficult to accurate selection statistic numerical value.And using based on Mike The commercial simulation software of this Wei Fangcheng is although field strength distribution can accurately be predicted, but needs to initially set up the three-dimensional propagating scene Geometry and material model, very time and effort consuming.During the application deployment such as ETC in UHF RFID, it is desirable to have effect design three dimensions Identification region geometric ranges, and several by optimizing reader antenna height, angle, beam angle, or even lane width etc. What parameter, carrys out the discrimination of optimized design identification region.

Content of the invention

The technical problem to be solved is, not enough for prior art, provides a kind of UHF RFID ETC application Label receiving power Forecasting Methodology.

For solving above-mentioned technical problem, the technical solution adopted in the present invention is：A kind of mark of UHF RFID ETC application Sign receiving power Forecasting Methodology, comprise the following steps：

1) ETC typical case's application scenarios are divided into that Wu Lin road vehicle case, one side face vehicle case, bilateral faces vehicle feelings Three kinds of situations of shape；

2) be based on mirror method, according to ETC application scenarios, respectively computing engines REGPARA face, face one on vehicle reflecting surface Secondary reflection point P₁、P₂、P₃Coordinate：

Wherein, H_readerFor reader height；H_carBonnet height for identified vehicle；D_lAnd D_rFor facing vehicle two Individual side is to the distance in ETC track；D_laneFor lane width；P is calculated during Wu Lin road vehicle case₁, when vehicle case is faced in one side Calculate P₁And P₂, or calculate P₁And P₃, bilateral face situation calculate P₁, P₂, P₃；If position of transmitting antenna is cartesian coordinate initial point T (0,0,0), tag coordinate is R (x, y, z)；

3) incidence wave and the echo direction unit vector of three groups of primary event rays are calculated respectivelyWithReflecting surface method VectorM=1,2,3

4) calculating azimuth in free space is (θ, φ), electric field vector E at range transmission antenna r (r, θ, φ)：

Wherein：

P_TIt is reader antenna transmission power, G_θ(θ, φ) and G_φ(θ, φ) is the increasing in θ and φ direction for the transmitting antenna respectively Beneficial component, andWithRepresent the unit vector of this both direction respectively；ψ_θAnd ψ_φBe electric field at r, θ with φ component relative Phase place；β is wave number, and ω is the operating carriers angular frequency of RFID-ETC, and c is the light velocity；η₀For free space impedance；

5) calculate incident field strength E of primary eventⁱVertical componentAnd parallel component

Wherein：

,

Wherein, for bonnet primary event, that is, vehicle primary event is faced in m=1, left side, i.e. m=2, and right side is faced Road vehicle primary event, i.e. m=3, have respectively：

6) calculate reflected field intensity：Wherein：

Wherein ε_rFor relative transmittance,For the angle between incidence wave and reflecting surface；

7) calculate label at electric field intensity and：

Wherein, for E_m(θ_m,φ_m), m=0,1 represents sighting distance and bonnet reflection, m=3 respectively, and 4 represent both sides respectively The large-scale car that faces reflects；

8) calculate label receiving power P：

Wherein, G is label antenna gain, and λ is carrier wavelength, and X represents the polarization between label antenna and reader antenna Distribution coefficient, τ represents the matching attribute between label chip and antenna, L_wsRepresent windshield penetration loss coefficient.

X value 0.5, τ interval [0.8,1], L_wsValue 3dB, η₀For 377 Ω.

Compared with prior art, the present invention had the advantage that for：Precision of prediction of the present invention is higher than existing logarithm Normal state and this statistical model of Lay；Amount of calculation is less than the business computing software of electromagnetic field；When can be used for ETC application deployment, adjustment is read Read the geometric parameters such as device aerial angle, height, obtain optimum discrimination；The present invention is in the RF identification of Internet of Things field ETC application, has significant theory and technology advantage, has very high using value.

Brief description

Tu1Wei Wulin road vehicle case；

Tu2Wei Youlin road vehicle case.

Fig. 3 is power and discrimination distribution situation schematic diagram on track.

