COPYRIGHT © 2010 JCIT, ISSN 2078-5828 (PRINT), ISSN 2218-5224 (ONLINE), VOLUME 01, ISSUE 01, MANUSCRIPT CODE: 100709

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An Approach of Location Management in GSM using GIS

Kazi Shamsul Arefin, Aloke Kumar Saha, Adnan Anwar, and Shaila Rahman

Abstract—This paper provides with an easy to understand, step-by-step approach to location determination and management - crucial knowledge for exploiting location as a value-added service enabler for mobile communications. It presents a model of location management of Mobile Station (MS) using Geographic Information System (GIS) in GSM (Global System Module) network. There are two techniques to find out the position of MS. One is hand set based technique and another is network based technique. To finding the MS position in hand set based traditionally GPS (Global Positioning System) is used. In this paper, we used network-based technique to locate the MS by successfully integrating Time of Arrival (TOA) with GIS.

Index Terms—Mobile Station (MS), Time of Arrival (TOA), Geographic Information System (GIS), Mobile Station Location Centre (MSLC), Angle of Arrival (AOA), Time Difference of Arrival (TDOA), Mobile Station Location (MSL).

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1 INTRODUCTIONhe subject of this paper is the Mobile Station Location problem. The core of this problem is to obtain the posi-

tion of any cellular phone from the network. Although such a location-service can have many applications, the main reason for this study is the needs of the emergency call cen-ters. Emergency call centers have experienced an exploding use of cellular phones, and thus many problems with locat-ing the callers. This has led to a demand for a location ser-vice [1].

As this need was recognized, theoretical studies were done to examine how Mobile Station Location could be rea-lized. One of these is the paper “GSM Mobile Station Locat-ing” [2], by Jean-Marc Latapy at NTNU. In that paper, La-tapy showed theory on how Mobile Station Location can be performed. However, a practical method for implementa-tion was not presented.

In order to carry out further research on location proce-dures in cellular networks, it is desirable to develop a plat-form for further research on Mobile Station Location. Such a platform would be an outline of an implementation of Mo-bile Station Location, including the necessary signaling in a real mobile network. This paper aims at presenting such an outline for the GSM network.

2 OBJECTIVE OF LOCATION MANAGEMENT The main reason behind this and other works on the issue of Mobile Station Location is the need for emergency call centers to locate MSs.

2.1 The Emergency Call Centre In modern societies, many services exist to protect the inha-bitants. Some of these services need to react quickly to be able to protect the inhabitants properly. Among these are the police, the fire brigade, and medical emergency teams. To simplify the contact procedure, one or several emergen-cy call centers have been established. These can be reached by calling a simple number, and will react quickly to emer-gencies.

2.2 The Location Problem Many emergency call centers have a feature called “mark-ing of origin”. The phone number of the caller is transmit-ted to the network, and the address corresponding to the phone number can be found in the database of the phone network provider. By using digital maps and mapping ap-plications, the position of the address can be shown on the map instantly as calls arrive. Such a function is very valua-ble for the emergency call operator, as the help can be sent in the correct direction more quickly [3].

For these reasons, it is desirable for the emergency call centre that a location service for cellular phones is estab-lished. We call this location service Mobile Station Location (MSL). The call emergency centers have the following re-quirements to MSL:

1. The location information must be unique within the GSM coverage.

2. The accuracy must be reasonable - within a few hundred meters.

3. The position must be calculated within a few

———————————————— Kazi Shamsul Arefin is with the Department of Computer Science and

Engineering, University of Asia Pacific (www.uap-bd.edu), Dhanmondi, Dhaka-1209, Bangladesh. E-mail: arefin@uap-bd.edu.

Aloke Kumar Saha is with the Department of Computer Science and Engineering, University of Asia Pacific (www.uap-bd.edu), Dhanmondi, Dhaka-1209, Bangladesh. E-mail: aloke@uap-bd.edu.

Adnan Anwar is with the Department of Electrical and Electronic Engi-neering, University of Asia Pacific (www.uap-bd.edu), Dhanmondi, Dha-ka-1209, Bangladesh. E-mail: adnan@uap-bd.edu.

Shaila Rahman is with the Department of Computer Science and Engi-neering, University of Asia Pacific (www.uap-bd.edu), Dhanmondi, Dha-ka-1209, Bangladesh. E-mail: shaila@uap-bd.edu.

