Ray Tracing Short

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An Improved Ray-Tracing Propagation

Model for Predicting Path Loss on Single

Floors

Zhong Ji1, Bin-Hong Li

2, Hao-Xing Wang

2,

Hsing-Yi Chen3 and Yaw-Gen Zhau4

1Zhong Ji,

97034BA Shanghai Jiao Tong University,

1954 Hua Shan Road,Shanghai 20030,

China.

2Bin-Hong Li,

Dept. of Electronic Engineering,

Shanghai Jiao Tong University,1954 Hua Shan Road,

Shanghai 20030,China.

3Hsing-Yi Chen,

Dept. of Electrical Engineering,

Taiwan Yuan-Ze University,

Taoyuan,Taiwan 320,

China.

4Yaw-Gen Zhai,

Division of Research and Development of

Taiwan Yuan-Ze University,

Taoyuan,Taiwan 320,

China.

Corresponding author: Zhong Ji

Email: [email protected]

Tel: 86-21-64853090

ABSTRACT: An improved ray-tracing propagation prediction

model for predicting path loss on single floors in indoor

environments is developed. It utilizes the results of two-

dimensional (2D) ray tracing technique to deal with three-

dimensional (3D) problem. This approach is more efficient thanusual 3D ray tracing model and more accurate than usual 2D ray

tracing model. Simulation results agree well with measurement.

Key words: ray-tracing, propagation model, path loss.

1. INTRODUCTION

Indoor wireless communications such as personal communications (PCs)

and wireless local area networks (W-LANs) are expanding today. The

need for an efficient way to evaluate radiowave propagation in buildings

is also increasing. Recently, ray-tracing technique has been used to

predict radiowave propagation in indoor environments. 2D ray tracing

model and 3D ray tracing model are both used widely [1]-[4]. 2D model

requires less computation time but has lower accuracy and 3D model just

has the opposite advantage and disadvantage.

There have been some investigations on indoor radio propagation

modeling on single floors [5][6]. In Reference [5] the authors explored

features of office buildings that influence propagation and used ray-

tracing model. In Reference [6], the authors used a direct-transmitted ray


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(DTR) model combined with a patched-wall model.

The objective of our work is to study the character of propagation on

single floors and present an accurate and fast model. In our model multi-

reflection by the ceiling and the floor is included. It has the advantages of

both 3D model and 2D model. The predicted path loss is compared with

the measured one of 1.7GHz radio propagation at a room of the teachingbuilding in our campus.

2. MODEL DESCRIPTION

Indoor environments are composed of floors, ceilings and walls verticalto the floor. On single floors, if taking the floor as the x-y plane and the

direction vertical to the floor as z-axis direction, we can find the

following properties of propagation when using ray tracing technique (Inthis coordinate system, transmitter and receiver are regarded as a point in

3D space, respectively.):

1) When the floor or the ceiling reflects a ray, the incident ray and the

reflected ray have the same azimuth angle. Namely, perpendicularprojections of the two rays on the floor are in a line.

2) When a wall vertical to the floor reflects a ray, the fact that the angle

of incidence is equal to the angle of reflection is also valid to theirprojections on the perpendicular projection plane, i.e., on the floor.

3) The angle between the ray reflected by a wall and z-axis is equal tothat between the incident ray and z-axis.

4) The source rays having equal azimuth angle in 3D space have the

same perpendicular projection on the floor.

In our model, we firstly project all walls, the transmitter and the

receiver (except the ceiling and the floor) perpendicularly on the floorand use 2D ray-tracing model on the projection plane and then apply 3D

ray-tracing technique based on results of 2D ray-tracing to thepropagation problem. This can be explained in Figure 1. Figure 1 (a) is

simple indoor environment with a wall, a ceiling and a floor. The height

of the transmitter and the receiver are h1 and h2 above the floor,respectively. The height of the ceiling is h above the floor. In Figure1 (b),

the wall, the transmitter and the receiver are projected perpendicularly on

the floor. By 2D ray tracing on the projection plane, there are only two

paths from the projection of transmitter to the projection of receiver. If no

reflection by the ceiling and the floor is considered, there are only two

actual paths in 3D space when using 3D ray-tracing model. One is the

direct path from the transmitter to the receiver; the other includes

reflection by the wall.

When multi-reflection by the ceiling and the floor is considered, the

situation is different. In Figure 1 (b), suppose the unfolded length of one

2D path is d, which can be obtained during 2D ray tracing, and the

azimuth angle of projection of the corresponding 2D-source ray is .

