Mobility management in heterogeneous wireless networks

638 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 24, NO. 3, MARCH 2006

Mobility Management in HeterogeneousWireless Networks

Abdoul Djalil Assouma, Ronald Beaubrun, Member, IEEE, and Samuel Pierre, Senior Member, IEEE

Abstract—In heterogeneous wireless networks, mobile users areable to move from their home networks to different foreign net-works while maintaining access capability to their subscribed ser-vices, which refers to global mobility. One of the key challengesin global mobility management is intersystem location manage-ment, which consists of keeping track of mobile users who roaminto foreign networks. This paper presents an overview of mobilitymanagement in heterogeneous wireless networks and introduces ascheme which improves location management efficiency in termsof total signaling costs and intersystem paging delay. More specifi-cally, cost reduction reaches about 50% when comparing the pro-posed architecture with conventional architectures.

Index Terms—Global mobility, heterogeneous wireless network,intersystem location management, paging delay, signaling cost.

I. INTRODUCTION

CURRENT wireless networks allow mobile users carryingmultimode terminals to move from their home networks to

different foreign networks while being able to fully access theirsubscribed services [1]–[11], [21], [22]. This refers to globalmobility and service portability. In this context, locating a useror allowing him to access his services requires interoperabilitybetween several fixed and mobile subsystems that do not neces-sarily implement the same technology, which may increase thesignaling traffic and decrease the network performance.

In a mobile network, the service area is divided into locationareas (LA), and each LA covers several cells [13]–[15]. In prin-ciple, whenever a mobile terminal enters a new LA, it must up-date its location information with the network, which allows thenetwork to know exactly its current LA at any time [17], [31].Implementing LA-based methods for mobility management re-quires the use of a home location register (HLR) and several vis-itor location registers (VLR) [12], [24]. In fact, when a mobileuser first subscribes to wireless services, a permanent record ofhis profile is created in the HLR. Since this user may move fromone LA to another, his current location is usually maintained in aVLR and must be identified before the setup of any connection.

Heterogeneous wireless networks consist of several subsys-tems which use different protocols and access technologies[29]–[33]. Each subsystem divides its service area into a

Manuscript received January 16, 2005; revised May 25, 2005. This work wassupported in part by NSERC, FQRNT, and the NSERC-Ericsson Chair. Thispaper was presented in part at the IEEE WiMob 2005.

A. D. Assouma and S. Pierre are with the Mobile Computing and NetworkingResearch Laboratory (LARIM), Department of Computer Engineering, ÉcolePolytechnique de Montréal, Montréal, QC H3C 3A7, Canada (e-mail: [email protected]; [email protected]).

R. Beaubrun is with the Mobile Network Applications Research (MONARC)Group, Department of Computer Science and Software Engineering, UniversitéLaval, Laval, QC G1K 7P4, Canada (e-mail: [email protected]).

Digital Object Identifier 10.1109/JSAC.2005.862407

Fig. 1. Conventional procedure for intersystem registration.

number of location areas. In this context, intrasystem roaminglimits users’ movements between LA within a particularnetwork, whereas intersystem or global roaming considerssubscribers’ movements between subsystems using differenttechnologies. In the same vein, intersystem location updateconcerns updating the location information on a mobile ter-minal performing intersystem roaming; whereas, intersystempaging is aimed at searching for the called terminal roamingbetween different service areas. It turns out to be importantto develop a strategy for global mobility management whichfacilitates interoperability between the different subsystems.

Therestof thepaper isorganizedas follows.Section IIpresentsand analyzes several well-known approaches proposed for globalmobility management. Section III introduces a new mobilitymanagement scheme, as well as proposed procedures for inter-system registration, updating, and paging processes. Section IVpresents performance analysis of the proposed architecture, interms of total signaling costs and intersystem paging delay;whereas, Section V presents some concluding remarks.

II. BACKGROUND AND RELATED WORK

Recently, a number of methods have been proposed to analyzethe impact of global roaming on network performance [4], [16],[18]–[20], [23], [24], [28]. Among them, conventional methodsdo not use any equipment to interconnect subsystems using dif-ferent technologies, as intersystem location management is madeby means of signaling messages directly exchanged between thesubsystems. More specifically, suppose a mobile user wants tomove from subsystem to subsystem . In this case, intersystemregistration is possible if there is an agreement between operatorsof both subsystems. If so, the registration process may be com-plex since the mobile user must have an entry within the HLR ofthe visited subsystem (i.e., HLR ). Such a process is illustratedin Fig. 1 and described as follows.

1) The user sends a registration request to MSC/VLR .2) The MSC transmits this request to HLR .

0733-8716/$20.00 © 2006 IEEE

ASSOUMA et al.: MOBILITY MANAGEMENT IN HETEROGENEOUS WIRELESS NETWORKS 639

Fig. 2. Conventional procedure for intersystem location update.

