6) Modulation, Coding & DVB-S2X
π Theory β 6) Modulation, Coding & DVB-S2X
I. Digital Modulation
β’ Amplitude, frequency and phase shift keying.
β’ PSK and APSK families dominant.
β’ Trade-off: spectral efficiency vs power efficiency.
II. Modulation Schemes
β’ QPSK β 2 bits/symbol, robust.
β’ 8PSK β 3 bits/symbol.
β’ 16APSK β 4 bits/symbol.
β’ 32APSK β 5 bits/symbol, high SNR needed.
III. Forward Error Correction
β’ Adds redundancy to detect and correct errors.
β’ LDPC β DVB-S2X standard, near-Shannon.
β’ BCH outer code.
β’ Code rates 1/4 to 9/10.
IV. DVB-S2X
β’ Successor to DVB-S2.
β’ More ModCods, smaller roll-offs.
β’ Beam hopping.
β’ ACM β Adaptive Coding & Modulation.
V. Link Adaptation
β’ ACM changes modcod based on C/Nβ.
β’ During rain, drop to QPSK for reliability.
β’ In clear sky, use 32APSK for throughput.
VI. Coding Gain
β’ 3β8 dB typical gain for LDPC.
β’ Allows lower power or higher data rate.
β’ Trades against latency and complexity.
π Level 1
β 0 points
π Advanced Essay (AI-Marked)
Critically analyse the choice of modulation and coding in satellite links. Discuss the trade-offs between spectral efficiency and power efficiency, the role of LDPC FEC and DVB-S2X, and how ACM adapts to dynamic channel conditions.
π Practice MCQs (15)
Q1: How does ACM differ from alternatives?
Q2: Explain 8PSK in satellite communication.
Q3: What is LDPC?
Q4: Why is 16APSK important?
Q5: What are the limitations of DVB-S2X?
Q6: Explain ACM in satellite communication.
Q7: What is Turbo code?
Q8: Why is 32APSK important?
Q9: Explain LDPC in satellite communication.
Q10: Why is LDPC important?
Q11: Why is ModCod important?
Q12: What are the limitations of Coding gain?
Q13: What is 32APSK?
Q14: What are the limitations of 8PSK?
Q15: Explain 16APSK in satellite communication.
Module score: 0/0