09-01-2012, 04:08 PM
MOBILE COMPUTING LOCATION MANAGEMENT
[attachment=15923]
Introduction
Managing location information of mobile nodes is an important issue in mobile computing systems. Location management is one of the fundamental issues in cellular networks. It deals with how to track subscribers on the move and how to update his or her movements. In mobile communication environment, they are going to accommodate more subscribers; the size of the cell must be reduced to make more efficient use of the limited frequency spectrum allocation. This will add to the challenge of some fundamental issues in cellular networks. Location management consists of updating the location of the user, searching the location and performing search-updates. Various strategies can be discussed in this paper for the efficient performance of updating, searching and search-updating strategies +throughout the execution.
In a cellular network, a service coverage area is divided into smaller hexagonal areas referred to as cells. A base station serves each cell. The base station is fixed. It is able to communicate with mobile stations such as cellular telephones using its radio transceiver. The base station is connected to the mobile switching centre (MSC), which is, in turn, connected to the public switched telephone network (PSTN). The frequency spectrum allocated to wireless communication is very limited, so the cellular concept was introduced to reuse the frequency. Each cell is assigned a certain number of channels. To avoid radio interference, the channels assigned to one cell must different from the channels assigned to its neighbouring cells. The radio interference between them is tolerable. By reducing the size of the cells, the cellular network is able to increase its capacity, and therefore to serve more subscribers.
A mobile station communicates with another station, either mobile or land, via a base station. A mobile station cannot communicate with another mobile station directly. To make a call from a mobile station, the mobile station first needs to make a request using a reverse control channel of the current cell. If the request is granted by the MSC, a pair of voice channels will be assigned for the call. To route a call to a mobile station is more complicated.
The network first needs to know the MSC and the cell in which the mobile station is currently located. How to find out the current residing cell of mobile station is an issue of location management. Once the MSC the cell of the mobile station, it can assign a pair of voice channels in that cell for the call. If a call is in progress when the mobile station moves into a neighbouring cell, the mobile station needs to get a new pair of voice channels in the neighbouring cell from the MSC so that the call can continue. This process is called as ‘ handoff ‘or ‘ handover ‘. The MSC usually adopts a channel assignment strategy that prioritizes handoff calls over new calls.Providing connection-oriented services to the mobile host requires that the host be always connected to the rest of the network in such a manner that its movements are transparent to the users. This would require efficient location management in order to minimise the time taken for updates and searches, so that there is no loss of connection. The ability of mobile hosts (MHs) to autonomously move from one part of the network to another part in a mobile computing system sets it apart from static networks. Unlike static networks, the network configuration and topology keep changing in mobile computing systems. The mobility of some nodes in the network raises interesting issues in the management of location information of these nodes.
