C Co o on n nt t te e en n nt t ts s s

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D D De e es s si i i g g gn n no o of f fT T Ta a ag g gA A An n nt t te e en n nn n na a aa a an n nd d d T

T Ta a ag g gT T Tr r ra a ac c ck k ki i i n n ng g gS S Sy y ys s st t te e em m m M M Mo o od d de e el l l i i i n n ng g gi i i n n n3 3 3D D D f f fo o or r rA A Ac c ct t ti i i v v ve e eR R Ra a ad d di i i o o o- - -f f fr r re e eq q qu u ue e en n nc c cy y yI I Id d de e en n nt t ti i i f f fi i i c c ca a at t ti i i o o on n n

S S Sy y ys s st t te e em m m

指

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2000000666年年年 777月月月 韓韓韓國國國海海海洋洋洋大大大學學學校校校 大大大學學學院院院

電電電 波波波 工工工 學學學 科科科 T

TTrrraaannnVVViiieeetttHHHooonnnggg

C

C Co o on n nt t te e en n nt t ts s s

Abbreviation···iii Nomenclatures ···iv

Abstract···v

C CChhhaaapppttteeerrr111...IIInnntttrrroooddduuuccctttiiiooonnn ···111 1.1Background ···1

1.2Objective ···4

C CChhhaaapppttteeerrr222...DDDeeesssiiigggnnnooofffTTTaaagggAAAnnnttteeennnnnnaaa ···555 2.1Backgroundandobjective···5

2.2AntennaDesign ···10

2.3Summary ···19

C CChhhaaapppttteeerrr333...TTTaaagggTTTrrraaaccckkkiiinnngggSSSyyysssttteeemmm MMMooodddeeellliiinnngggiiinnn333---DDD···222111 3.1Backgroundandobjective···21

3.2Modeling ···23

3.3Simulation···30

3.4Summary···41

C CChhhaaapppttteeerrr444...CCCooonnncccllluuusssiiiooonnn···444222 4.1Donework···42

4.2Futurework ···43

References ···45 PublicationsandConferences ···47 Acknowledgement

A A Ab b bb b br r re e ev v vi i i a a at t ti i i o o on n ns s s

BER GBP GPS LOS PIFA RFID UHF USN

Biterrorrate

Gain-BandwidthProduct GlobalPositioningSystem Light-of-sight

PlanarInverted-F Antenna Radio-frequencyIdentification Ultra-highFrequency

UbiquitousSensorNetwork

N

N No o om m me e en n nc c cl l l a a at t tu u ur r re e es s s

_

′

″



_

′

″

′









_





_

Relativepermittivity

Realpartofrelativepermittivity Imagepartofrelativepermittivity Dielectrictangentloss

Relativepermeability

Realpartofrelativepermeability Imagepartofrelativepermeability Magnetictangentloss

Speedoflight[] Wavenumber[^{ }]

Refractiveindex(miniaturizationfactor) Wavelength[]

Wavelengthatresonantfrequency[] Frequency[]

Intrinsicimpedanceofdielectric[] Intrinsicimpedanceoffreespace[]

요 요 요 약 약 약

본 논문은 두 부분으로 구성되어 있다:하나는 새로운 매질을 사용한 RFID 태크용 소형 안테나를 설계하고,다른 하나는 많은 물체가 고려된 실제 환경에서 동작하는 리더와 태크간의 통신에 적용하기 위한 3차원 태크 추적 알고리즘을 제안한다.

첫 번째,magneto-dielectric 매질을 사용하여 안테나의 크기를 최대한 줄였다.하지만 안테나의 크기가 작고 매질의 내부 손실 때문에 안테나의 이득이 -4.3 dBi로 낮은 값을 가진다.이득은 안테나의 크기를 유지시키면서 매질의 유전율과 투자율을 변화시겨 약 -2dBi로 향상시켰다.

두 번째,항만 물류 관리 분야에서의 RFID 시스템을 고려하였다.

컨테이너와 같은 물체들은 태크의 인식률을 떨어뜨리게 된다.

따라서 이러한 환경에서 성능에 영향을 끼치는 요소를 찾기 위해 태크의 위치를 추적하는 알고리즘을 제안하였다.이 알고리즘을 이용한 시뮬레이션 결과는 측정 결과와 일치하는 것을 보였으며, 물체가 있는 RFID 시스템의 분석을 기준의 방법에 비해 보다 쉽고 간단하게 해준다.

C C Ch h ha a ap p pt t te e er r r1 1 1. . . I I In n nt t tr r ro o od d du u uc c ct t ti i i o o on n n

1

11...111BBBaaaccckkkgggrrrooouuunnnddd

Although radio frequency identification(RFID)technology has been available for more than fifty years, it has only been recently developed ata high speed forseveralyears.Itis now the base for many applications such as automated logistics management (even global supply chain, with the support of satellite and globalpositioning system(GPS)),ubiquitous sensor network(USN),realtimelocating system,assetsmanagement,etc.

Itsapplication increaseseveryday,and RFID isthehotissuein manyplacesintheworld.

Let's review some key points in RFID system.The basic configurationofastand-aloneRFID system isshowninFig.1.1.

Fig.1.1 Basicconfigurationofastand-aloneRFID system

Readertransmits the power,clock,and data to tag by radio wave. The tag receives power and answers the reader by reflecting the wave (passive tag)ortransmitting a radio wave

back to the reader(active tag)[1].The data thattag sends to readeris the information aboutthe objectto which the tag is attached.On tag'sside,thechip willcontrolthecommunication process.Onreader'sside,acomputerwillmanageallinformation receivedbyreaders.

Activetagshavetheirownpowersupplierandoperatemostly in UHF bands which offers good balance between range and performance.The distancecan be as faras hundreds ofmeter.

Because of these advantages and rapid grow of active RFID system in near future,this thesis concentrates to active RFID system.

Fig.1.2showstheprocessesindesigninganRFID system.

