Study on feasibility of SATCOM for railway communication

Final Report
DVB-RCS+M was an enhanced version (actually an extension) of the former DVB-RCS to include
options for mobile channels, being able this way to take into account aspects such as periodic fadings
on railway channel due to power arches (or posts with horizontal brackets) and catenaries, for
example. For that reason spreading was includes into this extension, and also a continuous carrier
(CC) mode based on DVB-S2 waveform.
After last version of DVB-RCS (extension +M), a second generation of this standard was created, the
DVB-RCS2, published in 2011. It included many improvements such as the ACM (Adaptive Coding
and Modulation) within the return channel, complementing this way the ACM of the forward link (by
means of the DVB-S2). This way, with this new improvement the use of this standard within higher
frequency bands (such as Ka) was enabled (making possible the use of ACM in forward and return).
This RCS2 added 16 new state turbo codes in addition to additional modulation schemes, providing
this way better performance for mobile channels such as railway.
This second generation of the RCS standard also provides a Random Access (RA) return link access
method. Therefore, it is not required to request capacity in advance (a good access method when data
to be transmitted is intermittent and typically represents a small capacity).
Finally, a new mobile extension to RCS2 (i.e. DVB-RCS2+M) is ready to serve professional,
commercial and governmental markets since 2012. It adds support for mobile/nomadic terminals and
direct terminal-to-terminal (mesh) connectivity. DVB-RCS2+M features include live handovers
between satellite spot-beams, spread-spectrum features to meet regulatory constraints for mobile
terminals, and continuous-carrier transmission for terminals with high traffic aggregation. It also
includes link-layer forward error correction, used as a countermeasure against shadowing and
blocking of the satellite link.
6.4.3 DVB-SH
In addition to DVB-S/S2/S2X and DVB-RCS/2 standards family, there exist some other standards with
different purposes, such as the DVB-SH (Digital Video Broadcasting – Satellite services to
Handhelds), derived from previous DVB-H and ETSI SDR. It was created around 2007 with the aim of
delivering IP base media content (video/audio) and data to handhelds terminals and vehicles based on
hybrid satellite/terrestrial forward link. Due to the use of small terminals (handhelds), a low frequency
band were thought to be used with this standard, just like the S-band.
Since DVB-SH are based on hybrid satellite/terrestrial systems, it allows the use of satellite to achieve
coverage of large areas. And in areas where there is no satellite coverage, a terrestrial gap filler can
be used seamlessly to provide coverage.
DVB-SH defines two different schemes:
- SH-A: based of OFDM (Orthogonal Frequency Division Multiplexing) for both satellite
and terrestrial links
- SH-B: based on TDM (Time Division Multiplexing) only on the satellite link (and OFDM
for the terrestrial link)
OFDM is a powerful modulation method that divides a high data rate modulating stream into many
slowly modulated narrowband close-spaced subcarriers, making this way the signal less sensitive to
frequency selective fading. OFDM has become a mature technique implemented in several systems
such as WiMax, DVB-T or LTE.
Doc.Nº: SRAIL-FNR-010-IND
Edit./Rev.: 1/1
Date: 16/02/2017
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