Modern railway signalling systems play a major role in providing safety networks to prevent accidents due to human errors. Furthermore, railways traffic management improve the utilisation of scarce and expensive resources like the railways infrastructure. One of the major breakthroughs has been the introduction of an interoperable European standard known as European Rail Traffic Management System (ERTMS), which not only allows speed limits to be transmitted to the driver, but can also continuously monitor the driver's response to this information. An on-board computer effectively compares the speed of the train with the maximum permitted speed and automatically applies the train's braking, if the limit is exceeded. The existing implementation of the ERTMS requires significant investments in ground infrastructures (used for both positioning and telecommunication purposes), preventing its wider deployment.
So far, high speed lines and international freight transport lines have been the primary target for these systems, which are implemented using infrastructures deployed along the rail tracks (e.g. balises (electronic beacons), track circuits, cablings, GSM-R network) that are expensive to procure, install and maintain. Such highly expensive have so far prevented the adoption of advanced train traffic management systems in regional and remote railways lines, where traffic level is typically low. Both railways and train operators are interested in the introduction of advanced safety systems along this type of lines, which therefore represents today an untapped market.
A promising way to reduce the costs associated with the implementation and maintenance of ERMTS compatible solutions is to reduce the extent of deployment of the track side infrastructure using SatNav and SatCom to complement or replace the ground-based infrastructure.
3InSat is a project aiming at developing and validating a new satellite-based platform to be integrated into a ERTMS system. This satellite supported solution is not yet available on the market because of the very challenging safety requirements (Safety Integrity Level 4 SIL4 requirement) that a railway signalling system shall comply with.
A validation campaign is planned on a specific Test Site to be carried out in Sardinia on a 50km line.
The 3InSAT demonstration project will develop, test and validate in a real set up a new satellite-based platform suitable for a Train Control and Management System meeting the SIL4 safety requirements and compatible with the ERTMS standard. The requirements will be driven by the market needs and by the accreditation and certification strategy.
The 3InSat project has the objective to introduce a train monitoring and control system compliant with the state of the art European and international regulations adopting satellite based navigation and telecommunications systems. In such a way, the investments required along the rail tracks will be minimised, which will enable efficient and safety improved operations where today this cannot be sustained.
More specifically the objectives are:
Furthermore 3InSat has the objective to validate these solutions along a regional railways line in Sardinia on 1 test train.
The Italian railway infrastructure manager (RFI) and the German one (DB Netz) are reference users and partners of the project; they contribute to the user requirements definition, the tests and demonstration activities.
Other reference users are:
The worldwide potential market for satellite-based train control systems is quite large. The demand is driven by different indicators: the growth of the core signalling market (+6% year), the government directive in the USA and to some extent in Russia, the new private players (the mining sector) and the need to modernise the old and low traffic lines in Europe.
An important market force is the need to deploy new lines in critical areas where the cost of maintenance of the railways is prohibitive (South Africa, Russia, Australia, Brazil). These needs can be fulfilled with the adoption of satellite technologies in order to reduce track-side circuitry and equipment to the largest possible extent.
3InSat project will design, develop and validate specific solutions able to be employed for Safety of Life applications in the railway environment. Such solutions shall meet the mandatory safety requirement imposed in railways operations SIL4 (Safety Integrity Level 4).
SIL-4 compliant localisation system shall be developed in accordance with the CENELEC norms and the tolerable hazard rate (THR) for train GNSS Location Determination System (LDS) shall be derived by means of the hazard analysis and risk assessment for ETCS Level 2 applications (through the reference of the ETCS Class 1 documents). This analysis will be reviewed by an assessor.
The 3InSAT project will include the following four main developments:
1. The GNSS simulator to analyse achievable performance under different conditions (e.g. rail network topology, head-ends, confidence errors, environment). The overall architecture of the simulator is composed of the three main parts representing the whole GNSS-LDS System:
a. RS - Reference Stations;
b. TALS - Track Area LDS Safety server;
c. OBU - On Board Unit.
GNSS-LDS simulator can work either with real data or with simulated data.
2. The LDS multi-sensors/multi-constellation (GPS, GLONASS, GALILEO, BEIDOU) system which, through association of different SatNav receivers and on-board sensors (gyros, accelerometers, tachometer) will provide a SIL4 compliant positioning solution able to reach high integrity values and improve the overall availability and resiliency. The LDS will make use of Satellite Based Augmentation System SBAS (e.g. EGNOS for Europe) in combination with Ground Based Augmentation System GBAS for both differential corrections and integrity monitoring. Additionally the LDS will have independent integrity monitoring on-board capability to further mitigate GNSS errors and autonomously assess the GNSS location integrity in case of augmentation data unavailability (e.g. EGNOS SIS unavailability).
3. Bearer-independent Telecommunication Network, which will combine mobile satellite services with terrestrial solution (3G/4G) to guarantee the necessary coverage and Quality of Service in relation to the overall system requirements, and compatibility with the existing on board train control system interfaces.
4. The Track Area Augmentation and Integrity Monitoring Network to be installed along the railways tracks. This element will be mainly used in regions out of the SBAS footprints
As illustrated by the block diagram below the project adopts a modular architecture with the possibility to implement and deploy individual blocks according to the market evolution and SBAS Signal in Space coverage.
The functions are distributed among the following elements:
1) Space segment (GPS, GALILEO, GLONASS constellations + EGNOS + SATCOM)
2) Augmentation and Integrity Monitoring network
3) On board unit (multi-constellation GNSS receiver + Multi-sensor Localization Determination System (LDS) + Hybrid (satellite and terrestrial) telecommunication module)
The primary task of the space segment is to provide the reference satellite signals needed for train position computation as well as to distribute real time corrections related to satellite ephemerides, clock offsets, propagation delays, and Signal In Space (SIS) integrity.
