ABSTRACT On Finding Optimal Registrations in Presence of Overlapping Registration Areas

Personal Communication Services (PCS) standards such as IS-41 and GSM use a location management scheme which is based on registration areas (RA). Overlapping of registration areas has been proposed to reduce the overhead of location updates in such systems [4]. Overlapping RAs form regions in which a mobile has a choice in selecting which RA to register to. The choice of current RA has implication on the number of registra-tions a mobile may require in the future. In this paper we inves-tigate the problem of finding the best (or optimal) registration for a user in a cellular PCS environment with overlapping Reg-istration Areas (RAs). We study two versions of the problem: (i) the deterministic version, where the entire trajectory of the mobile is known a-priori, and (ii) the stochastic version, where the trajectory of the mobile is not known a-priori but the sys-tem has the knowledge of mobility pattern of the mobile. The mobility pattern is modeled as a stochastic random walk across regions. In the deterministic case the method presented com-putes an optimal solution to the registration problem. In the stochastic case we present a method which determines the reg-istration which minimizes the expected number of registrations by looking ahead at the probable paths which may be traversed by the mobile in future. The paper also proposes a preemptive and a non-preemptive version of the stochastic method which in-cur different numbers of hard and soft registration operations