Thursday, 14 April 2011

GSM Tracking

Mobile phone tracking tracks the current position of a mobile phone even on the move. To locate the phone, it must emit at least the roaming signal to contact the next nearby antenna tower, but the process does not require an active call. GSM localisation is then done by multilateration based on the signal strength to nearby antenna masts.
Mobile positioning, which includes location based service that discloses the actual coordinates of a mobile phone bearer, is a technology used by telecommunication companies to approximate where a mobile phone, and thereby also its user (bearer), temporarily resides. The more properly applied term locating refers to the purpose rather than a positioning process. Such service is offered as an option of the class of location-based services (LBS).

The technology of locating is based on measuring power levels and antenna patterns and uses the concept that a mobile phone always communicates wirelessly with one of the closest base stations, so if you know which base station the phone communicates with, you know that the phone is close to the respective base station.
Advanced systems determine the sector in which the mobile phone resides and roughly estimate also the distance to the base station. Further approximation can be done by interpolating signals between adjacent antenna towers. Qualified services may achieve a precision of down to 50 meters in urban areas where mobile traffic and density of antenna towers (base stations) is sufficiently high. Rural and desolate areas may see miles between base stations and therefore determine locations less precisely.
GSM localization is the use of multilateration to determine the location of GSM mobile phones, usually with the intent to locate the user.
Localization-Based Systems can be broadly divided into:
  • Network-based
  • Handset-based
  • SIM-based
  • Hybrid


Network-based techniques utilize the service provider's network infrastructure to identify the location of the handset. The advantage of network-based techniques (from mobile operator's point of view) is that they can be implemented non-intrusively, without affecting the handsets.
The accuracy of network-based techniques varies, with cell identification as the least accurate and triangulation as moderately accurate, and newer "Forward Link" timing methods as the most accurate. The accuracy of network-based techniques is both dependent on the concentration of base station cells, with urban environments achieving the highest possible accuracy, and the implementation of the most current timing methods.
One of the key challenges of network-based techniques is the requirement to work closely with the service provider, as it entails the installation of hardware and software within the operator's infrastructure. Often, a legislative framework, such as E911, would need to be in place to compel the cooperation of the service provider as well as to safeguard the privacy of the information.


Handset-based technology requires the installation of client software on the handset to determine its location. This technique determines the location of the handset by computing its location by cell identification, signal strengths of the home and neighboring cells, which is continuously sent to the carrier. In addition, if the handset is also equipped with GPS then significantly more precise location information is then sent from the handset to the carrier.
The key disadvantage of this technique (from mobile operator's point of view) is the necessity of installing software on the handset. It requires the active cooperation of the mobile subscriber as well as software that must be able to handle the different operating systems of the handsets. Typically, smart phones, such as one based on Symbian, Windows Mobile, iPhone, or Android, would be able to run such software.
One proposed work-around is the installation of embedded hardware or software on the handset by the manufacturers, e.g. E-OTD. This avenue has not made significant headway, due to the difficulty of convincing different manufacturers to cooperate on a common mechanism and to address the cost issue. Another difficulty would be to address the issue of foreign handsets that are roaming in the network.


Using the SIM in GSM and UMTS handsets, it is possible to obtain raw radio measurements from the handset The measurements that are available can include the serving Cell-ID, round trip time and signal strength. The type of information obtained via the SIM can differ from what is available from the handset. For example, it may not be possible to obtain any raw measurements from the handset directly, yet still obtain measurements via the SIM.


Hybrid positioning systems use a combination of network-based and handset-based technologies for location determination. One example would be some modes of Assisted GPS, which can both use GPS and network information to compute the location (although in most A-GPS systems all computations are done by the handset, and the network is only used to initially acquire and use the GPS satellites).
Locating or positioning touches upon delicate privacy issues, since it enables someone to check where a person is without the person's consent. Strict ethics and security measures are strongly recommended for services that employ positioning, and the user must give an informed, explicit consent to a service provider before the service provider can compute positioning data from the user's mobile phone.
In Europe, where most countries have a constitutional guarantee on the secrecy of correspondence, location data obtained from mobile phone networks is usually given the same protection as the communication itself. The United States however has no explicit constitutional guarantee on the privacy of telecommunications, so use of location data is limited by law.

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