1. There are two Generations of the DVB-S standard.
• Was developed from 1993-1997.
• Defined by European Standard EN 300 421.
• Just describes the physical link characteristics and the framing.
• The overload transport stream delivery falls under MPEG-2
• Was developed in 2003.
• Defined by European Standard EN 302 307
• The standard was ratified in March 2005.
• Mainly designed to accommodate larger data rates to provide HDVT, Internet access, and data distribution.
C) In March 2014 the DVB-S2 specification became a 2-part document to accommodate the new DVB-S2 Extensions (DVB-S2X).
• The DVB-S2 will remain a stand-alone specification and the DVB-S2X specification is optional.
• DVB-S2 = BlueBook A83-1 / EN302307-1
• DVB-S2X = BlueBook A83-2 / EN302307-2
• Uses the MPEG-2 video standard
• Uses the MPEG-4 AVC video standard.
For Satellite TV:
• C-band (4-8GHz), 24 channels
• Ku band (12-18GHz), 32 channels
• Bandwidth is about 27-50MHz
DVB-S2 is the most accepted and widely spread standard in the satellite market. The standard has a deep market penetration in Sports and News Contribution, Professional Video Distribution solutions, IP trunking and Cellular backhauling, Broadband VSAT solutions up to Government and Defense networks over satellite. In a fast moving satellite world new technologies (HTS, HEVC, UHDTV) emerge, data rates increase at an accelerated pace and end-users expect to get connectivity anywhere anytime. Within applications such as Contribution and IP Trunking the efficiency requirements are already testing the limits of the DVB-S2 standard. The risk for a massive take-over by proprietary technologies with better performance is realistic. A proprietary scenario would disperse the satellite industry, increase the cost of satellite communications as well as prevent interoperability and result in vendor lock-in. The new DVB standard, called DVB-S2X (or extension to DVB-S2), with improved efficiency will give the satellite industry more breathing space to increase profitability and allow for business growth throughout all applications, from High Speed IP to Broadcast to VSAT. The efficiency technologies of the new DVB standard boost the satellite link up to 20% in Direct-To-Home networks and 51% in other professional applications compared to DVB-S2.
Up until now the DVB-S2 standard has been the solution for a wide scope of applications over satellite including distribution applications such as Direct-to-Home (DTH). For distribution activities broadcasters are likely to continue to use the existing DVB-S2 standard for some time. But with the new higher resolution technologies like ultra high definition TV (UDHTV) and High Efficiency Video Coding (HEVC) video compression about to hit the market, and the drive for more content, in the longer term the new S2 Extensions will be adopted for DTH networks as well. We are likely to see an immediate take-up in applications that require high throughput over satellite for professional use and in applications that suffer for bandwidth or need better margins to remain profitable. The applications that will adapt quickly to the DVB-S2X are:
• IP Trunking & IP/Telecom Backbones
• Broadcast Contribution and Exchange
• IP Backhauling & Professional IP Access
• Government High Speed Communications & Disaster Recovery
• Multiservice networks over satellite
When comparing the current DVB-S2 standard against the full implementation of DVB-S2X staggering efficiency gains up to 51% can be achieved for professional applications over satellite. When combined with Wideband an extra 20% can be added to the equation. For DTH networks up to 20% efficiency increase can be obtained. These gains already exceed the results by proprietary systems in the market today.
2. DVB-S2X IMPROVEMENTS
1. Smaller Roll-Offs
2. Advanced Filtering
3. Supporting Different Network Configurations
4. Increased Granularity in MODCODs
5. Higher Modulation Schemes up to 64/128/256APSK
6. Very Low SNR MODCODs
7. Linear and non-linear MODCODs
8. Bonding of TV streams
9. Additional standard scrambling sequences
10. Wideband Support
A first innovation inside the new standard implements a smaller Roll-Off (RO) percentage than currently used in the DVB-S2 standard. In the DVB-S2 standard the 20% and 25% Roll-Off percentages are common and are an integral part of the modulated carrier (i.e. symbol rate plus Roll-Off). Reducing Roll-Offs to 5%, 10% and 15% results in a direct gain in bandwidth. Looking at the spectral image when implementing smaller Roll-Offs the slope of the carrier becomes steeper compared to DVB-S2 but still fits nicely in the allocated bandwidth. The efficiency gain by implementing smaller roll-offs can go up to 15%. When implementing smaller roll-offs every network and/or link needs to be checked individually as immediately switching towards 5% roll-off does not always bring the best efficiency. In some cases 10% roll-off will give better results.
Advanced Filtering Technologies for Improved Carrier Spacing
The second innovation deals with noise levels (side lobes) on both sides of the carrier. These side lobes prevent putting satellite carriers close to each other. Applying advanced filter solutions has an immediate effect on bandwidth savings as the spacing between carriers can be put as close as 1.05 times their symbol rates (or even closer in some specific use cases).
Supporting Different Network Configurations
The Roll-Off and filtering innovations within the new standard can be applied in satellite links with single carriers (mainly Roll-Off effect), multiple carriers (Filtering and Roll-Off effects) or carriers sharing the same transponder with other providers. In the latter case DVB-S2X carriers can easily co-exist with adjacent carriers from other operators within the same transponder. The improved roll-offs and filtering technologies are only applied on the allocated carriers. Neighboring carriers will not be affected and do not notice any form of interference
Improvement 4:Increased Granularity in MODCODs
As a next step the DVB-S2X standard increase the modulation and coding (MODCOD) schemes and Forward Error Correction (FEC) choices compared to DVB-S2. By introducing an increased granularity the highest resolution for optimal modulation in all circumstances can be provided. The current DVB-S2 quantization steps are quite far apart. By adding granularity in the upcoming standard the service provider can further optimize the satellite link depending on the application. In combination with Adaptive Coding and Modulation (ACM), where the highest MODCOD is selected automatically, full efficiency can be gained. The amount of MODCODs has grown from 28 in DVB-S2 up to 112 in DVB-S2X bringing efficiency as close to the theoretical Shannon limit as possible.
