Transcript CNS/ATM

Augmentation
systems in
CNS/ATM
prepared by: N. Vedadian
communications satellites
• Communications satellite: stationed in space
for the purposes of Telecommunication .
Modern communications satellites use
geostationary orbit, or low polar Earth orbits
(molniya).
• The concept of the geostationary
communications satellite was first proposed by
Arthur C. Clark in 1929.
communications satellite
• For fixed services, communication satellites
provide a technology complementary to that of
fiber optic submarine communication cables.
• They are also used for mobile applications such
as communications to ships and planes, for
which application of other technologies, such as
cable, are impractical or impossible.
communications satellite
• Geostationary orbit: The satellite appears to
be in a fixed position to an earth-based
observer. A geostationary satellite revolves
around the earth at a constant speed once
per day over the equator.
• The geostationary orbit is useful for
communications applications because
ground based antenna, which must be
directed toward the satellite, can operate
effectively without the need for expensive
equipment to track the satellite’s motion.
communications satellite
• Molniya orbits can be an appealing
alternative in such cases. The Molniya
orbit is highly inclined, guaranteeing good
elevation over selected positions during
the northern portion of the orbit. (Elevation
is the extent of the satellite’s position
above the horizon. Thus a satellite at the
horizon has zero elevation and a satellite
directly overhead has elevation of
90 degrees).
•
communications satellite
• Furthermore, the Molniya orbit is so designed
that the satellite spends the great majority of its
time over the far northern latitudes, during
which its ground footprint moves only slightly.
Its period is one half day, so that the satellite is
available for operation over the targeted region
for eight hours every second revolution.
communications satellite
• low Earth orbit: a circular orbit about 150
kilometers above the earth’s surface and,
correspondingly, a period (time to revolve
around the earth) of about 90 minutes. Because
of their low altitude, these satellites are only
visible from within a radius of roughly 1000
kilometers from the sub-satellite point. In
addition, satellites in low earth orbit change
their position relative to the ground position
quickly. So even for local applications, a large
number of satellites are needed if the mission
requires uninterrupted connectivity.
communications satellite
• Low earth orbiting satellites are less expensive
to position in space than geostationary satellites
and, because of their closer proximity to the
ground, require lower signal strength (Recall
that signal strength falls off as the square of the
distance from the source, so the effect is
dramatic). So there is a trade off between the
number of satellites and their cost. In addition,
there are important differences in the onboard
and ground equipment needed to support the
two types of missions
communications satellite
• As mentioned, geostationary satellites are
constrained to operate above the equator.
As a consequence, they are not always
suitable for providing services at high
latitudes: for at high latitudes a
geostationary satellite may appear low on
(or even below) the horizon, affecting
connectivity and causing multi pathing
(interference caused by signals reflecting
off the ground into the ground antenna).
communications satellite
• The first satellite of Manoliya series was
launched on April 23, 1965 and was used
for experimental transmission of TV signal
from Moscow uplink station to downlink
stations, located in Russian Far East, in
Khabarovsk, Magadan and Vladivostok.
• In November of 1967 Soviet engineers
created a unique system of national TV
network of , called orbita, that was based
on Molniya satellites.
INMARSAT
• The world’s first global mobile satellite
communication operator , and is still the
only one to offer a mature range of modern
communication services to maritime , land
mobile, aeronautical, etc.
• Starting with a user base of 900 ships in
1980, it now supports links for phone, fax,
and data communication to more than
240,000 ships, aircraft and land vehicles.
INMARSAT
• Frequency:
satellite to land earth stations (LES):
6 GHZ (C band)
satellite to mobile: 1.5 GHZ(L band)
mobile to land: 1.6 GHZ
mobile to satellite: 4 GHZ
INMARSAT
• INMARSAT-3 F1: launched in 1996 to cover
Indian Ocean Region (IOR)
• INMARSAT-3 F2: launched in 1998 to cover
Atlantic Ocean Region-East (AOR-E)
• INMARSAT-3 F3: launched in 1999 to cover
Pacific Ocean Region (POR)
• INMARSAT-3 F4: launched in 2000 to cover
Atlantic Ocean Region-West (AOR-W)
INMARSAT
• Global coverage except polar regions
above about 80 degree latitude.
SBAS
SBAS systems improve the performances •
of GPS. This is accomplished by providing
the geostationary signals of a set of
corrections that improve the position and
time calculation performed by the user
satellite receiver.
