Study on feasibility of SATCOM for railway communication

Final Report
developed in the frame of the ANTARES (AeroNauTicAl REsources Satellite based) project, which
was part of the Iris programme. The satellite-based Communication Standard is able to cope with
future Air Traffic Control (ATC) and Airline Operational Control (AOC) communication needs, allowing
seamless operation with terrestrial standards.
Taking into account that the commonalities regarding safety features from both type of communication
systems (i.e. railway and ATM), it is considered relevant to analyse this communication standard in the
scope of this project in order to identify if it can be adopted in railways, although some modifications
could be required.
This satellite Communication Standard was focused on the design of the physical and link layers (also
called bearer) that provided the desired performances to cope efficiently with the ATM
communications requirements.
The specific characteristics of the aeronautical communications have been the design drivers for the
new Communication Standard (CS), namely:
stringent Quality-of-Service (QoS) requirements (continuity, integrity and latency)
L-band aeronautical mobile propagation channel (characterized by multipath effects),
limited L band spectrum resources,
bursty traffic generated by a large population of aircrafts (consisting of a short packets with
low mean data rate),
aircraft mobility (with speeds up to 2.5 MACH and maximum accelerations of 50 m/s),
support of any aircraft type flying under Instrument Flying Rules (IFR) (fixed and rotary-wing
aircraft). It is worth to notice that rotary wing is causing degradation (i.e. shortcuts or fast
fading) similar to the catenaries post along the rail track.
support of aircraft manoeuvres which can lead to fast degradations of the propagation
channel.
Besides, the new CS has been conceived to be compatible with multiple satellite orbital
configurations, in particular, Geostationary orbit (GEO), Highly Elliptical Orbits (HEO) and
Medium Earth Orbits (MEO) in order to ensure a global coverage including the Polar regions.
Most of these drivers are also applicable to railway domain and some of them are indeed more
stringent than required in the railway critical applications.
This communication standard specifies the Medium Access Control (MAC) and physical layer of both,
Forward and Return links.
In particular, the forward link is based on a Multi-Frequency Time Division Multiple Access (MF-
TDMA) access scheme, which allows an efficient support of distributed Ground Segment (GS) with a
high number of Ground Earth Stations (GES) sharing forward link carriers. The new Communication
Standard foresees several mechanisms to counteract the aeronautical propagation channel
impairments, such as channel interleaving, use of pilot symbols and adaptive Coding and Modulation
(ACM)
Concerning the return link, an Asynchronous-Code Division Multiple Access (A-CDMA) scheme
is proposed in which the traffic from active aircraft is transmitted by means of asynchronous packets
with low channel baud rates from 1.25 kbauds up to 2.5 kbauds depending on the selected waveform
configuration. The Physical Layer relies on the 3GPP W-CDMA technology (spreading based on
OVSF and complex scrambling codes) while RA is based on the Enhanced Spread Spectrum ALOHA
Doc.Nº: SRAIL-FNR-010-IND
Edit./Rev.: 1/1
Date: 16/02/2017
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