OUTDOOR-TO-INDOOR PROPAGATION MODELLING WITH THE IDENTIFICATION OF PATH PASSING THROUGH WALL OPENINGS.pdf

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OUTDOOR-TO-INDOOR PROPAGATION MODELLING

WITH THE IDENTIFICATION OF PATH PASSING THROUGH WALL OPENINGS

Yuko MIURA, Yasuhiro ODA, and Tokio TAGA

Wireless Laboratories, NTT DoCoMo, Inc.

3-5 Hikari-no-oka, Yokosuka-shi, Kanagawa, 239-8536, Japan

E-mail: [email protected]

Abstract - This paper proposes a new propagation model to

accurately predict outdoor-to-indoor propagation loss.

Account is taken of the structural openings along the paths;

it is assumed that outdoor-to-indoor paths are possible only

through wall openings such as doors and windows.

Introducing the angle dependency of the losses with the

paths that penetrate the indoor area makes it possible to

accurately predict outdoor-to-indoor propagation loss.

Measurements in a microcellular environment show that theproposed model can predict outdoor-to-indoor propagation

loss more accurately than the COST231 model.

Keywords - Mobile communication, radio propagation,

Building penetration, Path passing through wall opening,

Indoor angle dependency.

I.INTRODUCTIONDue to the increased use of mobile phones, it is

becoming more important to ensure that mobile

communication systems cover more indoor areas [1]. In

some buildings, the indoor service area is established by

exclusive indoor base station antennas. Actually, however,

most indoor mobile communication is established by radio

paths from outdoor base stations.

Path losses into buildings are influenced by the

building's wall structure and indoor furniture arrangement.

The COST231 model [2] assumes that the radio waves

penetrate the building's external wall that is in direct view

(line of sight) of the base station, and that the penetration

point on the wall is the point closest to the mobile station.

External walls are assumed to be uniform and made of

ferroconcrete or other such common materials. Generally

speaking, the penetration loss of ferroconcrete walls is larger

than wood or glass walls [3]. It seems obvious that mostbuildings have several wall openings such as doors and

windows, and that the penetration paths through these

openings have lower penetration loss than the wall

penetration paths assumed by the COST231 model [4]. The

difference will lead to errors predicting the outdoor-to-

indoor propagation path losses, especially on large buildings.

This paper proposes a new penetration model that

considers the paths through wall openings when calculating

the outdoor-to-indoor propagation loss. This paper is

structured as follows. Section II explains the COST231

model briefly. Section III presents proposed penetration

model and describes its parameters. It also derives

expressions and discusses issues such as angular

dependency of incoming and outgoing paths at wall

openings, indoor attenuation coefficient, and application

approaches for macro or micro cell environments. Section

IV"presents some coefficients of an actual building asdetermined by measurements. Section V describes

measurement results at a department store on an urban

microcell environment, and discusses the validity of theproposed model in a comparison to the COST231 model.

Finally, Section VI summarizes the results.

II.COST231 MODELIn the COST231 model, the penetration point is the point

on the line-of-sight wall closest to the mobile station

regardless of wall structure (Fig. 1). The radio waves

transmitted by the base station penetrate the wall at this

point and propagate inside building to the mobile. Outdoor-

to-indoor propagation loss is calculated by the following

expression:

Lp=Lf(S+d)+We+WGe (1- cos)2+ (d-2) (1- cos)2, (1)

where S is the distance between the base station and the wall

penetration point, and d is the distance from the external

wall to the mobile station. is the grazing angle of the

external wall. Lf() is the free space propagation loss for the

distance between base-mobile station. TermWe is the loss in

dB of an externally illuminated wall with perpendicular

Door

d2

External Wall

Lp

BS

d1

Proposed Model

LOS Wall

Door 2

1

S2

1

2

1

2

Path 1

Path 2

MS

Door 1

S

COST231 Model

We

S

d

Figure 1. COST231 model and proposed model

0-7803-7589-0/02/$17.00 2002 IEEE PIMRC 2002


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penetration, =0. WGe is the additional loss in dB in the

external wall when =90. is the specific indoor

attenuation constant and has units of dB/m.

III.PROPOSED MODELRadio waves transmitted by the base station firstpropagate outdoors to the building's external wall. Next, the

radio waves penetrate the building's external wall. Last, the

penetration waves propagate inside the building to the

receiver.Outdoor-to-indoor propagation loss is estimated by

predicting the propagation losses of these three parts. The

losses of these three propagation processes can be calculated

individually, and the path loss between base station and

mobile station can be expressed as the sum of these losses in

dB.

