PROPAGATION IN URBAN MICROCELLS WITH HIGH RISE BUILDINGS

Transcription

1 PROPAGATION IN URBAN MICROCELLS WITH HIGH RISE BUILDINGS K. Rizk +, A. Mawia *, J.-F. Wagen #, an F. Gaiol + +LEMA, Swiss Feeal Institute of Technology, 1015 Lausanne, Switzelan (izk@lemahp6.epfl.ch, gaiol@lema.epfl.ch) *KPN Reseach, PO BOX 421, 2260 AK Leischenam, Nethelans (A.Mawia@eseach.ptt.nl) #Swiss TELECOM PTT, FE 421, 3000 Ben 29, Switzelan (wagen_j@vptt.ch) Abstact In this pape 2D an 3D ay-tacing-peictions base on UTD ae compae to measuements in uban micocellula envionments chaacteize by an iegula mixtue of builing heights ue to the pesence of elatively high ise builings. It is shown that the 2D ay-tacing uneestimates the measuement in aea fa fom the tansmitte. The theoetical stuy an the peliminay compaisons with measuements in Rotteam (NL) showe that the 3D backwa iffaction by high ise builings might account fo the popagation in aea fa fom the tansmitte an ovecome the limitation of the 2D moel in these aeas. Tees wee foun to influence heavily the 2D peiction. Taking into account the same 3D contibutions becomes even moe impotant when thee ae obstuctions such as tees in the 2D plane. A easonable ageement with measuement can be obtaine with a combine 3D an 2D (consieing the absoption effects of tees) peictions. I. INTRODUCTION Accuate path loss peictions in uban micocellula envionments ae equie to impove the planning of emeging high capacity cellula netwoks. Two imensional (2D) ay-tacing fo popagation peiction in micocells simplifies the envionment by consieing infinitely high builings, an thus leas to elatively fast computation at the expense of neglecting the effects of popagation ove the ooftops [1]. At some istance fom a base station, compaisons between measuements pefome in a micocellula envionment (tansmitte below ooftops) in Ben (Switzelan) an 2D ay-tacing peictions showe that the compute 2D contibutions (eflection an iffaction) uneestimate the measuements. The missing contibutions ae expecte to come fom scatteing on builing walls o moe pobably fom ove ooftop popagation. Maciel, Betoni an Xia [2] use the multiple half sceen appoach to account fo the enegy taveling fowa ove ooftops fom the tansmitte to the eceive. Cichon, Kune an Wiesbeck [3] applie the Unifom Theoy of Diffaction (UTD) to account fo the popagation in the vetical an tansvesal planes containing the tansmitte an the eceive. Outsie these two planes, only fist oe scatteing contibutions wee accounte fo. In this pape 2D an 3D ay-tacing-peictions base on UTD ae investigate. Up to thi oe combinations of eflections by vetical builing walls an iffactions by hoizontal builing weges ae consiee in the whole 3D space, i.e., not only in the vetical plane containing the tansmitte an eceive as in [3]. As oppose to [2] this pape stuies ove ooftop popagation in envionments with an iegula mixtue of builing heights. The 2D an 3D ay tacing methos use hee ae biefly pesente in section II. Section III pesents a theoetical investigation of ove ooftop popagation in micocellula envionments. The measuements ae escibe in section IV. Compaison between aoun builings (2D) an ove ooftop (3D) peictions an measuements ae pesente in section V. Finally section VI aws conclusions on some popagation phenomena in micocells. II. MODEL DESCRIPTION The 2D ay tacing algoithm investigate accounts fo all combinations of eflecte ays by builing walls an iffaction by builing cones up to a cetain peetemine oe. Abitay layout of builings can be hanle. The absoption effects of tees ae also consiee in the moel as escibe in section V. The 3D ay tacing package we ae using (FiPe) is a UTD base popagation peiction tool of Technical Univesity of Einhoven. It was oiginally evelope fo application in Satellite communication systems fo etemining site shieling effects [8-9]. Late on it was evelope futhe in coopeation with KPN Reseach fo application to teestial mobile systems [10]. In this wok we ae using a subset of FiPe peiction, i. e., the ove ooftop component. Thus ou 3D package accounts fo combinations of eflecte an iffacte ays in the 3D space up to an oe of thee. Reflections occu on the vetical builing walls. Reflections by builing ooftops ae not consiee. Abitay layout of flat ooftop builings can be hanle. In this pape, since we ae only inteeste in ove ooftop contibution, we o not consie the iffaction by the vetical weges of builings. At least one iffaction is involve in any ay path. In both the 2D an 3D algoithms eflecte wave fiels ae compute accoing to the well known fomula fo the Fesnel eflection coefficient fo vetical polaization. The epolaization effects ae neglecte. The heuistic extension of the UTD vali fo a wege with impeance faces [5] is use to account fo the iffaction. In the 3D algoithm, a slope iffaction [6] component is consiee when ouble iffaction occus on the same builing ooftop. The electical paametes attibute to the builing walls in both the 2D an 3D peictions wee 5 fo the elative pemitivity an 10-3 [S/m] fo the conuctivity. These values, easonable fo builing mateial, wee foun to give a goo fit between peictions an measuements in Ben [1] an Fiboug in Switzelan.

