Towards a model of user mobility and registration patterns

The evaluation of a great deal of research on ad hoc networks, as well as cellular networks, depends on models of user mobility. Many models have been developed and utilized, such as the random walk and random waypoint models. These are simple to implement and analyze but unlikely to be realistic. We develop a model based on extensive experimental data from a campus Wi-Fi LAN installation, representing traces from about 6000 users over a period of about 2 years. This data does not enable us to develop a user mobility model directly. However, as a first step, we develop a model of the time and sequence of locations at which user devices register. Note that this can be very useful, for instance to evaluate protocols that attempt to manage routing or resource allocations at different nodes. This paper reports work in progress on developing a user registration model. It shows the key time domain as well as space domain features we have extracted from the data. In particular, we show that the time features indicate heavy-tailed, although not power-law, distributions. The spatial features strongly indicate registration localization and hierarchy. The model itself can be represented as a set of probability distributions for various parameters. The modeler, for example a protocol designer, can then generate traces that conform to these distributions while varying the scale of the model in terms of the number of users. We close with a brief discussion of further work to refine and extend the model.