LU/Elizabeth Line 4G update

[JonnyM]

The Elizabeth Line core uses CBTC which transmits instructions from the signalling system directly to the train via radio frequencies. I believe those frequencies overlap with WiFi and/or some cellular network bands, hence the concerns.

I am still amazed as why this wasn't spotted during the planning stages of mobile connectivity on the EL. Surely, any comms engineer would have looked at these plans and thought to themselves that with the mixture of railway signalling and telecoms frequencies wouldn't work together?

 

[MrJeeves]

... which aren't 2.4GHz

But out of band emissions (OOBE) exist, which means that noise outside of those bands is inevitably created when transmitting on those frequencies. I think it's much less a case of "does this interfere" and more a case of "have we tested that this doesn't interfere".

I am still amazed as why this wasn't spotted during the planning stages of mobile connectivity on the EL. Surely, any comms engineer would have looked at these plans and thought to themselves that with the mixture of railway signalling and telecoms frequencies wouldn't work together?

To be fair, the CBTC contract was awarded back in Nov 2012. 4G had been around for a month only on EE, and 3G only used 900 MHz and 2100 MHz in the UK. I don't think we had really realised how important it'd be for the future at that point, and it's only in the last few years (probably 2018 onwards) that it's become truly apparent that there's a need for mobile coverage in underground transport.

 

[Gigabit]

Presumably London Underground signalling works in a different way hence no interference?

 

[MrJeeves]

Presumably London Underground signalling works in a different way hence no interference?

I think most of LUL uses SelTrac, now sold by Thales (sadly not the team I used to work with!), and that typically uses low frequency communications compared to what we see with Siemens' Eurobalize ERTMS implementation.

 

[mrmartin]

But out of band emissions (OOBE) exist, which means that noise outside of those bands is inevitably created when transmitting on those frequencies. I think it's much less a case of "does this interfere" and more a case of "have we tested that this doesn't interfere".

But *in band* emissions exist on 2.4GHz - eg wifi and bluetooth or many wireless mics. That is surely much more of a problem than any overspill from LTE2300 for example. In theory you could have a microwave oven with poor shielding absolutely bombarding the 2.4GHz channel too (perhaps in a staff room nearish the tracks - I had one that would completely kill all WiFi and bluetooth when it was on even in the next room out of the box).

If you're using the 2.4GHz channel you have to expect a high degree of interference simply by its nature. It is not restricted and many devices of varying quality and RF emission standards will operate in it (frankly I think it is a totally mad choice of channel for such a safety critical feature, you'd be better off using pretty much anything else for this reason).

 

[MrJeeves]

But *in band* emissions exist on 2.4GHz - eg wifi and bluetooth or many wireless mics. That is surely much more of a problem than any overspill from LTE2300 for example. In theory you could have a microwave oven with poor shielding absolutely bombarding the 2.4GHz channel too (perhaps in a staff room nearish the tracks - I had one that would completely kill all WiFi and bluetooth when it was on even in the next room out of the box).

If you're using the 2.4GHz channel you have to expect a high degree of interference simply by its nature. It is not restricted and many devices of varying quality and RF emission standards will operate in it (frankly I think it is a totally mad choice of channel for such a safety critical feature, you'd be better off using pretty much anything else for this reason).

I haven't seen any evidence that 2.4 GHz is what they're using other than your claim that's the case with a pdf that doesn't seem to mention it anywhere.

As far as I'm aware the main concern was with n78 5G (3400-3800 MHz), hence why the stations have gone live without this.

 

[mrmartin]

I haven't seen any evidence that 2.4 GHz is what they're using other than your claim that's the case with a pdf that doesn't seem to mention it anywhere.

As far as I'm aware the main concern was with n78 5G (3400-3800 MHz), hence why the stations have gone live without this.

Sorry I thought it did, but you're right. Anyway I'm 90% certain it uses 2.4GHz or alternatively the same frequency as 5GHz WiFi.

https://core.ac.uk/download/84004038.pdf

"The radio system used in the Copenhagen S-train CBTC
system, called Airlink [42], is based on Wi-Fi. However, previous generations of Airlink still use proprietary custom-built
radio technology, based on spread-spectrum and operating in
the 2.4 and 5.9 GHz bands. The latest project using this spreadspectrum based system is the recently contracted NYCT’s
Queens Boulevard Line [60]."

https://core.ac.uk/download/pdf/154333578.pdf

Nearly all CBTC installation today work in one of the three, license-free ISM bands:
900 MHz, 2.4 GHz, and 5 GHz. Of these, 2.4 GHz is the most popular among CBTC
suppliers, followed by 5 GHz [83].

