What is DVB-S2?
DVB-S2 (Digital Video Broadcasting — Satellite Second Generation) is the international standard for forward-link satellite transmission, ratified by ETSI in 2005. It replaced DVB-S and has become universal for satellite broadband, direct-to-home TV, news gathering, and professional video contribution. DVB-S2 introduced LDPC (Low-Density Parity-Check) forward error correction — much more efficient than DVB-S's convolutional coding — and support for higher-order modulations up to 32APSK, dramatically increasing spectral efficiency.
DVB-S2X: the enhancement
DVB-S2X was standardised in 2014 as a performance extension (not a replacement) of DVB-S2. Key improvements include: up to 51% throughput gain over DVB-S2 through finer-granularity MODCOD points (doubling the number of modulation-coding combinations); support for 256APSK modulation (optional) for the highest spectral efficiency; roll-off factors of 5%, 10%, and 15% (vs. 20–35% in DVB-S2), enabling carriers to pack more tightly; very low C/N support down to −10 dB for mobile platforms in heavy rain; and transponder bonding to aggregate multiple transponders into a single high-capacity pipe.
Adaptive Coding and Modulation (ACM)
Both DVB-S2 and S2X support ACM: the modulation and coding scheme is adjusted dynamically per terminal based on channel conditions. During clear sky, a terminal uses high-order modulation (32APSK, 64APSK) for maximum throughput; during rain fade, it falls back to a more robust lower-order scheme (QPSK) to maintain link availability. ACM is essential for Ka-band HTS systems operating in regions with variable weather.