DVB-RCS & DVB-RCS2 Standards

DVB-RCS & DVB-RCS2 Standards

DVB-RCSDVB-RCS is the first generation of open international standard for TDM/TDMA satellite networks. The standard was published in 2001 and updated several times since.  SatLink Communications was the first company to implement it, on our SatLink product line, and was also instrumental in developing the standard. Today DVB-RCS is supported by multiple satellite network suppliers and used in hundreds of networks world-wide. SatLink Communications is the leading supplier of DVB-RCS networks.

DVB-RCS2In March of 2011 the second generation of this standard (DVB-RCS2) was published. DVB-RCS2 specifies new technology providing significant advances in TDM/TDMA performance for better efficiency, more throughput, and greater network reliability. See DVB-RCS2: Advancing TDM/TDMA Technology.

SatLink Communications was first to demonstrate technology using the new DVB-RCS2 standard in June 2011 (press release). SatLink Communications announced commercial availability of DVB-RCS2 on its SatLink product line in March of 2012 (press release).

Currently SatLink Communications is the still the only supplier offering DVB-RCS2 networks, and continues to offer support for DVB-RCS, both concurrently within the same network.

Today these two "RCS standards" provide the only open, fully documented standards for TDM/TDMA satellite networks of any kind.

For introductory information on TDM/TDMA see Satellite Technology for IP.

 

The Importance of the DVB Standards in Satellite Networks

All DVB standards are developed and/or endorsed by the DVB Project (see www.dvb.org) which is an industry association of over 200 suppliers and users of equipment and software committed to open technical standards for digital television and data services. While traditional digital television broadcasting standards remain important, increasingly the DVB standards of greatest interest and future impact are those that deliver high-speed digital communications for IP (the Internet Protocol) and Internet access over satellite, such as DVB-RCS2 and DVB-S2.

DVB-RCS, and especially its second generation (DVB-RCS2), are of great importance in this regard by supporting high-speed interactive (two-way) satellite communications at up to 150 Mbps or more for downloads (Rx) and 75 Mbps or more for uploads (Tx) when supplied with adequate transponder capacity and VSAT configurations. Therefore much higher speeds over wireless connections to subscribers are possible than with 4G terrestrial mobile networks today.

"RCS" is an acronym for "Return Channel via Satellite", reflecting the fact that early uses of satellite networks for two-way communications in the 1990's sometimes had to rely upon slow terrestrial circuits (i.e., dial-up modems) for return channels. At the time DVB-RCS was originally developed, VSATs (small ground terminals) with two-way capabilities were quite expensive and typically quite slow (<500 kbps).

In the last decade, DVB-RCS gained rapid prominence and support from government and industry with its capability for enabling low-cost and high-performance in VSATs with two-way capabilities. These needs became critical in many government and private commercial networks. and especially for public Internet Access into broad segments of the population around the world that continue to lack good terrestrial digital options. With DVB-RCS2 the ability to meet these dual needs has taken another major step forward.

The DVB-RCS family embraces and specifies the use of either DVB-S or DVB-S2 for their TDM carriers (or Forward link) in a TDM/TDMA network. DVB-S2 is the "gold-standard" for digital satellite communication links today. These DVB standards are widely adopted for high-performance digital TV broadcasts over satellite and commonly used for the DTH (i.e., Direct-to-Home) television services provided to hundreds of millions of homes around the world. But these TDM carriers can equally well support the delivery high-speed digital data, either for Internet downloads or other uses when combined with a TDMA "Return Channel".

As current industry-wide efforts on the evolution of DVB-S2 make progress towards a next generation standard for TDM supporting even higher carrier capacities (e.g., 500+ Mbps) and higher efficiencies with new "High-Throughput Satellites", SatLink Communications will be quick to embrace this leap forward in its continually advancing SatLink product line and DVB-RCS2 support.

These DVB standards are published and supported by ETSI (European Telecommunications Standards Institute) as well as the DVB Project. Therefore these DVB standards are recognized by many governmental and commercial organizations around the world, as open, international, well-documented technical standards that encourage industry-wide adoption and the long-term viability. This is key for the advancement of the next generations of large scale, high-throughput digital satellite networks serving both public and private communications around the world.

 

Summary of DVB-RCS: The First Generation TDM/TDMA Standard

Published by ETSI as EN 301 790, the first version of DVB-RCS was released in 2001. It has been revised and extended several times since the last major revision in 2009.

Over this time it matured considerably and added several important new features and options as more industry participants contributed to the effort. This standard is accompanied by ETSI TR 101 790 providing technical recommendations on implementation and network operation and ETSI TR 102 768 on the use of DVB-RCS in mobile VSAT networks.

DVB-RCS specifies in detail the burst wave forms (i.e., burst size, structure, modulation type & FEC methods) for networks using dynamic MF-TDMA with fast frequency hopping, as well as the TDMA synchronization methods and tolerances, the IP (Internet Protocol) encapsulation methods, and all required control & signaling messages (both syntax and semantics) for TDMA return channel operation.