EGNOS provides these corrections not •
only for GPS but also for GLONASS.
SBAS
The difference between the theoretical •
and the real measurement performed in a
known position can be found, with similar
values, in other real measurements
performed in the nearby of the known
position.
In fact, where several reference points are •
available, a wide area correlation law,
which models the difference in distance
measurements, is possible.
SBAS
The data collected by a network of •
reference stations are processed and
then transmitted to the users, by means
of geostationary satellites, on a signal
having the same frequency as GPS
(L1=1575.42 MHz) and a different data
format.
At present, SBAS are being developed •
to cover the following areas:
SBAS
Europe: •
EGNOS (European Geostationary
Navigation Overlay Service) covers the
European Civil Aviation Conference
(ECAC) region.
United States: •
Wide Area Augmentation System
(WAAS) covers the United States,
Canada, Hawaii and Puerto Rico.
SBAS
• Japan:
MTSAT Satellite-Based Augmentation
System (MSAS), covers Japan.
•
SBAS
• India:
The Indian Space Research Organization
(ISRO) along with the Airport Authority of
India (AAI) has worked out a joint program
to implement GAGAN, a Satellite Based
Augmentation System using
GPS/GLONASS over Indian Airspace.
WAAS
• WAAS stands for Wide Area
Augmentation System.
• It's a system of satellites and ground
stations that provide GPS signal
corrections, giving position accuracy up to
five times better.
WAAS
WAAS is an extremely accurate •
navigation system developed for
civil aviation by the Federal Aviation •
Organization (FAA) in conjunction with the
United States Department of
Transportation.
WAAS
• Its accuracy is less than 3 meters 95% of
the time, and it provides integrity
information equivalent to or better than
receiver autonomous integrity monitoring
(RAIM).
• This is achieved through 25 ground
stations throughout the US and Alaska
which measure the difference between
their surveyed location and the GPS signal
which measure the difference between
their surveyed location and the GPS
signal.
WAAS
• These ground stations send the measured
difference to a master relay station which
sends the corrections to two geostationary
satellites at the same longitudes as the
East and West coasts. Those satellites
beam the correction signal back to Earth,
where WAAS-enabled GPS receivers
apply the correction to their computed
GPS position.
WAAS
• WAAS is based on a network of
approximately 25 ground reference
stations that covers a very large service
area. Signals from GPS satellites are
received by wide area ground reference
stations (WRSs). Each of these, precisely
surveyed reference stations receive GPS
signals and determine if any errors exist.
These WRSs are linked to form the U.S.
WAAS network.
WAAS
• Each WRS in the network relays the
data to the wide area master station (WMS)
where correction information is computed.
The WMS calculates correction algorithms
and assesses the integrity of the system.
• A correction message is prepared and
uplinked to a geosynchronous satellite
via a ground uplink system (GUS).
WAAS
• The message is then broadcast from the
satellite on the same frequency as GPS
(L1,1575.42 MHz) to receivers on board
aircraft (or hand-held receivers) which are
within the broadcast coverage area of the
WAAS.
• These communications satellites also act
as additional navigation satellites for the
aircraft, thus, providing additional navigation
signals for position determination.
WAAS
The Wide Area Augmentation System
(WAAS) uses a system of ground stations
to provide necessary augmentations to the
GPS SPS navigation signal.
A network of precisely surveyed ground
reference stations is strategically
positioned across the country including
Alaska, Hawaii, and Puerto Rico to collect
GPS satellite data.
WAAS
• The WAAS supplies two different sets of
corrections:
• corrected GPS parameters (position,
clock, etc) :
The first set of corrections is user position
independent - they apply to all users
located within the WAAS service area.
WAAS
Ionospheric parameters:
• The second set of corrections is area
specific. WAAS supplies correction
parameters for a number of points
(organized in a grid pattern) across the
WAAS service area.
WAAS
• The user receiver computes ionospheric
corrections for the received GPS signals
based on algorithms which use the
appropriate grid points for where the user
is located.
EGNOS
• EGNOS: European Geostationary Navigation
Overlay Service
EGNOS
• June 2006: the signal broadcast by the
EGNOS satellite IOR-W has been used
for EGNOS Initial Operations.
• June 2006: the EGNOS satellite
ARTEMIS has been used by Industry to
perform various tests on the system.
• July 2006: the signal broadcast by the
EGNOS satellite AOR-E has been used
for EGNOS Initial Operations.
