GPS (Global Positioning System) – Working

In this article, we will discuss the GPS (Global Positioning System). The GPS stands for global position system, which is basically a satellite-based navigation system. It provides exact time and location information anywhere, anytime, 24 hours a day, and in all-weather conditions. It is a 24-satellite network system present in the orbit of the US Department of Defense. In the beginning, it was started for military purposes, but in 1980, the government developed a system for civilian purposes. This system has no subscription fees or setup charges; basically, it is free of charge. This system is known as Navstar (navigation satellite timing and ranging). It also has many applications in microcontroller-based projects. We can see a global position system shown in the figure below.

Segments of GPS

The GPS system consists of three segments, or parts, which are as follows:

  1. Space Segment
  2. Control Segment
  3. User Segment

GPS Space Segments

The GPS space segment consists of orbiting GPS satellites or space vehicles in parlance with GPS. This was manufactured by Rockwell International. This segment consists of 24 satellites and three circulating orbits. Initially, eight satellites were used to circulate in each orbit. But later, with modifications and changes, four circulating orbits mean six satellites circulate in each orbit with a 55-degree inclination angle and a 60-degree right ascension angle. Their orbiting period is one half of the sidereal day.

GPS Control Segment

The control segment consists of four dedicated ground antennas, six dedicated monitoring stations, a master control station (MCS), and an alternative master control station. These antennas receive the satellite’s transmission signals, and monitoring stations monitor the satellite to track its exact position in space. This helps make sure they are operating correctly. The master control stations constantly monitor the satellite and use the radar to check its position, altitude, and speed. The alternate master control station works in the absence of the master control station.

GPS User Segment

The user segment consists of hundreds or thousands of user receivers that could be hand-held or placed in vehicles. Normally, the receiver consists of antennas for tuning the frequencies that the satellite transmits, a highly stable clock, and a receiver processor. It also consists of a display screen for providing the exact speed and location of the user.

Coordinates of GPS

The GPS system uses a geographic coordinate system, which is basically a coordinate system that enables every specific location on earth to have a set of symbols, letters, or numbers. The choice of coordinates is based on the fact that one number represents the vertical position. and two or three numbers represent the horizontal position.

The GPS based system use the three coordinates angle of latitude, angle of longitude and angle of longitude. Latitude is angle that specifies the north -south position of the point that exist on earth surface and its range is in between 0 degree to 90 degrees. Longitude is coordinate that specifies the east-west position of the point that exist on earth surface. It is used for angular measurement and is denoted by Greek letter lambda. Latitude and longitude are mostly used together for displaying the exact location of point that exist on earth surface. The elevation is a coordinate that tells the exact height of the point with respect to the reference point. It tells the specified point is above or below the reference point.

Working of GPS

The global positioning unit takes the microwave signal in space from satellites, which circulate in orbit around the earth. In space, there are almost 30 satellites that circulate around the earth’s orbit. Each orbit has a radius of approximately 16500 mi and is approximately 12600 mi above the earth. The GPS unit receives the signal from the north and south poles of 6 to 12 satellites. Each satellite has an atomic clock that is set by NORAD carefully a number of times in a day. The microwave signal contains a very good position and time of the satellite with its ephemeris.

The GPS unit consists of a receiver that subtracts the current time of a signal from the sending time of the signal, and this difference tells how much distance the signal travels. This time difference multiplies with the speed of light for calculating the distance from the satellite. This system uses the trigonometric function for solving or calculating the satellite position and distance. For solving the trigonometric function, there should be at least four equations. The GPS system is so fast that the receiver calculates the position in less than one second. It then calculates the speed and direction by changing the change in time and change in position.

Sources of GPS Signal Error

There are some sources which generates the error in global positioning system signal.

  1. Satellite Geometry Error
  2. Satellite Orbit Error
  3. Multipath Effect Error
  4. Atmospheric Effect Error
  5. Clock inaccuracies and Rounding Error

Satellite Geometry Error

When the satellite is in a circulating position, we calculate the time, but we can’t calculate the exact time. That is due to the generation of an error when we calculate the position, and this error is the satellite geometry error.

Satellite Orbit Error

The generation of errors in the orbit of a satellite is due to the slight effect of sun and moon waves, which result in the satellite slightly drifting from its orbit. This error is a satellite orbit error.

Multipath Effect Error

When the GPS signal arrives at the earth, the local obstruction might reflect it before it gets to the antenna receiver. Due to this effect, the GPS signal arrives at the earth with some delays, and this error is a multipath effect error.

Atmospheric Effect Error

Some errors occur due to the atmospheric effect, such as the water vapors in the atmosphere. These errors are the atmospheric effect errors.

GPS Module

A GPS module is basically the GPS receiver that is available in smartphones and many automobiles for social dealing between people. This is a tiny device that can tell us our exact location, position, and time and also communicate with another GPS device. This tiny device has three components: a GPS antenna for sending and receiving the signal, a microbattery for powering the GSP module, and a USB interface port to interface with the computer. When the data comes down to earth from the satellite, it is actually in the form of different pieces of information, and the GPS module receives this data and calculates the exact time and position of this data. The GPS module interfaces with our computer or any other LCD to display the data position and time. We can see a GPS module in Figure 2.

Houlux M-89 GPS module

Applications of GPS Module

There are so many applications of  module some of which are given below.

  1. These applications include the Nano Quad Copter for monitoring their position.
  2. The automobiles industry also uses this for the exact navigation of their vehicles.
  3. Their use in smart mobile phones is for social communication between people.
  4. These are useful in smart power meters for the exact calculation of consumption power, for communication between the meters, and to overcome the problems of electricity theft.
  5. These modules are used in Nano-drones to determine the exact location and position of the target.
  6. These modules are used in fish finder devices for catching fish in an easier way.
  7. These modules are used in those devices, which are used for wildlife tracking.


In conclusion, this tutorial provides an in-depth overview of GPS system. It covers its workings, segments, tracking, errors and applications to help us better understand the concept. You can utilize these GPS modules in your embedded projects. Hopefully this was helpful in expanding your knowledge.

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This concludes today’s article. If you face any issues or difficulties, let us know in the comment section below.

1 thought on “GPS (Global Positioning System) – Working”

  1. Hello MALIK,
    I have been following your post for some days now which i got attracted and have interest in them.
    So, i love the GPS post and would love to know more of it. In the process of reading this post, Some ideas came to my mind which i think i will like to implement.
    How can i use the a GPS for solar tracking?
    I will to see your response as soon as possible. Thanks Bilal Malik


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