GOVERNMENT OF INDIA MINISTRY OF RAILWAYS Handbook on …

GOVERNMENT OF INDIA

MINISTRY OF RAILWAYS

Handbook on

TETRA Technology & its Applications in

Indian Railways

CAMTECH/S/PROJ/2021-22/SP3/1.0

August 2021

INDIAN RAILWAYS

Centre for Advanced Maintenance Technology

Maharajpur, Gwalior (M.P.) Pin Code – 474 005

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Handbook on

TETRA Technology & its Applications in Indian

Railways

CAMTECH/S/PROJ/2021-22/SP3/1.0

August 2021

Contact person: Director (S&T)

Indian Railways


Maharajpur, GWALIOR (M.P.) - 474 005

Tel: 0751-2470185, FAX: 0751-2470841

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Foreword

Presently, Railway Signalling & Telecommunication systems use variety of

wayside Signal & Telecommunication equipments, which require considerable

maintenance efforts and budget. With the advancements in technology, Railway

authorities now-a-days want to replace these wayside equipments with radio based

digital Signalling & Telecommunication systems. The radio based signalling &

telecommunication systems permit to connect between various control centres &

train crew and can easily replace the existing conventional/analog communication

systems. The need of the day is an efficient, scalable, flexible & advanced radio

based train control system to ensure the safety required for the existing train

control system and satisfy the existing as well as the future operational

requirements. The focus is on the application of “Terrestrial Trunked Radio”

(TETRA) system for Railway radio systems to fulfill the requirements of train

control centers and field staff.

TETRA communication system is a versatile system, which transmits Voice and

Data (V+D) more efficiently & optimally. It permits Direct Mode Operation

(DMO) to connect between mobiles even when mobile station is out of coverage. It

also ensures secure communication as only authorized persons can access the

information. In addition to bearer services, which are available in the existing

systems, TETRA also provides teleservices which includes features like individual

calling, group calling, broadcast calling & enhanced data services.

In continuing its efforts in documentation and upgradation of information,

CAMTECH has prepared this handbook for S&T personnel to get them familiar

with TETRA Technology & its applications in IR for its efficient operation and

maintenance.

CAMTECH, Gwalior Jitendra Singh

Principal Executive Director

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Preface

In India, as per Action Plan of Vision 2020 and safety concerns highlighted by the High Level

Safety Review Committee report, a beginning has been made to put MTRC into use in the

railways. The present day communication requirements are not just voice transmission, but also

along with voice, the system shall be capable of handling data also. “Terrestrial Trunked

Radio” (TETRA) technology fulfilled many of the needs of the rail community and was adopted

by several metros and tramways around the world for their communication requirements. One of

the advantages of TETRA is the integration of voice and data, allowing both critical control

information and speech to be sent to and from the same radio terminal simultaneously. Full

duplex speech calls allow safe driver-to-control room communications, as well as effective

communication with in-train passengers during emergencies. Group calls provide fast and

efficient speech communication between drivers, control centres, maintenance teams, security

organisations and many others. A packet data service is extensively used for messaging and

location applications. More recently, the TETRA Enhanced Data Service provides much higher

speeds for data without any compatibility or interference issues with the standard voice and data

service.

CAMTECH has prepared this handbook with an objective to disseminate the information on

TETRA Technology & its applications in Indian railways among officials and maintenance staff

of S&T (Telecom) department who deals with Radio communication. This handbook contains

overview of TETRA technology (including its comparison with traditional systems), technical

details, architecture, services, security features & other important aspects. The detailed

application part covers the newly commissioned CCG-VR communication link in Mumbai

suburban section of WR. The future perspective of TETRA technology along with emerging

wireless communication standards are also covered in brief.

We are sincerely thankful to M/s Consort Digital Pvt. Ltd., M/s Damm Cellular Systems India

Ltd. and S&T personnel of Indian Railways who helped us in preparing this handbook. Since

technological upgradation and learning is a continuous process, you may feel the need for some

addition/modification in this handbook. If so, please give your comments on email address

[email protected] or write to us at Indian Railways Centre for Advanced Maintenance

Technology, In front of Adityaz Hotel, Airport Road, Near DD Nagar, Maharajpur, Gwalior

(M.P.) 474005.

CAMTECH, Gwalior Vijay Garg

Director (S&T)

mailto:[email protected]

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Table of Contents

Foreword ...................................................................................................................................................... iii

Preface .......................................................................................................................................................... v

Table of Figures ............................................................................................................................................ ix

Issue of correction slips ................................................................................................................................ x

Disclaimer..................................................................................................................................................... xi

Our Objective .............................................................................................................................................. xii

1.1 INTRODUCTION ................................................................................................................................... 1

1.1.1 What is Radio Trunking? .................................................................................................................. 1

1.1.2 Benefits of Radio Trunking: .............................................................................................................. 2

1.1.3 Why a New Standard?...................................................................................................................... 2

1.1.4 What is TETRA Technology? ............................................................................................................. 3

1.1.5 Salient features of TETRA technology: ............................................................................................. 4

1.1.6 Analog vs. Digital Radio systems ...................................................................................................... 4

1.2 DESCRIPTION ....................................................................................................................................... 5

1.3 TETRA ARCHITECTURE ......................................................................................................................... 6

1.3.1 TETRA standard interfaces: .............................................................................................................. 7

1.4 Operation modes ................................................................................................................................ 8

2.1 RADIO COMMUNICATION ................................................................................................................... 9

2.1.1 Channels ......................................................................................................................................... 10

2.1.2 Channel Access ............................................................................................................................... 10

2.1.3 Frame structure ............................................................................................................................. 10

2.1.4 Source and Channel coding ............................................................................................................ 11

2.2 TETRA Data services .......................................................................................................................... 12

2.2.1 Short Data Service .......................................................................................................................... 12

2.2.2 Packet Data Service ........................................................................................................................ 12

2.2.3 Multi-Slot Packet Data ................................................................................................................... 13

2.2.4 High Speed Data ............................................................................................................................. 13

2.2.5 TEDS ............................................................................................................................................... 13

viii

2.2.6 TETRA Services: Technical characteristics ...................................................................................... 14

3.1 SECURITY ........................................................................................................................................... 17

3.1.1 Authentication ........................................................................................................................... 17

3.1.2 Encryption methods ................................................................................................................... 17

4.1 Railway Radio communication Systems between Train and Trackside (RSTT): ................................ 18

4.1.1 Generic Architecture of RSTT ......................................................................................................... 19

4.1.2 Main applications of RSTT .............................................................................................................. 19

5.1 Mobile Train Radio Communication (MTRC) system in Indian Railways: ......................................... 21

5.1.1 TETRA system for Train Control Communication: ......................................................................... 23

6.1 WESTERN RAILWAY SUBURBAN SYSTEM (CHURCHGATE TO VIRAR): .............................................. 24

6.1.1 Need of Mobile Train Radio Communication for Suburban Trains of Mumbai: ............................ 25

6.1.2 Digital MTRC System for Suburban Trains of Mumbai: ................................................................. 26

6.1.3 System Components: ..................................................................................................................... 26

6.1.4 Useful Features of Digital MTRC for Suburban Trains of Mumbai: ................................................ 28

6.1.5 Advantages of TETRA based Digital MTRC: .................................................................................... 28

6.1.7 Technical system details: ............................................................................................................... 30

6.1.8 Usefulness of the System: .............................................................................................................. 34

7.1 What does the future hold…? ........................................................................................................... 34

References .................................................................................................................................................. 36

CAMTECH Publications................................................................................................................................ 37

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Table of Figures

Figure 1: Comparison of voice quality between Analog & Digital Radio systems ......................................... 5

Figure 2: Addressing domains within TETRA ................................................................................................. 7

Figure 3 : TETRA Infrastructure ..................................................................................................................... 8

Figure 4 : TETRA modes of operation ............................................................................................................ 9

Figure 5 : TDMA frame structure ................................................................................................................ 11

Figure 6 : Main applications of RSTT ........................................................................................................... 21

Figure 7 : Schematic of TETRA based MTRC CCG-VR .................................................................................. 27

Figure 8 : Network Layout of TETRA based MTRC CCG-VR ......................................................................... 29

Figure 9 : Train Radio System ...................................................................................................................... 30

Figure 10 : Train Radio Control Panel ......................................................................................................... 31

Figure 11 : Network Devices ........................................................................................................................ 32

Figure 12 : SEPURA SRG 3000 Series Radios ............................................................................................... 33

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Issue of correction slips

The correction slips to be issued in future for this report will be numbered as follows:

CAMTECH/S/PROJ/2021-22/SP3/1.0# XX date .......

