Journal of Digital Information Management  Volume 3 Number 3  September 2005 192 An Enhanced Adaptive Location Update Scheme for Next Generation PCS Networks OLA EL-SONOSY Faculty of Computer and Information Systems Ain Shams University, Cairo, Egypt Sonoso@hotmail.com AHMED HAMAD Faculty of Computer and Information Systems Ain Shams University, Cairo, Egypt Amhamd13@yahoo.com AMAL ELNAHAS Faculty of Media Engineering and Technology The German University in Cairo, Egypt amal.elnahas@guc.edu.eg Abstract: Locating users as they move from one place to another in a cellular network is a key issue that allows unrestricted mobility, yet poses several challenging constraints to the network designers. In this paper, an enhanced adaptive location update scheme is proposed to decrease the total cost of the location management process. The proposed scheme relies on the deployment of a direction based location update scheme along with a simple prediction line paging technique to decrease the paging cost. The proposed protocol is implemented over both random walk and random waypoint mobility pattern. Results obtained proved a reduction in the overall cost up to 47% compared to the direction based location update scheme without prediction. Further, the accuracy of the prediction technique for users with varying speed is increased by issuing a location update message periodically. The slight increase in the update cost is compensated by the savings in the paging cost. This enhancement is implemented over two set of experiments with different cost coefficients. Both produced a reduction in the location management overall cost up to 26% compared to the proposed protocol without the enhancement. Categories and Subject Descriptors C.2.1 [ Network Architecture and Design]: Network Communications: Wireless Communication. C.2.2 [Network Protocols] General Terms Wirelss Networks, Cellular Communication Keywords: Location management, prediction technique, location updates, line paging, cellular networks Received 15 Nov. 2004; Reviewed and accepted 10 April 2005 1. Introduction Rapid technological advances in wireless networks and cellular communication have led to the emergence of the mobile computing paradigm, where information is accessible anywhere and at any time. This new paradigm enables almost unrestricted mobility to the users which poses new set of constraints and new kind of challenges that need to be considered in the design of network protocols and information services. The two main key issues that affect network protocols are mainly mobility and wireless links characteristics. Since mobility became the norm rather than the exception, a user’s location information is an additional parameter that needs to be taken into consideration in protocol design. A cost effective technique should be deployed to locate a certain user as well as efficient data structures and algorithms to manage this fast changing data. A location management algorithm usually involves two main activities: location update and location paging. The location update is the process that is established by the mobile user to specify its location to the wired network. The paging process is the one in which the network is searching for the exact location of the mobile user for call delivery. Both paging and update consume scarce resources like wireless network bandwidth and mobile equipment power, and each have a significant cost associated with it. The total cost for locating mobile user is the cost of the update process performed by the mobile user added to the paging cost established by the network to search for the user. A tradeoff between updating the user’s location information as it varies and searching for the user whenever needed has to be maintained. This problem is aggreviated in the third and fourth generation wireless networks where the cell size is expected to shrink and the user population is increasing exponentially. There exist two main approaches for the adjustment of the number of update and paging processes performed. The first approach focuses on decreasing the number of update messages performed by the user without a great increase in the number of the paging processes. This can be accomplished by requiring from the users to send an update message only when it is necessary. On the other hand, the aim of the second approach is to decrease the paging cost incurred by the network without increasing the update messages. This can be achieved if an intelligent paging technique is deployed that will avoid paging unnecessary cells. A survey of both approaches is presented in [1, 2]. In this paper, we propose an adaptive location update scheme that aims at reducing the overall cost of the location management process by applying a two phase enhancement to the direction based location management scheme proposed in [3]. In this scheme, an update message in sent to the network with the current user location whenever a change in the moving direction of the user is detected. On call arrival, the user is paged for call delivery starting from the last reported cell. The proposed enhancement basically targets the paging cost by deploying a simple prediction technique that will allow for the intelligent paging of cells and hence minimizes the paging cost and at the same time reduces the paging delay. In the proposed protocol, the update message sent to the network includes the user’s average speed in addition to its current location. On call arrival, a simple prediction technique is then applied to predict the cell that the mobile user probably moves to, then the paging process starts from that cell and then moving up and down through the user’s moving direction line. The direction line of movement for the user is established from the mobility information reported by the user in the last update message. The proposed protocol is implemented over both random walk and random waypoint mobility pattern. Results obtained proved a reduction in the overall cost up to 47% compared to the direction based location update scheme without prediction, assuming users are moving within their average speed reported in their update message. This approach is highly recommended for mobility patterns that applies the trip concept with nearly constant speed. The second phase of the enhancement aims at adapting to the users moving with varying velocity in order to increase the accuracy of the prediction technique. The same update method is implemented where an update message is sent to the system with the mobile