SIGNALLING AND TELECOM DEPARTMENT

Signaling and telecom department can be divided into three groups:1) Signaling2) Telecommunication3) AFC( automatic fare collection)

The basic components of telecommunication department can be stated as follows:

1) FOTS( Fiber Optics Transmission System)2) PAS(Public Address System)3) PIDS(Public Information Display System)4) Master Lock5) CCTV(Close Circuit Television)6) Radio System7) Telephone System8) NP SCADA( Non Power Supervisory Control And Data Acquisition)

All of the above are parts of telecom department and have been discussed briefly in later allots. All of them combine to form a highly efficient communication system and all of them are needed for smooth functioning of metro rail.

AFC (AUTOMATIC FARE COLLECTION)

In this we study about the fare collection system of DMRC. The AFC is composed of:

One central computer for all system One station computer for all stations Several equipments of different types( Ticket office machine, bulk

initiation machine, gate, portable ticket decoder)The main features of the Central Computer are:

To communicate with all station computers(SC) To locate the details of the CSC & CST usage, accounts, operational

& auditing data To store the transaction & audit data in order to assume the central

functions based on collected transaction To maintain & distribute the DMRC equipment operating data(EOD)

which includes system parameters fare table & program to the equipment via the SC

To transmit the equipment keys defined by an OCC To perform equipment management To inform operator about the equipment alarms & events To monitor the communication channels between itself and the SCs To provide multiple security access levels To provide time synchronization To provide reports on transport activity

There are different types of equipments used in DMRC, which are as follows:

Ticket Office Machine (TOM): The Tom provides the AFC system with all services involved by the transport ticket delivery to the users. This point of sale terminal is a semi automatic machine manually operated by employees of DMRC. The machine is a standard personal computers connected to different peripherals. The main services of TOM are:

Ticket sale Ticket reloading Ticket refund Ticket cancel Replacements of damaged cards

Bulk Initialization Machine: it provides the AFC system with all services involved by the transport ticket initialization. The machine is a standard PC connected to Ps. Available function enable agents of DMRC Company to answer to the agents. Its main functions are Ticket Initialization and agent & creation.Gate: The excess to the railway lines is controlled by the gate equipment, made up of stainless steel housing. The gate equipment is computer based automatic machine that consists of a stainless steel cabinet managing central retraceable barrier leaf also called flap. The gate allows to check the entrance into the paid area. The gate is linked to the station network in order of dialing with the station computer.Portable Ticket Decoder: it is a small portable device used by the ticket inspectors in order to perform the routine day to day inspection of central station computer & facilitates the passenger survey.

FIBER OPTIC TRANSMISSION SYSTEM (FOTS)

FOTS is the backbone of communication in DMRC. Optic fibers are used in this for transmission of data. Transmission phenomenon is based on the total internal reflection of light rays.

Design considerations:The first step in any fiber optic system design requires making careful decisions based on operating parameters that apply for each component of a fiber optic transmission system. The main questions, given in the table below, involve data rates and bits error rates in digital systems, bandwidth, linearity, transmission distances and signal to noise ratios in analogue systems. These questions of how far, how good and how fast define the basic system constraints.System signal considerations:

System Factor Considerations/ChoicesTransmission distance System complexity increases with

transmission distanceTypes of optical fibers Single mode or multi modeDispersion Incorporate signal regenerators or

dispersion compensationFiber nonlinearities Fiber characteristics, wavelengths

and transmitted powerOperating wavelength 780, 850, 1310, 1550 and 1625 nm

typicalReceiver sensitivity/overload characteristics

Typically expressed in dBm

Detector type PIN Diode, APD or IDPTransmitted power Typically expressed in dBmSource type LED or LaserModulation code AM, FM, PCM, or digitalSignal to noise ratio Specified in decibels(dB)Number of connectors or splices in the system

Signal loss increases with increase in number of connectors or splices

Environmental requirements & limitations

Humidity, temperature, exposure for sunlight

Mechanical requirements Flammability, indoor/outdoor application

TYPES OF OPTICAL FIBRES:There are two basic types of fiber: multimode fiber and single mode fiber. Multimode fibers are best designed for short transmission distances and are suited for use in LAN and video surveillance. Single mode fiber is best designed for longer transmission distances, making it suitable for long distance telephony and multi channel television broadcast systems.

