Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-04-22
2002-01-22
Nguyen, Lee (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S067700, C455S504000, C342S359000
Reexamination Certificate
active
06341223
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates generally to a radio wave prediction technique using an urban canyon model. The invention is particularly useful in wireless communication system design. 2. Description of the Related Art
In a digital microcellular communication system, repeater antennas are distributed throughout a geographical coverage area, particularly an urban area, to communicate directly with wireless communication devices. The repeater antennas are typically hard wired to a main base station (BTS) serving a cell through copper cables, optic cables, or optic waveguides. An important consideration in the design of a microcellular system is where to place these antennas to prevent the occurrence of dead zones where insufficient signal strength is present. A dead zone may be caused by multiple reflections off buildings, etc., that converge at a specific location to cause the signal the fade in and out.
Empirical approaches may be used to optimize the placement of the repeater antennas to minimize performance degradation caused by multiple reflections. However, these approaches are both costly and time-consuming. As such, it is desirable to employ a method for modeling and predicting radio frequency (RF) propagation in the urban environment to arrive at suitable antenna locations. One such model is referred to as an urban canyon model, which defines a canyon formed in the space between a pair of buildings and the ground. The buildings and the ground are all assumed to be lossy dielectrics. A transmitting antenna and receiving antenna are assumed to be standing perpendicular to the ground surface. The RF energy transmitted produces a multiplicity of reflection waves off the buildings and ground. If the propagation pathways of the radio wave from the transmitting antenna to the receiving antenna are known, the reflection coefficients at the respective reflection points may be obtained. A number representing how many times the reflections have occurred in the propagation pathways of the respective reflection waves can also be found. For this purpose, an image technique is employed.
FIG. 1
illustrates the environment of the prior art urban canyon model. As illustrated, a straight road including a ground
3
, a building #
1
1
, and a building #
2
2
are modeled as forming a dielectric canyon
10
. Permittivities (&egr;
1
, &egr;
2
, &egr;
g
) and permeabilities (&mgr;
1
, &mgr;
2
, &mgr;
g
) are assigned for the respective media of building #
1
, building #
2
, and the ground as indicated in FIG.
1
. Within the canyon is a transmitting antenna
4
with three dimensional coordinates (x
t
, y
t
, z
t
) and a receiving antenna
5
with coordinates (x
r
, y
r
, z
r
). The radio waves (i.e., rays) emanating from transmitting antenna
4
are assumed to be radiated in all directions. One of the radio waves is a direct wave reaching the receiving antenna directly without any reflection. Other radio waves are multiple reflection waves reaching the receiving antenna by reflecting off one or more wall surfaces of the two buildings
1
,
2
and the ground surface
3
. The image technique is adopted to find the exact points on the wall surfaces and/or the ground at which the multiple reflection waves are reflected.
It is assumed in
FIG. 1
that the surfaces of the two buildings are infinite in the y and z directions, and the ground is infinite in they direction. This assumption is allowable because the sizes of the respective reflection surfaces are much larger than the wavelengths of the transmitted radio waves. On account of this, image antennas are assumed to be infinitely generated upon the two surfaces of the buildings
1
,
2
. Other image antennas are generated beneath the ground. Each image antenna, whether above or below the ground, is intended to correspond to a reflection off one of the buildings or off the ground surface; the location of each image antenna depends on the location and direction of its corresponding reflection ray. Once all image antennas are defined, the received power at the receiving antenna
5
can be computed using a free space model that sums the RF energy contributions from the various image antennas. An equation defining the received power caused by the direct waves received at the receiving antenna
5
and the multiple reflection waves, is:
P
r
=
P
t
(
λ
4
π
)
2
&LeftBracketingBar;
∑
n
=
0
∞
G
n
R
n
ⅇ
j
kr
n
r
n
&RightBracketingBar;
2
EQ
.
1
where, P
t
is the transmitting power, &lgr; is the wavelength of the radio wave, k is the wave number (2 &pgr;/&lgr;), n is the number of propagation pathways, G
n
is the square root of the gain product of the transmitting and receiving antennas in the n
th
propagation pathway, R
n
is a pathway reflection coefficient, and r
n
is the distance of the propagation pathway between the transmitting antenna
4
and the n
th
receiving image antenna. If n=0, then this indicates the direct wave; all other values of n indicate reflection waves. Considering the directivities and beamwidths of the transmitting and receiving antennas, the value of G
n
may be varied depending on the relative locations of the transmitting and receiving antennas. The parameter R
n
represents the product of the reflection coefficients of the waves reflected on the surfaces of buildings
1
,
2
and/or ground
3
, multiplied by the reflection counts. EQ. 1 assumes that the radio waves are all vertically polarized (&thgr;-direction). Only the radiation field strength, and not the polarization effect, is taken into account.
FIGS. 2A and 2B
illustrate a prior art procedure of generating and numbering the image antennas.
FIG. 2A
illustrates the generation of the image antennas and x-coordinates, and
FIG. 2B
illustrates the numbering of the image antennas.
The following is an explanation of a prior art algorithm which finds the propagation pathways of the direct waves and the multiple reflection waves existing in the canyon model.
Referring still to
FIG. 1
, image antennas corresponding to the reflection waves off the wall surfaces are generated because of the two dielectric surfaces, that is, the wall surfaces of the buildings. Image antennas beneath the ground surface correspond to reflection waves that include a reflection off the ground surface. R
nv
indicates the image receiving antennas generated due to reflection off the surfaces of the two buildings
1
,
2
and the ground surface
3
, where n is the number of a particular image antenna, and v is a number representing whether that image antenna is above or below the ground surface. For an image antenna above the ground surface, the number v is assigned “0”, and for an image antenna beneath the ground surface, v is assigned “1”. Therefore, the n
th
image receiving antenna above the ground surface is designated as R
no
and the n
th
image receiving antenna beneath the ground surface is designated as R
n1
.
The indefinite image antennas generated by the surfaces of the two buildings are numbered as follows:
Actual receiving antenna
5
is assigned n=0, thereby being denoted by R
00
. Image antennas generated by the reflections from the walls of both buildings are numbered as follows: those residing in the x<0 area are assigned odd numbers, and those residing in the x>0 area are assigned even numbers, in sequence.
FIG. 2A
shows the numbered antennas, and the numbering rule is illustrated by the square wave of FIG.
2
B. For each propagation pathway to be considered, the transmitting antenna is assumed to generate two image antennas R
10
and R
20
. Images R
10
and R
20
correspond to reflections off the left and right building surfaces, respectively. Image antennas generated from R
10
are denoted with the numbers in the lower part of the square wave, and image antennas generated from R
20
are denoted with the numbers in the upper part of the square wave. Thus, image R
10
(i.e., R
1
in
FIG. 2A
or “1” in
FIG. 2B
) pro
Dilworth & Barrese LLP
Nguyen Lee
Samsung Electronics Co,. Ltd.
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