Wireless Network Design: Optimization Models and Solution ...

278 Marina Aguado, Jasone Astorga, Nerea Toledo and Jon Matias
Fig. 12.4 Standard Normal Curve
ters each time, but with varying random number seed values. The total number of
seed values chosen (i.e., the number runs) is critically important in determining the
confidence interval, but the actual seed values themselves are not as important. 1 As
an example, Figure 5(a) represents the obtained results with different seed values
in the OPNET Modeler simulation framework [21] for a specific statistic (WiMAX
delay) in a simulation scenario when the mobile node modifies its speed from 30 to
120 Km/h. Once all executions have taken place, multiple values for the same abscissa
value are observed in Figure 5(b), each value corresponding to an experiment
with the same abscissa parameter value (speed) but a different seed value as input
[22]. It is then possible to select a desired confidence interval using the previous
formula. For each abscissa value, the specific interval is plotted as shown in Figure
5(c).
As a final general recommendation, it is important to be aware that a general
common goal to be achieved by any simulation study is that similar results can be
obtained in different emplacements under similar constraints. Following the recommendations
below helps to ensure that the experiment may be repeated somewhere
else achieving similar results:
a. Identify and clearly characterize the type of data traffic involved in the simulation.
b. Specify the simulation platform and version.
c. Specify the number of simulation runs.
d. Specify confidence intervals.
e. Specify correctly the network topology and the values for the different configuration
parameters for each node.
1 Although the sequence of numbers produced by a pseudo-random number generator may appear
to be random, the procedure used to generate the sequence from a given seed value is actually deterministic.
Thus, the sequence will eventually repeat, and the number of pseudo-random numbers
generated before the sequence repeats can be affected by the random number seed value.