Review on Buildings

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Review on radio propagation into and withinbuildingsD. Molkdar

Indexing terms :Radiowave propagation (microwave),Radiowave propagation (terra in effects)

Abstract: The paper reviews the published infor-mation on radio propagation into and withinbuildings particular to microcellular portablemobile radio channel at frequencies from150MHz upwards. However, no particular atten-tion has been paid to the work carried out atmillimetre wavelengths. The review has beencarried out because such propagation informationis required for the design of future portable mobilecommunication systems.The need for propagation information and thetypes of information required is described. Thebuildings, where a portable handset is likely to beused, have been categorised to put bounds on thereceived signal statistics and provide channelmodels for any particular type of building. Theresults published by different authors are thensummarised by considering all the proposedcategories. The results have been divided intonarrowband and wideband measurements. Thisinformation is tentative as it is based on only afew measurements. As more measured resultsbecome available the design information andchannel models can be modified. Suggestions fornew measurements required are made in the lightof existing information.

1 IntroductionConsidering the statistics of the present mobile radiomarket, it is evident that more sophisticated systems willbe needed to provide a variety of services for a largenumber of users. Steps are being taken to provide ini-tially such radio services with mobility provided, if notuniversally, over a restricted area. The types of systemswhich are at present in evolution are mobile radio(cellular), cordless telephone [ , 23, paging, etc. The inte-gration of such systems will eventually lead to a universalportable radiotelephone or terminal for both speech anddata communication [3-61. Such a system will be basedon microcellular structure leading into cells as small as abuilding. In particular, to provide services for denselypopulated buildings, creating a traffic many times greaterthan that of the vehicular mobile radio systems, a floor oreven a room may represent a cell. In addition, it has beenrealised during the past few years that radio communica-Paper 7710H (Ell), first received 9th February and in revised form 21stSeptember 1990The author is with G E C Alsthom Transportation Projects Limited,Locomotive and Systems Engineering, PO Bo x 134, Manchester, M60IAH, United KingdomI EE PROC EEDI NGS -H, V o l . 138,N o . I , FEBRUARY 1991

tions are not only convenient but also are cost effectivesolutions for providing data and speech services inindoor environments because of their inherent advan-tages over the convent ional wire links. Some of theseadvantages are elimination of wiring around buildings,providing services for a larger number of users, roaming,ths flexibility of shifting terminals and equipment around ,more immunity t o natural and m an made disasters, rela-tively easy maintenance, an increase in quality of serviceand flexibility of introducing or changing communicationservices in existing buildings without the need for expen-sive and time consuming rewiring. Cordless telephonesystems are examples of providing speech services with alimited amount of mobility in an indoor environment.The advantages of using such systems, particularly insmall and large office buildings, exhibition centres, etc.,have provided a potential market of a very large numberof users. To meet this demand new systems have been,and are being, designed to provide a wide variety of ser-vices in indoor environments.One of the key factors in designing the future vehicularand personal microcellular mobile radio systems isundoubtedly a comprehensive knowledge about propaga-tion characteristics over different types of environmentsand, more specifically, buildings. Propagat ion studies aretherefore essential because the radio propagation charac-teristics are relatively unknown in indoor environments.Such studies will lead to channel models and statisticalparameters which could be used to design intelligentsystems.It should be noted that the propagation characteristicsof the microcellular structure for vehicular mobile radiosystems are different from those of microcellular portablemobile radio systems. This is because the former systemsare the miniaturised versions of the existing vehicularcellular systems, hence the problems are similar to thoseof the more familiar terrestrial propagation [7-111 andwill not be considered here.This paper reviews all the published works which havebeen carried out regarding the propagation into andwithin buildings. First, an introduction to the propaga-tion into and inside buildings will be given. Owing to astrong dependency of the received signal statistics on thetypes of buildings, a classification of different buildings isproposed. Based on this classification, the received signalstatistics and channel models for any particular type ofbuilding are given by treating narrowband and widebandmeasurements separately. The important statisticalparameters are then summarised, representing theirvariabilities over different types of buildings. Most of thestudies regarding the propagation into and within build-ings have been carried out at around 900 MHz. Thecongestion of the radio spectrum at this band hasresulted in looking for another gap in the radio spectrum.61

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The frequencies of interest are 1-2 GHz and 60 GHz.Unfortunately there does not statistically exist a largeamount of measured dat a describing the portable channelcharacteristics at these frequencies compared with90 0 MHz. It is also intended here to put together all theavailable results regarding the different frequencies, withexception of those at millimetre wave. Finally, conclu-sions and proposals for the future measurements are dis-cussed.2 Propagation studiesThe way in which propagation studies should be directeddepends on a particular systems specifications as well asits scientific nature. In particular, the data rate of asystem is an important factor which determines whetherthe statistics of the received signal envelope (narrowband)are of concern or the dispersion characteristics(wideband) are also required. The dominant factor thatdetermines both the narrowband and the wideband sta-tistics is, however, the type of environment in which asystem is to be set up. Another factor which should betaken into account is system planning. For example, therange over which a system should operate, the relativeposition of the transmitter and receiver antennas and, inthe case of indoor systems, the position of the transmitterantenna, that is whether it is used to illuminate a buildingfrom outside or is positioned inside a building.

Propagation into and inside buildings, hereafter calledthe portable channel, has to some extent a morecomplex multipath structure than that of the terrestrialmobile radio channel. This is mainly because of thebuilding structure, layout of rooms and, most important-ly, the type of construction materials. For example, afactory building is quite different to an office buildingboth in its structure and in the materials used. There arealso many variations in the types of materials used ininternal partitions, walls to outside and floors as well asthe sizes and percentage of windows.The age of buildingsalso creates problems as far a s the effects of the structureand construction materials are concerned. Similar com-parisons can be made among other types of buildings, e.g.sports halls, railway stations, airports and undergroundrailways. The types of objects inside the buildings, whichmay be lossy or good reflectors, also provide an undeter-ministic situation. In addition, depending how the systemis laid out, the condition of transmission will be different.For example, if both transmitter and receiver are inside abuilding the situation will be more complex. In this case,the surroundings and the motion of scatterers have amore pronounced effect on the received signal statisticsbecause the transmitter and receiver antennas are moreshadowed. Considering these, certain objects should beplanned to measure and analyse the effects of the follow-ing:(i) different types of the exterior wall construction suchas steelframed, glass, brick, concrete, any shielding,layout of rooms, equipment, etc.(ii) the difference between urban and suburban build-ings because of the density of the surroundings(iii) the difference between urban and suburban build-ings in terms of construction and the furniture inside(iv) the density of the personnel in a building whichhave been shown to have a pronounced effect on thereceived signal statistics(v) the conduction of transmission, e.g. both transmit-ter and receiver inside or transmitter outside illuminatinga building, etc.