3) HLR sends a query to HLR to obtain its authorization.4) HLR updates the user profile and sends a confirmation

message to HLR .5) HLR sends a confirmation message to MSC/VLR .6) MSC/VLR registers the user profile in its database and

sends a response to HLR .7) HLR sends a confirmation message to HLR .

At the end of the process, the mobile user may be served bysubsystem .

Moreover, intersystem location update concerns movementsfrom an old MSC/VLR to a new one within the visited sub-system [25]–[27], [34]. In the context of conventional methods,the procedure for such a process is illustrated in Fig. 2 and de-scribed as follows.

1) The mobile terminal sends a service request to the newMSC/VLR .

2) The new MSC/VLR transfers such a request to HLR .3) HLR sends an update message to HLR in order to keep

subsystem informed of the user movement.4) HLR sends a confirmation message to HLR .5) HLR transmits a cancellation message to the old

MSC/VLR .6) The old MSC/VLR sends a confirmation message to

HLR .7) HLR transfers the confirmation message to the new

MSC/VLR which creates an entry for the user.Furthermore, with conventional methods, intersystem paging

involves searching a mobile user in both adjacent subsystems.More specifically, HLR looks for the user in subsystem first.If this user is not found in subsystem , he will be searchedfor in subsystem . This scenario is illustrated in Fig. 3 anddecomposed as follows.

1) A call arrives at HLR , which sends a message to the lastMSC/VLR that registered the user in subsystem .

2) That MSC/VLR replies to HLR that the mobile user hasnot been found in its LA.

3) HLR sends a message to all adjacent HLR to ask for thecurrent user location.

4) HLR replies that the mobile user is in its service area.5) HLR transmits a request message to MSC/VLR (which

serves the mobile user).6) MSC/VLR sends a temporary location directory number

(TLDN) to HLR .7) HLR transfers the TLDN to HLR which forwards it to

the calling MSC/VLR.

Fig. 3. Conventional procedure for intersystem paging.

More recently, approaches for global mobility managementhave used specialized equipment to facilitate interoperabilityof subsystems using different technologies [4], [5], [18], [19],[32]. In particular, the approach presented in [4] uses a Wire-less INterworking Gateway (WING) in order to reduce signalingtraffic in the context of global mobility management. However,it has not taken into account the delay generated during thehandoff process, which may result in a degradation of the net-work quality of service. A similar approach presented in [19]is based on the user profile to manage global mobility. Thisapproach implements the intersystem update process by usingdynamic regions called boundary location areas (BLA). EachBLA is controlled by a boundary intersystem unit (BIU) and isevaluated in a function of the speed and the quality of service re-quired by the user application. Intersystem paging is based on aboundary location register (BLR) which is connected to eachMSC/VLR of both subsystems and contains data from userswho cross a BLA. It has been proven in [31] that this approachmay significantly reduce the signaling costs for high-mobilityusers. However, it does not specify how the registration processis set up when the mobile user turns on his terminal only after ar-riving at the visited subsystem. Furthermore, since a BLR is con-nected to each MSC/VLR of both subsystems, an intersystempaging process requires the network to consult the HLR of bothinvolved subsystems, which may increase the signaling trafficgenerated during the process.

III. PROPOSED LOCATION MANAGEMENT SCHEME

This section introduces an architectural model which im-proves network performance in the context of intersystemlocation management as well as the procedures for intersystemlocation registration, updating, and paging management.

A. Basic Idea and Principle

In the context of global mobility, it is imperative to have an ar-chitecture which not only guarantees the connections for mobileterminals roaming between heterogeneous networks but alsosupports service portability between wireless subsystems. Suchan architecture may be possible through the use of a special-ized equipment called Location Register and INternetworkingGateway (LR-ING), which interconnects the HLR of adjacentsubsystems. This interconnection is different than that presented


Fig. 4. Interconnection of subsystems i and j with an LR-ING.

Fig. 5. Procedure for intersystem registration with LR-ING.

in [19], as it enables us to reduce not only the financial link costbut also the total signaling cost resulting from global mobility.

Fig. 4 gives an example of the interconnection of two adja-cent subsystems and in accordance with the proposed ar-chitecture. In this case, the LR-ING (denoted LR-ING ) facili-tates interoperability between subsystems and by convertingsignaling information exchanged between them. Furthermore, itcontains a database which enables us to collect and register userprofiles as well as information related to the sessions of userswho change subsystems. As a result, during the paging process,the LR-ING uses its database to retrieve the mobile terminal inthe visited subsystem, which enables us to decrease the pagingdelay during the intersystem handoff.

