Mobile Location System: Methods And Techniques

To create a literature survey (review paper) in a technical area of your choice.Ideally this should be in an area where you may be able to pursue an MSc project next semester.The area chosen should be related to your named award.

GPS-based Mobile Location System

Mobile location system is a newly developed system that takes the help of the GIS to locate the position of the mobile, in both the conditions of moving and stationary.

The concept of localizaiton of the mobile is usually done in two methods.

GPS is a GNSS (Global Navigation Satellite System), which was developed by the Department of Defence in the US and later got fully functional, all around the globe. The system makes use of the constellation of medium Earth Orbit satellites of 24 and 32 and transmits precise signals of microwave[1]. The system enables the receivers of GPS for determination of the current velocity, time and current location. The position is calculated by the GPS receiver, by timing signals, precisely, sent by the satellites of the GPS, much above the surface of the earth [4].

The mobile location system makes use of the GPS to calculate the current location, by the signals received by the GPS receiver, from the GPS satellites. The receivers find information from the 27 GPS satellites, revolving around the Globe [3].

However, mobile devices find it difficult use the information provided by GPS, though standard GPS can provide the details of accurate location. So, these limitations of the GPS can be circumvent with the use of A-GPS (Assisted – GPS) with S-GPS (Simultaneous – GPS), possibly, by the modern mobile devices.

A-GPS transmits GPS almanac together with some other vital information, by using the mobile network, to the mobile device [9]. When the mobile network is used, it allows the almanac data to be transmitted faster that fasten the determination of current location of the device. Such method also improves the overall time taken to acquire the location of the GPS.

The Standard GPS enabled mobile devices communicate with the satellite of GPS, by using of the same hardware and to enable phone calls. So, at one point of time, only one action can be taken place. This issue is addressed by S-GPS by adding more hardware, allowing both the cellular network and GPS radio network operating simultaneously [7]. When both these two radios get active, this ability speedup the transmission of the GPS data, as receiving data is allowed, when the radio of cellular network is active.

In this process, the mobile needs to emit the roaming signal at least to contact the antenna tower, which is nearby the phone. An active cell is not needed for this kind of process. But the key factor is the signal strength of the phone, which is again dependent over the Global System for Mobile Communications, to nearby antenna masts. It makes use of dedicated trackers or GSM mobile phones, usually, to locate the user, using the mobile phones also [5].

The Role of A-GPS in Mobile Location System

The actual mobile phone coordinates are disclosed by the mobile positioning that include the location based service, a telecommunication technology used by the same companies, for approximating the mobile phone location and so its uses too.

The basis of the locating of the mobile phone is basically, on the measurement of power levels and also the patterns of antenna. The logic behind this technology is that when the mobile phone is in the condition of powered, it wirelessly communicates, continuously with a base station that is closeby [6]. Hence the base station location knowledge would imply the nearby cell phone.

There are advance systems developed and available for mobile tracking system. In this system the exact location of the mobile system can be roughly estimated, with approximate distance, from the mobile phone to the base station. Then interpolation of signals is done, in between the antenna towers that are adjacent, for further approximation. However, this distance approximation is varied for both rural and urban areas. Close to 50 meters of precision distance can be achieved, in the urban areas, for basically three reasons, first for comparatively higher antenna tower density, high mobile traffic and when qualified services are considered [8]. However, it is several miles distance found in between phones and base antenna, in rural areas, because of the contradicting features and hence, the locating results in less precision.

While this is the technology and logic in tracking the mobile location, there are different ways and techniques used to locate the mobile phones.

The key point here is the network infrastructure of the service provides and it helps to locate the position of the mobile phones. This technique of network based has the advantage that it does not affect the handsets, as it is implemented non-intrusively [10]. The technique was developed much before the GPS widespread usage on the mobile handsets.

The network based technique performs mobile location with varied accuracy and precision.

1. Advanced Forward Link Trilateration – This is the most advanced network based technique based on the method of timing and is determined to be most accurate.
2. Triangulation – This technique  performs the location process with moderate accuracy of locating the handsets.
3. Cell Identification – This technique locates the position of the mobile phone with least accuracy

Though there are different methods of the network-based technique, there are certain factors that influence the accuracy and precision of the location of the mobile phones [11]. The two important key factors are cell base station concentration and urban environment. The cell base station concentration, when in higher levels allows finding the mobiles with more precision and the same with the urbanization, because of possible more number of cell towers and current timing methods.

Though network based technique works fine with the best methods, it has got certain challenges that the process works much closer to the service provider, since it demands hardware and software installation within the infrastructure of the operator.

Network-based Mobile Location System

A new system of mobile location has been enhanced with the help of the installation of specific client software on the mobile phone. The location of the mobile phone is determined by this technique by specifying and pointing the location of the mobile through home cell and neighbouring signal strength that is sent to the carrier, continuously, along with the cell identification. More precise location of the mobile can be obtained, when the mobile handset has also GPS equipped within it, to send to carrier [12].

There is also another method deployed with this technique, called fingerprinting-based technique. The technique is employed to determine the location of the handset, in real time, through recording signal strength, at various points, both at the home cells as well as neighbouring cells, by war-driving and get matched. It does not need the involvement of the carrier.

The handset-based technique has a disadvantage that it demands software installation on the mobile handset. So, active cooperation of the software and mobile subscriber is needed so that different operating systems can be handled in the mobile phone. Usually, such software, like Google Maps is enabled to be run, only in the smartphones that are based on Windows Phone, Symbian, BlackBerry OS, Android, Windows Mobile, iOS.

