On the Forwarding Performance under Heterogeneous Contact Dynamics in Mobile Opportunistic Networks

In this paper, we focus on how the heterogeneous contact dynamics of mobile nodes impact the performance of forwarding algorithms in mobile opportunistic networks (MONs). To this end, we consider two representative heterogeneous network models, each of which captures heterogeneity among node pairs (individual) and heterogeneity in underlying environment (spatial), respectively, and examine the full extent of difference in delay performance they cause on forwarding algorithms through formal stochastic comparisons. We first show that these heterogeneous models correctly capture non-Poisson contact dynamics observed in real traces. We then rigorously establish stochastic/convex ordering relationships on the delay performance of direct forwarding and multicopy two-hop relay protocol under these heterogeneous models and the corresponding homogeneous model, all of which have the same average intercontact time of a random pair of nodes. In particular, we demonstrate that the heterogeneous models predict an entirely opposite ordering relationship in delay performance depending on which of the two heterogeneity structures is captured. We also provide simulation results including the delay performance of epidemic routing protocol to support the analytical findings. Our results thus suggest that the heterogeneity in mobile nodes' contact dynamics should be properly taken into account for the performance evaluation of forwarding algorithms. Our results will also be useful for better design of forwarding algorithms correctly exploiting the heterogeneity structure.