Study On Position Location Technologies Computer Science Essay

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Current Status of Technologies used to locate the position of mobile device simply says that Mobile location-based services are generating renewed interest as both the market and technology. There are many major technologies which are support the growing set of usable and wanted services being released and in development today. This development today makes Location API's and combination of technology development to making developers to get position information. This documentation retrieve how location technologies work and there behavior. Also how those technologies are implemented and work with real situation.

Mobile location-based services are more useful in entire computer world. GPS, A-GPS, WI-Fi MAC, Cell-ID, OTDOA and Combination of these types (XPS) are primary positioning technologies in use today. Each location technique also is more successful in different environments (namely urban vs. rural and indoors vs. out-doors). Luckily, the strengths and weaknesses of many of these position technologies are complementary, motivating further exploration of hybrid location approaches. But main idea is about there are no any good LBS but only had technologies good at several situations in different location. Also integration of more technologies together is more useful.

These different technologies use different methodologies to evaluate position through the mobile. They use satellites, network base station databases, network triangulation (signal strength-based) and network triangulation (time based).those methods use for find device position. But it depends on network behavior and geography.

Determine or think about how it is use those position determination methodologies. When these LBS's evaluating have main measurement of there positioning accuracy and uncertainty, positioning latency or time to first fix (TTFF), positioning determination ubiquity. When Consider About these method that each position determination technique has strengths and weaknesses across each dimension. Newly mobile got features like get location using these methods (namely the Apple iPhone, HTC, Nokia, RIM and others).

Telecommunication is a very fast growing technological area. In this information era telecommunication is the major roll .For telecommunication providers to complete with each other they need to provide new and innovative ways to create differentiation .To achieve this differentiation they provide personalize services in the devices. One such service would be Mobile location-based services (LBS).This service provide the user with identify current location. Knowing the location is one of the important services currently provided in mobile devices witch desktop and laptop don't have and also Hs opened up new market for mobile developers, network operators and service providers

To provide Mobile location based servicers different providers, developers and venders used different technologies. Some used a single method or combination of much method. The popular methods currently available and used are

Global Positioning System (GPS)

Assisted Global Positioning System (A-GPS)

Network Base Station Database



Location identification by signal strength

Time base location identification

Time Difference of Arrival (TDOA)

Advanced Forward Link Triangulation (AFLT)


GPS is a global navigation satellite system that provides location based and time based information. This information can be obtained anywhere on or near the earth at any time when four or more GPS satellite is in line of sight. This system consists of 32 satellites (as of 2008) orbiting 12,600 miles above the earth. US department and defense created this system to originally run with 24 satellites system was designed such that 6 (and usually more) satellites should be visible from any vantage point on earth\\\\The space and the control segment is operated by U.S. Air Force

GPS consist of three parts


\item Space segment


\item This segment consist of satellite of the GPS system


\item Control segment


\item Control station, monitor station and antennas consist of segment


\item User segment


\item This segment consist of military, civil, commercial and scientific GPS service users






\caption{Satellite Map of earth}



The GPS receiver calculates the longitude, latitude, altitude and time using GPS satellite signals. Triangulation is used to calculate this information with signals of three or more satellites. The satellite signal consist a message with the following information


\item Massage transmission time

\item Exact location of the satellite (orbital information)

\item Rough position of the other satellites



\subsection{\textrm{Position calculating with GPS}}

GPS Receiver calculates x, y, z coordinates and tc the time correction of receivers clock. Firstly distance between the satellites is calculated by the time difference between time the signal was sent and received. Using distance of other satellite can find the position. Calculation of the position using three satellites is call 2D position fix and using four satellites is call 3D position fix.2D position fix gives only the 2 Dimension and 3D position fix gives height above the earth surface as a result. All clocks of 32 satellites are absolutely precise (atomic clock). But the GPS receiver may differ so it might affect above distance calculation.

