Metros
– recordingsystems. Metros are equipped with Automatic
Train Stop (ATS) systems in case they pass a red light, exceed
speed limits, or an obstruction is detected on the track
ahead. “ATS is very important for both safety and security,
as there must be a way to automatically stop the train,”
says Davalo. “When this happens, the TETRA
system can be used to share this information among the
relevant professionals.”
Davalo also points out that in metros, instead of using
telephone numbers they often allocate functional numbers
relating to the train number or the metro line number
based on the TETRA Dynamic Group Number Assignment
(DGNA) feature.
“A DGNA is allocated to each train departure and released
as soon as the train arrives at its destination. at way, the
control centre can call the train or line number and get hold
of the right driver, rather than trying to nd a particular
driver via his individual handheld radio subscriber number.
It’s a role-based numbering system,” explains Davalo.
He adds that the DGNA application also automatically
changes the talk group every time a train enters a new
station, so the driver can talk to the station sta. “at kind
of thing is designed into TETRA,” he notes.
Data systems
Skinner reveals that some metro customers just use TETRA
for voice with no integration with other systems. “But
other metro customers are using TETRA in a much more
integrated way with other systems. TETRA provides short
data services (SDS), packet data and TEDS (TETRA
Enhanced Data Services), so there is a data pipe available
with TETRA, albeit it is still a fairly narrowband one,” he
points out.
Nonetheless, TETRA can support a wide range of data
applications within metros. TETRA equipment is integrated
with the onboard control and signalling systems, which
enables the system to report back on what is going on in
the metro. Fontecha cites three levels of data applications.
“ere’s critical data like rolling stock monitoring,
emergency/re detection alarms and event management,
vehicle diagnostics, location information from trackside and
GPS location systems, door opening, air-conditioning and
braking systems.
“en there is vital data such as the communication
system to support data rail signalling applications, and
then there is non-critical data for online video
surveillance and other applications to support the
metro operation and improve the passenger experience,”
says Fontecha.
“If there has been an incident on a metro line and you
need to quickly change the passenger information systems,
you can send a message via the TETRA system,” says
Skinner. “You can also change the passenger announcement
structure remotely from the control room, thereby allowing
the driver to concentrate on driving the train. If a station
ahead is closed, you can automate the PA announcements
to tell passengers to alight at the station before or after,
forexample.
“By sending timely relevant information around the
train you provide a better service as an operator. Likewise
telemetry data can provide early fault notication, which
TETRA was attractive to metro
operators looking to move to digital.
TETRA is an open European standard,
there are lots of suppliers and the
equipment is all interoperable
allows you to respond faster, keep the service and trains
running with less downtime, and that improves revenue.”
Fault detection and remote diagnostics telemetry data
can be sent over the TETRA IP backbone, allowing remote
monitoring of the location and condition of all carriages
in real time. Some operators are using this kind of data for
preventative maintenance.
e operator builds up a historical database of types of
faults and the frequency of failure rates of particular assets to
try to identify the main factors causing the fault. Algorithms
analyse the data and identify anomalous patterns of events,
which may indicate something is about to fail. e potential
problem can then be xed before the component fails.
Building the network
A typical TETRA network in a metro line will comprise
an operations control centre with CAD systems, base
stations in each metro station, mobile radios in each train,
handheld radios for station and maintenance sta and
drivers/conductors and connections to the passenger PA and
information systems.
Teltronic’s Fontecha says: “e main objective must be
‘no single point of failure’. Our experience in metro projects
June 2019 @CritCommsToday 25