Where “XX” is the serial number of the concerned correction slip (starting from 01

onwards).

CORRECTION SLIPS ISSUED

Sr. No. of

Correction

Slip

Date of issue Page no. and Item

No. modified

Remarks

xi

Disclaimer

It is clarified that the information given in this handbook does not

supersede any existing provisions laid down in the IR Telecom

Engineering Manual, Railway Board and RDSO publications. This

document is not statuary and instructions given are for the purpose of

guidance only. If at any point contradiction is observed, then Signal

Engineering Manual, Telecom Engineering Manual, Railway

Board/RDSO guidelines may be referred or prevalent Zonal Railways

instructions may be followed.

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Our Objective

To upgrade Maintenance Technologies and Methodologies and achieve

improvement in Productivity and Performance of all Railway assets and

manpower which inter-alia would cover Reliability, Availability and Utilisation.

If you have any suggestion & any specific comments, please write to us:

Contact person: Director (Signal & Telecommunication)

Postal Address : Centre for Advanced Maintenance Technology, Opposite

Hotel Adityaz, Near DD Nagar, Maharajpur, Gwalior

(M.P.) Pin Code – 474 005

Phone: 0751 - 2470185

Fax: 0751 – 2470841

Email: [email protected]

CAMTECH/S/PROJ/2021-22/SP3 1

TETRA & its Applications in IR AUGUST/2021

TERRESTRIAL TRUNKED RADIO (TETRA) NETWORK

1.1 INTRODUCTION

1.1.1 What is Radio Trunking?

First trunked radio standard introduced was analogue MPT 1327 from ROHDE & SCHWARZ in

January 1988 by the British Radio communications Agency and is primarily used in the United

Kingdom, Europe, South Africa, New Zealand, Australia and China.

Trunking encompasses:

Sharing of a pool of resources.

All users share the same „pool‟ of available radio channels.

Radio units are allocated a channel only for the duration of a speech call.

Resources are allocated automatically, on demand.

Resources could be -

○ Radio Channel

○ PABX or PSTN Connection

○ Intersite Connection

● 'Trunked' radio systems differ from 'conventional' radio systems in that a conventional

radio system uses a dedicated channel (frequency) for each individual group of users,

while 'trunking' radio systems use a pool of channels which are available for many

different groups of users.

● Unlike conventional radios, trunked networks do not have user channel selection.

Instead, a central system dynamically assigns channels to users by group. This is a more

efficient use of the available spectrum, a simplification of the user experience, and an

improvement in security.

● Trunked radios use several channels or frequencies and allow those channels to be shared

by a large number of users, in multiple talk groups, without their conversations interfering

with each other. This allows for the channels to be shared by multiple talk groups,

achieving a more efficient use of the band.

● When a trunked radio user wishes to communicate with another user or group, the

computer automatically assigns them the first free available channel to make each call.

The underlying principle of trunking is that not all users or groups who need to

communicate in a channel will do so at the same time.

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● Trunked systems use a control channel, called the trunk, which transmits data packets

which allow a talk group to carry on a conversation by telling members of a talk group

which frequency to communicate on when they key up. This allows for a large number of

users to communicate using only a small number of frequencies, and more efficient use of

those frequencies.

1.1.2 Benefits of Radio Trunking:

Spectrum Efficiency

Automatic Management of traffic resources

Autonomy of operation to users/groups

Enhanced Services

More reliable than Analogue Radio System

Flexible

Reduces wasted time by finding an available channel and making the selection.

Has connectivity with internet

Low noise

Through the use of trunking, radios can utilize the same sets of frequencies with less cross-

talk, interruption and errors.

1.1.3 Why a New Standard?

In recent years, when disasters have struck in Europe, emergency response teams from several

European nations had a difficult time communicating with each other, due in part to the lack of

standardization in their mobile radio equipment which was the main reason for the evolutions of

TETRA.

TETRA is a set of standards developed by the ETSI that describes a common mobile radio

communications infrastructure across Europe which was later adopted by countries throughout the

world.

Use of earlier analog Radio systems requires new features, such as those listed ahead:

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Features lacking in the past Supported by TETRA standard

a) Voice encryption (most current FM- or PM-

modulated systems can be tapped)

a) Digital speech transmission

Additional encryption supported

b) Data transmission at higher rates

(e.g. MPT 1327 allows only 1.2 kbit/s)

b) 7.2 kbit/s per channel (unprotected)

28.8 kbit/s with multislot

operation(Unprotected)

c) Late entry to group calls c) Supported by TETRA standard

d) Possibility to operate without a base station d) Direct Mode Operation (DMO)

e) Higher spectrum efficiency

Short data services

e) Four channels per 25 kHz (TDMA)

Short data services (SDS)

f) Other supplementary services

f) More than 20 supplementary Services

defined, such as Ambience Listening, Call

Barring, Call Hold, Call Diversion

1.1.4 What is TETRA Technology?

At the start of the 1990s, the European Telecommunications Standards Institute (ETSI) was

commissioned by the EU to create a European standard for professional digital radio. The most

important parts of the TETRA standard (Terrestrial Trunked Radio) were adopted at the end of

1995 in national votes. It is the worldwide digital standard for professional mobile radio, which

offers excellent speech quality, high data transmission rates, secure & encryptable connections.

It is a professional land mobile radio standard specifically designed for use by government

agencies, emergency services, public safety networks, rail transport, transport services and the

military. It is a European Telecommunications Standards Institute (ETSI) standard, whose first

version was published in 1995. It uses Time Division Multiple Access (TDMA) with π⁄4 QPSK

modulation with four user channels on one radio carrier and 25 kHz channel raster. Both point-to-

point and point-to-multipoint transfer can be used. Digital data transmission is also defined in the

standard.

TETRA mobile stations can communicate in direct-mode operation (DMO) or using trunked-

mode operation (TMO), using switching and management infrastructure (SwMI) made of TETRA

base stations (TBS). It also allows direct communication in situations where network coverage is

not available. DMO also includes the possibility of using a sequence of one or more TETRA

terminals as relays. This functionality is called DMO gateway (from DMO to TMO) or DMO

repeater (from DMO to DMO). In emergencies, this feature allows direct communications

underground or in areas of bad coverage.

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In addition to voice and dispatch services, the TETRA system supports several types of data

communication. Status messages and short data services (SDS) are provided over the system‟s

main control channel, while packet-switched data or circuit-switched data communication uses

specifically assigned channels. TETRA provides for authentication of terminals towards

infrastructure and vice versa. For protection against eavesdropping, air interface encryption and

end-to-end encryption is available. The common mode of operation is in a group-calling mode in

which a single button push will connect the user to the users in a selected call group and/or a

dispatcher.

1.1.5 Salient features of TETRA technology:

The TETRA standard is a living standard. While systems are deployed to the current

standard, a range of new applications can be opened up simply by adding features to the

specifications.

Tetra is the most mature digital trunking standard in the world.

Tetra is specifically designed and optimised to serve mission critical organisations and

their users.

Tetra is scalable and allows networks to be built on both small and large scales even

nation-wide.

Tetra systems are traditionally designed to incorporate extensive redundancy a multiple

level thus eliminating any single point of failure.

1.1.6 Analog vs. Digital Radio systems

● Analog radio systems, although still widely used, has many downsides. A standard analog

radio is going to decrease in signal the closer we get towards its maximum range, at which

point all we hear is white noise only.

● TETRA being a digital radio is going to remain much more consistent in sound

quality regardless of distance to or from the maximum range. It improves voice quality,

spectrum efficiency, security and ensures effective radio fleet management.

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Figure 1: Comparison of voice quality between Analog & Digital Radio systems

1.2 DESCRIPTION

For its modulation, TETRA uses π⁄4 differential quadrature phase-shift keying. The symbol

(baud) rate is 18,000 symbols per second, and each symbol maps to 2 bits, thus resulting in

36,000 bit/s gross.

Since a form of phase shift keying is used to transmit data during each burst, it would seem

reasonable to expect the transmit power to be constant. However it is not. This is because

the sidebands, which are essentially a repetition of the data in the main carrier's modulation, are

filtered off with a sharp filter so that unnecessary spectrum is not used up. This results in an

amplitude modulation and is why TETRA requires linear amplifiers. The resulting ratio of peak to

mean (RMS) power is 3.65 dB. If non-linear (or not-linear enough) amplifiers are used, the

sidebands re-appear and cause interference on adjacent channels. Commonly used techniques for

achieving the necessary linearity include Cartesian loops, and adaptive predistortion.

