The DVB-S standard (Digital Video Broadcasting - Satellite) was released in its first version in 1995 and aimed at normalizing the physical link characteristics and framing structure for satellite television. However, digital satellite transmission technologies have evolved considerably since this first publication as new coding and modulation schemes have been developed, permitting greater flexibility and more efficient use of capacity. Moreover, demands for new services such as HD television, interactive services, VoIP and internet access to name a few have grown exponentially.
This context led to the definition of a new standard defining a new generic transport mechanism that can handle IP packets and MPEG-4 audio video streams. This standard was ratified by ETSI in 2005 and called Digital Video Broadcasting - Satellite Second Generation or DVB-S2 .
A key feature added in DVB-S2 is a near-Shannon forward error correcting scheme that is based on low-density parity check codes (LDPC). This outperforms DVB-S in power efficiency by more than 30%. Higher order modulation schemes like 32APSK and 16APSK in conjunction with better filter roll-off values (20% against 35%) values allow for better spectral efficiency. All of this results in more flexibility and lower costs for operators.
The table below summarizes the main differences between DVB-S and DVB-S2:
|Usage||Broadcast only||Transparent to all data|
|Mode||CCM||CCM / Multistream ACM|
|code||RS and Viterbi||LDPC and BCH|
|Roll off||35% - 25%||20%|
The DVB-S2 standard also introduced a return channel (for ACM features for example). It is described in the DVB-RCS (Return Channel via Satellite) standard.More recently a new optional extension of DVB-S2, called DVB-S2X, has been standardized by the DVB project in March 2014. It brings some improvements such as:
- Higher modulation Schemes (64/128/256 APSK).
- Even smaller roll-off factors.
- Improved filtering leading to smaller carrier spacing.