Multimode Fibers:Multimode fiber, the first to be manufactured and commercialized, simply refers to the fact that numerous modes or light rays are carried simultaneously through the waveguide. Modes result from the fact that light will only propagate in the fiber core at discreet angles within the cone of acceptance. This fiber type has a much larger core diameter, compared to single mode fiber, allowing for large number of modes, and multimode fiber is easier to couple than single mode fiber. Multimode fiber can be subcategorized into step index and graded index fiber.

Single Mode Fiber:Single mode fiber allows for a higher capacity to transmit information because it can retain the fidelity of each light pulse over longer distances andIt exhibits low dispersion caused by multiple modes. Single mode fiber also enjoys less fiber attenuation than multimode fiber. Thus more information can be transmitted per unit of time. Like multimode fiber, early single mode fiber was characterized, as step-index fiber meaning the refractive index of the fiber core is a step above than that of the cladding rather than graduated as in graded-index fiber. Modern single-mode fibers have evolved into more complex designed such as matched clad, depressed clad and other exotic structure.

ADVANTAGE OF OPTICAL FIBERS:

As compared to conventional metal wire (copper wire), optical fibers are: Less expensive- Several miles of optical cable can be made

cheaper than equivalent lengths of copper wire. This saves your providers (cable TV, internet) and you money.

Thinner-optical fibers can be drawn to smaller diameters then copper wire

Higher carrying capacity- as these fibers are thinner than copper wires, more fibers can be bundled into a given diameter cable than copper wires

Less signal degradation- the loss of signal is much lesser in optical fibers than in copper fibers.

Use of light signals- Unlike electrical signals in copper wires, light signals from one fiber do not interfere with those of the other fibers in the same cable. This means clearer phone conservation or TV reception.

Low power- because signals in optical fibers degrade less, lower power transmitters can be used instead of high power transmitters that are used in case of copper wires.

Digital signals- optical fibers are ideally suited for carrying digital information, which is especially useful in computer networks.

Non-Flammable- because no electricity is passed through optical fibers, there is no fire hazard.

Light Weight- an optical cable weights less than a comparable copper wire cable. Fiber optic cables takes up less space in the ground.

Flexible- as fiber optics are so flexible and can transmit and receive light, they are used in many flexible digital cameras, in medical field, for mechanical imaging and plumbing etc.

Because of these advantages we see the use of fiber optics in many industries, most notably telecommunications and computer networks. It is for the same reason that this technology is used in DMRC.

PULSE CODE MODULATION

Sampling a band-limited signal at or above the Nyquist sampling rate doesnot destroy any information content and fully characterizes the band limited signal. ASystem transmitting these sampled values of the band-limited signal is called a sampled data or pulse modulation system. In modern communication systems, these sampledSignals are often quantized and coded before transmission. We have pulse codeModulation (PCM).

Figure 1 Single Channel PCM Transmission System

An analogue message m(t) is first sampled at or above the Nyquist sampling rate. These sampled signals are then converted into a finite number of discrete amplitude levels. The conversion process is called quantization. Figure 2 shows how an analogue message is converted into 8 amplitude levels with equal spacing by an 8-level quantizer.

Figure 2 Message And Quantized Signal.

Quantization obviously reduces the degree of accuracy of representation of the sampled signal and introduces some error in the reproduction of the signal at the receiver. Error introduced by the quantiser is called quantization error or quantization noise. To reduce the quantization error, we simply increase the total number of amplitude levels (decreasing the spacing between adjacent levels).If the quantized samples are transmitted directly over a channel, we have a quantized PAM system. If, instead, we code each quantized sample into a block of digits for transmission, , we have a PCM system.

Some forms of PCM combine signal processing with coding. Older versions of these systems applied the processing in the analog domain as part of the A/D process; newer implementations do so in the digital domain. These simple techniques have been largely rendered obsolete by modern transform-based signal compression techniques.