It seems Airlink MT actually uses off the shelf WiFi itself as the communications protocol, which I find absolutely astounding. It would be trivial to jam it. WiFi is exceedingly easy to jam. And while they go to lengths to say it is encrypted with IPSec, it's probable in the lifetime of the trains that there will be many security flaws found in the protocol. I'm very doubtful as to whether they will keep the trains up to date security wise quickly enough.

 

[kacper]

Paddington EL has 5G for me on vodafone

 

[MrJeeves]

Paddington EL has 5G for me on vodafone

"5G" is meaningless unless you take the time to go and delve into the details of what exact frequency bands you're connected to.

Mobile networks simply need to set one parameter to "true" in order to make your device show the 5G icon when you're only connected to 4G. This is called "upper layer indication" or ULI.

There's a good video (from the 10 seconds I've skimmed) about this:

 

[TFN]

Paddington EL went live last week. The rest of the COS stations is going live very very soon.

Still no word on the tunnel sections.

 

[Benjwri]

Paddington EL went live last week. The rest of the COS stations is going live very very soon.

Still no word on the tunnel sections.

Had signal of some kind at Tottenham Court Road and Bond Street on Thursday as well.

 

[MrJeeves]

Had signal of some kind at Tottenham Court Road and Bond Street on Thursday as well.

Those core stations have been live since December.

 

[blueberry11]

I initially thought that wifi/4g would only be available to the new sections of the network (the 1979/1999 Jubilee line, 2008 Heathrow Terminal 5 and 2021 Northern line extension), plus the tunnel sections of Crossrail due to the fact that the underground was built way before the internet was a thing. I never thought they would extend it to cover most of the network due to the complexities. I also thought the Elizabeth line would have it from day one given the delays.

 

[thomalex]

I initially thought that wifi/4g would only be available to the new sections of the network (the 1979/1999 Jubilee line, 2008 Heathrow Terminal 5 and 2021 Northern line extension), plus the tunnel sections of Crossrail due to the fact that the underground was built way before the internet was a thing. I never thought they would extend it to cover most of the network due to the complexities. I also thought the Elizabeth line would have it from day one given the delays.

Technically it's not that complicated. Once you've got the equipment in at the stations all you then need is a cable run down the tunnels, the 'leaky feeder'. There's plenty of cables already run down the sides of the older tunnels so this just adds another one.

 

[MrJeeves]

Technically it's not that complicated. Once you've got the equipment in at the stations all you then need is a cable run down the tunnels, the 'leaky feeder'. There's plenty of cables already run down the sides of the older tunnels so this just adds another one.

And there are even existing leaky feeders down the old tunnels too!

Part of the reason why 4G/5G has to cover all of the underground is for the future Emergency Services Network (ESN) which runs off of EE's network and is set to replace Airwave/Tetra when it's finished being delayed.

 

[Gigabit]

And there are even existing leaky feeders down the old tunnels too!

Are these being re-used? My guess is no?

Actually I find the scope of the project very comprehensive, which makes it more baffling that they are seemingly skipping low hanging fruit at certain stations. But perhaps they'll come back and do these in the future - one can dream.

 

[MrJeeves]

Are these being re-used? My guess is no?

Nope, not suitable for it. Airwave (both police and LU's "Connect" system) use ~380-420 MHz, while the lowest 4G band in the UK until 600 MHz clearance is 700 MHz.

Antennas and feeders have to be designed for frequency bands in order to be effective at transmitting them. It would be possible, but would result in a terrible experience.

Plus I don't think a fault with some mobile network equipment breaking police radios or LU's cab radio system would be something people would be particularly happy about!

 

[Gigabit]

I assume above ground coverage on the Underground is already comprehensive although I've found it weak in places. I wonder what the metrics they use for "covered" are.

 

[Taunton]

I will actually be quite glad if the Wireless on the Liz is not extended.

One of the groups who quite rapidly appeared is those zealots who take up position right by the doors, straddling with their bodies jammed against the door frame, fiddling away with their game, most commonly by dextrous thumb movements, who regard other passengers, particularly those wishing to push the Door Open button they are obstructing, as some infringement of their personal liberty.

This is all before WiFi is fully rolled out. Goodness what it will be like afterwards.

 

[MrJeeves]

I assume above ground coverage on the Underground is already comprehensive although I've found it weak in places. I wonder what the metrics they use for "covered" are.

Very little data is needed for voice-only push-to-talk which ESN uses, so realistically as long as you could make a phone call okay somewhere it's probably fine.

ESN also uses something called guaranteed bitrate (GBR) bearers which means they are "guaranteed" a certain amount of bandwidth on the network, so if a site was fully loaded in a tourist hotspot, or (more likely) the low frequency band is heavily loaded by a bunch of people using the network indoors, ESN users would get priority over "normal" network users.