6 2

(vi) different transmitter heights both inside andoutside a buildingAs far as a system design is concerned, the propagationstudies should first be divided into two major classes.These are narrowband and wideband which result in therelevant statistics and channel models. Secondly, differenttypes of buildings should be classified to provide boundson the received signal statistics for any particular type ofbuilding. In the following section a classification of build-ings is proposed.3 Building classificationIn presenting the results of experimental data in a multi-path environment, it is essential to include a gooddescription of the areas under the test. However, for theportable channel, some comprises must be made. This isbecause it has been shown that the received signal sta-tistics are dependent on many factors which vary signifi-cantly for different types of buildings. A detaileddescription of a building under test would make the clas-sification of similar types of buildings difficult. Hence, itis attempted here to provide a classification which, tosome extent, disregards the detailed structure of any par-ticular building. Such a classification will result in thewide variation of the statistics of the received signal overbuildings belonging to a same category. However, asmore measurements are carried out, new categories maybe introduced which may provide a better classificationin terms of the variability of the signal statistics [l2, 131.Table 1 represents the proposed categories based onthe reviewed literature on narrowband [14-361 and wide-Table 1 : Building classifications

Proposed categoriesCategory number Description

78

Residential houses in suburban areasResidential houses in urban areasOffice buildings in suburban areasOffice buildings in urban areasFactory buildings w ith heavy machineryOther factory buildings, sports halls,Open environment, e.g. railway stations,Underground, e.g. subways, underground

exhibition centresairports, etc.streets, etc.

band [3746] measurements. It should be noted that theposition of transmitter, whether it is inside or outside abuilding, will provide two distinct situations. Hence,there will be 16 categories regarding both situations.However, as far as system planning is concerned the 16categories may be reduced. For example, for categories 1and 2 a more practical system implementation is toinstall the transmitter outside. Similarly, it is more appro-priate to have the transmitter inside for categories 3, 4, 6and, in particular, 8. There may be, however, cases inwhich a number of buildings or small factories need to beserved with a single transmitter. However, we assumethat statistics for each category apply to both situations.Future measurements should be planned to compare theeffects of the position of the transmitter both inside andoutside.There are four points which should be noted as far ascategories 3, 4, 6, 7, and 8 are concerned. First, it mightbe argued that sports halls, exhibition centres (in cate-I E E P R O C E E D I N G S - H , Vol . 138, N o . I , F E B R U A R Y 1991


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gory 6 ) are fairly similar to railway stations and airports(in category 7) in their structure. However, a typicalrailway station or airport is much more open with lessconfined halls and usually has very tall ceilings. Secondly,by open environment (in category 7) we do not meanentirely open . Buildings in this category are not like oficebuildings or sports halls, in which a large area is parti-tioned into smaller areas. Thirdly, office buildings incategories 3 and 4 include commercial, laboratory andworkshop types of environments. Fourthly, category 8does not include tunnels which can be modelled as wave-guides consisting of rough surfaces and metallic obstacles(trains and vehicles). There are many papers [47-521dealing with measurements, characterisation and model-ling of such an environemnt.Table 2 shows all 8 categories with the correspondingreviewed references which fall into different ones. Tables3 and 4 show the reviewed references and their corre-sponding categories together with the position of trans-Table 2: Categories with their corresponding referencesCategory Narrowband Widebandnumber reference reference1 16, 21, 22, 24, 35 3923 18, 20, 21, 22, 23, 26, 27. 20. 33, 35, 434 14, 15, 17, 23, 27. 28. 29, 30, 34, 35. 435 29 ,36 41 ,45 ,466 45 45

- -37, 38, 39, 42, 4343, 44

I8 25, 32

- -

Table 3: Narrowband references with their correspondingcategoriesReference Category Transmitter Transmitter Frequencynumber number outside inside (MH z)1415161718192021222324252627282930313233343536

4 *4 *1 *4 *3 *331 . 31 . 3 *3.4,5 *1 *83 o r 4 ? *3 o r 4 ? -3. 4 *4. 54 *38341,3,4,5 -5

---

-

------

35,150250,400860,1550,2569150,250900900900,60 GHz900800850800200 - 12.4 GHz1200900851, 927835441,900,1400900250-12.4GHz900,1700441,900,1400900,16501300

Table 4: Wideband references with their correspondingcategoriesReference Category Transmitter Transmitter Frequencynumber number outside inside (MH z)37383940414243444546

-31 , 3 *1 . 3 *533 o r 4 ? -45, 6 -5

-

--

--

**-*******

85085085085013001500910, 1750850, 17009101300

I E E P R O C E E D I N G S - H , Vol. 138, N O . , F E B R U A R Y 1 9 9 1

mitter relative to a building under test. It should be notedthat, although References 23 and 35 represent a numberof categories, their results do not represent the statisticalvariations of the received signal specific to a particulartype of building. Hence it is not possible to attribute theirresults to any particular proposed category. For some ofthe references it is not clear whether the building undertest was located in a suburban area or in an urban areaas indicated by '?, in Table 3. Tables 3 and 4 also showthe frequencies at which the measurements were carriedout. The following sections present the published resultsfor categories listed in Table 1.4 Narrowband measurementsWhen the data rate of a system is less than the coherencebandwidth of the channel, the narrowband statistics ofthe received signal are of concern. The useful statistics,when characterising the narrowband portable channel,are the distance/power law gradient, penetration loss andthe spatial and temporal distributions of the receivedsignal.From the reviewed literature, it has been observed thatthe rate of decay or distancefpower law gradient in anindoor environment is a strong function of building type,the layout of the rooms and corridors, the number offloors and walls, windows, furniture, etc. The loss due tothese and more important ly the variation of loss at differ-ent frequencies produces a large variation in rate ofdecay. In Reference 53 a theoretical equation for indoorradio propagation is derived which can be used, in partic-ular, at any frequency to estimate the median value of thereceived signal power. However, simpler distance/powerrelationships have been used by many researchers to esti-mate the ra te of decay of a transmitted signal, hence pre-dicating the median of the received signal at a givendistance. Such a relationship, as that used in References22 and 24, is as follows

1Power =-D"or

P(dB) = m log Dwhere m and D are the gradient and distance betweentransmitter and receiver, respectively. The distance/powerlaw relationship in eqn. 2 was modified in Reference 33 asfollows:

P = S + m log D (3)where S is the path loss at l m in dB. This factor is addedto take into account the performance of the antennaswhich are frequency dependent.Penetration loss or building loss was first defined byRice [14] as the difference between the received signalinside a building and the average of the received signalaround the perimeter of that building. The measure of thepenetration loss is important for the reuse of a frequencyin a cellular type of system. In general, it has been foundthat the penetration loss is dependent on the construc-tion materials of a building, building orientation withrespect to transmitter, internal layout, floor height andthe percentage of windows in a building. Therefore, thevariability of penetration loss makes the indoor environ-ment different from that of land mobile radio as far asinterference is concerned.The prediction of an area coverage and hence limitingthe interference caused by other users is therefore very

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difficult. Unfortunately, a direct comparison for differentpenetration loss results obtained by different researchersmay not be applicable because the outside reference levelhas not been found in a similar way.Spatial and temporal distributions are also different inan indoor environment compared with a land mobileradio. The spatial fading rate is much lower in an indoorenvironment because of the slower motion of the receiver.Nulls between 20 and 30 dB are observed when the recei-ving antenna is moved through small distances, as illus-trated in Fig. 1 [26]. In this figure, T-1 to T-5 represent

IO-

( T - 3 ) ( T - 4 ) (T-5 1( T - 2 ) I / / /I , ' ,wave iarriva! a/nglem m i u ng .I / / ~

Im: : concrete posts+I b-. .

B A.corridor

t 1\wooden door0

= 201

the positions of the transmitting antenna with respect toa room in the building under test (category 3). The tem-poral fading is much higher in an indoor environmentbecause the antennas are not shielded and are not at ahigh elevation as is the case in land mobile radio. Bursttype of fades of the order of 17-30 dB with 20-40 s dura-tion have been measured [27, 361 as shown in Fig. 2The following paragraphs summarise these parametersfor each category of Table 1 using the reviewed refer-ences. It should be noted that the frequency of operationis not mentioned since the behaviour is the same, apartfor some parameters which are brought to attentionwhere necessary.

~ 2 7 1 .