Moreover, the proposed approach defines a boundary loca-tion area (like in [32]) to guarantee that the update procedure,as well as authorization, and resource reservation are executedbefore entering the visited subsystem. This area is dynamic, i.e.,

configurable according to the user profiles. To evaluate the ap-proach performance, we define the following parameters:

transmission cost from an MSC/VLR to HLR;transmission cost from HLR to LR-ING;access cost to MSC/VLR;access cost to HLR;access cost to LR-ING.

B. Procedures for Intersystem Registration, Handoff, andLocation Update

Consider two adjacent subsystems and . When a subscriberof subsystem turns on his terminal for the first time in sub-system , he has to register in . As shown in Fig. 5, the regis-tration process is triggered by the MSC/VLR of the visited sub-system, i.e., MSC/VLR . In fact, when MSC/VLR detects thepresence of an unknown user in its LA, it sends an authentication


Fig. 6. Procedure for intersystem handoff with LR-ING.

request to HLR . Using the global title translation (GTT) pro-cedure, HLR recognizes that the user comes from subsystem

and notifies it to LR-ING . The latter updates its databaseby creating an entry for the user profile then transfers this in-formation to HLR . More explicitly, the registration process isexecuted as follows.

1) The user sends an authentication request to MSC/VLR .2) MSC/VLR transfers this request to HLR .3) HLR transfers the same request to LR-ING .4) LR-ING registers the subscriber profile in its database

then sends an update request to HLR .5) HLR updates its database and sends a confirmation mes-

sage to LR-ING .6) LR-ING sends a response to MSC/VLR so that it reg-

isters the subscriber in its database.

At the end of the process, the user may be served by subsystemwhich uses the LR-ING to keep track of each mobile user

coming from other subsystems.Moreover, when a subscriber from subsystem moves into

subsystem during a communication, an intersystem handoffis engaged to allow him to access his services from sub-system . More specifically, when a mobile terminal enters theboundary location area, it sends an intersystem update requestto LR-ING . The latter translates the signaling message into aformat comprehensible by subsystem , authenticates the useridentity, sends an update request to subsystem , and updatesthe user profile in its database. Such operations are illustratedin Fig. 6 and decomposed as follows.

1) The mobile terminal notifies MSC/VLR that it is movinginto subsystem .

2) MSC/VLR transfers the request to HLR .3) HLR sends the same request to LR-ING .4) LR-ING creates an entry to the mobile user in its data-

base then sends a connection request to HLR .5) HLR sends to LR-ING the parameters required to

maintain the connection, such as bandwidth and availablechannels.

6) LR-ING transfers such information to MSC/VLR .7) LR-ING transfers such information to the mobile ter-

minal via MSC/VLR .In the same vein, when a subscriber moves throughout the

LA of subsystem (i.e., from an old MSC/VLR to a new one),he has to update his location. In the context of the proposedarchitecture, the procedure for intersystem location update isillustrated in Fig. 7 and consists of the following operations.

1) The mobile terminal sends a service request to the newMSC/VLR .

2) The new MSC/VLR transfers the request to HLR .3) HLR transfers the same message to LR-ING .4) The new MSC/VLR sends a cancellation message to the

old MSC/VLR in order to update its database.5) The old MSC/VLR sends a notification message to the

new MSC/VLR .6) LR-ING sends a notification message to the new

MSC/VLR .

C. Procedure for Intersystem Paging

Intersystem paging requires determining the current locationarea, regardless of the subsystem the mobile user is located at.In this context, two possible scenarios have been identified forthe user location in accordance with the proposed architecture.

Scenario 1: Called Terminal is Located at BLA of Home Sub-system: This scenario represents the situation where the calledterminal makes an intersystem registration request, while stillbeing located at the boundary location area in its home sub-system. In this context, the procedure for intersystem paging isillustrated in Fig. 8 and consists of the following steps.

1) A call arrives at HLR , which realizes that the mobileuser has already made an intersystem registration request.Thus, it transfers the request to LR-ING .

2) LR-ING notifies HLR that the user is still located atsubsystem .

3) HLR sends a signaling message to MSC/VLR , whichcontrols the current user location.


Fig. 7. Procedure for intersystem location update with LR-ING.

Fig. 8. Procedure for intersystem paging: Scenario 1.

Fig. 9. Procedure for intersystem paging: Scenario 2.

4) MSC/VLR finds the user location, assigns a TLDN to thecalled terminal, and transfers this information to HLR ,which forwards it to the calling MSC/VLR.

Scenario 2: Called Terminal is Located at Visited Sub-system: In this context, the procedure for intersystem pagingis illustrated in Fig. 9 and consists of the following steps.

1) A call arrives at HLR which transfers the message toLR-ING .

2) LR-ING notifies HLR that a user from subsystem hasto receive a call.

3) HLR sends a signaling message to MSC/VLR , whichcontrols the user location.

4) MSC/VLR assigns a TLDN to the terminal and transfersthis information to HLR via LR-ING .

