Global flow of information to on-board computers for calculating

Global System for Mobile Communications –
Railway (GSM-R) is
a wireless communications standard used globally for railway communication and
applications. It uses a specific frequency band around 800/900 MHz (primarily
based on 2G technology). It has replaced analog systems which were widely being
used previously. It is based on European Integrated Railway Radio Enhanced
Network (EIRENE) – Mobile Radio for Railways Networks in Europe (MORANE) specifications

GSM-R offers the highest level of
interoperability in accordance with EIRENE. It also supports seamless
integration of regional applications and services such as the European Train
Control System (ETCS) signalling system standard (Requiring fewer fixed
installations, ETCS is more cost-effective than conventional trackside signalling).
As the chosen data technology for ETCS, it is an integral component of the (European
Rail Traffic Management System) ERTMS. It provides substantial benefits by
providing continuous flow of information to on-board computers for calculating
speeds and braking profiles  

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GSM-R enables higher train speeds (assures
performance at speeds up to 310 mph (500 km/h) without any communication loss) and
traffic density with a high level of safety by carrying the signalling information
directly to the train driver. It enhances voice and data communication with
trains and allows drivers to communicate freely throughout transcontinental
journeys (even through tunnels) enabling significant improvement of reliability,
security and safety of rail services. It is also used for various other kinds
of applications like cargo tracking, passenger information systems, video surveillance
etc.

GSM-R status

GSM-R standard was envisioned with the goal of
achieving interoperability using a single communication platform. It is a
result of over a decade of collaboration between various European railway
companies. It is a part of the European Rail Traffic Management
System (ERTMS) standard. The specifications were finalised in the year 2000,
basis the European Union funded MORANE (Mobile Radio for Railways Networks
in Europe) project

GSM-R Technology

The radio sub system of the GSM-R network is
typically implemented using base transceiver stations and communication towers
with antennas which are placed close to the rail track with intervals of 7-15
km. The same is 3-5 km in China (with redundancy) to ensure higher availability
and reliability. GSM-R has to satisfy tight availability and performance
requirements of the HSR radio services

Through GSM-R, trains have a constant circuit
switched digital modem connection to their respective train control centre. The
trains will automatically stop if the modem connection is lost. The enhanced
Multi-Level Precedence and Pre-emption service (eMLPP) provides different
levels of precedence for call set-up and for continuity in case of handover,
thereby giving trains a greater priority compared to normal users

GSM-R Frequency Spectrum

GSM-R typically uses a lower extension of the
900MHz frequency: 876 MHz — 915 MHz for data transmission (uplink) and 921 MHz
— 960 for data reception (downlink). However, frequency
bands used differ from country to country. In Europe, the 876 MHz to 880 MHz and the 921 MHz to 925 MHz bands are
used for uplink and downlink respectively. In China, GSM-R occupies a 4 MHz
wide range of the E-GSM band (900 MHz-GSM)

GSM-R is a Time Division Multiple Access (TDMA) system which
means that the data transmissions consists of periodical frames with periods of
4.615 ms for each physical channel. The modulation used is GMSK and channel spacing is 200 kHz

 

 

Limitations of GSM-R

Capacity: The 4-MHz bandwidth of
GSM-R can support 19 channels of 200-KHz width. This is sufficient for voice
communication, as voice calls are limited in time and do not occupy resources
continuously. In the next-generation railway system, where each train needs to
establish a continuous data connection with a radio block centre (RBC), and
each RBC connection needs to constantly occupy one time slot. Hence, for the
next-generation railway system, the current capacity turns out to be insufficient.
However, the radio capacity can be increased by using more spectrum resources.

Interference: The interference
between GSM-R and other public networks increases because both railway and
public operators would like to have good coverage along the rail tracks. This
results in an inevitable fight for coverage between them. Ideally, such
interference can be avoided if public operators do not use frequency bands
adjacent to those of GSM-R for the areas close to rail tracks. However, this is
not well implemented in practice

Capability: As a narrow-band
system, GSM-R cannot provide advanced services and adapt to new requirements.
The maximum transmission rate of GSM-R per connection is 9.6 kb/s, which is
sufficient only for applications with low demands. Delay is in the range of 400
ms, which is too high to support any real-time application and emergency
communication

 

1            
GSM-R
for ETCS (applications and flexibility)

ETCS is a signalling system used for railway
control and GSM-R network acts as its data carrier.  It uses GSM-R radio network to send and
receive information from trains

It has three levels of operation. GSM-R is used
only for voice communications on the first level (ETCS-1). It is mainly used for
data transmissions on the other two levels (ETCS-2 and ETCS-3). It is very
relevant to ETCS-2 and ETCS-3, where the train travels at a speed up to 350
km/h. Hence, it is necessary to guarantee a continuous supervision of train speed
and position. The train has to automatically reduce the speed to 300 km/h
(ETCS-1) or lower, when the call is lost

2            
LTE
and Status of LTE-R standardization

LTE offers many advantages in terms of capacity
and capabilities that GSM-R doesn’t. It is better suited for data
communications, since it is a fully packet-switched-based network. Lower packet
delay is one of the crucial requirements for providing ETCS messages. LTE
offers a more efficient network architecture and hence has a reduced packet
delay

LTE consists of a number of improvements that
increase spectral efficiency, such as advanced modulation and multiplexing.
Therefore, it has a high throughput radio access. It is also a well-established
and off-the-shelf system and provides standardized interworking mechanisms with
GSM-R. It also offers improved security protection over GSM-R

Features of
LTE-R

LTE-R inherits all the important features of
LTE. It also offers an extra radio access system to match HSR-specific needs
and exchange wireless signals with On-Board Units (OBUs). However, LTE-R has
many differences in comparison to public LTE networks such as architecture, system
parameters, network layout, services, and QoS. Since the network must be able
to operate at 500 km/h in complex railway environments, LTE-R will be
configured for reliability more than capacity. Hence, quadrature phase-shift
keying (QPSK) modulation is preferred

LTE-R Challenges

Currently, there is no large scale operation of LTE-R anywhere in
the world. There are many
scientific issues which are yet to be solved at LTE-R band e.g. propagation
loss, geometry distribution of multipath components (MPCs), and
two-dimensional/three-dimensional angular estimation in those HSR-specific
environments. It is therefore necessary to look for extensive channel
measurements and develop a series of channel models for the link budget and network
design of LTE-R