INDOOR AND OUTDOOR PROPAGATION MODELING IN PIC0 CELLS

Transcription

1 PMRC 94 AB NDOOR AND OUTDOOR PROPAGATON MODELNG N PC CELLS D. J. Cichon (EEE Student Member), W. Wiesbeck (EEE Fellow) nstitut fir Hochstfrequenztechnik und Elektronik (ME) University of Karlsruhe Kaiserstrasse 12, D Karlsruhe, Germany Tel.: FAX: djc@ihewap.etec.uni-karlsruhe.de ABSTRACT: t is the purpose of this paper to present a deterministic approach for UHF/EHF outdoor and indoor propagation modeling in micro and pic cells. The approach takes into account multiple reflected and multiple wallpenetrated ray paths as well as combinations of multiple reflected/penetrated ray paths. Building walls are modeled as multi layered media with different material parameters. For micro and pic cells the important issue of building penetration from outdoors to indoors can be regarded as well as indoor propagation. This modeling approach results in an area wide prediction of path loss. Further on, the channel impulse response in magnitude, phase, delay, angle-of-departure, and angle-of-arrival is obtained for arbitrary selected receive locations. Simulation results are presented and a comparison with measurements is given.. NTRODUCTON This paper deals with the modeling of wave propagation in urban micro and pic cells (outdoors and indoors) at frequencies of about 1 GHz up to mm-wave bands. n micro/pico cell radio systems the antenna heights of both base station and mobile unit is generally below roof top level. Therefore the outdoor propagation is mainly characterized by wave propagation within street canyons. Multiple reflections on building walls, building edge diffraction, and radio penetration into buildings are the dominant propagation mechanisms. n case of indoor propagation both the base station and the mobile unit are located within a building. A detailed description of building walls (thickness, materials, door and window positions) and significant moveables, etc., is required to obtain a reasonable modeling of radio propagation. Modern radio systems, like Digital Mobile Radio, PCN, DECT, Radio LANs, etc., are established in the UHF up to EHF bands. The wave length is small with respect to the details of the physical environment, which have to be taken into account necessarily, thus a ray optical approach is justified. At the nstitut fur Hachstfrequenztechnik und Elektronik (HE) at the University of Karlsruhe, several ray optical propagation models for rural and urban terrain have been developed [1],[2]. A new efficient ray launching propagation model for outdoors and indoors is presented in the following. 11. MODELNG OF THE ENVRONMENT The cell size of pic cellular radio systems is not exactly defined in the literature. n this paper the name pic cell is used for radio cells with an approximate diameter of less than = 2 m. t considers indoor and outdoor coverage from base stations located inside or outside a building. A typical pic cellular environment is depicted in Fig. 1. The building data have to provide all information for the modeling of outdoor propagation, indoor propagation, and outdoorhndoor (vice versa) wall penetration. The urban environment is two-dimensionally described by an arbitrary number of walls, or further windows, doors, etc., each defined by a pair of Cartesian coordinates (xli,yli) and (~2i~2i). Usually, windows are the sections with the lowest penetration loss. Thus its position and extension should be known very well. Building walls are usually composed of several layers of material, which are described by its thickness and material parameters. A general formulation of reflection and penetration coefficients for EEE

