Wireless Network Design: Optimization Models and Solution ...

274 Marina Aguado, Jasone Astorga, Nerea Toledo and Jon Matias
12.2 Simulation Methodologies: a Taxonomy
Different strategies for simulation modeling may be identified; each of them presenting
different characteristics, advantages and disadvantages:
• Emulation: an emulator is a piece of software that allows running a program in
a different platform (hardware architecture or operating system) than the one it
was originally developed for. Unlike a simulator, which only tries to reproduce
the behavior of a program, an emulator tries to model precisely the device or
system being emulated.
• Monte-Carlo simulation: this is a static simulation methodology typically used
for the evaluation of numerical expressions. Monte Carlo methods are based on
the systematic sampling of random variables, and they include a set of techniques
that allow for the resolution of mathematical and physical problems by the execution
of random repetitive tests. However, in practice the random tests are usually
replaced by the result of certain calculations performed with random numbers.
• Discrete event simulation: this type of simulation allows for modeling systems
that evolve over time and whose state variables are discrete and change instantaneously
in separate points along time. A discrete system can be characterized by
the fact that the system activities cause discrete changes to the value of the state
variables. Typically, these changes take place at particular time instants known as
events. The description of the state of such a system includes, apart from the values
of the variables, the possible transitions between events. Therefore, a model
of a discrete event system basically consists of three elements: the state variables,
the events that change the value of those variables and the relationships between
events.
• Trace driven simulation: this type of simulation is used to model dynamic systems
and it is characterized by using a real trace as entry data. A trace is in fact
a register of events, ordered in time, which is obtained from a real system. This
approach has the advantage of providing high credibility as there is a great similarity
between the model and the real system. However, it is also true that such
models are more complex and not as representative of the real system since the
trace has a finite length.
Another classification makes reference to the support elements involved in the
specific simulation. In accordance to this, three types of simulations are identified.
These include software, hardware, and hybrid approaches. Hybrid simulation
approaches combine software and hardware simulation methods. In particular,
hardware-in-the-loop (HITL) simulations can be quite powerful for testing existing
hardware platforms and gaining insight into their performance characteristics while
modeling other aspects of the system in software. One of the case studies described
in Section 12.5 makes use of this technique.
Another global classification is the distinction between system level simulation
versus link level simulation. System-level simulation concentrates on evaluation
of the performance when multiple base stations (BSs) and mobile stations (MSs)