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 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 services that disclose 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.
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.
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 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.
Localization-Based Systems can be broadly divided into:
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 is that they can be implemented non-intrusively
without affecting the handsets.
Network-based techniques were developed many years prior to the widespread availability
of GPS on handsets, see US 5519760, issued 1996-05-21 for one of the first works relating
to this.
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.
Frequently the compulsion associated with a legislative framework is required before
a service provider will deploy a solution.
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 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 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. Google Maps.
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.
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 Maps.
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 can obtain permission to position phones in emergency cases where
people are missing.
The U.S. Department of Justice 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 In re Application of the United States for Historical Cell Site Data, 724 F.3d 600,
the United States Court of Appeals for the Fifth Circuit held that the government does
not need a warrant to compel cell phone providers to disclose historical cell site information.
In United States v. Davis, the United States Court of Appeals for the Eleventh Circuit
ruled in a criminal case that obtaining cell phone location data "without a warrant is
a Fourth Amendment violation.”
In the United States, 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.
See also
References
External links GSM Localization on Mobile Phones
Location tracking of GSM cellphones: now easier than ever