2 In the 2D peictions all combinations of eflecte an iffacte ays ae accounte fo up to nine eflections an one iffaction pe path. The oe of eflection was fixe to ensue that a highe oe of eflection will not change the esult of the peictions. III. THEORETICAL INVESTIGATION OF OVER ROOFTOP PROPAGATION This section focuses on the two scenaios shown in Fig. 1. The two scenaios illustate an example of backwa an fowa popagation by a high ise builing. The tem fowa popagation enotes the mechanism in which the enegy tavels in the vetical plane containing the tansmitte an the eceive in a fowa way fom the tansmitte to the eceive as stuie in [2]. The tem backwa popagation enotes any othe mechanism in an outsie the vetical plane containing the tansmitte an the eceive. The mechanism epicte in Fig. 1(a) is an example of backwa popagation in the vetical plane. Obviously, many othe backwa popagation scenaios coul exist in a eal envionment. Ove ooftop popagation when builings have the same height o when the tansmitte is at the same as the builings is not consiee in ou stuy since the UTD fomulas consiee hee cannot be applie when successive iffactions occu in the tansition egion. At least two iffactions ae involve in each of the scenaios shown in Fig. 1. The iffactions occu at angles whee it was athe ifficult to eive a simple accuate analytical expession to account fo the ove ooftop loss consieing all the geometical paametes escibing the envionment. Instea, we pefome peictions in the two scenaios illustate in Fig. 1 consieing iffeent geometical paametes fo the envionment. Base on these peictions, a qualitative analysis of the influence of the iffeent geometical paametes escibing the envionment is given below. Fo the backwa popagation scenaio shown in Fig. 1(a) six geometical paametes ae equie to compute the path loss at the eceive L Rx : 1, 2, h av,, h Tx an w. Fo the fowa popagation scenaio shown in Fig. 1(b) anothe paamete w bl is also equie. We consie the vaiation of: a) the elative height of the high ise builing fom 3 to 30m, b) the aveage builing height h av fom 10 to 25m an c) the istance between the tansmitte an the eceive 2 fom 100 to 1000m. Two steet withs w 10 an 20m wee consiee. The elative base station height h Tx is set to 5m an 1 to 15m. Fo the fowa popagation case a h Tx equal to 2m was also consiee. Tiple iffaction oes not occu in the tansition egion fo the paametes consiee. Fig. 2 shows an example of the esults. The obseve ten of the fiel stength at the eceive L Rx ue to backwa an fowa iffaction by a high ise builing ae summaize in Table 1. Table 1 The obseve ten of the fiel stength at the eceive L Rx ue to backwa an fowa iffaction by a high ise builing in tems of the geometical paametes of the envionment (Fig. 1) Paametes of the Vaiation of Comments env. L Rx h av : 10-25m 6B the angle β (Fig. 1) becomes less : 3-30m 6B (see note below) 2 : m ~15-25B h Tx : 2-5m no vaiation w : 10-20m no vaiation favoable the iffaction by the high ise builing becomes lowe Note: In the fowa popagation scenaios the influence of the high ise builing becomes geate fo a high aveage builing height (h av ) an when the tansmitte is locate nea the tansmitte (2 ). In all the compute backwa popagation scenaios the ominant ay was the ay oubly iffacte by the high ise builing an then by eithe wege P o P shown in Fig. 1. In most of the fowa popagation scenaios compute the ominant ay was the tiple iffacte ay ove the high ise builing an then by eithe wege P o P shown in Fig. 1. When the high ise builing is at less than 50 m fom the steet in which the eceive is locate the ouble iffacte an then eflecte once becomes ominant. It is expecte that futhe than 50 m an up a to cetain istance