Towards a Mobility Metric for Reproducible and Comparable Results in Ad Hoc Networks Research

The performance of a mobile ad hoc network depends on its ability to adapt to changes in the network topology. It is therefore important to understand the relation between node mobility and topology dynamics. While the input parameters of a mobility model allow for generating different simulation scenarios (e.g., by selecting the speed, pause time, system area, and number of nodes), the relation to the actually generated degree of topology dynamics is usually not immediate. Thus, a translation of the mobility model to the resulting topology dynamics is required. A natural way to do this is to introduce the topology change rate (TCR), defined as the number of link changes per time unit as observed by a single node. If we measure the network performance versus the TCR instead of versus ‘incidental’ input parameters of a mobility model, a higher level of abstraction of the results will be achieved, and the reproducability and comparability of the results will be enhanced. This short paper derives in an analytical manner the TCR in a scenario where nodes move according to the random waypoint (RWP) model [5], being the most heavily used mobility model in reseach on ad hoc networks. Recent insights into RWP mobility have shown some unexpected behavior, e.g., with respect to the spatial node distribution [2] and the average velocity over time [8]. These results do not mean that RWP as a mobility model is ‘invalid’, but show the importance of proper use due to thorough understanding of the model. This contribution now provides the link between RWP mobility and the corresponding TCR. We • derive in an analytical manner the TCR as observed by a static node located at the center of a circular area in which mobile nodes move according to RWP model.