第 478 回電波研連 F 分科会資料 2003 年 10 月 23 日

1Experimental Study for Polarimetric Measurementof Non-specular Wave Scattering from Building
Surface Roughness
Hary Budiarto,Kenshi Horihata, Katsuyuki Haneda and Jun-ichi Takada
Tokyo Institute of Technology
2-12-1 Ookayama Meguro-ku Tokyo Japan 152-8552
email: hary@ap.ide.titech.ac.jp,haneda@ap.ide.titech.ac.jp, takada@ide.titech.ac.jp

0.04 mAbstract— This paper presents polarimetric measurement of
non-specular scattering from building surface roughness basedon experimental data. Both V-V and V-H polarizations were estimated independently. The superresolution method was applied
as an approach to handle signal parameters of the individual
incoming waves scattered from building surface roughness. In
order to comprehend the details of microscopic mechanismsof the scattering, signal parameters shall be incorporated into
multiple scattering approach based on ray optics.

AluminumFrame

0.80 m

0.85 m

n

io
ct

ra

ff
Di

0.5 m

Bricks I
1.5 m

0.85 m0.14 mθ2

θ1

0.16 m

n
ctio

h
Pat

0.1 m

le
Ref

0.12 m0.8 m

Fig. 1.

0.16 mBricks Roughness
0.1 x 0.05 m
3.7 m

ReceiverAntenna

In urban areas, buildings are the dominant scatterers determining radio propagation properties. Reflection, diffraction,transmission and scattering of the electromagnetic waves on
the building surfaces in the radio environment induce undesirable multipath propagation. Consequently, the transmitted
signal reaches the receiver through different propagation paths.
On the other hand, polarization rotation or cross polarization
directly adversely affect in the performance of polarization
diversity. The prediction of multipath on the building surface
that includes polarization effect will be beneficial for the radio
propagation models [7]. The multipath propagation characteristics of non-specular wave scattering from building surface
roughness have been reported in other papers [1][2][3][4].
This paper presents experimental study for polarimetric measurement of non-specular wave scattering from building surface roughness. The estimation of the vertical-vertical (VV) and vertical-horizontal (V-H) polarizations were carriedout independently. Signal parameters from the polarizationsof the individual incoming waves scattered from building
surface roughness were obtained using the superresolution
method. The experimental results show that the non-specular
scattering from building surface is more dominated by window
frames scatterers rather than brick scatterers. The averagepath gain difference between V-V and V-H polarizations was
12 dB. This is consistent between measurement by using
Vector Network Analyzer and signal parameters estimated byusing the superresolution method (Least Square 3D Unitary
ESPRIT).

thPa

Plain Glass

Index Terms— Polarimetric, Non-specular Scattering, Multipath Propagation, ESPRIT

I. I NTRODUCTION

0.1 m0.05 mGround1.5 m
Bricks II
Transmitter
Antenna

Building Surface Profile

II. E NVIRONMENT U NDER C ONSIDERATION
A. Building Surface Profile
The profile of the building surface is shown in Fig. 1. The
profile was taken from one of the buildings at Tokyo Instituteof Technology. The surface of the building has non-uniformity
due to the windows (glass), frames (aluminum), and walls(bricks). The surface has periodical irregularity of five periods.
One period of the surface equals 3.7 m. The windows are
made up of the sidewall, aluminum frames and plain glasses,
which in principle are the building roughness, as well as thewall surface. The dimensions of the window’s glasses of thebuilding are 0.85 × 1.5 m2 , 0.8 × 1.5 m2 , and 0.85 × 1.5 m2 .
The three different window frames have outer dimensions of
0.04 × 1.5 m2 , 0.05 × 1.5 m2 and 0.10 × 1.5 m2 . The first andthe third window frames have the same offset depth of 0.16 m
different from the second window frame that has 0.12 m offset
depth. The windows are elevated 1.5 m from the ground. The
wall surface, that has periodical roughness in both horizontal
and vertical directions, is made of 0.1 × 0.05 m2 bricks with
0.01 m gap among each other.
B. Transmitter and Receiver Model
Rectangular microstrip antennas, which are polarized linearly, were used as both transmitter and receiver antennas.
The ground plane size is 0.08 × 0.08 m2 and the patch
size is 0.0179 × 0.0179 m2 on a dielectric substrate with

