Module 2 : Global Positioning System
 Lecture 4 : Basic GPS
History of navigation system
  Determination of position has evolved from stone age to the satellite age as given below:      (http://www.rand.org/publications/MR/MR614/MR614.appb.pdf)
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The Stone Age
It involved use of stones, trees and mountains as points of reference.
. The Star Age
    It involved use of celestial bodies such as Sun, Moon and other stars as points of reference (Celestial Navigation).
. The Radio Age
It involved use of radio signals for positioning.
. The Satellite Age
It involved use of satellite-based radio navigation with satellites as points of reference.
 
Radio Navigation Systems

About the middle of this century, scientists used radio signals for distance measurements. Accurate measurement of radio signal travel time is required since one microsecond of error in measuring the travel time is equal to 300 meters of error in distance as speed of radio signals is the same as the speed of light. Some of the radio navigation systems used are as follows (http://www.fas.org/spp/guide/russia/nav/index.html)

Radio Navigation Systems
Frequency Using
Developed by
Working Principle
DECCA
Low-frequency hyperbolic navigation system
UK
 Comparison of phase difference of radio signals
GEE
VHF frequencies
UK
Measurement of time difference between the reception of pulses from ground transmitters
LORAN-A
 1850 KHz - 1950 KHz radio band
USA
 Phase comparison
LORAN-C
 100 KHz
USA
Phase comparison
OMEGA
Very low frequency (10 -14 KHz)
USA
 Phase comparison
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