Radio Navigation - Global Navigation Satellite Systems (GNSS)
34 important questions on Radio Navigation - Global Navigation Satellite Systems (GNSS)
4 main Global Navigation Satellite Systems (GNSS)
- USA NAvigation System with Timing And Ranging Global Positioning System (NAVSTAR GPS)
- Russian GLObal NAvigation Satellite System (GLONASS)
- European GALILEO
- Chinese BEIDOU
GPS health message
Two codes transmitted on L1 frequency
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C/A code
Satellites broadcast the PRN codes with reference to the satellite vehicle time which are subsequently changed by the receiver to UTC.
Satellite time reference
Master control station
Tasks of control segment
— navigation data upload;
— monitoring satellites.
GPS receiver used in aviation
GPS position fix
GPS distance determination
Determining a three-dimensional position
Receiver ground speed determination
NAVSTAR GPS integrity
Basic RAIM requires five satellites. A sixth is for isolating a faulty satellite from the navigation solution.
When a GPS receiver uses barometric altitude as an augmentation to RAIM, the number of satellites needed for the receiver to perform the RAIM function may be reduced by one.
Three components of GLONASS
— control segment, which contains the ground-based facilities;
— user segment.
Space segment GLONASS
— a near-circular orbit at 19 100 km at an inclination of 64.8° to the equator;
— each orbit is completed in 11 hours and 15 minutes.
Control segment GLONASS provides
— correction to orbital parameters;
— navigation data uploading.
Navigation message GLONASS
Immediate data GLONASS
— difference between onboard time scale of the satellite and GLONASS time;
— relative differences between carrier frequency of the satellite and its nominal value;
— ephemeris parameters.
Non-immediate data GLONASS
— coarse corrections to onboard time scales of each satellite relative to GLONASS time;
— orbital parameters of all satellites within the space segment;
— correction to GLONASS time relative to UTC (must remain within 1 microsecond).
Integrity monitoring GLONASS
— Special tracking stations within the ground-based control segment are used to monitor the space-segment performance. If a malfunction occurs, an ‘unhealthy’ flag appears within the ‘immediate data’ of the navigation message.
Timing section GALILEO
Navigational signals GALILEO
Navigation message GALILEO
Navigation antenna GALILEO
GPS, EGNOS and GALILEO
Most significant factors affecting accuracy
— dilution of position;
— satellite clock error;
— satellite orbital variations;
— multipath.
Inonospheric Propagation Delay (IPD)
In SPS receivers, IPD is currently corrected by using the ionospheric model from the navigation message, but the error is only reduced by 50 %.
Ionospheric delay is the most significant error.
Errors in the satellite orbits are due to:
— gravitation of the Sun, Moon and planets
GBAS ground subsystems provide two services
GBAS positioning service
Precision approach service GBAS
GBAS positioning service
SBAS consists of three elements
— the SBAS satellites;
— the SBAS airborne receivers.
SBAS approach and landing operations
Satellite-Based Augmentation Systems include:
— WAAS in the USA;
— MSAS in Japan;
— GAGAN in India.
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