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GNSS Navigation Principles
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GNSS Navigation Principles
GNSS Navigation Principles
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Question
What is the basic principle behind positioning in GNSS navigation?
Answer
Positioning involves receiving satellite signals and calculating the receiver's position in 3D coordinates (latitude, longitude, height) and time by solving ranges from at least four satellites.
Question
Why are at least four satellites needed to determine a GNSS receiver's position and time?
Answer
Three satellites provide ranges for latitude, longitude, and height, but a fourth satellite is needed to solve for the receiver's clock time error (dT) and to exclude illogical position solutions.
Question
How is the range between a satellite and a GNSS receiver calculated?
Answer
Range is determined by multiplying the time taken for the satellite signal to reach the receiver by the speed of light (Range = Time Taken × Speed of Light).
Question
What is a pseudorange, and how is it determined?
Answer
A pseudorange is a range measurement based on the time difference between the satellite's transmitted code and the receiver's generated code. It is calculated by comparing the received satellite signal with the receiver's internal version and considering the timing difference (∆T).
Question
What impact does the receiver's clock error have on GNSS range measurements?
Answer
Receiver clock errors (time error dT) affect the timing measurements, so GNSS positioning must solve for this time error to accurately calculate ranges and position.
Question
What are the three main components of a GNSS system?
Answer
The three main components are the Space Segment (satellites), the Control Segment (monitoring stations), and the User Segment (receivers).
Question
What is the significance of the User Segment in GNSS?
Answer
The User Segment consists of receivers that process satellite signals to provide navigation and positioning, with accuracy ranging from meters to millimeters, depending on the application and receiver quality.
Question
List some key advantages of GNSS for navigation.
Answer
GNSS is weather independent, does not require line of sight between points, offers high accuracy, operates 24 hours a day, saves time and manpower, provides a common coordinate system, and has no distance limitations within approximately 20 km.
Question
Name major Global Navigation Satellite Systems (GNSS) mentioned in the text.
Answer
Major GNSS are GPS (USA), GLONASS (Russia), Galileo (EU), CNSS (China), QZSS (Japan), and INSAT (India).
Question
Describe key features of the GPS system.
Answer
GPS was developed by the US Department of Defense in the early 1970s. It uses the WGS84 coordinate system with 31 satellites in 6 orbital planes at about 20,200 km altitude. It sends signals such as L1, L2, L2C, L5, and L1C, and satellites repeat their position every ~11 hours 57 minutes. It serves both military and civilian users.
Question
What distinguishes GLONASS from GPS?
Answer
GLONASS is managed by the Russian government, uses the PZ-90 coordinate system, has 26 satellites in 3 orbital planes at 19,100 km altitude, and completes one orbit every ~11 hours 15 minutes. It provides standard and precise positioning services.