Power and bandwidth optimization for personal communications mobility tracking

Mobile users maintaining communication with a wireline network via wireless links form the basis for personal communications. The wireline network tracks the current location of each user at a coarse level when the user is inactive, and refines this knowledge by paging when the user is called. Conventionally, this task of mobility tracking is achieved as follows. The geographical area of interest is divided into registration areas which consist of a large number of cells, where the cell is the coverage area of an individual radio port. Databases in the network keep track of which registration area the user is in. The user monitors beacons broadcast by the radio ports to detect a change in registration area, and notifies the network of such a change when it happens. When the user is called, all cells in that registration area are paged using wireless broadcast. Paging all cells in a registration area for each call (a call may refer to either voice or data communication) may be wasteful of downlink bandwidth if the user does not move much between calls. This may be particularly important if calls are actually bursts of data to a relatively immobile, though portable, computer. On the other hand, keeping closer track of a user´s location involves additional expenditure of portable power and uplink bandwidth for the user to announce his or her location more frequently to the network. In the paper, the author provides a mathematical formulation for this tradeoff