64

Category I :Residential houses in suburban areasThe most comprehensive measurements for this type ofbuilding were conducted by Cox et al. [22, 241. The mea-

time.50

160 2A O 3 6 0 4 6 0 5AO 6 0 0time,s

Fig. 2measured in Reference 27Temporal envelope and phase variation of the received signal

surements were carried out at 800M Hz for a variety ofhouses with different construction materials and struc-tures. In Reference 16 a satellite transmission was used asa source and the dependency of the attenuation on fre-quency and construction material was investigated. Thispaper is useful as it compares the received signal statisticsat frequencies of 860 MHz, 1550 M H z and 2569 MHz . Itis stated in Reference 35 that the measurements werecarried out over residential houses but no specific resultsare presented for this type of building.Eqn. 2 was used to estimate the distance/power lawgradient in References 22 and 24 . The results show thatdifferent gradients are obtained depending on which floorof the house the receiver is, whether it is inside or outside,the type of construction material and the density of thesurroundings. In general, the rate of decay was found tovary between 3.0 and 6.2 with an overall value of 4.5. Theattenuation provided by different houses was found to beas expected as far as their construction materials wereconcerned. However, some houses did not show theexpected attenuation, these were concluded to have beenaffected by the external environmental factors. Forexample, houses in high-density housing areas showedhigher attenuation than those in low-density housingareas. Values between 1. 4 and 4. 0 are obtained for therate of decay in Reference 21 .Building attenuation (penetration loss) for houseswhich are metallic, side metallic or wood constructedhave been found to vary from - 2 to 24 dB [16, 22, 241increasing with frequency [16].The median signal levels have been found to be log-normally distributed with standard deviations of 9 dBand 4. 4 dB for outside and inside paths, respectively [22,241. The small scale fading has been found to follow theRayleigh distribution [22].

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Category 2 : Residential houses in urban areasThere is no published measured data found by the authorfor this category.Category 3: Office buildings in suburban are asIt is seen from Table 2 that there have been more mea-surements carried out for buildings in this category. Mea-surements in References 18, 22, 23, 26 and 28 wereconducted with the transmitter outside a building underthe test whereas in References 20, 21, 27, 33 and 35 thetransmitter was located inside. Of these, the References18, 20, 21, 22, 26, 27, 28 and 33 present results for build-ings particular to this category and References 23 and 35present results averaged over these and other types ofbuilding.The distance/power law gradient is treated best in Ref-erence 21 for a variety of office buildings with differentpartitioning materials, density of rooms and floors. Therate of decay was found to vary between 1.2 and 6.5. Thecoverage area, defined as the range over which thereceived signal has a BER better than was found tovary between 8 and 6 0 m. The coverage area is comparedwith 6 0 GHz in Reference 20 representing a substantialreduction. In general, it is concluded that coverage at6 0 G H z is limited at most to two rooms compared withseveral rooms at 900 MHz. In Reference 33 the rate ofdecay and attenuation through the floors and walls wereinvestigated at frequencies 900 MHz and 1.7 GHz . Eqn. 3was used in Reference 33 to find the distance/power lawgradient. It was found, however, that a better fit to theexperimental data can be achieved, with a marginalspread about the fit, by introducing the correcting factorF representing the attenuation provided by each floor,therefore

P + kF = S + m log d (4 )where k is the number of floors. This equation is particu-larly useful for buildings in categories 3 and 4 because thefloors of these types of buildings are usually constructedof materials which attenuate the signal considerably. Thevalues of F were found to be 10 and 16 dB at 900 MHzand 1700 MHz, respectively. The values of m were foundto be of the same order at both frequencies and were 4when eqn. 4 was used [33]. The signal decay throughsubstantial walls was found to be 1 1 dB higher at1700 MH z that at 900 MHz in Reference 33. These showthat area coverage is greatly reduced at 1700 MH z thanthat at 900 MHz. For an outside to inside path Reference28 compares the median path loss with that over a freespace. It should be noted that in Reference 28 the trans-mitter was located at a height particular to vehicular cel-lular mobile radio systems. It was found that on averagethe median path loss was about 12 dB higher than freespace with a standard deviation of about 2dB in theregion of 900 MHz.The penetration loss has been found to vary between1.5 and 36 dB for this category [18, 22, 261. The mostcomprehensive results for this parameter are given inReference 26 which investigates the effects of windows(shielded or unshielded) and transmitter orientation. Itwas found in Reference 26 that the penetration lossincreased linearly with the departure of the incident wavefrom the perpendicular.The difference between the local mean of a shieldedwindow and a nonshielded window was found to be, onaverage, 7 dB and up to 15 dB for windows with alu-minium shields. The attenuation loss of a wall or a floorwhich was defined as the difference between the theoreti-

cal free space magnitude and the actual received medianlevel was also obtained in Reference 26. These were mea-sured by placing the transmitter and receiver in rooms,one or four floors below or separated by two rooms. Itwas found that the attenuation through concrete wallsand through floors were on average 8.5 dB and 10dB,respectively. The decrease in attenuation by the wallsmay be described physically as the existance of differentmodes of propagation when both the transmitter andreceiver are on the same floor. These modes are diffrac-tion by the doors or wave guiding through the corridors.In Reference 22 , it was found that the attenuation wasgreater in the metal type buildings than in those of woodconstruction. On average at 800 MHz, an attenuation of23 dB was observed for metallic buildings, 9 dB for metalsidings and 3 and 1.5 dB for wood structures. On rareoccasions for wood structures the signal was strongerinside than outside.The spatial distribution over small distances wasfound to be Rayleigh distributed [l8, 22, 26, 281. This isan approximation a depends on the amount of clear-ance between the\ra itter and the receiver. Forexample, for a clear line of sight (LOS) the distributionfollows Rician more closely than Rayleigh. In Reference27, the spati al distribution of the signal was found to beRician with k = -2 . In Reference 28, the large scale dis-tribution, for mostly LO S situations, was found to fit theSuzuki (Rayleigh and log-normal) distribution best, witha standard deviation of 7 dB.The temporal behaviour has been investigated com-prehensively in Reference 27, representing the variationof phase as well as the amplitude of the received signal. Ithas been observed that the motion of personnel aroundthe terminals has a considerable effect on the signalstrength and phase (see Fig. 2) . The cumulative distribu-tions of the temporal variation of the received signal havebeen observed t o follow a Rician distribution with arandom/specular ratio ( K ) between -6.8 and - 1 dB[27]. There have also been cases with Rayleigh distribu-tion.Some results of the comparison of the narrowbandstatistics, between frequencies 900 MHz and 1.7 GH z, arepresented in Reference 43 . For example, the temporalbehaviour is shown to be less dynamic at 900 MHz thanat 1.7 GH z. In fact, the average fading was found, in Ref-erence 43 to be about 10dB higher at 1.7 GHz . The tem-poral distribution was also found, in Reference 43 , to beRician with K ranging from - to - 6 dB at 900 MHzand from - 6 to - 8 dB at 1.7 GHz .Category 4 : Off i cebuildings in urban a reasIn the reviewed references regarding the measurements inoffice buildings, it is not always pointed out where thebuildings under test were located. Hence, the results ofcategory 3 and 4 could be related for the condition of thetransmitter and receiver being inside. This means that weare assuming that there is sufficient building attenuationto make the effects of the surroundings insignificant.The rate of decay has been found to be close to that infree space for distance up to 10m Cl5, 271, however itincreases with distance. In particular, the rate of decay isshown in Reference 29 to vary between 2.6 and 2.9 formeasurements taken on a same floor. On different floors,i.e. keeping the transmitter on one floor and moving thereceiver on floors above and below, it is shown to varybetween 4.7 and 8.6. These are estimated using eqn. 2,hence there is no correcting factor for the floors as in eqn.4. It was found in Reference 28 that, on average, the

