The universal use of mobile Internet and the increased use of rail travel nicely complement one another. Although there are some that argue that a relaxed train journey is an opportunity to sit back and not be connected, there are others that value the opportunity to work and use social media while on a train. With the use of modern mobile computing technology, a train journey can be far more productive than driving a car.

The connected train also has many operational and retail uses and, with the wide-scale society use of the Internet, both for leisure and business purposes, there is an expectation that a connection to the internet will be available on trains. To keep up with this trend and maintain competition, railway operators need to enhance passengers’ experience with high-speed Internet access across the complete journey (from waiting rooms in stations to on-board the train), both for professionals to extend their mobile office to the train and also to other passengers for infotainment.

But on-board Internet access is not just for passengers. Communications and preventative maintenance are key to enhancing operational efficiency. By permanently and remotely monitoring the status of key elements of the train and infrastructure, maintenance interventions can be planned upon the detection of warning information before a fault occurs.

Real-time energy-use monitoring is possible as well as track and ride condition, which can be reported back to the infrastructure maintainer in order for them to take prompt action. On-board real time ticketing sales via debit/credit card are possible, along with seat occupancy reporting and real time seat reservations.

The Internet of Things will make the connected train even more important. While GSM-R/TETRA will provide the wireless connection for ERTMS /CBTC movement authority, an Internet connection could be used for backup in times of radio failure, subject to security issues being addressed.

The problem

Why is there not already good mobile coverage on rail? The obligation from Ofcom in 2010 was for Mobile Network Operators (MNO) spectrum licence holders to roll out services to 90 per cent of the UK population by location. Many of the rail corridors do not run through areas of large population, so there has been no incentive for MNOs to provide infrastructure along these routes.

The rail network in Great Britain extends for some 15,750km, of which 1,270km is freight only track and 14,480km is passenger and freight track. Across the network there are approximately 6,300km of cuttings of various depths and 335km of tunnels – the key topographical factors that create difficulties for providing continuous coverage from radio base stations.

By their construction, train vehicles create attenuation which degrades the usable signal into train vehicles. There are approximately 3,300 passenger train sets (around 12,000 vehicles), varying in design from 40-year old simple one or two-car diesel units to modern sealed and pressurised train sets. The degree of signal attenuation varies between -5 to -35dB, depending on the rail vehicle profile. As decibels (dB) work on a logarithmic scale, a reduction of 3dB represents a halving of the available power.

The on-train user experience varies as a result of the differing levels of signal attenuation due to a significant mix of different devices, with an increasing trend towards the use of multiband smartphones and tablets. Multiband devices incorporate wider band receivers which weaken the performance for any one single band. This, coupled with multiband antennas becoming integrated into the handsets themselves, makes reception on-board trains even more challenging.

So what’s to be done?

There is a significant cost involved in the design and implementation of additional MNO radio sites along rail routes and it’s not clear where the funding will come from. Careful consideration is required for any additional coverage to avoid radio signal interference with the railway’s operational radio systems. One of the current problems with GSM-R is interference from nearby 4G MNO sites and, while solutions are available, they are costly.

MNO coverage is getting better all the time with 4G roll out. Even higher data speeds and lower latency will be possible when 5G is introduced from 2020. However, there are ways of making the best use of the available coverage.

Mobile Communications Gateway and switch 2 [online]

Mobile communications gateway and switch.

Digital on-board repeaters and Femtocells

Internet connectivity can be improved by providing digital on-board repeaters (D-OBR). A D-OBR is an active multi-band, multi-operator repeater which is designed to provide coverage within train vehicles by amplifying and re-radiating (repeating) the external 2G, 3G and 4G/LTE mobile operator signals through dedicated ceiling-mounted antennas, overcoming the problem of train vehicle attenuation. A D-OBR will provide Internet access to mobile phones without a Wi-Fi facility; however, with the near universal provision and use of Wi-Fi, such mobile phones will soon be obsolete.

Another option is to provide an on board Femtocell. A Femtocell is a small low-power cellular base station providing localised mobile coverage, typically connected via Internet Protocol (IP) to the mobile network operator(s) infrastructure. Interference is one of the main problems in Femtocell provision. The interference includes those between neighbouring Femtocells and between macro cells and Femtocells due to the sharing of the same licensed frequency spectrum with existing macro cells. The issue is greater with a moving train.

