Railway Signalling using Wireless Sensor Networks

Railway Signalling is safety critical domain, where still traditional technology is in use. There are many reasons for using traditional technology; one of the main reasons being the proven Safety performance of the older systems (Relay Based). As the rail traffic is increasing and with higher speed of trains there is an acute need for modernization of Railway Signalling Technology. Even with the advent of Microprocessor based technology, the problems have not been solved. The current railway signalling technology involves huge amount of physical wiring used to receive inputs and drive outputs to the field functions, which is very difficult to maintain and up-gradation of this infrastructure is every signal engineer's nightmare. This paper proposes the use of Wireless sensor networks in Railway Signalling domain which combines the Ground base signalling and the On–Board Signalling using customized routing algorithm, which is suitable for high Speed Railway Traffic which reduces the physical wiring to the bare minimum by applying distributed architecture to the field functions which are connected by Wireless Network.

The most important part of the railways is to carry out operations like safe movement of trains, this is achieved by Signalling. The Railway signalling is governed by a concept called Interlocking. Many interlocking system still in use follow either relay based technology or the Microprocessor based technology called Electronic Interlocking System (EIS). Relay based systems are very huge in size and have cumbersome wiring to perform operations. The advent of Electronic Interlocking systems reduced the relays and wiring to some extent, but still uses traditional copper cabling to be connected to the field functions such as signals, Track Detection equipment, points (Switches). In modern signalling systems, the signal and switch status needs to be sent to the On-Board Computers in the locomotives, this involves traditional radios connected to the wayside field functions that communicate this information to the OBC. This involves laying out track loops or balises that send this information to the OBC, these loops are venerable to climatic conditions such as ballast resistance, water flooding during rains, etc. Due to the failsafe nature of these systems the cabling has to be redundant, this results in large maze of complex wiring that is very difficult to maintain and upgrade. There is need to upgrade the existing Railway Signalling Infrastructure and addition of new technologies like failsafe wireless communications which shall combine both the ground based signalling (Interlocking Systems) and the Locomotives (On Board Computers of the train) which directly leads to simple distributed architecture which are highly maintainable and easy to upgrade in future.

Safety Integrity Levels

Real Time Data Processing Techniques

Various Signal Processing Techniques are available for analysis of real time data relative to reference data:

 

Data Cluster method – This involves recording the characteristics of a parameter of a subsystem under different simulated conditions and then using this as a reference to validate the real time data. This method is different from template matching, since it not entirely based on matching the plotted characteristics.

 

Template matching – Entails comparing complete data sets with pre-recorded examples of data resulting from known fault conditions. The method can be used effectively in some circumstances, provided a representation of the data that produces good discrimination between pattern classes can be made. However, this requires a substantial amount of experimentation with different transformations of the data sets to find such distinctions, and would be a computationally intensive process.

 

Statistical and decision theoretic methods – Matches are made based on statistical features of the signal. For example, the mean and peak-to-peak value are evaluated for each vector, and plotted in feature space, whereby different patterns are distinguishable because they form clusters for each class that are located apart from the fully functioning case.

 

Structural or syntactic methods – Involves deconstructing a pattern or vector into structural components, to enable comparisons to be made on more simple, sub-segments of data rather than a complete vector. Mathematically, these methods are similar to fractal-based compression routines.

 

Principles of Train working and need for Signalling

All over the world Railway transportation is increasingly used, as this mode of transport is more energy efficient and environmentally friendly than road transportation. Trains move on steel rail tracks and wheels of the railway vehicle are also flanged Steel wheels. Hence least friction occurs at the point of contact between the track & wheels. Therefore trains carry more loads resulting in higher traffic capacity since trains move on specific tracks called rails, their path is to be fully guided and there is no arrangement of steering. Clear of obstruction as available with road transportation, so there is a need to provide control on the movement of trains in the form of Railway signals which indicate to the drivers to stop or move and also the speed at which they can pass a signal. Since the load carried by the trains and the speed which the trains can attain are high, they need more braking distance before coming to the stop from full speed. Without signal to be available on the route to constantly guide the driver accidents will take place due to collisions.

 

There are basically two purposes achieved by railway signalling.

1. To safety receive and dispatch trains at a station.

2. To control the movements of trains from one station to another after ensuring that the track on which this train will move to reach the next station is free from movement of another train either in the same or opposite direction. This Control is called block working. Preventing the movement from opposite direction is necessary in single line track as movements in both directions will be on the same track.

 

Apart from meeting the basic requirement of necessary safety in train operation, modern railway signalling plays an important role in determining the capacity of a section .The capacity decides the number of trains that can run on a single day. By proper signalling the capacity can be increased to a considerable extent without resorting to costlier alternatives.