The base stations normally transmit continuously and (simultaneously) receive continuously from

various mobiles on different carrier frequencies; hence the TETRA system is a frequency-division

duplex (FDD) system. TETRA also uses FDMA/TDMA (see above) like GSM. The mobiles

normally only transmit on 1 slot/4 and receive on 1 slot/4 (instead of 1 slot/8 for GSM).

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https://en.wikipedia.org/wiki/Phase-shift_keying

https://en.wikipedia.org/wiki/Sideband

https://en.wikipedia.org/wiki/Amplifier#Linearity



Speech signals in TETRA are sampled at 8 kHz and then compressed with

a vocoder using algebraic code-excited linear prediction (ACELP). This creates a data stream of

4.567 Kbit/s. This data stream is error-protection encoded before transmission to allow correct

decoding even in noisy (erroneous) channels. The data rate after coding is 7.2 Kbit/s. The capacity

of a single traffic slot when used is 17/18 frames.

A single slot consists of 255 usable symbols; the remaining time is used up with synchronization

sequences and turning on/off, etc. A single frame consists of 4 slots, and a multiframe (whose

duration is 1.02 seconds) consists of 18 frames. Hyper frames also exist, but are mostly used for

providing synchronization to encryption algorithms.

The downlink (i.e., the output of the base station) is normally a continuous transmission consisting

of either specific communications with mobile(s), synchronization or other general broadcasts. All

slots are usually filled with a burst even if idle (continuous mode). Although the system uses 18

frames per second only 17 of these are used for traffic channels, with the 18th frame reserved for

signalling, Short Data Service messages (like SMS in GSM) or synchronization. The frame

structure in TETRA (17.65 frames per second), consists of 18,000 symbols/s; 255 symbols/slot; 4

slots/frame, and is the cause of the perceived "amplitude modulation" at 17 Hz and is especially

apparent in mobiles/portables which only transmit on one slot/4. They use the remaining three

slots to switch frequency to receive a burst from the base station two slots later and then return to

their transmit frequency (TDMA).

1.3 TETRA ARCHITECTURE

The different addressing domains relevant to TETRA are shown in figure 2. The TETRA domain

is shown as intersecting three other domains (PSTN, ISDN and PDN). This indicates that a given

individual TETRA subscriber address may be associated with one address in each of these public

domains.

Within the TETRA domain, the TETRA identities can have different roles.

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https://en.wikipedia.org/wiki/Vocoder

https://en.wikipedia.org/wiki/ACELP

https://en.wikipedia.org/wiki/Time_division_multiple_access



Figure 2: Addressing domains within TETRA

1.3.1 TETRA standard interfaces:

Air Interface (AI):

The most important interface in the ETSI TETRA specification for this work is the Air Interface

(AI), which ensures the interoperability between radio terminals and base stations enabling

the basic communication mode commonly referred to as Trunked Mode Operation (TMO).

Peripheral Equipment Interface (PEI): The PEI allows data communication between TETRA

radio terminal and other data terminal equipment.

Inter System Interface (ISI):

The interconnection of two or more TETRA networks is enabled by the ISI. These inter-

operating networks can be supplied either by a single or different manufacturers.

Direct Mode Operation (DMO):

The DMO is the second air interface that is defined by the ETSI TETRA standard. It enables

terminals to communicate directly without the main TETRA network infrastructure.

Network Management Interface/System (NMI/NMS):

The NMI allows the network configuration and maintenance functions. During standardization

activities it was noticed that a common NMI was impractical thus this interface does not belong to

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the standard. Based on the standardization work of the NMI a comprehensive implementation gui-

-de was made by the TETRA Association to assist users.

Figure 3 : TETRA Infrastructure

Figure 3 describes the infrastructure of TETRA Network.

A typical TETRA system consists of Base Stations (BS) and Mobile Stations (MS). The BS

resends information from an MS to requested receiver. The base stations are connected to a base

station controller (BSC), which in turn is connected to a mobile switching centre. MS are also able

to connect directly to each other even though outside the range of a base station.

1.4 Operation modes

TETRA has three different main operation modes with different objectives allowing both voice

communication and data transmission.

Voice plus Data (V+D)

Direct Mode Operation (DMO)

Packet Data Optimized (PDO)

In the Voice plus Data (V+D) mode it is possible to switch the communication type between data

and speech or use both at the same time. In the Direct mode communication through voice or data

is between two mobile units even if they are outside the base stations range. The last mode is

Packet Data mode which is for data transmission only.

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Simplex, Semi-Duplex, Full Duplex

In trunked mode operation, there is always a base station and network to switch information

between one or several users. Any type of communication can be:

• Full duplex (both users can speak and listen at the same time).

• Semi-duplex, where only one party can speak at a time, usually a Press-To-Talk button is used

and the end of speech is announced by “Over”.

• Simplex, this can be a broadcast message.

Figure 4 : TETRA modes of operation

In order to avoid interference, base station and mobile station use different frequencies with a

fixed duplex offset, e.g. 10 MHz

2.1 RADIO COMMUNICATION

Transmission and Reception steps in the TETRA standard depends on what mode is used, but the

basics are more or less the same for V+D and DMO. The protocol architecture of the TETRA air

interface consists of three layers:

Physical layer: Controls the radio characteristics, such as (de)modulation and

synchronization.

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Data Link Layer (DLL): It is divided into two sub layers with different functionalities:

Logical Link Control (LLC): Handles data transmission and re- -

transmission etc.

Medium Access Control (MAC):Handles channel access, channel

(de) coding and (de) interleaving.

Network Layer: It handles network procedures.

The MAC layer is further divided into upper and lower layer, where the upper MAC layer handles

access control and multiplexing and the lower MAC layer handles channel coding, slot stealing

and routing.

The Network layer is only for Network services meaning that all speech and data only uses the

Physical layer and the DLL.

2.1.1 Channels

The interface between the protocols and the radio subsystem is represented by logical channels

divided into two categories; traffic channels that carries information about speech and data and

control channels sending signalling messages and packet data. Information between i.e. the upper

and lower MAC layer is passed through logical channels where the different channels either pass

specific information in one or both directions. Information transmitted from the base station is

passed in the uplink whilst information received to the base station is passed through the

downlink. In other words, information from the MAC to the physical layer is uplink information

whilst information from the physical layer to the MAC is downlink information.

2.1.2 Channel Access

The TETRA standard uses Time Division Multiple Access (TDMA) to access the channel. TDMA

makes it possible for multiple users to share the same radio frequency (RF) but in different

timeslots. Simple Frequency Division Multiple Access (FDMA) assigns a carrier frequency for

each user while TDMA uses the basic principle of FDMA but dividing the frequencies into

timeslots introducing even more possible users. In this case each RF carrier is divided into four

timeslots allowing 4 users per carrier and each carrier has a 25 kHz spacing. The multi-slot

solution results in a greater transmission rate making it more efficient.

2.1.3 Frame structure

The TDMA structure is built on TDMA frames lasting roughly 566 ms, these consist of four

timeslots each lasting around 142 ms. The TDMA frames are in turn grouped in multiframes

consisting of 18 TDMA frames. The 18th frame is always a control frame which means that the

first 17 frames actually consist of 18 frames of information which is neatly solved by simple data

compression. For example encryption synchronisation and other methods that require large repeat

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frame structures take use of the final frame structure called hyper-frame consisting of 60

multiframes, they last a little over 60 seconds.

Figure 5 : TDMA frame structure

One time frame consists of four time slots. Data is compressed and sent in one of the available

time slots.

On a traffic channel, every 18th frame is used to exchange additional control information between

the radio terminal and the base station as shown below:

one multiframe = 18 frames = 1.02 s

one frame = 4 time slots = 56.667 ms

one time slot = 255 symbols =14.167 ms

Several radio terminals may use the same carrier. So that they do not interfere with each other‟s

communication, each terminal is assigned its own time slot for the duration of the call. The

terminal sends its data in a burst, i.e. the radio power is turned on for a short period and turned off

again before another terminal transmits in the next time slot.

