SBCA Digital Transmission 2

Question 1

Which modulation technique is used in DVB-S2 to achieve higher spectral efficiency compared to DVB-S?

Accepted Answer

8PSK and 16APSK

Answer

DVB-S2 supports higher-order modulations including 8PSK and 16APSK, enabling greater spectral efficiency than DVB-S which uses QPSK.

Question 2

What is the primary purpose of a Reed-Solomon outer code in a digital satellite transmission chain?

Accepted Answer

Correcting burst errors after Viterbi decoding

Answer

Reed-Solomon outer coding corrects burst errors that remain after the inner Viterbi decoder, providing a concatenated error correction scheme.

Question 3

In MPEG-2 transport stream, what is the fixed packet size?

Accepted Answer

188 bytes

Answer

MPEG-2 transport stream packets are fixed at 188 bytes, consisting of a 4-byte header and 184 bytes of payload.

Question 4

What does the term 'spectral efficiency' measure in satellite digital transmission?

Accepted Answer

Bits transmitted per second per hertz of bandwidth

Answer

Spectral efficiency is measured in bits/s/Hz and indicates how effectively a transmission system uses available bandwidth.

Question 5

Which DVB-S2 feature allows the uplink to adapt modulation and coding in real time based on link conditions?

Accepted Answer

Adaptive Coding and Modulation (ACM)

Answer

ACM (Adaptive Coding and Modulation) dynamically adjusts modulation order and FEC rate per terminal based on real-time link margin.

(SBCA) Satellite Broadcasting and Communications Association Certification Practice Test