4G will be available across the tube by 2021, even in tunnels. They need an interesting type of antenna [0], basically a long wire running along the tunnel that

4G will be available across the tube by 2021, even in tunnels. They need an interesting type of antenna [0], basically a long wire running along the tunnel that 'leaks' radio signals, because 4G won't propagate down tunnels. The mayor is trying to take credit for it but it's actually supporting the new Emergency Services Network: an over ambitious plan to replace all police and emergency radios with 4G devices. [0] https://eandt.theiet.org/content/articles/2019/01/online-underground-the-technology-behind-the-tube-s-forthcoming-4g-network/ https://eandt.theiet.org/content/articles/2019/01/online-und...