FOR mission-critical radio communications, Swedish passenger and freight operators, like many of their contemporaries from around the world, utilise GSM-R, an international wireless communications standard for railway communication and applications, and the radio communications component of ERTMS.

The GSM signal provides a dedicated link between trains and control centres and in Sweden operates within the 900MHz band. Unfortunately GSM-R signals are very sensitive to interference caused by public 3G and 4G signals within the same band, a situation compfounded by the Swedish government's decision in 2011 to allow mobile operators to use the frequency for their future wideband 3G and 4G networks.

Nordic X62In Sweden, four mobile network operators are active with GSM, 3G and 4G networks in the 900MHz frequency, including two 5MHz UMTS networks and a 10MHz LTE network. The problems with GSM-R interference are caused either by wideband networks transmitting signals over a broad set of frequencies, which are stronger than the GSM-R receiver can handle or a higher level of noise (unwanted emissions) from the Process Management Object (PMO) base stations.

In practice interference can result in GSM-R radio coverage blackspots, a safety-critical issue for railways, and one that Trafikverket, and the government, are striving to avoid. To mitigate these problems, Sweden's mobile network operators were required in 2011 to limit the power of their networks close to railway lines to prevent any interference with the safety-critical GSM-R signal, with Trafikverket operating measurement trains to monitor that this was the case. In addition Trafikverket agreed to increase GSM-R signal levels to handle increased noise from unwanted emissions. However, at the beginning of 2015, this situation became untenable.

Permanent limitations of the signal is clearly not in the long-term interest of the railway, whose passengers want to access broadband internet services on the move, or mobile network operators who are obliged to provide universal coverage. As a result, the European Railway Agency (ERA) led a campaign to convince the European Commission of the severity of the situation and to approve a new Technical Specification for Interoperability (TSI) to allow the installation of filters or alternative radio modules which were proven to be effective at combating GSM-R interference.

Mr Jonas Lindh, manager of GSM-R systems and operations, at Trafikverket, says he first raised the issue in 2010, and the effort it took to convince the Commission of the severity of the problem was the biggest hurdle that the interested parties had to overcome. Indeed, once ERA was onboard, this process took three years, finally culminating in the decision in May 2015 to accept the new TSI permitting the use of the filters from July 1 2015.

With the decision coming at the same time as the expiration of an agreement for mobile operators to limit the power of their signals, a compromise was required because of the time it would take to complete installation across Sweden's entire train fleet.

Lindh says a "gentlemen's agreement" was subsequently reached in May 2015 between the mobile network operators, the train operating companies and agencies, and Trafikverket, under which the mobile operators agreed to extend restrictions of their services for a further year while the railway companies installed filters, improved radio modules or new cab radios in their vehicles.

The operators now have up July 1 2016 to complete the installation and by January 15, Lindh reports that 1489 of the required 3150 retrofits had taken place, with 3141 ordered.

"At the start progress was slower than we expected but now there are around 500 installations taking place each month, and if we continue at this pace in February, March and April, we will reach the target well ahead of the deadline," Lindh says.

The Swedish government is funding the programme to the tune of SKr 310m ($US 36.3m), including SKr 180m to increase GSM-R coverage levels and SKr 130m to provide subsidies for the installation of the necessary equipment. Train operators have a choice of the solution that they wish to deploy: installing a GSM-R filter, a new cab radio, or modifying the existing radio's modules, and Lindh says that as an incentive up to €4000 is available per installation up to the end of February. At this point the level of support is cut to €2000 and he expects up to 2500 of the installations to take place before this cut off point.

"This €4000 will cover 100% of the costs of installing the filter on the vehicle's antenna or to change the radio module," Lindh says. "For new radio modules and cab radios it is inevitably more expensive. For some, the cab radios in use are quite old and do not have another module available for the upgrade. In those cases they will probably upgrade the entire radio but whatever they decide to do it is up to the operator to show that they can operate the vehicle safely. At this stage we estimate that 200 new cab radios will be installed, 50 radio modules will be changed, and the remaining 2900 retrofits will choose the filter."

Kaelus, United States, and MicNordic, Sweden, are responsible for supplying the filters, while Funkwerk and Kapsch are supplying new cab radios and improved radio modules. Installation takes place at the respective fleets' depots, minimising any disruption to service.

In addition, with Sweden currently engaged in a nationwide ETCS rollout, modifications were necessary to the chosen onboard equipment. Lindh says that the sole supplier of onboard ETCS equipment in Sweden, Bombardier, which was awarded a framework contract in 2008, found that it could not modify its radio module to overcome the interference problems. "The only possible solution was the installation of an external filter," Lindh says.


With other European countries also hosting GSM-R and wideband mobile networks on the same frequency, the issue of GSM-R interference is not unique to Sweden. Mr Anders Åkesen, Trafikverket's head of ERTMS project, says that the company has received requests from other infrastructure managers about how they have tackled their respective issues.

"This will happen on a wide scale in Europe," Åkeson says. "We have already worked with Banedanmark and Jernbaneverket [in Norway] on this, and people are gradually becoming aware of the issues they may face."

Åkeson adds that the severity of the issue is reflected in a straightforward choice: "With no frequency, there is no traffic," he says, and he argues that this provides a strong case to tackle the issue head on and to work with the mobile operators to identify a solution.

As Sweden approaches the successful conclusion of its interference mitigation programme, it is setting the benchmark for effectively addressing the issue. Lindh says its success is the result of the good relationship between Sweden's rail sector and the mobile network operators. However, whether other countries will be able to follow this example remains to be seen.

"We have quite a good situation here because we have understood our different priorities from 2010 until today which has enabled us to work with the mobile operators to solve this problem side-by-side," Lindh says. "I think that one of the difficulties that other countries may face is that the operation of GSM-R and public mobile networks is not considered harmonious."