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Scale fading are pairwise mutually exclusive, but a channel can be described by both multipath effects due to the delay spread and the Doppler spread of the channel. That is, flat fading and frequency selective fading are mutually exclusive as well as fast and slow fading; however, a channel may be flat and fast fading or frequency selective and fast fading depending on the particular channel characteristics [7, 116]. Figure 2-5 contains the list of questions to be asked about the real-world fading environment before blindly implementing the default fading model in a simulator.

5 × 10−7 FIGURE 2-3. Example simulated instantaneous power delay profile using the SalehValenzuela wideband channel model [114]. receiver via different paths, can add constructively or destructively, hence improving or degrading signal reception. Mobility can also affect small-scale fading, where Doppler shifts can induce random frequency modulation into the desired signal [7]. As with large-scale fading, there are many commonly used small-scale fading models in the simulation community. This section describes the most popular models, including the Ricean and Rayleigh distributions.

First, how important is the inclusion of large-scale fading on the simulated output? And second, how do the three models presented help the simulation designer incorporate large-scale fading into his or her simulation? The first question is best answered with an example from [9], where the authors compare experimental data to common simulation assumptions. One such common simulation assumption is that if the receiver receives the transmitted signal at all, it is received without error. That is, large-scale fading is not considered at the receiver, only the binary function that within a threshold distance, the desired signal is received with probability 1 and outside of that threshold the signal is received with probability zero.