Fig.1.2 DesignprocessesofanRFID system Antennadesignfortag Chipdesignfortag

Attachmentoftagtoobject

Reader-Tagcommunication

Antennadesignforreader Softwaredesign

Thechallengeswhichcouldbemetineachprocess:

a.Antennadesignfortag

- Omni-directionalradiation pattern (so thatthe tag can beeasilyidentifiedfrom anydirection)

- Highgain

- Smallsize(toreducetheprice,easytomount) - Wideband(forUHF bands860MHz-960MHz)

- Can beattachedtoany kindofobject(variouskindsof material)

- Matchingwithchipimpedance b.Chipdesignfortag

- Highsensitivity

- Matchingwithantennaimpedance c.Attachmentoftagtoobject

- Change of quality factors of the tag antenna, e.g.

radiationpattern,gain,etc.

d.Reader-Tagcommunication

- Recognize the tag (communication protocols, anti-collisionprotocols,errordetection,etc.)

- Qualityeffectedbythechangesinenvironment(changes in tag when is attached to the object, changes in surroundingenvironment,e.g.weather,obstacles,etc.) - Readermanagement(locationofreaders)

e.Antennadesignforreader - Highgain

- Omni-directional or directive pattern (depends on application)

- Handheld (dependsonapplication) f.Softwaredesign

- Highaccuracy - Highspeed

- Databasemanagement

1

11...222OOObbbjjjeeeccctttiiivvveee

My long-term objective toward Ph.D degree is developing a completed active RFID system including tag and reader subsystems,and then investigating as wellas enhancing the performanceofthesystem.Hence,theworkstepsare:

- how to design antenna fortag and meettherequirements aswellasbalancethetrade-offsamongantennaproperties.

- how the environmentaffects to quality ofcommunication betweenreaderandtag.

- how to design antenna forreader(often array antennas), andlocatethereadersaswellasmanagethedatareceived from readers.

- designacompletedRFID system

Therefore,in this Master thesis,Iconcentrate to firsttwo steps.Someproblemsandsolutionsin designing antennaforthe tag will be presented in Chapter 2. In Chapter 3, the communicationbetweentagandreaderismodeledincaseofone containeryard and simulated to see the effects ofmultipath to the received signal.Chapter4 willgive conclusions to thefirst twostepsandproposethenextwork.

C C Ch h ha a ap p pt t te e er r r2 2 2. . . D D De e es s si i i g g gn n no o of f fT T Ta a ag g gA A An n nt t te e en n nn n na a a

2

22...111BBBaaaccckkkgggrrrooouuunnndddaaannndddOOObbbjjjeeeccctttiiivvveee

222...111...111 OOObbbjjjeeeccctttiiivvveee

Asmentioned in Chapter1,designing theantenna fortag is really an interesting butdifficultmatterwith many requirements havetosatisfied,evenwhentheyareconflictedtoeachother.

First,frequency for the antenna is chosen at 433.92 MHz, because in the UHF bands,which offers good balance between rangeand performance,itoffersmany uniqueadvantagesasan RFID frequency,such as an effective frequency,and authorized forRFID system usein many countries;ability toco-existwith otherdevicesinthesystem[2].

Second,thediscretegoalsfortheantennahavetobeclear.

- The omni-directional pattern is the must-have characteristic.

- Impedance matching between antenna and chip is not serious.In case ofpassive tag,due to the rectifierlayer inside the chip,which is used to receive the powerfrom the radio wave to supply for its own activities, the impedanceofchip hasahigh capacitivereactance.So,the impedancematching betweenantennaandchipisaserious problem inpassivetag.However,incaseofactivetag,the roleofrectifierisnotimportantandcanbeignorebecause theactivetaghasapowersupplierforitself.

- Otherrequirementsforhigh gain,butwideband and small sizeisreally amatterbecausethesepropertiesofantenna is trade-off.We have to balance these parameters in a rangethatsatisfiestheactiveRFID system.

222...111...222 AAAnnnaaalllyyysssiiisss

The omni-directionalcharacteristic is rathereasy to achieve with using omni-directionalantenna types like monopole,dipole, patch,etc.

Regularly,consumers expect that the electronic devices is provided with impressive improvement in size reduction for simplicity andmobility,especially in caseofRFID tag in mobile RFID system orUbiquitous SensorNetwork (USN).Hence the smallsize is often paid attention in antenna design.And so, smallsizeisthemostimportantgoalinthedesign.

There are many kinds of small antenna such as planar inverted-F antenna(PIFA),chipantenna,patch antenna,andetc.

Forthoseelectrically smallantennas,especially in low frequency range,somekindsofproblem arearisensuchas:

decrease ofradiation resistance,in otherwords,decrease ofefficiency.

increase ofinputimpedance due to increasing reactance, andinputresistanceisoften very low,causing impedance mismatch problem.Thisproblem can besolvedby adding loss. In addition, bandwidth is limited by impedance mismatch.

increaseofeffectfrom surroundingenvironment.

theefficiency isreducedalsobecausepoweristrappedin alimitedspacewithhighdensity.

The fundamentallimits on antenna size have been studied since40swhen Wheeler[3]and Chu[4]presented amathematical relationship between antenna size and Q. Because this limit cannotbechanged,thesolutionsforthisproblem canbe:

sharing the resource with radiated part (such as use printed circuit board for ground plane in embedded antenna,etc.).

optimize the topology ofradiating elements,fully utilize thevolumeforantenna.

usingnew electromagneticmaterial

system solutions(suchassmartantenna,etc.)

Theremain requirementisthegain and bandwidth.Weneed tocontrolthetrade-offbetweenthem.

222...111...333 CCChhhoooiiiccceee

From the above analysis, it is suggested that we use magneto-dielectricmaterialin antenna design.Magneto-dielectric material is one kind of dielectric material whose value of permeabilitycanbevariedeasily.Itisdifferentfrom conventional dielectricin which thepermeability isunit.With thepresenceof permeability,the bandwidth and gain of the antenna can be adjusted. By controlling the ratio between permeability and permittivity,the gain-bandwidth product,one factorto evaluate thequalityofantenna,canbechangedtomeettherequirement.

