Digital Signal Processing Reference
In-Depth Information
The Global Navigation Satellite System (GNSS) has a well defined structure,
initially designed by US and USSR and then is being followed by the systems like
Galileo and Beidou. The basic segments like space, control, user and augmentation
are discussed in next lines. The reference architecture is about the GPS as it is only
the fully operational at this moment with maximum information too. The signal
structure is also discussed briefly to understand the basic principle of navigation
and finding the position and time information.
1.2.1.1
Space Segment
It consists of constellation of satellites equipped with navigational payload, precise
atomic clocks, navigational antennas and other subsystems like thermal, propulsion,
attitude and orbit determination and control (AODC), Tracking, Telemetry and
Command (TT&C) and power subsystems. The constellation is designed consid-
ering the availability of at least four satellites at all times across the globe. The
satellites are arranged in different planes to provide the best geometric dilution of
precision (GDOP), a parameter of satellite geometry. Medium Earth Orbits (MEO),
20,000-30,000 km, are chosen for the constellation of satellites due to considerable
launch cost and global coverage.
1.2.1.2
Control Segment
It consists of master control centre along with some monitoring stations and
telemetry telecommand antennas spread all over the globe to perform the following
main tasks.
Measures the position of each satellite and controls its attitude and orbit
Monitors the signals broadcast by satellites
Sends information to satellites for a proper clock alignment
Sends information to satellites for the navigation message
1.2.1.3
User Segment
User segment consists of mainly the GNSS receivers to process the signals received
from the satellites and estimates the user's position. The functionalities common to
any kind of receiver can be summarized as identification of the satellites in view,
estimation of the user-satellite distance and Triangulation.
1.2.1.4
Augmentation Segment
It includes additional equipments like local elements, pseudolites or Geo-Satellites
allowing new services or improved performance. Differential GPS (DGPS), Local
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