IV. PERFORMANCE EVALUATION AND NUMERICAL RESULTS

To evaluate the performance of the proposed architecture, wehave estimated the total signaling costs and paging delay for in-tersystem registration, handoff, and location update, as well aspaging procedures. Afterwards, we have compared the total sig-

naling costs obtained from the proposed architecture with thoseobtained from existing models.

A. Total Signaling Costs and Intersystem Paging Delay

To evaluate the total signaling costs, we have defined the fol-lowing parameters:

number of calls per unit of time to mobile terminal;number of times a mobile terminal changes locationareas per unit of time;number of adjacent subsystems to a given subsystem;cost for paging a terminal using LR-ING and consid-ering scenario 1;cost for paging a terminal using LR-ING and consid-ering scenario 2;cost for paging a terminal using conventional method;cost for intersystem handoff between subsystems and

using LR-ING;cost for intersystem update procedure using LR-ING;cost for intersystem update procedure using conven-tional method;cost for intersystem registration using LR-ING;cost for intersystem registration using conventionalmethod;total cost for location update using LR-ING;total cost for location update using conventionalmethod;total costs for location update and paging proceduresusing LR-ING;total costs for location update and paging proceduresusing conventional method;paging delay in subsystem ;paging delay in subsystem .

Let be the probability of intersystem mobility. Then, isgiven by [19]

call duration sojourn time

a call arrives during

As a result, the total cost for paging a terminal using the LR-INGis expressed as

(1)


In the same vein, the total cost for paging a terminal using theconventional method is expressed as

(2)

Moreover, the total costs for location update using the LR-INGinvolve registration, handoff, and update procedures in sub-system . It is expressed as

(3)

As a result, the total costs for location update and paging proce-dures using the LR-ING are given by

(4)

On the other hand, the total cost for location update usingthe conventional method requires a supplementary update costsince there does not exist any equipment between the adjacentsubsystems. In fact, when a subscriber in communication entersa new subsystem, the communication is temporarily suspendedand restored once the subscriber registers in the new subsystem.As a result, the total update cost is given by

(5)

This enables us to evaluate the total costs for location update andpaging procedures using the conventional method as follows:

(6)

To evaluate the performance of the proposed strategy, we com-bine (4) and (6) to obtain a cost ratio as follows:

(7)

where CMR (call to mobility ratio) indicates the ratioof the number of calls per unit of time to the number of changesof location areas per unit of time for a mobile terminal.

Furthermore, to evaluate the costs of procedures defined inSection III and illustrated in Figs. 5–9, it is important to takeinto account the costs of accessing the databases, as well as thelink cost illustrated in Fig. 4. In this context, Fig. 5 enables usto evaluate by summing the costs of operations executed insteps 2–6 as follows:

Thus, is given by

In the same vein, Figs. 6–9 enable us to, respectively, evaluate, , , and as follows:

TABLE ILINK COSTS

TABLE IIDATABASE ACCESS COSTS

whereas Figs. 1–3 enable us to, respectively, evaluate the costfor intersystem registration, the cost for intersystem updates,and the cost for paging a terminal by using the conventionalmethod, as follows:

with as the number of adjacent subsystems.Moreover, to evaluate the intersystem paging delay, we

have considered both one-step paging and sequential pagingschemes, i.e., the mobile terminal may be located in one ormore polling cycles [32]. In this context, when using the con-ventional approach, if a mobile terminal is searched, it willbe paged in subsystem first. If this terminal is not found insubsystem , then it will be searched in subsystem . As a result,the intersystem paging delay using the conventional approachmay be expressed as

(8)

where is the probability of intersystem mobility.However, when the LR-ING is used for intersystem paging,

the mobile terminal is searched in only one subsystem. In thiscase, the intersystem paging delay is expressed as follows:

(9)

where is the probability of intersystem mobility. In particular,when , the mobile terminal is located in onepolling cycle [32]. In this case, we, respectively, obtain for (8)and (9): and .

B. Numerical Results and Analysis

For performance evaluation of the proposed architecture interms of generated signaling costs, we consider three series oflink costs (Table I) and three series of database access costs(Table II); whereas, the number of adjacent subsystems is ran-domly fixed to 5 and CMR .


Fig. 10. Cost ratio with database access costs negligible and P = 0:3.

We first consider the case where the link costs are more sig-nificant than database access costs, i.e., ;whereas, and are given in Table I. Fig. 10 illustratesthe behavior of the cost ratio given by (7) for . Forthe chosen values of link costs, the ratio is always smaller thanone, which means that the proposed architecture transmits fewersignaling messages than the conventional architecture. The de-creasing shape of the curves comes from the fact that, for smallvalues of CMR, the users change location areas more often thanthey receive calls. Since the proposed architecture involves theLR-ING, which constitutes a supplementary link, it generatesmore signaling messages for such a situation. On the other hand,for low-speed users, the improvement in the signaling cost isabout 45% for an intersystem mobility probability of 0.3.

