## 2 Public Safety Network
### Drones for Public Safety
#### 2.1.2 Probability of Line of Sight  
The line of sight means the straight path from the signal source to a targeted location in three-dimensional space. Environmental impacts and elevation angle play a vital role in determining propagation features from a drone to IoT devices on the ground. For the design of a communication system, the transmitted signal should be received with sufficient signal strength without distortion. The probability distortion for LoS corresponding to each elevation angle in each propagation environment was calculated in [63]. The LoS probability from a smart drone to IoT devices on the ground will be used to estimate the coverage area and capacity, which allow IoT devices in smart environments to move around and gather data in the drone coverage area. The primary application of the channel analyzer is the ability to optimize the performance of the smart drone rapidly. The altitude of a drone plays a vital role in determining the coverage area and received signal strength on the ground. Increasing the height of a drone will lead to enhancing the coverage area. Therefore, it will deliver services to a larger area and many users and devices will get services. Finding an optimized altitude is significant for maximizing the probability of coverage and small loss. If the height of the drone is h and the radius of the coverage area is R, then the distance between the drone and the ground receiver d is given in Equation (1):  
\[\mathrm{d}=\sqrt{\mathrm{R}^{2}+\mathrm{h}^{2}}, \tag{1}\]  
Figure 4: An extension of the public safety network by using a team of drones. Figure 5: Drone for IoPST in emergency services and disaster recovery. where the elevation angle \(\theta\) of the drone concerning the user on the ground depends on the height of the drone and the coverage radius. This is given in Equation (2):  
\[\theta=tan^{-1}(\frac{h}{R}). \tag{2}\]  
The path loss depends on the carrier frequency \(\mathrm{f_{c}}\), the distance between drone and receiver on the ground \(\mathrm{d}\), and light speed \(\mathrm{c}\). The path loss is given by [64], as shown in Equation (3):  
\[\mathrm{PL(dB)}=\left\{ \begin{array}{rl}&20\ \log(4\pi\mathrm{f_{c}d/c})+ \varepsilon_{\mathrm{los}}\mathrm{Los}\\ &20\ \log(4\pi\mathrm{f_{c}d/c})+\varepsilon_{\mathrm{nlos}}\mathrm{NLoS}\end{array}  \right., \tag{3}\]  
where \(\varepsilon_{\mathrm{los}}\) and \(\varepsilon_{\mathrm{nlos}}\) are the average additional losses to the free space loss. One of the most significant advantages of drone communication is LoS. Therefore, the LoS probability is crucial to correctly predicting signal attenuation among drones, IoT devices, robots or any objects on the ground. Prediction of accurate LoS probability determination helps to obtain more realistic path loss models. The elevation angle is the most critical parameter for predicting LoS probability. Plotting the probability of LoS depends on the parameter values of the environmental variables \(\alpha,\beta,\gamma\), which are given different values in different areas based on [65]. The investigation of the probability of LoS condition based on [65] and the final formula of LoS probability is:  
\[\mathrm{Plos}=\prod_{n=0}^{m}\left[1-\mathrm{e}^{-\frac{\left(\mathrm{h}+0.5 \right)\left(\mathrm{ht}-\mathrm{hr}\right)}{\frac{m+1}{2\gamma^{2}}}}\right] \tag{4}\]  
\[m=r\sqrt{\alpha\beta}-1 \tag{5}\]  
\[r=h\ tan(\theta)\, \tag{6}\]  
where \(ht\) and \(hr\) represent the height of the receiver and transmitter, respectively; \(r\) is the ground distance between the receiver and transmitter. However, plotting the resulting base on Equation (4) will smooth out because of the significant value of \(ht\). Therefore, \(Plos\) is considered to be calculated based on \(\theta\) and environmental parameter impacts [63]. [PERSON] et al. [63] directly suggested \(Plos\) as:  
\[Plos=C1-(C1-C2)/(1+(\frac{\theta-C3}{C4})^{C5}, \tag{7}\]  
where \(C1\ \dots\ C5\) are environments parameters are given in [63]. However, [PERSON] et al.