Implementation of High Speed Railway Mobile Communication System

International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169
Volume: 5 Issue: 8 41 – 44
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IJRITCC | August 2017, Available @ http://www.ijritcc.org
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Implementation of High Speed Railway Mobile Communication System
Prof. K.S. Solanki
Ujjain Engineering College, Ujjain (M.P.)
E-mail- khemsingh_solanki@rediffmail.com
Kratika Chouhan
Ujjain Engineering College, Ujjain (M.P.)
E-mail- chouhan.kratika@yahoo.com
Abstract—High speed railways (HSR) provide highly efficient transport mode which improves the quality of railway services, saves time of the
passengers which leads to greater customer satisfaction as well as improves the economics of the society. This has introduced significant
challenges like developing new technologies, improving the existing architecture and controlling costs etc. Due to the improvements in the
speed, ability to access internet and stream live media there is a requirement of an advanced high speed communication and signaling system.
This system demands higher bandwidth, higher reliability and shorter response time for efficient operation and safety. This paper introduces the
existing system deployed by the railway based on Global System for Mobile communication (GSM) , analyzes it and presents a much more
advanced communication and signaling system based on 4G Long Term Evolution (LTE) technology.
Index Terms—High speed railway, LTE, GSM, communication and signaling system,System Architecture Evolution (SAE). (key words)
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I. INTRODUCTION
With the ever increasing need of high speed transport
system,the railways has been developing new ways to increase
speed ,reliability,safety and security. Along with these demands
there is an immediate requirement to improve the railway
communication and signaling system as well as passenger
communication for providing high speed internet,high call
quality and streaming of live media. One of the widely used
train communication system is communication based train
control system (CBTC) which provides two way continuous
communication,safety control,speed control etc[3].
This control and communication method is old fashioned
and requires large number of human operators. Europe
introduced European train control system (ECTS) which
involves the usage of GSM for internal voice and data
communication and CBTC for control command system. Then
a railway communication system based on GSM known as
GSM-R was introduced which had the same basic network
architecture of GSM. However,when traveling speed increases
beyond 500 km per hour this system became incompetent to
cope up with information loss, handover and shift in Doppler
frequency and became unreliable to continue operations[3].
This GSM-R technology has been used for decades since it
proved efficient for speed in the range of 200 to 300 km/h.
Due to the introduction of high speed data networks and
high travel speed there is a need of a robust high speed system
that can maintain operations in high travel speed as well as high
speed data network. Thanks to the development of high speed
wireless communication techniques,3GPP long term evolution
(LTE) is a good option to deal with the discrepancies of the age
old GSM-R system[3]. With the rapid development of HSRs
LTE-R proves to be a reliable broadband communication
system for different HSR components.
International union of railways has been researching on the
future of HSR communication system to identify a suitable
replacement once the GSM-R becomes obsolete. HSR
applications have quality of service (QOS) measures such as
data rate ,delay in transmission and bit error rate (BER)[2]. Due
to this measures HSR communications generally use low cost
and off-the-shelf technologies and add applications over them
to fulfill specific demands and operations. GSM-R is a
successful example, based on the GSM standard which has
been used over 70000 km of railway lines[2]. The GSM-R
systems are being replaced as the public communication market
is evolving towards the third generation partnership project
(3GPP) also known as LTE. So a new system based on LTE
has to coexist with GSM-R for a long period of time. The
selection of a suitable wireless communication system for
HSRs needs to consider such issues as performance, service
attributes, frequency band, and industrial support. Compared
with third-generation (3G) systems, 4G LTE has a simple flat
architecture, high data rate, and low latency, making it an
acknowledged acceptable bearer for real-time HSR
applications. Fifth-generation (5G) systems, although currently
discussed in 3GPP, will be available only after 2020 and,
therefore, are not suitable for the HSR time frame. In view of
the performance and level of maturity of LTE, LET-railway
(LTE-R) will likely be the next generation of HSR
communication systems and the future vision for HSR wireless
technologies will thus rely on it[2].