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seconds after the beginning of the call. 4. The location information should be shown on a map. 5. Uncertainty in the location information should also

be shown on the map, so the operator can ask for additional information to decide.

2.3 Providing position information MSL has a simple direct commercial application: position-ing. With such a service, a user can get information about his position on request, and pay for the service via the phone bill. A straightforward implementation scheme would be to use the Short Message Service (SMS) for send-ing both the location request and the returning the position information. Such a service has a long range of potential applications. The implementation of this service could be greatly simplified.

2.4 Position specific information services Another potential application of MSL is position specific information services. Information can be given to the end-user, which is relative to his position. The user can for in-stance send the short message “Where is the nearest expen-sive restaurant”, and get an answer of the type “Straight ahead two blocks and then to the left”. It is also possible with today’s network to establish a staffed pay-per-call map service, where an operator can give directions to the user. In future systems, the user might be able to download to his cellular phone a map of the surrounding area with his own position marked.

3 LOCATION DETERMINATION There are several technology alternatives for locating cellu-lar phones. Some of the commonly used methods are: • GPS (Global Positioning System) • AOA (Angle of Arrival) • TOA (Time of Arrival) • TDOA (Time Difference of Arrival)

Among these AOA, TOA and TDOA are considered to be network based solutions while the GPS is considered to be a handset based method of location determination [6,7]. The difference between the two methods is as follows:

1. Network Based: This category is referred to as “network based” because the mobile network is used to position the mobile device.

2. Handset Based: This category is referred to as “handset based” because the handset itself is the primary means of positioning the user.

Figure 3.1: GPS is a location-based technology

3.1 Global Positioning System (GPS) GPS is a location-based technology relying on a network of

24 active satellites orbiting the earth at an altitude of 20,000 km. These satellites constantly transmit radio signals to earth stations and GPS receivers [5]. At any instant of time there will be at-least three satellites available anywhere un-der the sky. A configured GPS receiver can receive the sig-nals from all available satellites in sky and can decide the position of itself in the form of latitude and longitude val-ues.

To calculate a positional value, a receiver needs to ac-quire information from at least three satellites. The position is calculated based on triangulation method. The greater the number of satellites within line of sight ranges of the receiv-er, the greater the accuracy of the location data. Using the permutations of the same data, GPS can also calculate the vehicles speed and direction.

Figure 3.2: The mobile station location is at the intersection of these

circles.

3.2 Time of Arrival (TOA) TOA is based upon the measurement of the arrival time of a signal transmitted from a mobile station to several base sta-tions. The distance between the mobile station and the re-ceiving base station is determined from the time the signal took to get from the mobile station to the base station. The distance is c times T, where c is the velocity of light and T is time of travel from mobile station to base station. Geometri-cally, it represents a circle of radius c times T, on which the mobile station must lie. The mobile station location is at the intersection of these circles, as shown in Figure 3.2.There is always a need of at least three Base stations to determine the location of Mobile station correctly.

The mobile station is located at the intersection of the three circles of radii cT1, cT2 and cT3. “C” is the velocity of light, and T1, T2 and T3 are times taken by the signal from mobile station to BS1, BS2 and BS3, respectively. The disadvantage of this technique is that the mobile station has to behave like a transponder. Processing delays and non-line of sight propagation can cause error, resulting in false TOA estimation. To tackle this situation mathematical methods are used to find the approximate location.

3.3 Time Difference of Arrival (TDOA) TOA requires that all the base stations and the mobile sta-

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tion have precise synchronized clocks and the transmitting signals be labeled with the time stamps. Just one microse-cond of timing error would cause 300 meters of location error. For these reasons, TDOA measurements are a more practical means of position location for commercial systems and are now considered the leading candidate for future location systems.

The mobile station is located at the intersection of any two of the three hyperbolas. Only two hyperbolas (mini-mum of three base stations) are required to estimate the location.

Figure 3.3: More practical means of position location gives TDOA.

Hyperbola is a curve from where the difference in the distances to two fixed points is constant. The difference in distances of the two BTSs from the MS is estimated based on the TDOA of a signal from the mobile station to two base stations. This defines a hyperbola. Reading the intersection point of three hyperbolas gives the location of the mobile station, as shown in figure 3.3.

3.4 Angle of Arrival (AOA) The position of a MS is estimated from the angles of the incoming signals detected at the fixed BTSs.

Figure 3.4: Any two angles can determine the location from the triangle formed.

