Using mobile data collectors to federate clusters of disjoint sensor network segments

Wireless Sensor Networks (WSN) that operate unattended in harsh environments are susceptible to large scale damage, where many nodes fail simultaneously and the network gets partitioned into several disjoint segments. Restoring connectivity of structurally damaged WSN´s segments may be urgent considering that they are employed to assist in risky missions. To deal with these scenarios, Mobile Data Mules (MDMs) are employed to establish intermittent links by moving and carrying data between pairs of segments on an inter-segment minimum spanning tree (mst). In this paper, we study a constrained version of the federation problem when the number of MDM´s “k” is less than the number of edges on an mst, which makes the problem more challenging. We present a novel algorithm that groups the segments into k overlapping clusters based on the intersegment proximity. Each cluster is assigned a distinct MDM to tour its segments. A segment that belongs to two clusters serves as a gateway that enables data transfer across clusters. Our algorithm minimizes the tour length for each MDM and sets the speed of the individual MDMs to rendezvous at gateway segments so that buffering space and time for inter-cluster traffic are minimized. The simulation results confirm the effectiveness of our algorithm.