blog entry by
Aaron Croslow is reposted with permission of Linx Technologies.
Please click the hyperlink below for the original. Linx is a manufacturer
of satellite navigation system receivers. Please also see
Linx's GM Series GNSS Receiver Module Makes Tracking Multiple Satellite
Linx's FM Series GPS Receiver Module Brings High Position Accuracy
in Small Packages, and
Linx's RM Series GPS Receiver Module Offers an Economical Solution
to Precise Global Positioning.
December 20, 2013
The Beginner’s Guide to Different Satellite
navigation systems have become so widespread that they are almost taken
for granted. However, the fact that they are so useful is leading to
an expansion of available systems. Several countries are working on
systems so product selection may become more complicated. To start,
one must have a solid understanding of how satellite navigation systems
work, as well as the terminology that is commonly used when referring
to the technology.
(See infographic [to the right], and/or [click
it for a full-size version])
What is a satellite navigation system and how do they work?
A satellite navigation system (also known as a sat nav system) is
a system of satellites, usually managed by one company or country that
provides geo-spatial positioning, which is a technical term for a specific
location on or above the Earth in 3 dimensions. A sat nav system receiver
can be used to locate latitude, longitude, altitude, velocity and time
information. Commercial systems are accurate to within a few meters.
High-end systems are accurate to within centimeters. The satellites
broadcast a signal that contains orbital data and the exact time the
signal is transmitted. The orbital data is transmitted in a data message
that is superimposed on a code that serves as a timing reference. The
satellite uses an atomic clock (most accurate time and frequency standards
known) to maintain synchronization of all the satellites in the constellation.
The receiver compares the time of broadcast encoded in the transmission
with the time of reception measured by an internal clock, thereby measuring
the time-of-flight to the satellite.
The receiver measures signals
from several satellites at the same time so that it can use triangulation
to determine its location. Triangulation is the process of determining
the location of a point by measuring the angles to it from two known
points. The precise satellite locations are included in the transmission
and the time-of-flight of the signal is used to calculate the distance
to each satellite. The receiver then does some math and calculates its
location on the Earth. The more satellites the receiver can track, the
more accurate the location calculation.
The receiver calculates
4 parameters; latitude, longitude, altitude and time. As a result, the
receiver generally needs to see at least 4 satellites to calculate the
4 unknowns. It can give estimates for the values with fewer satellites,
but the potential error increases.
The basic triangulation math
is not that complicated, but the fact that the known points, the satellites,
are moving very fast and the fact that the Earth is a curved surface
adds quite a bit of complexity. In addition, the Earth is not a perfect
sphere and is not uniformly shaped or curved. This adds some error depending
on how far off the average curvature a specific location is. For this
reason, local augmentation systems are used. The receiver can also use
regional data sets that better describe the local geography and ultimately
give a more accurate position.
Why are there different
satellite navigation systems?
In the early days of the
U.S. run NAVSTAR GPS system, an error code was transmitted with the
satellite signal. This error decreased the accuracy of the system so
that it was not as effective for those outside the United States military.
Commercial organizations began to use terrestrial beacons on the Earth
to augment the system and account for the error. These beacons were
built along the coast and waterways by the United States Coast Guard
and similar organizations in other countries to help ships navigate
local coastlines and waterways. This required a separate receiver, which
increased the cost and really prevented the systems from becoming commercially
Other agencies in the United States and around the world
created their own augmentation systems to improve accuracy. This includes
the Federal Aviation Administration for commercial aircraft navigation
and the Coast Guard for maritime navigation. Similar systems were created
in Europe, Russia, Japan, India and others.
The error code was
deactivated in 2000 and GPS has since become very widely used. However,
the fact that the United States could turn the error code back on at
any time or even turn off the signals entirely has prompted other countries
to begin to develop satellite navigation systems of their own.
Did you know that "GPS" is NOT an umbrella term for satellite
Contrary to popular belief, GPS
(Global Positioning System) is NOT an umbrella term for all satellite
navigation systems. It used to be, but the term GPS has become associated
with the United States-owned NAVSTAR system. GNSS (Global Navigation
Satellite System) is an umbrella term used today for global systems,
but only two global systems exist at this time. There are also regional
satellite navigation systems, and some of those regional systems are
in the process of becoming global. Are you confused yet? That’s okay.
We hope to leave you with a basic understanding of these various systems
so you can determine which type of satellite navigation system would
be best for your application.
