Propagation Modelling for Indoor Wireless

8/13/2019 Propagation Modelling for Indoor Wireless

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Propagation modelling forindoor wirelesscornrnun cat onby W.K. Tam and V.N. Tran

It is important to characterise the indoor radio propagation channel to ensuresatisfactory performance of a wireless communication system. Sitemeasurements can be costly; propagation models have been developed as asuitable low-cost alternative. The existing models can be classified into twomajor classes: statistical models and site-specific propagation models. Statisticalmodels rely on measurement data; site-specific propagation models are based onelectromagnetic-wave propagation theory. The ray-tracing technique is veryuseful in site-specific propagation modelling. This paper gives an overview ofindoor propagation modelling and concentrates on a discussion of the ray-tracing modelling technique because of its practical appeal and its applicabilityto any environment.

IntroductionTh e explosion in wireless communications ha s resulted innew technologies and new applications for the personaluse of radio frequencies;personal communication systems(PCS) are now be ing developed worldwide. An importantconsideration for the successful implementation of a PCSis indoor wireless communication. This covers a widevariety of situations ranging from communication withindividuals walking in residential or office buildings,hospitals, factories, etc. to fixed stations sending controlme ssa ges to robots in motion in assembly lines in a factoryenvironment.The indoor environment isprone to interference. Owingto reflection, refraction and scatte ring of radio waves bystructures inside a building, the transmitted signal mostoften reaches th e receiver by more than o ne path, resultingin a phenomenon known as multipath fading. Multipathcauses deep fading and pulse spreading of the signal andhen ce intersymbol inte rferen ce can be caused in a digitalradio system.

Therefore, there h as been a special interest in developing apropagation model to predict the propagationcharacteristics of the indoor environment. Once apropagation model ha s been verified, an environment canbe quickly entered into such a model to providepropagation characteristics for initial evaluation. Itremains to carry out quick measurements at positionswhere the signal is poor. This approach is much cheaperthan an exhaustive measurement programme and thusinstallation costs are dramatically re duced .Many propagation models have been developed tocharacterise indoor radio propagation. They can beclassified into two major classes: statistical models and site-specific propagation models. The general statisticalimpulse-response modelling of the multipath fadingchannel was first suggested by Turin.' It has beensubsequently used in the measurement, modelling, andsimulation of the mobile radio channel by investigatorsfollowing Turin's line of workJ4 and by otherresearchers.'" More recently, the statistical impulse-response approach ha s been used directly or indirectly in

Although multipath interference seriously degrades theperformance of commu nication svstems. little can be done

indoor radio propagation channel modelling.'-" Keenanand Motley" attempted to formulate a statistical loss-to eliminate it. H owever, if we characterise the multipathmedium w ell, the siting of transm itters can be selected toachieve good propagation performance and hence toachieve better connectivity. In the extreme, if serviceproviders had to characterise the propagation medium bytaking radio propagation measureme nts of every buildingin which they deployed their syst em, the installation c ostwould be very high due to the labour costs involved.

distance model to predict radio coverage based on a fewbuilding param eters. Some oth er statistical loss-distancemodels'' '' have been developed recently with differentformulas and statistical data, In contrast, site-specificpropagation models are based on the use ofelectromagnetic wave propagation theory to characteriseindoor radio Prop agation. Recent re ports of the applicationof the analytical ray-tracing technique to site-specific

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indoor radio propagationmodelling have appeared in anumber of papers.'62' Thistechnique has beenproposed to predict path loss,the timeinvariant impulseresponse , and the RMSdelayspread. It promises toprovide fast and accurateprediction of indoor radiocoverage and channelimpulse respon se. Generally,sitespecific propagationmodelling is preferred inmany practical situations.

wall

wall

Fig. Multipath propagation2 Indoor electromagnetic wave propagationIndoor radio channels do not suffer from theenvironm ental effects of snow , rain, hail, cloud s ortemperature inversion as do outdoor radio channels butbecau se of the variation of building size, shape , struc ture,layout of rooms and , mo st importantly, the type ofconstruction materials, electromagnetic-wave propagationinside a building is a more complex multipath structurethan that of terrestrial mobile radio channels. For example,a factory building is quite different to an office buildingboth in its structure and in the materials used. Thevariation of type of materials used in internal partitions,out side walls, ceilings and floors, as we l as the size andpercen tage of windows, age of building , people density andactivity are also factors which complicate indoorelectromagnetic-wave propagation.Path loss

