Study on feasibility of SATCOM for railway communication

Final Report
Ka-band (26-40 GHz)
Fixed and Mobile Satellite Services and Military/Governmental
Table 9: Main SATCOM frequencies overview
For each one of the bands in the above table there are specific allocations for different regions of the
world and different type of services. The specific allocations in each region may use the same or
slightly different frequencies in each region. There exist allocations for SATCOM at S-band (2-4 GHz),
but its use for commercial and government services is currently very limited. On the contrary, Ka-band
has been majority used during the last decade for commercial services and today are still planned new
deployments for offering services at this frequency band. This band designates parts where mobiles
and fixed services can use the band whereas in other bands the allocation is for type of service.
An issue that has arisen in recent years for the lower frequency bands at L- and C-band is pressure
from terrestrial mobile communication for part or all of those frequencies to be either transferred to
terrestrial mobile use or shared between terrestrial and satellite. In some parts of the world the lower
parts of C-band used for satellite communication have already been re-allocated to terrestrial use and
the possibility of further re-allocations are to be discussed in the World Administrative Radio
Conference. No re-allocations of L-band have been made yet but there is pressure from the terrestrial
mobile communication industry for this to happen. Some S-band satellite services are due to start in
Europe soon and satellite and terrestrial services will share the band.
SATCOM ACCESS PROTOCOL
Finally, it is worth mentioning that for most of the data communications that take place, there is a
requirement for several users to share a common channel resource at the same time. For multiple
users to be able to share a common resource in a managed and effective way requires some form of
access protocol (i.e. Network Access) that defines when or how the sharing has to take place and
the means by which messages from individual users are to be identified upon receipt. This sharing
process comes to be known as multiplexing (e.g. TDM, FDM, CDM, etc) and multiple access in digital
communications (e.g. TDMA, FDMA, CDMA, etc). Regarding multiple access techniques, these ones
can be split between orthogonal (i.e. network synchronization is required) or non-orthogonal (i.e.
asynchronous networks).
The most typical DAMA (Demand Assignment Multiple Access) techniques are based on TDMA,
FDMA, CDMA or also OFDMA whereas the most popular non-orthogonal access techniques are RA
(Random Access) techniques like Aloha, S-Aloha (SA), SSA (Spread-SA). Recently, enhanced RA
techniques (i.e. E-SSA and CRDSA) have been investigated in order to be used for data applications
in the field of the M2M applications, ATM communications, etc., instead of its traditional use as for
network signalling (e.g. LOG on/off, network synchronization, etc).
4.1.1 Satellite communication system high-level breakdown
The general satellite system breakdown is presented below.
Doc.Nº: SRAIL-FNR-010-IND
Edit./Rev.: 1/1
Date: 16/02/2017
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