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median path loss was about 20dB higher than that offree space with a standard deviation of about 3 dB. Thisis for illuminating a building by a transmitter installed ata height particular to the base station antenna height inthe present cellular mobile radio systems. It is concludedin Reference 28 that this loss is mainly caused by themirror glass windows of the building under test.The penetration loss has been found to vary between 2and 38 dB [14, 17, 23, 27, 291. The value 2 d B corre-sponds to buildings which have 95% glass, i.e. coveredmostly with windows [29]. It should be noted that themethod of estimating the penetration loss is not stated inReference 29. Therefore, this value of penetration lossmay not be compared with other researchers resultsregarding this parameter. A comprehensive investigationof the effects of frequency and height on the penetrationloss fo r this type of building is given in References 30 and34. It is shown that the penetration loss decreases as thefrequency and height increase. The reduction of penetrat-ion loss due to the height is because of a clearer sightbetween receiver and transmitter. However, there havebeen cases observed for which penetration loss hasincreased by moving the receiver to higher elevations.This phenomenon is investigated in Reference 28 leadingto a conclusion that the penetration loss is not entirelydependent on the height, particularly for the LO S situ-ations.The small scale signal variation has been found tofollow the Rayleigh distribution at all frequencies, irre-spective of the transmission condition [28, 30, 341. TheRician distribution has also been observed to fit the mea-sured da ta [29]. The large scale signal variation has beenfound to follow the log-normal [30, 341 and Suzuki dis-tributions [28]. The latter, which is mostly for LO Ssituations, surprisingly shows that there may not be adominant component under such situations. The stan-dard deviation of the log-normal distribution was foundto be strongly dependent on the condition of transmis-sion in References 30 and 34. For example, for non-LOS,the log-normal distribution with standard deviation of4 d B fitted the d ata very well, while for a complete 10sand partial 10s the standard deviations were 8.9 and6.7 dB, respectively. The standard deviation of the largescale signal variation for a given condition of transmis-sion has been also observed to decrease at higher fre-quencies [30, 341.Category 5 : Facto ry buildings with heavy machineryThe most comprehensive results for this category are pre-sented in Reference 36 with some results given in Refer-ences 29 and 45. The measurements in Reference 36 werecarried ou t a t 1300 MHz a t five different factories rep-resenting typical factory buildings with a high density ofequipment and machinery. The surveyed sites were subse-quently divided into four categories as far as the topog-raphy was concerned. These categories were, line of sightwith light surrounding clutter, line of sight with heavysurrounding clutter, obstructed path with light surround-ing clutter and obstructed path with heavy surroundingclutter. These kinds of categorisations are useful insystem planning as far as the relative positions of trans-mitter and receiver antennas are concerned.

In Reference 36, the rate of decay was found to varybetween, 1.9 and 2.43, and, 1.79 and 2.81, over all differentsites and for different topographies, respectively. Thehigher values correspond to the obscured path withheavy surrounding clutter, whereas the lower values cor-respond to the LO S with light surrounding clutter. When

these gradients are compared with gradients of 1.5 to 6,corresponding to ofice buildings, it can be seen that thefactories are less hostile. The lower values of gradient inthe factories could be attributed to a more metallic struc-ture as well as more metallic inventory and machinery,providing the receiver with more intervening signals. InReferences 45 and 29 similar values of rate of decay arepresented.The only available results representing the penetrationloss by buildings in this category are given in Reference29. The penetration loss was measured to vary between 4and 22 dB with 4 dB standard deviation for a factorybuilding with metal siding. It should be noted again thatthe method of estimating the penetration loss is notgiven.Spatial fadings between 20 and 30 dB were observed inReference 36 when the receiving antenna was movedthrough a 1.3m track. The subsequent analysis of thereceived signal distributions showed that the log-normaldistribution was the best fit for signals below the medianand the Rayleigh distribution for other signal levels. Forspecific cases, such as LO S with light surrounding clutter,the Rician distribution with K ratio of - 2 dB was foundto be a better fit to the measured data. For a LO S withheavy surrounding clutter the Rician distribution with Kbetween -4 and -7 dB was found to be a better fit thanother distributions. However, the Rayleigh distributionwas concluded to be the best fit to the overall measureddata.Temporal fading was found to follow the Rician dis-tribution with K of - 10 dB [36]. This agrees with otherresearchers conclusions regarding other categories. Thedynamic range of the temporal fading was found to be ofthe order of 20dB which is 10dB less than those foundby Bultitude [27] for office buildings (see Fig. 2).Category 6 : Other fac tory buildings, sports halls andexhibition centresThe only published results for buildings in this categoryare given in Reference 45, representing results regardingthe rate of decay. The measurements were conducted infactories with lightly equipped surroundings and factorieswith large open areas, e.g. an inspection area forassembled cars. However, it can be assumed that sportshalls and exhibition centres are similar in size and ceilingheight to these types of factories. Hence, the results maybe applicable to sports halls and exhibition centres aswell. The rate of decay was found to vary between 1.39and 3.4 which represents a slightly higher rate of decaycompared with those factories in category 5.Category 7 : Open environment, e.g. railway stations, air-ports, etc.There is no published measured data found by the authorfor this category.Category 8 : Underground, e.g. subways, undergroundstreets, etc.There are relatively few published works for this type ofenvironment. This is, however, an important area inwhich an indoor radio system will have to serve a largenumber of users. There are useful results in References 25and 32 for an underground street which contains shopswith a high density of pedestrians. The only derivedstatistical parameter in References 25 and 32 is theattenuation constant (expressed in dB per 100 m) or thedistance/power law gradient. The results are presentedfor daytime, night-time and vertically and horizontally

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polarised antennas. Fig. 3 [25] shows the variations of ble received signal strengths for both polarised and cross-the received signal strength for different frequencies, pol- polarised antennas. A theoretical analysis is alsoarisations and times. The rate of decay has been found to presented in References 25 and 32, modelling an under-vary between 0.5 and 3.1 and 0.45 and 2.2 for vertically ground street as a waveguide with pedestrians as dielec-and horizontally polarised antennas, respectively. The tric slabs.C2

nigh t f10 GH zCVI.--mD

r 0 50 100 150 200 250 300distance, m

clC0 night f=5.5 GH z.m I

H-polarity 2.3dBl100m

> -maJ

c- V-p ola rit y 4.1 dBllOOmcc -E --r 0 50 100 150 200 250 300

distance,mb

night f = 800 MHzI\

ri ty 8.5 dBllOOm

0 50 100 150 200 250 300distance mL

Cf=210 M H z

H- po la ri ty 58.2 dB lOOm

.V-polarity 73.1 dBllOOm0 50 100 150 200 250 300

distance, md

- 0 50 100 150 200 250 300distance. me

f ~ 5 . 5 HzdaynH- po la ri ty 13.2dB1100m

distance, mf

da y f ~ 8 0 0 HzI

olarity 17.3 dBllOOm

0 50 100 150 200 250 300distance, m9

day f=210 M Hz

distance,mh

Fig. 3 Example of received field strength measured along an underground street in Reference 25bottom of the range corresponds to the frequency band10GHz while the top of the range corresponds to thefrequency band 210 MHz. This is not surprising sinceunderground railways (like corridors in a building) act aswaveguides channelling the signal energy. An interestingresult in Reference 25 is the measured low cross polarisa-tion (20dB lower signal strength in an orthogonalpolarisation) which is in contrast with results of othertypes of indoor environments [54, 291 showing compara-

4.1 Narrowband portable channel modelsThe preceding Section outlined the narrowband measure-ments which have resulted in determining the useful sta-tistical parameters and models over particular types ofbuildings. The wide variability of the values and modelsof these parameters make it difficult to determine exactmodels for different parameters which can be used for alldifferent types of buildings. For example, the rate ofdecay varies between 0.45 and 8.6 depending on the types

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of buildings, the relative position between transmitterand receiver, conditions of transmission, types ofmaterials used in a building and frequency. Penetrationloss also varies widely for different types of buildings aswell as frequencies ranging from -2 to 38 dB. Thesevariabilities which are mainly due to the character istics ofbuildings, as was discussed in Section 4, make systemplanning quite difficult. Alternatively, different modelsmay be classified according to each category as shown inTable 5 (a and b) summarising the narrowband statistics(models) for different categories.It should be noted that the statistics of categories 3and 4 could be related because the author has doubtsabout the location of buildings under test in some of thereviewed references. This approach is useful as it revealsthat the same model of a parameter may be used for dif-ferent categories.

