Spectrum for railway mobile applications to head in new directions

Robin Donoghue, Spectrum Expert with the European Communications Office, provides an overview of the relevant activities within ECC and the planned work in response to the EC Mandate

Railway networks across Europe make use of many different radio systems using many different frequency bands. In addition to traditional rail signalling infrastructure such as the Balise – a high frequency transponder which is placed between the rails of a railway to record when a train passes over it – the railways use other communications technologies. These include RFID – radio frequency identification – to record information on individual rolling stock, object detection radar and video surveillance.

There have, however, been two recent initiatives relating to rail that have triggered significant studies within the ECC:

• GSM-R replacement by Future Railway Mobile Communication System (FRMCS)
• Urban Rail intelligent transport systems (ITS)

FRMCS

The first initiative is FRMCS, which is seen as the potential successor to GSM-R, the rail variant of Global Systems for Mobile Communications (GSM).

GSM-R has been standardised for almost 20 years and has proven a successful solution for both voice and data communication to trains. GSM-R is used in all EU Member States with rail networks, and there are also a few other deployments across the globe. It is a relatively secure means of communication and it remains reliable for high-speed trains. ECC Decision (02)05 sets out the frequency designation in CEPT Administrations for GSM-R.

The future of GSM technologies is unknown. There are clear business cases such as smart metering where GSM could potentially continue to prove the ideal communications means. However, newer technologies including LTE and 5G NR may also provide these services, and there will be clear economies of scale in utilising these newer communications standards. As such it may become increasingly cumbersome to support GSM-R if the wider GSM networks and their supporting eco-systems become obsolete.

In Europe, GSM-R currently operates in the frequency bands 876–880 MHz (uplink) and 921–925 MHz (downlink) giving a spectrum allocation of 2 x 4 MHz.

In February 2017, ETSI published a Systems Reference Document (SRDoc) entitled GSM-R Networks Evolution (TR 103 333). This SRDoc noted the need for end-of-life planning and suggested GSM-R could be challenging to support beyond 2030. The SRDoc requested additional spectrum for FRMCS, asking for an extension of 2 x 3 MHz in the frequency bands immediately below the current allocations.

Then in 2018, following revisions to ERC Recommendation 70-03, the European Commission issued a Decision (2018/1538/EU) on short range devices (SRD), recognising that "the 874.4-876 and 919.4-921 MHz sub-bands should be reserved for potential future railway use". This Decision noted, however, that the "reservation of the 874.4-876 and 919.4-921 MHz bands for FRMCS is subject to further study".

Furthermore, within a few CEPT Administrations, GSM-R use is authorised on a national basis and in certain geographic areas over the wider frequency bands 873–880 MHz and 918–925 MHz (for use in shunting yards, for example).

Rail operators have invested heavily in building the infrastructure network to support GSM-R. There are clear commercial drivers to get as much value from the network as possible. Therefore the rail industry is looking to replace GSM-R with a network that provides maximum data throughput. This would mean that additional features can be added which will not only ensure rail travel safety but also improve punctuality and increase rail line capacity. Better and more timely signalling and control of rolling stock could allow more trains to use the rail network and those trains could be better coordinated in their movement.

ETSI TR 103 333 led to the European Commission issuing a mandate to CEPT (RSCOM18-05) on 12 July 2018 on spectrum for the future railway mobile communications system. The purpose of the mandate is "to consider the required amount of spectrum, identify appropriate spectrum bands, study technical feasibility and develop harmonised technical conditions for a sustainable and efficient use of such bands for the operation of the future railway mobile communications system (FRMCS), which is the successor of GSM-R". The mandate invites CEPT to study the frequency bands 874.4-880 MHz, 919.4-925 MHz, 1900-1920 MHz. In addition, further spectrum bands, for example the band 2 290-2 400 MHz on a tuning range basis, can also be considered.

Notably, the mandate also suggests that the use of commercial mobile networks may also be studied. This recognises that it may prove sensible to consider solutions such as network slicing of commercial networks as a solution, rather than building a new network to cover all rail eventualities in all geographic locations.

Within the ECC, WG FM's Project Team FM56 has been tasked with developing the CEPT reports in response to the mandate. Two reports are planned and FM56 has already developed the draft structure of the first of these CEPT Reports. The ECO has sent a questionnaire to CEPT Administrations about the current and future use of the 2290-2400 MHz range. The questionnaire closed on 23 August 2019.

For the frequency bands 874.4-880 MHz and 919.4-925 MHz, the studies appear relatively straightforward with FRMCS simply replacing GSM-R in the upper part of the band. In the lower part of the band it will share with pre-existing SRD, authorised in several CEPT Administrations. The technical parameters for the SRD were set to ensure protection of GSM-R (see ECC Reports 189 and 200).

