Modeling interference is difficult since it requires considering simultaneously the interactions between the interferer and the victim system. This is known as closed-loop performance modeling and will be discussed in greater detail in Chapter 4. In this chapter, we discuss several approximations to evaluating interference at the victim's receiver while ignoring the interactions between the interferer and the victim system. This open-loop evaluation is generally a lot easier to model.

The first model we discuss deals with approximating the interference with white noise and deriving a probability of bit error at the receiver. This theoretical bit error calculation depends on the modulation, the energy of the signal transmitted, and the noise or interference levels. While not feasible in real implementations, most receiver designs include a probability of bit error calculation in the function of the signal to noise ratio. The waterfall shape of the bit error curve helps determine the optimal operating point for a particular design.

The second model is concerned with an n-state Markov model for characterizing the state of the wireless channel. This technique goes back to early work by Gilbert that models the wireless channel using a two-state Markov chain where one state corresponds to a noisy channel and the other state corresponds to a noise free channel. We show how this model can be modified in order to model an interference limited and an interference free channel.