Mobility tracking is to keep track of the users' locations for call delivery. In standards, such as IS-41 and GSM, the two-level hierarchy of location databases Is used: the Home Location Register (HLR) and the Visitor Location Register (VLR), As the number of mobile subscribers increases, the HLR may become the system bottleneck. To alleviate the burden on the HLR, a number of auxiliary strategies based on the HLR VLR architecture have been proposed. These strategies include the forwarding strategy (FS), the anchoring strategy (AS), the caching strategy (CS), and the replication strategy (RS). However, each of these strategies is only suitable for a certain type of users with a specific range or call-to-mobility, ratios (CMRs). Ia reality, a wet may change his/her mobility patterns frequently. To cope with such time varying mobility patterns efficiently, an integrated strategy is proposed in this paper. In particular, the VLRs associated with a user's home and workplace, where the user spends considerable time periods, are selected as the user's local anchors (LAs), which are connected by a forwarding pointer chain. The VLRs from which relatively high call rates to the user originate are selected as the replicas. When the user changes registration area (RA) within a local signal transfer point (LSTP) region, the new location is updated at one of the LAs. Otherwise, the new location is reported to the HLR and the replicas. In the call delivery procedure, if a call originates from one of the LAs or replicas, the HLR does not need to be queried. An analytic model that can capture actual user mobility characteristics is used for performance evaluation. Results show that in terms of the end-to end call setup, delay and location update delay, the proposed strategy outperforms the standard scheme used in GSM and IS-41, the RS scheme, and the AS scheme over a wide range of system parameters.
