Cell identification codes for tracking mobile users

Location management is a crucial issue in wireless networks. The problem of tracking mobile users has been addressed by several studies, many of which attempt to reduce the wireless cost of users tracking. The basic idea shared by most of these works is that users update their location based on a pre-defined criterion. Unfortunately, some of these strategies require the use of information, such as the distance traveled from the last known location, that is not generally available to the user. For this reason, both the implementation of some of these strategies and the performance comparison to existing strategies is not clear. In this work we propose to use Cell Identification Codes (CIC) for tracking mobile users. Each cell periodically broadcasts a short message which identifies the cell and its orientation relatively to other cells in the network. This information is used by the users to efficiently update their location. We propose several cell identification encoding schemes, which are used to implement different tracking strategies. The best performance is achieved by a four-bit CIC, used to implement a distance-based tracking strategy in a two dimensional system. In addition, we propose a combination of timer and movement tracking strategy, based on either a one-bit or a two-bit CIC, depending on system topology and user mobility. An important property of our framework is that the overall performance cost, and hence its comparison to existing methods, is evaluated for each tracking strategy. The CIC-based strategies are shown to outperform the timer-based method over a wide range of parameters.