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ITU‐R provides statistical parameters related to the environment that determine the height, number, and density of the buildings or obstacles. For instance, in [36], the height of the buildings can be modeled by using the Rayleigh distribution. The average path loss for the AG propagation in [17] is given as

      (2.5)

      where and are the LoS and NLoS path loss, respectively, for the free space propagation. is the LoS probability given as

(2.6)

Table 2.2 Measurement campaigns to characterize the path loss and large‐scale AG propagation fading.

References	Scenario		(dB)	(dB)
Yanmaz et al. [8]	Urban/Open field	2.2–2.6	—	—
Yanmaz et al. [9]	Open field	2.01	—	—
Ahmed et al. [10]	—	2.32	—	—
Khawaja et al. [11]	Suburban/Open field	2.54–3.037	21.9–34.9	2.79–5.3
Newhall et al. [12]	Urban/Rural	4.1	—	5.24
Tu and Shimamoto [13]	Near airports	2–2.25	—	—
Matolak and Sun [14]	Suburban	1.7 (L‐band)	98.2–99.4 (L‐band)	2.6–3.1 (L‐band)
		1.5–2 (C‐band)	110.4–116.7 (C‐band)	2.9–3.2 (C‐band)
Sun and Matolak [15]	Mountains	1–1.8	96.1–123.9	2.2–3.9
Meng and Lee [16]	Over sea	1.4–2.46	19–129	—

where and are the constant values related to the environment, is the elevation angle between the ground user and the UAV, is the altitude of the UAV, and is the distance between the ground projection of the UAV and the ground device. According to Eq. (2.6), as the elevation angle increases with the UAV altitude, the blockage effect decreases and the AG propagation becomes more LoS. An advantage of this model is that it is applicable for different environments and for different UAV altitudes. However, it is unable to capture the impact of path loss for AG propagation in mountainous regions and over water bodies due to the lack of information related to their statistical parameters.

      Conventional well‐known channel models for cellular communications can be used for UAV communications for UAV altitude between 1.5 and 10 m. One such model for the macro‐cell network was designed for the rural environment by the 3rd Generation Partnership Project (3GPP) in [7,37].

      Since LoS and NLoS links are treated separately, the probability of LoS propagation is expressed as

(2.7)

Path loss and large‐scale fading can be calculated once the LoS probability is known from Eq. (2.7). As the communication nodes change their position, path loss also changes and can be found as

      (2.8)

      (2.9)Скачать книгу