Optimized Searching Technique for Locating Mobile Users in Cellular Network

Cellular telephony systems, where locations of a mobile users may be unknown at some times, are becoming more common. Mobile users are roaming in a zone and reports its location only if it leaves the zone entirely. Due to search bandwidth, delay constraints and very often the potential locations of different users overlap, the problem of a concurrent search for many users is different from the problem of searching for a single user. In reality, a cellular network has to serve many competing search requests sharing a limited bandwidth. The system develops a novel method of maximizing the expected rate of successful searches under delay and bandwidth constraints. An approximation algorithm is proposed, that is optimal for most probable cases, and nearly optimal for the worst-case condition. The proposed optimized search strategy outperforms a greedy search strategy, which considers only the users' location probabilities and ignores their deadline constraints. Under certain conditions, the expected rate of successful searches generated by the proposed method is twice the equivalent rate generated by the greedy search strategy. In addition, the proposed search strategy outperforms a simple heuristic algorithm that searches around the user last known location. INTRODUCTION Wireless communications have become very pervasive. The number of mobile phones and wireless Internet users has increased significantly in recent years. Traditionally, first-generation wireless networks were targeted primarily at voice and data communications occurring at low data rates. Recently, I have seen the evolution of secondand third-generation wireless systems that incorporate the features provided by broadband. In addition to supporting mobility, broadband also aims to support multimedia traffic, with quality of service (QoS) assurance. I have also seen the presence of different air interface technologies, and the need for interoperability has increasingly been recognized by the research community. Wireless networks include local, metropolitan, wide, and global areas. The proliferation of lightweight, portable computing devices and high-speed wireless local-area networks has enabled users to remain connected while moving about inside buildings. This emerging paradigm has generated a lot of interest in applications and services that are a function of a mobile user’s physical location. The goal here is to enable the user to interact effectively with his or her physical surroundings. Examples of such interactions include: printing a document on the nearest printer, locating a mobile user, displaying a map of the immediate surroundings, and guiding a user inside a building. As the surroundings change, so does the computing that happens. The interaction between computing and location may also be less direct. For instance, when in the boss’ office, pre-fetch facts and figures on business performance and projects for ready access, but while in the cafeteria, turn on the sports score and stock ticker. In a Cellular Network, when a call to a mobile user arrives, a mobility management scheme is responsible for finding the current cell in which the mobile user resides. Typically, a mobility management scheme constitutes of a location update scheme and a paging scheme. In the last decade, many location update schemes were proposed. Basically, these schemes were movement-based, timer-based, distance-based, state-based, velocity-based. Schemes that use a hybrid of the above strategies were also proposed. It was proven in that distance-based schemes achieve better performance compared to movement-based schemes and timer-based schemes. A novel information theoretic approach for location update and derivation of probabilistic information about locations of mobile users was proposed in. A location area is composed of a number of cells. Some researches assumed that a mobile user sends a location update message to the system whenever it enters a new location area and concentrated on the design of an optimal location area. Other researchers assumed that location areas are given and focused on the decision problem of whether a mobile user should send a location update message then it enters a new location area. Recently, a convex optimization problem was formulated to minimize the costs of location update and paging in the movement-based location update scheme. In a continuous formulation for the problem of one-dimensional location area design is proposed to overcome the computational difficulty associated with the original combinatorial formulation.