Advanced Avionics Questions and Answers on “Global Orbiting Navigational Satellite System”.
1. How are GLONASS satellites differentiated from each other?
a) FDMA
b) CDMA
c) TDM
d) WDM
Answer: a
Clarification: GLONASS satellites are distinguished and differentiated by radio frequency channel rather than spread spectrum code as in GPS. They use FDMA whereas GPS uses CDMA.
2. What type of antenna is used in GLONASS satellites?
a) Helical
b) Beam antenna
c) Parabolic antenna
d) Loop antenna
Answer: b
Clarification: A uniform power density is required for using GLONASS. A shaped beam antenna is used to produce uniform power spectral density on the ground.
3. What is the spectral separation between each satellite L1 signal in the GLONASS?
a) 50kHz
b) 2MHz
c) 1240MHz
d) 562.5kHz
Answer: d
Clarification: The unique frequency for L1 signal in the GLONASS system is given by the formula f= 1602.0 +0.5625i MHz where I=0,1,2,….,24. The separation between each of these satellites is 562.5 kHz.
4. What are the frequency channels that GLONASS use for normal operation?
a) i=-7 to +4
b) i=+5 to +12
c) i=-7 to +12
d) i=-2 to +7
Answer: a
Clarification: The GLONASS use i= -7 to +4 frequency channels for normal operation. This was done so that the signal does not interfere with the radio astronomy ground station which uses the same frequency band.
5. Why was the frequency channel used by the GLONASS shifted down after 2005?
a) Political issue
b) Less power requirements
c) Avoid future MSS interference
d) Reduce atmospheric interference
Answer: c
Clarification: The Frequency of the GLONASS channel was shifted down in 2005. This shift down in frequency is to avoid interference from future Mobile Satellite Services.
6. L1 and L2 signals are both contain PRN and navigational data.
a) True
b) False
Answer: a
Clarification: In GLONASS, both the satellite broadcast signals L1 and L2 are bi-phase modulated with PRN codes and navigational data. These are necessary for computing velocity and position of the user in 3D space.
7. How are the ephemeris data broadcast in GLONASS?
a) ECEF coordinates
b) ECI coordinates
c) Directional cosines
d) Geodetic spherical coordinates
Answer: a
Clarification: The GLONASS ephemeris data are broadcast as ECEF or Earth Center Earth Fixed coordinate system cartesian coordinates in position and velocity with lunar and solar acceleration perturbations parameters that are valid about 0.5 hour.
8. What are the frequency channels that GLONASS use as a technical channel?
a) i=-7 and +4
b) i=+5 and +6
c) i=-7 and +12
d) i=-2 and +7
Answer: b
Clarification: The GLONASS use i= +5 and +6 frequency channels as a technical channel. They are only used for a limited periods of time during orbital intersections or other periods of exceptional circumstances.
9. GLONASS time and GPS time follows leap the second correction.
a) True
b) False
Answer: b
Clarification: GPS time does not follow the leap second correction that UTC occasionally makes. GLONASS time does.
10. What is the spectral separation between each satellite L2 signal in the GLONASS?
a) 437.5kHz
b) 2MHz
c) 1240MHz
d) 562.5kHz
Answer: a
Clarification: The unique frequency for L2 signal in the GLONASS system is given by the formula f= 1246.0 +0.4375i MHz where I=0,1,2,….,24. The separation between each of these satellites is 437.5kHz.
11. GLONASS time is related to which of the following?
a) UTC(USNO)
b) UTC(Moscow)
c) UTC(London)
d) UTC(Beijing)
Answer: b
Clarification: The GPS segment provides correlations so that GPS time can be related to UTC(USNO) modulo 1sec to within 90nsec, whereas the GLONASS control segment provides correlations so that GLONASS time can be related to UTC(Moscow) to within 1μsec.