We have also considered the situation where the database ac-cess costs are more significant than the link costs, i.e.,

; whereas, , , and are given in Table II. Fig. 11illustrates the behavior of the ratio given by (7) for .For the given link costs, the proposed architecture is particu-larly efficient for series and , where the cost of accessing theLR-ING is less than or equal to the cost of accessing the HLR.More specifically, for series of Table II and high values ofCMR (i.e., the users change location areas less often than theyreceive calls), the proposed architecture improves the conven-tional model by about 50%. However, when , the pro-posed architecture becomes less efficient than the conventionalmethod since each location update is executed at the LR-ING,which generates more signaling traffic.

Fig. 12 illustrates the behavior of the ratio given by (7) forvarious probabilities of intersystem mobility while consideringthat the link costs is more significant than database access costs,i.e., , and , (series 2 ofTable I). Here, we have chosen to signify that theVLR manages all subscribers under its coverage; whereas, theLR-ING only manages the subscribers having changed subsys-tems. We realize that for the chosen link costs the performanceof the proposed architecture increases in function of the proba-bility of intersystem mobility. The best case corresponds to animprovement of the conventional model by about 60%.

Fig. 11. Cost ratio with link costs negligible and P = 0:8.

Fig. 12. Cost ratio with database access costs negligible and various P .

Fig. 13. Cost ratio with link costs negligible and various P .

Fig. 13 illustrates the behavior of the cost ratio given by (7)for various probabilities of intersystem mobility while consid-ering that the database access costs are more significant than thelink costs, i.e., , and , ,


Fig. 14. Ratio of intersystem paging delay.

(series of Table II). This supposes that the VLR managesfewer subscribers than the LR-ING and that the LR-ING man-ages fewer subscribers than the HLR, i.e., .For the chosen link costs, the performance of the proposed ar-chitecture increases in function of the probability of intersystemmobility and for small values of CMR. In fact, when mobileusers are moving from one subsystem to another, all update op-erations are executed at the LR-ING, avoiding the access to theHLR. In general, the proposed architecture improves the con-ventional model by about 60%.

The performance of the proposed approach has also beenevaluated by defining the ratio , where and are, re-spectively, given by (8) and (9). Such a ratio quantifies the im-provement of an intersystem paging delay obtained when usingthe proposed approach. Fig. 14 illustrates the behavior of thisratio in function of . We realize that the pro-posed architecture is capable of reducing the intersystem pagingdelay regardless of the paging scheme used in each subsystem.More specifically, if the mobile terminal is located in one pollingcycle, i.e., , the proposed architecture improvesthe intersystem paging delay obtained from the conventionalmodel by a maximum of 50%. This improvement may reach65% when a sequential paging scheme is used in subsystem

, or 30% when a sequential paging schemeis used in subsystem .

C. Comparison With BLR Protocol

In this section, we compare results obtained from the pro-posed architecture with those obtained from the BLR protocol(presented in Section II) [32]. In particular, we will estimate andcompare the intersystem update and paging costs obtained byeach procedure, which will enable us to conclude on the perfor-mance of each one.

1) Cost Evaluation: For comparison purposes, we define thefollowing parameters for the BLR protocol:

transmission cost from MSC/VLR to BLR;access cost to the BLR.

These costs have the same characteristics as those defined inSection III, with the difference that the BLR can communicate

with the HLR via the MSC. In this context, the total cost forlocation update using the BLR protocol is obtained by summingthe costs of all operations executed during the same procedureof intersystem handoff, paging, or update. As a result, is givenas

(10)

Furthermore, the cost for paging a terminal using the BLRprotocol is calculated as

(11)

Thus, the total costs for location update and paging proce-dures using the BLR protocol are given by

(12)

Moreover, in the context of the proposed architecture, onlythe total cost for location update changes, since we onlyconsider the intersystem handoff process. We thus have

Then, the total costs for location update and paging proceduresusing the LR-ING are given by

(13)

For performance comparison, we combine (12) and (13) to de-fine a cost ratio as follows:

(14)

where and are, respectively, given by (12) and (13).2) Parameter Definition: For comparison purposes, the link

costs are defined in Table III; whereas, the database access costsare defined in Table IV. Since is a parameter common toboth architectures, it remains the same for the performance com-parison. On the other hand, has been chosen to be less than,equal to, or greater than . For the database access costs,we consider that the VLR only contains the user informationin its LA, which is always smaller than the LA controlled bythe HLR, the LR-ING, or the BLR. As a result, is equal toone; whereas, all other cost parameters are greater than one. Onthe other hand, since the HLR serves more subscribers than theLR-ING or the BLR, we assume that and .

