Architecture of Global Positioning System (GPS)

Architecture of Global Positioning System (GPS)

GPS or Global positioning system is a satellite based navigation system that provides the exact location and time of an object at any place in the globe in all weather conditions. This is one of the best example of technological advancement in the field of science and technology. The basic concept of GPS technology involves the transmission of signals by the satellites that includes three things: the time at which the message was transmitted by the receiver, the orbital information and the general system health and rough orbits of all GPS satellites.

To run all the system of GPS technology properly, highly advance architecture of GPS has been developed that includes three major segments called the space segment (SS), control segment (CS) and a user segment (US). The first two segments i.e. Space segment and control segment is being controlled and operated by the U.S. Air force. The GPS satellites transmits the signals from the space which are received by the data receivers on the earth which are then used to calculate the three-dimensional location (latitude, longitude, and altitude) of the object along with time.

If we look upon the architectural framework of Global positioning system, the space segment consist of 24 operational satellites and 3 more satellites along with the payload adapters to the boosters required to launch them into orbit. These satellites are placed in the medium earth orbit. The central segment consists of a master control station, an alternate master control station, and a host of dedicated and shared ground antennas and monitor stations. The last segment, user segment constitutes thousands of military users and million of commercial and civilian users. The military users uses the GPS Precise Positioning Service while the others uses the Standard Positioning Service of GPS.

Space Segment

The space segment (SS) comprises the GPS satellites, or Space Vehicles (SV) in GPS parlance. The 24 GPS satellites in the GPS design is distributed into eight each in three circular orbits. Later it was divided into six orbital planes with four satellites each. Though, the orbits are centered on the Earth, they don't rotate with the earth and are fixed with respect to the distant stars. These orbits are arranged in such a way that at least six satellites should always lie within the line of sight from every part of earth surface. For this, four satellites are unevenly spaced within each orbit with angular difference of each orbit being 30, 105, 120, and 105 degrees apart. Thus, making a sum total of 360 degree.

Control segment

A control system of GPS is completed by the combination of a master control station (MCS), an alternate master control station, four dedicated ground antennas and six dedicated monitor stations. The control segment is responsible for the proper functioning of all the operations of global positioning system such as changing the unhealthy satellites with a healthy one if any satellite fails suddenly. It also provides the operational capability to the system that helps the global GPS users and keeps the GPS system operational and functional within specification every time. In addition to that the control segment is responsible for the security issues of the system also.

User Segment

The user segment comprises of thousands of U.S. and allied military users who uses the secure GPS Precise Positioning Service, and millions of civil, commercial and scientific users who uses the Standard Positioning Service of global positioning system. Commonly, the GPS receivers are composed of an antenna, which are tuned to the frequencies that are transmitted by the orbital GPS satellites, receiver-processors, and a highly stable clock called a crystal oscillator. In addition to that they consists of a display that the information about the location and speed to the user. A receiver is generally known by its number of channels which signifies how many satellites it can monitor at a time. Earlier, the number was limited to four or five but now a days the number of channels for a receiver has increased to 12 to 20.

This is how a Global positioning system is designed to get an accurate information about the location and speed of an object and is used for several purposes and has proved very useful in today's world.


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