The sqatial distribution of power at a distance d from atransmitter is, in general, a decr easin g function of d. Thisfunction is represented by a distan ce power law of the formP= l d . For free space, m sequal to 2 and it is said that thepower gain follows an inverse square law. In an enclosedenvironment, however, this isnot true anym ore. Saleh andValenzuela' an d Bultitude" show ed that when thetran smit ter and receiver were placed in the sam e hallway,in sight of each o the r, the po wer decayed with a value of mrangin g of 1.5 to 1.8; when the receiver was located withina room off the hallway,m anged from 3 to 4.

The path loss also varies with frequency. Owen andPun dey' made measurem ents inside office building at900 MHz and 1650 MHz. The measurement resultsindicate th at loss through floors is greater a t the higherfrequency. It is found that at wavelengths in the m illimetrerange the radio wave cannot penetrate most commonbuilding materials such a s brick and concrete block andthat signal attenuation occurs more rapidly with distance.Therefore the millimetre waveband seems to be a goodchoice for providing broadband se rvices n a high-capacityfrequency-reuse environment.AIe~and e?', '~ as given the valu es of m according to thebuilding materials used in the environment. Th e degr ee 01signal attenuation depends on the type of materials the

signal encounters. Conse-quently, the signal decay inan indoor environment canbe characterised by theconstruction materials.Fading PropertiesIn a typical indoor radiosystem, a f ixed b ase s ta t ionantenna ins ta l led in anelevated posi t ion commu-nicates with a number ofportable radios or f ixedreceiving terminals ins ide abuilding. Owing to thereflection, refraction andscat ter ing of radio waves by s tru ctures ins ide abuilding, the transmit ted s ignal most of ten reaches areceiver by more than one path, resul t ing in a

phenom enon known as multipa th fading, as shown inFig. 1.Th e s ignal compon ents arr iving from the indirec tpaths and the direc t pa th ( if it exis ts) combine andproduce a d is tor ted vers ion of the transm it ted s ignal . Innarrow-band transmission, the mult ipa th mediumcauses f luc tuat ion in the envelope and phase of thereceived s ignal . In wide-band pulse t ransmission, th eeffect is to produce a s er ies of de layed and a t tenuatedpulses (echoes) for each transmit ted pulse . Fig. 2 is as imula ted impulse response for a labora tory toillustrate the mu ltipath fading effect on wide-band pu lsetransmission.In the case of continuous-wave signal transmission, ithas been shown that th e statistics of the received signalenvelope are described by a Rayleigh distribution if nodominant signal path (i.e. a line-of-sight path or strongreflected path) exists between the receiver andtran smitt er. If a dom inant path do es exist the statistics ofthe sign al envelope are Rician.In digital pulse transmission, the delay spread of amultipath signal is important since it affects the datatransmission rate. Three parameters are often used todescribe the temporal spread of the channel: the meanexcess delay, the RMS delay sprea d and t he excess-delayspread. Mean excess delay describes the averagepropagation delay relative to the first-amving signalcomponent . Th e RMS delay spread measure s he temporalspread of the power delay profile about the mean excessdelay. The excess-delay spread X dB) indicates themaximum delay, relative to the first-arriving signalcomponent, at which the multipath energy falls to X d Bbelow the peak received level. These parameters areloosely related to outage and bit error rates for differentdigital modulation s che me s that do not use equalisation. Arule of thu mb is that a b it-error rate (BER) of less thanwill occur if the channel RMS delay spread is less than 0.2of the sym bol duration.Saleh and Valenzuela* observed from theirmeasurement at 1.5 GHz in a two-storey narrow buildingthat the RMS time delay spread values extended up to50 ns. Devasirvatham,L"making measurements in a large