3) Results Analysis: This section compares the perfor-mance of the proposed architecture with the BLR architecture.This analysis is based on (14), while using link costs definedin Table III and database access costs defined in Table IV. Wefirst consider the case where the link costs are more significantthan database access costs, i.e., ;whereas, , , and are given in Table III. Fig. 15illustrates the behavior of the ratio given by (14) forand CMR . We realize that when the BLRprotocol gives better results due to the fact that, for the pro-posed architecture, all signaling messages sent from an MSCto the LR-ING must transit via the HLR, which increases thelink costs. On the other hand, when , the proposedarchitecture transmits fewer signaling messages than the BLR


TABLE IIILINK COSTS FOR COMPARISON WITH BLR PROTOCOL

TABLE IVDATABASE ACCESS COSTS FOR COMPARISON WITH BLR PROTOCOL

Fig. 15. Comparison with BLR protocol (database access costs negligible andP = 0:3).

architecture. Furthermore, when , the proposedarchitecture enables us to reduce the signaling costs obtainedfrom the BLR protocol by about 40%. The decreasing shape ofthe curves comes from the fact that, for high values of CMR,the scenario for paging a terminal becomes more efficient usingthe proposed architecture. On the other hand, for low-speedusers, the improvement is about 45% of the total cost for aprobability of intersystem mobility of 0.3.

We now consider the situation where the database ac-cess costs are more significant than the link costs, i.e.,

; whereas, , , , andare given in Table IV. Fig. 16 illustrates the behavior of theratio given by (14) for and CMR . For thechosen values of database access costs, we realize that botharchitectures give similar results in terms of the number ofgenerated signaling messages. The main difference resides inthe interconnection of the added equipment: the LR-ING isconnected with the HLR of each subsystem, whereas the BLRis connected with all MSC/VLR in each subsystem, which is

Fig. 16. Comparison with BLR protocol (link costs negligible and P = 0:3).

Fig. 17. Comparison with BLR protocol for various CMR.

financially more expensive for an operator who intends to adoptsuch an architecture.

Finally, Fig. 17 illustrates the behavior of the ratio given by(14) in function of for various values ofCMR . The other parameters are chosen as follows:

, , , , , ,and . For such parameters, we realize that the more theCMR increases, the more the proposed architecture improvesresults obtained from the BLR protocol. The increasing shapeof the curves comes from the fact that when increases, thequantity of signaling messages generated by the proposed ar-chitecture becomes more important. In fact, for the BLR archi-tecture, each MSC/VLR has a direct access to the BLR, whichis not the case of the proposed architecture. Furthermore, whena request for location update is sent to the BLR and the user hasnot changed subsystem yet, the BLR does not know exactly inwhich location area to search. Consequently, it sends a signalingmessage to the HLR so that the latter can find the mobile user.This explains why the proposed architecture gives better resultswhen tends to zero. In general, the improvement reaches 30%approximately.


V. CONCLUSION

In this paper, we have proposed an architecture and newschemes for intersystem registration, updating, and searchscenarios in the context of global mobility management. Theproposed architecture essentially consists of adding at theboundary location area of two adjacent subsystems a spe-cialized piece of equipment called the LR-ING. The latteris connected to the HLR of each subsystem and maintainsroaming information on mobile users moving between differentsubsystems. This enables us to minimize the number of opera-tions executed by the databases in the context of global mobilitymanagement. Numerical results have shown that the proposedscheme enables us to significantly reduce the signaling costgenerated by the databases, as well as the intersystem pagingdelay. More specifically, the reduction cost reaches about 50%when comparing the proposed architecture with the conven-tional architecture and about 20% when comparing the samearchitecture with the BLR protocol. Further work should beoriented toward developing new strategies which decorrelatelocation update and search procedures and which take intoaccount the user classes in terms of mobility and type ofgenerated traffic. Then, it would be interesting to implementand test such strategies with real-time simulation software likeOPNET or NS-2.

ACKNOWLEDGMENT

The authors would like to thank the anonymous reviewers fortheir constructive remarks and suggestions.

REFERENCES

[1] L. P. Araujo and J. R. B. de Marca, “A comparative analysis of pagingand location update strategies for PCS networks,” in IEEE Int. Conf.Commun., Atlanta, GA, 1998, pp. 1395–1399.

[2] A. Bar-Noy and I. Kessler, “Tracking mobile users in wireless com-munications networks,” in Proc. 12th Annu. Joint Conf. IEEE Comput.Commun. Soc., vol. 3, San Francisco, CA, 1993, pp. 1232–1239.

[3] F. V. Baumann and I. G. Niemegeers, “An evaluation of location man-agement procedures,” in Proc. IEEE ICUPC, San Diego, CA, Sep. 1994,pp. 359–364.

[4] R. Beaubrun, “Gestion de la mobilité et ingénierie de trafic en conceptionde réseaux mobiles de troisième génération,” Ph.D. dissertation, Dept.Elec. Eng., École Polytechnique de Montréal, Montreal, QC, Canada,2002.