Lp = Lout + Lpn+ Lin (2)

Lout is outdoor propagation loss, Lpn is building penetration

loss, and Lin is indoor propagation loss.The COST231 model assumes that the radio waves

penetrate the external wall at the point closest to the

receiver (Fig. 1), but the penetration loss of external walls,

usually ferroconcrete or other such materials, is much larger

than the penetration loss of openings consisting of glass i.e.

windows [3][5][6]. It is reasonable, therefore, to assume that

paths through wall openings will have lower total path

losses than the wall penetration paths assumed by the

COST231 model, even though the propagation distance of

the paths through wall openings are longer. That is, if there

are wall openings on the building's external wall, the paths

through the wall openings dominate the reception process

and determine the path loss at the reception point. Thispaper proposes the following expression to calculate

building penetration loss for paths going through wall

openings. If there are several wall openings, the received

level is the sum of path levels of paths through all such wall

openings.

Lpn,1 = We + WGe (1- cos 1)2

+f(1) "(3)Equation (3) describes the penetration loss of path 1 in Fig.

1. The first term, We, is the loss across the wall opening with

perpendicular penetration (=90). The second term is the

outdoor angular dependency and equals the COST231 term

[2][7]. The third term is the indoor angular dependency from

wall opening to receiver. This paper assumes that pathsthrough wall openings are dominant, and that the paths from

the wall openings to the receiver are not, generally,

perpendicular to the wall. The propagation loss of these

paths is altered by the indoor grazing angle, i.e. such as

diffraction loss.

There are several indoor propagation models such as [8],

for simplicity, it is convenient to use a constant loss per unit

distance in this model. The following expression describes

the indoor propagation loss of path 1 calculated by this

model:

TABLE I EXPERIMENTAL CONFIGURATIONFrequency 8.45 GHz (CW)

Power +40 dBm

Transmitter antenna height 14 m

Receiver antenna height 0.3 m

300 m

10m Door

inside 13 m

Receiver

38 m

Tx2 Tx1

37 m

Figure 2. Measurement of indoor attenuation coefficient

150 m

300 m

100m

Copyright (C) 2000 ZENRIN CO.,LTD.

Transmitter

Chuo

Ave

.

Measured Building(Department store)

Figure 3. Map of We measurement

23.5 m

23.5 m

30.7 m 33.6 m

14.2 m 60.8 m 16 m5.4 m 5.4 m

5.9 m20.7 m

10.9 m

17.7m64.7

m

101.8m

13 m

Door

Door2Door3

Door4Door5

Door1

ChuoAve.

Measured Position

Figure 4. Indoor receiver position for We measurements


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Lin,1 = d1 (4)

is the attenuation coefficient for uniform indoor

propagation media and is generally is unique to each

building.

To well handle the various conditions of building and

base stations possible, the outdoor propagation loss, Lout, is

calculated by the propagation loss predicted for the macro

cell [9][10] or micro cell [11] as appropriate.

IV.PARAMETER MEASUREMENTIt is necessary to acquire We (penetration loss of wall

openings), (indoor attenuation coefficient) and f()

(indoor angular dependency) to implement the proposed

model. Term We and depend on the material and/or

structure of the building. A series of field tests was

conducted at a department store, and We and for this

building were measured. The indoor angular dependency

was also measured at the same time.

A.Measurement campaign of the parametersTABLE I shows the measurement conditions. The

building was a department store. A transmitter was set in

direct view of the building. An omni-directional antenna

was used when the distance between transmitter and the

building was equal to or less than 150 m, and a directional

antenna, 3-dB width of 60, was used when the distance was

300 m. Propagation loss was measured every 0.2 m inside

building.

B.Indoor attenuation coefficient ()Propagation loss was measured on an aisle nearly

perpendicular to the wall openings to remove the effect of

the indoor angular dependency. The transmitter was set 10

m outside the door (Tx1) and 300m from the door (Tx2) on

the same line-of-sight road. The propagation loss was

measured over a 38 m course along an aisle starting some

13m from a glass door (Fig. 2). Indoor attenuation

coefficient, , was taken as the coefficient of the 1 m

average of measured propagation loss over the measurement

course. Two values of , determined using transmitter

positions Tx1 and Tx2, were acquired. The mean value of

was 0.348 (dB/m).

C.Penetration loss of wall opening (We)The building had 5 doors that faced three different roads.

The transmitter was set at 150m and 300m from the building

on these roads (Fig. 3) and 5 m average propagation losses

were measured both outside and inside the line-of-sight door.

Inside propagation loss was measured some 13 m from the

door (Fig. 4). Term We was acquired from the path loss

difference between the propagation loss outside and inside

the door while subtracting the 13m indoor propagation loss

and the outdoor angular dependency. TABLE II shows that

the value of We ranges from 5 to 28 dB; its mean value is

17.2 dB.

