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GNSS (Basics)

Brief History

Different Navigation System has been developed throughout the centuries. Location and navigation is an old age concept. The magnetic compass was developed around 13th century. Only in the 20th century the major developments can be related to. The high frequency Radio-based was developed around 1950s to 70s, and Radio-based and transit in 1960s. Develpment of GPS was developed in 1980s and development of GLONASS was in 1993 being similar to GPS. International GPS service was developed in 1994 which is now known as GNSS. The major concepts of GNSS was in 2006. Similar developments of eLoran are seen after 2000. After 2010s, conceptualizaton of integrated receivers with GNSS, eLoran and eChayka.

NAVSTAR Global Positioning System: previous name of GPS, initially developed for military purposes around 1973 by US DOD; abbreviated from NAVigation Satellite Timing and Ranging Global Positioning System

Other System includes GLONASS (3 orbit) , Galileo (3 orbit) and Beidou (35 satellites).

A worldwide position and time determination system that. includes one or more satellite constellations, aircraft receivers and. system integrity monitoring, augmented as necessary to support the. required navigation performance for the intended operation. ICAO Annex 10, Vol. 1

How it works?

~ GPS works in ranging system (triangulation).

1. GPS receiver detects one way ranging signals. The transmission is time tagged and positon of satellite is contained.

2. The transmission time is noted which helps to its time of travel.

3. The delta-T is multiped by the speed of light to obtain the range: 

            P= (transmission time - reception time) * speed of light

4. Each range puts the user on a sphere about the satellite.

5. Intersecting several of these yields a user position.

GPS signals:

two carrier waves: L1 - 19cm and L2-23 cm

low power radio signals (C/A on L and P or Y on both L1 and L2)

Receivers: Single and Dual 

Rough Notes based on:

07 April 2021 Overview of Global Navigation Satellite System by Dr. Ashutosh Bhardwaj


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