Mobile phone tracking refers to the attaining of the current position of
a mobile phone, stationary or moving. Localization may occur either via
multilateration of radio signals between (several) radio towers of the
network and the phone, or simply via GPS. To locate the phone using
multilateration of radio signals, 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 is 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 the location of a mobile
phone, and thereby also its user (bearer). 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 powered mobile phone always
communicates wirelessly with one of the closest base stations, so
knowledge of the location of the base station implies the cell phone is
nearby.
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, or dedicated trackers, usually with the intent to
locate the user.
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 a 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
Handset-based technology requires the installation of client software[5]
on the handset to determine its location. This technique determines the
location of the handset by putting 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, smartphones, such as one based on Symbian,
Windows Mobile, Windows Phone, BlackBerry OS, iOS, or Android, would be
able to run such software. E.g. UonMap application.
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.
SIM-based
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.
WiFi
Crowdsourced Wifi data can also be used to identify a handset's
location. Poor performance of the GPS-based methods in indoor
environment and increasing popularity of WiFi have encouraged companies
to design new and feasible methods to carry out WiFi-based indoor
positioning. Most smartphones combine GPS with Wi-Fi positioning
systems.
Hybrid
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. Both types of data are thus used by
the telephone to make the location more accurate (i.e. A-GPS).
Alternatively tracking with both systems can also occur by having the
phone attain its GPS-location directly from the satellites, and then
having the information sent via the network to the person that is trying
to locate the telephone. Services allowing such cellphone include
Google Latitude. Other examples would be LTE's OTDOA and E-CellID.
There are also hybrid positioning systems which combine several
different location approaches to position mobile devices by WiFi, WiMAX,
GSM, LTE, IP addresses, and network environment data.
Operational purpose
In order to route calls to a phone, the cell towers listen for a signal
sent from the phone and negotiate which tower is best able to
communicate with the phone. As the phone changes location, the antenna
towers monitor the signal, and the phone is roamed to an adjacent tower
as appropriate.
By comparing the relative signal strength from multiple antenna towers, a
general location of a phone can be roughly determined. Other means make
use of the antenna pattern, which supports angular determination and
phase discrimination.
Newer phones may also allow the tracking of the phone even when turned
on and not active in a telephone call. This results from the roaming
procedures that perform hand-over of the phone from one base station to
another.
Bearer interest
A phone's location can be uploaded to a common website where one's
friends and family can view one's last reported position. Newer phones
may have built-in GPS receivers which could be used in a similar
fashion, but with much higher accuracy.
This may be controversial, because having this data on a common website
may mean that people who are not 'friends and family' may be able to
view the info, most obviously, the owners of the site.
Privacy
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.
Officially, the authorities (like the police) can obtain permission to
position phones in emergency cases where people (including criminals)
are missing. The U.S. Justice Department has argued that current laws
allow them to track suspects without having probable cause to suspect a
law is being violated. In some instances, law enforcement may even
access a mobile phone's internal microphone to eavesdrop on local
conversations while the phone is switched off.
The Electronic Frontier Foundation is tracking some cases, including USA
v. Pen Register, regarding government tracking of individuals.
In the US, an interpretation of The Patriot Act that is secret, but
confirmed to exist, has been linked to secret widespread location
tracking.
China has proposed using this technology to track commuting patterns of
Beijing city residents.Aggregate presence of mobile phone users could be
tracked in a privacy-preserving fashion.