IEEE Communications Magazine • August 199772Location Management Methods forThird-Generation Mobile Systems0163-6804/97/$10.00 © 1997 IEEEhe trends in telecommunications are proceeding with astrong tendency toward increasing need for mobility inthe access links within the network. Examples are:• Residential line access with the proliferation of cordlessphones (their penetration rate has passed that of fixedphones in the United States, for instance)• Business lines with wireless private branch exchange(PBX) access for voice services and wireless LANs forcomputer-oriented data communications (IEEE 802.11and HIPERLAN specifications have just completed theirstandardization)• Paging systems, which provide a low-cost, always-in-touchservice (delivering voice, numeric and alphanumeric mes-sages, and electronic mail) to a still growing part of thepopulation, especially young people• Cellular systems, which allow telecommunication accessesover wide areasFurthermore, the growth of mobility aspects in telecommu-nications networks can be seen at three different levels.• First, at a spatial level, within a few decades users whohave been able to roam with a mobile terminal, begin-ning locally and regionally (with conventional and trunkprivate mobile radio systems since the ’70s), nationallysince the early ’70s (with cellular systems), internationallysince the beginning of the ’90s (with international roam-ing, GSM for instance), and soon globally (satellite sys-tems; global mobile personal communications systemssuch as IRIDIUM, ICO, or GLOBALSTAR).• Second, from the penetration rate of mobile radio accesslines. Indeed, most optimistic surveys have nearly alwaysunderestimated the fantastic growth of cellular systems.For instance, Nordic countries like Sweden have penetra-tion rates of more than 30 percent [1].• Third, the traffic generated by each wireless user is con-stantly growing: on one hand, tetherless (e.g., cellular)subscribers use their mobile terminals more often thanthey used to (due to changing habits, cheaper call rates,wider mobility, ease of call); on the other hand, thearrival of more capacity-greedy services (Internet access-es, multimedia services, etc.) pushes the need for highercapacities per call (the high-speed circuit-switched datacapability defined for GSM Phase 2+ [2] or recent wire-less ATM studies [3]). GSM stands for Global System forMobile Communications.From all these considerations, it is easy to predict that thegeneralized mobility features will have serious impacts onfuture telecommunications networks. Mobility can be catego-rized into two areas:• Radio mobility, which mainly consists of the handoverprocess• Network mobility, which mainly consists of location man-agement (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 fluctuatingradio channel behavior [4].Location management schemes are essentially based onusers’ mobility and incoming call rate characteristics. The net-work mobility process has to face strong antagonism betweenits two basic procedures: location and paging. The location pro-cedure allows the system to keep the user’s location knowl-edge, more or less accurately, in order to be able to find him,in case of an incoming call, for example. Location registrationis also used to bring the user’s service profile near its locationand 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 sendingpaging messages in all cells where the mobile terminal couldbe located. Therefore, if the location cost is high (and thus theuser location knowledge is accurate), the paging cost will below (paging messages will only be transmitted over a smallarea). If the location cost is low (and thus the user locationknowledge is fuzzy), the paging cost will be high (paging mes-sages will have to be transmitted over a wide area).Sami Tabbane, ESPTTTABSTRACTThis article provides an overview of the means and techniques used for subscriber location management in present cellular mobile net-works. The overhead due to location management techniques used in the present cellular systems such as GSM, in particular in hightraffic spots, has already been a source of concern and is expected to augment dramatically in future wireless systems. Several proposalshave been made in the past addressing the problem associated with the cost of location management. The author provides an overviewof these contributions; in particular, he classifies the techniques, mainly into non-memory-based and memory-based approaches.Subsequently, a simple evaluation of the current location updating procedure used in GSM is presented in the context of a PCSframework to illustrate the load placed on the radio channels and on the MSC/VLR processing.IEEE Communications Magazine • August 199773In first-generation cellular mobilesystems, traffic was highly unbalanced.Less than one third of calls wereincoming calls; the remaining wereoutgoing. Therefore, the paging pro-cess (required only for incoming calls)was a rather rare event, and thus hadrather little impact on the mobilitymanagement traffic. The locationupdating procedure also had littleimpact due to the large cells. Besidesthe trends stated earlier, current sys-tems experiment with a balancebetween incoming and outgoing callrates. The paging process is thereforemore important, and thus the locationmanagement is also more important.For instance, recent statistics fromGSM operators show that, in the Parisdense urban environment, the locationupdating rate can be 10 times that of the call rate at peaktraffic hours.In the remainder of this article, we introduce the mainlocation procedures used in present systems. The GSM casewill be examined in particular. Then, we propose a classifica-tion of location management methods defined in the litera-ture for third-generation mobile systems.PRESENT LOCATION MANAGEMENT METHODSLEVEL 0: NO LOCATION MANAGEMENTIn early wide-area wireless systems (not yet cellular), humanoperators had to process the calls and the users’ location wasnot managed by the system. A user was able to generate a callthrough any base station (BS), and paging messages addressedto the called mobiles were transmitted through all BSs. Themain