Global positioning system (GPS) theory for 4th semester civil Engineering student

      Global positioning system (GPS) 

Introduction :

Global positioning system is a space based navigation system that consists of network of 24 satellite designed,laujched and managed by US government, that orbit the earth at an altitude of 20200km ,constantly emitting GPS coded signal for locating the point on the earth by measuring the distance from the satellites receiver. GPS receiver on the earth calculate their position by making measurement of distance to four or more satellites. 

  Working principle of GPS:

-Position of GPS :GPS satelites are floating up in the space. The high altitude of the satellite is actually a benefit as it causes the object at that level orbit the earth according to very simple mathematics without any friction in the atmosphere. 

-Satellite Ranging:All GPS position are based on the measurement of distance from the satellite to the GPS receiver on the earth. The GPS receiver provide the distance of each satellite.Resection or trilateration idea can be used for determination of position. In order to calculate the distance to each satellite the equation used is :

            distance= time *velocity 

-Time calculation :The GPS receiver determine the time taken by the radio signal to travel from the GPS satellite to the receiver. 

-Position calculation :There are four unknown to be determined for the calculation of a position. They are the position coordinate and travel time of the signal.