the ouble iffacte an then ouble eflecte ay will ominate ove the tiple iffacte ay. The tiple iffacte ay will only ominate in the aea fa fom the tansmitte. Howeve, ou 3D softwae oes not account fo ays with an oe geate than 3. The UTD peicts the contibution of the fowa iffaction to be about 15 B less than the backwa iffaction as seen fom Fig. 2. When applying the 3D algoithm to a eal envionment as in section V we will see that othe scenaios of backwa popagation by high ise builings coul exist leaing to less attenuation than the backwa scenaio shown in Fig. 1(a). IV. MEASUREMENTS The measuements wee pefome by KPN Reseach in August 94 in thee main cities of the Nethelans: Rotteam, the Hague an Amsteam. The measuements use thee iffeent tansmitte heights: 8, 11 an 15 m. The fequency was 945 MHz. A secto aveaging was applie on the measuement evey 10 m. In Fig. 3 the measuements in Rotteam ae shown as a function of the istance to the tansmitte on a log-log scale. The tansmitte height is 8 m. The epenency on the istance is not obvious especially in the aea nea the tansmitte (istance<500m). Although not shown hee, it was obseve that the epenency on the istance is weake in Rotteam which pesents a moe iegula mixtue of builing heights than the Hague. The weak epenency on the istance in both cities shows that

3 moe eteministic moel than the conventional empiical single o ual slope moels ae neee to accuately peict the coveage in uban micocells. V. COMPARISON WITH MEASUREMENTS IN ROTTERDAM This section pesents a compaison between ou 2D an 3D peictions an some measuements in Rotteam fo a tansmitte height of 8m. The map of the aea consiee in Rotteam an the obsevation oute ae shown in Fig. 4. The black ots epesent the 300 measuement points. The point numbes ae shown evey 5 points. The istance between two successive measuement points is about 10m. The peiction aea is 800x800m 2 an contains about 400 builings. The total numbe of builing walls is A ough layout of the tees is also shown. The 2D peictions with an without consieing tees ae compae to measuements in Fig. 5. The 2D peictions without consieing tees oveestimates the measuements along all the measuement oa even in the line of sight of the tansmitte (measuement point numbes an in Fig. 4). The oveestimation is most pobably ue to the tees suouning the tansmitte. In fact, a ough map of the tee locations was intouce in the 2D ay tacing algoithm as shown in Fig. 4. In the liteatue, tees ae epote to have an absoption [6] an scatteing [7] effects. None of these efeences was applie to micocellula popagation. Hee only the absoption effect is consiee. The efeence [6] epots an aveage absoption loss of 1.8 B pe mete fo tees with foliage at a fequency of 900 MHz. Howeve in [6] the stuy consiee a elatively shot path though tees: fom 2 to 15 m. In a micocell envionment the passage of the ay though tees coul vay fom a few metes to a few hune metes. The following appoximation of the tee loss L tee was foun to aequately coect the eo ue to tees: L tee = log( tee ) [B], tee 1m L tee = 1.8 [B], tee <1m whee tee is the passage of the ay though tees. This expession fits the esults epote in [6] fo shot passage though tees but oes not incease as apily fo tee > 15m. When tees ae consiee in the 2D peictions, an obvious impovement is notice in the line of sight (measuement point numbes an in Fig. 4) an in vetical steets (e. g., measuement point numbes 1-35 an in Fig. 4). Fig. 5 shows clealy the effects of vegetation on micocellula popagation. Futhe investigation is neee to etemine how the absoption vaies in tem of tee kin an the level of etails in which tees have to be escibe. In Fig. 6 the 3D contibution is ae to the 2D peiction consieing