In magneto-dielectric material,both _{ and} _{ are complex} numberdescribedas:

_ ′ ″  ′   _(2.1)

_ ′ ″ ′  ′ _(2.2) where _and′ aredielectriclosstangentandmagnetic losstangent,respectively.

The magneto-dielectric composite consists of some metallic components and/or ferrite material,so thatthe permeability of dielectric can be changed easily.Unfortunately,magnetic losses ofthe materialare rather high,due to the presence ofthose metalandferritecomponents.

In general,microstrip antennasarehalf-wavelength structures and areoperated atthefundamentalmode



_{ or}



_,with

theresonantfrequencygivenby[5]

 ≅ 

 

^_

 (2.3)

where 



^_{ iscalledminiaturizati}on factor,orrefractive index.

Mostmicrostrippatchantennadesignsuntilnow arebasedon the dielectric which is just changed the permittivity. If conventionaldielectric(_ _)isused,the_{ isrequiredatvery} high valuein orderto increasetherefractiveindex,so thatthe size of antenna is reduced. This makes the antenna design procedure simpler because only one parameter of dielectric coefficientsaffectstoantennaperformance.In anotherhand,this limitstheability ofeasily improving theperformanceofantenna,

and this causes some disadvantages such as narrow bandwidth and low efficiency with the high value of permittivity.Thus, magneto-dielectric material offers a little more number of parametersofdielectricinordertochangetheperformanceofthe antenna.

Incaseofmagneto-dielectricmaterialsubstrate,toachievethe samevalueof _(thesamesizeofantenna),_{ and} _{ can be} chosen at moderate values[6].Thus,the field confinement is minimized and the medium is farless capacitive.Moreover,the permeability value which is differentfrom unitin this dielectric alsoleadstosomeadvantagesasdescribedbelow.

Fig.2.1 Comparisonbetweentwokindsofdielectric.

Fig.2.1showsthecomparisonbetween ordinary dielectricand magneto-dielectricmaterial. _isintrinsicimpedanceofdielectric and_{ isintrinsici}mpedanceoffreespace,where

  _



^_{ (2.4)} So,iftheratiobetween_{ and}_ becomesto1,thematching betweentwointrinsicimpedancesisreached,orthecharacteristic impedanceofmagneto-dielectricmaterialmedium isclosetothat

of the surrounding medium,it allows for ease of impedance matching overawiderbandwidthandsuppressionofthesurface wave[7], and the efficiency of antenna increases, as the consequence.Theinteractionofenvironmentiseliminated.Hence, using magneto-dielectric material, many advantages can be achievedjustbyadjustingthepermeabilityandpermittivity.

Inadditiontousingofnew material,meanderlinetechniqueis also used to one more time reduce the size and utilize whole volumeoftheantenna.

2

22...222AAAnnnttteeennnnnnaaaDDDeeesssiiigggnnn

222...222...111 MMMiiinnniiiaaatttuuurrriiizzzaaatttiiiooonnn

Oneexampleofpatchantennaispresentedtoprovetheability of miniaturization from using magneto-dielectric material. In addition, its resonant frequency is 433.92 MHz and has omni-directionalradiation pattern.The antenna type is meander type,buttheusageofmagnetomaterialasdielectriccanbeused foranykindofantenna.

Fig.2.2 shows the structure ofantenna,using probe feeding method.

Fig.2.2 Structureofantenna

Theuppermetalplatecontainsameanderlinestructurewith 16 turns.The line width is 1 mm and the gap between two adjacent meandered sections is 0.5 mm.In the bottom metal plate, the ground size is also kept reduce to expect an omni-directional pattern. The permittivity and permeability is chosen at5.21– j0.012 and 2.39– j2.58 (one kind ofNi-Zn material).Thethicknessofthesubstrateis1.6mm.Thereturn loss ofthis initialmodelis shown in Fig.2.3 (circular-marked line).

Maintaining the antenna structure like in Fig. 2.2, the propertiesofmagneto-dielectricmaterialarechanged tooptimize the performance for the antenna.The aim of this parameter

16 turns

Ground

Top

Bottom

1.8

1 11

4 35

(Feeding point)

1.75

54 _{Unit :}

[mm]

0.5

Z Y

X

study is finding the optimized values of_{ and} _{ so thatthe} antenna resonates at433.92 MHz with a low return loss level. The results of return loss when varying the permittivity of magneto-dielectricisshowninFig.2.3.

Fig.2.3 Returnlossagainstpermittivitychange

Itcan be seen thatwhen dielectric constantincreases,the resonantfrequency shifted to low frequency area.At′ 

(rectangular-marked line),good resonantcharacteristic is earned with return loss ofmeander line antenna is -30 dB at433.92 MHz.

Second,in the permittivity component,only ″ is changed.

Value′ is fixed at1.71 and permeability is notchanged.The effectof″ changing appliesonly toreturn losslevelasshown inFig.2.4.

Fig.2.4 Returnlossagainstdielectrictangentlosschange

The resonantfrequency is almostsame.Itmeans thatthis loss property justaffects to the efficiency ofthe antenna.To havethebestreturnloss,0.004ischosenfor″ value.

Fig.2.5 and Fig.2.6 show the results of the permeability components of magneto-dielectric variation, ′ and ″ respectively, toreturnloss,when_   _.

Fig.2.5Returnlossagainstpermeabilitychange

Fig.2.6Returnlossagainstmagnetictangentlosschange

From Fig.2.5,when the permeability increases,the resonant frequency of antenna is lowered.This effect is well-known, similarwith the change ofpermittivity.A good performance at 433.92MHzisobservedinthecaseofrectangularline.

InFig.2.6,differentwiththechangeof″,″ participatesin changing resonantfrequency.Itis because ofmutualcoupling between adjacent sections, the magnetic tangent loss makes change to equivalentinductance ofthe meanderline,and so to resonantfrequency oftheantenna.Thevaluesof″ arechosen from database ofpopularmagneto-dielectric materialproperties.

These values are rather high. It is a disadvantage of magneto-dielectricmaterial.Thehighlossaffectstoefficiency,or gain,ofantennaasshowninFig.2.7.