D.Indoor angle dependency (f())When the receiver is in front of a wall opening, all

incident power that passes through the wall opening

propagates normally to the receiver. On the other hand,when the receiver is not in front of the wall opening, the

received power is decreased by the diffraction over the edge

TABLE II MEASURED We (dB)door

1 2 3 4 5Ave.

150 m 5.7 14.7 9.3 27.7 21.7 15.8

300 m 21.0 15.1 14.2 21.6 20.7 18.517.2

Chuo Ave.

Tx2

Tx1300 m

10 m

Door

13 m

12 mMeasured

Course

Inside

Figure 5. Measurement of indoor angle dependency

30 60 90

0

5

10

15

20

Measured Data

WGi sin

WGi (1- cos )2

-50

Angle (degree)

Loss(dB)

(a) Tx1

30 60 90

0

5

10

15

20

Measured Data

WGi sin

WGi (1- cos )2

-50

Angle (degree)

Loss(dB

)

(b) Tx2

Figure 6. Indoor angle dependency (WGi=20dB)


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of the wall opening. This diffraction loss depends on the

indoor grazing angle. We measured this angular dependency

by conducting the following field test.

The transmitter was set 10 m outside door Tx 1 and

300m from the door Tx2 on the same line-of-sight road. The

receiver (13 m from the wall) was moved over a 12m course

parallel to the wall from edge of the wall opening (Fig. 5).Loss for the indoor angle is plotted in Fig. 6(a)(b). Direction

0 represents the near edge of the wall opening. Both results

are close to the WGi sin . So the indoor angular

dependency is WGi sin and thus differs from the outdoor

angular dependency which is WGe (1- cos )2.

For the building examined, the calculation parameters

are = 0.348 dB/m, We = 17.2 dB, and f()= WGi sin ,

where WGi is 20 dB.

V.OUTDOOR-TO-INDOOR PROPAGATION LOSSMEASUREMENTS AND ANALYSIS

A.Measurement campaignWe measured the outdoor-to-indoor propagation loss in

a department store to estimate to the accuracy of the

proposed model. The measurement conditions were the

same as those for TABLE I, and the propagation loss was

measured every 0.2 m inside the building. The transmitter

was set at the 2 points shown in Fig. 7. Tx1 was right in

front of the building and an omni directional antenna was

used. Tx2 was 300 m from the building and a directional

antenna with 60 beam width was used. Figure 8 shows that

the building has 5 glass doors, and the receiver was moved

along a rectangular aisle 13 m from the external walls.

B.Results and analysisFigure 9(a)(b) show the measurement results for the

different transmitter positions. The values plotted are the 1

m averages of the propagation loss measured along the aisle

shown in Fig. 8. The solid line is the propagation loss

calculated by the proposed model. The dotted line is the

propagation loss calculated by the COST231 model. The

parameters listed in TABLE III were used in these

calculations.

There were 5 doors at measurement course distances of

about 20, 50, 100, 150 and 220 m. Figure 9 shows that the

measured propagation loss has some local minima at thesewall-opening positions and increases away from the

openings. In Fig. 9(a), the transmitter was placed right

outside the building at the measurement course distance of

180 m. The measured propagation loss is maximal at this

point and decreases as the receiver leave away and

approaches the wall openings, i.e. door4 or door5.

COST231 using the wall penetration loss predicts that

the minimum propagation loss would be seen when the

receiver was at 180 m because the receiver was closest to

the transmitter at this position. However, the measurement

Measured Bilding(Department store)

Transmitter

300 m

ChuoAve

.

Tx2

Tx1

100m

Copyright (C) 2000 ZENRIN CO.,LTD.

Figure 7. Measurement of building penetration loss

23.5 m

23.5 m

30.7 m 33.6 m

14.2 m 60.8 m 16 m5.4 m 5.4 m

5.9 m20.7 m

10.9 m

17.7m64.7m

101.8m

13 m

Door

Measured Course

start / goal

Aisle CDoo

r1

Door2 Door3

Door4Door5

ChuoA

ve.

Figure 8. Measured course

TABLE III CALCULATION PARAMETERSWGe (dB) 20

We (dB) 17.2

(dB/m) 0.348

f() WGi sin (WGi = 20 dB)

results contradict this prediction and show that the wall

penetration wave does not influence the outdoor-to-indoor

propagation loss at all. On the other hand, the proposed

model can predict the measured propagation loss well. In the

proposed model, propagation loss is calculated by the path

loss through wall openings, so the propagation loss depends

on the path loss through door4 or door5 at this position. The

indoor grazing angle is very steep around this position andthe propagation loss is greatly increased due to the indoor

angle dependency. Moreover, the propagation loss is

increased by the increase in path length from door4 and

door5. The wall penetration wave is insignificant and the

paths through the wall openings dominate the propagation

process.

