EC-603-C Satellite Communication - May 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aExplain the concepts of local mean solar time. How sun-synchronous orbits are used to maintain a consistent standard time for satellite observations?
   How to answer

   • Define local mean solar time (LMST) with reference to mean sun and longitude
   • Explain need for consistent illumination / standard time for observations
   • Explain sun-synchronous orbit principle - nodal precession matching Earth revolution
   • Applications to Earth observation / remote sensing
2. 7 Marks
   bGiven a satellite with an apogee of 36,000 km and a perigee of 500 km, calculate the semi-major axis and eccentricity of the orbit. Assume a circular Earth with a radius of 6,371 km.
   How to answer

   • Convert apogee/perigee altitudes to geocentric radii using $R_e = 6371$ km
   • Calculate semi-major axis $a = (r_a+r_p)/2$
   • Calculate eccentricity $e = (r_a-r_p)/(r_a+r_p)$
   • Present numerical values in km
3. 7 Marks
   aExplain the concept of orbit perturbations. Discuss the principle of inclined orbits.
   How to answer

   • Define orbit perturbations and causes - J2, drag, solar pressure, third-body
   • Explain effects on orbital elements
   • Define inclined orbits and nodal precession principle
   • Applications of inclined orbits
4. 7 Marks
   bDefine a geostationary orbit and explain its key properties. Why it is particularly useful for communication satellites.
   How to answer

   • Define geostationary orbit - equatorial, circular, 35786 km, 24h period
   • List key properties - zero inclination, fixed longitude, three-satellite coverage
   • Explain advantages for communications - fixed antenna, continuous coverage, no tracking
5. 7 Marks
   aDiscuss the various types of launching orbits used for placing a satellite into a geostationary orbit. Highlight the advantages and disadvantages of each.
   How to answer

   • List launching orbits - LEO parking, GTO/Hohmann transfer, direct injection
   • Explain sequence to GEO
   • Compare advantages - fuel, flexibility, launcher capability
   • Compare disadvantages - time, complexity, radiation exposure
6. 7 Marks
   bWhat is meant by cross-polarization discrimination? Write its importance in satellite communications.
   How to answer

   • Define cross-polarization discrimination (XPD)
   • Explain orthogonal polarization reuse concept
   • Explain importance - frequency reuse, capacity doubling, interference isolation
7. 7 Marks
   aBriefly describe the following subsystems of a satellite, emphasizing their importance in satellite operations:

   1. i)Attitude Control
   2. ii)Station Keeping
   3. iii)TT and C (Telemetry, Tracking and Command) Subsystem
   How to answer

   • Describe Attitude Control - orientation, sensors, actuators
   • Describe Station Keeping - east-west/north-south corrections, fuel
   • Describe TT&C - telemetry, tracking, command functions
   • Emphasize importance for mission life and operation
8. 7 Marks
   bExplain the function of transponders in satellite communication. Discuss different types of antenna subsystems used in satellites.
   How to answer

   • Explain transponder function - receive, amplify, frequency translate, retransmit
   • Explain bent-pipe vs regenerative types
   • Discuss antenna types - horn, reflector, phased array, spot/global beams
   • Link to coverage and gain requirements
9. 7 Marks
   aExplain the concept and components of a transmit-receive earth station in satellite communication.
   How to answer

   • Define transmit-receive earth station concept
   • List components - antenna, HPA, LNA, modem, tracking
   • Explain uplink/downlink signal flow
   • Role in satellite link
10. 7 Marks
    bFor a satellite circuit the C/N ratio are : uplink 23 dB, downlink 20 dB, intermodulation noise 24 dB. Calculate the overall C/N ratio in dBs. Also suggest a method to reduce intermodulation noise.
    How to answer

    • Convert dB C/N values to linear ratios
    • Apply reciprocal formula $1/(C/N)_{total} = \sum 1/(C/N)_i$
    • Convert back to dB for overall C/N
    • Suggest back-off / filtering to reduce intermodulation noise
11. 7 Marks
    aDefine EIRP and explain its importance in satellite communication.
    How to answer

    • Define EIRP as $EIRP = P_t G_t$
    • Explain components - transmit power and antenna gain
    • Explain importance in link budget and coverage
    • Relation to received power / flux density
12. 7 Marks
    bDiscuss the challenges and considerations in designing the uplink portion of a satellite communication link, including the effects of atmospheric conditions.
    How to answer

    • List uplink design factors - power, rain attenuation, interference
    • Explain atmospheric effects - absorption, scintillation, depolarization
    • Discuss HPA back-off, frequency choice, site diversity
    • Considerations for link margin and availability
13. 7 Marks
    aExplain the components and functions of a VSAT earth station. Discuss the basic transmission techniques employed in VSAT systems.
    How to answer

    • List VSAT components - small dish, ODU/IDU, hub, modem
    • Explain functions of each block
    • Discuss transmission techniques - TDMA, FDMA, CDMA, Aloha
    • Star vs mesh topologies
14. 7 Marks
    bDiscuss the error control methods used in digital DBS-TV. Highlight the importance of these methods in maintaining broadcast quality.
    How to answer

    • List error control methods - FEC, convolutional, Reed-Solomon, interleaving
    • Explain ARQ vs FEC in broadcast
    • Explain importance for BER and picture quality
    • Link to rain fade and threshold performance
15. 14 Marks
    Write short notes on any two :

    1. a)Satellite radio broadcasting
    2. b)Calculation of Link margins for a VSAT star network
    3. c)Kepler's three law of planetary motion
    4. d)Morelos and Satmex 5
    How to answer

    • Select any two topics from a-d
    • For each: give definition/principle, key features/formulas
    • Give satellite communication relevance/example
    • Conclude with applications/importance