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building at 850 MHz, observed median RMS time delaysprea d values of 125 ns. Rapp apoff6 reported resul ts ofmeasurement at 1300 MHz in five factory buildings.Multipath spreads ranged from 40 to 800 ns. Mean excess-delay and RMS delay spread values ranged from 30 to300 ns. The different results obtained were due to thedifference n t he type of building measured. Delay spreadswer e found to b e affected by factory inv entory, building-construction materials, building age, wall locations, andceiling heights. Buildings with more metal material havelarger delay spreads.3Both of the two main classe s of indoor radio propagationmodel- tatistical and site-specific -have stre ngt hs andlimitations when applied to the design and installation ofindoor wireless system s.Statistical modelsA general statistical impulse-response model for themultipath fading channe l was first suggest ed byTurin'.'foroutdoor radio propagation. Recently, this statisticalimpulse-response approach ha s been used for indoor radiochannel propagation modelling.Saleh and Valenzuela' used t heir measurem ent resu ltsin a m edium-size two-storey office building, toget her withmeasurement results from oth er researchers, to develop astatistical model of the indoor radio channel for thesimulation and analysis of various indoor com municationschemes. The model was shown to fit the m easurementsand may b e extended to other buildings by adjusting itsparameters. The model assumes that the multipathcomponents arrive in clus ters. The received amplitude ofeach component is an independent Rayleigh randomvariable, with a variance that decays exponentially withpropagation delay, as well as with time delays, within acluster. The corresponding phase angles for eachcomponent are independent uniform random variablesover [0,2n]. he clusters and multipath com ponents withina cluster form a Poisson-arrival process with different

Overview of indoor propagation models

the clusters have exponentiallydistributed inter-arrival times. Theformation of the clusters is related tothe building structure, while themultipath components within eachcluster are formed by multiplethe transm itter and the receiver. Themodel h as en oug h flexibility to permitreasonably accurate fitting of themeasured channel responses and ismodel is successful for application inoffice environm ents but its applicationto multipath data collected in several

reflection fr om obje cts in th e vicinity of

simple enough for simulation. The

factory environments has been

statistical model for indoor radio propagation based on theresul ts of extensive multipath propagation measurem entsin two office buildings. The data base for this modeldevelopment con sists of 12000 impulse respon se profilesof the channel collected in these office buildings. In thismodel, the data amval time is modelled as a modifiedPoisson distribution and the amplitudes were found to belognormally-distributed over both local and global areas,with a log-mean value tha t decre ases alm ost linearly withincreasing excess-delay. The simulation results of themodel agreed with measurement results in officeenvironments. Unfortunately, application of this model toimpulse- respons e d ata collection in factory environmentswas not successful.Keenan and Motley" formulated a radio coverageprediction model based on a few building parameters. Th eparameters in the formulae of this model were derivedfrom measurement data. The model provides a quick andsimple way to predict the path loss, in decibels, in an indoorenvironment. It isuseful for an initial coverage prediction.However, the model only provides path loss informationand may not work well in some complex indoorenvironments.Seidel and Rappaport" have proposed path loss modelsbased on data measured at 914 MHz.The m odels are basedon a simple d exponential path loss against distancerelationship. In open-plan buildings, the path lossexponent n isclose to 2. For environments with many moreobstructions between the transmitter and the receiver, thepath loss exponent can be much higher.Statistical distance-dependent path loss models areuseful for understanding the propagation of radio waves inbuildings. However, exhaustive measurements wererequired to obtain the data to determine th e appropriateparameters for the models for the se particular buildings.

Rappaport et al.' have developed a statistical channelimpulse response model for the design of radiocomm unication systems for use in factories and open-planbuildings. The m odel, called SIRCIM (simulation of indoorradio-channel impulse-response models), isbeing used bymany resea rchers to gen erate, on a com puter, impulse-

