# UAV Deployment Using Two Levels of Stigmergy for Unstructured Environments
## 3 Methods
### Slant Beacon Deployment (SLABE)
#### 3.2.3 Role Description
In addition, the angle recommended by the _beacon_ closest to the robot, which we will call \(\Lambda^{\hat{p}}\), and its intensity should also be obtained. \(P(\Lambda_{B_{t}}^{\hat{p}})\) is a probability distribution that stores the most promising angles in the area of influence of a _beacon_. \(\Lambda_{h_{t}}^{\hat{p}}\in[0,1]\) represents the recommendation intensity of the drone. In this way, the rotation is included in the drone's movement function by extracting a random angle following this distribution (\(\mathbf{draw}(P(\Lambda_{B_{t}}^{\hat{p}}))\)) and generating a unit vector \(\mathbf{\tilde{v}}\) with this angle by means of the function \(\mathbf{vangle}\). This unit vector is rectified by the recommendation intensity of _beacon_\(\Lambda_{h_{t}}^{\hat{p}}\). Speed in a previous instant is taken into account to produce fluid behavior. This velocity will be slightly altered by a random term extracted from a Gaussian distribution \(\mathcal{N}(\mu,\sigma)\) to include a noise term that accounts for possible modeling errors in the system. We will assume that the robot is stopped at the initial instant \(\|\mathbf{f}_{0}^{\prime}\|=0\). The normalizing terms \(\alpha_{i}\) allows the performance of the behavior to be adjusted based on the environment and the available sensors and actuators. For this article, we will assume constant values of these parameters. Repeater  
The purpose of the vehicles _beacon_ or _repeaters_ is multiple. On the one hand, given that the behavior guarantees that there will be at least one communication channel between two vehicles, they are in charge of providing a communication platform between the drones. This platform could be useful, for example, in case we want to manually inspect a specific area of the environment where the drones have had access. It will also be used, when calculating the angular recommendation intensity of each _beacon_, as we will see later. The behavior of these individuals is defined in Figure 5.  
When a robot performs the role of _repeater_ or _beacon_, it must move to a state of low consumption and therefore stop its engines, setting its speed to 0. As discussed in [23], in the case of a linkage system, it is preferable for the system to be located in areas as high as possible to maximize the perception and coverage. The robot can land in the nearby area that best achieves these effects. After stopped the robot becomes part of the swarm, the communication packages that it receives must be communicated to the rest of the drones with which it communicates.This resending process is conducted automatically by XBee devices using the appropriate protocol. However, the main goal was to provide a distributed pheromone system. Therefore, we wish to develop this behavior with simple drones (microdrones) without requiring specific sensors for the communication of pheromones: we propose the use of _repeater_ robots as sematectonic deposits. In this way, each _active_ drone that leaves the action range of the _beacon_ will recommend its exit angle to the _repeater_. The _repeater_ will store the angles recommended by each drone and will also take into account how many times the drones visit it. The number of visits will be used by the _repeater_ to calculate how good the vehicle's recommendation is. If a vehicle is displayed only once, this probably means that the drone was able to move away from the repeating area in the direction it took. However, if the robot reappears many times, it is likely that its starting angle will not be appropriate. Specifically, each vehicle \(b\) in the _beacon_ state will use a probability distribution \(P(\Lambda_{B_{t}}^{b})\) at time \(t\). This distribution will store the information about which angles are most promising for the entire swarm. In addition, the recommendation intensity \(\Lambda_{h_{t}}^{b}\) will determine the weight with which it takes into account the recommendations it makes.