LATS: A load-adaptive threshold scheme for tracking mobile users

Mobile user tracking is a major issue in wireless networks. Previous studie s and traditional approaches dealt only with tracking algorithms which adap t themselves to the user activity. In this work, we propose a novel approac h 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-ra te dependent not only on the user activity (such as the cab profile and mob ility pattern). Rather, it is also made dependent on the signaling load, wh ich reflects the actual cost of the update operation. Thus, at low-signalin g load locations, the users are to transmit location update messages more f requently. To carry out this approach, we propose a load-adaptive threshold scheme (LATS): the network determines for each cell, a registration thresh old level (which depends on the cell load) and announces it, as a broadcast message, to the users. The user computes its own registration priority and then transmits a registration message only if its priority exceeds the ann ounced threshold level. Thus, whenever the local load on the cell is low, t he registration activity increases, while in loaded cells the registration activity decreases. Our analysis shows that the LATS reduces the paging cos t, in comparison with other dynamic methods, without increasing the wireles s cost of registration. Moreover, if higher user density is coupled with le ss mobility (e.g., consider vehicles), then the LATS strategy offers furthe r performance improvement. The load-adaptive strategy can be used in additi on to any other dynamic tracking strategy. Furthermore, the computational c omplexity imposed on the user is identical to that required by an equivalen t load-insensitive scheme.