However, there is also a work around for the above drawback is that the software or embedded hardware installation can be implemented by the manufacturer of the handsets, like E-OTD (Enhanced Observed Time Difference). But, it is difficult in one way that a common mechanism has to be convinced by different manufacturers and issue of cost is another challenge. Yet another challenge would be the foreign handsets that become part of the network in roaming mode.

The technique uses the logic that the raw radio measurements can be obtained from the handsets, through using SIM (Subscriber Identity Module) in mobile handsets of UMTS (Universal Mobile Telecommunication System) and GSM. Signal strength, round-trip time and serving cell ID are the available measurements for the same [13]. The available information from the handset is different from that of the SIM, like measurements can be taken from the SIM,but not from the handset.

The mobile location can be tracked and identified through crowdsourced Wi-Fi data. New methods of carrying the indoor positioning on the basis of Wi-Fi are designed because of the gradually increasing Wi-Fi popularity and GPS based method’s poor performance. Eventually, most of the smartphones have been designed with the combination of GPS, GLONASS and GPS and other Global Navigation Satellite Systems with Wi-Fi positing systems.

Handset-based Mobile Location System

The hybrid positioning system makes use of the hand-set based and network-based technologies, for the determination of location. For example, Assisted GPS modes that make use of the network and GPS information can be used for location computation. This combined data helps to find more accurate location, when the telephone is used [18]. Both the systems are also used as an alternate tracking system, occurring through GPS location attained directly by the mobile phone, from the satellites and sending the information to the person through the network to locate the position. These systems, for instance, are, LTE’s OTDOA, Google Maps and E-CellID.

Some of the hybrid positioning systems make use of various approaches of location, in combination, to locate the mobile position, through GSM, IP address, WiMAX, network environment data and Wi-Fi.

1. Initially, the IMEI or phone number of the user is noted and then the respective Location Area Code, Mobile Country Code and Mobile Country Code are collected from the service provider. This information is used to find the cell tower location, nearby the SIM which is installed in the mobile, which is being tracked.
2. Usually, 3 to 4 cell tower information is obtained, for more precise location.
3. Then triangular method is used for the location calculation. Triangulation is an essential process of knowing the location of the mobile. The process involves drawing of three arcs or circles, so that a common point cna be obtained. GPS also conducts the location system, in the similar ways.
4. Usually, the mobile devices have to readjust to the path of receiving the radio signals, according to the distance of it, from the cell tower. Propagation delay is proportional to the distance. So, the feedback si sent continuously by the device, about the distance of it. Accordingly the transmitting tower also makes readjustments about lag or lead of the Wireless or Radio frequency signal, according to the feedback of the device [15]. So, the information about the distance is sent continuously by the mobile, a Measurement Report packet towards the network or cell tower.
5. According to the equipment of the network vendor, it enables special traces so that IMEI (Mobile Device Serial Number) or IMSI (Mobile Subscriber Number) related Measurement Reports can be captured.
6. These measurement reports are usually read and decoded by the Network Engineers, with some special software tools, like M2000, Omstar, Nastar, etc.
7. Then the distance in between the mobile phone and cell tower is obtained, with the values, given for example, below,
   1. 2G – Timing Advance = 0 (ranges from 0 to 550 meters)

= 1 ( 550 to 1100m)

= 2 (1100 to 1650m)

=3 (1650 to 2200m) and so on

1. 3G – Propagation Delay or TP = 234M

= 0 (ranges from 0 to 234m)

= 1 (234 to 468m)

= 2 (468 to 672m) and so on

1. 4G – Timing Advance = 78 meters

= 0 (0 to 78m)

= 1 (78 to 156m)

= 2 (156 to 234) and so on

As the technology gets progressing, the unit of the distance becomes smaller and smaller, finding more accurate information about the location to find.

Since only a single cell gets connected with the mobile device, in 2G, the process of triangulation becomes difficult and eventually, range becomes large. However, it is technically possible by a detailed Measurement Report analysis, like finding more values of TA for intense process of triangulation, at the cases of handing over the signal from one cell to another cell.

However, this process of triangulation becomes easier, when the device is enabled with 3G or 4G, especially, when there are multiple serving cells are involved for call or connection session. Hence, it is known as PCI for 4G and Active Set for 3G [16].

An expert RF engineer can better read the measurement reports that have other values of the Radio Frequency signals and analyze the location profile of the mobile device, like Receive Signal Quality, Receive Signal Level, Transmit Power of Mobile Device, etc.

Conclusion

Mobile Location System has been a prominent application, preferred by many users and hence the technology has been progressing accordingly to search and find the location of the mobile, through the technology. Such system becomes potential and viable, when the service provider, mobile handset designer & developer and satellite communication like GPS collaborate among them, to offer and provide the best technology and method for Mobile Location System.

References

1. 3GPP, 3GPP TS 23.271, Functional stage 2 description of Location Services (LCS), Release 10, 2011.
2. 3GPP, 3GPP TS 25.305, Stage 2 functional specification of User Equipment (UE) positioning in UTRAN,Release 10, 2010.
   2011. Pandey, Use of Mobile Devices for Location Tracking, IJCSt Vol. 2, Issue 2, June 2011.
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5. M. Borkowski, On applicable cellular positioning for UMTS, Tampere University of Technology, 2008.
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8. JCP, Java Specification Request (JSR) 179: Location API for J2METM,Final Release 3, 2011.
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13. Pourhomayoun, Fowler, Improving WLAN-Based Indoor Mobile Positioning Using SparsityAsilomar Conference on Signal Processing 2012, 2012.
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