0-50

-100

-150aH -200

-250-300

0 100 200 300 400 500 600 700 800time ns-350

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signal ray reflected ay

parallelplate 6partition)

transmitted raya

reflected rayignal ray

E,parallelplate,, D Fpartition)

transmitted rayb

Fig 3plate: a)electric vector perpendicular to plane ofincidence; b )electric vector parallel to plane ofincidencerespon se and path-loss measurements in office and factorybuildings. Th e m odel incorporates first- and second-orderstatistics to characterise the discrete impulse respo nses ofindoor radio channels for both line-of-sight (LOS) andobstructed (OBS) topographies. SIRCIM can be appliedthroughout the low microwave band, and the code iswritten to work up to 60 GHz. Data files produced bySIRCIM contain amplitudes, phases, time delays, and pathloss for individual multipath components, as well as l arg escale path loss, so that a comp lete propagation model iscreated. The m ost salient feature of the model is that itreproduces multipath channel conditions that are veryrealistic since they are based on real-world measure ments,and may th us b e used for meaningful system analysis infactories and open-planbuildings. It is possible to simulateother m ultipath channels, such as office buildings, basedon th e framework of the model by changing the values ofthe model. This mo del is attractive for the characterisationof ind oor propag ation channels. H owever, it relies onextensive measurement data to determine the appropriateparameters to model a particular type of indoorenvironment.

A signal wave inc ident obliquely on a parallel

Site-specific propagation modelsSitespecific propagation models are based onelectromagnetic-wavepropagation theory to characteriseindoor radio propagation. Unlike statistical models, si tespecific propagation models do not rely on extensivemeasurement, bu t a greater detail of the indoorenvironment is required to o btain an accurate prediction ofsignal propagation inside a building.In theory, electromagnetic-wave propagationcharacteristics could be exactly computed by solvingMaxwell's equations with the building geometry asboundary conditions. Unfortunately, this approachrequires very complex mathematical operations andrequires considerable computing power, beyond that ofcurrent m icrocomputers. Hence it is not econom ical forthe characterisation of indoor radio wave propagation.Therefore, approximate numerical methods are of interest.Ray tracing is an intuitively appealing method forcalculating radio signal strength, timeinvariant impulseresponse, RMS delay spread and related parameters in anindoor environment. '621 -Th e concept of ray-tracingmodelling is based on the factthat high-frequency radio waves behave in a ray-likefashion. Therefore signal propagation can be modelled asray propagation. By using th e concept of ray-tracing, aysmay be launched from a transmitter location and theinteraction of the rays with partitions within a buildingmodelled using well-known reflection and transmissiontheory. Two types of ray-tracing methods he imageand the bruteforc e ray-tracingmethod"- arebeing used in the characterisation of indoorelectromagnetic-wavepropagation. For scatters boundedby plane faces it is convenient to employ the im age methodto mirror the radio wave source at a particular face. Thepoint where the mirror face intersects the line conn ectingthe transmitter image and th e receiver is the point at whichspecular reflection occurs. This method is well suited toradio propag ation analysis n t he case of geometries of lowcomplexity and where a low num ber of reflections areconsidered. Th e bruteforce ray-tracingmethod considersa bundle of transmitted rays that may or may not reach th ereceiver. Th e number of rays employed and the distancefrom the transmitter to the receiver location determine theavailable spatial resolutio n and hence the ac curacy of themodel. This method requires more com puting power thanthe image method.Ray tracing can be much less demanding ofcomputation than meth ods based on M axwell's equations.With the computing powers currently available onpersonal computers and workstations, the ray-tracingapproach prov ides a challenging but feasible method ofpropagation modelling. Reliable sitespecific ray-tracingpropagation prediction models for each building based onits detailed geometry and construction can be veryeffective tools in designing indoor comm unicationsystems.4 Modell ing by ray tracingTh e ray-tracing approach approximates the scattering of

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electrom agnetic waves by simple reflection and refraction.The degree of transmission and reflection of a signalthrough and off an obstacle is related to the complexpermittivities of the obstacle.Transm ission and reflection ofa radio signalWhen a signal is transmitted through or reflected off awall or a partition, the degre e of signal attenuation and theamount of phase change depend on the complextransmission and reflection coefficients, respectively.Thes e are computed from the complex permittivities of thematerials the signal rays encounter. O ther factors affectingthe transmission and reflection of the signal are the angleof incidence and the relative polarisation.Th e complex transmission coefficient is defined as th eratio of the transmitted to the incident electric-fieldstrengths and the complex reflection coefficient isdefined as the ratio of the reflected to the incidentelectric-field stren gths . Referring to Fig. 3, a signal ray isincident on a parallel plate, which may be a partition o r awall. In Fig. 3a , th e signal has a horizontal polarisationwith reference to the parallel plate. The complextransm ission and reflection coeffic ients for horizonta lpolarisation are:

