A closed-loop modeling environment captures the mutual effects of interference on each end device including the protocol interactions. It generally consists of detailed simulation models for the MAC and PHY layers of the wireless technologies under consideration. Additionally, a major part of any network protocol simulation model is the accurate characterization of the application and the general configuration considered. This is commonly known as usage models that describe a user activity and the deployment environment.

Detailed simulation models vary in size and complexity. Given CPU and memory requirements to make use of detailed models, it is not uncommon to find detailed protocol simulations combined with mathematical models to approximate some parts of the system, most typically the channel and physical layer models.

In this chapter, we first describe what constitutes usage cases and overview the major components that define them. In particular, we overview application models, network topologies, and channel propagation models. Then we focus on the modeling of network protocols, including the MAC and PHY layers. We discuss how to speed up this model by using some mathematical approximations for the channel and PHY models. An example using the simulation modeling concepts is presented in the context of a case study for assessing the interference between IEEE 802.11b and Bluetooth. Finally, the simulation results obtained from the closed-loop model are compared with the open-loop model results described in Chapter 4.