Fig.2.7 Gainpatternofantennaat433.92MHz

Thegain limitation forsmallantenna hasbeen expressed by Harringtoninreferencenumber[8].



 ^  _(2.5) where k:wavenumber

a:radiusofsmallestsphereencompassingtheantenna In this case,the maximum attainable gain of this size of antenna is 0.55 dBi.From Fig.2.7,the maximum gain ofthe antenna is -4.3 dBi.However,compared with otherdesigns in the same resonantfrequency in reference number[9],the gain reductionisnotmuchasminiaturizationofantennasize.

The optimized parameters of magneto-dielectric substrate is achievedwith thevalueofpermittivity at_   _,and the value of permeability at _   _{. The small} antennas techniques are generally used dielectric with high permittivity. However, proposed meander antenna has low permittivity constant of 1.71, but the results show good performancewhilethesizereductionratioisstillhigh.

This antenna design has omni-directionalcharacteristic.As seen from Fig. 2.7, it is omni-directional in XY-plane. In ZX-plane,becauseoftheexistenceoftheground,thereisanull point.However,thehalfpowerbeamwidthisalsoverylarge.

222...222...222 GGGaaaiiinnn---BBBaaannndddwwwiiidddttthhhtttrrraaadddeee---oooffffffcccooonnntttrrrooolll

Gain-bandwidth product(GBP)isoneoffactorsusually used todescribetherelativequalityofanantenna[7].Itisdefinedas aproductofgainandbandwidthoftheantenna.

GBP =Gain^× Bandwidth (2.6)

wheregainisdimensionlessandunitofbandwidthisHz.Itis noticed thatthe gain calculated in dB (ordBi,dBd)cannotbe used in thisequation,becausethesign ofgain in thedB scale, which can be both positive and negative,may cause a wrong comparison.

Itiswell-known thatgain and bandwidth istrade-off.Some designs concentrate on improving the bandwidth,so the gain decreases as a consequence.Otherdesigns aim to increase the gain ofantenna and pay a price fornarrow bandwidth.Hence, any design with thegoalofenhancing theantennaquality must haveactualimprovementofGBP.

From referencenumber[10],thezero-orderbandwidth foran antenna over a magneto-dielectric material substrate can be approximatedby:



_{≈ }



^



^{  }



^_







^__



(2.7) where t:thicknessofthesubstrate

_:wavelengthatresonantfrequency

It is easily seen that when the permittivity-permeability productiskept,i.e.thesizeofantennaisunchangedbecauseof refraction index _,thebandwidth ofantennacan bebroaderby increasingtheratiobetweenpermeabilityandpermittivity.

Itisquitean interesting matter.Thesizeofantenna isstill small, and the quality can increase just by changing the parametersofsubstrate.Therefore,in thefollowing,theeffectof

__{ to GBP is anal}yzed because it affects not only to

bandwidthbutalsothegainofantenna.Theproduct__{ iskept} constantat4.087.The values of_{ and} _ are changed.Each pairof(_ _)value forms one material.There are 7 different cases are calculated.The resonant frequency at each case is checkedthatthey arenearly thesame.VarianceofGBP against

__{ isshown in Fig.2.}8,and detailed valuesarepresented in TableI.

Fig.2.8GBP againstpermeability-permittivityratio TABLE I

Gain-BandwidthProductAnalysis 0

10 20 30

0 1 2 3 4 5

/

G B P

µµµµ εεεε

MMMaaattteeerrriiiaaalll __ ^GGGa_(((dddB^aai_BB)ⁱⁱⁿⁿⁿ_{)) GGGaaaiiinnn (((MMMH}^BBBWW_H^W_{Hzzz))) GGGBBBPPP}

① 444...000888777 -2.70 0.537 46 222444...777000222

② 222...333888222 -3.45 0.452 51 222333...000555222

③ 111...333999888 -4.34 0.368 58 222111...333555111

④ 111...000888999 -4.71 0.338 59 111999...999444222

⑤ 000...777111555 -5.39 0.289 60 111777...333444444

⑥ 000...444222000 -6.10 0.245 58 111444...222111000

⑦ 000...222444555 -6.52 0.223 45 111000...000333555

From Fig.2.8,itisobviously seenthatGBP alwaysincreases when__{ i}ncreases.Thelimitedrangeforbothvariationsof_ and_{ i}sfrom 1to4.087.Theslopedegreeofthegraphishigh when __{ isi}n therangefrom 0to1.5.Afterthat,thegraph hassaturationtrend.

Thegain ofantennaalwaysincreases,butthebandwidth has a peak value.When __{ i}saround 1,thebandwidth isnearly unchanged,while the gain stillincreases.It is because when

__{ cl}osesto 1,theimpedancecontrastbetween dielectricand surrounding free space is much reduced, so the efficiency increases.Althoughbandwidthdoesnotincreasecontinuouslylike gain, the quality of antenna is still improved because GBP always increases.That is the advantage of magneto-dielectric material.

2

22...333SSSuuummmmmmaaarrryyy

Thischapterconsideraboutthedesign ofantenna foractive RFID tag.The chapterreviews allthe challenges and possible solutionsforthem.Onedesign ofantenna isshown to describe indetailedaboutthedesignprocesswithselectedtechniques.

The usage of magneto-dielectric material is proposed to satisfy almost requirements.The antenna resonates at 433.92 MHzwithreturnloss,bandwidtharerespectively-38dB,and58 MHz, as well as omni-directional pattern while the overall dimension is just ×  × _{. This size is}

achieved by choosing the optimized values of 4 substrate’s parameters,i.e.′ ″ ′ ″.The antenna structure is meander linetype,butthismethod can beapplied forany otherantenna structures.

The maximum gain of the proposed antenna is -4.3 dBi, ratherlow.Thisismainly becauseofthehigh concentration of electricand/ormagneticfieldswithin asmallvolumeofantenna structure due to smallsize,in addition to a lossy materialas magneto-dielectricmaterial.