(2),reflection coef. r = ~ = ~ ~E,C O % - (& n L @ l 'cos 1 + (E Sk5 JI) '

In Fig. 36 the signal is polarised vertically with re spect tothe parallel plate. Th e complex transm ission and reflectioncoefficients for vertical polarisation are:

transmission coef. t = EtE,2 COS@ 3)(3 os (1- %sin?@l)

4), @s@, - ( -E, & C O S & + (&-sin2@1)"reflection coe f. r = ~ =In eqns. 1-4, E is the complex permittivity of the parallelplate, E~ is the permittivity of free space, is the angle ofincidenc e, and E,, E , and Et are th e incident, reflected andtransm itted electric field stren gths, respectively.When a signal ray, as shown in Fig. 3 , encounters aparallel plate (a wall or partition) with thickness D thesignal is attenuated while going through the material. Thecomplex transm ission coefficient is then given as

5)

wheret, = ta x tB s a complex transm ission coefficientta = the complex transmission coefficient at AtB= the complex transmission coefficient at Ba = attentua tion factor andd = the distance travelled by a signal ray in the material.

The attenuation factor, a, isgiven as:

whereE , = real part of the relative complex permittivity of th e

materialE, = imaginary part of the relative com plex permittivity

of the material andh = wavelength.Line-ofs ight signal strength calculationFig.4 shows a signal transmitted through a partition.Th e received signal streng th at the rec eiver from a line-of-sight path isgiven by:

whereE, = the sou rce signal strength from the transmitterE,~,, = received lineof-sight signal strength at the

receiverdo = lineof-sight distance from transmitter to receivert, = comp lex transm ission coefficienth = wavelength of the signal.

Reflected signal strength calculationFig. 5 shows a first order reflection path of the signal.The signal strength at the receiver due to this path isgivenby:

partition

transmitter-_ d,I._ receiverFig. 4 Line of sight signalELECTRONICS 81COMMUNICATION ENGINEERING JOURNAL OCTOBER 1995 225



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Fig. shows a second order reflection path of the signal.Th e signal strength at the receiver due to this path isgivenby:

and th e multiple reflection signal strength at the receiver isgiven by:

whereE, = signal strength from the transmitterL^ = first order reflected signal strength at receiver

E2R = second o rder reflected signal strength atE m R = multiple reflection signal strength at receiver

+ l +...+ Lk k any positive integer = total reflectiondistancer,,, r,, ..., r,, = comp lex reflection coeffic ients at eachreflection point 1.2 , ...,m, respectivelytil tc2,.., t,, = complex transmission coefficients ateach wall or partition 1.2, ....,n espectivelyd = wavelength of the sign al.

receiver

Raytracing methodIn ray-tracingmetho ds, the locations of transmitters andreceivers are assigned to points referenced by three

Fig. 5 First order reflected signal

ig. 6 Second order reflected signal

dimensional co-ordinates. The walls, partitions, ceilingsand floors in an indoor environm ent are usually mod elledas plane surfaces of given thickness and complexpermittivity. For simplication, curved surfaces can bemodelled as piecewise planar surfaces. Th e rays from th etransmitter antenna are reflected off walls, partitions,ceilings, floors and tables etc. o r transmitted through wallsand partitions etc. to arrive at the receiver. As alreadymentioned, two common m ethods - he image methodand the brute-force method - ave been developed totrace the rays from the transmitter to the receiver.

