Mobile phone 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 localization is then done by
multilateration based on the signal strength to nearby antenna masts
Mobile positioning, i.e. 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).
Technology
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
Hybrid
Network Based
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 the most
accurate. The accuracy of network-based techniques is closely dependent
on the concentration of base station cells, with urban environments
achieving the highest possible accuracy.
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
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 or
the latitude and longitude, if the handset is equipped with a GPS
module. The calculated location is then sent from the handset to a
location server.
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 / iPhone OS, 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. 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.
Well, let us find an example to demonstrate the Network based location
tracking algorithm: According to global GSM structure and ETSI, the GSM
service providers information flows through the control channel and the
control channel is free to access. Interestingly, all the present GSM
modem/mobiles (Telit, SIMCOM, HTC, Nokia etc.) are coming with some
extra feature to monitor the neighbouring cells and its RSSI value.
Theoretically you should get 1+6=7 cell information (1 home cell ID, 7
BCCH info+ 7 RSSI). If you know the location of 7 cells, it is possible
to get a mobile phone location with very high accuracy (<100 meters).
hybrid
Hybrid positioning systems use a combination of network-based and
handset-based technologies for location determination. One example would
be Assisted GPS, which uses both GPS and network information to compute
the location. Hybrid-based techniques give the best accuracy of the
three but inherit the limitations and challenges of network-based and
handset-based technologies.
Examples of LBS technologies
Cell Identification - The accuracy of this method can be as good as a
few hundred meters in urban areas, but as poor as 35 km[4] in suburban
areas and rural zones. The accuracy depends on the known range of the
particular network base station serving the handset at the time of
positioning.
Enhanced Cell Identification - With this method, one can get a precision
similar to Cell Identification, but for rural areas, with circular
sectors of 550 meters.
U-TDOA - Uplink-Time difference of arrival - The network determines the
time difference and therefore the distance from each base station to the
mobile phone.
TOA - Time of arrival - Same as U-TDOA, but this technology uses the
absolute time of arrival at a certain base station rather than the
difference between two stations.
AOA - Angle of arrival - AOA mechanism locates the mobile phone at the
point where the lines along the angles from each base station intersect.
E-OTD - E-OTD is similar to U-TDOA, but the position is estimated by the
mobile phone, not by the base station. The precision of this method
depends on the number of available LMUs in the networks, varying from 50
to 200 m.
Assisted-GPS - A largely GPS-based technology, which uses an
operator-maintained ground station to correct for GPS errors caused by
the atmosphere/topography. Assisted-GPS positioning technology typically
falls back to cell-based positioning methods when indoors or in an
urban canyon environment.
Hybrid - As mentioned above, hybrid positioning systems use different methods depending on which signals are locally available.
