## 4 Pheromone-Based Alarm Delivery Concept
### Basic Simulation Parameters  
Based on the scenario presented in Section 3, the modeled and simulated environment was defined as a squared area in which static ground sensor nodes are randomly deployed with independent uniform probability (homogeneous Poisson point process in two dimensions, which generates a geometrical random graph). The sensor nodes are set to have a communication range of \(r_{c}=350\) m and deployed with a density of 50 nodes/km\({}^{2}\) for all area sizes tested, providing a connected network according to the conditions discussed in [33]. This is an important assumption, as gaps in the network connectivity negatively impact the results, since these gaps may stop the alarm forwarding process.  
The trail-search mechanism is set to choose a random direction (0, 2\(\pi\)) according to a horizontal reference from the alarm issuer nodes, and to change its direction when an alarm reaches the edges of the mission area, choosing an angle in the interval (0, \(\pi\)) in relation to the edge.  
UAVs in the model scenario patrol the area by flying at an altitude of 250 m according to a random waypoint movement pattern following the model presented in Figure 4, with a movement step length \(L_{j}\) equal to 500 m and a heading angle \(\psi\) randomly chosen in (0, 2\(\pi\)), and at 100 km/h speed. Their communication range \(R_{com}\) is 500 m. The choice of these setup parameters is based on the characteristics of the scenario analyzed in this work, considering the usage of small (Mini or Micro) UAVs that have operational range of 10 km [34], using COTS communication technologies such as those based on IEEE 802.15.4 (extended range version) radios. Unless stated differently, the trail-follow mechanism uses a backbone range \(R_{bb}\) equal to half of the UAVs' communication coverage range on the ground \(R_{cov}\). The pheromone decay rate \(r\), is established to 0.995 units per second, and, after 180 s, the sensor nodes consider that the pheromone mark disappears, _i.e._, its level is set to 0. The described parameters provide trails with width close to 1 km and maximum length of 5 km, which is reached when the UAV flies in straight line for a period equal to the trail lifetime (180 s). The main simulation parameters are summarized in Table 1.  
The simulations were divided into different sets, according to variations that allow the assessment of different features and considering a corresponding goal for each set. Additionally, 100 runs were performed for each set.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline Static Sensor Nodes Communication Range & 350 \\ Static Sensor Nodes Density & 50 nodes/km\({}^{2}\) \\ UAV Altitude & 250 m \\ UAV Movement Step & 500 m \\ UAV Speed & 100 km/h \\ UAV Communication Range & 500 m \\ Pheromone Decay Rate & 0.995 units/s \\ \hline \hline \end{tabular}
\end{table}
Table 1: Main simulation parameters and values.  
Squared areas with five different dimensions were used as test scenarios for the simulations, namely 2 km \(\times\) 2 km, 4 km \(\times\) 4 km, 6 km \(\times\) 6 km, 8 km \(\times\) 8 km, and 10 km \(\times\) 10 km. Figure 9 presents those areas in scale for comparison reasons.  
Each area presented in Figure 9a illustrates a pheromone trail in scale with dimensions described by the above parameters used for the simulations, while Figure 9b presents the areas used as test case scenarios, providing a visual perspective of how much of each area can be covered at most by a trail of one UAV, when it is flying in a straight line. The gray gradient of the trails in Figure 9a (and the corresponding parts of Figure 9b) represents the strength of the pheromone level stored by the ground sensor nodes in the corresponding positions, in which the lighter the gray is, the weaker the pheromone level is.