white paper - cbtc connectivity solutions (1)

8/11/2019 White Paper - CBTC Connectivity Solutions (1)

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Edition 2011

CBTC Connectivity SolutionsWhite paper


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Simplified 3D overview of a radio-based CBTC system architecture

Reliable RF and FO connectivity solutions


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Train control enhanced by moderncommunications technology

The overall performance of a rail rapid transit system depends largelyon the performance of the automatic train control (ATC) systememployed. A communication-based train control (CBTC) system is

devised by adding modern communication technologies to the ATCconcept.CBTC signalling is currently standardised in accordance withIEEE 1474.1 and has become the reference technology for metrooperators worldwide.

IEEE defines CBTC as a continuous automatic train control systemutilising

High-resolution train location determination, independent of trackcircuits

Continuous, high-capacity, two-way train-to-trackside datacommunications

Trainborne and trackside processors capable of performingessential functions

Train control enhanced by m oderncommunications technology

Radio-based CBTC

Connectivity components for backbonenetworks

Connectivity compo nents for radionetworks

Trackside equipment

Trainborne equipment

Conclusion

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Radio-based CBTCConventional ATC systems divide the railway track into fixed sections which are separa-ted by signals and signalling is automated by means of fixed balises, which act in a similarway to induction loops or RFID transponders. Due to the static nature of this system, thesections are called fixed bocks.

Radio-based CBTC enables continuous two-way digital communication between eachtrain and control centre. The control system benefits from enhanced information such astrain performance data and continuous train position and speed. Systems of this type cantherefore implement dynamic distance control, basically making the block locations andlengths consistent with individual trains. This is known as the moving block approachwhose most valuable benefit is to increase the capacity of a given line by reducing signifi-cantly the time interval between trains (headway).

Radio-based CBTC is based on a two-way communication network consisting of threeintegrated networks:

Backbone network

Radio network

Trainborne networkIn radio-based CBTC systems, the radio network comprises the trainborne radio andantenna equipment and trackside radio access points. Two alternative scenarios arepossible for the transmission and reception of the wireless signal by the trackside radioaccess points:

The waveguide scenario: radio waveguides or leaky cables are installed along thetrack

The free propagation scenario: antennas are positioned at distinct points along thetrack

This paper focuses only on the free propagation scenario, which tends to be the mosteconomical and flexible in terms of deployment and maintenance. In specific projects, thewaveguide scenario may, however, be chosen due to specific site or customerrequirements

ATC fixed block architecture

ATC moving block architecture


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CBTC connectivity s olutions

Connectivity components for backbone networks

The physical layer of backbone networks consists of single mode fiber optic cableshaving a relatively high capacity (e.g. 96 fibers) and specific characteristics due to theoperating environment (tunnels and/or outdoor installation). In particular, these cablesmust be made of selected sheath materials in order to

Comply with stringent f ire and smoke performance requirements

Resist fluids such as acid, alkali and tunnel-cleaning products

Be protected against rodents (armoured cables)

In the technical rooms or at interconnect points, the fiber capacity of these cables isorganised into fiber management systems in order to ensure safe, user-friendly anderror-free interconnections with any type of service and application.

Connectivity components for radio networks

Instead of developing proprietary radio technology, radio-based CBTC systemsimplement the IEEE 802.11a/g/p/n protocol (WiFi/WLAN). As it is an open standard,there is no supplier lock-in and components can be purchased off-the-shelf.The radio networks typically operate in the 2.4 GHz or 5.8 GHz frequency ranges.There are different advantages to using these microwave frequencies: First of all, micro-waves propagate very well in tunnels, and, secondly, these frequency bands are globallyavailable.With the free propagation scenario, an antenna network distributed along the track isused to exchange data with the trains via their on-board vehicular antennas. The train-borne ATC equipment continuously exchanges messages with the trackside ATC equip-ment as long as the wireless communication link is maintained. However, if a train loses itscommunication link, the ATC functions must ensure that the overall system is brought into asafe state, e.g. the trainborne ATC functions might apply a service braking.A redundant radio network is implemented in order to increase operational securit y,reliability and availability. This is indicated in the following figures by the red and bluefiber optic connections and the red and blue radio wave indications. Only one network isactive at a time (red or blue), the other one being in quiet back-up mode ensuringoperation continuity.Nevertheless, in order to guarantee system availability and operational efficiency, it iscrucial that every single connectivity component in the communication chain continues tooperate regardless of external factors such as environmental, mechanical or operation

constrains.In terms of hardware, train-to-track radio networks consist of two parts: the tracksideequipment and the trainborne equipment.

Example of an armoured fiber optic backbone cable


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Trackside equipment

Trackside equipment is built from radio access points distributed along the tracks atintervals ranging from several tens of meters to several hundreds of meters, dependingon the track topology, e.g. curves, straight sections, obstacles, etc. Subject to installationconstraints, The radio access points and its complementary equipment can be mounted,e.g. on a mast.

