In order to make the bacterial search algorithm useful in areas larger than the limitations of the e-puck's audio sensory capabilities, we proposed that a collective navigation strategy could be implemented that utilised other mobile agents as beacons throughout the environment. By creating a traversable structure in the environment that is rooted at the charging platform, a robot could traverse it and begin the recharging process when required. The process of Diffusion Limited Aggregation was identified as a suitable way of configuring the agents for this task in a decentralised way.
|A computer simulated DLA structure(Image courtesy paulbourke.net/fractals/dla)|
Diffusion Limited Aggregation
Diffusion Limited Aggregation is a naturally occuring process that results in a randomly grown rooted tree structure (snow flakes are an example). The process can be simulated by the following algorithm:
- Start with a seed at the origin of a lattice
- A second particle is added at a random location far from the origin. The particle randomly walks until it visits a location adjactent to the seed.
- Particles are continuously added in this manner to the lattice, randomly walking until joined to the cluster
A DLA-based collective navigation strategy
A collective navigation strategy was developed that built upon the bacterial search developed for the single robot. The strategy can be briefly described as:
- When agent x requires recharge, begin transmitting alert tone
- Alert tone is propogated throughout the swarm, agents begin random walking
- When an assisting agent detects a frequency freqIn >= freqPlatform, stop and begin transmitting freqIn + 1
- Agent x begins performing gradient search on lowest frequency detected >= freqPlatform.
- When platform detects that an agent has boarded it, disable beacon
- When assisting agents detect that freqIn has been disabled, disable output and resume primary task