Location Management Methods for Third-Generation Mobile Systems

0163-6804/97/$10.00 © 1997 IEEE he trends in telecommunications are proceeding with a strong tendency toward increasing need for mobility in the access links within the network. Examples are: • Residential line access with the proliferation of cordless phones (their penetration rate has passed that of fixed phones in the United States, for instance) • Business lines with wireless private branch exchange (PBX) access for voice services and wireless LANs for computer-oriented data communications (IEEE 802.11 and HIPERLAN specifications have just completed their standardization) • Paging systems, which provide a low-cost, always-in-touch service (delivering voice, numeric and alphanumeric messages, and electronic mail) to a still growing part of the population, especially young people • Cellular systems, which allow telecommunication accesses over wide areas Furthermore, the growth of mobility aspects in telecommunications networks can be seen at three different levels. • First, at a spatial level, within a few decades users who have been able to roam with a mobile terminal, beginning locally and regionally (with conventional and trunk private mobile radio systems since the ’70s), nationally since the early ’70s (with cellular systems), internationally since the beginning of the ’90s (with international roaming, GSM for instance), and soon globally (satellite systems; global mobile personal communications systems such as IRIDIUM, ICO, or GLOBALSTAR). • Second, from the penetration rate of mobile radio access lines. Indeed, most optimistic surveys have nearly always underestimated the fantastic growth of cellular systems. For instance, Nordic countries like Sweden have penetration rates of more than 30 percent [1]. • Third, the traffic generated by each wireless user is constantly growing: on one hand, tetherless (e.g., cellular) subscribers use their mobile terminals more often than they used to (due to changing habits, cheaper call rates, wider mobility, ease of call); on the other hand, the arrival of more capacity-greedy services (Internet accesses, multimedia services, etc.) pushes the need for higher capacities per call (the high-speed circuit-switched data capability defined for GSM Phase 2+ [2] or recent wireless ATM studies [3]). GSM stands for Global System for Mobile Communications. From all these considerations, it is easy to predict that the generalized mobility features will have serious impacts on future telecommunications networks. Mobility can be categorized into two areas: • Radio mobility, which mainly consists of the handover process • Network mobility, which mainly consists of location management (location updating and paging) Handover processes are essentially based on radio aspects, and the main difficulties in improving handover procedures’ performance come from unpredictable and highly fluctuating radio channel behavior [4]. Location management schemes are essentially based on users’ mobility and incoming call rate characteristics. The network mobility process has to face strong antagonism between its two basic procedures: location and paging. The location procedure allows the system to keep the user’s location knowledge, more or less accurately, in order to be able to find him, in case of an incoming call, for example. Location registration is also used to bring the user’s service profile near its location and allows the network to provide him rapidly with his services (e.g., the visitor location registration, VLR, functions in GSM). The paging process achieved by the system consists of sending paging messages in all cells where the mobile terminal could be located. Therefore, if the location cost is high (and thus the user location knowledge is accurate), the paging cost will be low (paging messages will only be transmitted over a small area). If the location cost is low (and thus the user location knowledge is fuzzy), the paging cost will be high (paging messages will have to be transmitted over a wide area). Sami Tabbane, ESPTT