Rail
challenges caused by technological changes (single
core systems, virtualisation and cloud computing, etc).
However, he is convinced “that the biggest challenge will
be spectrum and how to handle the onboard equipment
architecture in terms of migration and coexistence of
FRMCS bearers and GSM-R bearers”.
Let’s look at the issue of spectrum in more detail.
Currently, European railways use the 4MHz wide
876-880MHz/921-925MHz band for GSM-R, and
it has been harmonised for this use by CEPT (the
European Conference of Postal and Telecommunications
Administrations), through its Electronic Communications
Committee (ECC), and the EU. In addition, the 873-
876MHz (uplink)/918-921MHz (downlink) band is not
harmonised for GSM-R within CEPT, but it is used for
this purpose by some CEPT countries.
As the transition from GSM-R to FRMCS will be a
gradual one, an operator can’t simply refarm their existing
4MHz from GSM-R to FRMCS, and therefore additional
spectrum is required during the transition. There are three
candidate bands: 1.4MHz of spectrum for FDD (1.6MHz
including 200kHz guard bands – 874.4-876MHz/919.4-
921MHz) that sits directly below the harmonised
spectrum for GSM-R; a 10MHz spectrum block for TDD
in 1900-1920MHz; and a 10MHz spectrum block in the
2.3GHz band.
ECC Report 294 – Assessment of the spectrum needs for
future railway communications states that the capacity
provided by the 900MHz candidate band won’t be
sufficient in “dense railway networks, border areas and
high-density areas” during the transition, and therefore
the spectrum in 1900MHz “is a prerequisite for many
countries to manage the migration with dual networks
operating in parallel”. However, it notes that this band is
currently licensed to mobile network operators (MNOs)
in many CEPT countries and that the additional spectrum
used during the transition “will still be required to cover
railway’s long-term needs (including critical sensing/video),
border and hotspot areas”.
Rothbaum says one of the challenges with the use of the
1.4MHz ‘squeeze option’ is that currently it is not being
used by MNOs or other industries for LTE. This raises
the question as to “how many chipset vendors are going
to step up to the plate and deliver a chipset that supports
it?” given that the volumes required are far less than those
in the public safety industry – he notes the struggle to get
ProSe (proximity services – mobile broadband’s lowerrange
equivalent of TETRA’s direct mode operation) – into
silicon for use by public safety organisations.
“There could be niche chip vendors out there, but once
you do that you’re going to have a very narrow ecosystem
with handsets and modem cards onboard the locomotives
to cover that, so for that reason, it will be a little bit
challenging. Now once they go to 5MHz spectrum in
900MHz, the 920-925MHz band they’re going to get a
better response,” Rothbaum says.
As a brief aside (as I’ve mentioned ProSe) it’s worth
noting that FRMCS has an off-network requirement
referred in 3GPP terminology as a sidelink (GSM-R already
has this capability). Ingo Wendler, vice chair of ETSI RT,
says “off network is a challenging part” and it has been
decided that on-network communications have the first
priority, so that the first deployments can begin, with the
sidelink to come later (to possibly act as a fallback should
on-network communications be disrupted).
Returning to 900MHz, Rothbaum says another challenge
with using the 1.4MHz ‘squeeze’ option is its close
proximity on the downlink (919.4MHz at its lowest point)
to 3GPP Band 8’s uplink (880-915MHz). He says such a
small distance between an uplink and a downlink is “almost
unheard of in the whole radio spectrum” given that receivers’
filters don’t “drop on a dime”, so they would still be exposed
to blocking from transmitters operating in the adjacent
band, hence the need to determine the maximum power
that could be used without creating coexistence issues.
Rothbaum adds that this is less of an issue with the
candidate spectrum in the 1900MHz band because its
nearest neighbour is 3GPP Band 1 – 1920-1980MHz
(uplink); and there is 10MHz of spectrum available.
Despite the issues with 900MHz that Rothbaum has
highlighted, Tane says there has been recent progress in
CEPT. “It has progressed from a situation where the viability
of the 900MHz spectrum for railways use was questionable
from a commercial and technical standpoint to a situation
where operating conditions suitable for railways may be
reached (including when using the lower 1.6MHz portion of
their foreseen harmonised spectrum at 900MHz). We remain
cautiously optimistic, knowing that the associated regulatory
framework is not yet cast in stone.” He adds that the use of
this band for the transition to FRMCS is “quite key”, given
the large number of sites that European railways already
The Finnish
Transport
Infrastructure
Agency (FTIA) is
now using TETRA
via Frequentis’s
URCA system,
instead of GSM-R
One of the challenges with the use
of the 1.4MHz ‘squeeze option’ is
that currently it is not being used by
MNOs or other industries for LTE
18 www.criticalcomms.com October 2019
/www.criticalcomms.com