SBCA Network Design 4 — Questions and Answers
Question 1: What is the primary purpose of an uplink power control (UPC) system in a satellite network?
- To maximize transmit power at all times for best signal quality
- To compensate for atmospheric attenuation and maintain constant power flux density at the satellite (Correct answer)
- To reduce transmit power during off-peak hours to save energy
- To coordinate power levels between competing satellite operators
Correct answer: To compensate for atmospheric attenuation and maintain constant power flux density at the satellite
UPC automatically increases earth station transmit power during rain fade or atmospheric attenuation events to maintain a stable carrier level at the satellite transponder input.
Question 2: In satellite network design, what does 'transponder loading' refer to?
- The physical weight of equipment mounted on the satellite
- The aggregate power and bandwidth utilization relative to transponder capacity (Correct answer)
- The process of uploading software updates to satellite transponders
- The scheduling of maintenance windows for transponder downtime
Correct answer: The aggregate power and bandwidth utilization relative to transponder capacity
Transponder loading describes how much of the transponder's available power and bandwidth is being consumed by carriers, typically expressed as a percentage of total capacity.
Question 3: Which access method is best suited for a satellite network where thousands of terminals send very short, infrequent data bursts?
- FDMA with dedicated carriers per terminal
- TDMA with fixed assigned slots per terminal
- ALOHA or slotted ALOHA random access (Correct answer)
- CDMA with unique spreading codes per terminal
Correct answer: ALOHA or slotted ALOHA random access
ALOHA-based random access is ideal for large populations of terminals with bursty, infrequent transmissions where assigning dedicated channels would waste most of the capacity.
Question 4: A satellite network planner must prevent interference between adjacent satellite systems. What is the primary coordination mechanism used internationally?
- Bilateral agreements negotiated directly between satellite operators
- FCC spectrum auctions determining exclusive frequency rights
- ITU Radio Regulations coordination procedures and interference criteria (Correct answer)
- ATIS technical standards for minimum orbital separation
Correct answer: ITU Radio Regulations coordination procedures and interference criteria
The ITU Radio Regulations establish mandatory coordination procedures requiring satellite operators to coordinate with potentially affected networks before bringing a new satellite into service.
Question 5: In a DVB-RCS2 return link design, what determines the maximum number of terminals that can share a single return carrier?
- The number of available IP addresses in the subnet
- The aggregate traffic demand relative to carrier symbol rate and coding efficiency (Correct answer)
- The physical size of the hub antenna aperture
- The number of licensed frequency slots assigned by the FCC
Correct answer: The aggregate traffic demand relative to carrier symbol rate and coding efficiency
The carrier's total capacity (determined by symbol rate, modulation, and coding rate) must accommodate the aggregate traffic from all sharing terminals, setting the practical limit on terminal count.
Question 6: What is the effect of antenna pointing error on satellite link performance?
- It increases the effective noise temperature of the receive system
- It reduces the effective gain of the antenna, degrading both EIRP and G/T (Correct answer)
- It causes multipath interference from ground reflections
- It shifts the carrier frequency due to Doppler effect
Correct answer: It reduces the effective gain of the antenna, degrading both EIRP and G/T
Mispointing causes the antenna to operate off its peak gain point, reducing both transmit EIRP and receive G/T, which degrades the link budget on both uplink and downlink.
Question 7: In satellite network design, what is a 'bent-pipe' transponder architecture?
- A transponder that performs onboard signal processing and switching
- A transponder that simply amplifies and frequency-converts the received signal before retransmitting (Correct answer)
- A transponder with redundant amplifier chains for backup
- A transponder that combines multiple carriers into a single wideband signal
Correct answer: A transponder that simply amplifies and frequency-converts the received signal before retransmitting
A bent-pipe transponder is a transparent repeater that receives, amplifies, and frequency-converts the signal without any onboard demodulation, processing, or routing.
SBCA Network Design 4
What is the primary purpose of an uplink power control (UPC) system in a satellite network?