Specific embodiment

The basic step of Forecasting Methodology of the present invention is：Reader antenna is set to cartesian coordinate initial point, label Descartes Coordinate is set to independent variable, by application scenarios geometric parameter and geometrical relationship, obtains primary event face equation, i.e. automobile engine cover Plane, left side face vehicle right side face, the plane equation in vehicle left side face is faced on right side；Public by free space radio wave propagation Formula, calculates reader antenna to the sighting distance electric field vector of label；Based on image method, calculate reflection on above-mentioned reflecting surface respectively Point coordinates；Calculate incidence wave and echo at reflecting surface respectively by the primary event matrix equation of electromagnetic wave to reach at label Electric field vector；Ask label electric field intensity and, and label chip antenna match coefficient, Polarization match factor, final obtain Label receiving power calculating formula, for predicting three-dimensional label receiving power.

The concrete principle of the method is as follows：

The typical scene point situation that electric non-stop toll is applied considers, as shown in Figures 1 and 2, is divided into Wu Lindao Vehicle, one side face vehicle and bilateral faces three kinds of situations of vehicle.For every kind of situation, calculate and constitute electric field intensity at label Sighting distance ripple, the vector of primary reflection.Equivalent circuit diagram mated, by label chip sky by label chip and antenna chip Between line power transmission factor, reader antenna and label antenna Polarization match factor and the electric field intensity obtained and, calculate Label at any point in three-dimensional Cartesian space can receiving power.Concrete grammar is as follows：

By geometric parameter (reader height H_reader, identified bonnet of motor car height H_car, face vehicular sideview away from ETC Track is apart from D_lAnd D_r, lane width D_lane), based on mirror method, calculate three primary event point coordinates：

Wherein, if position of transmitting antenna is cartesian coordinate initial point T (0,0,0), tag coordinate is R (x, y, z).

Calculate incidence wave and the echo direction unit vector of three groups of primary event lines, reflecting surface normal vector respectively：

Calculate free space field intensity vector：

Wherein：P_TIt is reader antenna transmission power, G_θ(θ, φ) and G_φ(θ, φ) is transmitting antenna in θ and φ side respectively To gain component, andWithRepresent the unit vector of this both direction, ψ respectively_θAnd ψ_φBe electric field at r, θ and φ component Relative phase, β is wave number, and ω is the operating carriers angular frequency of RFID-ETC, and c is the light velocity.

Calculate the incident field strength of primary event：

Wherein：

Calculate reflected field intensity：

Wherein：

Wherein ε_rFor relative transmittance,For the angle between incidence wave and reflecting surface.

Calculate label at electric field intensity and：

Wherein, for E_m(θ_m,φ_m), m=0,1 represents sighting distance and bonnet reflection, m=3 respectively, and 4 represent both sides respectively Large-scale face car reflection, the geometric properties of its value and label and about scattering object are related.

Calculate label receiving power：

η₀For free space impedance (377 Ω).X represents the Polarization match factor between label antenna and reader antenna, τ table Show the matching attribute between label chip and antenna, L_wsRepresent windshield penetration loss coefficient.

Embodiment 1：

Step 1)：

With reference to electronic charging DSRC national standard (GBT 20851.1-2007) and ISO18000-6C mark Standard, determines application scenarios geometric parameter and radio frequency parameter, as shown in table 1.

Table 1 scrnario testing and simulation parameter

Step 2)：

Computing engines lid pip cartesian coordinate；

Step 3)：

Calculate with regard to the incidence wave of ground primary event, echo direction unit vectorAnd normal vector

Step 4)：

Do not exist and face vehicle primary event, then go to step 7, otherwise continue；

Step 5)：

For left side, right side vehicle, calculate pip cartesian coordinate P₂And P₃；

Step 6)：

Ask and face the echo of vehicle primary event, incidence wave direction unit vector with regard to left side and right sideAnd normal direction Amount

Step 7)：

Calculate the unit vector of vertical and horizontal incidence wave plane；

Step 8)：

By unit vectorCarry out cartesian coordinate to change to spherical coordinates；

Step 9)：

Calculate sighting distance electric field intensity E₀With each incident field strength

Step 10)：

Calculate echo electric field intensity

Step 11)：

Calculate field intensity vector at label；

Step 12)：

Calculate label receiving power, result of calculation is as shown in Figure 3.

