Exploring long lifetime routing (LLR) in ad hoc networks

In mobile ad hoc networks, node mobility causes links between nodes to break frequently, thus terminating the lifetime of the routes containing those links. An alternative route has to be discovered once a link is detected as broken, incurring extra route discovery overhead and packet latency. A simple solution to reduce the frequency of this costly discovery procedure is to choose a long lifetime route carefully during the route discovery phase rather than a simple random shortest-path route scheme. This simple solution, although straightforward, requires investigation of several questions before it can be implemented. Specifically, how much effect does node mobility have on the link lifetime? Correspondingly, how much effect does it have on the route lifetime? How much lifetime extension can we achieve by using a long lifetime route compared to a randomly chosen shortest-path route? How much benefit can we obtain by using these longer lifetime routes, and what is the tradeoff of using them? By answering these questions, we gain enough insight to determine under what circumstances long lifetime routes are worth being discovered and implemented. In this paper, we first formulate the distribution of a link lifetime and correspondingly the distribution of a route lifetime. Then we present an algorithm to determine the longest lifetime routes at different route lengths. We experimentally compare these long lifetime routes with traditional random shortest-path routes and reveal the tradeoff of using long lifetime routes of different lengths. All the fundamental results will serve as the guideline for our future implementation of a distributed long lifetime routing protocol.