As figure1 shows three intersection points (point B) are obtain due to the receiver time difference tc. So the receiver time should be change to obtain point A witch is the position of the receiver. From the distance calculated from different satellite are used to find x, y, z.

Di is the distance between the receiver and the 4 satellite


xi, yi, zi is coordinates from single satellite


Tt,i , tr,i are transmitted time and the received time


c = speed of light


Using these equation final position can be calculate

Location identification by signal strength

This method signal strength is use to identify the location. Mobile device communicate with base stations using Radio frequency (RF) signals. As the base station location is known using a RF signal propagation characteristic the distance the device is calculated. Resulting RF base map and signals received at the device to estimate the device's position this method is used as fallback when A-GPS is not available.

Time base location identification

In this method signal timing information from the network is used to identify the location. There are two technologies popularly available now they are


\item Time Difference of Arrival (TDOA)

\item Advanced Forward Link Triangulation (AFLT)


Between these two methods the main difference is where the timing difference is calculated, in-network or on-device. TDOA most use in GSM/WCDMA technology devices. AFLT is most used in CDMA devices.


Initially in the TDOA method estimation of the TDOAs of the signal from a source, between pairs of mobile devices through the use of time delay estimation techniques is done. Then those estimates are transforming in to range different measure between base stations. These would create a set of equation which is not linear. Using algorithm a solution is obtained which is position of the device TDOA is measured by two method, first is the difference between two time of arrivals measurements from two base stations. Next is by core relating the receive signal from one base station to a receive signal from another base station.


In this method the location is identified by taking the phone measurements of signals from nearby cellular base stations (towers) and taking in to record the time/distance readings back to the network


\subsection{Network Base Station Database }

Network service provider got property database and that base station location can use as device location. But mobile operators not share there base station information with third parties if not return the position of device.Network database collection had 2 major parts.

%Some operators share there CELL_ID and WiFi databases so it can find position of devise.


\item 3rd party driven (SkyHook)

\item user-generated (Google and Navizon)


\subsubsection{ Cell Id}

Cell-Id is collection of unique id's that knows service provider. The accuracy is depending on Network density. If there are more base stations in selected area there can be good accuracy but if there are rural area that may be bad accuracy level.

Mobile Network got Base station in different location. Each station coordinates base transceiver station. It got number of cells and each cell can identify by using there unique Ids. Mobile Station handles exchange data using those cells and traffic of network. Group of cells are manage by location area identifier. Network use only location area identifier to data transferring. Its not knows about mobile stations. When someone make call mobile station knows about cell-Id of current call. If you get the Cell ID it can generate appropriate Latitude and longitude. For this need a database of this mapping.

\cite {Bour}




\caption{Collection of Cells in Mobile Station}



There are many databases had data about Cell-Id with mapping to a longitude and latitude position. But some of databases not open like Google some of the database can get information about location free. There are many DBs like opencellid and using a query that retrieve the output of the position and appropriate data of cell id. Important thing is the all cell id's are unique all over the world. Cell id contains 4 numbers of data. There are cell ID, LAC, MNC, and MCC. It is not possible to get position by mobile every time because most of the mobile find sign for the software to run. Phone platform limited to Sign-certificate

Ex: Nokia s40, Nokia 3rd and Fp1 edition need operator or signing but S60 3rd edition and FP2 no singing is must.

But all thing right but there can be restriction by mobile service provider. When the query make empty because operators limited services





%\caption{Cell-Id mappint with database}




Lat Lon Mcc Mnc Lac Cellid Range Nbsamples Created at Updated at Needs computation Country Operator\\

-25.29934 -57.40994 744 4 502 13552 0 1 Sun Jun 20 00:42:46 +0200 2010 Sun Jun 20 00:42:46 +0200 2010 true Paraguay Telecel / Tigo\\

7.0666984 80.68805967 413 1 30300 53141 0 15 Tue Apr 27 10:28:36 +0200 2010 Tue Apr 27 10:29:04 +0200 2010 true Sri Lanka Mobitel Lanka Ltd.