the tees. In Fig. 6 the 3D contibution was only compute on the measuement points: 35-45, an The emaining points lie eithe in the line of sight o in vetical steets. In these aeas the 2D contibution is expecte to account fo the popagation phenomena an thus thee is no nee to consie the 3D contibution. Compaison between the 2D peictions attenuate by the tees (thick black line in Fig. 5) an the combination between the 2D peictions consieing tees an 3D peictions (thick black line in Fig. 6) shows that on the measuement points 35-45, an the measuements ae bette matche by the 3D peictions that the 2D ones. Thus, the 3D popagation is foun to account fo the popagation whee the 2D contibution is too low. In Rotteam, tees has le the 2D contibution to vanish aleay in the fist paallel steet (measuement points numbe ). The emaining ivegence between measuements an the 3D contibution, when it ominates (e. g., measuement point numbes in Fig. 4), coul be ue to the limite oe (thee) use in the 3D computation. In fact, as mentione in section II, the oe of eflection must be chosen to ensue that a highe oe will not change the esult of the peictions. Unfotunately ou 3D softwae cannot account fo contibutions with an oe of eflection highe than thee. Howeve, on the measuement points 35-45, , , the noticeable impovement obseve of the peiction when the eflection oe was incease fom 2 to 3 (not shown hee fo lack of space) tens to show that a highe oe is neee. The 3D peictions ae then expecte to be highe on measuement points 35-45, an an thus woul be close to the measuements. On measuement points an oe highe than 3 is not expecte to change the 3D peiction, which aleay fits the measuement, as the two an thee-oe-peictions wee foun to be close to each othe. On measuement points the 2D an 3D contibution ae simila an both fit the measuements. When the tansmitte is neithe locate in the line of sight no in a vetical steet no in the fist paallel steet (in case of low ensity of tees, othewise in any paallel steet) both 2D an 3D contibution have to be compute an the stongest contibution has to be consiee. The 3D contibution becomes moe impotant when thee ae obstuctions in the 2D plane such as tees. Fig. 4 shows the ominant 3D ay fo thee chosen locations. Thus, the mechanism of 3D popagation is thus bette unestoo. It is shown that the backwa popagation, as efine in section III, is the ominant mechanism. This mechanism is somewhat simila to the 2D mechanism in the sense that eflections by builing walls ae eplace by iffactions by the hoizontal weges of builings. When the hoizontal wege on which the iffaction occus is highe than the aveage builing height, i. e., when it occus on elatively high ise builings, the enegy is not obscue by othe builings an thus eaches aeas fa fom the tansmitte with elatively low attenuation. VI. CONCLUSIONS In this pape ove ooftop popagation in envionments with an iegula mixtue of builing heights ue to the pesence of elatively high ise builings was investigate. The theoetical stuy an the peliminay compaisons with measuements in Rotteam showe that the backwa iffaction mechanism by a high ise builing, as efine in section III, might account fo the popagation in aeas fa fom the tansmitte an theefoe ovecome the limitation of

