Database Reference
In-Depth Information
GPS Data
GPS is the fully-functional satellite navigation system that utilizes more than two
dozen satellites. It broadcasts precise timing signals by radio to GPS receivers,
allowing them to accurately determine their location (longitude, latitude, and
altitude) in any weather, day or night, anywhere on Earth. A GPS receiver
calculates its position by precisely timing the signals sent by GPS satellites high
above the Earth. Each satellite continually transmits messages that include:
The time the message was transmitted,
Precise positioning information, and
The general system health and rough orbits of all GPS satellites.
The receiver computes the distance to each satellite by using the messages it
receives to determine the transit time of each message. These distances along
with the satellites' locations are used to compute the position of the receiver. This
position is then displayed, perhaps with a moving map display or latitude and
longitude; elevation information may be included. Many GPS-enabled devices
show derived information such as direction and speed, calculated from position
changes. GPS-enabled devices provide us with all the required information for
trajectory tracking. They give us access in accurate, time-stamped locations for
each tracked moving point.
GSM Data
GSM is themost popular standard for mobile phones in the world, nowadays used
by more than 1.5 billion people across more than 210 countries and territories.
The ubiquity of the GSM standard makes international roaming very common
between mobile phone operators, enabling subscribers to use their phones in
many parts of the world. GSM networks consist of a number of base stations,
each responsible for a particular spatial area (known as “cell”). Hence, for each
GSM-enabled device we can collect information about the base stations it was
served by at different timestamps, and as such, assume its movement.
A GSM-enabled device can be tracked by collecting all the communication
signals transmitted (cell, signal strength) between this device and the network
infrastructure or by studying the log of the outgoing calls (UserID, data and time
of the call, duration of the call, the cell where the call began, the cell where the call
finished). However, in both levels the accuracy of trajectories that can be col-
lected is very low since the most detailed level of available information is the
network cell and not a spatial point.
Bluetooth Data
The movement of a Bluetooth device within an area can be tracked by consid-
ering the distance of the device from Bluetooth receivers and using trilateration