For the TDM forward link carriers, DVB-RCS specifies the use of DVB-S or DVB-S2, plus details on how to transport the TDMA control information, known as Service Information (SI) tables. To allow a single TDM carrier to offer both MPEG digital TV programming and interactive data services, methods for transporting and identifying SI tables had to be compatible with existing DVB standards at the time for digital TV. The use of MPEG-TS (transport steams) as the underlying mechanism for the transport of all digital information is specified for DVB-RCS with the use of Multiple Protocol Encapsulation (MPE) for IP packets.

In addition, the SatLabs Group (www.SatLabs.org) was established in 2005 to provide certifications to terminal suppliers for their conformance to the standard, as distinguished by several different conformance profiles specified in the above documents. Interoperability testing has also been supported by SatLabs with good results among the suppliers submitting products conformant to standards.

Over the last decade DVB-RCS has grown to become a force in the industry as many government and commercial customers demand the proven, open specification, operational efficiencies, and investment protection assured by certified DVB-RCS products and technology support by multiple suppliers.

SatLink Communications' SatLink VSATs were the industry’s first to be certified by SatLabs and comprised the first DVB-RCS network installation approved by Eutelsat, and have since gained the major share of the DVB-RCS market.

SatLink Communications' SatLink Hubs have also been used extensively in interoperability tests, given their broad and flexible implementation of the DVB-RCS standards, and thus their capability to support a diverse number of terminal types.

 

The Creation of the Second Generation: DVB-RCS2

The DVB-RCS2 standard was finalized by the DVB Project in March of 2011 and is published by ETSI as EN 301 545-2. However, this important second generation of DVB-RCS began to take form many years prior to the standardization effort.

An advanced development project for "next generation" TDMA burst modem technology, involving other companies and university research labs, was offered by SatLink Communications to the European Space Agency (ESA). This major project was funded by ESA and pursued jointly by the consortium, which was lead by SatLink Communications' R&D organization in Norway. SatLink Communications was responsible for proof-of-concept and the final demonstration of high-quality, working technology to ESA and to the Norwegian Space Centre.

The primary goals of this project were to achieve major advancements in TDMA burst modem performance at multiple levels, including:

  • New high-efficiency modulation types and FEC methods (i.e., MODCODs)
  • The implementation of ACM (Adaptive Coding and Modulation) per burst
  • Improvements in link availability for low SNR (Signal-to-Noise Ratio) environments
  • Improved bandwidth efficiency generally, but especially the intermediate range of SNRs
  • Improvements in the encapsulation method for IP packets

It was understood that meeting these goals would require a broad set of changes to the DVB-RCS standard, including fundamental changes to the burst waveforms, additional burst sizes, and even how burst sizes were defined. Burst sizes had to be kept fixed with respect to the number of "symbols", instead of "information bytes" as in DVB-RCS. This was essential to be a platform supporting ACM on each TDMA burst.

The return channel working group of the DVB Project that had produced the original DVB-RCS standard took on the task of standardizing this "next generation" solution, which was to became DVB-RCS2. Eventually this working group involved most major commercial TDM/TDMA network suppliers in active roles. SatLink Communications also participated actively in a key role.

In the progress of standardization it became clear to the working group that the logical structure for managing the TDMA environment (i.e., the superframe) as used in first generation DVB-RCS would have to change. Plus some new signaling information and revised SI table structures would be needed to support ACM and other enhancements and it would also necessary to keep SI table overheads low as TDMA networks grew larger and faster with more timeslots to manage.

The superframe structure was simplified by structuring each frame of a single TDMA carrier as a simple series of uniformly sized BTUs ("Bandwidth-Time Units") measured in time duration and frequency bandwidth. This was done so that it could be managed easily, regardless of network size or complexity. Each frame was associated with a fixed symbol rate. These changes were needed for a high-performance implementation of ACM per burst, operating dynamically across all the TDMA carriers within a single TDMA carrier group.

It was also decided by the standards working group to dispense with the required use of MPE and MPEG-TS at Layer 2 on DVB-S2 TDM forward links in DVB-RCS, as well as its Layer 2 framing (e.g., IP packet encapsulation) options on return links: MPE/MPEG-TS and AAL5/ATM.

Instead, GSE (Generic Stream Encapsulation), an existing ETSI standard, was added for the TDM forward links. And for TDMA carriers, a new form of IP encapsulation, informally called "RLE" (Return Link Encapsulation), was developed and specified, abandoning the legacy formats. Both of these changes improve efficiency for interactive IP networking over satellite links in DVB-RCS2, relative to DVB-RCS and proprietary TDM/TDMA suppliers.

Although the efficiency of SatLink Communications' "compressed MPE" option over MPEG-TS has similar efficiency to GSE on the TDM forward link, GSE has some advantages for ACM operation and for multi-protocol transport in DVB-RCS2 networks.

For more information on the details of DVB-RCS2 see DVB-RCS2: Advancing TDM/TDMA Technology.

The first public demonstration of this powerful new TDMA burst modem technology occurred in Norway at SatLink Communications' R&D labs, in front of staff members from ESA and the Norwegian Space Centre on June 2011, just a few months after approval of the DVB-RCS2 standard by the DVB organization (press release).

Many features of the new standard were, by then, fully implemented and demonstrated, including ACM.

SatLink Communications again proved itself to be a driving force for innovation in the satellite communications industry.

 (DVB-RCS = “Digital Video Broadcast, Return Channel via Satellite”)

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