[5] A. Bertrand, “Jambala mobility gateway-convergence and inter-systemroaming,” Ericsson Rev., vol. 76, pp. 86–93, 1999.

[6] J. M. Brazio and N. J. S. Silva, “Performance evaluation of a multi-layer location update method,” in Proc. IEEE Veh. Technol. Conf., vol.1, Atlanta, GA, 1996, pp. 96–100.

[7] T. X. Brown and S. Mohan, “Mobility management for personal com-munications systems,” IEEE Trans. Veh. Technol., vol. 46, no. 2, pp.269–278, May 1997.

[8] K. Buchanan, R. Fudge, D. McFarlane, T. Phillips, A. Sasaki, and H. Xia,“IMT-2000: Service provider’s perspective,” IEEE Pers. Commun., vol.4, no. 4, pp. 8–13, Aug. 1997.

[9] “Digital cellular telecommunications system (Phase 2+) (GSM); Uni-versal mobile telecommunications system (UMTS); Location manage-ment procedures,” ETSI, TS 123 012 V4.0.0 (2001-03), 3GPP TS 23.012version 4.0.0 Release 4, 2001.

[10] D. Gu and S. S. Rappaport, “A dynamic location tracking strategy formobile communication systems,” in Proc. IEEE Veh. Technol. Conf., vol.1, Ottawa, Canada, May 1998, pp. 259–263.

[11] M. Hellebrandt and R. Mathar, “Location tracking of mobiles in cel-lular radio networks,” IEEE Trans. Veh. Technol., vol. 48, no. 5, pp.1558–1562, Sep. 1999.

[12] J. S. M. Ho and I. F. Akyildiz, “Dynamic hierarchical database archi-tecture for location management in PCS networks,” IEEE/ACM Trans.Netw., vol. 5, no. 5, pp. 646–660, Oct. 1997.

[13] , “Mobile user location update and paging under delay constraint,”Wireless Networks, vol. 1, no. 4, pp. 413–425, 1995.

[14] R. Jain, Y. B. Lin, C. Lo, and S. Mohan, “A caching strategy to reducenetwork impacts of PCS,” IEEE J. Sel. Areas Commun., vol. 12, pp.1434–1444, 1994.

[15] J. Jannink, D. Lam, N. Shivakumar, J. Widom, and D. C. Cox, “Efficientand flexible location management techniques for wireless communica-tion systems,” in Proc. 2nd ACM Int. Conf. Mobile Comput. Netw., Nov.1996, pp. 38–49.

[16] K. K. Leung and Y. Levy, “Global mobility management by replicateddatabase in personal communication networks,” IEEE J. Sel. AreasCommun., vol. 15, no. 10, pp. 1582–1596, Oct. 1997.

[17] J. Li, Y. Pan, and X. Jia, “Analysis of dynamic location managementfor PCS networks,” IEEE Trans. Veh. Technol., vol. 51, no. 5, pp.1109–1119, Sep. 2002.

[18] Y. B. Lin and I. Chlamtac, “Heterogeneous personal communicationsservices: Integration of PCS systems,” IEEE Commun. Mag., vol. 34,no. 9, pp. 106–113, Sep. 1996.

[19] J. McNair, I. F. Akyildiz, and M. D. Bender, “An inter-system handofftechnique for the IMT-2000 system,” in Proc. 19th Annu. Joint Conf.IEEE Comput. Commun. Soc., Tel Aviv, Israel, 2000, pp. 208–216.

[20] A. Noerpel and Y. B. Lin, “Handover management for a PCS network,”IEEE Pers. Commun., vol. 4, no. 6, pp. 18–24, Dec. 1997.

[21] R. Pandya, D. Grillo, E. Lycksell, P. Mieybegue, H. Okinaka, andM. Yabusaki, “IMT-2000 standard: Networks aspect,” IEEE Pers.Commun., vol. 4, no. 4, pp. 20–29, Aug. 1997.

[22] S. Pierre, Réseaux et Systèmes Informatiques Mobiles: Fondements, Ar-chitectures et Applications. Montreal, QC, Canada: Presses Interna-tionales Polytechnique, 2003.

[23] J. F. Rizzo and N. R. Sollenberger, “Multiplier wireless access,” IEEEPers. Commun., vol. 2, no. 3, pp. 18–30, Jun. 1995.

[24] R. D. Ryan, “Roaming between heterogeneous 3rd generation wirelessnetworks,” in Proc. IEEE Wireless Commun. Netw. Conf., vol. 1, NewOrleans, LA, Sep. 1999, pp. 321–323.

[25] H. Safa, S. Pierre, and J. Conan, “A built-in memory model for reducinglocation update costs in mobile wireless network,” Comput. Commun.,vol. 25, no. 14, pp. 1343–1353, Sep. 2002.

