Minimizing the wireless cost of tracking mobile users: an adaptive threshold scheme

Mobile user tracking is a major issue in wireless networks. Previous studies and traditional approaches dealt only with tracking algorithms which adapt themselves to the user activity. We propose a novel approach for user tracking, in which the tracking activity is adapted to both user and system activity. The basic idea is to make the user location update rate dependent not only on the user activity (such as the call profile and mobility pattern); rather, it is made dependent also on the signaling load, which reflects the actual cost of the update operation. Thus, in low signaling load locations, the users are to transmit location update messages more frequently. To carry out this approach we propose an adaptive threshold scheme (ATS). The network determines for each cell a registration threshold level (which depends on the cell load) and announces it, as a broadcast message, to the users. A user computes its own registration priority and then transmits a registration message only if its priority exceeds the announced threshold level. Thus, whenever the local load on the cell is low, the users are requested to update their locations more often, while in loaded cells the registration activity is minimised. Our analysis shows that the adaptive threshold scheme reduces the paging cost, in comparison with other dynamic methods, without increasing the wireless cost of registration