Once the angle measurements have been made the MS location can be calculated from simple trigonometry or tri-angulation. The location in two dimensions can be found by the intersection of two lines of bearing, each formed by a radial from a BTS to the MS. A minimum of two BTSs are required to estimate the MS location. However, more than two BTSs are used for more accuracy and highly directional antennas are required. Therefore this method is difficult to

be implemented on handsets. But the problem in AOA is that due to Reflection, Dif-

fraction and Scattering the angle calculated at the base sta-tion maybe incorrect that may lead to situation below. In the below situation two BTSs are not able to correctly locate the MS and we need another BTS to locate MS correctly. This specially becomes more probable in urban conditions.

4 PRESENTATION OF THE LOCATION INFORMATION For the end-users, the presentation of the location informa-tion is very important. For emergency call-centre applica-tions, it is important that the location can be shown on a map; hence the operator can make a decision based on the location information.

4.1 Location Management Figure 4.1, 4.2 and 4.3 show how the MSL calculation works for one, two and three BTSs respectively. The probability for the distance from each BTS is considered circular.

Figure 4.1: Probable MS location for one BTS.

In the case of one BTS, the MS can be located anywhere within the probable area in circle. Therefore, this area must be presented to the end-users, hence that they can take decision. The area presented to the end-users will be as like in figure 4.1.

Figure 4.2: Probable MS location for two BTSs.

In the case of two BTSs, the resulting area will be the in-tersection of the two circles shown in figure 4.2. The MSL will then be presented with two circles of high probability. There are two probable points for the MSL where they in-tersected. Therefore they cannot decide where right location

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is. In some cases they may get exact position using two BTSs. However it does not work for all cases.

Figure 4.3: Probable MS location with three BTSs.

In the case of three BTSs, the area will be identified uni-quely by the subsequent BTS measurements, as shown in figure 4.3. This is because three circles intersected at a cer-tain point. Thus emergency call centers can locate the posi-tion of MSs.

Hence when emergency call centers use more than three BTSs then they will get more precise value. Therefore at least three BTSs are required to get the exact position of MS.

4.2 Discussion of Location Management Now the location information calculated during MSL can be shown efficiently using three BTSs and thus be very helpful for the operator of an emergency call centre. Which type of mapping application is used does not matter, as long as location areas can be efficiently shown on the map. However, the mapping application needs to implement the special protocol for the specification of location probability areas. Thus, this protocol needs to be agreed upon by the implementers of the MSLC and the mapping applications. We have used GIS for finding the location of MS using three BTSs. GIS provides us the position with longitude and latitude.

First end-users select the regions to get the service. MSs search the nearest three BTSs from its position. We used TOA technique to get the location of MS and view the posi-tion of MS in GIS with longitude and latitude. When we need to view the location of MSs precisely then we drag that positions and get different layers of the same map. Thus we can achieve the location precisely.

5 RESULT AND DISCUSSION We developed a system to indicate the specific location of MS. There are some methods to find the specific location. However, we used this method in the basis of rural areas. This is cost effective as well. Nowadays most of the people use mobile phone. Therefore we can cover even rural areas using this method. A place where MSs and BTSs are present that place can be covered in this mechanism. Hence it is beneficial to mobile operators to detect the locations. More-over, it is being essential to track someone for various emergency purposes.

Tracking MSs can be introduced as value added service in mobile companies. It is important for security or personal purposes and anyone can get benefit of this approach. GIS (Geographical Information System) plays an important role to detect the position of MS. It contains map of differnts layers. Many developed countries are trying to get benefit from this service. However, using our proposed system, the position of MS can be determined efficiently. A flowchart for MSL is described in figure 5.1.

Figure 5.1: Flowchart for location management system.

5.1 Discussion We simulated the system which is developed by Map suite version 2.0 and C#.net. It represents the exact position of MS to the emergency call centers. We shortly described with appropriate figures and analyzed results. It is clearly shown that how an exact position can be indicated with the help of GIS and GSM network.

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Figure 5.1: Towers can be added in different locations.

Mobile companies know where towers are located. First they setup the towers providing longitude and latitude in-formation in the Map.

Figure 5.2: Three circles intersected at a point and MS is located at that position.

Figure 5.3: Emergency call centers can locate the position precisely doing zoom then they will get another layer of the same map to get MS

position accuratly.

When emergency call centers get the radius based on signals where MS is located. Then on the screen they can see three circles intersected at a fixed point with a message. The message shows, the MSL and it is how far from BTSs with longitude and latitude information.