Moreover,magneto-dielectric materialhas anotheradvantage, i.e.thequalityofantennacanbeadjustedbycontrollingtheratio between permeability andpermittivity (__).Thebesttrade-off between gain and bandwidth is obtained when this ratio is a little greaterthan 1.Ifthis ratio increases,the antenna quality increases,butthepriceisdecreaseofbandwidth.

Therefore,wherethesizeofantennaismuch moreimportant than otherproperties,magneto-dielectricissuggested to usefor miniaturization.

C

C Ch h ha a ap p pt t te e er r r3 3 3. . . T T Ta a ag g gT T Tr r ra a ac c ck k ki i i n n ng g gS S Sy y ys s st t te e em m m M M Mo o od d de e el l l i i i n n ng g g i i i n n n3 3 3- - -d d di i i m m me e en n ns s si i i o o on n n

3

33...111BBBaaaccckkkgggrrrooouuunnndddaaannndddooobbbjjjeeeccctttiiivvveee

A.Theimportantroleofmodelingandsimulation

Thecomplexityofmoderncommunicationsystemsisamotive powerforthepopularuseofsimulation.Thiscomplexity results bothfrom thearchitectureofmoderncommunicationsystemsand from theenvironmentsinwhichthesesystemsaredeployed.

An important motivation for the use of simulation is that simulation is a valuable toolfor gaining insight into system behavior. A properly developed simulation is much like a laboratory implementation ofasystem.Measurementscan easily bemadeatvariouspointsinthesystem understudy.Parametric studies are easily conducted,the effects ofparameters'changes on system performance can be obtained withoutdifficulty.Itis also easily display the results graphically in many forms from waveform in time-domain to spectrum,histograms,etc.Most importantly,“whatif”studiescan beperformed using simulation moreeasilyandeconomicallythanwithactualsystem hardware.

In case ofactive RFID system,when the price ofexisting systems in theworld isvery high,as wellas RFID system is affected much from surrounding environment, modeling and simulation is a proper choice for experiment and evaluation beforemakingarealsystem.

B.Objective

RFID is also a wireless communication system,so the block diagram ofthemodelforRFID system islikebelow:

Fig.3.1Blockdiagram ofwirelesscommunicationsystem

This block diagram consists only mostbasic and important partsofthesystem,sothatwecanhaveanoverview aboutthe system.Variouskindsofwirelesssystem arealsohavethesame structure,butthedifferentpartischannelmodel.Every system hasitsown characteristicofthecommunication process.Thatis why the transmitting partand receiving partcan be the same, but the performance of the system will be different if the communication is conducted in different environment.Channel modeling isthemostimportantpartofmodeling wirelesssystem ingeneral,andRFID system inparticular.

Therefore,theobjectiveofthischapterisbuildingonechannel modelforcommunication between tag and readerin a complex environmentwithmany obstructions.In thismodel,thestructure ofan containeryard ispredefined,with theinputistransmitted signal, and position and size of obstructions. An effective algorithm is proposed to find allthe possible reflected waves insidetheenvironment.Attheoutput,thereceived signalisthe summationofmanyversionoftransmittedsignalafterreflections from obstacles,thathavejustfoundbytheabovealgorithm.The simulation resultsarecompared with themeasurementresultsin areducedscalemodel.

3

33...222MMMooodddeeellliiinnnggg

In this model,containeryard consists ofmany containers is considered.In thiscase,thestructureoftheyard can beeasily known. Some information like the number of container, the positions ofcontainers,located position ofreaderand tags,etc.

areknown.Theproblem istheanswerfortwoquestions:

-How canthesignalfrom readerarrivetothetag?

-Whatistheeffectofmanyobstacleslikecontainers?

Inthismodel,thetwoquestionswillbesolved.Thecontainer faces are assumed as metalreflection planes.The radio waves from thereaderaretransmitted to every direction in thespace.

Thiswavescanarriveattag,orarriveatcontainer,ground,etc.

When they arrive at other obstacles,they are reflected.This reflectioncausethechangeofsignalindirection,signalstrength,

and phase.Some ofthis kind ofsignalwillarrive atthe tag also.Therefore,receivedsignalatthetagisthesummationofall directwaveandreflectedwaves.

Fig.3.2 Directwaveandreflectedwaves

So,theconsiderationofreceivedsignalconsistsoftwotasks:

- Find allthe waves thatcan be arrived atthe receiverof thetag.

-Summationofallthosewaves.

A.Algorithm tofindreflectedwaves

Because the circumstance is known, it is called the site-specific model,one suitable method can be applied to this caseisray-tracing method.Originally,thismethodisoften used inopticalapplication.However,inradiopropagationbetweentwo points,thismethodisalsoapplicableandveryuseful.

Fig.3.3 Ray-tracingmethod[13]

As shown in Fig.3.3,the transmitteris assumed to radiate

"rays"atevery direction.With each ray,itspropagation path is observed (followed, or traced) as it bounced around the environment,untilitreachestheobservation pointorgetoutof theanalysed environment.Aswecan see,thepath A iscalled thedirectwave,and thethreepathsB,C,D can arriveatthe imageplaneasweexpected,exceptthepath E cannotarriveat theobservation point.Morespecifically,itiscalled forward ray tracing;thatis we follow the waves from theirorigin ofradio sourceandintotheenvironment,tracing theirpath in aforward direction,justasthewaveswouldhavetravelled.

The principle of this method is very simple for easy to understand,and effective,especially for reflection phenomenon.

However,ithasan drawback ofcomputationalexpense,and we cannottracethewaveatevery direction.Thespecificalgorithm fortracinginthemosteffectivewaymustbebuiltdependingon eachapplication.

Hence,returntoourcase,oneeffectivealgorithm isneededto developtofind thewavesarrived atthetag.In here,Isuppose threeideastoreducethecalculationcomplication.

1.Thereflection happensateverywherehasaplane.So,we consideronlyatavailablereflectedplanes.

2.Likethelight,a"wavebeam"hitstoaplanewillreflectas abeam (Fig.3.4).So,weconsidereverybeam ateachtime.

3.One "wave beam" is bounded by faces.These faces are formedfrom severalrayswhichistherayscomeatthevertices.