A Femtocell will require a reliable IP connection to the internet and, in the event of a loss of connection, could take several minutes to reinitialise once a connection is restored. Currently there are no multi-MNO Femtocells available, and coupling interaction between MNOs may create interference requiring careful antenna design.

A D-OBR or Femtocell will not provide tariff free wireless Internet access (WIA) to a customer; however either option will improve voice service connections from mobile phones within the train to the MNO network. D-OBR or Femtocell therefore should not be installed in quiet vehicles although passive provision should be provided if the quiet status of the vehicle changes.

The license to use a D-OBR or Femtocell will be owned by the MNO, which will be required to state the exact location of any installation – and this may be problematic with a moving train. Any 999 voice call handled by a Femtocell will require a method of advising the emergency operator where the Femtocell is located.

The Internet connectivity is not via Wi-Fi and will incur a tariff bandwidth charge to each user. On-board content is unable to be provided and D-OBR will do little to provide an Internet connection for the operational assets on a train.

On-train Wi-Fi

The most popular method of providing a train Internet connection service is via Wi-Fi throughout a train. One or more external mounted wideband antennas are provided and connected to a communications device known as a mobile communications gateway (MCG).

A wideband antenna capable of receiving a range of MNO services and 2.5GHz or 5GHz Wi-Fi connections at stations is provided. Care is needed on the location of the antennas so that they do not interfere with the train’s GSM-R antenna.

Antennas are one of the most critical items to deliver good connectivity on and off the train. Creating an efficient antenna solution will do much to improve system efficiency. Many of the radio frequency problems associated with train antennas also stem from poor fitment of feeder cables, which should be installed within the train in accordance with the manufacturer’s instructions.

The MCG (or number of MCGs) provides ‘a cloud’ of connectivity to the train via a number of MNO services and external Wi-Fi connections aggregated together. Fixed Wi-Fi at stations is a good way of enhancing the connectivity as this is in the control of the rail industry. At terminal stations, it can provide a good link to a train and this where many people open their device and ‘log on’.

In the future, would it be possible for Network Rail to replace signal post telephones (SPTs) with Wireless Access Points? The SPT will be made redundant by GSM-R, it would require some clever data compression technology, ideally with power, but there is already a copper connection to the SPT. Wi-Fi Calling provides voice over Wi-Fi, so could this be used as a back-up for GSM-R voice?

The connectivity to the MCG may also include satellite connections, although these can be troublesome with a moving train and with high latency; unlike a more stable platform like an aircraft, which is how an Internet connection is provided in the air industry.

The Internet connection is provided throughout the train via a number of internal wireless access points. If there is already a train Ethernet communication network with spare capacity, this may be used for the wireless connection, along with appropriate security and firewall protection. Some operators and integrators prefer to provide a separate train Ethernet network for the Internet wireless connection, but this will have a cost, size and weight implication. Should a new Ethernet bus be required, then a number of Ethernet switches will be needed throughout the train and these should be connected with Cat7 cable standards using Power over Ethernet (POE).

On Train Wi-Fi - source Dft [online]

Image: Department for Transport.

Inter-vehicle connections can use Cat 5 or 6 standards where Cat 7-approved electrical interconnectors are unavailable. While limiting the overall train data throughput, these are more readily available and are easy to replace and upgrade when the data throughput requires enhancement. Connectors should be the M12 industrial grade type, rather than the RG45 connectors that are found in homes and offices.

Point-to-point Wi-Fi may also be used for Inter-vehicle connectors using low power and directional antennas to minimise the risk of bleed-through to adjacent trains. For fixed formation units, different Wi-Fi Protected Access (WPA) encryption passwords can be used to minimise the risk.

The Ethernet network will be used to connect the MCG to a number of wireless access points (WAPs) inside the train. The WAPs may connect to discreet antennas, or WAPs with integrated ‘Smart’ antennas may be used. These are more efficient, with higher gain and better interference characteristics, and can provide better coverage/capacity. They require fewer and less expensive data cables rather than radio-frequency cable.