Taking above-mentioned properties of propagation into account, we find

that the source rays in 3D space with elevation of given by (1) and

azimuth of may reach the receiver. These 3D source rays are called


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useful 3D source rays. The paths from the transmitter to the receiver of

all these useful 3D source rays have the same perpendicular projection on

the floor.

d

hnharctan 0

2

2

++

=

(1)

Where 210 hhh = . The positive and negative sign is used whenthe total number of reflections by the ceiling and the floor is odd and

even, respectively.

1= . The positive and negative sign is used when the firstreflection (not include reflections by walls) occurs on the floor and the

ceiling, respectively.

n=0,1,2m. ( 0n when 1= ) n is an index related to theconsidered order of reflection by the ceiling and the floor and m is an

index related to the maximum order of reflection by the ceiling and thefloor. When m=0, two 3D paths are included. One has no reflection by

the ceiling or the floor and another has only once reflection by the floor.

When m=1, there are four 3D paths are included. The first one has once

reflection by the ceiling. The second one has once reflection by the

ceiling and then once reflection by the floor. The third one has once

reflection by the floor and then once reflection by the ceiling and the last

one has once reflection by the floor, once reflection by the ceiling and

then once reflection by the floor again. All these paths may include

reflections by walls. There are total 2+4m paths are included.

When there are many walls, the above principle also holds true.

During 2D tracing on projection plane, all 2D paths from the

projection of transmitter to the projection of receiver are recorded and

unfolded length of each 2D path is also calculated. After an integer m isgiven, 3D ray tracing is performed for all useful 3D-source rays to each

2D path. Because only part of all 3D-source rays is traced, much time of

computation can be saved. Based on Figure 1 (b), Figure 1 (c) showspaths in 3D space according to our model. If choosing m=1, there are 6

paths in 3D space corresponding to each 2D path in Figure 1(b).

Therefore total 12 paths in 3D space are considered as shown in Figure

1(c).

3. COMPARISON OF SIMULATION AND MEASUREMENTTo verify the model, the software using our model is developed to

predicted path loss on single floors of modern buildings. Patched-wallmodel is also used. Measurements were done in a room. The room has a

rectangular shape with dimensions 57.452.7m3

and is divided into

more than 20 patches. A CW signal at 1.7GHz with power range

0~15dBm is transmitted by a half-wavelength dipole antenna outside the

room and at a height of 1.5m above the floor. A half-wavelength dipoleantenna with same height receives the signal. Values of path loss at 9

locations within the room were measured.


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Figure 2 shows the predicted and measured results for the path loss

at each location of measurement. It indicates that predicted results of both

our model and usual 3D model agree well with measurements. But the

usual 3D model costs of about one hundred times computation time of

our mode.

4. CONCLUSION

In this article, we have proposed an improved propagation prediction

model on single floors in indoor environments by using results of 2D raytracing. The algorithm is easy to use and has almost the same accuracy as

usual 3D model, but it takes less computing time of usual 3D model to

get path loss.

REFERENCES1 U. Dersch and E. Zolllinger, Propagation Mechanism in Microcell and

Indoor Environments, IEEE Trans on Vehicular Technology,

Vol.43, No.4, 1994, pp1058-1066.2 S.H. Chen and S.K. Jeng, SBR Image Approach for Radio Wave

Propagation in Tunnels with and without Traffic, IEEE Trans. on

Veh. Technol., Vol.45, No.3, 1996, pp570-578.3 J.W. Mcjown and R.L. Hamilton, Jr., Ray Tracing as a Design Tool for

Radio Networks,IEEE Network Magazine, Nov.1991, pp27-30.

4 S.Y. Seidel and T.S. Rappaport, Site-Specific Propagation Prediction

for Wireless In-Building Personal Communication System Design,

IEEE Trans. on Veh. Technol., Vol43, No.4, 1994, pp879-891.

5 W.Honcharenko, H.L.bertoni, and J.Dailing, Mechanism governingpropagation on single floors in modern office buildings, IEEE

Trans. on Antennas and Propagation Vol. 41, No.4, 1992, pp.496-

504.6 T.R. Liu and J.H. Tarng, Modeling and Measurement of 2.44GHz

Radio Out-Of-Sight Propagation on Single Floors,Microwave and

Optical Technology Letters, Vol.14, No.1, Jan., 1997, pp56-59.

Legends for figures:Figure 1 The principle of our model (a) Simple room structure (b) 2D

paths on projection plane (c) Paths in 3D space

Figure 2 Path loss of prediction and measurement


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Figure 1 (a)

Figure 1 (b)


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Figure 1 (c)

0 1 2 3 4 5 6 7 8 9

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-1 9

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-1 4

Measurem ent

3D Mode l

O u r M o d e l

Me asure m en t L oc ation

Figure 2

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