4 the 2D moel in these aeas. Taking into account the 3D contibution becomes even moe impotant when thee ae obstuctions in the 2D plane such as tees. The theoetical investigation consieing canonical scenaios, peicts the contibution of the fowa iffaction to be less impotant than the backwa iffaction. Futhe compaisons between highe oe 3D peictions an measuements ae neee to etemine une which conitions the backwa o fowa popagation ominates in a eal envionment. The influence of combine hoizontal/vetical wege iffactions, not consiee in this stuy, nees also to be investigate. Tees wee foun to influence heavily the 2D peiction. Taking into account the tee absoption effects impove the 2D peictions. A easonable ageement with measuement can be obtaine with combine peictions using both 3D an 2D (incluing the absoption effects of tees) peictions. ACKNOWLEDGMENT The authos acknowlege the kin pemission of Pof.. G. Bussaa of the Technical Univesity of Einhoven given to us fo using FiPe in this collaboative eseach. The fist autho woul like to thank KPN Reseach fo poviing a thee months intenship uing which the majo pat of this wok was caie out. [1] K. Rizk, J.-F. Wagen an F. Gaiol, Ray Tacing Base Path Loss Peiction In Two Micocellula Envionments, Poceeings IEEE PIMRC 94, Septembe 18-23, 1994, The Hague, Nethelans. [2] L. R. Maciel, H. L. Betoni an H. H. Xia, Unifie appoach to peiction of popagation ove builing fo all anges of base station antenna height, IEEE Tans, Veh. Technol., vol. 42, pp , 1993 [3] T. Kune, D. J. Cichon, an W. Wiesbeck, Concepts an esults fo 3D igital teain-base wave popagation moels: An oveview, IEEE J, Selecte Aeas Commun., vol. 11, pp , 1993 [4] Luebbes R. J. Finite conuctivity unifom GTD vesus knife ege iffaction in peiction of popagation path loss, IEEE Tans. AP, Vol. 32, No. 1, pp , Jan [5] R. G. Kouyoumjian,. The geometical theoy of iffaction an its applications, in R. Mitta, eito, Numeical an asymptotic techniques in electomagnetic, Spinge-Velag, Belin, [6] W. J. Vogel an J. Golhish Tee attenuation at 869 MHz eive fom emotely pilote aicaft measuements, IEEE Tans. AP, Vol. 35, pp , 1987 [7] C. Matzle Micowave (1-100 GHz) ielectic moel of leaves, IEEE Tans. Geoscience an Remote Sensing, Vol. 32, pp , 1994 [8]van Dooen, G.A.J. & Sfoza, M., "FiPe: a Peiction tool fo the planning of Mobile an Fixe Satellite Communication Sevices", Poc. IEEE 1st Symposium on VT in the Benelux, pp , [9]van Dooen, G.A.J.: Ph.D. thesis at Technical Univesity of Einhoven. "A eteministic appoach to the moeling of electomagnetic wave popagation in uban envionments" [10] Klaassen, M.G.J.J., Mawia, A.: "A eteministic moel fo the planning of micocellula mobile aio communication systems", PIMRC94, pp , The Hague, 1994 REFERENCES h b l (a ) P P w b l (b ) w h a v h T x 1 2 b u il in g R x T x 1 2 h a v β b u il in g R x Fig. 1. Two scenaios of ove ooftop popagation in a Micocellula envionment ue to a high ise builing: (a) backwa an (b) fowa iffaction - Path loss [B] =3m =30m Backwa w=20m h av =15m h Tx =5m 1=15m w bl =20m -170 =30m =3m -180 Fowa [m] 1000 Fig. 2. Vaiation of the path loss ue to backwa an fowa iffaction by a high ise builing in tems of the elative height of the high ise builing an the istance between the tansmitte an the eceive 2 (see Fig. 1). - Path loss + 42 [B] Rotteam istance [m] Fig. 3. Measue secto aveages signal (ots) vesus the istance to the tansmitte in Rotteam (Nethelans)

5 Fig. 4. Map of Rotteam. The coss inicates the positions of the tansmitte. The squae ots inicate the 300 measuement locations numbee by steps of 5. The hatche polygons epesent the tees. The six builing gay levels inicate six levels of builing heights: fom up to 10m (light) to moe than 35m (ak). The ominant ay in the 3D peiction is shown on thee obsevation points. The lettes an enote eflection an iffaction - Path loss [B] D Measuement 2D Tees Point numbe Fig. 5. Compaison in Rotteam between measuements an the 2D peictions with an without tee effects - Path loss [B] Measuement 2D(tees) + 3D Point numbe Fig. 6. Compaison in Rotteam between measuements an combine 2D peictions consieing tee effects an 3D peictions.