第 478 回電波研連 F 分科会資料 2003 年 10 月 23 日

Cable (20 m)

Transmitter Antenna(Microstrip)

TABLE IE XPERIMENTAL PARAMETER

Receiver Antenna(Microstrip)

Spatial Scanning or
Synthesized Uniform
Rectangular Array (URA)

Network Analyzer(Agilent 8720ES)

2

Antennas

Port 1
Port 2
S21 Measurement

Cable(0.5 m)
PC

Cable (6 m)

Position Setting

GPIB

GPIB

Measurement
PointsX-Y Positioner(DEVICE D3425AV1/O-D)

and Controller(DEVICE DX3165AV1/O-C)

Snapshot
Estimations
Parameters

Control and Data Acquisition

Fig. 2.

Tx & Rx Microstrip
Reflection coefficient is bellow−10 dB in 4.85 − 5.05 GHz.
Beam width in E and H planes are 45◦
Spatially 10 ×10 points(25 mm interval ),21 points over frequency(4.85 − 5.05 GHz).
20 times
The number of waves andeach wave’s azimuth, elevation,
delay and path gain
LS 3-D Unitary ESPRITPreamp (30 dB)(Agilent 8449)

Equipment Arrangement²r = 2.55. Frequency of the antennas was 4.85-5.05 GHz.
The wavelength was comparable with or smaller than thedepth of building surface roughness. The height of the transmitter antenna was 1.9 m. The transmitter and receiver antennas were fixed at 2.7 m in front of the building surface.
The antennas were aligned to transmit and receive the VV followed by V-H polarizations. Figure 2 shows equipment
arrangement for transmitter and receiver model. During theexperiment, the V-V and V-H polarizations were measured
independently under the same environment. The measurementof V-H polarization were conducted by rotating the receiverantenna −90◦ toward the right direction of the receiver when
it was in V-V polarization. The measured cross-polarization
discrimination (XPD) of the antenna is around 20 dB in an
anechoic chamber. The transfer function between transmitterand receiver antennas were measured using a vector network
analyzer (VNA). Measurement of transfer function and theshifting of receiver antenna were operated automatically using
a personal computer connected to the controller of the x-y
positioner through the General Purpose Interface Bus (GPIB),
in order to attain high accuracy and easy measurement. The
X-Y positioner is used for automatically shifting the receiverantenna with spatial scanning accuracy of 1 mm. Table 1
shows the detailed parameters of the experiments.
C. The Spatial Scanning Model
The spatial scanning was configured to resemble an array
antenna, also called synthesized uniform rectangular array(URA). The measurement points during the spatial scanningwere discretized for every 0.025 m toward the horizontal andvertical directions. The measurement was performed along 0.5
m in the vertical direction. The middle of the vertical direction
scanning region was at the same height as the transmitter
antenna. Figure 3 illustrates model of the spatial scanning.
The model performs the measurement 8.125 m along thehorizontal direction. The transmitter antenna is positioned
facing towards the bricks’ surface of the building. The firstvertical direction of measurement is 0.7 m away from thetransmitter antenna, which corresponds to 10◦ incident angle
in the specular direction.

Signalprocessing
Smoothingin ESPRIT
Wave
Polarization
Cross-Polarization
Discrimination
Normalization

BricksSpatially 4 times and7 times over frequency
Vertical-Vertical
Vertical-Horizontal
20 dB
Face-to-face, the distance
between Tx and Rx is 1 m
at experiment location

Building Surface Roughness

Glass

Frame

2.7 m

one period

Rx1

z

Tx

Rxn

x

Spatial Scanning 0.5 x 8.125 myFig. 3.