LTE-R architecture is based on LTE wireless
communication standard and developed from existing
GSM/WCDMA core network so, it is backward compatible to

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older GSM-R based technology. LTE-R architecture reduces
operation expenses as well as capital expenditure and features
on smooth and simple operation with cost effectiveness
deployment therefore LTE technology can be used in a high
speed railway communication system as per our demand.
II. GSM-R
GSM-R is similar to the basic network architecture of
GSM. MS (mobile station) indicates moving vehicle and radio
terminals loaded on the vehicle. Several BTSs (base transceiver
stations) deploy along the railway tracks, a SSC (base station
controller) controls STSs. The core component of GSM-R
system is the network switch subsystem[3]. It includes data
gateways, SGSN (service GPRS supporting node) and GGSN
(gateway GPRS supporting node), and MSCs (mobile switch
centers). Information of users is stored in HLRs (home location
registers) and VLRs (visitor locatin registers) assosiated with
each MSC in the network. GCR (group call register) stores
information about group calls, their configurations and users
involved. OMC (operational and maintenance center) manages
the entire GSM-R network and billing center collects and
records information about GSM-R network used for business
and operational purpose[3].
Figure 1. network architecture of GSM-R
The various services offered by GSM-R are voice group
call service (VGCS), voice broadcast service (VBS), enhanced
multilevel precedence and preemption (EMLPP), functional
addressing and location dependent addressing. Although GSM-
R is immensely popular and still growing the increase in
interference from other networks limits the use of GSM-R
while due to the nonavailability of high bandwidth limits its
capacity[2]. Some more limitations of GSM-R are as follows:
1. Interference: interference between GSM-R and other
public network causes hindrance in voice and data
communication and also loss of network coverage
between several meters of railway tracks. Interference
may increase in future due to the growth of GSM-R
network as well as other public networks.
2. Capacity: GSM-R supports 19 channels in its 4MHz
bandwidth with each channel of 200KHz. width this
bandwidth is sufficient for voice calls however it may
be insufficient for advanced railway systems where
each coach needs to established a continuous data
connection with the base station known as radio block
center (RBC) and each connection needs to occupy
one time slot.
3. Capability: GSM-R is in capable to adapt to new
requirements. the maximum transmission rate of
GSM-R is 9.6 kbps which is very low by standard and
also it has a message delay of 400 ms which is very
high and can cause discrepancies in real time
applications and emergency systems. In future there
will be a requirement of a system that supports large
data bandwidth and shorter message delay[2].
These above limitations are covered by LTE-R which can
replace GSM for the following reasons:
1. LTE has far greater capacity,bandwidth and speed.
2. Since LTE is fully packet -switched based network, it
is better for data communication.
3. LTE offers reduced packet delay and a more efficient
network architecture.
4. LTE has advanced multiplexing and modulation
which helps to improve the spectral efficiency which
results in high throughput radio access.
5. LTE provides well established and standardized inter
working mechanism[2].
III. LTE-R
LTE acts as a unified architecture which provides real time
and non real time services with high speed data rate, optimized
packet and low latency wireless access technology. Here we
will combine the advantages of LTE as a wireless
communication system and LTE-R as a new railway mobile
communication system based on LTE/System Architecture
Evolution (SAE) and analyze it to determine why it is better
then existing GSM-R system.
A. ARCHITECTURE
The network architecture of LTE-R is basically similar to
LTE/SAE. The existing network architecture of LTE-R is as
follows:

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Figure 2. network architecture of LTE-R
The network access structure in LTE-R is called E-UTRAN
which replaces Base Station Controller (BSC) in GSM-R. It
consist of evolved-NodeB (eNodeB) which is the only network
equipment in it as compared to Base Transceiver Station (BTS)
and BSE. This network node transmits signal to terminals and
receive signals from terminals in one or more cells. It performs
functions at physical layer of the architecture related to
transmission and reception of radio interface,
modulation,demodulation,channel encoding and decoding[1]. It
also provides wireless mobility management and can be
connected to network router directly without any intermediate
nodes as in GSM-R. This results in better compatibility with
the follow up networks.