The (Track Area) Augmentation and Integrity Monitoring Network plays a role similar to the EGNOS Range and Integrity Monitoring subsystem and, in fact, it will be deployed only on those areas out of EGNOS footprint.
The on board unit trough the Localization Determination System (LDS) subsystem computes the train position by using the GNSS signal, the augmentation information for integrity monitoring and the data from other sensors as Inertial Navigation Systems (INS) and tachometers. The on board bearer-independent telecommunication subsystem will take care of ETCS messages and other important system information.
3InSat solution will contribute to demonstrate how satellite can bring competitive advantage in terms of costs to for the deployment of high safety standard (e.g. ERTMS) for local/regional lines and remote lines where is important to minimize the deployment of the track-side equipment and telecommunications infrastructures. This cost reduction shall anyhow assure high safety standard at the same level as conventional systems based on balises and ground deployed equipment . Additionally, it could increase the network capacity and efficiency, by implementing short virtual blocks to reduce the train separation in the high traffic nodes.
3InSat project can facilitate the ERTMS evolution standardization process, demonstrating how satellite based positioning solution can be included in the future baselines.
The 3InSat project is strategic to create a synergy between the rail and space technology to build-up a system centred on the ERTMS standard and able to bring to it the flexibility that GNSS and SatCom can guarantee. Such potential enormous benefits will be transferred to the train operators and railways infrastructure managers and in general to the citizens.
For the railways industrial side the expected returns are mainly on the provisioning of a cheaper ERTMS train control system solution, and for the satellite industry the delivery of new applications and services based on GNSS and SatCom .
In this respect the key technologies are relevant to the SIL-4 localization systems and the satellite telecommunications which are expected to play a major role in the evolution of the train control systems. SatCom networks can provide interesting alternative solutions to complement/replace the GSM-R technology that will be phased out in the next years for the obsolescence of the technology and the imminent introduction of the IP based standards
The project is expected to last 30 months starting from March 2012. The system design will be driven by the User's Requirements. A GNSS simulator will be developed in order to analyse the achievable performance of positioning algorithms under different conditions (e.g. rail network topology, head-ends, confidence errors, environment). The simulation will rely on the raw measurements (SIS and RF signal receptions are out of scope) and will deal with algorithms for the pseudorange processing. Following the successful verification of the technical and operational feasibility of the solution by mean of a safety case, the different elements of the 3InSat system will be developed.
The pre-operational service provision (demonstration stage) will be carried out in Sardina along the Olbia-Cagliari regional line. This test will be involving 1 train fully equipped with the identified solution. The environment is the typical one of a regional-local network that has no automatic train protection system. Therefore this environment which has been selected by RFI is fully representative of the real operational scenario targeted by the satellite-based solutions.
The main challenges of the project are related to the GNSS based LDS design and development because of the stringent SIL4 requirement.
The Track Area Augmentation and Integrity Monitoring Network represents another challenge since its performance in terms of availability will contribute to the fulfilment of the SIL4 requirement.
Last but not least, bearer-independent Telecommunication Network shall demonstrate a good trade-off between performances and costs which can guarantee a sustainable a competitive service of the 3InSat solution.
The localisation service will be based on the provisioning of a safety service including the liability obligations versus the service level agreement. The signalling industry is used to design, develop and deliver solutions which have been certified according to the safety requirements. Since the Localiser is a key component of the train control system solution, the system integrator has to guarantee the customer for the whole operational life of the system. In this respect the system integrator is also the service provider to allow the operation of the localizer with its augmentation network in the specific railway corridor.
Concerning the telecommunication component of the train control systems, the system integrator has to procure the dedicated network fully optimised with its train control system. With the exception of some customers who procure and operate the telecommunication network by themselves, such a network is under the responsibility of the system integrator. In the case of satellite based systems the dominant part of the delivery becomes the service, which implies that a service provider should be selected. Such a service provider will have to manage the delivery of the train equipment and the relevant service according to a proper service level agreement. This type of services represents new business opportunities that cannot be explored by the space industry alone.
The advent of satellite telecommunication network will inevitably shift the responsibility of the operation towards a service provider while the operation of the satellite localisation represents a new activity/service in the current value chain. Future service providers are expected to offer the localisation services with guaranteed quality of services and for different performance.
Compared to a traditional system, the life cycle cost (LCC) of a satellite-based train control system will be much lower. The market expectations for a LCC reduction are in the range of 20-40% including the costs of the new equipment and the relevant investments. Concerning the telecommunication component, the target LCC reduction compared to ground-based systems (assuming 10 years operations) is 30% to 60% including the amortisation of investments to customize and certify the terminals.
Demo Qualification Review DQR was successfully concluded for the Localization Determination System (LDS) unit and for the terrestrial telecommunications subsystem. For the latter, the EURORADIO over IP protocol and the selected terrestrial solution (Vodafone M2M) have been tested.
The DQR of the SatCom terminal is expected in February 2014.
The design activities concerning the dimensioning of the proprietary augmentation network are proceeding.
Currently, two passenger trains equipped with a prototype of the LDS are running along Pontremolese Line (Italy) with the objective of acquiring satellite data and fixed reference from the balises along the track .
These two sets of data will be used to check the degree of overlap between the fixed reference (balises) and the GNSS positioning solution; this will allow, through post processing activities via the developed simulator, to choose the best algorithms to be deployed in the system to comply with the system requirements.
Telecommunications system installations for the first demonstration phase in Sardinia are foreseen by the end of Q1 2014.
DB has joined the project as new partner with an important role to review and amend the users requirements for the local and regional lines in Germany and assess the economical sustainability of the 3InSat technology for the German scenario. DB and RFI will contribute to the analysis of European scenario and the identification of a roadmap for a standard solution.