Figure 5.4: Emergency call centers can zoom as they need to locate the MS position precisely. Therefore they can locate the position of MS.

5.2 Distance measurement This paper explains the major methods and procedures for use in positioning mobile terminals in GSM networks. The standards-based architecture, network element function and operations are described, as are the challenges to ensur-ing end-users security and privacy and location procedures involved in positioning the GSM mobile station and the use of location information for applications. We will also learn the function and procedures of each network element in support of GSM emergency services and commercial appli-cation in addition to the limitations of each positioning technology and the appropriate use of various methods and procedures for different applications. In addition to emerg-ing commercial applications there are numerous ramifica-tions and implications of GSM positioning in military, na-tional defense and emergency response applications.

Figure 5.5: Distance, D of BTSs from MS.

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MSs always send signals to the base stations Let the signal is Y(x,t) = A*Sin( ω t – ωx / c)

Let, ØX = ω t – ωx/c Now for MS

ØX1 = ω t1 –ωx1 / c Øy1 = ω t1 –ωy1 / c

For BTS ØX2 = ω t2 – ωx2 / c Øy2 = ω t2 – ωy2 / c

Now, Δ ØX = ØX2 – ØX1 = ω/c * (x1-x2) If (x1, y1) = (0,0) MS at origin Δ ØX = ω /c * (x1-x2) = ω /c * ( 0 -x2) = - ω x2/c

x2 = - Δ ØXc / ω y2 = - Δ Øyc / ω (Similarly)

We know equation radius for circle, D = √ (x1-x2)2 + (y1-y2)2 = √ ( 0 - x2 )2 + ( 0 - y2 )2 = √ ( x22 + y22 ) = c/ ω * √ (Δ ØX2 + Δ Øy2 ) Where, c = velocity of light = 3 X 108 m/s and ω = 2∏f = 900 MHz Thus (Δ ØX2 + Δ Øy2 ) = Δt where, Δt = time difference to get same phase This way the radius of circle can be measured. Three

BTSs make three circles and that intersect at a fixed point where MS is located.

5.3 Obtained Results The aim of this paper is to present an outline of how an im-plementation of Mobile Station Location can be realized. It is proposed to place the Mobile Station Location procedure in a separate entity in the GSM network. This separate enti-ty, called MSLC (Mobile Station Location Centre), can per-form mobile station location upon request from external phone-network entities, such as an emergency call centre. The data necessary for performing the location can be ob-tained from the GSM network by using a combination of GSM application protocols (MAP) and GSM Operations & Maintenance protocols (O&M). The procedures for the lin-kage of the MSLC to the GSM-network, and the procedures for gathering the necessary data has been specified in SDL, and tested in a simulating implementation.

The paper presents procedures for calculating the posi-tion from the obtained data. The different methods differ in complexity, and are suitable for different types of MSL im-

plementations. A system for geographical location informa-tion has been chosen, and a way of storing and communi-cating location probability areas using this system has been identified. On the subject of finding the best calculation me-thod to provide as good accuracy as possible, further re-search is needed. Such research can for instance be carried out on an implementation of the MSLC in a real GSM net-work.

5.4 Economical Considerations The main reason behind the slow progress in the work on Mobile Station Location up to today has been the belief that MSL is very expensive to implement. The reason for the high expenses is the need for software or hardware changes in the entities of the GSM network. Since these entities have to be rigorously tested, changes in these entities will induce high costs.

The results in this paper present an implementation ap-proach that will reduce the costs of implementing MSL sig-nificantly. By making the implementation in a separate enti-ty, the function of the GSM network does not have to be disturbed. Thus, the MSLC implementation can be realized on a normal workstation with connections to the signaling network. By using a workstation, both the hardware and software costs can be kept low.

Additionally, it has been shown that MSL have potential commercial applications. With a relatively cheap implemen-tation, the mobile network providers should be able to gain profit from implementing MSL.

6 CONCLUSION The emergency call centers have a need for Mobile Sta-tion Location. The mobile network providers have been hesitant to implement MSL up to date, because of the high costs of such an implementation. With the new im-plementation scheme presented in this paper, the costs of an implementation will no longer be high. The network providers might even find it profitable to implement MSL. With the reduced costs, the mobile network pro-viders should be able to implement Mobile Station Loca-tion for the benefit of the emergency call centers.