5 Wideband measurementsWhen the data rate of a system is more than the coher-ence bandwidth of the channel, the wideband channelresponse is of concern. All the wideband measurementsregarding the portable channel have been conducted in

the time domain using pulse techniques by which theaverage power delay profile response of the channel canbe measured. From this, useful statistical parameters andmodels can be extracted. Such parameters are root meansquare (RMS) time delay spread, coherence bandwidth,excess time delay, etc. In particular, the R M S time delayspread is an important parameter which can be used toassess the performance of digital systems [55-591.The environment where the terrestrial mobile radiosystems operate is relatively open and usually high powertransceivers are used. The multipath power delay profileof such a channel usually contains significant signal com-ponents at long time delays. In contrast, low powertransceivers would be used in an indoor environment.Owing to this, as well as building attenuation, signalcomponents with significant levels are improbable. Thesurroundings and the motion of scatterers in indoorenvironments have relatively more effects on the channelresponse because of more shadowed transmitter andreceiver antennas. Therefore, it is expected that the multi-path power delay profile in an indoor environment ismore compact but more susceptible to the surroundings.The published measured wideband statistics, in particularthe R M S time delay spread, for the proposed categoriesof Table 1will now be summarised.

Table 5A : Summary of narrowband statistics for portable channelCategory Penetration loss Rate of decaynumber dB Reference Reference

-2-24 [16, 221

- -1.5-36 18, 22, 23, 262-38 [14, 17, 23, 2629, 30, 341

3-3.93 4 . 21 . w . o1.2-6.5422.6-2.9(over one f loor)(over many f loors)1.8-2.41 .&3.40.5-3.1 (V-po l . )0.45-2.2 (H-pol.)10 GHz-210 MHz

-

4.7-8.6

-

Table 5b : Summary of narrowband statistics for portable channelCategory Spatial Temporalnumber

Fading Reference Fading Reference--1 Small scale Rayleigh [221Large scale log -normal [22, 241

4

- - -3 Small scale Rayleigh [18, 22, 26, 281 Rician ~271Large scale Suzuki [281 K=-l -lGd B [27]

(10s)0 = 7 dB [431Small scale Rician K = -2 [27] -Small scale Rayleigh [15, 30, 34, 281 Rician [27. 291~ = 4 - 1 0 B P O . 341 K=-1-16 d B [43]Large scale Suzuki [281(10s)0 = 7 dBLarge scale log -normal K= 10 [361a= 7 .1 dB [361

Large scale log -normal K=-6-11 d B [27]

5 Small scale Rayleigh [36] Rician [29. 361

- -678- - -- - -

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Category I :Residential houses in suburban areasThe only published wideband measurements found bythe author for this category were carried out by Devasir-vatham [39]. The measurements were conducted for tworesidential houses over an inside-outside path a t afrequency of 85 0 MHz. The worst average power delayprofiles (average of eight power profiles over a smalldistance) for these two residences are shown in Figs. 4and 5. The subsequent analysis showed the worst RMStime delay spread of 42 0 ns.

-7 0

- 70

-

-1101 ' ' ' ' ' ' ' ' '0 0.2 0.4 0.6 0.8 1.0 1.2 14 16 1.8t1me.s

Fig. 4measured in Reference 39Residence I : worst case averaged power delay pro@ (no 10s)

-1101 ' ' ' ' ' ' ' ' '0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8t1me.s

Fig. 5in Reference 39Residence 2: worst case averaged power delay profile measured

Over the LOS, RMS time delay spreads of 100 ns wereconsistently measured. The unexpected values of RMStime delay spreads for residential houses show that theprediction of wideband statistics based on the geometryof the buildings may produce misleading results.Category 2 : Residential houses in urban areasThere is no published measured data found by the authorfor this category.Category 3 :Office buildings in suburban environm entsThe wideband measurements carried out for this categoryare the most abundant [37, 38, 39, 42, 431. Fig. 6showsthe worst case power delay profiles measured inside twodissimilar oftice buildings [38]. These were measured bytransmitting +26 dBm and having both transmitter andreceiver inside the two buildings. It is seen from thisfigure that, although the two buildings under test arestated to have been quite different in their structures,their responses are very similar. The similarity betweenthe worst cases of the two buildings suggests that the pre-diction of the time delay spread of the channel within aI EE PROCEEDI NGS -H, V o l . 138, N o . 1, FEBRUARY 1991

building should not be based on the building itself andthe surrounding should also be considered. This is impor-tant when channel models similar to those of GSMmodels [60] are derived for indoor channels, makingsuch channel modelling more difficult. In Reference 39,the measurements were carried out in the same building

t ime,usFig. 6similar buildings measured in Reference 38

~ 1 worst profile in NO~ _ _ _ worst profile in HO H

A comparison of worst-case power delay profiles within two dis-

as one of those in Reference 38 . However, the transmitterwas positioned outside this building in Reference 39 . It istherefore possible to see the variation of the RMS timedelay spread as the transmitter is moved inside for thisparticular building. Such a comparison is the worst caseof RMS time delay spread which was found to be 218 nsand 32 0 ns in References 38 and 39, respectively, rep-resenting the impact on the channel response for differenttransmitter positions. In Reference 42 the measurementwhich were carried out at 1.5 GHz showed a worst caseand median RMS time delay spread values of about50 ns and 25 ns, respectively. These values are very opti-mistic and larger values are expected in such buildings.Category 4 : Office buildings in urban a reasThe wideband channel responses of the buildings fallinginto this category are investigated in References 43 and44 . Interestingly, these two references compare the wide-band statistics of the indoor channel at two frequencies85 0 MHz and 1.7 GH z (in Reference 43 , the frequenciesare 90 0 MHz and 1.7 GHz). In Reference 44 it is shownthat the power delay profiles and the RMS time delayspreads at the two frequencies are very similar. In fact,the regression analysis of the scatter plots of the mea-sured RMS time delay spreads at both frequenciesshowed a linear fit of slope of 1 . The maximum RMStime delay spread of 1 0 0 ns was measured in this type ofbuilding [44]. In Reference 43 similar results wereobtained, however there were differences between theRMS time delay spreads for different buildings. Forexample, in one building the measured RMS time delaysspreads were slightly higher at 90 0 MHz than those at1.7 GHz and in another building it was the other wayround.Category 5 : Facto ry buildings with heavy machineryThe most comprehensive analysis of the wideband sta-tistical parameters for this category are presented in Ref-erences 41 and 46 . Reference 45 also gives some results.In References 41 and 46 the measurements were carriedout in five different factories. The wideband results arepresented in terms of four different topographies as dis-cussed in Section 4 (category 5). Fig. 7 represents typical

