DVB-S / DVB-S2 / DVB-S2X
DVB stands for Digital Video Broadcasting.
Over time, processors have become faster and memory has become cheaper. Taking advantage of faster processors and more memory enables equipment to solve a more complex forward error correction problem and this enables the channel capacity to get closer to the Shannon Bound. The evolution of the DVB standards is a result of this advancement in technology. The industry continues to impress with more and more efficiencies based on the advanced computational math involved in Forward Error Correction.
DVB-S is the original DVB standard for Satellite Television and dates back to 1995. The first implementation was by Galaxy in Australia enabling digitally broadcast, satellite-delivered television to the public. DVB-S is used on satellites serving every continent of the world in both Multiple-Channel-Per-Carrier (MCPC) and Single Channel Per Carrier (SCPC) for broadcast networks as well as direct-to-home or direct broadcast services.
The DVB-S standard specifies physical link characteristics and framing and mandates that the overlaid transport stream is MPEG-2 also known as the MPEG transport stream (MPEG-TS).
DVB-S2 stands for Digital Video Broadcast - Satellite - Second Generation. Designed as a successor to the popular DVB-S standard, it improves adding a couple of significant features:
- LDPC Forward Error Correction
- Variable Code Modulation (VCM)
- Adaptive Code Modulation (ACM)
- Enhanced Modulation Schemes up to 32 APSK
- A Generic Transport Mechanism for IP Packet Data including MPEG-4 audio-video streams while supporting MPEG-2 TS based streams.
DVB-S2 achieves approximately 30% better spectral performance than DVB-S allowing for an increase in bit rate over the same satellite transponder bandwidth. When combined with compression improvements from MPEG-4, an HDTV service can be delivered in the same bandwidth that a DVB-S MPEG-2 SDTV could be delivered in.
DVB-S2X is an enhancement that supports higher spectral efficiency for Carrier-to-Noise (C/N) typically found in satellite contribution or IP trunking links. It also supports very low C/N down to -10 dB for mobile applications such as maritime, aero, trains etc.
DVB-S2X uses LDPC Forward Error Correction schemes in combination with BCH FEC as an outer code and introduces the following :
- Smaller filter roll-off options of 5% and 10% in addition to 20%, 25% and 35%
- More granularity of modulation and coding modes
- New constellation options for linear and non-linear channels
- Additional scrambling options for critical co-channel interference situations
- Channel Bonding of up to 3 Channels
- Very Low SNR operation supporting C/N of down to - 10dB
- A Super Frame Option
DVB-S2X's usable C/N range is extended by additional framing, coding and modulation options. This extended C/N range enables the use of smaller antennas. For VSAT applications, DVB-S2X opens up possibilities to support advanced techniques for future broadband interactive networks e.g. intra-system interference mitigation, beam-hopping as well as multi-format transmissions. These will result in significant gains in capacity and flexibility and are made possible by the optional Super-Framing structure.
Channel Bonding and Finer Granularity of FEC and Modulation combined with sharper Filter Roll-offs are the most significant advantages from DVB-S2X. Channel Bonding of up to 3 Aggregate Satellite Channels support higher aggregate data rates and allow for statistical multiplexing gain.