As David Briginshaw discovered at the UIC's GSM-R conference, solutions to the threats are being developed, and a way forward is emerging.
THE theme of asset and evolution management chosen for the International Union of Railways' (UIC) GSM-R conference staged at its Paris headquarters in September was apposite as these are the two main concerns of railways and suppliers alike. GSM-R has wrought real benefits for railways by providing them with far better track-to-train communications than existed before and it plays a vital role as the data transmission element of ERTMS which enables ETCS to function. But growing interference from public networks is hampering the use of GSM-R while the assigned radio frequencies limit its capacity.
Mr Achim Vrielink of DB Networks summarised the two threats to GSM-R. "The interference by public networks is still increasing," he told delegates. "Actually 340 interferences have been registered since 2007, of which only 60 have been resolved. The use of new technologies such as broadband LTE and multicarrier base transceiver stations (BTS) within public networks will increase the risk of interference."
Mr Dirk Schattschneider, the UIC's frequency manager, said that interference results in severe impairment of voice and data communications as well as network loss over several hundred metres of track. He said the UIC Interference Database currently lists more than 650 locations in Europe which suffer from interference.
Schattschneider says the level of interference has reached a plateau recently because the roll-out of GSM-R is nearing completion. Nevertheless, the UIC thinks this is only a temporary respite because of the planned roll-out of public broadband systems in adjacent frequency bands and close to railways.
Mr Libor Lochman, executive director of the Community of European Railways and Infrastructure Companies (CER), said significant progress had been made with the interference test campaign. "A valid solution for filters could be defined in the next Eirene release this year, and detailed specification should be included in the control, command and signalling subsystems technical standards for interoperability (CCS TSI) in 2014," Lochman explained.
Mr Fabio Senesi, head of control and command systems and telecommunications with Italian Rail Network (RFI) and president of the ERTMS Users Group, revealed that a new system called Dejamm-R is now available which will continuously monitor the GSM-R spectrum in proximity to railway lines. Dejamm-R will:
• measure the quality of the signal transmitted by the radio block centre (RBC) and trains
• detect malicious or non-malicious interference, and
• constantly update a remote analysis centre on the current status including a spectrum analysis.
Dejamm-R consists of two elements Sentinel and a Monitoring Centre (MoC). In Italy, Dejamm-R Sentinel will be installed near high-speed lines to scan GSM-R frequency bands and report to the MoC the status and parameters of all 38 GSM-R channels in less than 3 minutes. The MoC can receive data from up to 20 Sentinel connections and records and stores the data. It can interrogate the Sentinels and works like a remote spectrum analyser.
Mr Philippe Branly, GSM-R product manager with Sierra Wireless, says filters can be fitted in the BTSs of public operators provided a suitable and affordable deal can be reached, and GSM-R coverage could be improved
by inserting additional radio sites, improving antenna design, and redesigning existing radio coverage. Other network solutions include fine-tuning the engineering parameters and better frequency band management by for example reallocating carriers onto other frequencies and software-based actions.
Branly says several companies such as his own, as well as Alstom and Siemens, have developed solutions that are now available and are compatible with existing on-board equipment.
Increasing capacity
Vrielink outlined some of the consequences of inadequate capacity. "Due to a lack of capacity, some large shunting yards on the DB network have to use a mixture of GSM-R and analogue radio," he told delegates. ETCS using GSM-R circuit-switched data services limits capacity in high traffic areas, but by using the E-GSM-R band and changing to ETCS over packet-switched data using GPRS or Edge will solve this problem.
Mr Ingo Wendler with the UIC summarised the main differences between circuit mode and packet mode over GPRS for GSM-R ETCS bearer service. With circuit switching you get a dedicated transmission resource per ETCS session, the average GSM-R traffic channel duty cycle varies between 5 and 20%, there is sufficient transmission robustness, and low air interface transmission capacity utilisation. Whereas packet switching enables shared transmission resources between several ETCS sessions, the bearer service bandwidth depends on the line speed and the radio network design, improved protection algorithms against transmission errors, and multiplexing of several ETCS sessions which improves resource utilisation. Other benefits of packet switching include a delay transmission resource release by the network, reduced call charges and real-time treatment of ETCS applications.
