GSM-R Interference from Commercial 900MHz Networks – Case Study: Finland
Finnish Transport Agency (FTA) selected Omnitele to design the RAILI and VIRVE radio networks for the City Rail Loop. The City Rail Loop is a subterranean urban railway line for commuter trains under the Helsinki city centre, starting from Pasila and running via Töölö, Helsinki city centre and Hakaniemi and then back to Pasila.
The City Rail Loop facilitates more efficient and smoother railway transportation by changing the Central Railway Station track architecture from an end-point layout into a circle. As the trains will no longer need to change direction in the final destination, the track system can have higher utilisation and accommodate increased traffic.
Besides the commercial mobile communication services (e.g. GSM, HSPA, LTE), two additional professional radio communication systems are needed in the City Rail Loop, namely RAILI and VIRVE. RAILI is a mobile network based on GSM-R standard and built for the special communication needs of railway transportation. It serves traffic controllers, train drivers and other railway system staff and covers over 5000km of railroads in Finland. VIRVE is a countrywide radio network based on TETRA standard and designed to provide a secure and reliable mobile communications channel for public safety organisations such as police forces, fire departments and Finnish Defence Forces.
As the City Rail Loop is an underground train system, the existing radio network infrastructures cannot provide sufficient coverage for reliable communications. Given the critical nature and extremely high availability demands of VIRVE and RAILI networks, a dedicated subterranean radio network is a mandatory requirement.
Designing radio networks in tunnels is challenging and it differs greatly from traditional macro-cellular radio planning. Special applications and radio components are required to ensure sufficient robustness against malfunctions while keeping the total network cost on acceptable level.
“In typical train tunnel networks old school basestation antennas cannot be used as the trains themselves would block the radio propagation in the tunnel. Instead, the radio designer needs to apply an efficient combination of repeaters, leaking cables and other special components. Given the critical nature of VIRVE and RAILI systems, the handovers need to work without call drops even if one basestation falls. Meeting this requirement while using leaking cables was not trivial. Eventually we found an innovative and elegant solution based on low-cost RF components. Another aspect always needing extra attention with GSM-R design is mitigating the co-existence and interference issues with public mobile networks. The 3GPP UMTS900 standard for instance is not very well defined to sustain interference from GSM-R,” comments Kalle Tuominen, Senior Consultant and Project Manager from Omnitele.
The GSM-R and UMTS900 co-existence challenge is more widely covered in Omnitele whitepaper “Co-Existence of UMTS900 and GSM-R Systems”. Full whitepaper available online here.
Esa Vesterinen, Vice President Sales & Marketing, Omnitele Ltd
Jussi Lindberg, City Rail Loop Project Manager, Finnish Transport Agency
About Omnitele Ltd. Omnitele Ltd., founded in 1988 to set up the first GSM network in the world, is a pioneer within the wireless industry with over two decades of leading edge network and business consulting experience worldwide. Omnitele’s strengths lie in the experience gained from 1.000+ projects conducted in 80+ contries worldwide. The expertise areas of the company include technology strategy, network design and quality assurance. For more information, visit www.omnitele.com
About Finnish Transport Agency The Finnish Transport Agency – FTA is a government agency operating under the Ministry of Transport and Communications, and it is responsible for maintaining and developing the standard of service in the transport system’s traffic lanes overseen by the government. FTA aim is to promote the efficient functioning of the traffic system as a whole, to improve transport safety and to contribute to a balanced and sustainable development of the regions. For more information, visit http://portal.liikennevirasto.fi/sivu/www/e
About GSM-R GSM-R is a mobile communication system based on GSM standards and designed for the special communication needs of railway systems. It provides a secure platform for voice and data communication between railway operational staff, including drivers, dispatchers, shunting team members, train engineers, and station controllers. It delivers features such as group calls (VGCS), voice broadcast (VBS), location-based connections, and call pre-emption in case of an emergency. This will support applications such as cargo tracking, video surveillance in trains and at stations, and passenger information services. As the GSM-R signalling information is carried directly to the train itself, the system makes higher train speeds and greater traffic density possible while increasing the level of safety. For more information, visit http://www.etsi.org/technologies-clusters/technologies/intelligent-transport/railway-communications
About TETRA Terrestrial Trunked Radio (TETRA) is a digital trunked mobile radio standard developed to meet the needs of traditional Professional Mobile Radio (PMR) user organisations such as: Public Safety, Transportation, Utilities, Government, Military, PAMR, Commercial & Industry. Some unique PMR services of TETRA are: Wide area fast call set-up “all informed net” group calls, Direct Mode Operation (DMO) allowing “back to back” communications between radio terminals independent of the network, High level voice encryption to meet the security needs of public safety organisations, Emergency Call facility that gets through even if the system is busy, Full duplex voice for PABX and PSTN telephony communications. For more information, visit http://www.etsi.org/technologies-clusters/technologies/tetra