Optimizing Message Ferry Scheduling in a DTN.

We consider a special type of Delay Tolerant Network (DTN), called "Local-Ferry-based network" (LFN), which enables communication among multiple nodes distributed over a geographic terrain. LFN utilizes controllable special purpose vehicles called "pigeons" to transfer messages among neighboring nodes: some (or all) nodes own these message ferries (a.k.a. pigeons), which help in establishing communication links among local nodes, cumulatively setting up the whole network. One research challenge is to schedule the pigeon movement between local nodes (i.e., deciding the pigeon's visiting sequence of the local nodes) to achieve good networking performance (e.g., message delay). Solving this research challenge poses promise for many exciting applications, such as using drones to enable communication among segregated regions in disaster recovery, to augment/connect in-situ IoT deployments, and more. In this paper, we address the above challenge whereas we contribute the following. First, we analyze what it takes to optimize the scheduling algorithm for a pigeon. Second, using the above results we design multiple variants of scheduling algorithms, and we compare their performance with the theoretical optimal delay and with the state-of-the-art algorithms through simulation experiments. Both theoretical analysis and simulation results show the efficacy of our solution. For instance, our best scheduling algorithm achieves (within 5% margin) the theoretical optimal (per-hop) message delay.