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Radio Navigation > 13 Satellite Navigation Systems > Flashcards

13 Satellite Navigation Systems Flashcards

1
Q

What are the key segments of a GNSS?

A
  • Ground segment
  • Space segment
  • User segment
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2
Q

What is the purpose of the Ground segment of a GNSS?

A
  • Monitors satellite orbits and times (produced by atomic clocks)
  • Sends corrections to the satellites
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3
Q

Approximately what frequencies do GNSS transmit on for:

  • Link 1
  • Link 2
A
  • Link 1: 1600 Mhz

- Link 2: 1200 Mhz

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4
Q

Describe the difference between Link 1 and Link 2 on a GNSS and who are they used by?

A

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
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5
Q

Regarding a GNSS, how does using link 2 in conjunction with link 1 provide a more accurate position?

A

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

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6
Q

Who are the main users of:

  • SPS
  • PPS
A
  • Standard Position Service: Civilian Users

- Precision Position Service: Military Users

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7
Q

Describe the principle of operation a GNSS?

A
  • The principle of operation is TIME
  • Satellites broadcast ranging codes and an accurate time
  • Receiver measures signal transit time to determine range from satellite
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8
Q

Regarding a GNSS, what does each satellite allow the receiver to calculate?

  • 1st satellite
  • 2nd satellite
  • 3rd satellite
  • 4th satellite
A
  • 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
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9
Q

How many atomic clocks does a NAVSTAR satellite have?

A

4

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10
Q

Regarding a GNSS, how does a receiver correct for timing errors?

A
  • 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
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11
Q

Regarding a GNSS, what is included in the Navigation Message?

A
  • Ionospheric propagation correction data
  • Timing information
  • Satellite health data
  • Orbital data
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12
Q

What type of sequence is a C/A code?

A

Pseudo Random Noise (PRN) sequence

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13
Q

What does RAIM stand for?

A

Receiver Autonomous Integrity Monitoring

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14
Q

What is the minimum number of satellites a GNSS fix with RAIM requires?

A

5

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15
Q

What is the minimum number of satellites a GNSS fix with RAIM and redundancy requires?

A

6

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16
Q

Regarding a GNSS antenna on an AC:

  • what type of antenna is used
  • where on the AC is it positioned
A
  • Helical antenna

- On the top side of the fuselage, near the CoG

17
Q

With regards to GNSS, what is the principle of operation of GBAS?

A
  • 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
18
Q

With regards to GNSS, what is the principle of operation of SBAS?

A
  • 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
19
Q

With regards to GNSS, what is the principle of operation of ABAS?

A
  • 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
20
Q

For the following GNSS, how many satellites do they have:

  • NAVSTAR
  • GLONASS
  • GALILEO
A
  • NAVSTAR: 24 (21 in operation and 3 spare)
  • GLONASS: 24
  • GALILEO: 30
21
Q

For the following GNSS, how many different orbits do they have:

  • NAVSTAR
  • GLONASS
  • GALILEO
A
  • NAVSTAR: 6
  • GLONASS: 3
  • GALILEO: 3
22
Q

For the following GNSS, how many degrees inclined with the equator are the orbits:

  • NAVSTAR
  • GLONASS
  • GALILEO
A
  • NAVSTAR: 55 degrees
  • GLONASS: 64.8 degrees
  • GALILEO: 56 degrees
23
Q

For the following GNSS, what is the height of the orbits:

  • NAVSTAR
  • GLONASS
  • GALILEO
A
  • NAVSTAR: 20,200 km
  • GLONASS: 19,100 km
  • GALILEO: 23,222 km
24
Q

For the following GNSS, What is the time of each orbit:

  • NAVSTAR
  • GLONASS
  • GALILEO
A
  • NAVSTAR: 12 hrs
  • GLONASS: 11 hrs 15 mins
  • GALILEO: 14 hrs
25
Q

For the following GNSS, what is used as the navigation reference:

  • NAVSTAR
  • GLONASS
A
  • NAVSTAR: WGS-84

- GLONASS: PZ90

26
Q

What is the difference between RAIM (Receiver Autonomous Integrity Monitoring) and AAIM (AC Autonomous Integrity Monitoring)?

A
  • RAIM only uses GNSS provided information

- AAIM uses GNSS provided information as well as additional onboard system data such as IRS

27
Q

What frequencies does the GNSS NAVSTAR broadcast in?

A
  • L1: 1575.45 MHz

- L2: 1227.6 MHz

28
Q

What frequencies does the GNSS GLONASS broadcast in?

A
  • L1: 1.6 GHz

- L2: 1.2 GHz

29
Q

What frequencies does the GNSS GALILEO broadcast in?

A
  • Band 1: 1164 to 1215 MHz
  • Band 2: 1260 to 1300 MHz
  • Band 3: 1559 to 1591 MHz
30
Q

Regarding GNSS, what is the most accurate combinations of satellites and positions?

A
  • 3 satellites positioned 120 degrees apart
  • Each low on the horizon
  • A 4th satellite directly overhead
31
Q

What the 3 major methods of augmentation when using D-GPS?

A
  • GBAS
  • ABAS
  • SBAS
32
Q

For the GALILEO GNSS, what two clocks are to be used?

A
  • Rubidium Frequency Standard clock

- Passive Hydrogen Master clock

33
Q

With regards to GNSS, what is the ‘Search the sky’ procedure?

A

A procedure which starts when turning on a receiver which has no stored satellite data available

34
Q

With regards to the NAVSTAR GNSS, describe Selective Availability?

A
  • 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
35
Q

With regards to GNSS, what does the ‘All in View’ term on receiver mean?

A
  • The receiver is currently tracking all visible satellites above the mask angle
  • Is able to instantly replace any faulty satellite
36
Q

With regards to GNSS, what does the Almanac Information transmitted by the satellites contain?

A
  • Contains approximate position information for each satellite
  • Updated every 24 hours
  • Allows for faster identification of received signals
37
Q

What is height computed by NAVSTAR GPS?

A

Height above the WGS-84 ellipsoid

38
Q

What is the range of GBAS?

A

19nm

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