For the frequency band 1900-1920 MHz, the studies will be more complex as there are more than just rail systems requesting access to this band. Unmanned aerial systems are being considered in Project Team FM59 and proposals for DECT are expected from ETSI in the near future.

Urban rail ITS

The second initiative relates to urban rail networks such as the Paris Metro. Urban rail intelligent transport systems (ITS) are intended to move vast numbers of people around cities at relatively high speed. They are essential in keeping the movement of people around cities flowing.

In exactly the same way as applies to other rail networks, safety and capacity can be improved with better signalling and control systems.

ITS in general provide an opportunity for transport networks to work more efficiently. In a simple example, two vehicles can travel closer behind one another if the following vehicle knows everything about velocity changes in the lead vehicle and can alter its own velocity accordingly. Clearly in this example, latency limitations become a key parameter in ensuring the safe operation of both vehicles. Where the communication is by radio, the radio link needs to be sufficiently robust to ensure the timely communication between the two vehicles.

ITS are currently designated to operate in the 5.9 GHz band. ECC Decision (08)01 is intended to harmonise, in CEPT Administrations, the frequency band 5875-5925 MHz for ITS, with the sub band 5875-5905 MHz designated on a non-exclusive basis to traffic safety applications. ECC Recommendation (08)01 suggests CEPT Administrations make the band 5855-5875 MHz available for non-safety ITS applications. Within the EU, the sub band 5875-5905 MHz has been harmonised for ITS by all Member States (Decision 2008/671/EC). These current designations resulted from ETSI making proposals for ITS in 2006 through two technical reports (TR) – TR 102 492-1 (critical road safety applications) and TR102 492-2 (non-safety related ITS applications).

Deployment of operational ITS has been slow. One factor has been the existence of alternative communications technologies (such as ETSI G5 and LTE-V), with vehicle manufacturers and road operators yet to decide how to accommodate or not, multiple ITS technologies.

In alignment with ECC Decision (08)01 spectrum designation, but also recognising the slow deployment of ITS, the Commission issued a mandate to CEPT (RSCOM17-26) in October 2017 asking CEPT to study the possibility of harmonising the whole band 5875-5925 MHz. The mandate asked that "in addition to road transport, allowing other means of transport such as Urban Rail1 (using Communication Based Train Control, (CBTC)) in the EC harmonised safety-related ITS band".

In March 2019 the CEPT responded to the mandate with CEPT Report 71.

CEPT Report 71 proposes harmonisation of the frequency band 5875-5925 MHz for safety-related ITS applications thereby removing any restriction limiting the use to road transportation. However, road ITS should have priority over Urban Rail ITS in the frequency bands below 5915 MHz and Urban Rail ITS above 5915 MHz. Additionally, CEPT Report 71 proposes to harmonise the frequency band 5925-5935 MHz for safety-related urban rail ITS applications, subject to national coordination with existing fixed service networks and/or national studies to determine the sharing conditions. The above mentioned ECC Decision (08)01 were recently revised taking these elements from CEPT Report 71 onboard. It is subject to public consultation ending 15 November 2019.

These proposals followed the technical analysis undertaken in ECC Report 290.

The issue is further complicated by channel arrangements for the specific train technology CBTC. CBTC is an evolving technology. For example, the channel arrangement may not fit the 10 MHz channelling arrangement assumed to date for other ITS installations.

CEPT Report 71 notes the ongoing work in ETSI to finalise "polite" protocols and/or proper co-channel sharing mechanisms that could allow all ITS applications, including between road technologies and rail technologies, to operate within the same frequency band. It therefore suggests reviewing the current proposed framework after no more than three years.

Added importance to keep the designation of dedicated spectrum to Urban Rail ITS under this three-year review comes from the need to allocate additional radio spectrum for wireless access systems including radio local area networks. Mobile data offloading reduces the amount of data being carried on the cellular bands, freeing bandwidth for other users. For Europe to fully experience the benefits foreseeable from the introduction of 5G, mobile data offloading is likely to be essential.

Following ECC creating a work item on 5925-6425 MHz WAS/RLAN and ETSI developing the System Reference Document on WAS/RLANs in the 5925-6725 MHz band, the European Commission issued a further mandate to CEPT to "study feasibility and identify harmonised technical conditions for wireless access systems including radio local area networks in the 5925-6425 MHz band for the provision of wireless broadband services".

Draft CEPT Report 73, in response to that mandate, has been developed and is currently under public consultation ending 13 September 2019.

The work in ECC in developing the CEPT Reports will enable the benefits of ITS for road and rail to be realised in the very near future, while being mindful of the need to bring 6 GHz WAS/RLANs into everyday use.