A major new telecoms programme is currently being rolled out across London’s Tube, providing passengers with cellular coverage throughout the entire network for the first time.
When Wi-Fi was first introduced on the London Underground ahead of the 2012 Olympics, it felt like a watershed moment. Although connectivity could sometimes be patchy and was confined to stations, it marked the beginnings of a 21st century makeover for the capital’s ageing metro, a digital bridge between the subterranean Victorian world and the data-saturated landscape above. Over a decade on, however, and that makeover doesn’t feel so fresh, struggling to keep pace with modern demands for 24/7 connectivity.
In response, Transport for London (TfL) is undertaking a major programme to deliver a new communications network for the London Underground, known as the Telecommunications Commercialisation Project (TCP). As well as providing a digital backbone for the railroad’s own operations, the vast array of new cellular and fibre optic infrastructure will provide customers with ‘always-on’ coverage throughout their Tube journeys for the first time.
“It’s all really about customers and the customer experience,” Matthew Griffin, head of Telecoms Commercialisation at TfL, told The Engineer. “The Holy Grail is obviously getting connectivity everywhere, all the time… fundamentally for the customer, it’s going to be a whole different experience.”
Finding space to site the telecoms equipment a major challenge
Working in partnership with telecoms specialist BAI Communications, TfL is currently in the process of fitting out 137 stations and 400kms of tunnel pairs with a host of new equipment. In the stations, commuters’ phones connect to radio frequency (RF) antennas – typically six per platform – which in turn connect to cabinets up to 90 metres away over structured cabling.
At the cabinets, the RF signals are converted to optical light, which then travels up to 11 kilometres to one of 10 data centres currently being built in partnership with the four main mobile network operators (MNOs): Three, EE, Vodafone, and Virgin Media O2. The data centres convert the signals back to RF, joining the rest of the MNOs’ cellular traffic.
“Stations like Kings Cross have a massive amount of antennas,” explained Ken Ranger, chief operating officer at BAI Communications UK. “Smaller stations like Warwick Avenue, a lesser amount of antennas. As an example, there’s approximately 600 of these cabinet locations and approximately 8,000 antennas throughout all the stations.”
With Wi-Fi connectivity in most Tube stations old hat at this point, BAI and TfL shouldn’t expect much praise from blasé London commuters for enhancing those signals. The real showstopper of the TCP – the trick that will get tongues wagging, both literally and figuratively – will be the inter-station connectivity as trains careen through tunnels, comms blackspots now suddenly illuminated with cellular coverage and high-speed data. This is achieved by the presence of a linear antenna – known as a ‘leaky feeder’ – that runs the length of the tunnels, linking London’s depths to the information superhighway.
The Holy Grail is obviously getting connectivity everywhere, all the time… fundamentally for the customer, it’s going to be a whole different experience
“It’s about 175mm by-diameter cable that has to run at window height all throughout the underground, so we have to find space to put this cable against the wall,” said Ranger. “Your phone radio frequency goes through the window of the Tube, into the antenna. Every 500 metres or so, there’ll be a high-power radio and that’s where it converts it back to optical light, 11 kilometres to the data centre.”
Needless to say, the Tube was not originally designed to house advanced telecoms infrastructure. Rolling it out across the network is not just a major engineering challenge, it’s a project management task of labyrinthine complexity, requiring high levels of coordination between BAI, TfL and the various teams of workers needed to carry out the installations.
“It’s a lot of work,” said Ranger. “It’s time constricted. There’s not a lot of space. The antennas at the station, time constricted, not a lot of space. But finding where the cabinets go and these high-power radios, that’s the complex part, because you have to do the fire engineering, the electrical upgrades, the cooling of the equipment. Power, is there enough? Is the floor strong enough to take the structural loads imposed. So that’s all the works in the project, in a network that runs for 20 hours a day to the public and only closes four hours a day, but then it’s doing other maintenance activities at night.
Given the complexity of the TCP, it’s perhaps not surprising that there’s been a 10-year gap between the original Wi-Fi installation and the current programme. According to TfL’s Griffin, several plans were hatched in the interim, but most never made it off the drawing board. Where the new project has succeeded, he said, was in the tightknit coordination between TfL and BAI from the outset.