Thismeanswecanrepresentallraysreflectedatoneplanejust byseveralrays.Thisisthekeypointofmyproposedalgorithm.

Fig.3.4 Reflectionataplane

In thisalgorithm,weconsidertheperfectreflectedplanes.So, thetechniquetospecifythereflectedraysisbasedontheimage pointtechnique,asshowninFig.3.5.

Fig.3.5 Usingimagepointtodeterminethereflectedpoint We also note thatthere is reflection from the ground.To solve this,we can simply consider as there are another radio source at the position of image point of reader through the ground.

The following is an example to visually presentthe above algorithm.

Fig.3.6 Wavebeams

InFig.3.6,thesourcepointisatA.Therearetwoobstacles.

The red beam is the coming wave beam to the rightobstacle.

This beam is represented by 4 rays Aa,Ab,Ac,and Ad.The reflected wave beam (dark red color)is found by using image pointA'ofA through the plane.This reflected wave beam is represented by 4 rays:ae,be,df,and cf.This reflected beam continues reflecting at the ground (green color,found by the image pointA" ofA' through ground)and arrive atthe left obstacle.

Fig.3.7 Extracttheray

The meaning ofthis processisidentifying the space volume thatthe wave from A can reach.Forexample,in Fig.3.7,if there is a pointB inside the green beam,there is a ray come from A toB.B isinsidegreenbeam,so,itisdefinedbyA".

The intersection ofline A"B and the ground willdetermine thereflectedpointB"in theground.Next,B"isinsidedark-red beam,so,the intersection ofA'B" willdetermine the reflected pointB'attheplane.Finally,wefoundthewavegofrom A to B',reflected atthe face (abcd)to B",then reflected one more timeattheground toB.Thisexplainshow wecan extractthe rayfrom thewavebeam thatwealreadyfoundbefore.Moreover, with exactposition ofA,B',B"and B,we can calculate the direction   oftheraysothatitcanbelookedupinthegain pattern ofantennaforthegain atthatdirection,andsuppliedto theequationsasfollowing.

B.Summationofallwavesatthereceiver

When radio wavepropagatesfrom onepointtoanotherpoint inthefreespace,itsamplitudewillbedegradedaccordingtothe distance.Italsotakesaperiod oftimeto go from sourcepoint to destination point,we callthat time the delay time.If the transmitted signal is , then the received signal will be calculatedfrom equation3.1.

  __  _



_^{    (3.1)}

where:

-_:directwave

-_ :thedegradationofamplitudeofdirectwave -_ :thedelaytimeofthedirectwave(s)

-_ :thedegradationofamplitudeofeachreflectedwave -_ :thedelaytimeoftheeachreflectedwave(s) - :numberofreflectionpaths

Thedegradation ofamplitudeandthedelay timeiscalculated from equation3.2and3.3.

_



^





^{   (3.2)}

_ 

_

(3.3) where:

-_:distancefrom sourcetoreceiver(m)

-__ _:gainoftheraytransmittedfrom sourceantenna at_ _ direction(dimensionless)

-__ _:gainoftherayreceivedatreceivingantenna at_ _ direction(dimensionless)

- :lightvelocity(m/s) - :wavelength(m)

From thereceivedsignal,thereceivedpowercanbecalculated from equation3.4.

_ 



_^{}_^{ (3.4)}

where _{isaperiodoftime.}

3

33...333SSSiiimmmuuulllaaatttiiiooonnn

Thealgorithm iscodedby Matlab tosimulateforverification.

Matlab is chosen because ithas usefulbuilt-in functions and routines especially used in communication field. Besides, it providesawiderangeandflexibilityfordisplayin3-dimension.

Thesimulation program willbeapplied toan simpleexample system asshowninFig.3.8.

Fig.3.8Anexampleofcontaineryard

Inthismodel,inputdataincludes:

positionofreaderandradiationpatternofreaderantenna positionoftagandradiationpatternoftagantenna

position ofeightpointsdefining theposition and sizeofeach containers.In thisexample,therearethree48-feetcontainersat potition1and2,three40-feetcontainersatposition3and4,and one20-feetcontaineratposition5towhichthetagisattached.

First,thesimulation program willberun to find allpossible propagation paths between reader and tag.Second,the signal arrivedattag willbesummedandcalculatethereceivedpower.

The received power is calculated so that we can compare simulationresultswithmeasurementresults.

A.Findpossiblepropagationpaths

Allbeam andreflectedbeam ateachplane(ofcontainers)are shown in Fig.3.7 (a-d).Actually,the simulation program will find allsimultaneously.However,in ordertodisplay foreasy to understand,thebeam ateach planeisdisplay separately,except for containers atposition 1 and 2 because the reflected beam from containeratposition2goestoandreflectsatcontainersin position1.

(a)Reflectedbeamsatcontainersatpostion1and2

(b)Reflectedbeamsatcontainersatpostion3

(c)Reflectedbeamsatcontainersatpostion4

(d)Allpropagationpaths

Fig.3.7 Allbeam andextractthepropagationpaths

Firstly,we check the light-of-sight path and the reflected path directly from the ground to thetag.Thereare both these two paths.Next,from Fig.3.9(a),and Fig.3.9(b)we can see thattheradiowavecannotreach atthetag afterreflected from these containers. Fig. 3.9(c) shows the reflected beam at containers atposition 4 can arriveatthe tag.From thisbeam, we extractone more propagation path.So,finally we have 3 pathsasshowninFig.3.9(d)

B.Comparewithmeasurementresults

We use received power to compare simulation results with measurementresultsforverifying theaccuracy ofthealgorithm, because we do not have enough equipment to show another parameterssuchasthesignal,orthebiterrorrate(BER)ofthe communicationprocess.

Besides,we notice thatthe actualsize ofcontaineryard is very big, hundreds of meters. In this example, the size is assumed of150 m x 150 m.We have to reduce this size 30 times for measurement in anechoic chamber. Hence, the frequency is also needed to proportionally increase from 433.92 MHz to 13 GHz.Moreover,the transmitsignalis analog sine function.So,in the simulation program,these parameters must befollowed.ThesettingsformeasurementisshowninFig.3.10.

