# UAV Deployment Using Two Levels of Stigmergy for Unstructured Environments
## 3 Methods
### Sematectonic Pheromone Deployment (SEPHE)
#### 3.3.2 Role Description  
Active drones are drones that are in flight exploring the environment. The behavior of these individuals is defined in Figure 8. Like the SLABE behavior, active drones determine their movement based on several factors. On the one hand, they determine their position with respect to the repeater vehicles, but in this case, the positioning is much more accurate (not only do they know that they are in rank with a repeater, but they know their position relative to it). On the other hand, they also take into account, in the event that two or more active robots coexist, their relative location, as long as they are within the detection range. We will assume that they also use an onboard collision sensor that will allow them to obtain a repulsion vector for areas that can generate collisions. The main novelty with respect to SLABE is that a pheromone map sent by the nearest _repeater_ is now available, which will enable them to make more informed decisions. A pheromone type of variable intensity that will lose intensity over time will be used. While _active_ robots navigate through the environment, they will leave a path of pheromones, which will be stored in the _repeater_ robots. The navigation process will continue until either the robot does not have sufficient battery power to continue developing its active task or it is in the limit communication range (_exit_range_). The pheromone emission of an _active_ robot is characterized by its intensity \(\Psi_{na}\) and its radius \(\Psi_{ra}\). Specifically, the motion of an active robot will be determined mainly by its onboard collision sensors and the local pheromone map. If deployment strategies that allow the coexistence of several active robots are tested, the local location of those robots within a certain detection range will also be used as planning information. All these parameters will be combined to obtain the robot speed. \[C = \left\{(x,y)|\sqrt{x^{2}+y^{2}}\leq\Psi_{ra}\right\} \tag{9}\] \[\mathbf{f}_{t+1}^{r} = \gamma_{1}\sum_{l=1}^{|O_{t}^{r}|}(o_{i}-\text{pos}(r_{t}))+\gamma _{2}\cdot\sum_{c\in C}\left(\frac{\langle y,x\rangle}{\|\langle y,x\rangle\|^ {2}}\cdot\Psi_{field_{y,x}}\right)+\gamma_{3}\cdot\mathbf{f}_{t}^{r}\mathcal{N} (\mu,\sigma) \tag{10}\]  
where \(C\) is the set of local Cartesian coordinates \((x,y)\) that are within the detection radius of the pheromone sensor \(\Psi_{rb}\). \(O_{t}^{r}\) is the set of obstacles detected by robot \(r\) at time \(t\), \(\langle y,x\rangle\) is a vector formed by the coordinates \(y,x\) normalized by its squared norm. \(\Psi_{field_{y,x}}\) is a matrix that stores the reading of the corresponding pheromone sensor in position \(y,x\). The speed of the drone \(\mathbf{f}_{t+1}^{r}\) at instant \(t+1\), which is defined by the sum of terms in the previous equation, is adjusted by \(\gamma_{i}\in[0,1]\), whose overall sum is one. Repeater  
As in the SLABE behavior, the repeaters are responsible for maintaining the communication channel. The behavior of these individuals is defined in Figure 9. In this case, this channel is of special importance since we are not considering sporadic communications with very little bandwidth (as in the previous case) but a channel that is used to update the pheromone map and the local location of the swarm individuals. Repeaters will be responsible for forwarding the required packages to all drones in their range of action. As soon as a drone transitions from the _active_ state to the _repeater_ state, it will emit a pheromone halo of \(\Psi_{hb}\) intensity and radius \(\Psi_{rb}\). The repeater robot will enter a state of low power consumption and should therefore be located in an area of the environment that maximizes its perception and coverage, if possible. In this behavior, repeaters must provide local positioning mechanisms and must have sufficient memory to store their local pheromone map.