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.