a) I mage r ne th ~ d: ~ . ~his method assumes everyplane face in an indo or environment to be a mirror. Forline-of-sight propagation, it is easy to trace the ray byconnecting the transmitter and receiver. For single-reflection propagation, the radio sourc e is mirrored at aparticular face. Th e point of intersection of th e mirro r faceand the line connecting the transmitter image to thereceiver is the point where specular reflection occurs.Th e single-reflection propagation path can th en b eobtained by connecting the so urce point, reflection pointand receiver point. For repeated reflection, the image ofthe radio so urce with reference to a particular plane faceis found first. The next step is to find an image of thesource image with reference to ano ther plane face wherethe second point of reflection will be located. Followingthe same rule, all the points of reflection at the relevantplane faces can be obtained. The multiple-reflectionpropagation paths can then be obtained. The methoddescrib ed above, starting at the sou rce image, is referredto as th e forward ray-tracing method. It is also possible tobe start at the receiver image and trace back to thetransmitter. This is called the backward ray-tracingmethod.Consider a rectangular room as shown in Fig. 7. T h etransmitting antenna is located at point T, while thereceiving antenna is located at point R To trace the pathfrom T to R reflecting off walls 2, 4 and 3, three imageshave to be found. First the first order image, 13 of thereceiver an tenna in wall 3 is found. Then , the second orderimage, at point is found by reflecting the first orderimage in the semi-intiniteplane co ntainin g wall 4. Finally,th e co -ordina tes of the highest order image, at point 13,4,2.are foun d by reflecting in wall 2. Once all the imageshave been found, the com plete path and all the reflectionpoints can be found as sho wn in Fig. 7. The s ignal s trengthof this propagation path can then be calculated usingeqn. 10.

(b) Brute-force rayfr acin g method: * This methodaccounts for all possible propagation paths. Thetransmitters and receivers are modelled as points atdiscrete locations in three-dimensional space. All thepossible angles of departure and arrival at the transm ittersand receivers are considered to determine all possiblerays that may leave the transmitter and arrive at thereceiver.Ray tracing is accom plished by an exhau stive search of aray tree taking into acco.int deco mpo sition of the ray ateach planar intersection. First the model determineswheth er a line-of-sight path ex ists and if so computes the

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received signal.Next, the model traces a source ray in a specifieddirection and detects whether an object intersectionoccurs. If no intersection is found, the process stops and anew source ray in a direction making an angle with theoriginal ray is initiated. Once an intersection has occurr ed,a check is made to see whether t he ray can be consideredto have reached any of the specified rece iver locations. Ifthe ray is found to rea ch a receiver location , the receivedsignal is computed. After checking the reception, theincident ray is divided into a transmitted and a reflectedray, each of which is traced to the next intersection in thesam e way. Thi s recursion c ontin ues until the ray intensityfalls below a specified thres hold o r no further intersectionsoccur.As multiple scatte ring of a ray will not contri butesignificantly to the received power s ince the amplitude ofthese scattered rays decreases rapidly with distance, theexisting ray-tracing models using this approach do notinclude multiple scattering and also do not trace scatteredrays recursively.At each step in the creation of a ray tree, thecorresponding ray segme nt is tested to see whether it canbe considered to have reached specified receivinglocations. To do this, a reception spher e is constructedabout th e receiving location with a radius proportional tothe unfolded path len gth from transm itter to receiver andthe angular spacing between neighbouring rays at thesource. f the ray intersects the sphere , the ray is taken ascontributing to the received signal. Otherwise, the ray istreated a s not having reached the receiver location.

The reception sphere effectively accounts for thedivergence of the rays from the source. For sufficientlysmall ray separation 0 the ray intercepting th e sph ere willbe an ac curat e measure of the ray that would pass directlythrough the receiving point, Th e physical interpretation ofthe reception s phe re can be justified with the aid of Fig. 8.This Figure is a two-dimensionalrepresentation of a ray being traced.Two adjacent rays launched at t 0relative to the tes t ray are also shown.Note that in three dimensions anyray will have m ore th an two adjacentrays and angular separation of theadjacent rays will not necessarilycoincide with the co-ordinate axes.As shown in Fig. 8, a receptionsphere with the correct radius (=W 2 an receive exactly one of therays. If the radius is too larg e. two ofthe rays could be received andwould, in effect, count the same raypath twice. Likewise, if the radius istoo sm all, it is possible tha t non e ofthe rays will intercept the sph ere andthe ray path energ y will he excluded.The path loss error du e o perceivingtwo rays would be a few decibels. Amissed spec ular ray could lead to amuch larger error if a significant

