# Simulation of Autonomous Underwater Vehicles (AUVs) Swarm Diffusion
## 2 Materials and Methods
### The Swarm Architecture  
We designed a \"swarm intelligence\" approach for our system: The behavior of the single drone is similar to social animals that solve problems or perform a task thanks to interaction with the other members of the group. In our case, this takes on the appearance and the collective strategy of a swarm of insects.  
We avoided concentrating all the necessary intelligence on a single vehicle, otherwise, it would have become too big and expensive: Instead, we spread it over a larger number of machines whose relatively modest cost makes it an expendable item if necessary. For this purpose, we imagine using it in areas with strong contamination, or near intense flames or highly corrosive substances.  
The strengths of the \"swarm paradigm\" are basically six:  
1. the swarm is composed of a large number of vehicles (depending on the desired density);
2. all swarm vehicles are the same and interchangeable between them;
3. each swarm vehicle is placed independently in its own position: Its fix point (starting point for performing a task) is not predetermined;
4. the single vehicle is \"stupid\" if taken individually and is simple to operate;
5. the single vehicle has its own sensors and is programmed to communicate with a reduced number of \"neighbors\": Communication with the central control takes place only in an emergency or in the event of serious malfunctions;
6. each drone goes offline autonomously when it self-assesses that it is unable to carry out the mission, being equipped with internal self-purging routines.  
From the operative point of view instead, the most important advantages of a drone swarm are:  
* **Reliability**: The overall reliability of the system is very high.
* **Scalability**: Every component of the swarm can easily engage in a task or disengage without affecting the efficiency of the swarm or the performance of a task.  
Figure 3: Short Range Optical Communication System: signal structure.  
Figure 2: Short Range Optical Communication System: transmitter/receiver chain.  
* **Parallelism**: The swarm can perform more than one task simultaneously and also different and diversified tasks.
* **Economy**: The single UAV has an extremely reduced cost for design, for its small size and for low complexity.  
One of the main strengths of the \"swarm paradigm\" is precisely the fact that the need to program every single drone in detail is lacking: Each of these instead constitutes an entity that is granted great decision-making autonomy on a small scale. We, therefore, have two operational levels, one \"tactical\" and the other \"strategic\": We decide the strategy on a higher scale level, that is, we decide what is accomplished with the fulfillment of the final mission, which can be the monitoring of a stretch of coast or the analysis of substances dispersed in marine water. The drone, on the other hand, operates on a small scale, precisely on a tactical level: It is programmed with an extremely simple philosophy and invited to \"get away with it\" without having to bring your decisions back to a higher level; moreover, it will decide in complete autonomy if its state of \"health\" allows it to carry out a mission or not [19].