2.1.4 Source and Channel coding

The TETRA standard uses a version of Code-Excited Linear Predictive (CELP) code for speech

source coding. The error control structure or channel coding consists of three main processing

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parts. The input information bits are packed into, so called, MAC blocks and encoded by a block

code. The block coded bits are then encoded by a convolutional code, more precisely a Rate-

Compatible Punctured Convolutional Code (RCPC Code). The next step is to interleave and

reorder the bits. Interleaving spreads out the symbols over many code words making it possible to

correct errors even if there are bursts of errors.

2.2 TETRA Data services

In modern TETRA PMR systems, utilization of data communication is greatly increasing while

voice remains the primary form of communication. The main driver for increasing the use of data

applications is to improve productivity, operational efficiency and cost effectiveness. Also the

data communication services are often designed so that spectrum utilization is improved without

degradation of other services bringing also benefits to network operators. Several data transport

services have been defined by the TETRA standard, these being: Short Data Service (SDS),

Packet Data Service, Multi‐Slot Packet Data Service, and High Speed Data. The most common

applications relate to control room management, mobile data, telemetry, mapping, imaging,

billing, location and many more. Current implementations for the TETRA location services are

commonly utilizing the SDS messaging service which is why this service is focused here.

2.2.1 Short Data Service

The TETRA standard specifies the Short Data Service (SDS) which enables a point‐to‐point and

point‐to‐multipoint communication capability by short message transmissions. The messages are

divided into SDS types 1‐4 which in turn are categorized in terms of data quantity accordingly

from 16 bits up to 2039 bits. The lengths of SDS‐1, SDS‐2 and SDS‐3 are specified in the TETRA

standard to 16 bits, 32 bits and 64 bits respectively. An important factor for this thesis is the data

carrying capacity of SDS type 4 what is user definable with the maximum of 2039 bits to be used

for user defined short message services. The SDS bearer service provides reliable delivery of user

defined data over the AI and can be thus utilized effectively for location service data

transportation. The bearer service provided by the SDS ensures reliable delivery of data over the

TETRA AI. To ensure application level inter‐operability while using SDS messages additional

header information must be implemented to support the SDS Transport Layer (SDS‐TL) data

transfer service.

2.2.2 Packet Data Service

TETRA provides IP packet data possibilities in a similar way to GSM. A single slot can provide a

data bearer service of 7.2 kbit/s for packet data use. This gross bit rate gives a net bit rate of 2.4 to

4.8 kbit/s depending on a utilized level of protection. This is sufficient for services like Wireless

Application Protocol (WAP), e‐mail and compressed images or even slow‐speed video.

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2.2.3 Multi-Slot Packet Data

TETRA can also support data transmissions up to a gross rate of 28.8 kbit/s. The resulting net bit

rate after implementing data protection is from 9.6 kbit/s to 19.2 kbit/s. This transmission rate is

enabled by using a maximum of four time slots for data transmission. The ability to support even

higher rates enables TETRA usage of multiple other more demanding applications.

2.2.4 High Speed Data

To enable more data throughput over TETRA networks requires a trade‐off between higher data

rates and increased frequency spectrum use. For making this possibility available to user

organizations, the TEDS standard is being implemented. It is planned to include a variety of data

rates in 25 kHz, 50 kHz, 100 kHz and 150 kHz channel bandwidths.

2.2.5 TEDS

TEDS is the new TETRA High Speed Data (HSD) service that has been introduced recently. To

achieve the higher data rates, TETRA TEDS uses different RF channel bandwidths and

modulation schemes.

TEDS is fully backwards compatibility with TETRA Release 1 and as a result it enables easy

migration from Release 1 to Release 2. Further details for the TETRA TEDS technology are given

below:

The TETRA Enhanced Data Service, TEDS achieves much higher data rates than was previously

achievable with the TETRA Release 1 radio system. It achieves this by using wider bandwidths

and adaptive modulation schemes.

TETRA TEDS uses four different RF channel bandwidths:

25 kHz

50 kHz

100 kHz

150 kHz

It also allows for adaptive modulation, choosing the optimum modulation format for the

prevailing conditions and requirements. The modulation schemes supported in TEDS are:

π/4 DQPSK - used for common TETRA V+D and TEDS control channel.

π/8 D8PSK - for early migration requiring modest increase in speed.

4QAM - used for efficient links at edge of coverage.

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16QAM - used for moderate data rates.

64QAM - for high data rates.

The different combinations of modulation and channel bandwidth enable a variety of different

data rates to be achieved.

MODULATION CHANNEL TYPE

25 KHZ 50 KHZ 100 KHZ 150 KHZ

π/4 DQPSK 15.6

π/8 D8PSK 24.3

4QAM 11 27 58 90

16QAM 22 54 116 179

64QAM 33 80 175 269

64QAM 44 107 233 359

64QAM 66 160 349 538

Using the adaptive modulation schemes and variable channel bandwidths user data rates of

between 10 and 500 kbps can be expected. This is sufficient for many new applications, allowing

video to be transmitted over some links as required.

With the move towards more rich media services such as video, TEDS also allows up to 8

multimedia applications and QoS negotiation for real-time class data applications, such as voice

and video and telemetry, with the QoS attributes negotiated being; throughput, delay, priority and

reliability. In this way the system is able to provide the optimum service for the available

bandwidth, user priorities and channel conditions.

A further advantage of TEDS is that there is support for sectored cells.

2.2.6 TETRA Services: Technical characteristics

TETRA provides a number of services which are characterized as bearer services and teleservices.

The bearer services are the same as general networks, while the teleservices are similar to mobile

communication including the bearer services.

TETRA provides encrypted data communication in each of the following

● Individual call (point to point)

● Group call (point to multipoint)

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● Acknowledged group call

● Broadcast call

Enhanced Services

Feature/Facility Advantages Benefit

1. Busy queuing with

automatic call back

when a channel is free

The radio user only has to initiate a

call request once knowing that even

in busy periods the call will be

automatically established once a

traffic channel becomes free.

Less user stress and frustration

when contending with other

users on a busy system

resulting in increased

productivity and user

confidence.

2. Priority Access

Selected radio users can be

assigned different grades of service

during system busy periods

dependent on their operational

importance. For example, front line

police officers high priority, traffic

warden‟s low priority.

Systems can be designed to be

more cost effective by using

fewer channels. Similarly, a

PAMR operator can tier their

subscription fees based on

grade of service requirements.

3. Emergency Calls

Radio users can quickly establish

an emergency call even if the

system is busy.

Radio user health and safety in

problematic environments and

overall public safety.

4. Individual Calls

Allows one to one calls such as

radio terminal to terminal, fixed

telephone to terminal, terminal to

fixed telephone.

Increases an organisations

operational effectiveness and

productivity as well as

providing a degree of privacy

between individual users.

5. Broadcast Calls

Allows permitted radio users

quickly to inform everyone on the

system of important information.

Increases an organisations

operational effectiveness and

productivity.

6. Dynamic Grouping Allows a system operator or

dispatcher to dynamically assign

different radio user into the same

talk group.

Allows an organisation to

group together specific radio

users to communicate more

effectively when addressing an

event or incident, thereby

increasing operational

efficiency.

7. Cell Handover

Radio units are automatically

handed over to adjacent base

station sites as they move from RF

coverage on one site to that of

another.

Maintaining communications

integrity independent of a radio

user‟s geographic location.

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Feature/Facility Advantages Benefit

8. Area Selection The system operator can assign

different geographic coverage (base

station site access) to specific radio

users and/or talk groups.

System capacity and loading is

optimised in accordance with

radio user‟s geographic

coverage needs.

9. Efficient Wide Area

Group Call

Wide area multiple base station site

group calls are only supported on

traffic channels at those base station

sites were talk group users are

registered.

Improved network capacity and

grade of service for wide area

group call support.

10. Status Messaging

Regular repeated voice messages

such as enroute to incident, at

incident, returning to base, at base,

gone to lunch, unavailable for

work, available for work, etc., are

replaced by a simple and very short

duration coded message.

The operational status of all

users can be quickly and easily

stored electronically thereby

improving an organisation‟s

operational efficiency. Also,

valuable voice channel

resources can be saved thereby

increasing a system‟s overall

grade of service.

11. Short Data Service

Dispatch messages containing

information such as name, address,

nature of work, etc., can be

replaced by a short duration

alphanumeric message.

An improvement in an

organisation‟s operational

efficiency. Also, valuable voice

channel resources can be saved

thereby increasing a system‟s

overall grade of service.

We can use TETRA for data communication with data rate (< 10 kb/s) such as GSM-R. The vital

information which would be specially the precedent train position or speed limit conditions in the

wireless train control systems depends on several factors which are control methods, data format

and encryption methods and so on.

