13 Satellite Navigation Systems Flashcards
What are the key segments of a GNSS?
- Ground segment
- Space segment
- User segment
What is the purpose of the Ground segment of a GNSS?
- Monitors satellite orbits and times (produced by atomic clocks)
- Sends corrections to the satellites
Approximately what frequencies do GNSS transmit on for:
- Link 1
- Link 2
- Link 1: 1600 Mhz
- Link 2: 1200 Mhz
Describe the difference between Link 1 and Link 2 on a GNSS and who are they used by?
Link 1:
- Provides Course/Acquisition (C/A) code
- Associated with Standard Position Service (SPS)
- Used by civilian users
Link 2:
- Provides Precision (P) code
- Associated with Precise Position Service (PPS)
- Used in conjunction with Link 1 by Military users
Regarding a GNSS, how does using link 2 in conjunction with link 1 provide a more accurate position?
By using 2 different frequencies, it is possible to measure the difference in time between the two through the ionosphere and apply the required corrections
Who are the main users of:
- SPS
- PPS
- Standard Position Service: Civilian Users
- Precision Position Service: Military Users
Describe the principle of operation a GNSS?
- The principle of operation is TIME
- Satellites broadcast ranging codes and an accurate time
- Receiver measures signal transit time to determine range from satellite
Regarding a GNSS, what does each satellite allow the receiver to calculate?
- 1st satellite
- 2nd satellite
- 3rd satellite
- 4th satellite
- 1st: gives position on a sphere
- 2nd: gives a circular position where the two spheres intersect
- 3rd: gives an unambiguous position
- 4th: allows timing errors to be corrected
How many atomic clocks does a NAVSTAR satellite have?
4
Regarding a GNSS, how does a receiver correct for timing errors?
- The receiver produces a ‘Pseudo Range’
- By deliberately introducing a delay in the received time
- Increases the distance reported by the satellite
- Gives a position range
- 4th satellite is used to correct for this timing error
Regarding a GNSS, what is included in the Navigation Message?
- Ionospheric propagation correction data
- Timing information
- Satellite health data
- Orbital data
What type of sequence is a C/A code?
Pseudo Random Noise (PRN) sequence
What does RAIM stand for?
Receiver Autonomous Integrity Monitoring
What is the minimum number of satellites a GNSS fix with RAIM requires?
5
What is the minimum number of satellites a GNSS fix with RAIM and redundancy requires?
6
Regarding a GNSS antenna on an AC:
- what type of antenna is used
- where on the AC is it positioned
- Helical antenna
- On the top side of the fuselage, near the CoG
With regards to GNSS, what is the principle of operation of GBAS?
- Ground Based Augmentation System
- A pseudo satellite is placed on the ground
- This receives signals from the GNSS satellites
- Applies time corrections
- Sends this data to the AC
- AC must tune into it like an ILS
With regards to GNSS, what is the principle of operation of SBAS?
- Satellite Based Augmentation System
- Uses geostationary satellites such as EGNOS
- Their positions are known
- Checks their position against where the GNSS satellites think they are
- Not limited by line of sight
With regards to GNSS, what is the principle of operation of ABAS?
- Air Based Augmentation Systems
- Satellite provides position to AC
- AC knows it’s position and sends back to satellite
- Satellite sends any corrections from AC to ground station
- Ground station verifies correction
- New position sent to satellite and on to AC
For the following GNSS, how many satellites do they have:
- NAVSTAR
- GLONASS
- GALILEO
- NAVSTAR: 24 (21 in operation and 3 spare)
- GLONASS: 24
- GALILEO: 30
For the following GNSS, how many different orbits do they have:
- NAVSTAR
- GLONASS
- GALILEO
- NAVSTAR: 6
- GLONASS: 3
- GALILEO: 3
For the following GNSS, how many degrees inclined with the equator are the orbits:
- NAVSTAR
- GLONASS
- GALILEO
- NAVSTAR: 55 degrees
- GLONASS: 64.8 degrees
- GALILEO: 56 degrees
For the following GNSS, what is the height of the orbits:
- NAVSTAR
- GLONASS
- GALILEO
- NAVSTAR: 20,200 km
- GLONASS: 19,100 km
- GALILEO: 23,222 km
For the following GNSS, What is the time of each orbit:
- NAVSTAR
- GLONASS
- GALILEO
- NAVSTAR: 12 hrs
- GLONASS: 11 hrs 15 mins
- GALILEO: 14 hrs
For the following GNSS, what is used as the navigation reference:
- NAVSTAR
- GLONASS
- NAVSTAR: WGS-84
- GLONASS: PZ90
What is the difference between RAIM (Receiver Autonomous Integrity Monitoring) and AAIM (AC Autonomous Integrity Monitoring)?
- RAIM only uses GNSS provided information
- AAIM uses GNSS provided information as well as additional onboard system data such as IRS
What frequencies does the GNSS NAVSTAR broadcast in?
- L1: 1575.45 MHz
- L2: 1227.6 MHz
What frequencies does the GNSS GLONASS broadcast in?
- L1: 1.6 GHz
- L2: 1.2 GHz
What frequencies does the GNSS GALILEO broadcast in?
- Band 1: 1164 to 1215 MHz
- Band 2: 1260 to 1300 MHz
- Band 3: 1559 to 1591 MHz
Regarding GNSS, what is the most accurate combinations of satellites and positions?
- 3 satellites positioned 120 degrees apart
- Each low on the horizon
- A 4th satellite directly overhead
What the 3 major methods of augmentation when using D-GPS?
- GBAS
- ABAS
- SBAS
For the GALILEO GNSS, what two clocks are to be used?
- Rubidium Frequency Standard clock
- Passive Hydrogen Master clock
With regards to GNSS, what is the ‘Search the sky’ procedure?
A procedure which starts when turning on a receiver which has no stored satellite data available
With regards to the NAVSTAR GNSS, describe Selective Availability?
- An intentional error which the US defence department could introduce to the civilian L1 code
- This is achieved by oscillating (or dithering) the satellite clock
With regards to GNSS, what does the ‘All in View’ term on receiver mean?
- The receiver is currently tracking all visible satellites above the mask angle
- Is able to instantly replace any faulty satellite
With regards to GNSS, what does the Almanac Information transmitted by the satellites contain?
- Contains approximate position information for each satellite
- Updated every 24 hours
- Allows for faster identification of received signals
What is height computed by NAVSTAR GPS?
Height above the WGS-84 ellipsoid
What is the range of GBAS?
19nm