The Major Satellite Navigation Systems
As stated in the prior paragraph, there are two types of satellite
navigation systems: global and regional. Global navigation satellite
systems (GNSS) provide coverage all over the world. Regional satellite
navigation systems provide coverage just to one area. Regional systems
typically augment a global system, but some can be used as stand-alone
systems. First, we will cover GNSS.
Global Navigation Satellite System (GNSS)
Global Positioning System (GPS)
GPS system is composed of 24 satellites, and was created by the U.S.
Department of Defense. It can be accessed anywhere on or near the Earth
where there is an unobstructed line-of-sight to four or more GPS satellites.
The system provides critical capabilities to military, civil and commercial
users worldwide and is freely accessible to anyone with a GPS receiver.
Global Satellite Navigation System (GLONASS)
GLONASS is also composed of 24 satellites but was developed in the
Soviet Union and is operated by the Russian Aerospace Defense Forces.
This sat nav system is the only other navigational system in operation
with global coverage and of comparable precision.
Galileo is a global navigation system
currently being developed by the European Union and European Space Agency
intended primarily for civilian use. Named after the Italian astronomer
Galileo Galilei, one of the goals is to provide a high-precision positioning
system for European nations that is independent from the Russian GLONASS,
U.S. GPS, Indian IRNSS and Chinese Compass systems. The 30-satellite
system is expected to be completed in 2019. The use of the basic services
will be free and open to everyone, while the high-precision capabilities
will be available for paying commercial users and for military use.
Compass (In development)
Compass is a global
navigation system currently being developed in China. It is the second
generation of its regional BeiDou Satellite Navigation System (BDS),
also known as BeiDou-2. Its completion is expected in 2020 and will
consist of 35 satellites.
Regional Satellite Navigation Systems
Quasi-Zenith Satellite System (QZSS)
Quasi-Zenith Satellite System (QZSS) is a proposed three-satellite regional
time transfer system and Satellite Based Augmentation System for the
Global Positioning System that would be receivable within Japan and
Australia. QZSS is targeted at mobile applications to provide communications-based
services and positioning information. Its three satellites, each 120°
apart, are in highly-inclined, slightly elliptical, geosynchronous orbits.
Because of this, they do not remain in the same place in the sky. Their
ground traces are asymmetrical figure-8 patterns, created to ensure
that one is almost directly over Japan at all times.
BeiDou Navigation Satellite System (BDS)
Navigation Satellite System (BDS) consists of two separate satellite
constellations. The first is a limited test system that has been operating
since 2000 known as BeiDou-1. The BeiDou-1 consists of three satellites
and offers limited coverage and applications. Its navigation services
have been mainly for customers in China and neighboring regions. As
mentioned previously, the second generation is a full-scale global navigation
system that is currently under construction and will be known as Compass,
Indian Regional Navigational Satellite System
The Indian Regional Navigational Satellite System
(IRNSS) is a regional satellite navigation system being developed by
the Indian Space Research Organization. When complete, it will be under
control of the Indian government. IRNSS will provide standard service
for civilian use and an encrypted restricted service for authorized
deciding on which module to use for your design, the desired coverage
is just one factor. There are definite advantages to using global systems
and also multiple systems in terms of coverage and accuracy. However,
there are case-by-case scenarios where a regional system may be more
beneficial, but that is beyond the scope of this article.
we’ve helped you gain some insight into the complex world of satellite
navigation systems. If you have any questions or need help figuring
out what type of satellite navigation system to use for your application,
let us know. We have a variety of
receiver modules that work with a variety of applications and satellite
About Aaron Croslow
received his BS degree in Energy Systems Engineering from Oregon State
University in 2013 and came to work at Linx Technologies shortly after.
He currently focuses on sales and technical support. Aaron resides in
Oregon and enjoys the plethora of available outdoor activities.
About Linx Technologies
Technologies makes wireless simple by developing and manufacturing wireless
products that are easy
for engineers of all skill levels to use.
The company’s RF modules, remote controls, antennas and connectors make
it easy for engineers to integrate wireless features without the hassle
and expense of engineering RF functionality from scratch.
customers who need help implementing Linx modules, Linx offers design
services including board layout assistance, programming, certification
advice and packaging design. For more complex RF solutions, Apex Wireless,
a division of Linx Technologies, creates optimized designs with RF components
and firmware selected for the customer’s application.
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Merlin, OR, US 97532
Phone: +1 800 736 6677
+1 541 471 6256 (outside U.S.)
Fax: + 1 541 471 6251
Posted January 1, 2014