[26] , “An efficient location management scheme for PCS networks,”Comput. Commun., vol. 24, no. 14, pp. 1355–1369, Aug. 2001.

[27] S. Tabbane, “An alternative strategy for location tracking,” IEEE J. Sel.Areas Commun., vol. 13, no. 6, pp. 880–892, Jun. 1995.

[28] Q. Tian and D. C. Cox, “Location management in a heterogenousnetwork environment,” in Proc. IEEE Wireless Commun. Netw. Conf.,Chicago, IL, Sep. 2000, pp. 753–758.

[29] K. Ushiki and M. Fukazawa, “A new handover method for next gen-eration mobile communication systems,” in Proc. IEEE GLOBECOM,Sydney, Australia, Nov. 1998, pp. 1118–1123.

[30] W. Wang and I. F. Akyildiz, “A predictive paging scheme for IMT-2000systems,” in Proc. IEEE Veh. Technol. Conf.-Fall , vol. 3, Boston, MA,Sep. 2000, pp. 1424–1430.

[31] , “Intersystem location update and paging schemes for multitierwireless networks,” in Proc. MobiCom Conf., Boston, MA, Aug. 2000,pp. 99–109.

[32] W. Wang, “Location management techniques for next generationwireless systems,” Ph.D. dissertation, School Electrical Comput. Eng.,Georgia Inst. Technol., Atlanta, GA, 2002.

[33] J. Xie and I. F. Akyildiz, “A novel distributed dynamic location manage-ment scheme for minimizing signaling costs in mobile IP,” IEEE Trans.Mobile Comput., vol. 1, no. 3, pp. 163–175, Jul.–Sep. 2002.

[34] H. Xie, S. Tabbane, and D. J. Goodman, “Dynamic location area man-agement and performance analysis,” in Proc. IEEE Veh. Technol. Conf.,Secaucus, NJ, May 1993, pp. 536–539.

Abdoul Djalil Assouma was born in Cotonou, Republic of Benin, on July 1,1979. He received the B.Eng. degree in electrical engineering and the M.Sc.A.degree in computer engineering from École Polytechnique de Montréal, Mon-tréal, QC, Canada, in 2002 and 2004, respectively.

His research interests include mobility and quality-of-service problems in thenext-generation wireless systems. He is currently working on telecommunica-tion network management in Montreal.


Ronald Beaubrun (M’02) received the B.Eng., M.Sc.A., and Ph.D. degrees inelectrical engineering from École Polytechnique de Montréal, Montréal, QC,Canada, in 1994, 1996, and 2002, respectively.

From 1994 to 1999, he worked as a Research Assistant at the LICEF ResearchCentre, Montréal, and Ericsson Canada, where he contributed to many projectsrelated to multimedia telecommunications systems, virtual campus, virtual lab-oratories, and reliability of 3G wireless networks. He is currently an Assis-tant Professor at Université Laval, Laval, QC, Canada, where he teaches com-puter networks and mobile communications in the Department of ComputerScience and Software Engineering. His research interests include topics relatedto the next-generation wireless networks planning, such as radio coverage, ar-chitecture, global roaming, resource management, traffic modeling, as well asvalue-added services and applications.

Samuel Pierre (SM’97) received the B.Eng. degree in civil engineering fromÉcole Polytechnique de Montréal, QC, Canada, in 1981, the B.Sc. and M.Sc. de-grees in mathematics and computer science from the UQAM, Montréal, in 1984and 1985, the M.Sc. degree in economics from the Université de Montréal, in1987, and the Ph.D. degree in electrical engineering from École Polytechniquede Montréal, in 1991.

From 1987 to 1998, he was a Professor at the Université du Québec à Trois-Rivières, prior to joining the Télé-Université of Québec, an Adjunct Professor atUniversité Laval, Ste-Foy, Québec, an Invited Professor at the Swiss Federal In-stitute of Technology, Lausanne, Switzerland, and the Université Paris 7, France.He is currently a Professor of Computer Engineering at École Polytechniquede Montréal, where he is Director of the Mobile Computing and NetworkingResearch Laboratory (LARIM), Chairholder of the NSERC—Ericsson Chairin Next Generations Mobile Networking Systems, and Director of the MobileComputing and Networking Research Group (GRIM). His research interests in-clude wireline and wireless networks, mobile computing, artificial intelligence,and telelearning.

Dr. Pierre is a member of the Association for Computing Machinery (ACM).He is a Regional Editor of the Journal of Computer Science, an Associate Ed-itor of IEEE COMMUNICATIONS LETTERS, and the IEEE Canadian Review, andserves on the Editorial Board of Telematics and Informatics, edited by ElsevierScience. He has received many distinctions such as the Prix Poly 1873 for excel-lence in teaching, in 2001, and Fellow of the Engineering Institute of Canada,in 2003, among others.

Mobility management in heterogeneous wireless networks

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