2 492 AB 5.2 PMRC '94 wave incidence at oblique angles upon N layers of planar slabs is given in [3]. glass 1? rod ray n+l Fig. 1 : 2D-map of an exemplary pic cell 111. PROPAGATON MODELNG APPROACH Ray optical modeling of multiple reflection propagation can either be done by imaging the source when walls are considered as reflectors and determining the corresponding ray paths between a given transmitter and receiver location ([4],[5]), or by launching rays in arbitrary different directions and follow them until certain conditions are fullfilled ([6],[7]). The imaging source method usually requires high computation time depending on the number of regarded reflections, the description of the environment (resolution, etc.), and kind of practical application (pointto-point calculation, area extended predictions, etc.). But especially for coverage predictions of path loss or delay spread, a relatively low computation time is necessary to integrate the model into a radio network planning tool. The introduced ray launching propagation model for outdoors and indoors has been developed under consideration of these requirements. Up to now, only reflected and penetrated rays within a horizontal propagation plane are accounted for in the model. Nevertheless, first usable results have been obtained, as will be shown in section V. At the transmitter location (source) a certain number of rays are successively launched in discrete directions, which are equally distributed over 2n within the azimuthal propagation plane (Fig.2). Each ray launched from the source can be illustrated in a binary tree. An intersection with a wall is represented by a node in the tree. The incident ray is decomposed into a wall-reflected ray and a wall penetrated ray, as depicted in Fig.3. Fig. 2: computation depth k= K= Fig.3 2D ray launching in the azimuthal (horizontal) propagation plane Tx ]rry n Binary tree structure of ray tracing t is assumed that the reflected ray propagates in specular direction (incidence angle equal aspect angle), and the wall-penetrated ray keeps the direction of the incident ray. Both rays are propagating to the next intersection, where the decomposition process is repeated. This procedure is continued until a assumed total number of regarded nodes (computation depth) K for consideration of K-1 wall intersections is reached. Rays die either by exceeding an assumed maximum path loss, or by leaving a defined propagation area, or by succeeding the maximum computation depth. t is the purpose of the introduced propagation model, to efficiently predict the Tx-Rx channel impulse response.

3 PMRC 94 AB (CR) for arbitrary Rx locations in the azimuthal (horizontal) propagation plane. For coverage predictions the Rx locations are equidistantly defined in a pixel matrix format corresponding to a Cartesian coordinate system. A simulated ray n contributes to the complex CR hx-y at pixel (x,y). if its ray sector overlaps this pixel. Fig.4 illustrates the pixel overlapped by the ray sector. The total CR for a pixel (x,y) is given in (1). n=l u=l v=l Number of incident rays assigning pixel x,y Number of reflections of ray n assigning pixel X9Y Number of wall penetrations of ray n assigning pixel x,y u-th wall reflection coefficient of ray n assigning pixel x,y v-th wall penetration coefficient of ray n assigning pixel path length of ray n assigning pixel x,y excess run time of ray n assigning pixel x,y The pixel resolution (computation resolution) is 1 cm. Hence, the coverage prediction in the 6 m x 6 m indoor area results in a 6 x 6 elements path loss matrix, as shown in Fig.5. The ray optical character of the propagation simulation is obviously seen. Further on, the dependence of penetration loss on incidence angle and material parameters is shown in the image. Tx Fig. 4: Central ray, corresponding ray sector, and exemplary assigned pixel The spread width of the ray tube is proportional to the path length of the ray. Hence, to ensure a run length independent consideration of the building geometry (windows, doors, wall edges, etc.), a typical ray-splitting algorithm is applied. V. SMULATONS AND VERFCATON A propagation simulation at 1 GHz is presented for the exemplary building map depicted in Fig. 1. Fig. 5: Simulation of indoor propagation at 1 GHz Outdoor propagation simulations with the new ray launching model have been performed by DeTeMobil company in a fairly straight street canyon site in Munster, Germany [8]. The shape of the buildings and the transmitter location is shown in Fig.6. The frequency is 189 MHz (according to DECT systems). Up to 5 reflectiodpenetration processes (no ground reflection) per ray have been considered. The angular ray launching discretization is 5 degree. Fig.6 shows the resulting path loss coverage of the street canyon. A first comparison between measured and simulated power delay profile for the Tx/Rx configuration shown in Fig.6, is given in Fig.7. The measured values are approximately extracted from Fig.3~ of COST-231 document [8]. Antenna heights have been below roof top level.