'Differential' (or 'Delta') 'pulse-code modulation' encodes the PCM values as differences between the current and the previous value. For audio this type of encoding reduces the number of bits required per sample compared to PCM by about 25%.

'Adaptive DPCM' is a variant of DPCM that varies the size of the quantization step, to allow further reduction of the required bandwidth for a given signal-to-noise ratio.

Bandwidth Reduction Technique

Binary coding is just one special case of a coding method in a PCM system. In general, we can code a quantized sample into a group of m pulses every T seconds, each pulse with a duration of = T/m seconds and n possible amplitude levels. Clearly, the total number of amplitude levels that a quantized signal can have is M = nm. The ability to choose n and m gives us some freedom to reduce the transmission bandwidth. Figure 3 shows the bandwidth reduction effects when we vary n and m. If n is fixed, we can reduce the transmission bandwidth by reducing the value of m. This is shown in Figure 3(a). If M is fixed, we can reduce the transmission bandwidth by increasing the value of n and reducing the value of m. This is shown in Figure 3(b). The collapsing of successive pulses onto one much wider pulse reduces the transmission bandwidth. However, there is one major drawback for the fixed M case. If the spacing between adjacent levels

is fixed, the required peak power goes up as n increases. On the other hand, if the peak power or amplitude swing is fixed, adjacent levels get closer to each other. This makes easier for noise to obscure adjacent levels. Not a very good bandwidth reduction technique! The technique is only useful for very-low-noise environments.n = 2 is the most noise-immune choice. As we are only dealing with on-off signaling, the exact magnitude is not important. Reshaping of signals by repeaters facilitates the signal decision process at the receiver.

Figure 3 Bandwidth Reduction Technique . (A) Fixed N, (B) Fixed M.

SYNCHRONOUS DIGITAL HEIRARCHY With the advent of semi conductor circuits and the increasing demand for telephone capacity, a new type of communication called the Pulse Code Modulation (PCM) made an appearance in 1960’s. PCM allows multiple use of a single line by means of a digital time-domain multiplexing. The analogue telephone signal is sampled at a bandwidth of 3.1 KHz, quantized & encoded & then transmitted at a bit rate of 64KBPS. A transmission rate of 2.408KBPs results when 30 such coded channels are collected together in a frame along with the necessary signaling operation. The growing demand for more bandwidth meant that more multiplexing were needed through the world. A practically synchronous (or, more properly, plesiochronous) digital hierarchy is the result. Slight differences in timing signals mean that stuffing is necessary when forming the multiplexed signals. Inserting or dropping an individual 64KPBS channel to or from a higher digital hierarchy requires a considerable amount of complex multiplexing equipment. Towards the end of 1980s, SDH was introduced. This paved the way for a unified network structure on a worldwide scale, resulting in a means of efficient & economical network management for network providers. With the introduction PCM technology in 1960s, communication networks were gradually converted to digital technology over the next few years. To cope up with demand for ever higher bit rates, plesiochronous digital hierarchy (PDH) evolved. The bit rates starts with the multiplex rate of 2 MBPS with further stages of 8, 34, 140 MBPS. Because of these different developments, gateways between one network and another were difficult and expensive to realize. The 1980 saw a start in development of the SDH with the intention of eliminating the disadvantage inherent in PDH.The minimum value of data to be realized in SDH is 2 MB. So, we have to use an additional multiplexer if a data of value smaller than 2 MB is to be entered in the SDH. This multiplexer multiplexes smaller data into a size of 2 MB. The SDH of different stations form a ring. This ring consists of the SDH equipment and two sets of wires- one for incoming data and one for outgoing data. The work of the ring is that when one path breaks, communication may continue through the reverse path. One such ring includes 6 to7 stations.

