An analytical study of fundamental mobility properties for encounter-based protocols

Traditionally, mobility in ad hoc networks was considered a necessary evil that hinders node communication. However, it has recently been recognized that mobility can be turned into a useful ally, by making nodes carry data between disconnected parts. Yet, this model of routing requires new theoretical tools to analyse its performance. A mobility-assisted or encounter-based protocol forwards data only when appropriate relays encounter each other. To be able to evaluate the performance of mobility-assisted routing schemes, it is necessary to know the statistics of various quantities related to node encounters. In this paper, we present an analytical methodology to calculate a number of useful encounter-related statistics for a general class of mobility models. We apply our methodology to derive accurate closed form expressions for popular mobility models like Random Direction, as well as for a more sophisticated mobility model that better captures behaviors observed in real traces. Finally, we show how these results can be used to analyze the performance of mobility-assisted routing schemes or other processes based on node encounters. We demonstrate that derivative results concerning the delay of various routing schemes are very accurate, under all mobility models examined.