The core network of LTE-R is called Evolved Packet Core
(EPC). The difference between the core network of LTE-R and
GSM-R is that all the services are built on PS Domain which
indicates that EPC is an all IP mobile core network. User
registration information is managed by Home Subscriber
System (HSS). Mobile Switch Centers (MSC) in GSM-R core
network are replaced by IP Multimedia Sub System (IMS)
which provides IP Multimedia Services. IMS supports
generation of standard IP services by applying Session
Initiation Protocol (SIP) as well as effective packet
transmission. As a result, LTE-R architecture is relatively flat
so the maintenance of the number of devices and network
nodes is decreased which makes the network deployment
significantly easier with reduced cost[1].
B. TECHNOLOGY
QPSK, 16 QAM and 64 QAM are used in downlink
modulation which consist of physical downlink shared channel
(PDSCH) and Physical Multi broadcast Channel (PMCH). In
Physical Broadcast Channel (PBCH) QPSK is used. For
Physical Hybrid ARQ Indicator Channel (PHICH) BPSK
(Binary phase shift keying) technology is used. In uplink
modulation, QPSK,16QAM and 64QAM technologies are
used. For physical uplink shared channel (PUSCH),
QPSK,16QAM and 64QAM also can be used. BPSK,QPSK is
used for physical uplink control channel(PUCCH)[1]. To
reduce the peak to average ratio BPSK, Spectrum Shaping,
Selected Mapping and partial transmit sequence technology is
used.
In GSM-R system parity code, fire code and block
convolution code were used for channel coding. For LTE-R
system Turbo code is used. Turbo coding utilizes parallel
concatenation to combine convolution code and random inter
leaver together which is also known as random coding. Soft
input and soft output (SISO) decoding algorithm is used to
decode random coding where each decoder has three different
type of inputs which are parity,priori and information bits.
LTE-R system uses frequency division multiplexing and
multiple input multiple output (MIMO) schemes for
modulation. OFDM splits a high-rate data stream into lower-
rate data stream by assigning it to mutually orthogonal sub-
carriers with low transmission rate. Since the lower rate
parallel sub-carriers have longer symbol duration, the
dispersion in time caused by wireless channel delayed spread
which is also known as multi path delay is decreased. Also
guard intervals can be introduced in every OFDM symbol to
eliminate inter symbol interference (ISI). While in the guard
time, the OFDM symbol can be extended to avoid inter carrier
interference (ICI). In LTE-R system OFDMA which is the
multi user version of OFDM also can be used to make the
scheduling more flexible in the time frequency domain. Users
are assigned to different sub carriers to avoid frequency
selective fading, based on frequency channel response.
QPSK,16 QAM and 64 QAM are used on different sub carriers
to transmit downlink data which is time frequency scheduled
for different service requirements and channel conditions[3].
Because of higher peak to average power ratio (PAPR)
OFDM is not applicable for uplink in LTE-R system. Also it is
difficult to use a power amplifier to solve this problem. Data
which is sent to eNodeB simultaneously can cause frequency
offset problem in uplink transmission due to multiple users so
single carrier FDMA (SC-FDMA) is used for uplink
transmission. SC-FDMA transmits information symbols in a
sequential manner by using different orthogonal frequencies
which reduces the envelope fluctuations in the transmitted
signal. As a result SC-FDMA signal has a lower peak to
average power ratio a compared to FDMA signal. This helps in
reducing the physical size, high power consumption of the
power amplifier and makes it cost effective.
