Hello friends this blog is helpful those people who don't know about GPS and want to work with it. This is my first blog that I am trying to write. This blog is really helpful for project and also seminar point of view. We only know that GPS is Global Positioning System for navigation but we don't know how it navigate? and how to use this in project or application? you will get all in this blog.
HOW WE CAN LOCATE POINT ON EARTH?
Using latitude and longitude we can locate any any point on earth surface this is only two dimension. But what if the point is at certain height above the earth surface? the answer is we should know altitude. See the following map which will clear idea. GPS do the same it gives the information about latitude, longitude and altitude of an object which we want to navigate.
SOME BASIC IDEA
See following fig. if A, B and C are three fixed points. And a point 'P' which is not fixed is located at distance x, y, z from A, B, C respectively. We can find out its position. Just draw circles of radii x, y, z with center A, B, C these three circle will intersect each other at a point that point will be 'P'. GPS also works with the same idea. Now suppose these three points A, B, C are three transmission station continuously transmit three different frequency of EM waves. And a receiver is receiving these signal continuously suppose ' P'. Time require to receive the signal by P is time require to travel this signal from transmitter to this receiver. Let A station transmitting signal at time T1 and P receives this signal at T2 then time require to travel these signal will be (T2 - T1). We all know that EM waves travel at the speed of light (C = 3x10^8 m/s). So the distance between A and P is calculated as x' = (T2 - T1) * C and similar way for y' and z' for B and C. In this way receiver P can find its own position.
In old days there was Ground based navigation system but. GPS is a space based global navigation system which consists three part.
Part A- GPS satellite revolving around the earth.
Part B- Monitoring Station.
Part C- User GPS module or receiver.
Part A- GPS satellite revolving around the earth.
There are total 24 GPS satellite revolving around the earth and in six different orbit. Each orbit consists four satellite. As shown below for navigation at least four satellite should be visible to the GPS receiver. Each satellite broadcast its orbiting information continuously. These satellite are located at around 20000 km from the earth surface. In following fig. you can see there are 24 satellite which are revolving around the earth and blue dot shows GPS receiver and black dots are the satellite those are visible to the receiver and receiving their signal.
It consists of monitoring station which control all the activities of the satellite. And also it keep tracking all the satellite and their flight path. If the satellite changes its orbit GPS receiver doesn't receive its signal because receiver mark it as unhealthy. For this purpose monitoring to these satellite also necessary.
Part C- User GPS module or receiver.
This is important part of this system to develop the GPS based system. It consists of GPS receiver module which receives all the signal transmitted by the GPS satellite those are visible to it. And also it compute all about its position information in the form of latitude, longitude and altitude. We are interested to know how this module can be used in our application ? like vehicle tracking system, human tracking system. This is important to note GPS module never transmit signal to the satellite it just receive the signal.
In next post I will explain different GPS module available in the market and how module can be interface with the micro-controller. There is lot more to explain for Part A and B but I am not going with that.
