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DVB-S2 and DVB-S2X – What Are They?

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August 24, 2018 / Patrick Gannon

A client recently requested a quote for a 10 Mbps x 10 Mbps service. It sounds simple enough, but as has been discussed in another article about modcods (modulation and coding), there are several factors involved in quoting a broadband satellite circuit.  The satellite band, beam, signal strength, the climate, the size of the antenna and power of the BUC enter into the equation, and now BusinessCom Networks is generating quotes with two options:  DVB-S2/ACM and DVB-S2X/ACM. What is this all about?

History

DVB-S or Digital Video Broadcasting Satellite was developed and first launched in 1994 in Thailand and South Africa. This format became popular for delivering digital TV broadcasts and is used to deliver services to every continent in the world. DVB-S supports MCPC (Multiple Channel Per Carrier) and SCPC (Single Channel Per Carrier), which are used to deliver broadband and private data circuits. The system also supports direct-broadcast satellite television from providers such as Sky, Astra, Dish Network, Globecast and Bell TV.  With advances in technology, and the need for higher speeds and throughputs, the DVB-S standard needed to be advanced.

DVB-S2

While the driving factor behind DVB-S2 was support for HDTV services, the new standard had advantages for broadband as well.  Some of the improvements include:

- Low Density Parity Check (LDPC) Forward Error Correction.  This is a method for sending a message over a noisy transmission channel.

- Variable Code Modulation (VCM) provides variable levels of error protection to different components within the service. This is performed by permitting various combinations of modulation and FEC (Forward Error Correction) to be applied to different parts of a data stream.

- Adaptive Coding and Modulation (ACM) provides an extension to VCM.  It provides a feedback path so that various levels of error protection can be applied in near real time as signal propagation changes.  In practical terms, this takes available link margin that is normally used to overcome deteriorating weather conditions and converts it to performance gains for data.  ACM provided a real benefit to broadband satellite services.  Rain fade, antenna pointing errors, local noise and interference, can all interfere and cause satellite performance to degrade.  To overcome slowdowns or outages from these conditions, operators apply or reserve “link margin” or some amount of capacity that is essentially “set aside” and used as needed when conditions degrade.  This works but is highly inefficient.  Rather than sitting idle, ACM allows this link margin to be used to transmit data, when conditions are optimal, thus addressing both efficiency and availability.

- DVB-S2 standard added 8-PSK, 16-APSK and 32-APSK. What these modulation options do is provide better spectral efficiency – or bits per symbol.  This allows more data to be sent in the same bandwidth.

- Support added for MPEG-2 TS based systems and MPEG-4 audio/video streams. MPEG is a standard for compressing moving pictures.  MPEG 2 TS is designed for streaming live events.  MPEG 2 supports data rates from 1.2 Mbps to 15 Mbps.  MPEG-4 provides improved coding efficiency.  It can encode mixed media such as video, audio and speech.  Robust transmission is provided with advanced error resilience features.

DVB-S2 provided a 30% improvement in spectral efficiency over the original DVB-S. The standard was published as an ETSI (European Telecommunications Standards Institute) in 2005. Vendors such as iDirect who had developed a proprietary TDM solution that outperformed DVB-S, switched to DVB-S2 when it came out, because it offered even greater efficiency.

DVB-S2X

DVB-S2X is not a new DVB-S model but is an extension.  Specified in the mid 2000’s, it adds additional technology and features including DTH (Direct to Home), VSAT and DSNG (Digital Satellite News Gathering).  DVB-S2X is focused on emerging markets such as 5G.  New features include:

- Greater granularity of modulation and coding modes, supporting more “fine-tuning” of networks

- Smaller filter roll-off options of 5%, 10%, 20%, and 35%.  The ROF or roll-off factor determines how much capacity can be squeezed into a particular band of spectrum.  The satellite’s signal is filtered or masked and the “edges” of the signal drop off and are not used for transmission; i.e. wasted.  The lower the ROF, the more of the signal that can be used to transmit data.

- Channel Bonding up to 3 channels.  This provides a mechanism to deliver very large circuits with high aggregate data rates.

- More scrambling options for critical co-channel interference situations

- Very low SNR operation supporting C/N of down to -10dB

- Super Frame option is a development intended to help address beam hopping, as in a maritime vessel or airplane passing from satellite beam to satellite beam.  It also supports switching in multi-spot-beam satellites, such as most of the HTS (High Throughput Satellites) being launched today.

Why it Matters

The DVB-S2X standard was published in 2015 and has been swiftly implemented by satellite vendors.  The new features enable efficiencies at higher capacities, and more granularity or control over how they are implemented.  The new features pave the way to intelligent terminals that are defined by SDN (Software-Defined Architecture), allowing new capabilities to be added as they arise – for example support for LEO and MEO (Low and Medium Earth Orbit) satellites, as well as supporting increasing data rates.  DVB-S2X enables satellite networks to scale more cost effectively, managing many Mbps of capacity across multiple spot beams, creating virtual bandwidth pools.  The tools are in place to support integration with other terrestrial and 5G mobile services, tying existing OSS and BSS (Operational Support Systems/Business Support Systems) into the satellite platform. Finally, as mentioned above, the new features enable air, maritime and even “connected car” services, to maintain internet connections, as users pass from beam to beam.

DVB-S2X is a relatively new standard, and we have yet to see all the features that it will unleash and support.  For now, what we have is an option to quote dedicated circuits at better prices. At BusinessCom Networks, we frequently quote dedicated circuits using both DVB-S2 and DVB-S2X options. The ODU (outdoor unit) is generally the same, but the DVB-S2X modems can cost significantly more.  However, the cost savings will generally justify the more expensive hardware in a relatively short time.  Clients who expect the circuit to remain in place for a long time will almost always benefit from taking the DVB-S2X option.

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