Advantages of SDH over PDH:1) high transmission rate2) simplified add & drop function3) high availability & capacity matching4) reliability5) future proof platform for new services6) interconnection

PIDS (PASSANGER INFORMATION DISPLAY SYSTEM)

This system allows passengers to know when the train is expected to arrive, time left as well as the destination of the train. This system also allows the data input transmission and diffusion of information concerning the movement of train in real time to all station users and the same for the application in the main centre using Ultra Bright LED Display Panels. The system has capability to control virtually infinite number of stations, which can be done by the configuration of network design. This system has several functions such as displaying train scheduling information & data related to train circulation like arrival and departure time.

The system is divided into two main parts:1) BLOCK (OCC)- All the equipments installed in the OCC the details

of which are Server, Assistance to chief controller PIDS/PAS workstation & PIDS control backup control panel.

2) STATION SYSTEM: this refers to all equipments installed in the terminal station, which includes Work Station, Ultra Bright LED Display Panels.

Features of PIDS are:1) Simple to use2) It gives information in real time, in a clear attractive way, to the

station through the usage of LED with matrix display on serial link3) It simplifies the maintenance operations through the possibilities of

help in diagnosis offered by the central system responsible for the display.

4) It is based on standard wide spread computer equipment & on the structured & modulated software. The software allows the possibilities of adapting it to the further needs of the railway station,

inter connection with other computer system, adding new functions, etc.

The station function is relevant to make the audio programmed signal available & the digital to analogue conversion. It will also dispatch to the required zones, all the messages maintaining a hierarchy priority scheme between the stations.

PAS (PUBLIC ADDRESS SYSTEM)

The PAS is one of the systems that creates a user friendly ambience in the DMRC computer services and it plays a very important role as well. It is provided to broadcast voice message to passenger/staff in all stations, depots &OCC & DMRC headquarters.It shall be used for emergency evacuation broadcast in case of emergencies. It has control equipment located at the equipment room of each station depots, OCC and DMRC HQ. the station PAS shall be interfaced to FOTS for connection to the equipment located in CER to facilitate control from OCC. The PAS at depots shall be stand-alone without any control from OCC. At station it is asserted from:

Platform supervisory booth (PSB) Station Control Room (SCR) OCC

It shall be capable of maintaining required intelligibility at all times regardless of changing environment including crowd, density, temperature, humidity &noise level.This system collects data from TIMS (Train Information Management System), which is something similar to a train timetable, and as per the present time it sends information to the system and announcement is made. This is one of the reason that a universal clock is needed, and thus the system is incorporated with a master clock server.The scheme is such that, the train driver has information about timing and he has to see that a train reaches a particular station as per the time frame, it has been allotted, which is similar to northern railways. The thing which makes it a bit different from the railways is that, this time table is a static one & so is fixed &totally computerized, while that in railways is a dynamic one& is user controlled.The present addressing scheme is in the following way:

1. when the countdown reaches two minutes, then there is an announcement about the train timing and its platform

2. Exactly at the end of the countdown, it makes an announcement that the train is going to leave the platform.

3. In the case of the announcement that is to be made from the SCR, it can be made by using the system that is available in their control room.

4. From the OCC, the operator can select s station and the platform in which the announcement is to be made.

The PAS system works in three modes:1) Automatic mode- The diffusion of messages will be held through a

weekly scheduled program. In automatic mode, the PAS central system receives messages from the central passenger information system involving data about train movement. The information is analyzed by the PAS that automatically launches announcements to the designated stations. Each issued message will interrupt another of lower priority being diffused. The interruption will signal locally to the equipment trying to access the system. The connection between the OCC and each station will be established through FOTS channel.

2) Manual central mode- The system will be operated through the OCC that will direct manual messages to the microphones.

3) Manual Local Mode- The station operator, independent from the OCC, will control the system. The local PAS at each train station is able to accept signal from the local exchanger Net Client Unit to activate prerecorded announcement from the train station.

The different types of messages provided by PAS are: Fixed messages Pre formatted with data to be added Instantly recorded Live audio broadcast Priority of PAS announcement Live audio broadcast from PSB Live audio broadcast from SCR Live audio broadcast from OCC Announcement initiated from TCS Pre formatted messages from SCR/OCC.