Nth Specular
Direction

0.7 mFirst Specular
Direction

Top View of the Spatial Scanning Modelsurement system was required to eliminate equipment effects.
The transfer function measured by the VNA can be expressed
as follows,
X(f ) = H(f ) × G(f )(1)where G(f ) is transfer function of the cable, amplifier andantenna complex directivity at broadside, and H(f ) is Friis
free space transfer function, which is given as,λ2π(2)exp(−j d)4πdλwhere d is propagation path, and λ is wavelength. All measurement data resulted from this experiment were alreadycalibrated by applying function G(f ), which was obtained
from the measurement using the transmitter and receiverantennas positioned face-to-face with 1 meter distance fromeach other, in an open space.
Figure 4 shows mean values and standard deviations of datameasurement for V-V and V-H polarizations. Mean values andstandard deviations were calculated from the vertical spatial
scanning. The figure shows them in the errorbar graph with 0.1
m discretized at the horizontal spatial scanning. The average
difference between V-V and V-H Polarizations is 12 dB.
H(f ) =

III. S IGNAL P ROCESSING

D. Data Measurement Method
Since the VNA measured the transfer function of the cableand amplifier simultaneously, a calibration of the data mea-

In order to obtain signal parameters of the arrival wave,
measurement data are formulated. Suppose that L waves are
impinging at the receiver have three parameters of azimuth

第 478 回電波研連 F 分科会資料 2003 年 10 月 23 日

3

-20
10

Average Deviations = 12 dB

Azimuth Angle (degree)

Path Gain (dB)-30

Specular Angle
Vertical Window Frames
Ground Scatterer
Bricks II Scatterer
Bricks I Scatterer
Windows Scatterer
Direct Ray

20

Mean of V-V Polarization
Mean of V-H Polarization
Standard deviation

-40

-50

-60

0
-10
-20
-30
-40
-50
-60
-70

-70

0

1

2

3

4

5

6

7

-80

8

-90

Horizontal Spatial Scanning (m)0angle (φl − π2 ), elevation angle ( π2 − θl ) and delay time τl ,where 1 ≤ l ≤ L. With the X-Y positioner, the receiverantenna performs spatial scanning both in the horizontal andvertical directions where the intervals of the sampling points
are ∆x and ∆y . The numbers of sampling points are M1
and M2 , respectively. At each sampling point, it carries out
M3 points of sampling over the frequency where the intervalof sampling is ∆f and the center frequency is fc . If theelectrical lengths of the aperture of the array, 2π
λc M1 ∆x and
2π
M
∆
,
are
both
sufficienttobeassumedas constant2yλc
within the bandwidth M3 ∆f , i.e, M1 ∆x · M3 ∆f ¿ c, andM2 ∆y · M3 ∆f ¿ c, where c is a light velocity, then themeasured data yk1 ,k2 ,k3 can be expressed as,
¸
L · Y
3
X
(k )
jµl r
zk1 ,k2 ,k3 =sl(3)e+ nk1 ,k2 ,k3
l=1

=

(2)

=

(3)

=

µl
µl

2

3

4
5
6
Tx-Rx Distance (m)

7

8

9

Azimuth Angle of Arrival Wave for V-V Polarization

Specular Angle
Vertical Window Frames
Ground Scatterer
Bricks II Scatterer
Bricks I Scatterer
Windows Scatterer
Direct Ray

20
10
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
0

Fig. 6.

1

2

3

4
5
6
Tx-Rx Distance (m)78Azimuth Angle of Arrival Wave for V-H Polarization

r=1

where 0 ≤ kr ≤ (Mr − 1) 1 ≤ r ≤ 3 indicates a locationof each sampling point, nk1 ,k2 ,k3 is a white Gaussian noiseof zero mean, sl is a complex amplitude of the lth wave at a(r)
reference point and µl is denoted by(1)µlFig. 5.

Azimuth Angle (degree)

Fig. 4. Means Value and Standard Deviations of Data Measurement for V-V
and V-H polarizations

1

2π
π
π
∆x sin(φl − ) cos( − θl ),
λc
2
2
2π
π
∆y sin( − θl ),λc
22π∆f τl .

(4)
(5)
(6)

These values include parameters of the incident waves so thatthe objective is to obtain these L sets of 3-D mode parameters.
Then, vectorization of data measurement can be defined asz = [z1,1,1 z2,1,1 . . . zM1 ,1,1 z1,2,1 . . .

where ¦ denotes the kronecker product of each row of thematrices and
(r)

(r)

A(µ(r) ) = [a(µ1 ) . . . a(µL )] ∈ C Mr ×L ,

(9)

(r)
(r)
(r)
a(µ1 ) = [1 e−jµr . . . e−j(Mr −1)µ ]T ∈ C Mr .

