By Steven Soenens, VP Product and Market Management and Kerstin Roost, Public Relations Director at Newtec
Earlier in 2014 a new satellite transmission standard, developed specifically for professional satellite communications, was introduced to the market following calls from key players in the satellite industry. Kick started by Newtec in the course of 2012, the following article explains how the new standard DVB-S2X improves overall efficiency over satellite links and the innovations behind it.
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.
The new DVB standard called DVB-S2X (or extension to DVB-S2) improves transmission efficiency, giving the satellite industry more breathing space to increase profitability and fuel business growth throughout all applications, from High Speed IP to broadcast to VSAT.
The efficiency technologies contributed by Newtec to the new DVB standard boost the satellite link up to 20% in Direct-To-Home (DTH) networks and up to 51% in other professional applications compared to DVB-S2.
The road to DVB-S2X
The satellite world has changed a lot since DVB-S2 was first published in 2005. Higher speeds, more efficient satellite communication technology and wider transponders are required to support the exchange of large and increasing volumes of data, video and voice over satellite. Moreover, end-users expect to receive connectivity anywhere, anytime they travel, live or work. Video is the key driver to achieving higher transmission efficiency: more content and higher quality HD and UHDTV video are expected to boost bandwidth needs significantly throughout the value chain.
Higher transmission rates will be required initially in video contribution and exchange networks, but in the long run more throughput will also be required for DTH applications. The new DVB-S2X standard in fact, has specific features included to the DTH market, including channel bonding to support the rise of Ultra High Definition Television (UHDTV). Many technology suppliers, operators and satellite specialists within the industry have worked together with DVB towards realization of this new standard. Finally in February 2014, the new standard, called DVB-S2X was officially launched.
The Innovations behind DVB-S2X
The successor to the DVB-S2 standard is a combination of innovative technologies that improve overall efficiency over satellite links.
Improvement 1: Smaller Roll-Offs
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% RO percentages are common and are an integral part of the modulated carrier (i.e. symbol rate plus RO). Reducing ROs to 5%, 10% and 15% results in a direct gain in bandwidth. Looking at the spectral image when implementing smaller ROs - 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.
Image 1: Low Roll-Off: 5/10/15%
Improvement 2: 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 satellite carriers (being put) 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).
It is important to note that even with 35%, 25% and 20% roll-offs, better filtering results are obtained. The improvement has the best effect when the ground station High Power Amplifier (HPA) is driven close to saturation. The spectral regrowth at a frequency offset (= symbol rate) will be lower with the better filtering. Meaning, at saturation, the result will have a much cleaner signal spectrum.
Image 2: Optimal Carrier Spacing
Improvement 3: 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.
Image 3: Shared Transponder Support
S2 Extensions MODCOD and FEC Upgrades
Improvement 4: Increased Granularity in MODCODs
As a next step the DVB-S2X standard increases 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 116 in DVB-S2X bringing efficiency as close to the theoretical Shannon limit as possible.
Improvement 5: Higher Modulation Schemes up to 256APSK
Adding higher modulation schemes such as 256 APSK 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). Newtec sees the 32 APSK boundary being reached frequently with its auto-adaptive FlexACM® technology during clear weather conditions. In these situations having higher modulation schemes such 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 (see image 4).
Image 4: DVB-S2X compared to DVB-S2 (64/128/256APSK & increased granularity)
Improvement 6: Very Low Signal to Noise Ratio (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 (VLSNR) 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 VLSNR 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.
Improvement 7: 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.
Improvement 8: Wideband Support
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, High Throughput Satellite (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 an extra 20% efficiency gain.
Improvements for DTH Transmissions
Improvement 9: Channel Bonding
The channel bonding feature inside the DVB-S2X standard finds its main implementation in the DTH application and is a direct response to the increase in rates with the introduction of UHDTV transmission over satellite. The size of a UHDTV channel requires four times the transmission capacity of a High Definition Television (HDTV) channel, even using the improved encoding technology called HEVC ( H.265). Below are 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% and as such no extra program can be added in this context.
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 for the video statistical mux algorithm
Improvement 10: 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.
Newtec’s DVB History & Implementation of the New Standard
Newtec played an important role in the new DVB-S2X standard as many of the developments inside the new standard are based on Newtec technology. The smaller roll-offs and advanced filtering technologies were already introduced by Newtec as early as September 2011 as a first step towards the new DVB-S2 extension through Newtec’s Clean Channel Technology® (CCT).
Image 5: DVB Standards Performance History; from DVB-S (black) to DVB-S2X (red) to be closer to the Shannon limit.
CCT is available on Newtec’s professional equipment and VSAT systems. Both as a software field upgrade for install-based equipment as well as new Newtec equipment.
In the meantime Newtec has invested a lot in its innovative technology to add to the new S2 Extensions standard. Today, Newtec’s contribution to the new standard comes in two flavors. On one hand the pre-standard technology candidates called Newtec’s S2 Extensions (with Clean Channel Technology, 64APSK, increased granularity and 72 Mbaud wideband) support existing installations and satellite networks that prefer to remain ‘closed’ but lower cost in terms of CAPEX. On the other hand the official brand new DVB-S2X standard as defined by the DVB organization is available. Both flavors are already implemented on the Newtec professional equipment (modems, modulators, demodulators and hubs).
How to Increase Efficiency and Availability of a Satellite Link beyond DVB-S2X
Pre-distortion technologies are typically designed to compensate for the effects of imperfections in the filters and amplifiers of the satellite.
Newtec’s implementation of pre-distortion technology, Automated Equalink®, improves the performance of the end-to-end satellite communication channel by up to 2dB and allows for the use of higher modulation schemes such as 16/32APSK or 64/128/256APSK on carriers occupying a full transponder.
The improved link performance can but used to either push more content over the same transponder, increase service availability (QoS), reduce the size and cost of the outdoor units, or a combination of the three.
The satellite industry has come to a consensus that a successor to the DVB-S2 standard is required to accommodate for increased profitability, interoperability and growth in the professional satellite communications market. Newtec has taken the lead and teamed up with other DVB-members in order to define and develop the update to the DVB-S2 standard. At this moment in time, many trials of the new standard are taking place, and initial deployments are on-going.