Mobile Ad-hoc Networks: Mobility-induced Metrics, Performance Analysis, and System Design

Abstract

Mobile Ad-hoc Network (MANET), a type of self-configuring wireless ad-hoc network, comprises of mobile elements equipped with wireless communication devices. The mobility pattern of mobile nodes and the packet forwarding strategy crucially decide MANET performance. The node mobility leads to time-varying network topology. Conventional routing schemes fails due to the infeasibility to set up the end-toend path before data transmission. The mobility pattern affects system performance through mobility-induced metrics such as contact time and inter-meeting time. These metrics are critical in determining the MANET performance, as well as choosing various scheduling/forwarding algorithms. In this dissertation, we study the effect of mobility patterns on the MANET performance through the mobility-induced metrics, e.g., inter-meeting time. The intermeeting time is typically assumed to be exponentially distributed in MANET performance studies. However, recent empirical results disclose clear power-law behavior of inter-meeting time distribution. This outright discrepancy potentially undermines our understanding of the performance tradeoffs in MANET obtained under the assumed inter-meeting time with exponential distribution, and thus calls for further study on the power-law (or more generally, non-exponential) inter-meeting time including its fundamental cause, mobility modeling, and its effect. We first prove that the finite/infinite domain with respect to the time scale of interest critically decides the exponential/power-law tail of the inter-meeting time distribution. We then show a convex ordering relationship among inter-meeting times of various mobility models indexed by their degrees of correlation, which is in good agreement with the ordering of network performance under a set of mobility patterns whose inter-meeting time distributions have power-law ‘head’ followed by exponential ‘tail’. Finally, we analyze various characteristics of the relative mobility of a random pair of nodes in MANET to show that they produce inter-meeting time with different aging properties. The aging property allows us to establish for the first time that the approach based on exponential inter-meeting time assumption can always underestimate or over-estimate the actual system performance, under stochastic mobility patterns with specific aging properties. Our results also provide theoretic guidelines on how to exploit the memory structure toward better design of protocols under general mobility.