In step with the continued advances in wireless communications, geo-positioning, and consumer electronics in general, an infrastructure is emerging that enables services and applications that rely on the tracking of the continuously changing positions of entire populations of mobile-service users. This scenario is characterized by large volumes of updates, for which reason location update technologies become important.

This talk will describe an approach to tracking that offers accuracy guarantees for the positions of the moving objects that are stored on the server side. In this approach, the server and each mobile client share a representation of the client's changing current position, and each client issues an update to the server when its position as given by this shared representation deviates from its GPS position by more than a certain threshold.

A key issue is how to represent the changing position of a moving object so that tracking can be done with as few updates as possible. A range of tracking techniques are described that utilize progressively more information about an object's movement, ranging from assuming that an object remains in its most recently reported position to assuming that past movement trajectories of an object through a road network are known. The talk reports on experimental evaluations of the tracking techniques based on real GPS data and a corresponding real road network.