Study on feasibility of SATCOM for railway communication

Final Report
6.4 SATELLITE COMMUNICATION PROTOCOLS (STANDARDS AND PROPRIETARY)
This section describes different satellite communication standards in order to check their features and
if some of them have been thought or adapted for its use on railway applications, i.e. considering main
impairments due to the ‗railway channel‘, such as catenaries, power arches, tunnels, multipath, etc.
Although communication standards (CS) are mostly describing the OSI layers (defined by ISO) of a
communication protocol, within the scope of this project it is only considered L1 (physical layer) and L2
(Link (LLC/ MAC) layer), since both characterize the ―bearer‖.
CS is mainly detailing the transmission scheme. Regarding receivers, each manufacturer is
responsible for its implementation. However, sometimes there exist guidelines for the receiver
implementation in order to indicate the highest reachable performances.
It is worth mentioning that the use of a standard communication protocol is an interesting solution,
since standardization of the bearer enables interoperability, ease the availability of COTS and reduce
deployment costs.
Despite CS are conceived to provide particular services taking into account a dedicated satellite
constellation and frequency band, they are analysed hereafter as SATCOM technologies separately
from the final SATCOM orbit and frequency band, since there are some of them supporting several
bands and some of them supporting GEO and non-GEO orbits, as well.
6.4.1 DVB-S / S2 / S2X
DVB-S/S2 and their extensions are the most known satellite standards originally created for the
transmission of DVB signals via satellite.
The former DVB standard for satellite, DVB-S, was originally created to provide Direct-To-Home (DTH)
services for consumer Integrated Receiver Decoders (IRD), as well as cable TV head-end stations and
collective antenna systems.
But this first standard and SATCOM technology evolved a lot since the publication of former DVB-S
and a second generation of the DVB standard for satellites was created. Therefore, a second
generation of the first standard, or DVB-S2, is the standard designed to improve the former DVB-S
adding some new features, like LDPC codes, Variable and Adaptive Coding and Modulation (VCM and
ACM) and some enhanced modulations (up to 32 APSK). This standard is widely used, even in the
railway field (although with non-safety applications), within projects/services like Mowgly or 21Net.
DVB-S
(~1995)
SVB-S2
(~2005)
DVB-S2X
(~2014)
Figure 39: Evolution of DVB standards for satellite
More recently, a new extension to DVB-S2 (also kown as DVB-S2X) provides additional features and
technologies for several services, such as Direct to Home (DTH), contribution, VSAT (Very Small
Aperture Terminal) or DSNG (Digital Satellite News Gathering), but also to emerging markets such as
mobile applications.
Doc.Nº: SRAIL-FNR-010-IND
Edit./Rev.: 1/1
Date: 16/02/2017
Page 98 of 285