Claims (2)

1. a kind of label receiving power Forecasting Methodology of UHF RFID ETC application is it is characterised in that comprise the following steps：

1) ETC typical case's application scenarios are divided into that Wu Lin road vehicle case, one side face vehicle case, bilateral faces vehicle case three Plant situation；

2) be based on mirror method, according to ETC application scenarios, respectively computing engines REGPARA face, to face vehicle reflecting surface last anti- Exit point P₁、P₂、P₃Coordinate：

$P_1:(\frac{x(H_{reader}-H_{car})}{2H_{reader}-2H_{car}+z},\frac{y(H_{reader}-H_{car})}{2H_{reader}-2H_{car}+z},-H_{reader}+H_{car})$

$P_2:(\frac{1}{2}{D}_{lane}+D_r,\frac{y(\frac{1}{2}{D}_{lane}+D_r)}{x+D_{lane}+2D_r},\frac{z(\frac{1}{2}{D}_{lane}+D_r)}{x+D_{lane}+2D_r})$

$P_3:(-\frac{1}{2}{D}_{lane}-D_l,\frac{-y(\frac{1}{2}{D}_{lane}+D_l)}{x-D_{lane}-2D_l},\frac{-z(\frac{1}{2}{D}_{lane}+D_l)}{x-D_{lane}-2D_l})$

Wherein, H_readerFor reader height；H_carBonnet height for identified vehicle；D_lAnd D_rFor facing two sides of vehicle Face is to the distance in ETC track；D_laneFor lane width；P is calculated during Wu Lin road vehicle case₁, calculating during vehicle case is faced in one side P₁And P₂, or calculate P₁And P₃, bilateral face situation calculate P₁, P₂, P₃；If position of transmitting antenna be cartesian coordinate initial point T (0, 0,0), tag coordinate is R (x, y, z)；

3) incidence wave and the echo direction unit vector of three groups of primary event rays are calculated respectivelyWithReflecting surface normal vectorM=1,2,3

${\hat{k}}_1=\frac{{\mathrm{TP}}_1}{\left|{\mathrm{TP}}_1\right|},{\hat{k}}_2=\frac{{\mathrm{TP}}_2}{\left|{\mathrm{TP}}_2\right|},{\hat{k}}_3=\frac{{\mathrm{TP}}_3}{\left|{\mathrm{TP}}_3\right|}$

${\hat{k}}_1^{\′}=\frac{P_{1}R}{\left|P_{1}R\right|},{\hat{k}}_2^{\′}=\frac{P_{2}R}{\left|P_{2}R\right|},{\hat{k}}_3^{\′}=\frac{P_{3}R}{\left|P_{3}R\right|}$

${\hat{n}}_1=(0,0,1),{\hat{n}}_2=(1,0,0),{\hat{n}}_3=(-1,0,0)$

4) calculating azimuth in free space is (θ, φ), electric field vector E (r, θ, φ) at range transmission antenna r：

$E(r,\mathrm{\θ},\mathrm{\φ})=\left(A_{\mathrm{\θ}}\right(\mathrm{\θ},\mathrm{\φ}){\hat{e}}_{\mathrm{\θ}}+A_{\mathrm{\φ}}(\mathrm{\θ},\mathrm{\φ}\left){\hat{e}}_{\mathrm{\φ}}\right)\frac{e^{-j\mathrm{\β}r}}{r}$

Wherein：

$A_{\mathrm{\θ}}(\mathrm{\θ},\mathrm{\φ})=\sqrt{\frac{P_T{\mathrm{\η}}_0}{2\mathrm{\π}}}{g}_{\mathrm{\θ}}(\mathrm{\θ},\mathrm{\φ})$

$A_{\mathrm{\φ}}(\mathrm{\θ},\mathrm{\φ})=\sqrt{\frac{P_T{\mathrm{\η}}_0}{2\mathrm{\π}}}{g}_{\mathrm{\φ}}(\mathrm{\θ},\mathrm{\φ})$