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power impulse responses, averaged over small spatial dis-tances for different topographies [41], one of whichshows a component at 80 0 ns time delay ( 8 b ) . It wasfound that, in general, building age, inventory, wall loca-

The measured multipath power delay profiles of thiscategory are relatively shorter than those of category 5.This statement is not, however, statistically valid. Themedian and the worst values of the RMS time delay

a,-s 1.0L05 '-

fac-0 100 2 0 0 300 LOO 500z o

t i m e , n sa-

'.OrL0C

L

$ 0a

t i m e , nsd

L

0.5a5a.-L-

'0 100 200 300 400 500z

t i m e , nse

t i m e , n sb

'0 100 200 300 40 0 500t i m e , n s

CFig. 7a LOS light clutterb LO S heavy clutterc LOS adjacent to fire walld Obstructed light cluttere Obstructed heavy clutter

Typic al fac tory m ultipath power delay proJles measured in Reference 41

tions and ceiling heights are key factors in determiningthe shape and the length of the multipath profile. Themaximum RMS time delay spreads of 30 0 and 15011swere obtained for the LO S and obscured LOS, respec-tively, [46] while the median values varied between 96 nsfor LO S and 105 ns for obscured paths. In Reference 45the analysis of the measurements in the similar type offactories showed lower values of RMS time delay spread.The median of the RMS time delay spread was found tovary between 48 and 53 ns with the worst case of 152 ns.Category 6 : Other fac tor y buildings, sports halls andexhibition centresThe only published wideband measurements for this cate-gory are presented in Reference 45 . The measurementswere carried out in five different factories three of whichfall into this category.

spreads were found to vary between, 15 and 20 ns, and,40 and 146 ns, respectively [45].Category 7 : Open environments, railways, airports, e tc.There is no published measured data found by the authorfor this category.Category 8 : Underground, e.g. subways, undergroundstreets , e tc .There is no published measured data found by the authorfor this category.5.1 Wideband portable channel modelsThe plan for modelling the wideband portable channel isto some extent similar to that of terrestrial mobile radiochannel. This plan consists of two major phases. In thefirst phase, the available data should be used to model

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Table 6: Summary of wideband statistics for portable channelCategory Typical R M S Worst case R M S Time spannumber References Reference ns Reference ns

150-25-1 2525-5019-1 0515-20--

420 [39] 1100 [39]-[391[37, 38. 39. 42.431[43, 441 100[45. 461 40-300 [41, 45,461 -00 [46][451

40-320 [37, 38, 39, 42, 431 -00-600 [37, 39, 421

40-146 [45]--

the channel on small scale basis, e.g. over a building. Thismodelling should be carried out by estimating the sta-tistical parameters such as RMS time delay spread inconjunction with appropriate statistical distributions forindividual paths, e.g. the distributions of amplitude,phase and time delay for each path. In the second phase,the derived small scale statistical parameters should beused to put bounds on their values over the similar typesof buildings (categories). This will lead to large area char-acterisation similar to that of terrestrial mobile radiochannel [61, 621. Alternatively, the measured channelresponse can be used to produce models similar to thoseproposed by GSM [60].Modelling the portable channel based on the distribu-tions of the amplitude, time delay, and phase of the indi-vidual multipath component has been carried out inReferences 63, 64 and 42 . It has been shown that theportable channel exhibits similar behaviour to that of aland mobile radio. That is, the amplitude has a Rayleighdistribution, phase has a uniform distribution and timedelay components follow the modified Poisson distribu-tion [64].Channel models similar to those proposed by G SMfor similar types of buildings are more useful becausecomparisons can be made between different resultsregarding the performance of a particular system when itis tested under different channel conditions. Such com-parisons will result in time efficiency and more reliablesystem design specifications. These models consist ofexponential functions whose numbers, time constants andthe tails depend on a particular type of building. Thereare not many measured wideband channel responseswhich provide such channel models for indoor environ-ments.Table 6 summarises the wideband statististcs, RMStime delay spread and time span for all categories. Timespan (multipath spread) is defined as the time delay of thelast multipath component which has a level within 30 dBof the maximum with respect to first arrival.6 ConclusionsPrevious papers concerning the propagation into andwithin buildings have been reviewed. Narrowband andwideband statistics and channel models particular toportable channels have been presented. The results showthat characterisation of the portable channel is a morecomplex task than that of land mobile radio channel. Forexample, the penetration loss caused by the buildingsconstruction materials has an average value of 20 dB.with a large deviation of 2 G2 5 dB. The more dynamictemporal variation of the received signal (as much as30 dB) in an indoor environment also creates problemsfor a reliable radio link over a given time. The narrow-band statistics have been shown to be frequency depen-dent. For example, at higher frequencies moreI E E P R O C E E D I N G S -H , Vol . 138, N O . 1, F E B R U A R Y 1991

attenuation is encountered in buildings due to the fur-niture, equipment, floors and walls. Consequently, thecoverage is reduced. On the other hand, attenuationdecreases as the frequency increases in corridors of abuilding, underground streets and in general, in environ-ments which can be modelled as waveguides. Similarly,for the type of systems to be implemented in an indoorenvironment, with base stations either inside or outside,the multipath spread of the signal may impose some diffi-culties in realising a simple handset. Although the multi-path power delay profile of the portable channel is morecompact (mult ipath spread of up to 1100 ns) then that ofterrestrial mobile radio channel, but the required bit ratein indoor environment which may be as high as 2 Mb/swill not be supported without some counter measures.For example, reported RMS time delay spreads of up to45011s would limit the da ta rate to some 400 Kb/swithout the need for equalisation.There is still a great need for more narrowband and, inparticular, wideband measurements at frequencies ofinterest to put proper bounds on the statistical valuesand produce comprehensive channel models. The mea-suring system should be capable of producing either nar-rowband or wideband data at different frequencies fordirect comparison and hence a more efficient systemdesign. More measurements should be carried out overdifferent types of building which will eventually produceadequate data for individual groups of buildings. Thecondition of transmission, i.e. the relative position oftransmitter and receiver, also has effects on the receivedsignal statistics. Measurements with different condition oftransmission would facilitate intelligent service planningfor different types of buildings. For example, owing toexcessive attenuation for large office buildings it may benecessary to install the base stations inside. On the otherhand, it may be more useful to have the base stationsoutside in residential areas. Future systems may have cellsizes ranging between 50 and 500 m therefore the futuremeasurements should cover a variety of distances.The following measurements and plans are required t omodel the portable channel as close to a practical situ-ation as possible:(i) measurements with a transmitter outside and recei-ver inside for categories 3, 4, 5 and 6 to obtain param-eters such as the rate of decay; attenuation due tomaterial of the buildings, etc.(ii) measurements for determining the penetration lossin basements where excessive attenuation has beenobserved(iii) measurements over a greater range covering dis-tances up to 500 m(iv) measurements both wideband and narrowband inareas like shopping centres sports halls and under-grounds (category 7 and 8) where the density of peoplemoving about is much higher and the constructionmaterial is quite different from that of office buildings

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and residential houses. In fact, to date, there are nopublished results available describing the statistics ofsuch environments apart from some narrowband mea-surements for category 8. However, these are placeswhich will have a high demand for radio services. In par-ticular, when there are exhibitions held or major eventsare taking place(v ) measurements with fixed transmitter and receiverto determine the temporal variation of the received signalover longer periods of time. This will reveal the extent ofthe fading for differently populated buildings, in particu-lar, for places where there is a burst of populationmoving around(vi) measurements with transmitting antenna placed ata ceiling height and receiving antenna at a normal height