 

[Gigabit]

Very little data is needed for voice-only push-to-talk which ESN uses, so realistically as long as you could make a phone call okay somewhere it's probably fine.

ESN also uses something called guaranteed bitrate (GBR) bearers which means they are "guaranteed" a certain amount of bandwidth on the network, so if a site was fully loaded in a tourist hotspot, or (more likely) the low frequency band is heavily loaded by a bunch of people using the network indoors, ESN users would get priority over "normal" network users.

I was thinking more for consumer use, for example some of the sections on the District Line outdoors can be a bit hit and miss.

 

[MrJeeves]

I was thinking more for consumer use, for example some of the sections on the District Line outdoors can be a bit hit and miss.

No idea honestly.

I'm sure EE and the Home Office have researched TfL's network extensively and identified a large number of areas that require improved coverage, and are also hard at work to rectify those to ensure the swift rollout of ESN into the real-world! /s

 

[Gigabit]

No idea honestly.

I'm sure EE and the Home Office have researched TfL's network extensively and identified a large number of areas that require improved coverage, and are also hard at work to rectify those to ensure the swift rollout of ESN into the real-world! /s

Thanks for your candid response.

We're going to end up in a weird world at some point, with a lot of the actual underground being a lot faster and more reliable than the overground parts which seems a missed opportunity to me but I am sure somebody has done the numbers on it.

 

[MrJeeves]

We're going to end up in a weird world at some point, with a lot of the actual underground being a lot faster and more reliable than the overground parts which seems a missed opportunity to me but I am sure somebody has done the numbers on it.

Welcome to the wonderful world of mobile networks.

 

[Gigabit]

Welcome to the wonderful world of mobile networks.

Just seems to be something that doesn't seem that complicated to actually solve as other countries seem to have done. But I am sure I am not as knowledgable as you on the "why".

 

[jon0844]

We're going to end up in a weird world at some point, with a lot of the actual underground being a lot faster and more reliable than the overground parts which seems a missed opportunity to me but I am sure somebody has done the numbers on it.

That was the case when Wi-Fi was first introduced. Many a train was let go so I could upload files at a high speed, compared to (at the time) slow 3G or ropey Wi-Fi in a Starbucks type environment.

Even with mobile, a controlled environment underground can quite easily offer a far better and more consistent experience than above ground where you are competing with nearby offices, residential areas and all the structures that can impact your signal just by moving a few steps one way or another.

With contiguous 5G coverage, I can imagine people loving the ability to leave an event, photo shoot or whatever, and upload the data at high-speed (or download files) while on the move.

 

[Gigabit]

That was the case when Wi-Fi was first introduced. Many a train was let go so I could upload files at a high speed, compared to (at the time) slow 3G or ropey Wi-Fi in a Starbucks type environment.

Even with mobile, a controlled environment underground can quite easily offer a far better and more consistent experience than above ground where you are competing with nearby offices, residential areas and all the structures that can impact your signal just by moving a few steps one way or another.

With contiguous 5G coverage, I can imagine people loving the ability to leave an event, photo shoot or whatever, and upload the data at high-speed (or download files) while on the move.

I am not sure if the service on the overground sections can be described as "contiguous" but TfL seem to think it already is.

 

[jon0844]

I am not sure if the service on the overground sections can be described as "contiguous" but TfL seem to think it already is.

I wouldn't expect it to be, as there are going to be gaps and differences in service quality if only because various sites will have different capabilities (backhaul, bands etc). Just as it is as you walk or travel around the city at ground level, or enter buildings etc.

On the underground sections it should be far more organised and consistent.

 

[Gigabit]

I wouldn't expect it to be, as there are going to be gaps and differences in service quality if only because various sites will have different capabilities (backhaul, bands etc). Just as it is as you walk or travel around the city at ground level, or enter buildings etc.

On the underground sections it should be far more organised and consistent.

My point is that TfL don't seem to see a need to do anything about the above ground coverage on the Underground, as it is the problem of the MNOs. I can take their argument to a certain degree but they'd surely be intelligent to build infrastructure at least in some of the above ground stations!

 

[jon0844]

My point is that TfL don't seem to see a need to do anything about the above ground coverage on the Underground, as it is the problem of the MNOs. I can take their argument to a certain degree but they'd surely be intelligent to build infrastructure at least in some of the above ground stations!

I am not sure they'd want to pay for anything more than they have to. If it's above ground and outdoors, they'd be happy to rely on whatever coverage there is. Of course that leads to the obvious problem of coverage blackspots, especially with some of the old station construction materials and corridors/tunnels etc.

The best they could/should do is allow access to their property to add small cells or whatever, but that would likely be separate to the company rolling out dedicated equipment within stations. I see how that might seem confusing, but the two things are separate - even if a phone user, hopefully, swaps from one to another without issue.