TETRA only has data rate which is inferior to 10kb/s, theoretically, the data rate of the wireless

train control systems should be lower than 10 kb/s.

TETRA provides a number of services which are characterized as bearer service and teleservices.

The bearer services are the same as general networks, the teleservices is similar to mobile

communication included the bearer services. The teleservices provides the complete capability for

wireless communication between base stations and mobile terminal and includes attributes of the

higher layers (4 to7) of OSI stack.

The teleservices uses multiple carrier frequency such as different offsets from multiple 25 kHz

which space between carriers.

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3.1 SECURITY

When talking about security there are three main areas to take into consideration in order to keep

information safe:

Confidentiality: Making sure that only authorized persons or items can access the

information.

Integrity: Only authorized persons or items can write or change the protected information.

Availability: Making sure that authorized persons have access to the information when

ever needed.

These areas are often referred to as CIA. The TETRA standard uses a few different

security measures in order to keep the information safe. There are four main categories of

functionality:

Security mechanisms: independent functions with a specific purpose

Management features: which are functions that manage the security mechanisms.

Cryptographic algorithms: specific mathematical functions that together with

cryptographic keys as parameters give reassuring security for the security mechanisms.

Lawful interception mechanisms: Functions used together with communications systems

to supply the lawfully required access to information and communication.

3.1.1 Authentication

One way of assuring that a network or Mobile Station (MS) can be trusted is authentication. If

they share a valid key then communication is established. The authentication is, among other

things, used to control the MS access to the network services, provide confidentiality and create a

secure channel for sharing sensitive information. The authentication mechanism is only used in

V+D mode. For DMO Static Cipher Keys (SCKs) are used for mutual authentication. Each MS

has an authentication key K, which is stored both in the MS itself and in the Authentication Centre

(AUC) where all authentication keys in the network are stored.

3.1.2 Encryption methods

When communicating through a wireless system eavesdropping is a very common security risk. In

order to prevent eavesdropping, among other threats, in the air interface between the MS and the

network, Air Interface Encryption (AIE) and End-to-end encryption (e2ee) is used. These methods

encrypt the information and make it impossible for anyone not having the required decryption

algorithm to make sense of the encrypted information. The encryption is done before the channel

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coding when transmitting and after the channel decoding when receiving. When placing the

encryption in that order the MAC headers are left unencrypted which in turn allows the receiver to

determine the relevancy of the received message.

A) Air Interface Encryption

AIE uses a shared key to encrypt both the traffic and signalling information between transmitter

and receiver when MS and BS are communicating with each other. It encrypts all the data on the

radio path and messages on the control channel. There are four AIE TETRA Encryption

Algorithms (TEAs) for the TETRA standard called TEA1, TEA2, TEA3 and TEA4. They have

slightly different areas of application, they are all designed for Public Safety and Military

Organisations. TEA2 is only permitted within the European Union and associated countries

whereas the others are suited for civil use, where security is required, as well.

B) End-to-end encryption

E2ee protects information within the network and the information is encrypted and decrypted in the

end terminals. The e2ee algorithms and key management is not standardized, because the

requirements differ from organizations, but the synchronization is standardized. There are some

requirements set by ETSI, these include that the same mechanisms should work in both directions,

there has to be independent synchronization processes in both directions and the encryption has to

be located in the U-plane. Since the e2ee encrypts information in the traffic channel and not the

control channel it has to be used together with AIE.

4.1 Railway Radio communication Systems between Train and Trackside

(RSTT):

Railway transportation is a mean of conveyance of passengers and goods (freight). It is also

commonly referred to as train transport. Various radio communication systems/technologies have

been used for many years for railway operational applications. There are various degrees of

implementation of numerous technologies among countries. Radio communication networks are

critical to train operations including stringent requirements for reliability, availability, safety and

security for these operations. Different security measures are considered based on the assumption of

transmission error or communication blackout in RSTT.

In general, radio communication for railway operations are considered as “mission critical” for

train operations in general and the management of train emergency situations. Furthermore, railway

radio communication systems require the support of legacy technology and to have a long life

cycle.

RSTT provide improved railway traffic control, passenger safety and security for train operations.

RSTT carry train control, voice dispatching, command, operational information as well as

monitoring data between on-board radio equipment and related radio infrastructure located along

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trackside. To date, RSTT have included narrowband wireless technologies for carriage of train

control, command, and operational information, as well as monitoring data between on-board

equipment and related radio infrastructure located along the trackside.

Such legacy systems also usually took the form of dedicated mobile radio systems for dispatching,

train control and other operational safety-related and efficiency needs of railway transportation

systems.

Radio communication systems supporting RSTT generally need system interoperability and

seamless continuity, especially for tracks crossing borders or tracks operated by multiple railway

network entities. As such, regional and global standardization and harmonization efforts of the

railway industry become essential.

4.1.1 Generic Architecture of RSTT

The main elements of the RSTT may consist of on board radio equipment, radio access units and

other trackside radio infrastructure. Other systems, such as the core network, etc., are supporting

systems for the RSTT.

Radio access unit: including antenna and base station, to provide radio access to the

terminals (especially cab radio)

On board radio equipment: Radio equipment installed on train as well as handsets

(for example, mobile terminals of automatic train control – ATC)

Other trackside radio infrastructure: Radio infrastructure operating along trackside

(for example: shunting radio devices)

4.1.2 Main applications of RSTT

i) Train radio: The train radio application is a part of a railway radio communication system used

for communication between train and track side for signalling and traffic management with the

aim to contribute to safe train operation. Train radio provides mobile interconnect to landline and

mobile-to-mobile voice communication and also serves as the data transmission channel within

various bearer services. For voice communication Train radio provides call functions (point to

point / group / emergency / conference) with specialized modes of operation (e.g. location

depending addressing, call priorities, late-entry, and pre-emption).

ii) Voice/Dispatch: System for voice/dispatch includes point-to-point voice calls, public

emergency voice calls, broadcast voice calls, group voice calls and multi-party voice calls.

One of the main functions of RSTT is to provide dispatching communication, which is to provide

specific voice communication features for railway

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iii) Maintenance: This application provides voice communication (point-to-point, point to multi-

point call, or group-call) and data communication for maintenance services in railway

infrastructure.

iv) Train Control (Interlock/movement authorization): This application provides reliable

communication bearer for train control system in order to ensure efficient data transmission

between the on-board equipment and trackside equipment. The limitations of the trains distance to

run are sent in the form of a Movement Authority1 from the trackside.

The train control application can be categorised into decentralised and centralised modes. In a

decentralised operation, the train movements are controlled by local interlocking stations. The

operators of neighboring interlocking stations communicate with each other by means of

communications. In a Centralised Traffic Control (CTC) as one way of train control, all points and

signals inside the controlled area are directly controlled by the dispatcher.

v) Emergency: Emergency applications allow an authorized user setting up an emergency

communication to other users within an automatically configured area or group, which is based

upon the originator‟s location or characteristics and those users likely to be affected by the

emergency.

vi) Train information: Generally, railway information transmitted by RSTT could be classified

into two categories:

to provide the railway transportation information for the train operators, such as train

operating status, mobile ticketing and check-in services;

to provide relevant railway transportation information for passengers, such as travel

information.

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Figure 6 : Main applications of RSTT

5.1 Mobile Train Radio Communication (MTRC) system in Indian Railways:

Since its inception in 1853, Indian Railways have progressed a long way. Presently, India has the

third largest railway network in the world, covering a total length of around 65,000 Kilometers.

With the passage of time, Railways have become a commonly used medium for long distance

transport in India. More and more passengers are using Railways as a means of travel. Millions of

tones of goods are now being transported by trains. Indian Railways transport 7651 billion

passengers and over 921 million tones of goods annually.

As the world is getting technologically advanced, more complications have set in regarding safety

and security of passengers. The report of the High Level Safety Review Committee of 2012

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estimates that almost 15,000 number of persons gets killed every year in train accidents. Apart

from this, security in trains is also a major concern. Considering all these necessities, the need of

the hour is to develop an effective and a technologically advanced communication system in the

Indian Railways.

