On the Invariance of Spatial Node Density for Realistic Mobility Modeling

In this paper we show that human mobility exhibits "persistent" behavior in terms of the spatial density distribution of the mobile nodes over time. Using real mobility traces, we observe that the original non-homogeneous node spatial density distribution, where some regions may be quite dense while others may be completely deserted, is maintained at different instants of time. We also show that mobility models that select the next node position based on the position of other nodes, a la "preferential attachment", do not preserve the original spatial node density distribution and lead to behavior similar to random mobility as exemplified by the Random Waypoint model. To the best of our knowledge, this is the first time that these phenomena have been reported. Based on these observations, we propose a simple mobility model that preserves the desired spatial density distribution. Moreover, when simulating the operation of a network moving according to the proposed model, we found that performance results expressed by a number of network metrics also match closely results obtained under mobility governed by real traces. We also compare our results to models whose steady-state do not preserve the original non-homogeneous density distribution and show that network performance under such regimes deviates from performance under real trace mobility.