GNSS
BY
ADARSH S
INTRODUCTION
• GNSS stands for global navigation satellite system. A Global Navigation
Satellite System (GNSS) consists of a constellation of satellites orbiting
the Earth in very specific trajectories. For global coverage, it is estimated
that a constellation requires 18 to 30 satellites
• Global Navigation Satellite Systems (GNSS) are a type of satellite-based
navigation system that provides location and time information to users on
Earth.
• GNSS is often generically referred to as GPS (Global Positioning System)
but that acronym actually refers specifically to the United States
constellation. There are several GNSS constellations provided by
governments around the world, including:
• BeiDou – China
• Galileo – European Union
• GLONASS – Russia
• GPS (originally Navstar GPS)- United States
Historical Development
• The basis of GNSS and its technologies is in using radio waves for
communication and tracking a position. These efforts were applied to
space when the Soviet Union launched Sputnik 1 into a low orbit in
1957.
• Transit became the first satellite-based geo-positioning system in 1960
and was used primarily by the Naval service starting in 1964. This
positioning technology was still based around using the Doppler effect
to determine your position to or from a satellite, which only provided
sub-metre accuracy.
• To calculate a more accurate position, the US Navy developed the
Timation satellite that would broadcast an accurate time reference for a
ranging signal. This new approach to satellite positioning – of a satellite
broadcasting its location and specific time at that location – was the
precursor to the United States developing the Global Positioning System
(GPS), launched in 1973.
• Satellite navigation system constellations continued to develop: the Soviet Union’s Parus eventually
expanded into the Global Navigation Satellite System, as GLONASS in 1982
• China introduced their system BeiDou in 2000
• Japan’s Quasi-Zenith Satellite System (QZSS) in 2010
• the European Union launched Galileo in 2005
• and, India’s Indian Regional Navigation Satellite System (IRNSS) in 2013, now known as NavIC.
Components
of GNSS
The space segment
•Components of This refers to the actual satellites orbiting around the earth. The GPS satellite
GNSS constellation is arranged in six equally spaced planes. Each plane has at least four
satellites, and this arrangement ensures that at least four satellites are available at all
times to every receiver, be it a phone, wristwatch, smart car, etc.
The control segments
For every GNSS system, there are built stations located around the equator to
control, monitor, track and communicate with the satellites. This ensures that the
satellite clocks are synchronized and monitored for maintenance like any
IT infrastructure. Information on the satellite’s orbit is also transmitted back to the
satellites and the earth-bound receiver using the L1 carrier wave.
The user segment
This covers anything with a receiver, such as mobile phones, cars, law enforcement
systems, airplanes, etc
A GNSS receiver comprises two elements, a processor and an antenna. The antenna
picks up the signal, and the processor decodes the necessary information. Some
receivers may have two antennas, the primary and secondary antennas.
Types Of
GNSS
• GPS
• Galileo
• GLONASS
• BeiDou
• IRNSS
Global
Positioning System (United
States)
• GPS is the oldest GNSS system. It initiated its
operations in 1978 and was available for
global use from 1994
• Currently, GPS has a 33 satellite
constellation, out of which 31 are in orbit and
operational. It is maintained by the US Air
Force
• use to provide location information and
navigation to missile submarines, surface ship
and also to hydrographic survey and geodetic
surveying to the US army. With time, GPS
was opened up for public use.
GLONASS (Russia)
• Global Navigation Satellite System or
GLONASS is global navigation system
of Russia.
• GLONASS became operational in year
1993 with 12 satellites in 2 orbits at the
height of 19,130 km.
• At present, there are total 27 satellites in
orbit and all are operational. GLONASS
is operated by Russian Aerospace
Defence Forces and is the Second
alternative navigational system in
operation
This Photo by Unknown author is licensed under CC BY-NC-ND.
Galileo (EU)
• Galileo is European Union’s GNSS
constellation, which is being put together by
the European Space Agency, and the European
GNSS Agency will operate it.
• Galileo is global navigation system available
for civilian and commercial use. The fully
deployed Galileo system will consist of 30
operational satellites and 6 in-orbit spares.
• As of now 22 out of 30 satellites are in orbit.
Galileo started offering Early Operational
Capability from 2016 and is expected to reach
full operational capability by 2020.
This Photo by Unknown author is licensed under CC BY-SA-NC.
BeiDou (China)
• BeiDou is Satellite Navigation System of China.
• It has total 22 Operational satellites in orbit and the full
constellation is scheduled to comprise 35 satellites.
• BeiDou has two separate constellations, BeiDou-
1 and BeiDou-2. BeiDou-1 also known as first generation
was a constellation of three satellites.
• BeiDou-2, also known as COMPASS, is the second
generation of the system
• It became operational in year 2000 and offered limited
coverage and navigation services, mainly for users in China
and neighboring regions. Beidou-1 was decommissioned at
the end of 2012
This Photo by Unknown author is licensed under CC BY-SA.
IRNSS ― NAVIC (India)
• The Indian Regional Navigation Satellite
System (IRNSS), which was later given the
operational name of NavIC or Navigation
with Indian Constellation, is the regional
satellite navigation system of India.
• Launched and operated by the Indian Space
Research Organization (ISRO), IRNSS covers
India and nearby regions extending up to 1,500
km.
• All the seven satellites are in orbit, but the first
satellite – IRNSS A – is not functioning now
since some time last year ISRO reported that all
three atomic clocks on it have failed.
This Photo by Unknown author is licensed under CC BY-SA-NC.
