Subject: [NEXTEL-1] Walfisch-Ikegami loss model for Cellular System Planning

From: [email-masked]
Date: Thu, 02 Oct 2003 10:12:04 -0400

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Walfisch-Ikegami loss model for Cellular
System Planning

Introduction

This applet allows the propagation loss (dB)
to be determined as a function of distance (km) from the Walfisch-Ikegami model.
In this models, the cell radius, often referred to as the link distance, ranges
from 0.02 km to 5 km. The valid frequency range is 800 MHz to 2000 MHz. The
formulae used to code this applet and the explanation of the different losses
incurred, may be found by referring to the hypertext document “WIEqns1”. Some notes
on coding using a linear-log scale can also be accessed by clicking on the
hypertext.  A companion applet that
uses the Hata, COST 231-Hata and CCIR
model for small cells, has a link distance that ranges from 1 km to 20 km and a
frequency range from 150 MHz to 1000 or 2000 MHz, depending on the model.

Explanation of the parameter input controls

Figure 1 is a screen capture of
the controls used to input data in order to select the appropriate model and
set up the parameters corresponding to the environment.

Figure 1                Applet
controls

Choice pull
down menu (default “Metropolitan”)

Figure 2 shows the available pull
down options for the choice menu. These options are the different environments
that are applicable for determining the frequency dependent loss that is part
of the multiscreen loss formulae.

Figure 2                Environment
choices that are available

The “Metropolitan” choice, which
is short for metropolitan centres, provides a loss (dB) that is twice that of
the “Medium city & suburban” choice.  The “Medium city &
suburban” is a short form of medium sized cities and suburban centres
with moderate tree density. The reader is referred to the document “WIEqns1” in order to
consider the formulae for each of the two environments.

Scrollbars

Building
height, hroof (m) (default 30 m) (range 5 m to 200 m)

The building height is an
important parameter that occurs in the calculation of the multiscreen
diffraction loss Lmsd. It is usually used in conjunction with the
base station antenna height for determining the shadowing gain (negative loss)
and in determining the quantities that are dependent on cell radius and
frequency. The larger the difference between the building and the base station
height, where the base station is higher than the building rooftop, the lower
will be the path loss. In the absence of data, the nominal building height may
be taken to be 3 x number of floors + 3 m if the roof is pitched instead of flat.

Road width,
w (m) (default 15 m) (range 2.5 m to 100 m)

The road width occurs once in the
Walfisch-Ikegami formulae. That is, when determining one of the loss components
comprising the loss due to roof-top-to-street diffraction Lrts. The
wider the road, the lower the overall path loss. It doesn’t appear in any
other of the formulae used. In the absence of data it may be taken as half the
building separation b.

Building
separation, b (m) (default 35 m) (range 5 m to 200 m)

The building separation is one of
the terms that comprise the multiscreen diffraction loss Lmsd. The
wider the building separation, the lower will be the overall path loss. In the
absence of data, it may be taken to be between 20 m and 50 m.

Road
orientation, phi (deg) (default 90°) (range 0 to 90°)

The angle f° that the direct radio wave makes with the
building or road orientation determines the orientation loss Lori.
This orientation loss is another loss that comprises the roof-top-to-street
diffraction loss Lrts. If the angle is set to 28.25° or 90°, then Lori
becomes zero. A maximum loss of 4 dB occurs at 55°. In the absence of data, f may be taken
to be 90°.

Frequency
(MHz) (default 850 MHz) (range 800 MHz to 2000 MHz)

The Walfisch-Ikegami model
frequency range is from 800 MHz to 2000 MHz. This frequency is usually chosen
to be the centre frequency of the band under consideration.

Base station
height h1 (m) (default 30 m) (range 4 m to 50 m)

For the model, the valid range is
4 m to 50 m. As mentioned above when considering the building roof top height,
this is an important parameter in the determination of the multiscreen
diffraction loss Lmsd. It is usually used in conjunction with the
building height for determining the shadowing gain (negative loss) and in
determining the quantities that are dependent on cell radius and frequency. The
larger the difference between the building and the base station height, where
the base station is higher than the building rooftop, the lower will be the
path loss.

Mobile
station height h2 (m) (default 1.5 m) (range 1 m to 10 m)

The mobile station height is used
only once in all the Walfisch-Ikegami formulae. It is used in the determination
of the loss component of the roof-top-to-street diffraction Lrts
that occurs due to the difference between the building roof top height and the
mobile height. The higher the roof top is above the mobile station height, the
greater will be the path loss.

The graphing
canvas (default - blue dot at the
intersection of the cell radius and loss axes)

NOTE: – Please click and drag to initialize the canvas

Figure 3 shows a screen shot of
the graph canvas.

Figure 3          The
graphing canvas for Walfisch-Ikegami propagation model where, hroof = 30 m, w =
15 m, b= 35m, f = 90°,
f = 850 MHz, h1 = 30 m, h2 = 1.5 m, “Metropolitan”, cell radius =
0.253 km.

The canvas shows plotted three
curves. Because of the log-log scale, the curves appear as straight lines on
the canvas. The free space path line-of-sight (LOS) and the Walfisch-Ikegami
LOS or “Street Canyon” model (WIM-LOS) are used for comparison
purposes, so that the additional loss of the Walfisch-Ikegami model (W-I) over
the different line-of-sight (LOS) models can be observed.

To activate the canvas the mouse
must be clicked and dragged anywhere on the canvas above the “cell radius”
axis. In this case it is dragged above the 0.253 km point on the “cell
radius” axis. Once the mouse is released, a vertical line will be drawn
from the “cell radius” axis to the LOS curves and a blue dot and a
black dot placed on these curve giving some rough indication of the path loss.
In addition, the vertical line will continue from the LOS curves to
Walfisch-Ikegami curve and a black dot will be placed on this curve. Where the
mouse was released is a blue dot, which in this case is above the W-I curve. No
vertical line is drawn to this blue dot from the W-I curve. This blue dot may
be used for comparison purposes. For example, if the blue dot is dragged to one
of the curves and the parameters changed (except for the distance), the
difference in loss due to these changes can be observed.

The
information canvas

Figure 4 shows a screen shot of
the information canvas.

Figure 4          The
information canvas for Walfisch-Ikegami propagation model where, hroof = 30 m,
w = 15 m,        b=
35 m, f
= 90°,
f = 850 MHz, h1 = 30 m, h2 = 1.5 m, “Metropolitan”, cell radius =
0.253 km.  (Corresponds to figure 3).

The information canvas provides
all of the parameters that have been entered into choice pull down menu and
scrollbars. In addition, it provides the values of the path loss for each of
the models for a specified distance which is specified by the click and drag of
the mouse on the graphing canvas.
Determination of the power law for a particular curve can be determined,
as long as there exists a decade on the canvas. That is the range of distance
values that can be used to determine the power law for a particular curve is
0.1 km to 0.5 km. This is because 1 km to 5 km are also shown displayed on the
graphing canvas. Once the distance is greater than 0.5 km, no power law (Gamma)
will be displayed.

The Graphing and Information
canvas, when used together, provide detailed information about the path loss
and the parameters used. By using a screen capture programme, a permanent
record of a specific W-I curve, together with its relevant information may be
obtained and printed for future reference.

For your comments and suggestions, mail the
author: A.A.R.Townsend

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