( 1 .&1.8 m). This may produce less temporal fading due tothe personnels and hence a reduction in fade marginresulting in a higher system capacity. Such measurementshave been conducted using leaky feeders [29].(vii) Measurements to determine more accurately theattenuation loss caused by the walls and floors in a build-ing. This has an important implication in frequency reuseplanning.(viii) a universal definition of the narrowband andwideband statistical parameters of the received signal.(ix) presentation of results in a similar manner to facili-tate direct comparisons, e.g. plot of power delay profile indB scale.Finally, the statistics and channel models presented inthis paper have been based on few measurements. Thefuture measurements and plans such as those outlinedabove should provide adequate information for produc-ing statistically valid bounds on the values of the sta-tistical parameters and for deriving more practicalchannel models.7 AcknowledgmentsThe author wishes to thank the DTI for support infunding this work. He also wishes to acknowledge Pro-fessor P.A. Matthews for his advice during preparation ofthis paper.8 References1 SWAIN, R.S. : Cordless telecommunications in the UK, British2 MOTLEY, A.J.: Advanced cordless telecommunications service,3 COX, D.C.: Universal portable r adio communications, I EEETrans. , 1985, VT-34, (3), pp. 117-1214 COX, D.C.: Universal digital portable radio communications,Proc. IEEE, 1987,75, (4), pp. 43 647 75 COX, D.C.: Universal digital portable communications: A systemperspective,I EEE J., 1987, SAC-5, (5), pp. 764-7736 STEEL, R.: Towards a high-capacity digital cellular mobile radiosystem, I E E Proc. F, 1985, 132, (S), pp. 405 41 57 CHIA, S.T.C., STEEL, R., GREEN, E., and BARAN, A.: Propaga-tion and bit er ror ratio measurements for a microcellur system, J. ofInst. Electron. and Radio Engineers, 1987, 57, (6) (Supplement), pp.8 WHITTEKER, J.H.: Measurements of path loss at 910 MHz forproposed microcell urban mobile systems, IEEE Trans. , 1988,9 HARLEY, P.: Short distance at tenuation measurements at

900 MHz and 1.8 GH z using low antenna heights for microcells,10 BULTITUDE, R.J.C., and BEDAL, G.K.: Propagation character-istics on microcellular urban mobile radio channels at 910 MHz,11 RUSTAK O, A.J., AMITAY, N., OWENS, G.J., and ROMA N, R.S.:Propagation results at 11 GH z for microcellular radio, Electron.Le t t . , 1989, 25, (7), pp. 453 454

Telecom Technol . J. , 1985,3, (2), pp. 32-38IEEE J., 1987, SAC-5, (5), pp. 7 74 782

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VT-37, (3), pp. 125-129

IEEE J . , 1989, SAC-7, (l) , pp. 5-1 1

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12 GURD ENLI, E., HUISH , P.W., KING, L.E., and NICHOLLS,M.J.: Land usage factors in mobile radio propagation prediction.Fourth Int. Conf. on Land Mobile Radio, University of Warwick,Coventry, 15th-17th December 1987, pp. 97-10513 MOLKDA R, D., and MATTHEWS, P.A.: Measurements a ndcharacterisation of the U HF mobile radio channel, Part 1: measure-ments over the band 853-885 MHz, IERE J . , 1988, 58, (6)(Supplement), pp. 145-15614 RISE, L.P.: Radio transmission into buildings on 35 and 150 MHz,Bell S ys . Tech . J. , 1959,383, (l) , pp. 197-21015 TSUJIMURA, K., and KUWABARA, M.: Cordless telephone andits propagation characteristics, IEEE Trans. , 1977, VT-26, (4), pp.16 WELLS, P.I.: The attenuation of UHF radio signals by houses,

IEEE Trans. , 1977, VT-26, (4), pp. 358-36217 KOMURA, N., HOGIHIRA, T., and OGASAWARA, M.: Newradio raging system and its propagation characteristics, IEEETrans. , November 1977, VT-26, pp. 362-36618 HOF FMAN , H.H., and COX, D.C.: Attenuation of 900 MHz radiowaves propagation into a metal building, IEEE Trans. , 1982,19 ALEXANDER, S.E.: Radio propagation within buildings at900 MHz, Electron. L et t . , 1982, 18, (21), pp. 913-91420 ALEXANDER, S.E., and PUGLIESE, G.: Cordless communica-tion within buildings results of measurements at 900 MHz and60 GHz, Brit ish Telecom Technol . J. , 1983, 1, (I) , pp. 99-10521 ALEXANDER, S.E. Characterising buildings for propaga tion at900 MHz, Electron. L et t . , 1983, 19, (20), pp. 86022 COX, D.C., MURRAY, R.R., and NORRIS, A.W.: Measurementsof 800-MHz radio transmission into buildings with metallic walls,Bell Sys . Tech . J ., 1983,62, (9), pp. 2695-271723 WALK ER, E.H.: Penetra tion of radio signals into buildings in thecellular radio environment, Bell S y s . Tech . J ., 1983, 62, (9), pp.2719-273524 COX, D.C., MURRAY, R.R., and NORRIS, A.W.: 800-MHzattenuation measured in and around suburban houses, Bell Sys .Tech. J ., 1984,63 , (6), pp. 921-95525 YAMAGUCHI, Y., ABE, T., and SEK IGU CHI, T.: Experimentalstudy of radio propagation characteristics in an underground streetand corridors, IEEE Trans. , 1986, EMC-28, (3), pp. 148-15526 HORIKO SHI, J., TANAKA, K., and MORINAGA, T.: 1.2 GHzband wave propagation measurements in concrete building forindoor radio communications, IEEE Trans. , 1986, VT-35, (4), pp.146-15227 BULTITUD E, R.J.C.: Measurements, characterisation and model-ling of indoor 800/900 MHz radio channels for digital communica-tions, IEEE Communications Magazine, 1987, 25, (6), pp. 5-1228 BARRY, P.J., and WILLIAMSON, A.G.: Modelling of UHFradiowave signals within externally illuminated multi-storey build-ings, J . I E R E , 1987,57, (6) (Supplement), pp. S231-S24029 CAMWEL, P.L., and McROY, J.G.: Experimental results of inbuilding anisotr opic propagation at 835 MHz using leaky feedersand dipole antenna. IEEE MONTECH 87 Conf., Montreal,Canada, 9th-11th November 1987, pp. 213-21630 TU RKMANI , A.M.D., PARSONS, J.D., and LEWIS, D.G.: Radio

propaga tion into buildings at 441, 900 and 1400 MHz. Fourt h Int.Conf. on land mobile radio, 15th-17th December 1987, Universityof Warwick, Coventry, Publ. 78, pp. 129-13931 ALEXANDER, S.E.: 900 MHz propagation within buildings. IEE2nd Int. Conf. on Radio Spectrum Conservation Techniques, May1984, pp. 51-5532 YAMAGUCHI, Y., ABE, T., and SEK IGUCHI , T.: Radio propa-gation characteristics in underground streets crowded with ped-estrians, IEEE Trans. , 1988, EMC-30, (2), pp. 13LL13633 MOTLEY, A.J., and KEENAN, J.M.P.: Personal communicationradio coverage in buildings at 900 MHz and 1700 MHz, Electron.Let t . , 1988, 24, (12), pp. 763-76434 TURKMANI, A.M.D., and PARSONS, J.D.: Measurement ofbuilding penetration loss on radio signals at 441, 900, and1400 MHz, J . I E R E , 1988,58, (6) (Supplement), pp. 169-17435 OWEN, F.C., and PUNDEY, C.D.: In-building propagation at900 MHz and 1650 MHz for digital cordless telephone. 6th Int.Conf. on Antenna and Prop., ICAP 89, Part 2: Propagation, pp.27628 136 RAPPAPO RT, T.S., and Mc GILLEM, C.D.: UHF fading in facto-ries, IEEE J., 1989, SAC-7, (l ), pp. 4 W 837 DEVASIRVATHAM, D.M.J. : Time delay spread measurements ofwideband radio signals within a building, Electron. Le t t . , 1984, 20,(23), pp. 95LL95 138 DEVASIRVATHAM, D.M.J.: A comparison of the time delayspread measurements within two dissimilar office buildings. IEEEInt. Conf. on Communications, June 22nd-25th 1986, Toronto ,Canada, pp. 852-856

