4.6 Navigation Satellite System
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satellite-based augmentation, ground-based augmentation, precise point positioning
and regional short-message communication services. In March 2015, the first BDS-3
satellite (the 17th BDS satellite) was launched successfully. On June 23, 2020, the
55th BDS satellite was successfully launched into the orbit, which marks the BeiDou
global navigation satellite system is officially built, forming the BDS constellation
with 45 operational satellites, with the visible satellite number anywhere on the
Earth’s surface of more than 6.
The time reference for the BDS is called the BDS Time (BDT), which is a continuous timing system with a second defined in the International System of Units (SI) as
a basic unit and without the leap seconds, and its initial epoch was defined at 0:00:00
UTC on January 1, 2006. The BDT is traced to the UTC through the UTC (NTSC),
which is maintained by the National Time Service Center (NTSC) of China. The
offset between the BDT and UTC is less than 50 ns (modulo 1 s). The leap second
information between the BDT and UTC is broadcasted in the navigation message.
The BeiDou Coordinate System (BDCS) is an Earth-centered, Earth-fixed terrestrial reference system, which is defined in accordance with the specifications of the
International Earth Rotation and Reference System Service (IERS) and aligned with
the latest International Terrestrial Reference Frame (ITRF). The definition of the
BDCS frame is: the origin is the center of Earth’s mass; the Z-axis points to the
direction of the IERS reference pole; the X-axis points to the intersection of the
IERS reference meridian with the plane passing through the origin, and is normal to
the Z-axis; the Y-axis together with the Z-axis and X-axis constitutes a right-handed
orthogonal coordinate system; the length unit is with a meter of the SI; the orientation is given by the Bureau International de l’Heure (BIH) orientation of 1984.0;
the time evolution in orientation will create no residual global rotation with regard
to the crust. As of June 2020, the latest version of the BDCS is 2019V01, and the
differences between the BDCS (2019V01) and ITRF2014 are with the Root Mean
Square (RMS) of 0.74 mm on three coordinate axes [12].
The BDS has achieved the global signal coverage, with the horizontal positioning
accuracy of 10 m (2-sigma), the vertical positioning accuracy of 10 m (2-sigma)
and the timing accuracy of 20 ns (2-sigma). In the Asia–Pacific Region, the BDS
positioning accuracies are 5 m (2-sigma) horizontally and vertically. With the full
navigation capability of the BDS, a relatively complete application industry has been
formed, including fundamental products, application terminals, system applications
and operation services. The BDS application is gradually extended to various fields,
such as transportation, marine fishery, hydrological monitoring, meteorological forecast, forest fire prevention, communication time system, power dispatching, disaster
relief and reduction, which is bringing up a wide range social, economic and military
benefits.
4.6.3.4 Galileo System
In March 2002, the European Union (EU) member states and the European Space
Agency (ESA) finally reached an agreement after many discussions to launch the
239
satellite-based augmentation, ground-based augmentation, precise point positioning
and regional short-message communication services. In March 2015, the first BDS-3
satellite (the 17th BDS satellite) was launched successfully. On June 23, 2020, the
55th BDS satellite was successfully launched into the orbit, which marks the BeiDou
global navigation satellite system is officially built, forming the BDS constellation
with 45 operational satellites, with the visible satellite number anywhere on the
Earth’s surface of more than 6.
The time reference for the BDS is called the BDS Time (BDT), which is a continuous timing system with a second defined in the International System of Units (SI) as
a basic unit and without the leap seconds, and its initial epoch was defined at 0:00:00
UTC on January 1, 2006. The BDT is traced to the UTC through the UTC (NTSC),
which is maintained by the National Time Service Center (NTSC) of China. The
offset between the BDT and UTC is less than 50 ns (modulo 1 s). The leap second
information between the BDT and UTC is broadcasted in the navigation message.
The BeiDou Coordinate System (BDCS) is an Earth-centered, Earth-fixed terrestrial reference system, which is defined in accordance with the specifications of the
International Earth Rotation and Reference System Service (IERS) and aligned with
the latest International Terrestrial Reference Frame (ITRF). The definition of the
BDCS frame is: the origin is the center of Earth’s mass; the Z-axis points to the
direction of the IERS reference pole; the X-axis points to the intersection of the
IERS reference meridian with the plane passing through the origin, and is normal to
the Z-axis; the Y-axis together with the Z-axis and X-axis constitutes a right-handed
orthogonal coordinate system; the length unit is with a meter of the SI; the orientation is given by the Bureau International de l’Heure (BIH) orientation of 1984.0;
the time evolution in orientation will create no residual global rotation with regard
to the crust. As of June 2020, the latest version of the BDCS is 2019V01, and the
differences between the BDCS (2019V01) and ITRF2014 are with the Root Mean
Square (RMS) of 0.74 mm on three coordinate axes [12].
The BDS has achieved the global signal coverage, with the horizontal positioning
accuracy of 10 m (2-sigma), the vertical positioning accuracy of 10 m (2-sigma)
and the timing accuracy of 20 ns (2-sigma). In the Asia–Pacific Region, the BDS
positioning accuracies are 5 m (2-sigma) horizontally and vertically. With the full
navigation capability of the BDS, a relatively complete application industry has been
formed, including fundamental products, application terminals, system applications
and operation services. The BDS application is gradually extended to various fields,
such as transportation, marine fishery, hydrological monitoring, meteorological forecast, forest fire prevention, communication time system, power dispatching, disaster
relief and reduction, which is bringing up a wide range social, economic and military
benefits.
4.6.3.4 Galileo System
In March 2002, the European Union (EU) member states and the European Space
Agency (ESA) finally reached an agreement after many discussions to launch the