Active tracking: Locating mobile users in personal communication service networks

The problem of tracking mobile users in Personal Communication Service (PCS ) networks is discussed. We propose a novel approach for reducing the wirel ess cost of tracking users. The basic idea is to use non-utilized system re sources for initiating queries about the location of mobile users, in addit ion to the process of user registration. Queries are applied at each cell, independently of the other cells, whenever the load on the local control ch annel drops below a pre-defined threshold. Our study focuses on two issues: (1) proposing the initiated queries approach and an algorithm for its appl ication, and (2) studying and quantifying the value of location information and evaluating the parameters affecting it. Our analysis shows that the ex pected benefit due to location knowledge in a Markovian motion model depend s, among other things, on the determinant of the transition matrix and on t he variability of the location distribution function. The active tracking a pproach, as opposed to other dynamic strategies, does not require any modif ication of user equipment. The importance of this property is in its practi cality: An implementation of a new registration strategy in current systems would require a modification of the users equipment. Moreover, the propose d method can be easily implemented in addition to any known tracking strate gy, to reduce further the tracking cost. The performance of the active trac king method is evaluated under two registration strategies: The geographic- based strategy, currently used in cellular networks, and the profile-based strategy, suggested elsewhere. Under both strategies, it significantly redu ces the tracking cost.