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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) ModifyingAbove PL With bar equals double-struck upper P Subscript LoS Baseline times normal upper P normal upper L Subscript upper L o upper S Baseline plus left-parenthesis 1 minus double-struck upper P Subscript LoS Baseline right-parenthesis times normal upper P normal upper L Subscript upper N upper L o upper S Baseline comma

where normal upper P normal upper L Subscript upper L o upper S and are the LoS and NLoS path loss, respectively, for the free space propagation. double-struck upper P Subscript LoS is the LoS probability given as

(2.6) double-struck upper P Subscript LoS Baseline equals StartFraction 1 Over 1 plus í’œ e Superscript minus script upper B left-parenthesis theta minus í’œ right-parenthesis Baseline EndFraction comma

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 í’œ and script upper B are the constant values related to the environment, theta equals arc tangent left-parenthesis StartFraction h Over d EndFraction right-parenthesis 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) double-struck upper P Subscript LoS Superscript normal upper G Baseline equals Start 2 By 2 Matrix 1st Row 1st Column 1 comma 2nd Column if d less-than-or-equal-to 10 m comma 2nd Row 1st Column e Superscript minus StartFraction d minus 10 Over 1000 EndFraction Baseline comma 2nd Column if 10 m less-than d period EndMatrix

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)

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