THE COMPUTER BASED INTERLOCKING SYSTEM ARCHITECTURE

Generally following two types of redundancy techniques are used for achieving fail-safety

in the design of signaling systems:

Hardware Redundancy – In this case, more than one hardware modules of identical design with common software are used to carry out the safety functions and their outputs are continuously compared. The hardware units operate in tightly syncronised mode with comparison of outputs in every clock cycle. Due to the tight syncronisation, it is not possible to use diverse hardware or software. In this method, although random failures are taken care of, it is difficult to ensure detection of systematic failures due to use of identical hardware and software.

 

Software Redundancy – This approach uses a single hardware unit with diverse software. The two software modules are developed independently and generally utilize inverted data structures to take care of common mode failures. However, rigorous self check procedures are required to be adopted to compensate for use of a single Hardware unit.

 

Hybrid Model - The hardware units have been loosely synchronized where the units operate in alternate cycle and the outputs are compared after full operation of the two modules. Therefore, it is no more required to use identical hardware and software. Although the systems installed in the field utilize identical hardware and software, the architecture permits use of diverse hardware and software. Moreover, operation of the two units in alternate cycles permits use of common system bus and interface circuitry.

 There are two methods of programming the SSI for a particular station, namely – Geographical Programming & Free-wire Programming. Most of the SSI systems adopt geographical programming where Control Table of the station is fed to the SSI system. This gives great relief to the user as he is not required to make the circuit diagram, data for any station can be programmed very easily. However, this method does not provide flexibility in terms of change of interlocking practice or interlocking rules. Adoption of change in interlocking practice of a particular railway requires changes to be made in the executive software and entails revalidation of the software. On the other hand, Free-wire programming, which requires circuit diagram to be prepared for each station and programmed into the EPROM as Boolean expressions, provides total flexibility as any given circuit can be programmed without touching the executive software. The price, however, is to be paid in terms of preparation of circuit diagram for each station.

Need of Electronic Interlocking System (EIS) for Indian Railways

Indian Railway is in acute need of Electronic Interlocking System for many reasons. The design and the verification process of these signalling systems needs to be inline with the (European Standards) CENELEC standards, which over the time have proven their usefulness in dealing with vital equipment. Apart from all these, the Indian railway has its own needs, which are quite different from other countries.  There has to be indigenous solution to these problems. The below points try to describe the attributes of an indigenous developed EIS

 

1. To improve the safety standards and increase the revenue by increased line speeds.
2. To invest less in maintenance of signalling infrastructure and thereby increase the profits.
3. To decrease the installation and commissioning time compared to RRI.
4. To give the flexibility in changing the software, whenever there is change in the yard layout.
5. To give flexibility of centralized control from operations control centre , instead of localized control panels
6. To decrease the burden on operators and maintenance staff by giving warnings about the signalling equipment due for replacement.
7. To give more flexibility for the maintainer to sit at his desk and monitor the yard.
8. To eventually move from localized operations to Computer aided dispatch systems (CAD)
9. To support a supervisory control centre, to look at movement of trains.
10. To support coded track circuits in future for ATP operations in locomotive.
11. To eliminate the use of separate data and event loggers.
12. To support the interface to web browsers to supervisory activities.
13. To eventually support CAB signalling to communicate with trains.
14. To support delivery of automated messages to control centers in case of device malfunctions.

 

 

What is ERTMS - Introduction

The European Railway Traffic Management System (ERTMS) is a major industrial project developed by six UNIFE members – Alstom Transport, Ansaldo STS, Bombardier Transportation, Invensys Rail Group, Siemens Mobility and Thales – in close cooperation with the European Union, railway stakeholders and the GSM-R industry.

ERTMS has two basic components:

• ETCS, the European Train Control System, is an automatic train protection system (ATP) to replace the existing national ATP-systems;
• GSM-R, a radio system for providing voicGSM-R, a radio system for providing voice and data communication between the track and the train, based on standard GSM using frequencies specifically reserved for rail application with certain specific and advanced functions.

ERTMS aims at replacing the different national train control and command systems in Europe. The deployment of ERTMS will enable the creation of a seamless European railway system and increase European railway's competitiveness.

Why does Europe need ERTMS?

Currently there are more than 20 train control systems across the European Union. Each train used by a national rail company has to be equipped with at least one system but sometimes more, just to be able to run safely within that one country.

Each system is stand-alone and non-interoperable, and therefore requires extensive integration, engineering effort, raising total delivery costs for cross-border traffic. This restricts competition and hampers the competitiveness of the European rail sector vis-à-vis road transport by creating technical barriers to international journeys. For instance, the Thalys train sets running between Paris-Brussels-Cologne and Amsterdam have to be equipped with 7 different types of train control systems, which brings considerable costs.

A unique train control system for Europe and beyond

As a unique European train control system, ERTMS is designed to gradually replace the existing incompatible systems throughout Europe. This will bring considerable benefits to the railway sector as it will boost international freight and passenger transport.

