Commuter trains may need over 3Gbps of mobile data capacity by 2025

By the year 2025, a crowded London commuter train is likely to need 3.6Gbps of mobile data capacity to meet the connectivity needs of its passengers, if current trends continue, according to a new report from telecoms regulator Ofcom.

The regulator has just published details of how demand for data capacity is likely to grow, and what must be done to support that. Ofcom was asked in December 2017 to provide technical advice to support the policy work of the Department for Digital, Culture, Media and Sport (DCMS) on delivering fit-for-purpose mobile data services for rail travellers.

Ofcom’s findings cover three main areas – the level of data required per train, what radio spectrum might be needed to meet this requirement, and how the regulator can make it available.

Taking demand from a train as a whole by aggregating demand from all passengers on board using a device at the same time, Ofcom’s findings have focused on “unconstrained” demand, meaning passengers have access to free on-board Wi-Fi or their own mobile data service.

Using this methodology, it said, a 550-capacity mainline train needs 80Mbps of capacity today, rising to 1.7Gbps in 2025; a crowded 800-capacity, eight-coach commuter train needs 120Mbps today, rising to 2.4Gbps in 2025; and an overcrowded 1,200-capacity, 12-coach commuter train, such as those operated on the busiest routes in southeast England, needs 180Mbps today, rising to 3.6Gbps by 2025.

The 2025 figures relate to the highest usage scenario and reflect a requirement of 1.5Mbps per passenger averaged over all passengers, as well as what the average monthly mobile data consumption per person might be, given anticipated growth in data-hungry applications, uplifted to reflect the propensity of consumers to use much more data on a Wi-Fi connection than on a 4G LTE connection.

Ofcom found that only the millimetre-wave spectrum bands truly have the capacity to meet a demand level of 1Gbps or more. The upper 26GHz band (26.5-27.5GHz) should be straightforward to press into service as it is already expected to be widely used for future 5G mobile deployments; the lower 26GHz (24.25-26.5GHz) band contains less potential as there are already a number of bodies using it extensively for fixed links with individual licences; and the 66-71GHz band is currently vacant and in the process of being made available on a licence-exempt basis, although this may be less suitable for rural lines because transmit power will be quite low, requiring more trackside base stations.

“We believe the 26GHz band is likely to offer the best prospects for track-to-train connectivity solutions that meet our demand scenarios for the mid- to late 2020s,” said the report’s authors.

“This is due to its combination of high bandwidth, more straightforward coexistence environment, large potential equipment ecosystem, and comparatively modest opportunity cost in the rail connectivity application.”

Ofcom said its preferred approach would be one in which it could make spectrum licences available on demand to “any applicant for the purpose of providing track-to-train connectivity along a rail corridor”. It added that work could begin on putting such a regime in place within the next 12 months, in the case of the upper 26GHz band.

“Designing a network to provide track-to-train connectivity will involve many different considerations other than the choice of spectrum band, such as determining the business model on which such a service would be run, how the deployment would be funded, and potential interoperability across multiple routes or TOCs [train operating companies],” said Ofcom.

“We will continue to work with industry and the government as they further develop their plans for the enabling and deployment of any solutions to improve passenger connectivity on rail routes where these plans involve the use of radio spectrum.”