A

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5 ConclusionIn this paper, we have pointed out the importance ofpropagation m odels in the development of indoor wirelesscomm unications. Propagation models provide estim ates ofsignal strength and time dispersion in many indoorenvironments. These data are valuable in the design andinstallation of indoor radio syst ems .Propagation models can be classified into statisticalmodels and site-specific propagation models. Statisticalmodels need extensive measurement data and do notprovide site-specific information. Site-specific propagationmodels provide site-specific information hut requireconsiderable detail of the layout of the indoorenvironment.Statistical models can h e used for preliminary designand analysis whereas site-specific propagation modelscan be used for fast and accurate prediction of indoor

adjacent raycorrectreception sphere

d

/

transmiller

undersized reception sphereoversized reception sphere

Fig. 8length s d . The reception sphere radius varies with Hand dTwo dimensional view of t he reception sphere. The unfolded ray path

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r ad i o co v e r ag e . S i t e - s p ec if i c p ro p ag a t i o n m o d e l l i n g b ys o l v i n g M ax wel l s eq u a t i o n s i s co s t l y an d i m p rac t i ca l .R a y t r a c i n g i s p r o m i s i n g as an a p p r o x i m a t e m e t h o d f o rs i te - s pe c i fi c p r o p a g a t io n m o d e l l i n g . R a y t r a c i n g m a k e su s e o f the fact that a l l o b j ec t s o f i n t e r e s t w i t h in thep r o p a g a t i o n e n v i r o n m e n t a r e l a r g e r t h a n a w a v e l e n g t h ,so i t i s s u i t ab l e f o r ap p l i ca t io n i n the h i g h e r r a d i of r e q u e n c y r a n g e s . The i n c l u s i o n o f d if f r ac t i o n t h eo ry ca nb ro a d en i t s ap p li ca t i o n to l o w e r r a d i o f r e q u e n c i e s . Thea c c u r a c y of r a y - t ra c i n g t e c h n i q u e s d e p e n d s h e a v i l y ont h e a c c u r a c y a n d d e t ai l o f the s i t e - s p ec if i c r ep res en t a t i o nof the p r o p a g a t i o n m e d i u m . The avai labi l i ty of fas ti n t e r a c t iv e - c o m p u t i n g e n v i r o n m e n t s a n d h i g h - a c c u r a c yg r a p h i c s d a t a b a s e s g re a t l y i m p r o v e s the e f f ic i e nc y a n da c c u r a c y o f r a y- t ra c i ng m o d e l l i n g . I t i s r e c o m m e n d e dt h a t h i g h - a c c u r a c y r a y - t r a c i n g m o d e l s he d e v e l o p e d .Nev er t h e l e s s , a s i m p l e , f a s t an d l o w-co s t P C -b as ed r ay -t r a c i n g p r o p a g a t i o n m o d e l i s h e l p f u l to e n g i n e e r s i n thep r e l i m i n a r y d e s i g n a n d a n a l y s i s of i n d o o r w i r e l e s ss y s t e m s . The d e v e l o p m e n t of s u c h a m o d e l i s h i g h l yd es i r ab l e .References1 TURIN. G.L.: Communication through noisy, random-

multipath channels. 1956 IRE Convention Record, part 4,pp.154-166

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3 SUZUKI, H.: A statistical model for ur ban radio propagation,IEEE Trans. Commun.,July 1977, CO M- 25 , pp.673-6804 HASHEMI, H.: Simulation of the urban radio propagation

channel, IEEE Trans. Veh. Technol., August 1979, VT-28,pp.213-2245 BAJWA, AS.: UHFwideband statistical model an d simulation

of mobile radio multipath propagation effects, IEE Proc. F.,August 1985,132, 51, pp.327-333

6 RAPPAPORT, T.S., SEIDEL. S.Y., and SINGH, R : 900 MHzmultipath propagation measurements for US digital cellularradio telephone, IEEE Trans. Veh. Technol., May 1990,

7 RAPPAPORT, T.S., SEIDEL, S.Y., and TAKAMIZAWA, IC:Statistical channel impulse respo nse m odels for factory andopen plan building radio communication system design,IEEE Trans. Commun.. May 1991.3 9, (5). pp.794-807