EGNOS
• For the last six years, the ESTB improved
the application of navigation, positioning
and timing services in a multitude of fields
such as farming, aviation and maritime
tests, road applications, and many others.
By doing this, ESTB made significant
preparations for the coming era, where the
completed EGNOS system will serve
Europe in a fully operational and
commercial mode, later also co-operating
with the Galileo system.
EGNOS
• The ESTB signal focused mainly on
accuracy and, therefore, did not provide
the availability and integrity data that
EGNOS will provide but was a great tool
for expanding the expertise and know-how
relating to satellite navigation in Europe
and preparing for future developments
leading to Galileo.
EGNOS
• In contrast to the 15-20 meters accuracy
offered by GPS, the European system is
accurate to less than two meters and
unlike GPS, which is a military system, the
European version offers guaranteed signal
quality.
EGNOS
• EGNOS will provide the information
needed to use navigational signals from
GPS and GLONASS satellites for such
safety critical applications. It will improve
the accuracy of positions from about 20 m
to 5 m, inform users of the errors in
position measurements and warn of
disruption to a satellite signal within six
seconds.
EGNOS
• Three geostationary satellites and a
complex network of ground stations will
carry out the task. The three satellites will
send out a ranging signal similar to those
transmitted by the GPS and GLONASS
satellites. However, the signals will be
more than another opportunity for users to
fix a position.
EGNOS
• The EGNOS receiver, which is more
sophisticated than a standard satellite
navigation receiver, will de-code the signal
to give a more accurate position than is
possible with GPS or GLONASS alone
and an accurate estimate of errors.
EGNOS
• The EGNOS signal will be broadcast by
two Inmarsat-3 satellites, one over the
eastern part of the Atlantic, the other over
the Indian Ocean, and the ESA Artemis
satellite which is in Geostationary Earth
orbit above Africa. Unlike the GPS and
GLONASS satellites, these three will not
have signal generators on board.
EGNOS
• A transponder will transmit signals uplinked to the satellites from the ground,
where all the signal processing will take
place. The sophisticated ground segment
will consist of 34 ranging and integrity
monitoring stations (RIMS), four master
control centers and six up-link stations.
EGNOS
• The RIMS measure the positions of each
EGNOS satellite and compare accurate
measurements of the positions of each
GPS and GLONASS satellite with
measurements obtained from the
satellites’ signals. The RIMS then send
this data to the master control centers, via
a purpose built communications network.
EGNOS
• The master control centers determine the
accuracy of GPS and GLONASS signals
received at each station and determine
position inaccuracies due to disturbances
in the ionosphere. All the deviation data is
then incorporated into a signal and sent
via the secure communications link to the
up-link stations, which are widely spread
across Europe.
EGNOS
• The up-link stations send the signal to the
three EGNOS satellites, which then
transmit it for reception by GPS and
GLONASS users with an EGNOS receiver.
• Considerable redundancy is built into
EGNOS so that the service can be
guaranteed at practically all times
EGNOS in Middle East
In 2002 three RIMS stations were added to
provide eastern mediterranean coverage
for EGNOS flight trials at Cairo.
These tests were conducted by the Italian
ATS Provider ENAV, in cooperation with
the EGNOS project office.
These Cairo flight trials were first discussed
in March 2000 at ICAO MIDANPIRG
GNSS task force meeting.
EGNOS in Middle East
Three additional transportable RIMS were •
deployed in Cairo, Jeddah and Bahrain.
MSAS
MSAS (Multi-functional Satellite •
Augmentation System) is a Satellite Based
satellite Augmentation System, i.e. a
navigation system which supports
differential GPS (DGPS)
designed to supplement the GPS system. •
MSAS
Through of the use of these •
systems an individual GPS augmentation
receiver is able to correct its own position,
offering a much greater accuracy.
GPS signal accuracy is improved from 20 •
meters to about 2 meters in both vertical
and horizontal dimensions.
GAGAN
INDIA plans to build its own version of a •
Satellite-based regional GPS augmentation
system.
The program is called GAGAN (GPS and
GEO Augmented Navigation).
The Indian SBAS or GAGAN would be
implemented in three phases.
GAGAN
After implementation of the project, GAGAN
will play an important role in the
introduction of satellite based navigation
services in asia pacific region.
The major objective is to bridge the gap
between the European EGNOS and Japan
MSAS.