Metros
to use TETRA for CBTC, but I am not aware of any
metro line using TETRA as the primary CBTC channel
today,” says Davalo. “ere have been trials and I know of
at least one case where TETRA is used operationally as a
back-up solution, but TETRA has its limitations in terms
ofbandwidth.”
LTE on metros
Broadband LTE has the necessary bandwidth and is being
looked at for CBTC systems, as well as for supporting other
functions such as onboard CCTV, passenger internet and
information (and entertainment) systems.
Broadband technology is also required to support
driverless, fully automated metros known as GoA4 (Grade
of Automation 4) systems, which are becoming increasingly
popular, especially in China.
e International Association of Public Transport
(UITP) reports that in March 2018 the total line length of
operational fully automated metros reached the milestone of
1,000km with the opening of the Pujiang Line in Shanghai.
While this only represents seven per cent of the total length
of installed metro assets, 32 GoA4 lines are due to enter
revenue service in 16 Chinese cities by 2022.
GoA4 metros require even more specialist equipment,
including remote surveillance of tunnels, tracks and
platforms and automated platform barrier doors. e
trains need extra safety precautions including automated
emergency braking, smoke detectors, re extinguishers,
emergency lighting, audible signals and door monitoring. An
obstacle detection feature and carriage derailment detector
that will automatically brake the train are also required.
As there are no onboard crew, the control centre must
be able to address passengers and vice versa to provide
journey updates or guidance if there is an emergency. “In full
GoA4 mode the control room needs to be aware of things
happening on the train. You need CCTV in the cabs, so if
there is an incident you can see who has requested help or if
they are just messing around,” says Motorola’s Skinner.
All this takes a lot of bandwidth, but if LTE is to replace
Wi-Fi for CBTC and be deployed for GoA4 metros then
spectrum has to be found. China is forging ahead as it has
allocated some 1.8GHz spectrum for critical industries,
including transportation, for private LTE networks.
“But lack of availability of LTE spectrum in many parts
of the world is the big issue for private LTE networks,” says
Airbus’s Davalo. “In France, there are discussions around
using 2.6GHz spectrum for train and metro networks, but
no decision has been taken and applications are ongoing.
For an industry that needs a solution that can span many
countries, there is the question of whether it is economically
viable to develop it if only one country adopts 2.6GHz.”
He adds that the 700MHz band is being looked at as an
alternative, but so far all the licensed spectrum has gone to
mobile network operators with a few exceptions where some
guard bands have been allocated to public safety (with the
exception of the USA) as public protection disaster relief
(PPDR) spectrum.
ose countries are discussing how this PPDR band could
also be used for critical industries such as transportation. It
is complicated as the 700MHz band comes with a problem.
What happens when public safety
personnel come into a railway or
metro station and both are using the
700MHz spectrum? The rules need
to be dened
Strong global growth in metro lines
According to the International Association of Public
Transport (UITP): “At the end of 2017, there were metros
in 178 cities in 56 countries, carrying on average a
total of 168 million passengers per day; 75 new metros
have opened since the year 2000 (+70 per cent). This
massive growth is to be credited largely to developments
in a few countries in Asia.
“As of 31 December 2017, the 178 metro systems
together made up an installed asset base of 642 lines
for a total length of 13,903km and 11,084 stations.
1,901km of new infrastructure was put in revenue
service between the start of 2015 and the end of 2017.
This includes the new lines that opened in the 19 new
metro cities in China, India and Iran (577km), but also
new lines in already established metro cities (820km) as
well as line extensions (504km).”
This hectic growth shows no signs of slowing down.
UITP estimates that in the next ve years, more than
200 new lines and even more extensions are expected
to open in most regions, including in Sub-Saharan
Africa. In the summer of 2018, some 5,400km were
reported to be under construction or at testing stages,
with another 1,700km in design and tender stages.
Source: UITP Statistics Brief: World Metro Figures
(September 2018)
Both public safety and transportation are mission-critical
sectors, so which will have priority on the network?
“ere is not much spectrum that could be used. What
happens when public safety personnel come into a railway
or metro station and both are using the 700MHz spectrum?
e rules need to be dened,” says Davalo.
Fontecha feels that in the short term, the most likely
scenario is that TETRA will continue to be used with LTE
as an overlay for some features. “TETRA part manages the
voice communications and critical data, while LTE supports
CBTC signalling applications, video, passenger information
systems and the like.”
Skinner agrees. “I can see TETRA being continued
for voice services for quite some time yet. When 3GPP
MCPTT LTE has been around for long enough and the
metro industry is condent about it and sees a clear way of
migrating between the two, they will move to LTE for both
voice and data. Metro operators are not agile users. ey like
to know the technology they use is mature and safe.”
June 2019 @CritCommsToday 27