For the first time Alstom demonstrated ERTMS over IP at the conference as part of GPRS experiments conducted in cooperation with the UIC and the GSM-R Industry Group. The demonstration included the end-to-end connection of an Alstom Atlas ERTMS system over an IP link and introduced new GPRS-compatible on-board equipment and the corresponding trackside network gateway. The software for the radio block centre, the maintenance support system and the on-board unit did not require modification.
Alstom says the new equipment is compatible with both existing communications across GSM-R and the future internet protocol (IP)-based bearer-independent Future Railway Mobile Communications Standard (FRMCS), as well as being fully interoperable according to the latest TSI. Compatibility with existing GSM-R equipment is vital so that investments made so far by railways are preserved. Independent tests have shown that the transmission delay has fulfilled the requirements of the standards and the communications channel and allowed greater capacity as a result.
Alstom plans to start conducting live demonstrations for some of its customers next year and will begin to roll-out the first full-scale GPRS deployment in Denmark as part of the national ERTMS programme in 2017.
Lochman said the introduction of GPRS will be just the first step in an evolution to railway telecommunications based on IP. "This will allow us to unbundle the safety part - the train control system - from the telecommunications part and to evolve each separately.
Mr Markus Myslivec, lead customer solution designer with Frequentis, said ETCS, recording, and fixed-line voice communication will evolve to IP, along with the GSM-R infrastructure network, fixed terminal subsystems and mobiles, and several interfaces. However, legacy interfaces and subsystems such as lineside telephones and voice mobiles might continue to use circuit-switched technology.
Myslivec listed some of the benefits of switching to IP. There would be one multi-service network for different types of applications. Reliability and availability will improve while efficient use will be made of the limited capacity at the interfaces in question. By using off-the-shelf components and systems installation and operating costs will be lower. Existing infrastructure can be used while new applications are added. Finally, there is the ease of interconnectivity which comes with IP-based networks.
Nevertheless, there are a number of challenges to overcome. These include security concerns when switching from non-disclosed dedicated circuits to a free-to-connect IP cloud, and operating IP systems and interfaces in a trusted environment.
Mr Ola Bergman, head of GSM-R standardisation with NSN, said today's GSM-R functionality must be supported by the new generation system as both systems will be in use side-by-side during migration which will last several years. "A train driver moving from the GSM-R area to a new generation area should not have to behave differently in each location, but should benefit from the additional services," he said.
Bergman listed some of the extra services he expects to see. These include transferring train data for maintenance, facilitating energy-efficient train driving, transferring on-board CCTV recordings to a control centre as well as images from a level crossing to the driver, and providing detailed information to passengers and train crew. Surplus capacity could be leased by public mobile operators to provide regular, high-quality mobile services to passengers.
Bergman believes the new generation system will be a cellular mobile network just like GSM-R with radio base stations along lines and in stations and shunting yards, possibly supported by satellite-based services for special needs. The new generation will be an "application" on top of a regular mobile service based on 3GPP services tailored for a much larger user community than just railways. However, he believes the new generation system will be owned by the railways as the public networks will presumably not guarantee the required round the clock availability. Yet, Bergman says whatever the frequency allocation may be, it is imperative that sufficient spectrum is granted.
Mr Chiel Spaans with the UIC said the UIC launched the FRMCS project this year to provide information for decisions to be taken on the successor to GSM-R. It will run until 2016 and will look at functionality, spectrum, technology and architecture. The scope of the project will be defined this year together with what can be delivered. Funding will be secured from the UIC and the European Union's TEN-T programme.
Looking further ahead, Mr Serge Bertrand from Alstom foresees a smooth migration to the new technology around 2025-2030. Let's hope so, because the industry has given a commitment to support GSM-R until 2025.
New cab radio unveiled in Paris
KAPSCH CarrierCom displayed a new cab radio at the UIC GSM-R conference in Paris. The RC900 is designed for the transmission of speech and data via GSM-R and is available either as a digital-only unit or as a dual-mode cab radio.
The cab radio comprises digital transceiver units, a control and interface module to connect external units, and a unit for power supply. It interfaces with the GSM-R mobile wireless network to carry out all the functions required by the Eirene UIC standard.
Kapsch says the RC900 offers other functions which effectively turns it into a smart phone for trains. The radio supports ER-GSM and has an inbuilt Wi-Fi module and GPS receiver. Software monitors the functions and automatically reroutes the speech or data traffic if there is a fault.