(10)

The 3D unitary ESPRIT algorithm [4][5] was used to obtainthe signal parameters. It is a superresolution direction finding
method of the arrival wave. In physical terms, the ESPRIT isequivalent to finding out the parameters of the arrival wave
using the phase difference between groups of uniformly positioned elements of sensor array. The ESPRIT array data had asize of (10 × 10) or (25 × 25) cm2 for each observation point.
The arrival wave analyses were performed at 60 observation
points with an interval of 12.5 cm.

zM1 ,M2 ,1 z1,1,2 . . . zM1 ,M2 ,M3 ]T ∈ C,
= As + n,(7)

where s ∈ C L and n ∈ C M (M = M1 M2 M3 ) are thecomplex amplitude vector and noise vector respectively. The
multi-dimensional mode matrix A ∈ C M ×L is generated bymode matrices each of which corresponds to a parameter as
A = A(µ(3) ) ¦ A(µ(2) ) ¦ A(µ(1) ) ∈ C M ×L ,(8)

IV. E XPERIMENTAL R ESULTS
A. Directional Profiles
Figures 4 and 5 show the 3D unitary ESPRIT results for
azimuthal angle of the arrival wave for V-V and V-H polarization, respectively. The line perpendicular to the x-axis depicts
the range of the azimuthal angle for one observation point.
Negative azimuthal angle means the wave is coming from the第 478 回電波研連 F 分科会資料 2003 年 10 月 23 日

4

-60

35

-70

30

0

Path Gain(dB)

-10
-20
-30
-40

Direct Ray
Ground Scatterer
Bricks II Scatterer
Bricks I Scatterer
Windows Scatterer
Horizontal Window Frames
Bricks/Ground Boundary
Ground Specular Angle

-50
-60
-70
-80
-90
0

Fig. 7.

1

2

3

4
5
6
Tx-Rx Distance (m)

7

8

9

-30
Direct Ray
Ground Scatterer
Bricks II Scatterer
Bricks I Scatterer
Windows Scatterer
Horizontal Window Frames
Bricks/Ground Boundary
Ground Specular Angle
0

Fig. 8.

Path Gain(dB)Elevation Angle (degree)

-20

-90
1

2

3

4
5
6
Tx-Rx Distance (m)

7

5
0
1

2

3
4
5
6
Tx-Rx Distance (m)

7

8

9

Free Spc. Delay Tm.

Fig. 9. Power and Delay Time of Arrival Wave for Windows Scatterer with
V-V polarization

-10

-80

10

Path Gain
ESPRIT Delay Tm.

0

-70

-100

0

10

-60



15

-120

20

-50

20
-90

-110

Elevation Angle of Arrival Wave for V-V Polarization

-40

25

-80

-60

35

-70

30
25

-80

20
-90



15
-100

10

-110

5

-120

0
0

1

2

right-hand side of the receiver or source side. The legends
in figures 4 and 5 show the type of scatterers. The numberof legends on the vertical line corresponds to the numberof multipath signals. The multipaths can be detected frommany scatterers, such as ground, window’s glass, window’s
frame, bricks I, bricks II and directly from the transmitter[3]. The scattering points in the figure are categorized as
specular reflection, specular diffraction and diffuse scattering.
The specular diffraction that satisfies Keller’s law of diffraction
can be observed when the scattered waves arrive from verticalframe of the windows. The scatterer wave on the vertical
windows frame is dominated by the V-V polarization. Figures
6 and 7 show the elevation angle of the arrival wave for V-V
and V-H polarizations, respectively. The diffraction effects areobserved when the distance between transmitter and receiverantenna was 3.5-5 m with large elevation angle. It corresponds
to horizontal frame of the windows. Likewise, the scatterer
wave on the horizontal windows frame is dominated by theV-H polarization. Due to the fact, the V-V polarization has
wider spread in azimuth and narrower spread in elevationcompared with V-H polarization. Therefore, it can be statedthat V-H polarization is concentrated on specular direction forthe scattered wave at the building surface. The explanation forthis is that frame of windows are the dominant scatterer. Owing

3

4

5

6

7

8

9

Tx-Rx Distance (m)8Elevation Angle of Arrival Wave for V-H Polarization

Time Delay (ns)Elevation Angle (degree)

10

Time Delay (ns)20

Path Gain
ESPRIT Delay Tm.

