Deficit Round-Robin Based Message Ferry Routing

Message Ferrying is a mobility assisted scheme in which a special node, called a message ferry, is tasked with delivering data among a set of disconnected wireless nodes. One key challenge for such scheme is to design the ferry route in a way that improves certain network characteristics such as average data delivery delay or data loss ratio. Previous work has optimized ferry travel time, rather than directly optimizing message delivery performance metrics. In this paper, we revisit the basic ferry route design problem for stationary nodes with the goal of providing a framework for optimizing delay performance. We start with a Markovian Decision Problem (MDP) formulation which produces the optimal ferry route that minimizes the average data delivery delay. While this formulation, in principle, enables optimal ferry route design, it is numerically intractable for moderate to large size problems. Solutions to small problems, however, yield insight into the properties of optimal ferry routes. These insights, in turn, lead us to propose a ferry route design algorithm that takes advantage of the similarity between our problem and the link scheduling problem in traditional networks. Our algorithm is inspired by the Deficit Round Robin (DRR) algorithm which has provable properties for delay optimization when applied to link scheduling. Using simulations we show that our DRR-based algorithm produces ferry routes that are close to optimal when compared to the MDP-derived solutions for small problems. Our results also show that our algorithm produces ferry routes for moderate to large problems that significantly outperform existing solutions.