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39 DEVASIRVATHAM, D.M.J .: Time delay spread and signal levelmeasurements of 85 0 MHz radio waves in building environments,IEEE Trans. , 1986, AP-34, (ll), pp. 1300-130540 DAVASIRVATHAM, D.M.J.: Multipath time delay spread in thedigital portable radio environment, IEEE Communicat ion Maga-zine, 1987, 25, (6), pp. 13-2141 RAPPAPORT, T.S., and McGILLEM, C.D.: Characterising theUHF factory radio channel. Electron. Lett., 1987, 23, (19), pp. 1015-101742 SALEH, A.A.M., and VALENZUEL, R.A.: A statistical model forindoor multipath propagation, IEEE J., 1987, SAC-5, pp. 128-13743 BULTITUDE, R.J.C.: A comparison of indoor radio propagationcharacteristics at 91 0 MHz and 1.75 GHz, IEEE J., 1989, SAC-7,44 DEVASIRVATHAM, D.M.J.: Time delay spread measurements at85 0 MHz and 1.7 GHz inside a metroplitan ofice building, Elec-tron. Lett., 1989, 25, (3), pp. 194-19645 PAHLAVAN, K., GANESH, R., and HOTALING, T.: Multipathpropagation measurements on manufacturing floors at 91 0 MHz,Electron. Lett., 1989,2 5, (3), pp. 225-22746 RAPPAPORT, T.S.: Characterisation of UHF multipath radiochannels in factory buildings, IEEE Trans. , 1989, AP-37, (ti),pp.47 FARMER, R.A., and SHEPHERD , N.H.: Guided radiation . . . thekey to tunnel talking, IEEE Trans. , 1965, VC-14, pp. 93-10248 MARTIN, D.J.R. : Radio communication in mines and tunnels,Electron. Lett., 1970, 6 , (18),pp. 563-56449 CHIBA, J., INABA, T., KUWAMOTO, Y., BANNO, O., andSATO, R.: Radio communication in tunnels, IEEE Trans. , 1978,50 DERYCK, L.: Natural propagation of electromagnetic waves intunnels, IEEE Trans. , 1978, VT-27, (3), pp. 145-15051 MARTIN, D.J.R.: Leaky feeder communication in tunnels, W i r e -less World,88, 1982, pp. 33-37, 7G7552 CHIBA, J., and SUGIYAMA, K.: Effects of trains on cutoff fre-

quency and field in rectangular tunnel as waveguide, IEEE Trans. ,53 ISHII, T.K.: RF propagation in buildings, in Radio frequencydesign. Vol. 12, Pt. 7, 1989, pp. 45-4954 COX, D.C., MURRAY, R.R., ARNOLD, H.W., NORRIS, A.W.,and WAZOWICS, M.F.: Cross-polarisation coupling measured for800 MHz radio transmission in and around houses and large build-ings, IEEE Trans. , 1986, AP-34, (l ), pp. 83-8755 GLANCE, B., and GREENSTEIN, L.J.: Frequency selective fadingeffects in digital mobile radio with diversity combining, IEEETrans. , 1983, COM-31, (9), pp. 1085-109456 BAILEY, C.C., and LINDENLA UB, J.C.: Further results concern-ing the effect of frequency selective fading on differentially coherentmatched filter receivers, IEEE Trans. , 1968, COM-16, pp. 749-75157 CHUANG, J.C.-I.: Simulation of digital modulation on portableradio communication channels with frequency selective fading,

(11,PP. 2 ~ 3 0

1058- 1069

MTT-26, (6), pp. 4 3 9 4 3

1982, MTT-30, (5), pp. 757-759

Proc. IEEE Glo-becom 8, Houston, lst4th December, 1986, pp.112G112658 BELLO, P.A., and NELIN, B.D.: The effect of frequency selectivefading on the binary error probabilities of incoherent and differen-tially coherent matched filter receivers, IEEE Trans. , 1963, CS-11,pp. 170-18659 JAKES, W.C.: Microwave mobile communications (John Wiley &Sons) 197460 GSM Recommendation on Channel Models: Propaga tion condi-tions, COST207, TD(86)51, rev. 3 (GSM/WP2 Doc. 40/87)61 MOLKDAR, D., and MATTHEWS, P.A.: Measurements andcharacterisation of the mobile radio channel, Part 2, character-isation over the band 869-877 MHz, I ERE J., 1988, 58, (6)(Supplement), pp. 157-16862 BAJWA, A.S., and PARSONS, J.D.: Large area characterisation ofurban UHF multipath propagation and its relevance to the per-formance bounds of mobile radio systems, IEE Proc. F, 1985, 32,63 SEXTON, T.A., and PAHLAVAN, K.: Channel modelling andadaptive equalisation of indoor radio channels, I EEE J., 1989,64 GANESH, R., and PAHLAVAN, K.: On arrival of paths in fadingmultipath indoor radio channels, Electron. Lett., 1989, 25, (12),

(2), pp. 99-105

SAC-7, (I), pp. 114-121

pp. 763-765

9 Further reading65 RAPPAPORT, T.S.: Indoor radio communications for factories ofthe future, IEEE Communicat ion Magazine, May 1989, pp. 15-2466 DEVASIRVATHAM, D.M.J. Multipath time delay jitter measuredat 850MHz in the portable radio environment, IEEE J., 1987,67 COX, D.C., MURRAY, R.R., and NORRIS, A.W.: Antenna height

dependence of 80 0 MHz attenuation measured in houses, IEEETrans. , 1985, VT-34, (2), pp. 108-1 1568 WHITE, P.D., GURCAN, M.K., and MACAMEE, R.J.G.:900 MHz digital cordless telephone, IEE Proc. F, 1985, 132, (5),pp. 425-43269 BARRY, P.J., and WILLIAMSON, A.G.: Radiowave propagationinto and within a building at 92 7 MHz, Electron. Lett., 1987, 23, ( 5 ) ,70 RAPPAPORT, T.S.: Delay spread and time delay jitter for theUHF factory multipath channel. 38th IEEE Vehicular TechnologyConference, Philadelphia, 15th-17th June 1988, pp. 1 8 6 1 8 971 PALMER, D.A., and MOTLEY, A.J.: Controlled radio coveragewithin buildings, Brit ish Telecom. Technol . J . , 1986,4 , (4), pp. 55-5872 MOTLEY, A.J., and PALMER, D.A.: Reduced long-range signalreception with leaky feeders, Electron. Lett., 1983, 19, ( I Q pp. 714-715

SAC-5, (5), pp. 855-861

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I EE PROCEEDI NGS -H, Vol . 138, N o . I , F E B R U A R Y 1991 73

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