## 3 Networked Mobile Robot System Design Issues
### Holonic Reconfigurability  
Robotic researchers have always shown interest towards reconfigurable and scalable distributed robotic structures. Holonic reconfiguration was the early attempt in reconfigurable and scalable networks. Holons, introduced by [PERSON], usually work in cooperation with other holons of a group, forming a modular flexible system [87]. The basic property of a system having a holonic architecture is that it is built from simpler components working in a colony so as to achieve a global behavior of a higher order [87, 88].  
In holonic robotic structures, the overall system behavior is determined not only by the individual autonomy of each primitive robot subsystem that forms the whole structure, but also by cooperation between those subsystems. Distributed decision-making and control yield the capability of cooperation in such systems. Many works exists in the literature using modular systems that pertain to the principle of independence and cooperation, although not all of them are called as holonic.  
[PERSON] and [PERSON] [89] studied the optimum configuration of assemblies built up from modular robots for a given task. They consider kinematic geometry joined by joint elements. The optimum task oriented kinematics is obtained using genetic algorithms due to the discrete nature of the problem. [PERSON] _et al._[90] focused on the robotic systems called CEBOTs (Cellular Robotics Systems), which are functionally different robots that work together to achieve a given task by sharing subtasks. They make use of Genetic Algorithm in the trajectory planning of each module called a cell.  
[PERSON] [91] designed his own modular robotic system and produced a few prototypes. The main points in his work are the strong coupling between the modules, producing stiff structures that can also accomplish reconfiguration. Because of the self-reconfiguration ability of these systems, he calls them \"metamorphic\". These modules are designed in a hexagonal geometry due to fact that symmetry brings a great simplification to the analysis and control of self-reconfigurable systems. [PERSON] used the simulated annealing method to decide on the action of each module in the reconfiguration phase. Similar to [PERSON], [PERSON] worked on the self-reconfiguration of modular structures made up of symmetric modules. Since their hexagonal symmetric structure is similar to fractal structures, he calls each of the modules a \"fractum\" [92]. As is also the case for the metamorphic robots of [PERSON], fractums move within the structure by \"sliding\" over each other. In both of the works [91, 92], the coupling principles of the modules are the same and are based on electromagnetic fields.  
The need for holonic systems arises from the unstructured nature of the media where the robot has to operate and from the changing nature of the task in that medium. In order to adapt such a medium, the system must change its structure in an optimum way so that a variable structure is achieved in the control and task spaces while keeping itself robust and accurate in behavior [93, 94, 95]. Cooperation of robot units towards reconfiguration of the distributed robotic system can only be feasible under seamless uninterrupted communication.