Fundamentals For An Autonomous Zebro Swarm

Abstract

In this thesis, a swarm is defined as:
”A swarm is a large number of homogenous, unsophisticated agents that interact locally
among themselves and their environment, without any central control or management to
yield a global behaviour to emerge.”
The bigger perspective is to have the units within a swarm operate for a potentially infinite amount
of time, thus making algorithms and energy use as effective as possible. The research is split up in
different sections: sensors, communication and behaviour. The behaviour is split again: individual
behaviour, anti collision behaviour and swarming behaviour.
The research on the sensors and communication points out that the Bluetooth Low Energy (BLE)
sensor is the most suitable for an autonomous Zebro Swarm. BLE can be used to transfer data as well
as serve as a range sensor. As a communication device, BLE offers the ability to advertise data an has
a range of 50 meters which is sufficient for application in a swarm. As a sensor, BLE offers fairly
accurate measurements in distances below 1 meter. Due to the properties of radio signal strength and
the always present radio frequency noise, the accuracy decreased with increasing distances.
The individual behaviour aims at exploring as much area as possible, with the amount of energy
available. The energy use therefore has to be minimised and the explored area maximised. Since
little is known on the energy use, this is assumed constant. Maximising area, however, has some
key elements. The first is to keep moving; standing still results in energy use without exploring new
terrain. The second is to make only gentle turns; the rotational centre must be outside of the detection
distance. When this centre lies inside of the detection distance, the inner turn will cover area for a
longer period making the turn ineffective.
The anti collision behaviour should prevent units from making physical contact. By using a contactless
sensor an approaching collision can be detected. Changing the parameters of the movement
of the units at the moment they enclose more than a certain value prevents the collision.
The anti separation behaviour should prevent units from separating from eachother. This can be
done by making units turn 180 degrees once the relative distance reaches a certain limit. The turning
on a certain limit is a simple algorithm and thus requires little processing power.
Apart from the anti collision behaviour and the anti separation behaviour, there is another approach
to deal with these behaviours. Since the units are able to communicate with each other, they can also
advertise their location to other units. There are several methods for a unit to acquire their location.
These methods are divided in approximate and exact location estimation methods. The Trial and Error
method is placed in the first category, the exact location estimation methods are: Time Based, Internal
Reference, External Reference and Radar. The External Reference method is considered the most
applicable of these methods since it is relatively accurate, simple and provides a direct location.