Updating DVB’s satellite toolbox to serve non-geostationary constellations

Avi Freedman (SatixFy)

NGSO (Non-Geostationary Orbit) satellites are taking an increasing role providing ubiquitous, low-latency broadband services, with new constellations planned and launched. Most enterprises initiating those constellations opted to use proprietary, non-standard air interfaces for their systems. However, the key to market growth and global acceptance of any telecommunication system is standardization. It allows the development of innovative services as well as lowering the cost of access to the market by opening it to competition.

DVB standards have been the leading standards for satellite communications for many years. Starting from DVB-S (1995), which focused on broadcast television, going through DVB-S2 (2005), enabling generic data streaming, and closing the loop by adding a return channel and higher layers with DVB-RCS (Return Channel Satellite, 2001) and DVB-RCS2 (2012).

DVB-S2 extensions

With DVB-S2X (2013) the operation range of the air interface was enhanced. Higher order modulations were added for more efficient operation of applications that require high data rates and enjoy good signal-to-noise ratio. Furthermore, a set of modulation and coding schemes enabling the operation of small terminals at very low signal-to-noise ratios were added, enabling applications like Internet-of- Things to make use of the standard as well.

Other DVB specifications – DVB-GSE (Generic Stream Encapsulation) and DVB-SI (Service Information) – provide higher layer support and signalling to complete the picture.

Technically speaking, the DVB-S2/S2X air interface for the forward link is best suited for satellite communication:

  • The air interface is based on single carrier APSK modulation* enabling the satellite power amplifier to operate at its most efficient working point.
  • The forward error correction scheme provides spectral efficiency close to the theoretical limit. Furthermore, by adding a very small overhead it allows the satellite link to adapt to varying signal-to-noise conditions, including fading, for example due to rain.
  • The single carrier waveform is also resilient to Doppler shift, which gives it yet another advantage for NGSO satellites.

Beam hopping

In 2020, DVB published an amendment to the DVB-S2X standard to support beam hopping, and recently added related signalling support to the relevant specifications. Beam hopping is an important technology that enables a satellite to adjust its resources according to the actual demand it serves. While this technique provides better utilization of satellite assets for geosynchronous satellites, it is especially essential for NGSO satellites to adapt the transmitted signal to the coverage area of each satellite, and area that rapidly varies along its orbit.

The DVB-RCS2 specification for the return link enjoys similar advantages to those described above for DVB-S2/S2X on the forward link. Still, DVB is currently working on an amendment to better adapt DVB-RCS2 to the requirements of an NGSO system.

This amendment includes a new format for informing the RCS2 terminal of the satellite trajectory, extending the supported bit rate and packet size, and introducing the option of using DVB-S2/ S2X on the return link as well, for applications that are more symmetrical in terms of capacity required in both directions. This work item is expected to be concluded in June 2024.

To summarize, DVB continues to support its satellite communication standards, and adapts them according to the requirements of the market. Through those efforts it offers the industry the most effective standard solution for its evolving needs.

(Image: Copyright © Telesat)

* Amplitude and phase-shift keying, APSK, is a digital modulation scheme that conveys data by modulating both the amplitude and the phase of a carrier wave.

Avi Freedman is a director of system engineering at SatixFy, involved in R&D for modems and smart antennas for satellite communications. He has been active in DVB standards development efforts over a decade.

Vittoria Mignone (Rai), David Peilow (ESA) and Fernando Díaz Canales (Telesat) also contributed to this article, which first appeared in issue 63 of DVB Scene magazine.