What is GPS and how it works

1. GPS TRACKING
Abstract
Global Positioning System tracking is a method of working out exactly where something is. A
GPS tracking system, for example, may be placed in a vehicle, on a cell phone, or on special
GPS devices, which can either be a fixed or portable unit. GPS works by providing information
on exact location. It can also track the movement of a vehicle or person. A GPS tracking system
uses the Global Navigation Satellite System (GNSS) network. This network incorporates a range
of satellites that use microwave signals that are transmitted to GPS devices to give information
on location, vehicle speed, time and direction. So, a GPS tracking system can potentially give
both real-time and historic navigation data on any kind of journey.
Introduction
Global Positioning System (GPS) is a worldwide radio-navigation system formed from the
constellation of 24 satellites and their ground stations. The nominal GPS configuration consists
of a network of 24 satellites in high orbits around the Earth, but up to 30 or so satellites may be
on station at any given time. Each satellite in the GPS constellation orbits at an altitude of about
20,000 km from the ground, and has an orbital speed of about 14,000 km/hour. The Global
Positioning System is mainly funded and controlled by the U.S Department of Defense (DOD).
The system was initially designed for the operation of U. S. military. But today, there are also
many civil users of GPS across the whole world. The civil users are allowed to use the Standard
Positioning Service without any kind of charge or restrictions. . It became fully operational in
1995. The tracking unit is basically a GPS receiver which continuously receives signals from the
satellites to know its current location on earth. Visibility of the receiver to at least 3 satellites is
important to know the location of a receiver (latitude and longitude) and a 4th
satellite is needed
to know the altitude which gives a somewhat accurate idea of where the receiver is.

2. Figure 1 GPS SATTELITES IN ORBIT
Types of GPS trackers
1. Data loggers
A GPS logger simply logs the position of the device at regular intervals in its internal memory.
Modern GPS loggers have either a memory card slot, or internal flash memory card and
a USB port. Some act as a USB flash drive. This allows downloading of the track log data for
further analysis in a computer. They are also called “passive” trackers.
2. Data pushers
Data pusher is the most common type of GPS tracking unit, used for asset tracking, personal
tracking and Vehicle tracking system. Also known as a GPS beacon, this kind of
device pushes ("sends") the position of the device as well as other information
like speed or altitude at regular intervals, to a determined server, that can store and instantly
analyze the data. Newer GPS-integrated smartphones running GPS tracking software can turn the
phone into a data pusher (or logger) device. Most GPS trackers provide data "push" technology.
In vehicular tracking system, tracking device is most often hardwire installed in the vehicle;
connected to the CAN-bus, Ignition system switch, battery. They are also called “active”
trackers.

3. Many modern vehicle tracking devices combine both active and passive tracking abilities. When
a cellular network is available and a tracking device is connected it transmits data to a server,
when a network is not available the device stores data in internal memory and will transmit
stored data to the server later when the network becomes available again.
How GPS tracking works
The operation of the tracking using GPS is based on a simple mathematical principle called
trilateration. Trilateration falls into two categories: 2-D Trilateration and 3-D Trilateration. In
order to make the simple mathematical calculation the GPS receiver must know two things. First
it must know the location of the place is to be traced by at least three satellites above the place.
Second, it must know the distance between the place and each of those Space Vehicles.
Each GPS satellite continually broadcasts a signal that includes a message of the time of
transmission (TOT) of the signal and the satellite position at that time. Now suppose we have to
find the position of a receiver. The receiver receives the signal transmitted by the satellite “A”.
From the time difference between the TOT and the time at which it is received by the receiver
the time taken by the signal to reach the receiver can be calculated. This time multiplied by the
speed of the signal which is equal to the speed of light can give us the distance of the receiver
from the satellite “A”. This is shown by the sphere centered at satellite A in Fig 2 as the receiver
can be anywhere on the sphere.
Figure 2

4. Also the same procedure can be done with two other satellites “B” and “C” shown in Fig 3 and
Fig 4. These three spheres will intersect at a point in the space( the space being on earth) which
can give us location of the receiver on earth.
Figure 3 Figure 4
This method is Trilateration. The more the number of satellites the more accurate the position of
the receiver can be known. But because of the atmospheric disturbances the position of the
receiver is affected. The ionosphere tend to refract the signals sent by the satellites thus
increasing the time it is received and affecting the location. This can be corrected by using the
differential correction signal which takes the atmospheric disturbances into account for more
precise location and tracking.
Figure 5 Figure 6

5. After finding the location of the receiver the information can either be stored or sent using active
or passive trackers.
Applications
 Robotics: self-navigating, autonomous robots using a GPS sensors, which calculate
latitude, longitude, time, speed, and heading.
 GPS aircraft tracking
 Vehicle tracking system
 Geotagging: applying location coordinates to digital objects such as photographs and
other documents for purposes such as creating map overlays
 Fleet tracking: the use of GPS technology to identify, locate and maintain contact reports
with one or more fleet vehicles in real-time
 Navigation: navigators value digitally precise velocity and orientation measurements.
References
 Bertagna. (2010). eetimes. Retrieved 5 June, 2016, from
http://www.eetimes.com/document.asp?doc_id=1278363
 Nasa larc office of education. (2005). Youtube. Retrieved 5 June, 2016, from
https://www.youtube.com/watch?v=0n0T992ccik
 Lefebure. (2009). Youtube. Retrieved 5 June, 2016, from
https://www.youtube.com/watch?v=YjcfmZw23Wg
 Koran. (2014). Youtube. Retrieved 5 June, 2016, from
https://www.youtube.com/watch?v=4O3ZVHVFhes
 Global positioning system( 2016,31 May).Retrieved from
https://en.wikipedia.org/wiki/Global_Positioning_System