The Mobile Train Radio Communication (MTRC) system seems to be the right answer to these

concerns. MTRC uses the “Global System for Mobile Communications-Railway (GSM-R)” &/or

the TETRA technology to facilitate an instant and constant interaction with the train crew with the

Control Centre and Station Master. It ensures safety of passengers by providing effective

communication between Driver and Control Room. The MTRC system can be used to warn the

drivers beforehand of the running trains as well as the concerned officials. In case of any security

problem, concerned staff can immediately intimate the concerned security establishment. If any

accident takes place, the MTRC system will facilitate better post-disaster management. In the

present day, Railways need not just effective voice transmission, but also have the capability to

analyze all the technical data to arrive at the correct decision to be taken on the spot.

In India, as per Action Plan of Vision 2020 and safety concerns highlighted by the High Level

Safety Review Committee report, a beginning has been made to put MTRC into use in the

railways. The MTRC project is being implemented by the Indian Railways Project Management

Unit (IRPMU), and it is expected that this technology will help to improve the Railway

communication in India manifold and make Railways a safer and better mode of transport for the

common man.

Indian Railways decided to move ahead and introduced Mobile Train Radio Communication

based on GSM-R technology. It all started with the introduction of the full duplex communication

based system in the Nagpur-Itarsi section, Mughalsarai-Howrah, and the Delhi-Mughalsarai

section. It marked the beginning of the MTRC revolution in India. The system lacked the essence

of the MTRC in real sense as it could facilitate communication only between the driver and the

control room or the guard and the control room, lacking the ability to aid direct communication

between the concerned staff.

Railways’ Present Day Requirements:

The Train Mobile System‟s present day requirements are not just voice transmission, but also

along with voice the system shall be capable of handling data also. Typical applications for the

Modern Train Mobile System are as under.

● Text and status message transmission

● Automatic Train operation‟s critical alarms

● Train status and alarm information

● Passenger information system control

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● Train passenger emergency system

● Closed circuit TV system

5.1.1 TETRA system for Train Control Communication:

From the outset, TETRA fulfilled many of the needs of the rail community and was adopted by

several metros and tramways around the world for their communications requirements. One of the

advantages of TETRA is the integration of voice and data, allowing both critical control

information and speech to be sent to and from the same radio terminal simultaneously. Full duplex

speech calls allow safe driver-to-control room communications, as well as effective

communication with in-train passengers during emergencies. Group calls provide fast and

efficient speech communication between drivers, control centres, maintenance teams, security

organisations and many others. A packet data service, allowing the transport of users‟ IP packets,

was an early enhancement to the standard, and provides a multislot packet data service that

enables any number of timeslots from one to all four on a channel to be devoted to the data

service. The Short Data Service is extensively used for messaging and location applications. More

recently, the TETRA Enhanced Data Service provides much higher speeds for data without any

compatibility or interference issues with the standard voice and data service. Direct Mode

Operation allows direct communication between on-train staff, or between on-train and trackside

staff without the need for base station coverage nearby. A standardised interface on mobile and

portable radios – the PEI (Peripheral Equipment Interface) – facilitates use of the radio as a

modem to carry application data. The security mechanisms on TETRA were designed to be

strong, with government use in mind, which is of increasing importance in the transportation

market. Importantly, the services are specified in ETSI standards, which when combined with an

independent interoperability testing regime overseen by the TCCA (TETRA and Critical

Communications Association), allows a competitive multi-vendor supply process.

TETRA has been successfully deployed in a number of high-speed and a large number of

METRO projects around the world and is being considered in many European countries as well.

In metro and tramway applications, TETRA has been consistently used for speech and data centric

applications. The open interfaces have allowed different suppliers to build their own train

dispatching and train control applications on top of the underlying TETRA network and terminal

equipment. TETRA equipment is integrated with the on-board control and signalling systems,

enabling the TETRA network to be used to report back location information from trackside and

GPS location systems. Telemetry relating to the health of the train can be reported to control and

maintenance systems and images from on-board camera systems can also be transmitted, for

example in alarm situations.

The speech services are routinely used for on-board announcements and passenger emergency

service support, as well as for communications between train and control room. TETRA has high

performance group calls, with set-up times usually quoted as 300msec, for efficient staff

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communications (and efficient use of radio channels). The individual calling facilities are

available in full duplex as well as the push-to-talk half duplex mode.

As well as track-to-train applications, the data services are used for passenger information

systems. Telemetry from remote locations can ensure that the security and safety of unattended

facilities are continuously monitored. Speech services are regularly used by station staff and

maintenance crews. TETRA networks are extremely efficient for speech, providing up to four

calls in one 25 kHz channel, and with calls that are fast to set up and fast to clear, avoiding

wasting airtime.

TETRA has also been adopted for main line railway communications. Sometimes the deciding

factors have included the available spectrum – the GSM-R band is not available in all countries,

and TETRA is specified to operate from VHF to 1GHz. TETRA networks are most commonly

installed in the 400MHz bands, and this provides some economies compared with GSM-R due to

the greater ranges from base stations that are obtainable at lower frequencies.

Another factor which may aid the take up of TETRA in safety critical signalling applications is

the completion of specifications for the use of GPRS (the General Packet Radio Service of GSM)

to carry ETCS data. The TETRA packet data service provides the same capabilities as GPRS with

respect to improved efficiency over a circuit switched service, and is flexible in its ability to

deliver different packet latencies and bit rates with the different services (single slot packet data,

multislot packet data and TEDS) available. Also, signalling vendors are already producing

solutions that operate independently of the underlying radio technology, which further eases the

ability to use TETRA for safety critical schemes where this is possible.

Studies conducted on TETRA train communication systems at speeds of up to 500 km/h show that

the performance of the channels at higher speeds is not significantly different from that at lower

speeds. This is due to the forward error correction applied, which has better performance at higher

speeds. Fading causes bursts of errors for the duration of a fade, and TETRA compensates for this

by interleaving bits over a timeslot so that the error bits during a fade are spread out in between

„good‟ bits before the error correction mechanism operates on the decoded information. As speed

increases, whereas the fades become closer together, the duration of each fade becomes shorter,

affecting fewer bits. TETRA systems are also used for High speed Train communications in some

countries and operate at speeds of 300 km/h.

6.1 WESTERN RAILWAY SUBURBAN SYSTEM (CHURCHGATE TO VIRAR):

A Tetra based Mobile Train Radio Communication system is commissioned on Mumbai suburban

between Churchgate -Virar in Western Railway. It is the first of its kind on Indian Railways. It has

an intrinsic role in ensuring Safety & reducing delays through effective communication.

Mumbai suburban Section of western railway from CCG to VR covers 64 km. This section

consists of 28 Stations. Electric Multiple Units (EMUs) of 9 cars, 12 cars and 15 car runs between

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Churchgate and Virar. These EMUs are differentiated as slow and fast locals. Slow trains halt at

all stations, while fast ones halt at important stations only and are preferable over longer distances.

Mumbai Suburban EMU fleet consists of 90 rakes running on AC (25 kV) power.

Now, Mumbai local train service to be safer and punctual! In a first, a Tetra based Mobile Train

Radio Communication system has been commissioned on Indian Railways‟ Mumbai suburban rail

network between Churchgate and Virar section, which falls under the Western Railway zone.

According to the Railway Ministry, the Tetra based Mobile Train Radio Communication system is

a first of its kind system on the Indian Railways network. The system, which was inaugurated on

1st March, 2021 on Mumbai suburban section between Churchgate and Virar section, has an

intrinsic role in ensuring safety as well as reducing delays through effective communication.

Following are some key features of the Tetra based Mobile Train Radio Communication system:

The system will provide seamless communication between motorman or guard and

controller or station master and cab to cab of different EMU‟s (electric multiple units).

The system boasts the lowest call setup time for the fastest communication.

The Tetra based Mobile Train Radio Communication system will ensure enhanced safety

as well as reduce train delays

It has been installed in 200 cabs of 100 rakes

Meanwhile, the Western Railway zone is introducing several fully reserved special trains to

various destinations across the country including passenger/DEMU/MEMU special train services

for the convenience of passengers. According to Western Railways, the competent authority has

accorded approval to run a total of 33 special trains with 65 services having a composition with

second general class, DEMU and MEMU coaches as unreserved trains instead of reserved special

trains with effect from 4 March 2021 till further advice. As many as 29 trains of these 33 special

trains will be of passenger train category, while the rest of the three trains will be of Mail/Express

category. The national transporter has requested all railway passengers to ensure social distancing,

wear face masks and follow all other protocols of COVID-19.