Higher Modulation Schemes up to 256APSK
Adding higher modulation schemes such as 256APSK proves to be useful considering the professional applications that work with improved link budgets provided by, for example, bigger antennas (more powerful satellites that become available). In these situations having higher modulation schemes as 64, 128 and 256APSK is highly beneficial. When combining the increased granularity (MODCODs and FECs) and higher order modulation immediate efficiency gains up to 51% can be achieved compared to DVB-S2.
Very Low SNR for Mobile Applications
DVB has added 9 extra MODCODs to the DVB-S2X standard in the QPSK and BPSK range in order for satellite networks to deal with heavy atmospheric fading and to enable the usage of smaller antennas for applications on the-move (land, sea, air). These Very Low Signal-to-Noise Ratio (VL SNR) MODCODs will increase the robustness and availability of the satellite link. Some BSPK MODCODs in the new standard use spread spectrum technology. The term ‘spread spectrum’ refers to the deliberate expansion of the signal bandwidth by several orders of magnitude (factor 2 in DVB-S2X). The power is equally spread over a wider occupied bandwidth resulting in a lower carrier’s spectral density (dBW/Hz). By reducing the spectral density levels smaller antennas can be used (for mobile applications on land sea and air) while overcoming adjacent satellite interference. Moreover the link security and availability can be increased. In addition the header of the VL SNR MODCODs has been modified (with an extended Physical Layer Header) with better error-correcting capabilities for operations with signal-to-noise ratio values as low as -10dB.
Different Classes for linear and non-linear MODCODs
Different to DVB-S2, the MODCODs in DVB-S2X have two different classes for linear and non-linear MODCODs. Since the DVB-S2 MODCODs are focused on DTH, the constellations are well suited for distribution applications with quasi-saturated transponders. For high-speed data and contribution applications other constellations can be considered where the performance gain is larger than 0.2dB. Although the MODCODs might use the same code/name, the linear and non-linear MODCODs are not interchangeable. Additionally the MODCODs and FECs themselves have been improved compared to the DVB-S2 standard to achieve even better efficiency levels.
The DVB-S2X standard supports technology for typical wideband transponders that become/are available today hosting high-speed data links. The wideband implementation in DVB-S2X typically addresses satellite transponders with bandwidths from 72 MHz (typically C-band) up to several hundred MHz (Ka-band, HTS). In principle it would be possible to allocate several narrower channels inside the wideband transponders, but this would require the operation of the satellite transponder with reduced downlink power and therefore at sub-optimal efficiency. The DVB-S2X demodulator will receive the complete wideband signal up to, for example. 72 Mbaud resulting in a very high data rate. The introduction of the wideband technology adds extra 20% efficiency gain.
Improvement 9: Channel Bonding
The channel bonding feature inside the DVB-S2X standard finds its main implementation in the Direct-to-Home application and is a direct response to the increase in rates with the introduction of Ultra High Definition Television (UHDTV) transmission over satellite. The size of a UHDTV channel requires four times the transmission capacity of a High Definition Television (HDTV) channel. With the introduction of improved encoding technologies such as HEVC (High Efficiency Video Coding – H.265) the compression efficiency can be doubled compared to AVC (Advanced Video Coding – H.264). Below some typical rates for HDTV and UHDTV in DTH.
• HDTV with AVC coding = 10 Mbps
• UHDTV with AVC coding = 40 Mbps
• UHDTV with HEVC coding = 20 Mbps
In a traditional 36 MHz transponder it was possible to transmit 6 HDTV channels or 60 Mbps. The amount of channels could even be increased to 7 when taking a 20% statistical multiplexing gain into account. For UHDTV however only 3 channels can be provided over the same 36 MHz transponder. The gain from statistical multiplexing has been reduced to 12%. DVB-S2X introduces channel bonding specifically to increase the statistical multiplexing for UHDTV transmissions. With this feature a single big transport stream is sent over several different transponders at the same time. The capacity of these transponders is merged and will provide extra gain (extra 12% for 3 bonded channels). The accumulated gain will allow in the end to accommodate an extra UHDV channel in the big Transport Stream by using the spare capacity of the individual transponders.
Additional Standard Scrambling Sequences
With the increase of data traffic, rich media and TV channels over satellite resulting in a steady growth of DTH services, HTS and multi-spot beam satellite payloads the topic of co-channel interference (CCI) could no longer be ignored when the new DVB-S2X standard was being developed. The new standard today has a mechanism to mitigate CCI by providing a better differentiation between neighboring services. The differentiation between these services is based on the addition of physical layer (PL) scrambling sequences within DVB-S2X. Whereas DVB-S2 only had one default code (PL scrambling sequence number 0) another six codes have been defined for the new standard. On the reception of a scrambled signal a typical DVB-S2X receiver will firstly try the default code and only afterwards cycle though the new codes to de-scramble the signal.
3. DVB-S2X Technology Results When comparing the current DVB-S2 standard against the full implementation of S2 Extensions (activating smaller Roll-Offs, advanced filtering and 256APSK) staggering efficiency gains up to 51% can be achieved for professional applications over satellite. By implementing Wideband an extra 20% gain can be added to the equation. For DTH networks up to 20% efficiency increase can be obtained. These gains already exceed the results by proprietary systems in the market today.