GSM: Tailor-made for Railways

Spanning over a total length of 63,000 km and with about 8520
passenger trains running every day, the Indian Railways is the second largest
railway in the world. Wireless technologies play a major role in running the
numerous operations here on a 24x7x365 basis just as is done in other railways
all across the world. The systems in use however, belongs to an earlier
generation of radio systems, and utilize analog technologies and varied
frequency ranges. This results in inefficient use of radio frequencies, high
operations and maintenance costs, and slow response times during crises.

Hence, European railway operators, equipment vendors, and
research organizations came up with the idea of developing a pan-European radio
system for satisfying the mobile communication needs of the European railways.
As a result, the global system for mobile communications for railways (GSM-R)
was developed. GSM-R, uses state-of-the-art technology to satisfy the mobile
communication needs of the European railways and provide it with an evolution
path for meeting the future requirements.

The GSM-R standard, which is being adopted by major railways
across the world, was first initiated by members of Union Internationale des
Chemins de Fer (UIC) in 1992, on a new specification called European Integrated
Railway Radio-enhanced Network (Eirene). The Eirene group is in-charge of the
development of GSM-R specifications in cooperation with European
Telecommunications Standards Institute (ETSI) and the Mobile Radio for Railways
Networks in Europe (Morane) consortium. The overall objective of the Morane
project was to specify, develop, test, and validate the prototypes of this new
radio system so that it met the global requirements of railways. This project
was successfully finished with the users approving the GSM-R prototypes by the
end of 2000.

Therefore, GSM-R is tailored for railway operators to achieve
the goals of interoperability with other railway networks, increase operational
efficiency, and reduce operational cost to enable the delivery of added
passenger safety and comfort. GSM-R utilizes standard GSM technology and a few
other additional features customized for railway operations. GSM-R also
integrates data transfer capabilities through general packet radio service (GPRS).
GPRS is used for data-transport-supporting applications, such as: remote
control, passenger services like ticketing and reservations and cargo-data
services like freight tracking and tracing. GSM-R users can be connected to the
network via base station subsystem of public operators, provided a roaming
agreement exists between the public and the railway operator. However, within
the roaming environment, only functionalities supported by the public operator
are available. Even though GSM-R is based on the GSM technology, significant
feature enhancements had to be made to suit railway-specific applications and
maintain high quality of service (QoS) for communications with high-speed
trains.

The network features and functions that GSM-R offers can be
categorized broadly into two categories: railway-specific functions and railway
applications. Railway-specific functions include advanced speech call items (ASCI)
services, which are standardized within ETSI as a part of GSM Phase 2+ and
services meant for railways operation aspects. ASCI services include the
following.

Enhanced Multi-level Precedence and Pre-emption (eMLPP):
By subscribing to eMLPP services, users can explicitly–or by default–select
a priority value while originating a call. This priority value is used within
the network to provide high-priority-value call precedence in cases of
congestion. This feature is useful in emergencies.

Voice Broadcast Service (VBS): VBS is for speech
teleservice calls only, providing a user the ability to broadcast a speech call
to a pre-defined set of terminating subscribers in a pre-defined geographical
broadcast area. A VBS call can be established either by a service subscriber or
by a dispatcher. Only the user who establishes the call can talk while others
have only listening capabilities. Further, a standard full-duplex channel is
provided to calling subscribers and dispatchers while simplex downlink channels
are allocated to all terminating service subscribers, with one common downlink
per cell of the VBS broadcast.

Voice Group Call Service (VGCS): VGCS is for voice
calls only and has been standardized on the basis of VBS. VGCS allows speech
conversations between a pre-defined set of destination subscribers in
pre-defined geographical areas. A VGCS call can be established by a service
subscriber or a dispatcher. It can be terminated by the calling subscriber, or
any nominated dispatcher, by using an operator determined dual tone multiple
frequency (DTMF) tone sequence or by detecting silence on the voice channel.

Within the railway-specific functions, GSM-R incorporates
services that support certain railway operations aspects.

Functional Addressing: This service allows a call
setup based on the function of the call terminator instead of the mobile station
integrated services digital network number (Msisdn) of the equipment that the
user may be currently using. Users have to subscribe to the functional
addressing service and register a functional number for the mobile equipment
that they may using, before at the commencement of their functional task.

Access Matrix Screening: Calls can be subject to
access matrix screening based on the functional number and functional number
types of the call originator and the call terminator(s). The access matrix
screening limits the connectivity between different users of a GSM-R system.

Location-dependent Addressing: This can route calls
for a given function to a destination address that is dependent upon the user’s
location. This location can be provided to the network in different ways. A
minimum requirement is that the location shall be based on the cell from which
the call is originated.

Confirmation of High Priority Call: This is used for
post-incident analysis. At the end of a high-priority call, the mobile generates
an acknowledgement message at the acknowledgement center connected to the mobile
switching center (MSC), for storage and further analysis.

The second category of functionalities, that can be provided
using GSM-R technology, is the railway applications. These applications are
defined to support and enhance railway operations for trains, drivers,
controllers, on-board and ground-based staff, as well as passenger services.

Controller-driver Communications: This function
provides communication between the controller(s) and driver to control and
enhance the safety of train movements. It supports voice communication flows
from one controller to one or a group of drivers, or from one driver to one or
more controllers. Controller-driver communication also supports point-to-point
data communication between drivers and controllers. Potential users would
include: primary train controllers, secondary train controllers, traffic
controllers, electricity power supply controllers, catering controllers,
maintenance controllers, and station controllers.

Automatic Train Control: This is the process by which
some of the movements of a train can be influenced without any action by the
driver. This feature also supports data communications for sending of position
information messages from the train to the train-control center and the sending
of movement-authority messages from the train-control center to the train as
well as information such as target speed and distance/ time to travel.

Remote Control: This supports bi-directional data
flows between fixed centers and the train–or other fixed locations–for
management of on-board or ground-based equipment. These include remote
management of equipment, such as: air-conditioning, brake-testing equipment,
shunting locomotives, cranes, and gantries.

Emergency Area Broadcast: This is required to alert
other railway staff, in a specific area, in case of an emergency situation.

Shunting Communications: These are the radio
communications between a shunting team and among different shunting teams.

Trackside Maintenance Communications: This is the
voice communication for voice-group calls between workers at a site and for wide
area communications.

Train-Support Communications: This is voice and data
communications for on-board staff and passengers including customer-support
services, such as: public addresses by voice, seat reservations, and timetable
information.

Local Communications: These are communications for a
wide range of personnel at a single site, such as: stations and depots. Only
voice communications are supported.

Wide Area Communications: These are meant for
trackside, non-train originated communication and railroad-maintenance
communications. They support voice and data communication for road vehicles,
track inspectors, railway police, and provide access to the public service
telephone network (PSTN).

Passenger Services Communications: These enable
railways to offer passenger services such as coin-operated telephone, telefax
communication, and Internet access for on-board passengers. They have a strong
potential for generating additional revenues.

While the benefits of the features offered by GSM-R
technology are quite apparent, the most important factor is that the railways
now have a single-ubiquitous network meeting all their communication
requirements instead of having disparate systems for disparate communication
needs. GSM-R provides railways with 100 percent network coverage, availability,
reliability, and high QoS; offering solutions for all the critical requirements
of a railway telecommunication network.

Rajan Mehta, VP, Nortel
Networks India