SBCA Network Design 2 — Questions and Answers
Question 1: In a VSAT star topology network, what is the primary role of the hub station?
- To relay traffic between remote sites without central processing
- To aggregate all remote site traffic and connect to the terrestrial network (Correct answer)
- To provide redundancy for satellite transponder failures
- To manage frequency coordination with adjacent satellites
Correct answer: To aggregate all remote site traffic and connect to the terrestrial network
In a star topology VSAT network, the hub station aggregates all inbound traffic from remote sites and connects the network to terrestrial infrastructure such as the internet or private WAN.
Question 2: What is the key advantage of a mesh topology satellite network over a star topology?
- Lower latency for site-to-site communications (Correct answer)
- Simpler network management
- Lower cost hub infrastructure
- Higher transponder efficiency
Correct answer: Lower latency for site-to-site communications
Mesh topology allows direct site-to-site links, eliminating the double-hop latency (approximately 500ms round-trip) required when all traffic must pass through a central hub.
Question 3: Which modulation scheme provides the highest spectral efficiency in modern satellite broadband networks?
- BPSK
- QPSK
- 8PSK
- 16APSK (Correct answer)
Correct answer: 16APSK
16APSK offers the highest spectral efficiency among the listed options, delivering approximately 4 bits per symbol, though it requires higher Eb/N0 and is used on high-quality links with sufficient CNR.
Question 4: A satellite network designer must plan for rain fade on a Ku-band link. Which design technique directly compensates for rain attenuation?
- Frequency reuse
- Adaptive coding and modulation (ACM) (Correct answer)
- Polarization diversity
- Orbital slot selection
Correct answer: Adaptive coding and modulation (ACM)
ACM dynamically adjusts the modulation and coding rate based on real-time link conditions, reducing throughput during rain fade to maintain link availability.
Question 5: What does the term 'figure of merit' (G/T) represent in satellite terminal design?
- The ratio of antenna gain to system noise temperature (Correct answer)
- The ratio of transmit power to receive sensitivity
- The ratio of EIRP to transponder bandwidth
- The ratio of signal power to interference power
Correct answer: The ratio of antenna gain to system noise temperature
G/T (Gain-to-noise Temperature ratio) is the figure of merit for a receive system, expressing antenna gain relative to system noise temperature in dB/K.
Question 6: In satellite network capacity planning, what does 'overbooking ratio' refer to?
- The ratio of peak to average transponder power
- The ratio of committed information rate to actual provisioned bandwidth
- The ratio of total subscribed bandwidth to available satellite capacity (Correct answer)
- The ratio of uplink to downlink frequency allocations
Correct answer: The ratio of total subscribed bandwidth to available satellite capacity
Overbooking ratio is the ratio of total subscribed (sold) bandwidth to available satellite capacity, exploiting the fact that not all subscribers transmit simultaneously.
Question 7: Which satellite frequency band is most susceptible to rain fade and therefore requires the largest link margin in network design?
- L-band (1-2 GHz)
- C-band (4-8 GHz)
- Ku-band (12-18 GHz)
- Ka-band (26-40 GHz) (Correct answer)
Correct answer: Ka-band (26-40 GHz)
Ka-band experiences the highest rain attenuation due to its shorter wavelength, requiring significantly larger link margins (often 10 dB or more) compared to lower frequency bands.
SBCA Network Design 2
In a VSAT star topology network, what is the primary role of the hub station?