REFERENCES [1] http://www.telecom.no/mobil/?id=1284397 [2] C. William, Y. Lee, “Mobile Communications Engineering”,

McGraw-Hill Telecommunications, second edition, 1998. [3] Jean-Marc Latapy, Gsm mobile station locating, Master's thesis,

Norwegian University of Science and Technology, 1996. [4] Sudeep K. Palat, “Replication of user mobility profiles for location

management in mobile networks”, PhD thesis, Norwegian Uni-versity of Science and Technology, 1997.

[5] Functional description of the ISDN user part of the Signaling Sys-tem No 7. Q. 761, ITU-T recommendation.

[6] MobileIN.com Research, “Mobile Positioning & Location Manage-ment”, April 2005.

[7] Sumant Mallavaram, U. Sunday Tim, “Application of GIS Tech-

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nology in Watershed-based Management and Decision Making”, August 2003.

Kazi Shamsul Arefin has been serving as a Lecturer and Convener of Research and Publi-cation Unit (RPU) with the Department of Com-puter Science and Engineering (CSE), Universi-ty of Asia Pacific (UAP). He joined at UAP in October 2009 after completion his M.Sc. Engg. (CSE). Right now he teaches courses on Data-base Management System (DBMS), Software Development, and Programming on Artificial

Intelligence and Expert Systems. Besides this, he is an Editor-In-Chief of Journal of Computer and Information Technology (JCIT), ISSN 2078-5828.

In addition to this, he is engaged in research activities throughout his undergraduate years and has 9 (Nine) international research pa-pers (in IEEE Conference ICICT, ICCIT, ICECC, ICEESD, IJECS, and IJCTE). Moreover, he is a member of International Association of Com-puter Science and Information Technology (IACSIT), Membership No: 80337708.

Furthermore, Mr. Arefin is CTO (Chief Technical Officer) of BD IT Solution (www.bd-its.com). Besides, he is an ex-employer of Warid Telecom International Limited. Warid Telecom takes pride in being backed by the Abu Dhabi Group (The Dhabi Group is a multinational company based in the UAE), one of the largest groups in the Middle East and in Pakistan. He worked for 2(two) years in Bangladesh opera-tion. For more information, please visit: www.arefin.biz.nf.

Aloke Kumar Saha is Head of Computer Science and Engineering Department of Univer-sity of Asia Pacific (UAP), Dhaka, Bangladesh. He usually teaches courses on Digital Logic Design, Numerical Methods, Data Structures, Discrete Mathematics, Computer Graphics and Basic Electrical Engineering. His current re-search interests are Algorithm, Artificial Intelli-

gence and Software Development. For more than 13 (Thirteen) years, he is also working with the undergraduate students of UAP, as a part of their paper works, on the software development and implementation, Bi-Directional Heuristic Search Algorithm etc.

Adnan Anwar has been serving as a Lecturer and Co-Convener of Research and Publication Club with the Department of Electrical and Electronic Engineering (EEE) in UAP. He obtained his B.Sc. Engg. degree from Islamic University of Technology (IUT) with First Class Honours. After his graduation he joined NovoTel Limited which is an International Telecom Gateway Operator. However, due to

enormous interest in research and teaching, he joined UAP in April 2009. He got merit scholarship from Dhaka Board, Bangladesh due to his brilliant result in Higher Secondary Examination.

Shaila Rahman joined in The University of Asia Pa-cific (UAP) at 1999 after completing her M.Sc from Dhaka University (DU). She secured 4th position in M.Sc. She also secured the 4th position in B.Sc (Hons) in Applied Physics & Electronics from the same institution. Shaila Rahman teaches courses on Computer Networks, DataCommunications, Informa-tion Systems, Microprocessors, Assembly Language,

Computer Interfacing, Digital System Design, C/C++, Data Structure and Algorithms. She is conducting the course Mobile Communication in Masters Program of CSE (MCSE). Her current research interest in-cludes Computer Networks and Distributed System, Wireless Net-works, Wireless Ad hoc network, Sensor Network, Network Security. She supervised the thesis works of several undergraduate students at UAP. It is praiseworthy to mention that more than fifteen thesis groups in undergraduate level completed successfully under her acute super-vision. Her research works published in IEEE, ICCIT, NCCPB, ICCPB. Ms. Rahman has also published two journals on Cryptography and Outsourcing. Ms. Rahman serves as acting head when the head of the

department remains on leave. She also serves as an external examiner in the CSE department of Dhaka University. Moreover, She is the con-vener of the Cultural and Debating club. She is also member of Re-search and Publication Unit and Programming Contest Clu