\subsubsection{\textrm{WIFI MAC}}

These got high frequency than Cell id. This technology depend on property of both the SSID and MAC address of the access point.MAC address is used to identify the uniqueness of the device location and List of Access point get using SSID. But problem is that signal propagates maximum 150 m. but this technology works on urban areas or indoor environments


\subsection{\textrm{XPS Positioning Accuracy and Uncertainty Positioning Latency}}

With integrating multiple technologies and developed a new core engine by Skyhook. This is creating a more accurate position that works on indoor, outdoor, rural and urban areas. Skyhook's integrate


\item Wi-Fi Positioning System (WPS)

\item GPS satellites

\item Cell-Id





\caption{XPS developed by Integration Of technoogy}



This quickly tracking software is accurate to 10 to 20 meter. This integration calls XPS. These advance hybrid location method uses combine and make technological software to make position fast and accurate

Performance Table


Accuracy 10 meters 10 meters 30 meters

Availability 99.8% 80.0% 95%

Time-To-First-Fix 1 sec 65 sec 30 sec




\caption{Accuracy Level Of XPS}




\section{\textrm{Evaluating Positioning Technologies}}

\subsection{\textrm{Positioning Accuracy and Uncertainty}}

Main option of those technologies position making is must be very accurate. According to above technologies these accurate levels change like 5-20m (GPS) to 50-5000m (Cell-ID) like that. Second measurement is availability and time take to connect if its get more time to fix there had be problem in some work. The best solution is make hybrid approach by integrating more technologies like XPS by skyhook's

\subsection{\textrm{Positioning Latency or Time to First Fix (TTFF)}}

This factor is more critical for emergency cases. because GPS is get 0-5min to first fix so when having emergency situation like firing its not best thing use GPS to find location but its more accurate than CELL Id or WIFI but cell id or WIFI not take that much its only less than 4 seconds.

But hybrid approach always on front because it's got every measurement very good because it's made with multiple technologies

\subsection{\textrm{Location API}}

This is the design of work with many location technologies .this produce physical position of the device .If device available feature its retrieve location data \\

Ex: Location API for Java ME\\

The API use for retrieve

Current latitude, longitude, altitude, direction, finds the speed of the phone and phone number Postal Address, country, and the building and its URL and land mark and many of information but main thing is all data find through location method or technology. Those location API add to nokia S60 device blackberry and some other mobiles


\section{\textrm{Real Example of LBS}}

Using JavaME to obtain GPS Positioning information\\\\

public String getCordinates(){\\

Double latitude=0;\\

Double longitude=0;\\

LocationProvider lp=null;\\

javax.microedition.location.Location location=null;\\


lp= LocationProvider.getInstance(null);\\

location = lp.getLocation(30);\\

Coordinates coordinates = location.getQualifiedCoordinates();\\

latitude = coordinates.getLatitude();\\

longitude =coordinates.getLongitude();\\

}catch(LocationException e){\\


}catch(InterruptedException e){\\




Using JavaME to obtain Cell Positioning information

1. {\\

2. �.\\

3. String cellid = System.getProperty("CellID");\\

4. String lac = System.getProperty("LocAreaCode");\\

5. String imsi = System.getProperty("IMSI");\\

6. // Example IMSI (O2 UK): 234103530089555\\

7. String mcc = imsi.substring(0,3); // 234 (UK)\\

8. String mnc = imsi.substring(3,5); // 10 (O2)\\

9. String location = mcc + mnc + lac + cellID; \\ A globally unique ID for a cell\\

10. }\\



Summary of the content is\cite {Bour}








\section{\textrm{Conclusions and Future Directions}}

The location technologies are play main part of the future world because in future every thing going with network with mobile so there can be security problem when develop world so that location technologies very essential to make security well.Also those technologies are not well at every time because there had geographical and technical problem with every make combination of technologies make accuracy and fast fix output. Those hybrid software is make best output with every position.


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