Study on feasibility of SATCOM for railway communication

Final Report
Criterion ID
CRT-TECH-1
CRT-TECH-2
Related
parameter
Link
availability
Reliability
Conclusion
Link availability is one of the most demanding requirements derived from
critical railway applications. Although it is very complicated to find a good
compromise between achieving high availability and enabling SOTM terminals
and/or handhelds, it is important to remark that it takes advantage of the very low
data rates of the applications.
Lower constellations (i.e. LEO, MEO) and Lower frequency bands (i.e. L, S C)
offers more favourable conditions than GEO constellation and higher frequency
band (i.e. Ku , Ka - band) where worse weather conditions have to be supported
The end-to-end QoS requirements of a communication call/session shall be
guaranteed according to user‘s SLA. It is reached for all of the solutions
proposed since backup and/or redundancy (i.e. duplication) for these critical
elements can be assumed in the most of the cases in order to reach the MTBF and
MTTR figures.
CRT-TECH-3
Error ratio
It is reached for all of the solutions proposed since several mechanisms are
nowadays provided for commercial communication standards (e.g. DVB-
S2/X/RCS2, etc.) to guarantee a high level of service continuity. Most of these
techniques are implemented at L1 and L2 layers (e.g. FEC, LL-FEC, ARQ, etc)
CRT-TECH-4
Transfer
delay
Latency requirement is other one of the most demanding requirements for
safety applications. It is observed that GEO systems are a priori discarded since
the double-hop required for terminal-to-terminal communications (in star
topologies) and larger distance to the earth supposes more than 0.5s. SATCOM
transmission delay can be similar to the one provided by terrestrial systems
only using non-GEO orbits (i.e. LEO or MEO). GEO satellites transmission delay
could be accepted or not according to final applications requirements.
CRT-TECH-5
Delay jitter
There exist mechanisms at IP level able to compensate the delay time variations
between packets. Such closed solutions (i.e. iridium, Inmarsat, Thuraya), which
offer voice services with Circuit Switched, are not providing relevant
differences in the quality of the voice services.
CRT-TECH-6
Network
registr. delay
It depends on the network synchronisation mechanism implemented by each
particular solution. The systems requiring localization information are not
meeting the requirements since cold acquisition time for GNSS systems are long
(e.g. Inmarsat…). ANTARES CS was designed in order to not require external
systems for assuring the operational requirements.
CRT-TECH-7
Call establ.
delay
The proposed closed systems (i.e. Iridium, Inmarsat, Thuraya), which are
using Circuit Switched for providing voice calls, are non-compliant. Use of
pure RA (e.g. ANTARES, S-MIM, Smart LNB) is taking advantage of
asynchronous access in order to minimise time delay for accessing to the
network. Other proposed solutions based on IP and DAMA access schemes can
meet the requirement with an appropriate sizing of the network resources.
Doc.Nº: SRAIL-FNR-010-IND
Edit./Rev.: 1/1
Date: 16/02/2017
Page 129 of 285