8 SALEH. A A M ., and VALENZUELA, RA.: A statistica l modellor indoor multipath propagation, IEEE J. Sel. AreasCommun., February 1987, SAC-5, 2), pp.12&137

9 HASHEM I, H., THOLL. D., and MORRISON , G.: Statisticalmodelling of the indoor radio propagation channel part I.Proc. IEEE Vehicular Technology Conference, WC92,Denver, C O, May 1992, pp.33&34210 HASHEMI, H., LEE, D., and EHMAN. D.: Statisticalmodeling of the indoor radio propagation channel: p rt 11.Proc. IEEE Vehicular Technology Conference, WC92,Denver, CO ., May 1992, pp.839843

11 HASHEMI, H.: Impulse respon se mode lling of indoor radiopropagation channels, IEEE J. Sel. Areas Commun..September 1993, SAC-11 pp.1788-1796

12 BULTITUDE, R.J.C.: Mea surem ent, characterization andmodeling of indoor 800/900 M Hz radio cha nnels for digital

VT-39, 2). pp.132-139

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15 RAPPAPORT, T.S.. and SANDHU, S.: Radio-wavepropagation for emerging wireless personal-communicationsystems, IEEE Antennas & Propagation Magazine, October1994 ,36, (5), pp.14-2416 VALENZUELA, R A : A ray tracing approach to predictingindoor wireless transmission. Proc. 43rd IEEE VehicularTechnology Confe rence,NJ. USA, 1 993, pp.214-21817 MCKOWN, J.W., and HAMILTON, R.L.: Ray tracing as adesign tool for radio networks. IEEE Network, November1991 ,5, (6),pp.27-30

18 SEIDEL, S.Y., and RAPPAP0RT.T.S.: Araytracingtechniqueto predict path loss and delay spr ead inside buildings. ProcIEEE GLOBECOM 92 Conference, Orlando, USA, 6th-9thDecember, 1992 pp.649-653

19 HOLT, T., PAHLAVAN, IC and LEE, J.F.: Ray tracinRalgorithm for indoo r radio propagation modeling. Proc 3rdIEEE Int. Symp. on Personal, Indoor and Mobile RadioCommunications, Boston, MG 19th-21st October 1992

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21 LAUREN SON, D.I., SHE1KH.A.U.H.. and McLAU GHLIN. S.:Characterization of the indoor mobile channel using a raytracing technique. Proc. 1992 IEEE Int. Conf. on SelectedTopics in Wireless Communications, Vancouver, BC,25th-26th June 1992 p p . 6 5 6 8

22 OWE N, F.C., and PUNDEY, C.D.: In-building propa gation at900 MHz and 1650 MHz lor digital cord less telephone. 6thInt. Conf. on Antennas and Propagation, ICAP 89, Part 2:Propa gation, 1989, pp.276-281

23 ALEXANDER, SE .: Characterising buildings for propagationat 900 MHz,Electron. Lett. eptem ber 1983.19 20). p.86024 ALEXANDER, S E : The propagation of radio signals at 900MHz within buildings. IEE Colloquium Digest 1986/030,Propagation in confined space s and tunnels, IEE, London,UK 1986,pp.7/1-7/425 DEVASIRVATHAM, D.M.J.: Ti me delay spreadmeasurements of wideband radio signals within a building.Electron. Lett. th Nov emb er 19&?4,20, (23). pp.951-95226 RAPPAPORT, T.S.: Characterization of UHF multipath radiochannels in factory buildings, IEEE Trans. Antennas &Propagation,August 1989,AF-37 p.1058-106927 SEIDEL, S.Y., and RAPPAPORT, T.S.: 914 MHz path lossprediction models for indoor wireless communications inmultifloored buidlings, EEE T rans. Antennas & Propagation.February 1992,AP-40 2). pp.207-217

EE:1995First received 1st Marc h and in revised form 14th July 1995The authors are with the Department of Communication andElectronic Eng ineerin g, Royal Melbou rne Institute ofTechnology, GPO Box 247fiV, Melbourn e, Victoria 3001,Australia.

228 E L E C T R ONIC S & C O M M U N I C A T I O N E N G I N E E R IN G JOURNAL O C T O B E R 1995

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Propagation Modelling for Indoor Wireless