DVB TELEVISION STANDARDS
DVB-S2X is an extension of the DVB-S2 specification that provides additional technologies and features. DVB-S2X has been published as ETSI EN 302 307 part 2, with DVB-S2 being part 1. S2X offers improved performance and features for the core applications of DVB-S2, including Direct to Home (DTH), contribution, VSAT and DSNG. The specification also provides an extended operational range to cover emerging markets such as mobile application.
Background
S2X supports significantly higher spectral efficiency for the Carrier to Noise Ratios (C/N) typical for professional applications such as contribution links or IP-trunking. It also supports very low C/N down to -10 dB for mobile applications (e.g. maritime,aeronautical, trains, etc.)
How Does it Work?
DVB-S2X is based on the well-established DVB-S2 specification. It uses the proven and powerful LDPC Forward Error Correction (FEC) scheme in combination with BCH FEC as outer code and introduces the following additional elements:
• Smaller roll-off options of 5% and 10% (in addition to 20%, 25% and 35% in DVB-S2)
• A finer gradation and extension of number 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 support down to -10 dB SNR
• Super-frame option
The usable C/N range is extended for values down to -10 dB by additional framing, coding and modulation options,which will enable satellite services for mobile (sea and air) and very small directive antennas. For VSAT applications the S2X specifications open up the possibility to support advanced techniques for future broadband interactive networks, i.e. intra-system interference mitigation, beam-hopping as well as multi-format transmissions. These may result in significant gains in capacity and flexibility of broadband interactive satellite networks and are made possible thanks to the optional Super-Framing structure.
DVB-S2 already offered excellent spectral efficiency for DTH applications and S2X therefore could not produce physical layer gains comparable to the transition from DVB-S to S2 (i.e. around 30%). Nevertheless, for DTH DVB-S2X fine-tunes both the physical and the upper protocol layers of DVB-S2, producing a highly attractive package (for new generation services, which would require new receivers in any case).The most relevant features for DTH are channel bonding and finer granularity of modulation and FEC options combined with sharper roll-offs. Channel bonding of up to 3 satellite channels will support higher aggregate data rates and allow for additional statistical multiplexing gain for high data rate services such as UHD.
The mandatory implementation of VCM (Variable Coding and Modulation) in receivers offers the possibility of increasing the spectral efficiency for UHD services, while guaranteeing service continuity during heavy rain by simulcasting highly protected SD components.A finer granularity of modulation and FEC options allows for improved operational flexibility. For Professional and DSNG applications high efficiency modulation schemes allow spectral efficiencies approaching 6 bps/Hz (with 256APSK). C/N values of up to 20 dB are now supported with an achievable gain improvement of up to 50%.