Example of trackside mast a rchitecture


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Fiber optic connectivity

The radio access points are linked by dedicated, redundant fiber optic distribution loops,thus ensuring high communication safety and availability level in a given zone area. Thezone areas are linked by the backbone network and each zone is under the control of azone controller.While the fiber capacity of the backbone network is relatively high, that of the distributionloops is generally lower (e.g. 12 or 24 fibers), as the zone areas are limited in size. Alter-natively, Cat5 or Cat6 copper cables can be used for the dist ribution loops in the zoneareas. However, fiber optic is often preferred for its intrinsic electromagnetic immunityproperties and because of unequalled low signal attenuation.The radio access points are often directly equipped with a fiber optic connector interfacewhich enables direct connection to the fiber optic distribution loop. Such connectors

must have high IP ratings (typically IP 67/68), robust design for harsh environments, andcompact footprints.

In some cases, the radio access point is equipped with copper-based electrical Ethernetports and a media converter is required in order to convert the electrical signal into anoptical signal.The actual connection between the trackside radio and the fiber optic distribution loopis achieved by using branching fiber optic cables. It is beneficial to use branching cableswhich are pre-terminated with fiber optic connectors for the trackside radio connection,providing a time-saving plug-and-play connection system. This may be missioncritical,since in most projects the implementation of new signalling equipment must be achievedwithout operational disruption, i.e. during limited time slots during the night.

On the backbone connection side, branching cables are generally connected to the

distribution loop cable by means of fusion splicing. The splice points are protected bydedicated splice closures having high waterproofing characteristics.

Compact IP 67/68 ODCfiber optic connector

Pre-terminated MASTERLINE fiber optic cable system


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For the connection of the fiber optic distribution loops to the backbone network optical

distribution frames are used. These are installed in technical rooms, e.g. located in railwaystations.

Radio frequency connectivity

The trackside radio access point is equipped with robust radio frequency (RF) coaxialconnectors to enable connection to the trackside antennas via RF feeder and jumpercable assemblies. RF power splitters are required in order to implement the safetyredundancy architecture.

RF power splitter Trackside antenna

All RF components and assemblies in general must withstand harsh environmentalconditions. Specif ic requirements due to operating conditions must be carefully evaluatedby the system designer. These may include, for example, air pressure pulses in tunnelinstallations due to approaching trains, risks to RF or CAT5 signal lines from lightning orfire.

Typical environmental requirements are:

Vibration and shock resistance

Enhanced fire performance for use in tunnels

Resistance to humidity

Protection against water IP rating

Wide temperature ranges

Solar radiation

Salt mist

Important functional requirements are:

Directional gain of antennas (low and medium gain)

Low attenuation of RF cables

High return loss of RF antennas, cable assemblies, and RF components

Example of a LiSA optical distribution frame


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Trainborne equipment

Due to the two-way operation of the trains and redundancy requirements, both driverscabs are equipped with the same setup, i.e. on-board ATC equipment and radio modems.Vehicular directional antennas are installed in the near area of each drivers cab and areconnected to the radio modems via RF low-loss cable assemblies. The radio modemsprovide the communication signal to the on-board ATC equipment.

Both antennas and RF cable assemblies must comply with the requirements of the rollingstock industry for on-board electronic equipment (EN 50155) as well as fire safety require-ments (e.g. CEN/TS 45545, NF F 16-101, DIN 5510, BS 6853, UNI CEI 11170).

Connectivity components for trainborne networks

The on-board ATC equipment in both drivers cabs continuously checks with each otherthat it receives identical information from the trackside ATC equipment. The requiredcontinuous communication is provided by a dedicated on-board CBTC bus also calledbackbone network.

State-of-the-art Ethernet backbones can be implemented as copper Cat5, Cat6 orfiber optic cabling. They must obviously also meet special fire and smoke requirements,e.g. according to the railway standard CEN/TS 45545 but also provide a sustainablemechanical robustness at the connection points between the train vehicles as these areasare exposed to high levels of environmental stress (dynamic movements, high temperaturevariations, water, etc,).

RF connectivity to vehicular antenna

On-board network backbone


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ConclusionContinuous two-way train-to-track communication is essential for ensuring the reliability ofa CBTC system. Failures in communication have an immediate impact on train operation.One of the key performance indicators for CBTC system suppliers is system and trainavailability.For these reasons, radio frequency and fiber optic connectivity components implementedin such systems must be selected with great care. They must be capable of withstandingsevere environmental conditions and meeting demanding functional requirements.HUBER+SUHNER delivers excellent radio frequency, fiber optic and low frequencyconnectivity solutions for both rolling stock and infrastructure applications. The companyalso offers customized solutions. HUBER+SUHNERs engineering teams are made up of

experienced specialists who have direct access to the comprehensive know-how of thegroup.

Project references

Brazil: Metro Sao Paulo Lines 1, 2, 3Canada: Toronto TTC Y-U-S LineChile: Metro Santiago L1China: Metro Beijing Line 2China: Metro Shanghai L10Italy: Metro Milano Line 1Mexico: Metro Mexico Line 12

UAE: Metro Dubai Red Line

Authors

Eric Louis-Marie Market Manager Railway, Fiber Optic DivisionDr. Peter Nuechter Market Manager Transportation and Industrial,

Radio Frequency Division


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Find more information in our catalogues

Train-to-shore communication

Item no. 84112422

Fiber OpticCabling SystemsItem no. 84104358

Railway products

Item no. 84110507

Edition2010/2011

Fiber OpticCabling Systems


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white paper - cbtc connectivity solutions (1)

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