Fig.3.10 Configurationofmeasurement

Signalgeneratorcontrolsthetransmittedpower.Theobstacles areatpositionsstandsforcontainers(thesizesarealsoreduced 30times).Receivedpowerismonitoredbymicrowavereceiver.

The gain patterns oftwo antennas are measured,and saved as textfile forthe program looking up in calculation process.

Thegain patternsofthetwo antennasin H-planeand E-plane at13GHzareshown in Fig.3.11forreference.Oneantennahas maximum gain of13dBiused as readerantenna and the other hasmaximum gainof5dBiusedastagantenna.

(a)Readerantenna (b)Tagantenna Fig.3.11 Gainpatternsoftwoantennas

Inmeasurement,thereceivedpowerisachievedby:

_ __ where:_ -actualreceivedpower

_{ -receivedpowerdisplayedinmi}crowavereceiver

_{ -totalcableloss}

In simulation, the calculation process is expressed in the following.

Weassumethatthetransmittedsignalis:

 _

Thetransmittedpowerwilldependson_. Withlight-of-sightpath,A-D:

_



^





^{ ′ ′   }

__



^{  }



^_  _ where _



^





^{ ′ ′}

__ _ :gainofreaderantenna

_′ ′ :gainoftagantenna

_ 

_

WiththepathA-B:

_



^





^{ }  

_



__  _

ThereisnoantennaatB,sotheantennagainatB is1.

WiththepathA-B-D:

_



^





^{′ ′  }

___  _ _ 

There is the minus sign because the reflect coefficient of perfectreflectedplaneis-1.Itmeansthephasedisreversed.

WiththepathA-C:

_



^





^{ }  

_



__  _ WiththepathA-C-D:

_



^





^{′ ′  }

___  _ _ 

Thereceivedsignalisthesummationofthreesignals:

  _ __

The received power is calculated by equation (3.4) with

  .This value is big enough to have the exact averagevalue.

The calculation results for propagation paths are shown in Table3.1.

Table3.1 Calculatedparameters

Now, we go to compare the simulation results and measurementresultstoverifythecorrectnessofthealgorithm.

We note that,as shown in the resultoffinding propagation paths,thecontainersatposition 1,2and 3donotparticipateto affect the received signalat the tag.Therefore,if they are removed,the received signalis notchanged.We willbase on this phenomenon to compare the received power with and withoutcontainers atposition 1,2 and 3.The simulation and measurementresultsareshowninFig.3.12.

Fig3.12 Simulationandmeasurementresultswithall obstacleandonlyobstacleatposition4

As we can see,the simulation result(rectangle-marked line) hasthesametrendwiththemeasurementresultswhenchanging the transmitted power.The differentis smallbecause ofsome reasons:

- Actually in simulation,thetransmitted signalisnotanalog asinmeasurement.Wehavetodigitalizethetransmittedsignal.

- In addition,thesetting in measurementsuch asposition of antennas and containers,direction oftwo antennas,surrounding environment,etc.maybehasalittledifferentfrom simulation.

The measurement results in two cases (triangle- and circle-marked lines) are also nearly the same.A very little difference is probably caused by the diffraction and scattering which are ignored in the simulation because theireffectis not much.

Thatisthecomparisononreceivedsignal.Wecanalsocheck the individualpaths.In here,allobstacles are removed,then thereremainsonly light-of-sightpath and directreflection from ground.We can putan absorberatthe reflection pointin the ground to remove the reflection path,only light-of-sightpath remains.Moreover,keeping thedistancebetween readerantenna and tag antenna, the relative direction of the two antenna changes.The measurementand simulation results are shown in Fig.3.13.

Fig.3.13 Comparisonofindividualpaths

In Fig. 3.13, ^ means the two antennas are faced at maximum gain direction.Positive degree values mean the tag antennamovestotheright,andnegativedegreevaluesmeanthe tag antenna moves to the left. The movement causes the differentdirection ofpropagation paths,andbecausegain pattern ofantennaisnotisotropic,sothegain in changed.Wecan see the degradation of received power when the gain of reader antenna changes.Mostimportantthing is the simulation results and measurementresults one more time have good agreement.

Thedifferencebetweenthetworesultsarenearlyunchangedand small.

From those comparison, we can say that the proposed algorithm iscorrect.Therefore,using thischannelmodel,wecan applytosimulationwholeperformanceofRFID system.

3

33...444SSSuuummmmmmaaarrryyy

In this chapter, an RFID system in container yard managementisconsidered.Theappearanceofcontainerscausesa complex effectto the identification performance ofthe tag.An effectivealgorithm isproposedfortracking positionofthetag in thisenvironmentin orderto find thefactorsthataffectsto the performance.This algorithm is based on ray tracing method to find allthe communication paths between readerand tag.The simulation resultsusing thisalgorithm showsa good agreement withmeasurementresults,andthisalgorithm makestheanalysis of the RFID system with obstacles much easier and simpler comparedwithconventionalmethod.

C C Ch h ha a ap p pt t te e er r r4 4 4. . . C C Co o on n nc c cl l l u u us s si i i o o on n n

4

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In thisthesis,solutionsfortwo problemsin design ofactive RFID communicationsystem ispresented.

First, design of antenna for active tag requires many propertieslikeomni-directionalradiation pattern,high gain,small size,and can beattached to any kind ofobject.Someofthese properties are trade-offcauses a really matterin balancing the particular requirements. In this thesis, one solution of using magneto-dielectric material is proposed to miniaturize size of antenna.The process ofusing this kind ofmaterialin antenna design is described in detailed. The final designed antenna resonates at 433.92 MHz with return loss, bandwidth are respectively -38 dB,and 58 MHz,as wellas omni-directional pattern while the overalldimension is just  ×  ×

× _.Although thegain oftheantenna isratherlow due to the high ratio ofminiaturization,magneto-dielectric material hasability to controlthetrade-offbetween gain and bandwidth while keeps antenna size and resonant frequency, just by adjusting its dielectric parameters.Magneto-dielectric is highly recommendedforverysmallsizerequirement.