WAPs may throttle back to support the slowest device in the vehicle, however locking one WAP to 2.4GHz and one to 5GHz will improve the overall data throughput on the train.

Customer bandwidth

An acceptable customer service in order to support email and social media browsing can be provided with a data bandwidth as low as a few  hundred kbit/s, but obviously the more bandwidth the better. Limiting each customer to a maximum of say 2Mbit/s will help to provide an acceptable service to all customers on the train. In order to provide a reliable non-discriminatory service, certain high-bandwidth applications, such as video and audio streaming services or peer-to-peer file sharing, may need filtering and restricting.

The on-train bandwidth requirement will vary, depending on the number of active Wi-Fi customers. As it is likely to increase in the future as customers become aware of Wi-Fi availability, additional bandwidth will be required.

Some predications are that bandwidth requirements may double every few years and smart device penetration within society is expected to reach 90 per cent by 2017, with many customers having more than one active device. By 2018, it is anticipated that each customer may wish to access 8Mbit/s in order to achieve the experience they desire.

The use of day-to-day technology used by customers may be very different in the future, with the introduction of wearable computing, the Internet of Things, IPv6 and heads-up display technology all increasing the use of the Internet, so 12Mbit/s to each customer may be required by 2022. Data compression technology is a method of reducing the bandwidth requirements and such techniques are used in F1 motor racing to provide high-bandwidth connections for data transfer between racing cars and the pit wall.

Buffering and infotainment

If more than one user requests the same popular information, data can be cached for a period of time to avoid it being sent again over the train-to- shore communication link, thereby saving bandwidth. Unfortunately, this may not work with some Smartphone and phone apps which use client-to- server dynamically generated type methods of connectivity, rather than static web pages.

Local, on-train content services to customers via the Wi-Fi can be provided for when coverage to and from the train communications link is not available. The updated and cached content may include data such as information services, retail announcements and popular Internet sites (for example, news, weather, travel and entertainment channels). TV shows or movies, as part of an infotainment solution in partnership with advertisers or production companies and acting as a form of in-vehicle media library, are other possibilities.

Web content from key media outlets (for example, BBC or commercial local radio/media sources) that has been already actively packaged for offline access may also be appropriate. However locally stored content will have licensing or copyright implications that will need consideration.

Advertisements and train operator information can also be stored and distributed via the Wi-Fi system, but there needs to be balance between infotainment and advertising in order not to disengage customers so that they don’t use the local content.

Security and privacy

The Wi-Fi system will be subject to a number of security threats to both equipment and personal data throughout its service life. These threats may compromise the service offered to customers and to the operational railway. Protection needs to be included from the earliest stages of a project as retrofit security solutions may leave vulnerabilities in the network. A thorough threat analysis needs to be carried out to identify both internal and external threats to security.


Defences should be implemented using a quality assurance system based on requirements, capture, specification, development, design, implementation, test and maintenance. The defences should be tested on a regular basis, including penetration testing. The risks and control measures can include:

» Risks to unauthorised access to the MCG and switches, including system settings, configuration data, cryptographic keys and software, mean that password or pin code security should be implemented on each device;

» Access to inappropriate or offensive services restricted and actively managed with conditions attached to the use of the Wi-Fi by customers;

» Customers’ personal information managed and safeguarded;

» Separation of customer Wi-Fi and operational networks through the use of a Virtual Local Area Networking (VLAN) with security firewalls and demilitarised zones, or separate LANs;

» Application of recognised good security management practice, such as the ISO/IEC 27000 series of standards, and the implementation of physical, personnel, procedural and technical controls.

Rail Industry Standard 0700-CCS

RSSB has completed a 12-month consultation with operators and on- train Wi-Fi suppliers and published a Rail Industry Standard for Internet Access on Trains for Customer and Operational Railway Purposes, RIS 0700-CCS. Due for publication in June 2016, this is intended to assist in the procurement of systems and services to enable the provision of Internet access on trains. It is a voluntary non- mandatory standard for operators to use if they choose and provides a number of requirements with comprehensive guidance to help to engineer the connected journey.