In addition, ERTMS is arguably the most performant train control system in the world and brings significant advantages in terms of maintenance costs savings, safety, reliability, punctuality and traffic capacity. This explains why ERTMS is increasingly successful outside Europe, and is becoming the train control system of choice for countries such as China, India, Taiwan, South Korea and Saudi Arabia.

By making the rail sector more competitive, ERTMS helps to level the playing field with road transport and ultimately provides significant environmental gains.

 

Bombardier Unveils First Contactless Tram

In a bid to improve energy use and create a more aesthetically pleasing railway, Bombardier has introduced its first completely contactless and catenary-free operating tram. The new train, which uses a contactless power supply and no overhead power lines, incorporates Bombardier's PRIMOVE inductive power transfer technology as well as the integrated MITRAC Energy Saver, which provides cost reductions by recharging energy. Director of advanced technology development at Bombardier, Dr Carsten Struve, said that unique technology used in the tram would provide energy savings and eradicate ugly overhead power lines. "The catenary-free operation offers an entirely new prospect, particularly for trams operating in historic city centres where impressive cityscapes can now exist unencumbered by visual pollution from overhead lines," Struve said. "Combined with the new Bombardier MITRAC Energy Saver technology, the PRIMOVE system can also save additional energy." The PRIMOVE technology system uses principles found in transformer technology with electric power components hidden under the vehicle and beneath the tracks to produce energy for the tram's operation. This makes the system easier to install, eliminates the effect of weather conditions, reduces wear on component parts, and allows the tram to operate with lower noise levels and fewer emissions. The vehicle is equipped with pick-up coils underneath the vehicle, which are connected to the tram's traction system through a cable. The vehicle is only energised when the connected ground segments are fully covered by the vehicle, ensuring safe operation in areas such as pedestrian zones.  The MITRAC energy saver uses a pair of innovative capacitors, which store the energy released each time the vehicle brakes and reuse it during acceleration or operation. The system, which attaches to the tram's roof, been proven to save up to 30% of energy, reducing emissions as well as costs. The PRIMOVE technology system is part of the BOMBARDIER ECO4 portfolio of technologies launched by the company last year.

Challenges in using Wireless Sensor Networks in Railway Signalling

The use of Wireless Sensor Networks in a safety critical Domain like Railways signalling poses challenges in implementation and Operation. Some of the issues and challenges are discussed in this chapter.

 

1. Sensor network communications must prevent disclosure and undetected modification of exchanged messages. Due to the fact that individual sensor nodes are anonymous and that communication among sensors is via wireless links, sensor networks are highly vulnerable to security attacks.

 

2. The gateway nodes are prone to failures just like any sensor node, and they consume significantly more energy since they transmit over longer distances compared with sensor-to-sensor links. Failure of a Gateway node results to catastrophic results because, there not information regarding the yard status to the base station

 

3. Sensor nodes have limited computing power and memory sizes. This restricts the amount of intermediate result a node can hold, also the type of data processing algorithm on a Sensor node.

 

4. Signals detected at physical sensors might have errors. Malfunction sensors might repeatedly generate false signals, also there could be bias caused by the placement of the sensor.

 

5. Sensor Nodes, Driver Node and Gate Way node have to work in High EMI Environment. Since sensor networks can be deployed in different situations, wireless medium can be greatly affected by noisy environments, and thus the signal attenuates in regard to the noise. Note that an adversary can intentionally interfere and cause enough noise to affect the communication. It is vital to ensure that communication is on time to respond to emergencies.

 

6. Wireless sensor networks at times may add delay in sending data to the base station due to the routing algorithms, etc, but Railway Signalling is very time critical job, any delay in receiving the data leads to Catastrophic results.

 

7. If a sensor node fails due to a technical problem or consumption of its battery, the rest of the network must continue its operation without a problem. Researchers must design adaptable protocols so that new links are established in case of node failure or link congestion. Furthermore, appropriate mechanisms should be designed to update topology information immediately after the environment changes so as to minimize unnecessary power consumption. 

 

8. The network should be scalable and flexible to the enlargement of the network's size. The communication protocols must be designed in such a way that deploying more nodes in the network does not affect routing and clustering. Rather, the protocols must be adapted to the new topology and behave as expected. In other words, the network must preserve its stability. Furthermore, introducing more nodes into the network means that additional communication messages will be exchanged, so that these nodes are integrated into the existing network. This must be done in a way that a minimum number of messages need to be exchanged among the sensor nodes, and thus battery is not wasted unreasonably.

 

9. As in Wireless Sensor Networks Both Ground based signalling (Way Side Signalling) and On-Board Signalling (Cab Signalling) get merged, so there is the complexity of linking the ground based control laws to the inputs received from the On-Board Sensors in the train

 

10. Design and development of failsafe, fault tolerant and energy saving  network routing algorithms is a complex design

 

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