Figure 9(b) shows that the measured propagation loss is

about 20 dB larger than that predicted by the proposed

model at measurement positions beyond 120 m. The

proposed model calculates the propagation loss of aisle C by


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the path loss through door3 line-of-sight from the transmitter.

Actually, however, there are obstacles such as shelves,

furniture and pillars around the aisle, so the radio wave

could not propagate directly to the receiver from the opening.

This is the reason for the 20dB discrepancy. This indicates

that paths that propagate deep into a building can be

influenced strongly by the internal structure and fixtures ofthe building. If we need to increase the accuracy of the

propagation loss prediction, we need to consider the indoor

structure of the building such as furniture and pillars, but

this consideration will complicate the model.

VI.CONCLUSIONSWe have proposed a new propagation model to

accurately predict outdoor-to-indoor propagation loss. The

new model assumes that outdoor-to-indoor propagation loss

is the sum of outdoor propagation loss, wall opening

penetration loss, and indoor propagation loss. The

propagation loss from wall openings to receiver, which is

proposed in this paper, requires knowledge of the wall

opening penetration loss, the indoor attenuation coefficient,

and indoor angular dependency. Some parameters, such as

the wall opening penetration loss, are unique to each

building and were measured by field tests.

Measurement results gathered from a large building in

an urban micro cell environment were compared to results

calculated by the COST231 model and by the proposed

model. The comparison showed that the proposed model

predicts the outdoor-to-indoor propagation loss more

accurately than COST231.

It is obvious that paths that propagate deeply into a

building will be influenced strongly by the internal structureof the building. Since the proposed model uses a simple

distance attenuation model to calculate the indoor

propagation loss, the propagation loss prediction error can

become large if the reception point is deep within the

building. This problem, however, does not influence the

prediction of the outdoor propagation losses and the

building penetration losses. More accurate outdoor-to-

indoor propagation loss predictions can be achieved by

using a more accurate indoor propagation model.

The measurements and consideration presented in this

paper examined a large room with no internal walls.

However, the proposed prediction method can be applied to

cases where there are some rooms inside the building by

using it twice; once to predict the path loss across external

wall openings to internal wall openings and then again to

predict the loss across the internal wall openings to the

mobile station.

REFERENCES

[1] M. Hata, Fourth Generation Mobile Communication Systems beyondIMT-2000, IEEE Proc. APCC/OECC, pp. 765-767, 1999.

[2] COST 231 Final Report, Chapter 4, Propagation Prediction Models,1996

[3] C. M. Brennan et al., EM shielding of building materials, TechnicalReport of Rome air development center, RADC-TR-67-446, Feb. 1968.

[4] Jun Horikoshi et al., 1.2 GHz Band Wave Propagation Measurementsin Concrete Building for Indoor Radio Communications, IEEE Trans.

on VT, Vol. VT-35, No. 4, Nov., 1986.

[5] Arthur von Hippel, Tables of Dielectric Materials and Applications,Artech House, 1995.

[6] J. H. Tarng, and T. R. Liu, Effective Models in Evaluating RadioCoverage on Single Floors of Multifloor Building, IEEE Trans. on VT,Vol. 48, No. 3, May, 1999.

[7] Henrik Borjson and Bernard De Backer, Angular Dependency ofLine-of-Sight Building Transmission Loss at 1.8 GHz, IEEE Proc.

PIMRC, pp466-470, 1998.

[8] David J. Y. Lee, and William C. Y. Lee, Propagation Prediction inand Through Buildings, IEEE Trans. on VT, Vol. 49, No. 5, Sep.,

2000.

[9] J.Walfisch and H. L. Bertoni, A theoretical model of UHFpropagation in urban environments, IEEE Trans. AP, Vol. 36, pp.

1788-1796, Dec. 1988.

[10]M. Hata, Empirical formula for propagation loss in land mobile radioservices, IEEE Trans. on VT, Vol. VT-29, pp. 317-325, 1980.

[11]L. R. Maciel et al., Unified approach to prediction of propagation overbuildings for all ranges of base station antenna height, IEEE Trans. on

VT, Vol. 42, pp 41-45, Feb.1993.

(a) Tx1

(b) Tx2

Figure 9. Measurement results (gray : door position)

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OUTDOOR-TO-INDOOR PROPAGATION MODELLING WITH THE IDENTIFICATION OF PATH PASSING THROUGH WALL OPENINGS.pdf