Second, an analytical model and a simulation model is proposed forconsidering communication process between reader and tag ofan active RFID system in application ofcontainer

yard management.Analyticalmodelconcentrates to dealwith communicationchannel.Angeographicalalgorithm isproposedto determine the propagation paths between reader and tag, including thereflectionfrom allobstacles.Thealgorithm ismore effective than the ordinary method with the complexity in calculation is reduced very much.The 3-dimension co-ordinate and radiation pattern ofantenna are also included.This is the new ideawhen otherstudiespay alittleorsimpleconsideration on antenna radiation pattern. Then this analytical model is applied to one example of stored yard of containers. The simulation modelshows the ability to estimate the performance ofcommunicationtoretrievemanypropertiesofthesystem.

4

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On the case ofusing magneto-dielectric material,due to the difficultiesand thehigh costin making thematerial,thisdesign temporarilystopsatanideadesign.

OnthecaseofcommunicationmodelingforRFID system,this is a very interesting issue,and needs to develop more.In this thesis,thisproblem isjustsolvedinchannelmodeling only.Itis requiredtoanalysewholethesystem andfindtheeffectofother factors to the identification performance ofRFID system.Itis also required some suitable measurementresults to verify the conclusionsfrom simulation.

Moreover,thisthesisjustsolvestwooffourproblemsbefore building thecompleted realactiveRFID system.Nextstep,two remaining problems,i.e.designofreaderantennaandbuilding of thereaderwillbeconductedtoform anfullyRFID system.

R

R Re e ef f fe e er r re e en n nc c ce e es s s

[1] Klaus Finkenzeller,RFID handbook - Fundamentals and Applications in Contactless SmartCards and identification, Secondedition,2003.

[2] FraserJennings,"ActiveRFID,"KEES2004RFID workshop [3] H.A Wheeler,“FundamentalLimitationsofSmallAntennas,”

Proceedings of the IRE, vol. 35, December 1947, pp.

1479-1484.

[4] L. J. Chu, “Physical Limitation on Omni-Directional Antennas,”JournalofApplied Physics,vol.19,December 1948,pp.1163-1175.

[5]Kin-LuWong,CompactandBroadbandMicrostripAntennas, JohnWiley& SonsInc.,2002.

[6]Hossein Mosallaei,and KamalSarabandi,“Magneto-dielectric materials in Electromagnetics: Concept and Applications,” IEEE TransactionsonAntennaandPropagation,Vol.52,No.

6,pp.1558-1567,June2004.

[7] J.T. Aberle, “A Figure-of-Merit for Evaluating the Gain-Bandwidth Product of Microstrip Patch Antennas,” IEEE Africon Conference Digest (Invited Paper), pp.

1001-1004,September1999.

[8]R.F.Harrington,“EffectofAntennaSizeonGain,Bandwidth, and Efficiency”,JournalofResearch ofthe NationalBureau ofStandards-D,RadioPropagation,vol.64D,no.1,pp.1-12, January-February1960.

[9] Kent Smith,“Antennas for low power applications”,RFM applicationnotes.

[10]R.Hansen,andM.Burke,“Antennaswithmagneto-dielectric materials,”MicrowaveOpticalTechnicalLetter,vol.26,no.2, pp.75-78,July2000.

[11]W.H.Tranter,K.S.Shanmugan,T.S.Rappaport,K.L.Kosbar, Principles of Communication Systems Simulation with WirelessApplications,PrenticeHall,2003.

[12] Henry L.Bertoni,Radio Propagation for Modern Wireless Systems,PrenticeHall,2000.

[13] Andrew S. Glassner, An Introduction to Ray Tracing, AcademicPress,1991.

P P Pu u ub b bl l l i i i c c ca a at t ti i i o o on n ns s sa a an n nd d dC C Co o on n nf f fe e er r re e en n nc c ce e es s s

1.Kyeong-Sik Min and Viet-Hong Tran,"A Study on Meander Monopole Antenna Applying to 433 MHz Active RFID Tag", 2005년도 전기학술대회논문집,pp.381-386,2005-06-23~25

2.Kyeong-SikMinandViet-HongTran,"SimpleModelingofan ActiveRFID System",2005년도 추계 마이크로파 및 전파전파 학 술대회,pp.359-362,2005-09-24

3.VietHong Tran,Chul-Keun Park,and Kyeong-Sik Min,"A Design of a Meander Antenna using Magneto-dielectric Material for 433.92 MHz band",2005년도 종합학술발표회, 2005-11-05

4.Kyeong-Sik Min,Jin-Woo Kim,Chul-Keun Park,Tran Viet Hong,"A Study ofCapacity Change Antenna forRFID Tag Depending on Ground Plane", Asia-Pacific Microwave Conference(APMC)2005,2005-12-04~07

5.Kyeong-Sik Min,Tran VietHong,Duk-WooKim,"A Design ofa MeanderLineAntenna using Magneto-Dielectric Material forRFID System",Asia-PacificMicrowaveConference(APMC) 2005,2005-12-04~07

A A Ac c ck k kn n no o ow w wl l l e e ed d dg g gm m me e en n nt t ts s s

Firstly,Iwould liketosend specialthanksand bestregards to ProfessorKyeong-Sik Min,my supervisor,forhis advisory, enthusiasm,and forhissupportduring my studying timeatthe Korea Maritime University.Iam also gratefulto professors in thedefencecommitteefortheirpatientreviewing thethesisand givinghelpfulsuggestionsandcomments.

Ialso thank allofmy Korean friends,who help meboth in life with Korean language,Korean culture,and in study with valuablediscussions,andmyVietnameseteachers,colleaguesand friendsfortheirsharingandfriendship.

Finally,warmly thanks to my parents,my wife,and my brotherfortheircaring,loving,encouragingandunderstanding.

ThisresearchwassupportedbytheProgram fortheTraining ofGraduateStudentRegionalInnovationwhichwasconductedby theMinistryofCommerce,IndustryandEnergyoftheKorean.

Busan,July2006 TranVietHong