$g_{\mathrm{\θ}}(\mathrm{\θ},\mathrm{\φ})=\sqrt{|G_{\mathrm{\θ}}(\mathrm{\θ},\mathrm{\φ})}|e^{{\mathrm{j\ψ}}_{\mathrm{\θ}}};$

$g_{\mathrm{\φ}}(\mathrm{\θ},\mathrm{\φ})=\sqrt{|G_{\mathrm{\φ}}(\mathrm{\θ},\mathrm{\φ})}|e^{{\mathrm{j\ψ}}_{\mathrm{\φ}}}$

$\mathrm{\β}=\frac{\mathrm{\ω}}{c}$

P_TIt is reader antenna transmission power, G_θ(θ, φ) and G_φ(θ, φ) is that the gain in θ and φ direction for the transmitting antenna divides respectively Amount, andWithRepresent the unit vector of this both direction respectively；ψ_θAnd ψ_φBe electric field at r, the relative phase of θ with φ component Position；β is wave number, and ω is the operating carriers angular frequency of RFID-ETC, and c is the light velocity；η₀For free space impedance；

5) calculate incident field strength E of primary eventⁱVertical componentAnd parallel component

$E_{\⊥}^i={\hat{e}}_{\⊥}\·E^i$

$E_{\left|\right|}^i={\hat{e}}_{\left|\right|}\·E^i$

Wherein：

${\hat{e}}_{\⊥}=\frac{\hat{k}\×\hat{n}}{|\hat{k}\×\hat{n}|}$

${\hat{e}}_{\left|\right|}=\frac{\hat{k}\×{\hat{e}}_{\⊥}}{|\hat{k}\×{\hat{e}}_{\⊥}|}$

${\hat{e}}_{\left|\right|}^{\′}=\frac{{\hat{k}}^{\′}\×{\hat{e}}_{\⊥}}{|{\hat{k}}^{\′}\×{\hat{e}}_{\⊥}|},$

Wherein, for bonnet primary event, that is, vehicle primary event is faced in m=1, left side, i.e. m=2, and car is faced on right side Primary event, i.e. m=3, have respectively：

$\hat{k}={\hat{k}}_m$

${\hat{k}}^{\′}={\hat{k}}_m^{\′};$

$\hat{n}={\hat{n}}_m$

6) calculate reflected field intensity： $\left[\begin{array}{c}{E}_{\left|\right|}^r\\ E_{\⊥}^r\end{array}\right]=\left[\begin{array}{cc}{\mathrm{\Γ}}_{\left|\right|}& 0\\ 0& {\mathrm{\Γ}}_{\⊥}\end{array}\right]\left[\begin{array}{c}{E}_{\left|\right|}^i\\ E_{\⊥}^i\end{array}\right],$ Wherein：

Wherein ε_rFor relative transmittance,For the angle between incidence wave and reflecting surface；

7) calculate label at electric field intensity and：

$E_{tag}=\underset{m=0}{\overset{3}{\Σ}}{E}_m({\mathrm{\θ}}_m,{\mathrm{\φ}}_m);$

Wherein, for E_m(θ_m,φ_m), m=0,1 represents sighting distance and bonnet reflection, m=3 respectively, and 4 represent that both sides are large-scale respectively Face car reflection；

8) calculate label receiving power P：

$P=\frac{{\mathrm{\λ}}^{2}G|E_{tag}{|}^{2}X\mathrm{\τ}}{8{\mathrm{\π\η}}_0{L}_{ws}};$

Wherein, G is label antenna gain, and λ is carrier wavelength, and X represents that system is mated in the polarization between label antenna and reader antenna Number, τ represents the matching attribute between label chip and antenna, L_wsRepresent windshield penetration loss coefficient.

2. the label receiving power Forecasting Methodology of UHF RFID ETC according to claim 1 application is it is characterised in that X Value 0.5, τ interval [0.8,1], L_wsValue 3dB, η₀For 377 Ω.