RADIO SYSTEMS:

System Overview:

The radio system is one of the most important parts of the DMRC. It enables us a choice when the FOTS breaks down (which is the worst case). So it adds a level of redundancy to the communication network of DMRC.It has all the features of the radio that is used in communication and resembles the mobile communication. The whole communication between the source and the destination does not take place through FOTSThe Motorola Dimetra (Digital Motorola European Trunk Radio) System is sophisticated radio equipment having full benefits of TETRA standards. Its system components can be easily reprogrammed to meet the future requirement of new technology. All available traffic channels are shared between all radio users.Frequency band used in DMRC network is from 380-400 MHz. For receiving, the signal it uses frequency band of 380-385 MHz and for transmission it uses a band of 390-395 MHz.Dimetra system is a time division multiplexed access (TDMA) system which enhances operation in trunking operation, as well as frequency can be shared with the traffic signals in different time slots. Dimetra is a flexible system. A single site system can grow into a larger multisided system and up gradation of existing to future enhanced Dimetra system can be done in a flexible manner.Group organization:Radio users are organized into groups. When a user placed group calls the user in the group can listen and outside so channel efficiency increases by proper group assignment.Trunking operations:This operation has three parts. Here in trunking operation there is one control channel and other many voice channels. The trunking works on TDM.Trunked call completion:When a call is finished, the subscribers in the talk group return to monitoring the channel and channel becomes available for others.

TYPES OF MODES OF COMMUNICATION:

There are two types of communications mode used in DMRC netwok:

1. Trunk Mode Operation: this mode of operation consists of three communication modes;

Group Mode: It is a half duplex communication mode in which many users can communicate each other by selecting a common talk group. The operation is as follows: 1) select a talk group to communicate. 2) Press PTT (Press To Talk) to speak. 3) Release PTT to listen.

Private Mode: It is a half duplex communication mode in which many users can communicate with each other privately without interfering the talk group. The operation is as follows: 1) Select the private mode by using mode key in radio. 2) Dial private ID. 3) Press PTT and release. A ring will be heard. 4) Press PTT to speak. 5) Release PTT to listen.

Phone Mode: it is a full duplex mode communication in which a radio user can talk to any dialed phone number within DMRC or external network connected to DMRC. It can also communicate in reverse direction, i.e., from phone to radio. The operation is as follows: 1) Select the phone mode by using mode key in radio. 2) Dial phone number 3) Press call/cancel key. 4) Talk when call is established. 5) Press call/cancel key to end call.

2. Direct Mode Operation: in its basic form, DMO represents direct communication between two or more TETRA DM terminals/mobile stations (DM-MS) without the use of trunking network infrastructure. The simplest form of DM is two-way communication between two or more MS terminals, back-to-back.

Types of radios used in DMRC network:1. MTP 700 (hand portable)2. MTM 700 used in station radio (zetron)3. Train radio4. RCW (Radio Work Station) in OCC

1) MTP 700: MTP stands for Motorola Tetra Portable. It looks like a mobile phone. In this we have different types of modes, which are explained above. It has different functions, which can be operated by pressing menu button.

2) MTM 700: MTM stands for Motorola Tetra Mobile. It is used in two different phases, i.e., station control room and train. It has the same function as that of MTP700. it seems like a telephone set & that set is known as ZETRON set. It is also used as a train radio.

The MTP700 hand portables are based on the new generation radio platforms incorporating the latest Digital Signal Processors (DSP) and Linear RF Power Amplifier technology.The ergonomically designed, ruggedised hand portables come with 3x4 keypads, rotatory switch dial, and a LCD for number dialing and maximum flexibility. Each hand portable is equipped with ultra high capacity batteries for longest standby and talk time of 24 hrs, i.e. 5% transmit, 5% receive and 90% standby. Each one comes with a remote speaker microphone lapel for easy communication.

TRAIN RADIO

Radio Control Head

Upon power on- DMRC TRIU VER X.XX will first appear and subsequentlyFirst line - TID\RAKE ID SEC CONTROLLERSecond line – Current Talk group (TG)

Radio Voice Functions

1. Talk group callIt is a half duplex call and is one to much communication.

2. Emergency callPress emergency key, the alarm shall go to TC\OCC.Press emergency and also press PTT alarm will go to all in that TG.To cancel emergency, press and hold the "X" button on the RCH until the emergency indicator disappears.