6.1.1 Need of Mobile Train Radio Communication for Suburban Trains of Mumbai:

In High Traffic Density Routes like Churchgate - Virar Suburban Section where trains run at

headway of just 3 minutes in peak hours, it is not practical to employ RE like, Socket based

Emergency Communication System, as the time lapsed in contacting Central Control can result

into detention of many trains. Also VHF based Emergency communication does not give facility

for communication between Crew of Running train and Controllers of Control Office. These

factors necessitated the requirement of MTRC in Mumbai Suburban Section. For the very First

Time, a Letter of Agreement for the Work for Analog MTRC in Mumbai Suburban section had

been issued in 1998. The Analog MTRC System was commissioned in the year 2002. The Work

had been carried out by M/s Bombardier Transportation Corporation, as a part of Train

Management System (TMS). This System had been based on Analog (UHF) Radio Trunking

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Technology. The necessary equipment for implementing Analog MTRC had been manufactured

by TAIT of New Zealand. Analog System had been successfully deployed and it served the

purpose throughout its codal life. However by 2010, the OEM-TAIT, New Zealand had stopped

supporting Analog MTRC equipment as its codal life was over. This necessitated a procurement

of a 2nd MTRC System.

6.1.2 Digital MTRC System for Suburban Trains of Mumbai:

Letter of Agreement (LoA) for the work of 2nd MTRC (Digital) System with 2 years of Warranty

and 5 years of AMC worth Rs. 5.98 Cr had been awarded to M/s Consort Digital of New Delhi on

06-02-2014. The 2nd MTRC System is TETRA based Digital technology employing TDMA on

Air Interface and Internet Protocol based Network Architecture with Distributed Switching

Architecture. The System is in service with effect from 01-01-2021.

Major Activities of the Work:

Survey to work out no. of Base Stations and number of new towers (in addition to existing

three towers).

Licenses obtained from DoT for: CMRTS License, WPC License for Frequencies, Import

License, SACFA License for Towers(Clearance required from Airport Authority and From

Defense), Operating License for entire System

Design and Approval for: New Towers (by IIT and WR), Man Machine Interface &

Network Architecture by WR.

Importing of Material after obtaining Import license.

Installation of equipment (Cab Radio, Power Supply, Man-Machine-Interface, Antenna,

Speaker and handset) in 200 Cabs, 6 Base stations, Central Control, Consist of Two New

Towers and One Pole Mast.

Integration with TMS: To develop Software Utilities on TMS and On Gateway PC of

MTRC.

6.1.3 System Components:

1. No. of Base Stations (Includes BTS and BSC): Total 6 (DAMM Cellular): Churchgate,

Mahalakshmi, Bandra, Jogeshwari, Borivali, Virar.

2. No of Existing Towers Utilized: Mahalakshmi (100m), Borivali (70m), Virar (100m)

3. No of New Towers and Pole Mast: 1 Pole Mast (6m) on Churchgate Station Building, Two

Towers (60m each) at Bandra and Jogeshwari.

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4. No of Mobile Radios: Total 205 (SEPURA, UK): 200 for Cabs of 100 Rakes and 5 for

Controllers.

5. Man Machine Interfaces (Consort make): Total 200: For 200 Cabs of 100 Rakes.

6. Dispatchers (Dell Win PCs, with DAMM Cellular GUI Software): 2 for Two Section

Controllers

7. Voice and Data Logger: 1 (Dell Win PC, with DAMM Cellular GUI Software): To record

Call voice and Call Details.

8. Network Management Terminal: 1 (Dell Win PC, with DAMM Cellular GUI Software)

9. Low-Profile Antenna for Mobile Cab Radio: Total 205 (Kathrein Make)

10. DC to DC Convertor: Total 200: (Consort Make) For 200 CAB Radio.

11. Omni Directional Antenna for BTS: Total 12: (Kathrein Make)

12. No of Frequencies: Out of 10 Carriers, 5 carriers have been allocated by DoT for CCG, MX,

BA, JOS and BVI. VR reuses carrier of CCG. Remaining 5 Carriers to be allocated by DoT

after submitting justification of the usage.

The following figure depicts the Tetra network schematic related with CCG-VR link of

WR.

Figure 7 : Schematic of TETRA based MTRC CCG-VR

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6.1.4 Useful Features of Digital MTRC for Suburban Trains of Mumbai:

1) To enable Call Communication amongst: Guard Motormen of same train, Guard, Motorman of

different trains, and Controllers in control office.

2) To broadcast announcements to all trains from Central Control, for motorman guards and/or for

passengers through Guard Intervention, when trains are held-up.

3) Single touch dialing to call any of the Two Section Train Controllers, Dy. Train Controller,

EMU Controller and Emergency call with over-ride facility to call Dy-CTNL.

4) Auto Call Answer for Cab Radios for Motorman and Guards to receive only audio. (Only from

Controllers and call from another cab of same rake)

5) Contact numbers of three controllers (TPC, SIG and TMS) are fed into the phonebook for easy

access while dialing.

6) Motormen/Guards of other trains can be called by first knowing the rake unit number of a

particular train.

6.1.5 Advantages of TETRA based Digital MTRC:

1. Numbering Scheme Employed: Mobile Unit Bears the same number as Rake Number of EMU

rake and Integration with TMS facilitates calling crew of any train by Train Number as shown

on the MIMIC Indication Panel of Train Management System.

2. Efficient utilization of Radio Frequency spectrum (TDMA working, 2 Pairs of Frequencies to

make 7 calls from Cabs to Controllers) their by reducing the License Fee charges.

3. Internet Protocol Based network Architecture, enables monitoring upto the end device.

4. Inter connectivity of BTS and Control Center in Daisy Chain, giving advantage of protection in

case of OFC cut.

5. Quality of Voice is Superior due to Digital Working.

6. Call set-up time in TETRA is lowest in the order of 300ms.

7. Voice Call Recording Facility for one 30 days is available.

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6.1.6 Working of MTRC:

Figure 8 : Network Layout of TETRA based MTRC CCG-VR

a. When Motorman/Guard wants to Call Section Train Controllers, Dy. Train Controller and EMU

Controller, he will press single specific key on the man machine interface provided in the CAB.

The Audio will come from the speaker, for speaking he has to lift the hand-set and speak.

Controllers‟ Dispatcher will give Ring Note. Controller will lift the handset to answer the call.

b. When Section Controller wants to call Motorman/Guard of a particular train, he will select train

number from the GUI of the dispatcher and lift the hand set. Mobile unit of the CAB will give

ring through the Speaker. Call will be Auto Answered. Voice of Section Controller will be

audible from the Speaker and Motorman/Guard will lift the handset if required to speak.

c. In case trains are held up, Section controller can initiate Broadcast call. All Motormen/Guards

of trains will receive Broadcast Call audio from the speaker, handset is not required to be lifted,

and with the intervention of Guard same announcement can be extended for passengers of the

train through PA system of the train for passengers.

d. When Motorman/Guard has to call Motorman/Guard of any train he has to ascertain the rake

unit number and dial the rake number corresponding to the cab.

e. When Motorman/Guard wants to call Sig/TPC/TMS controller he will select contact number

from the phonebook and press dial key.

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6.1.7 Technical system details:

DAMM‟s TetraFlex Solution provides a reliable and complete trunked TETRA

communications system, enabling private and secure voice and data communications across all

activities in Railway operations for increased efficiency and optimized safety. The DAMM IP-

based platform connects all network components – including base stations, dispatchers,

network management tools, external gateways and other applications – in one flat distributed

IP architecture. The DAMM TetraFlex system enables full scalability of both capacity and

coverage. This makes it possible to create integrated communications across multiple stations,

logistics facilities, depots, maintenance facilities and centralized operational control centers.

TetraFlex system‟s easy accessible Application Programming Interface (API) that allows

straightforward development and integration of customer-designed applications.

