SSPI Satellite Network Design & Operations 5 — Questions and Answers
Question 1: What is the significance of the 'threshold' in satellite receiver design?
- The minimum C/N or Eb/N0 below which demodulator performance degrades rapidly (Correct answer)
- The maximum transmit power allowed by the satellite license
- The frequency at which the LNB switches polarization
- The altitude at which satellites transition from LEO to MEO
Correct answer: The minimum C/N or Eb/N0 below which demodulator performance degrades rapidly
Below the receiver threshold, bit error rates increase dramatically, causing the link to become unreliable even with small additional degradations.
Question 2: In a satellite network employing MF-TDMA, what does the 'MF' prefix signify?
- Multiple Frequency — carriers are spread across several frequencies to increase total system capacity (Correct answer)
- Maximum Frequency — the highest frequency band in use
- Modulation Factor — the number of bits per symbol
- Multi-Footprint — multiple satellite coverage beams
Correct answer: Multiple Frequency — carriers are spread across several frequencies to increase total system capacity
MF-TDMA combines multiple frequency carriers with time division, allowing scalable capacity allocation across both frequency and time dimensions.
Question 3: Which phenomenon causes a satellite's apparent position to oscillate in a figure-eight pattern over the course of a year?
- Solar wind pressure
- Analemma effect due to combined inclination and eccentricity drift (Correct answer)
- Gravitational perturbations from the Moon causing libration
- Ionospheric refraction varying with solar activity
Correct answer: Analemma effect due to combined inclination and eccentricity drift
The analemma is caused by residual inclination and eccentricity of a nominally geostationary satellite, causing apparent north-south and east-west drift.
Question 4: What type of satellite orbit is best suited for continuous coverage of polar regions that GEO satellites cannot serve?
- Molniya orbit (Correct answer)
- Sun-synchronous orbit
- Equatorial MEO orbit
- Geostationary transfer orbit
Correct answer: Molniya orbit
Molniya orbits (highly elliptical, 63.4° inclination) spend most of their time over high latitudes, providing extended coverage of polar regions.
Question 5: What is the primary function of Doppler compensation in a LEO satellite terminal?
- To correct for the frequency shift caused by the satellite's high orbital velocity relative to the ground station (Correct answer)
- To reduce multipath interference from reflected satellite signals
- To compensate for atmospheric delay on the uplink
- To adjust antenna polarization as the satellite passes overhead
Correct answer: To correct for the frequency shift caused by the satellite's high orbital velocity relative to the ground station
LEO satellites move at ~7.5 km/s, causing significant Doppler shifts that must be pre-compensated to maintain accurate carrier frequency at the receiver.
Question 6: In satellite network design, what is the purpose of uplink power control (UPC)?
- To increase earth station transmit power during rain fade to maintain a constant signal level at the satellite (Correct answer)
- To reduce satellite EIRP during clear sky conditions to save fuel
- To control the number of simultaneous users accessing a transponder
- To adjust the satellite's transponder gain remotely from the NOC
Correct answer: To increase earth station transmit power during rain fade to maintain a constant signal level at the satellite
UPC counteracts uplink attenuation caused by rain by boosting earth station transmit power, keeping the satellite's received signal level within design range.
Question 7: Which document produced during satellite network design specifies the end-to-end performance requirements that the system must achieve, such as availability and BER?
- System Requirements Document (SRD) (Correct answer)
- Frequency Assignment Notice
- Master International Frequency Register (MIFR) filing
- Earth station type approval certificate
Correct answer: System Requirements Document (SRD)
The SRD formally defines measurable performance requirements (availability, BER, latency, capacity) that drive all subsequent design and verification activities.
SSPI Satellite Network Design & Operations 5
What is the significance of the 'threshold' in satellite receiver design?