3. LED indicatorsSolid green – In useFlashing green – In serviceSolid red – Out of serviceFlashing red – Connecting to the network at power onFlashing amber – Incoming callNO INDICATION – Switched off

DIVERSITY

As we go higher into the air from the ground surface, the density of air progressively decreases. Now, when a signal (wave) moves through the air, it continuously deviates from its original line of propagation.

The amount of deviation depends on the frequency of the propagating signal(wave).The consequence of this deviation is that the antenna might not get proper reception due to fading signal(wave).

Types of diversity:

A. Frequency DiversityThe signal is transmitted at two different frequencies so that even if one of the frequencies fails to give proper reception, then the other frequency would give the proper signal reception.

B. Space DiversityTwo RX antennas are installed, which are placed separately either vertically or horizontally in space.

a.)VERTICAL DIVERSITY b.)HORIZONTAL DIVERSITY

FINAL LINE OF PROPOGATIONORIGINAL LINE

OF PROPOGATION

C. Route DiversityTX from A to B can be done through any of the three different TX routes. Depending upon the persisting conditions at the moment (natural and man-made conditions which effect TX), the best route for TX of the signal is taken.

POINT “A”POINT “B”

ROUTE NO. 3

ROUTE NO.2 THROUGH OFC

ROUTE NO. 1

REMOTE CONTROL WORKSTATION (RCW)

It is also known as theatre room. As the name implies its function is to control all the activities like overhead power lines, rolling stock, fault management and others. It consists of following sub-units.

Traction Power Controller(RC)

Overhead lines power management on which trains run .power for metro is taken from two different grids of BSES.

Rolling Stock Controller:

It checks for the fault other than signaling and radio communication problem. Here faults of mechanical type like brake failure, MCB failure are handled.

Fault Management Controller :

Its function is to handle signaling and radio communication problem.

Time Table Management Auxiliary System Controller Traffic Controller :

Using real time software traffic controller can see the status of all RBs (radio base station). Talk group status and can even make contact on train. for contacting on train or other RBs if the real time software fails than there is a Zetron set through which contact can be made which further adds to the level of redundancy .

Traffic controller can do the following functions:

Private call(PRV) Interrupt call(INTP) Check(CHK) Message (MSG) Press to talk (PTT to make group call)

It also can view the train location on real time basis. It has the capability to hear voice inside the cab through centracom gold series i.e. do ambience. The zetron set is already described in SCR.

NP-SCADA (NON POWER SUPERVISING CIRCUIT AND DATA ADMINISTRATION)

1) It monitors various equipments of Rail and Metro Corridors 2) Provides data/information to maintain staff to access the need for

unscheduled preventive maintenance.3) In addition to above facilities, recording, analysis & printing of data

for effective maintenance.

Various systems monitored by NP-SCADA are:1) Rail Corridor:

Rail temperature at selected location. LV circuit at depot.

2) For Metro Corridor: Fire Detection And Suppression Systems Lifts And Escalators Pumps Environment Control System Seismic Activity System Intrusion Alarm Tunnel Ventilation system

Equipments to be monitored through NMS at OCC or Directivity: Master Clock System Fiber Optic Transmission System Telephone System Radio System Public Address System Passenger Information Display System Closed Circuit TV System UPS System

REFERENCE:

Radio manual (MTP/MTM) SDH manual (1660/1650) Alcatel manual www.delhimetrorail.com

ACKNOWLEDGEMENTS

I would like to express my regards and would like to thank following persons, without whom, this project would not have been possible:

Mr. D.K. Sinha, DGM, S&T, DMRC Mr. K.D. Sharma, Manager, Telecommunication dept. , DMRC Mr. Alok Ranjan, Assistant Manager, Telecom. dept. , DMRC Mr. Rajkumar Verma, Senior System Analyst, DMRC Mr. Rajkumar Meena, Senior System Analyst, DMRC