The details of equipments used for Train control communication are as follows:

A) Train Radio System:

Figure 9 : Train Radio System

● 5” TFT Screen

● Dedicated Emergency Key

● Specially designed for Indian Railways

● 40 Degrees to +85 Degrees

● LTE Technology Compatible

● Membrane Keypads

● Splash proof

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● MMI shall have minimum reading angle 160° at 25°C

B) Train Radio Control Panel:

Figure 10 : Train Radio Control Panel

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C) Network Devices:

● DAMM BS 418/421/422 Base Station

•Base Radio Transceivers

•Soft Switch

● Network Management

● PBX Gateway

● Dispatcher Workstation

● Integration Gateway

Figure 11 : Network Devices

D) Radio Terminals:

● Radios with Class-leading RF power

● Most proven gateway and repeater technology on the market

● GPS/Glonass location tracking

● Integral Bluetooth Option

● SD Data Storage

● Display clearly visible in direct sunlight

● Tamper-proof end-to-end encryption

● 10W RF Power

● Performance monitoring

● Multiple data ports

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● Common user interface with handhelds

● Intelligent call routing in gateway mode

● Tamper-proof end-to-end encryption

● Line in/out audio

● Installed at five allied controls

Figure 12 : SEPURA SRG 3000 Series Radios

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6.1.8 Usefulness of the System:

i. Cases of Trespassing Knockdowns can be communicated immediately on notice which helps in

utilizing the precious moments of golden hour to save the life and to regulate trains to minimize

detentions of other trains.

ii. Motorman can directly communicate defect of EMU to EMU Controller which reduces

detention of other trains.

iii. In case of an un-usual in which no of trains are held up, motormen and guards of trains can be

simultaneously informed through broadcast calls, also passengers of trains can be informed

through announcement through this system.

iv. Analog MTRC had proved its Remarkable worthiness by enabling Control to make calls to

inform motormen and guards of trains held up due to flooding during the 25th, 26th July 2005

deluge, during Mumbai bomb blasts & during many other cases.

7.1 What does the future hold…?

The public safety community, who were one of the driving forces behind the development and

adoption of TETRA, are looking to find ways to provide broadband communications. In most

cases, these are desired to operate alongside TETRA networks, with the TETRA networks

continuing to provide mission critical speech and wide area coverage, and for these broadband

communications to supplement the TETRA services with high speed data services. Considerable

investigation has taken place both with ETSI TCCE (TETRA and Critical Communications

Evolution) and in the TETRA and Critical Communications Association, the sector association.

Early work was carried out within ETSI to define the user services required, and to calculate the

amount of spectrum needed to carry public safety services. It was decided that the mission critical

industry was too small on its own to develop its own radio technology for mission critical

broadband use, and that 3GPP defined LTE (otherwise known as „4G‟) would be the best radio

solution provided suitable enhancements could be made to enhance mission critical aspects.

Additionally, consideration was given to continue mission critical service standardisation, which

started in ETSI TCCE, within 3GPP to embrace the global market. 3GPP responded by starting up

a new working group – the first new group within 3GPP for more than 10 years – which has the

responsibility for architecture for mission critical solutions. This group, SA6, started work at the

beginning of 2015.

Within 3GPP so far, one release (Release 13) has completed the standards work which provides

the first push-to-talk solutions for mission critical use (MCPTT). This first release is an initial step

on the journey, and provides basic PTT speech services. Enhancements are being added in

Release 14, and the first aspects of mission critical video and data are being developed. This may

sound slightly odd, as 4G LTE is already a very good „data pipe‟ for video and data, but it needs

enhancing to provide interoperable, prioritised services and group communications. Due to the

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relatively frequent nature of 3GPP releases

and the complexity of mission critical solutions, it is likely to be following Release 15 in late-

2018 before services are reasonably complete and ready for product implementation for use in

critical situations. This fits well with industry predictions of the first standards compliant mission

critical systems being available around 2020. Meanwhile within ETSI, recognising the need for

interworking between TETRA and mission critical applications over LTE, work has started to

define the interworking standards which will enable TETRA systems to work in parallel with

mission critical applications over LTE.

It is likely that the future of railway communications – both signalling and speech – will lie within

the 3GPP roadmap. Similarly to the public safety community, the rail industry is too small on its

own to develop specific new radio technologies. The first specific rail work study item, Future

Railway Mobile Communication System (FRMCS), is under way in 3GPP and will study whether

the mission critical features already in standardisation can suffice or if more are needed for the rail

community. This study is based directly upon UIC‟s Future Railway Mobile Communication

System – User Requirements Specification. However, mindful of the lessons of the past, a

separate offshoot of a mainstream development is not attractive, and the approach taken by the

mission critical community of developing standardised applications together with the minimum

necessary set of enhancements to the underlying platform is preferable. Of course, by doing this

within the 3GPP standards body, the solutions will also extend to next generation 5G services as

well as the 4G services which are the current baseline. It is hoped, therefore, that the railway

industry can join forces with the public safety community to work within the standards bodies to

find a common mission critical solution which generates the best economies of scale to meet their

mutual needs.

7.1.1 Conclusion: It would not be wrong to conclude that the MTRC system will have an

important role to play in the field of rail transport in the near future as India is entering into a

phase where Bullet Trains are shortly to be introduced starting from small sectors which will

have high speed of more than over 600 Km/Hr. Such high speed trains have a high risk of

derailment and other hazards like failure of signals, communication system, and human failure. To

successfully launch the system of Bullet Trains and to ensure its safe operation, the MTRC

system, undoubtedly, is not just essential, but a must.

Mobile Communication today is a fast growing field. No one can deny its role in Modern Railway

Operations. However there is a need of proper choice of technology looking into Railways'

Operational needs. It is beyond doubt that incorporation of Mobile Communication into Railways

will open new operational avenues, thereby reducing operational costs and increasing customer

satisfaction by providing better services. This shall not only help in increasing productivity, but

also help in increasing safety of operations. This is an age of communication. Indian Railways,

which is a lifeline of the nation, is also geared up to take the requirements of the new millennium,

which is knocking the door of this century…

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References

1) Introductory paper on Tetra technology – Selex Communications

2) Paper on Tetra technology – Emma Sodersrtrom

3) TRAI Recommendations on “Allotment of spectrum to Indian Railways for

Public Safety and Security services” – October, 2019

4) MTRC write-up of WR

5) Information available online.

6) M/s Consort Digital Pvt. Ltd. PPT slides on “Tetra Technology & its applications

in IR”.

7) M/s DAMM Cellular Systems India Ltd. PPT slides on “Overview of Tetra

Technology”

8) TETRA ETSI Manual

9) Testing Specifications Manual ETSI

10) Documents related with the work of TETRA based CCG-VR link of Mumbai

division, WR.

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CAMTECH Publications

CAMTECH is continuing its efforts in the documentation and up-gradation of information on

maintenance practices of Signalling & Telecom assets. Over the years a large number of

publications on Signalling & Telecom subjects have been prepared in the form of handbooks,

pocket books, pamphlets and video films. These publications have been uploaded on the internet as

well as Railnet.

For downloading these publications

On Internet:

Visit www.rdso.indianrailways.gov.in

Go to Directorates → CAMTECH Gwalior → Other Important links → Publications for download

- S&T Engineering

or click on link

https://rdso.indianrailways.gov.in/view_section.jsp?lang=0&id=0,2,17,6313,6321,6326

On Railnet:

Visit RDSO website at 10.100.2.19

Go to Directorates → CAMTECH → Publications → S&T Engineering

Or click on the link

http://10.100.2.19/camtech/Publications/CAMTECH%20Publications%20Online/SntPub.htm

A limited number of publications in hard copy are also available in CAMTECH library which can

be issued by deputing staff with official letter from controlling officer. The letter should be

addressed to Director (S&T), CAMTECH, Gwalior.

For any further information regarding publications please contact:

Director (S&T) – 0751-2470185 (O)(BSNL)

Librarian - 8957022152 (CUG)

Or

Email at [email protected]

Or

FAX to 0751-2470841 (BSNL)

Or

Write at

Director (S&T)

Indian Railways Centre for Advanced Maintenance Technology,

In front of Hotel Adityaz, Airport Road, Maharajpur,

Gwalior (M.P.) 474005

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http://www.rdso.indianrailways.gov.in/

https://rdso.indianrailways.gov.in/view_section.jsp?lang=0&id=0,2,17,6313,6321,6326

http://10.100.2.19/camtech/Publications/CAMTECH%20Publications%20Online/SntPub.htm

mailto:[email protected]



BLANK PAGE

Quality Policy

“We at RDSO Lucknow are committed to maintain and update transparent

standards of services to develop safe, modern and cost effective railway

technology complying with statutory and regulatory requirements, through

excellence in research, designs and standards by setting quality objectives,

commitment to satisfy applicable requirements and continual improvements of

the quality management system to cater to growing needs, demand and

expectations of passenger and freight traffic on the railways through periodic

review of quality management systems to achieve continual improvement and

customer appreciation. It is communicated and applied within the organization

and making it available to all the relevant interested parties”.

INDIAN RAILWAYS


Maharajpur, Gwalior (M.P.) – 474 005

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