Free Spc. Delay Tm.

Fig. 10. Power and Delay Time of Arrival Wave for Windows Scatterer with
V-H Polarization

to the antenna directivity, the direct wave for V-H polarizationand the ground reflected wave for V-V polarization could not
be detected at the distance farther than 5 m.
B. Delay Profiles
Figures 8 and 9 show the path gain and delay time of thearrival waves for windows scatterers. When the azimuthal andelevation angles of the arrival wave are known, the propagation
path from the transmitter to the receiver antenna can be
determined [3]. Therefore, the delay time based on free spacevelocity (3 × 108 m/s) of each path can be easily obtained.
The figures show that the delay time directly estimated byusing ESPRIT yields close agreement with the delay timeof the propagation path determined by using DoA estimatedby ESPRIT and free space velocity. These figures also showthat more than one scattered wave from windows (glass andframes) were found for every observation point. This may be
due to the shape of windows with slight curvature. Figures
10 and 11 show the path gain and delay time of the arrival
waves scattered from bricks I and bricks II. These figures showthat the path gain difference between bricks I and bricks II issignificant compared with its delay difference even if they are
the same material. It is probable that this is caused by diffuse

35

V. C ONCLUSION

-70

30

This paper presents polarimetric measurement of nonspecular scattering from building surface roughness. The results show that the non-specular scatterings from building
surfaces are more dominated by frame scatterers rather thanbrick scatterers. The vertical frames are dominant scatterers for
V-V polarization. Likewise, the horizontal frames are dominant
scatterers for V-H polarization. The second order scattering,which sometimes was found with low path gain and large
in delay time, was not discovered in the V-H polarization.
The scattering point of the V-V and V-H polarizations canbe observed as specular reflection, specular diffraction anddiffuse scattering. The average difference of path gain is 12
dB between V-V and V-H polarizations.

25

-80

20
-90



15
-100

10

-110

5

-120

0
0

1

2

3

4

5

6

7

8

9

Tx-Rx Distance (cm)Bricks I Path Gain
Bricks I ESP. Dly.
Bricks I Fre. Dly.

Bricks II Path Gain
Bricks II ESP. Dly.
Bricks II Fre. Dly.

-60

35

-70

30
25

-80

20
-90

Time Delay (ns)Fig. 11. Power and Delay Time of Arrival Wave for Bricks Scatterer with
V-V Polarization

Path Gain(dB)

5-60Time Delay (ns)Path Gain(dB)

第 478 回電波研連 F 分科会資料 2003 年 10 月 23 日



15
-100

10

-110

5

-120

0
0

1

2

3
4
5
6
Tx-Rx Distance (cm)Bricks I Path Gain
Bricks I ESP. Dly.
Bricks I Fre. Dly.

7

8

9

Bricks II Path Gain
Bricks II ESP. Dly.
Bricks II Fre. Dly.

Fig. 12. Power and Delay Time of Arrival Wave for Bricks Scatterer with
V-H Polarization

scattering or the reflection coefficient change due to the difference in elevation. The second order scattering from building
surface scatterers was not discovered in the V-H polarization.
The second order scattering was sometimes found with low
path gain and large in delay time. This is proven by the data in
table 2 that the delay time for V-H polarization is smaller thanV-V polarization. In the V-V and V-H polarization, the nonspecular scattering from building surfaces are more dominatedby windows frame scatterers rather than brick scatterers. Table
2 shows the average difference of delay time directly estimatedby using ESPRIT result and delay time of the propagation
path determined by using DoA estimated by ESPRIT and freespace velocity. The average of path gain difference between
V-V and V-H polarizations was 12 dB. This is consistent withthe measurement shown in Fig. 3.
TABLE IIAVERAGE D IFFERENCE OF D ELAY T IME AND PATH G AIN
TypeBricks I
Bricks II
Glass

Delay V-V
0.83 ns
0.51 ns
0.62 ns

Delay V-H
0.26 ns0.24 ns
0.38 ns

Path Gain
12.05 dB
11.98 dB
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Characterization in a Sub-Urban Non-Line-of-Sight Microcellular Environment”, IEEE J. Select. Areas in Comm., vol. 20, no. 3, pp.532-538,
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