Autonomous Airborne Wireless Networks. Группа авторов
(2.10)
(2.11)
(2.12)
(2.13)
with
For the obstructed AG propagation with the UAV altitude between 10 and 40 m, the LoS probability in the rural environment for the macro‐cell network can be computed as [7]
(2.14)
where
(2.15)
(2.16)
The path loss for LoS and NLoS links can be computed as
(2.18)
For a high‐altitude AG channel with
2.4.1.2 Small‐Scale Fading
Small‐scale fading refers to the random fluctuations of amplitude and phase of the received signal over a short distance or a short period of time due to constructive or destructive interference of the MPC. For different propagation environments and wireless systems, different distribution models are suggested to analyze the random variations in the received signal envelop. The Rician and Rayleigh distributions are widely used models in the literature of wireless communications, where both are based on the central limit theorem. The Rician distribution provides better fit for the AA and AG channels, where the impact of LoS propagation is stronger. On the other hand, when the MPC impinges at the receiver with random amplitude and phase, the small‐scale fading effect can be captured by the Rayleigh distribution [6].
Geometrical analysis, numerical simulations, and empirical data are used to obtain the stochastic fading models [38–40]. Geometry‐based stochastic channel model (GBSCM) is the most popular type of small‐scale fading model. GBSCM is subdivided into regular‐shaped geometry‐based stochastic channel model (RS‐GBSCM) and irregular‐shaped geometry‐based stochastic channel model (IS‐GBSCM). Time‐variant IS‐GBSCM was presented in [41] and RS‐GBSCM was presented in [42] and [43].These works illustrated Rician distribution for small‐scale fading. In [44], non‐geometric stochastic channel model (NGSCM) was provided, where small‐scale effects of AG propagation were modeled by using Rician and Loo models. Table 2.3 provides the measured characteristics of small‐scale fading of AG propagation in different environments.
Table 2.3 Measured small‐scale fading of AG propagation in different environments.
| References | Scenario | Frequency band | Fading distribution |
|---|---|---|---|
| Khawaja et al. [11] | Suburban/Open field | Ultra‐wideband | Nakagami |
| Newhall et al. [12] | Urban/Suburban | Wideband | Rayleigh, Rician |
| Tu and Shimamoto [13] | Urban/Suburban | Wideband | Rician |
| Matolak and Sun [14] | Urban/Suburban | Wideband |
|