Propagation loss models
There are two applets in this section. These
applets plot the graphs of path loss (dB) against distance (km) on a grid. The first applet covers the Hata, COST 231 – Hata
and the CCIR path loss models that predict the path loss between a base station
and a mobile station for a large cell link distance (or cell radius) up to 20
km. The second applet is concerned
with the Walfisch-Ikegami model that predicts the path loss between a base
station and a mobile station for a small cell link distance up to 5 km. To
select an applet click on the appropriate hypertext link above.
What the applet provides
Both applets automatically plot the graphs of path
loss (dB) against distance (km) on a grid. One curve for a specific model can
be chosen or, in some cases, more than one model can be chosen and displayed
for comparison purposes. In addition, each applet permits a distance to be
manually selected by dragging the mouse over the grid canvas to a distance
value on the range of distances provided (the x-axis) and obtaining, for the
curve or curves chosen, a screen dump of the value of the path loss for that
specified distance on a separate canvas. Any graphs existing on the canvas will
have a vertical line drawn from the selected distance and will show a black dot
where the vertical line intersects a curve. An extra blue dot is provided that
permits marking of the position of a path loss on a plot for later comparison
with a plot that doesn’t appear until the required frequency range is
entered and the original graph by that time has been removed from the canvas.
The separate canvas, known as the “information canvas” provides all
of the relevant details of the entries that you have provided and also
additional calculations such as the power law that is being used in the
Hata/CCIR models. The applet also provides, for comparison purposes, a plot of
the free-space line-of-sight curve (LOS) so that any of the curves plotted may
be compared against that for unobstructed free-space. Should the frequency
range of the model chosen not be appropriate, then no graph will be displayed.
Plotting the curves
A specific curve or specific curves are chosen
through the selection of checkboxes, a choice from a pull-down menu and entry
of parameter values by sliding to a value on a scrollbar. A text field is also
provided to allow data entry. Should the entry into the text field be
inappropriate, then an error message in the text field will be displayed. A
distance is manually selected by clicking and dragging the mouse on the yellow
grid canvas to a point anywhere above the distance required. The Hata and CCIR
models extend from 150 to 1000 MHz. After 1000 MHz the curves will not appear
on the canvas as they are out of range. The COST 231 – Hata curve
commences at 1500 MHz and extends to 2000 MHz. Outside of this range no curve
will appear.
For your comments and suggestions, mail the author: A.A.R.Townsend