4 ~~ ~ 494 AB 52 PMRC '94 Fig. 6: g -1 g -2 3 fl, -3 d a -4-5 Fig. 7: 124 m Propagation simulation in a street canyon at 189 MHz... :....* e :......j > time delay [nsl Comparison of simulated and measured delay profile at 189 MHz (by DeTeMobil, Germany) in the street canyon depicted in Fig.6 Finally, results of 3D indoor propagation simulation are presented in Fig.8 and Fig.9. An area wide path loss prediction at 856 MHz in an office building is shown in Fig.8. Moveables have not been considered yet. n the simulation the rays have been restricted to max. 1 wall penetration and 5 reflection processes. The ray launch discretization is 1 degree. Due to the ray optical modeling the effects of different wall types with certain material paramters and wall thickness are evident. To verify the model, a comparison to path loss measuremets, which have been performed by VTT Finland [9], is given in Fig.9. The numbers correspond to the measurement locations marked in Fig.8. An excellent agreement between the measurements and the three-dimensional simulations by the HE-NDOOR model is achieved. h m 9 () + 9 a Fig. 9: L... A...!... A... d...!... A......: measurement location Comparison with narrowband measurements (by VTT Finland) at 856 MHz However, further investigations and verifications have to be done to confirm the introduced ray optical modeling approach. Fig. 8: HE-NDOOR path loss prediction at 856 MHz in an office building

5 PMRC '94 AB V. CONCLUSON An efficient ray launching simulation model in the UHF up to EHF frequency range is presented. The model includes multiple reflected rays and multiple wall penetrating rays as well as combined multiple reflectedpenetrated rays. The model's major feature is the capability to efficiently predict path loss area wide. Each ray launched from the transmitter location has to be traced only one time to finally obtain the propagation matrix or further the complex CR for any receiver location within the defined area. To ensure a path length independent consideration of the building geometry (windows, doors, wall edges, etc.), a typical ray-splitting algorithm has been applied. The results achieved by the HE-NDOOR model are excellent as confimed by comparisons with measurements. Future work has to focuse on the effects of moveables for indoor propagation modeling. The combination of the ray optical micro cell outdoor propagation models [ 11, [ 111 with the ray optical indoor model will be necessary to come up with an comprehensive software tool for radio network planning in micro/pico cells. ACKNOWLEDGMENT The authors would like to thank Mr. J. Lahteenmaki from VTT/Telecomm. (Finland) and Dr. U. Kauschke from DeTeMobil (Germany) for proving measurements. REFERENCES [ll Th. Kiirner, D. J. Cichon, W. Wiesbeck, "Concepts and results for 3D digital terrain based wave propagation models - an overview," EEE Joumal on Selected Areas in Comm.; Wireless Personal Comm.: Part, vol. 11, no. 7, pp , September 1993, SSN [2] D. J. Cichon, Th. Kiirner, W. Wiesbeck, "Modellierung der Wellenausbreitung in urbanem Gelande," FREQUENZ, Band 47, Nr. 1-2, S. 2-11, 1993, SSN [3] C. A. Balanis, Advanced Engin. Electromagn., Chap. 11.3, John Wiley & Sons, nc., USA, 1989 [4] J. W. McKown, R. L. Hamilton, Jr., "Ray tracing as a design tool for radio networks," EE Proc. Part, vol. 138, no. 3, pp , June 1991 [5] M. C. Lawton, R. L. Davies, J. P. McGeehan, "A ray launching method for the prediction of indoor radio channel characteristics," Proc. of the EEE PMRC'9Z, UK, pp , 1991 [6] G. A. Deschamps, "Ray techniques in electromagnetics," Proc. of the EEE, vol. 6, no. 9, pp , September 1972 [7] T. Holt, K. Pahlavan, J. F. Lee, "A graphical indoor radio channel simulator using 2D ray tracing," Proc. of the PMRC'92, Boston, USA, pp , 1992 [8] U. Kauschke, "Measurements of power delay profiles and linked simulations for DECT in urban roads with antennas placed below roof top," COST-23 1 TD(93) 1, reland, Sept [9] J. Lahteenmiiki, "ndoor propagation between floors at 855 MHz and 1.8 GHz," COST-231 TD(94) 37, Lisbon, Portugal, 1994 [lo] D. J. Cichon, W. Wiesbeck, "Ray optical wave propagation modeling in urban micro cells," Proc. of the PMRC '94, The Hague, Netherlands, Sept [ll] D. J. Cichon, Th. Kiirner, W. Wiesbeck, "An unsupervised and comprehensive multipath wave propagation model for urban environments," submitted for publication in EEE Trans. on Ant. and Prop.