LTE-R system also supports multiple input multiple
output(MIMO) technology,spatial multiplexing, beam forming
and transmit density for meeting high needs of data rate and
high system capacity. A basic dpwnlink antenna in a LTE-R
system consist of 4 antennas: 2 transmit antennas and 2
receiving antennas. Whereas a basic uplink antenna consist of 1
transmit antenna and 2 receiving antennas. The channels are
divided into a number of mutually orthogonal sub channels and

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MIMO signal processing is applied in each sub channel which
can simplify the equalization and detection of frequency
selective MIMO channel. With the help of MIMO multiple data
streams can be transmitted and parallel independent channels
can be created at the same time. Since in each sub channel
MIMO is applied this improves channel transmission
rate,spectrum efficiency without increasing the channel
bandwidth.
IV. ADVANTAGES OF LTE-R OVER GSM-R
1. Information loss due to high speed train can be
overcome by installing roof top antenna which also
supports the increasing demand of large data
transmission. Roof top antennas are a part of
integrated train access unit which collects and
distributes information from devices used by the
travelers[3].
2. LTE-R systems deal with the doppler frequency
problem that hinders frequency handover by allowing
the devices accessing network to integrated train
access unit. This avoids the devices to get handover
without frequently requesting its home network for
handover due to frequent changing of cells. This also
ensures avoiding group handover problem caused by a
number of devices requesting for handover in groups.
3. Because of LTE's flat network architecture it is easily
deploy able as compared to GSM-R system and also
its lean signaling process makes it to complete the
handover in few miliseconds.
4. In a LTE system the minimum sub carrier channel
spacing of 15KHz which is tolerant to doppler
frequency shift without degrading the orthogonality of
the channel. In order to reduce doppler frequency shift
we can apply some other techniques like hybrid
automatic repeat request (HARQ) and frequency
offset correction algorithm (FOCA)[3].
V. CONCLUSION
In this paper we have described the older GSM-R system
and the new LTE-R system, its implementation,the technology
used and how it fares better than the GSM-R system. LTE-R
can solve the current problems with GSM-R and is more
effective in providing support for safety and security as well as
offering the passengers multiple high end services while high
speed traveling. Time has arrived to replace the older GSM-R
technology and move towards much more efficient LTE-R
technology to meet the ever increasing demand of the railway
system. However there are many challenges left for LTE-R to
further prove that it will be able to fulfill the requirements of a
high speed railway system.
REFERENCES
[1] Gao Tingting and Sun Bin “A High-speed Railway Mobile
Communication System Based on LTE,” Beijing, CHINA, pp.
414-417, ICEIE 2010.
[2] Ruisi He,Bo Ai,Gongpu Wang,Ke Guan,Zhangdui
Zhong,Andreas F. Molisc, Cesar Briso-Rodriguez, and Claude
Oestges “High-Speed Railway Communications,” pp. 49-58,
September 2016.
[3] Yan Sun, Chang-Young Lee,Jeong-min Jo,Young-Jae Han
“Study on the Effectiveness of High-Speed Railway
Communication and Signaling System Based on 4G LTE
Technology,” pp. 20-23, 2013.
[4] Marina Aguado and Eduardo Jacob, "Railway signalling
systems and new trends in wireless data communication,"
VTC, 2005, Fall
[5] LTE/SAE -The Future Railway Mobile Radio System? Long-
Term Visions on Railway Mobile Radio Technologies, UIC,
14.09.2009, V 0.4 Draft.
[6] Xiaohui Ma. The research on the key technology for LTE
downlink, Master Thesis of Xi'an University of Electronic
Science and Technology, 2009
[7] A. Sniady and J. Soler, “Capacity gain with an alternative
LTE railway communication network,” in Proc. 7th Int.
Workshop on Communication Technologies for Vehicles, St.
Petersburg, Russia, 2014, pp. 1–5.
[8] Richard Van Nee and Ranjee Prasad, "OFDM for wireless
Multimedia communications," Artech House, P33
[9] Harri Holma and Antti Toskala, "LTE for UMTS: OFDMA
and SC-FDMA based radio access," Wiley, P76
[10] Ralf Zartenar and Ralf Klber "LTE/SAE, Drivers, Benefits
and Challenges,"

Implementation of High Speed Railway Mobile Communication System

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Implementation of High Speed Railway Mobile Communication System