Bluetooth interference at Liverpool St station

[VauxhallandI]

When I travel to work I use my Bluetooth headphone.

However when I walk across the station to leave my music is cut out or broken up for a period of about 4 or five meters.

I am usually arriving at platforms 1-4 and exiting via the escalators up to Liverpool St.

The area is halfway across the concourse

Any ideas what may be causing it?

 

[ewsclass]

This is common in any densely populated area, it's just interference from other Bluetooth devices, as well as devices such as Wi-Fi Access Points. Interference from on-train equipment such as motor drives and just the nature of 25KV OHLE is also enough to generate RF noise that would be enough to interfere with BT.
Hope that helps

 

[jh64]

I don't know how large the Liverpool Street concourse is, but bluetooth connection problems in wide open spaces is a known thing.

The Verge’s Dan Seifert might have just figured the whole thing out, sharing his thoughts on Twitter. According to Seifert, headphone makers have told him that the reason for the cut outs is the fact that Bluetooth needs surfaces to bounce their connections off, whether they are walls or ceilings. Walking across a road is a situation where neither of these things are likely to be around, causing connection issues.

AirPods Or Bluetooth Headphones Cutting Out When Crossing Streets? Here's Why

Here's why your AirPods or any other Bluetooth headphones might be cutting out when crossing streets day in and day out.

www.redmondpie.com

I've experienced this myself at a particular road crossing near my house, my old headphones would reliably cut out at the same point each time I stepped over.

 

[danm14]

I don't know how large the Liverpool Street concourse is, but bluetooth connection problems in wide open spaces is a known thing.

AirPods Or Bluetooth Headphones Cutting Out When Crossing Streets? Here's Why

Here's why your AirPods or any other Bluetooth headphones might be cutting out when crossing streets day in and day out.

www.redmondpie.com

I've experienced this myself at a particular road crossing near my house, my old headphones would reliably cut out at the same point each time I stepped over.

Unfortunately, that article is complete and utter, absolute, unmitigated bull****.

Bluetooth uses the 2.4 GHz band. Radio waves at this frequency pass straight through objects such as walls and ceilings - not bounce off them.

Bluetooth also uses exactly the same frequencies as 2.4 GHz WiFi - so the suggestion that Bluetooth's 2.4 GHz radio waves behave differently to WiFi's 2.4 GHz radio waves is nonsense.

In fact, as WiFi can also use the 5 GHz band - not just the 2.4 GHz band like Bluetooth, if anything it is actually WiFi radio waves which will "bounce off walls and ceilings" - not Bluetooth

 

[185]

Manchester Picc too.

 

[VauxhallandI]

This is common in any densely populated area, it's just interference from other Bluetooth devices, as well as devices such as Wi-Fi Access Points. Interference from on-train equipment such as motor drives and just the nature of 25KV OHLE is also enough to generate RF noise that would be enough to interfere with BT.
Hope that helps

Odd as the point it happens is at the point I’m the furthest from any wall or ceiling.

There is a large to almost overhead?

 

[Ediswan]

Odd as the point it happens is at the point I’m the furthest from any wall or ceiling.

Maybe there is something under the concourse causing interference.

 

[VauxhallandI]

Maybe there is something under the concourse causing interference.

Quatermass!

 

[dosxuk]

Radio waves at this frequency pass straight through objects such as walls and ceilings - not bounce off them.

Actually you do get a significant amount of bounce, and digital signals can use the extra data received as a result of bounces to rebuild a transmission that would otherwise be too weak or corrupted.

I've personally bounced 2.4GHz signals off buildings before to get a signal to somewhere there wasn't otherwise the direct line of sight needed.

 

[Haywain]

Unfortunately, that article is complete and utter, absolute, unmitigated bull****.

Sounds like complete cobblers to me too. If it was true my headphones would stop working in the wide open spaces of the local park, but they don't.

 

[Omnishambles]

Get the same problem walking across Waterloo concourse arriving in the mornings. Have always just assumed interference from numbers of people using similar

 

[IceBlue]

It’s purely down to interference, due to the number of Bluetooth users in the area.

Bluetooth operates over 40 channels, and transmits packets (tiny pieces of data) over one channel at a time, but constantly and randomly changing the channel in use.

Should two nearby (<10m) devices attempt to send a packet on the same channel at the same time, they will likely interfere with each other and cause the data received to be incorrect. The receiving side detects when data is incorrect and can rerequest the data from the sender, with some level of packet loss a normal and expected part of Bluetooth use. This happens in fractions of a second and is completely unnoticeable to the user.

The problem is where there are high concentrations of people in relative proximity like a station concourse, a much higher proportion of channel collisions will be happening causing too many packets to be lost such that error correction can’t keep up, causing the interruptions to audio as reported here.

 

[VauxhallandI]

I can’t believe it’s because of lots of other people doing the same. It only happens in one area, every time so it must be a fixed source?

I think I’m going to have to start wandering about to check the facts now I will report back with my findings

 

[alf]

I plan to be at Liverpool Street very early next Sunday morning when nobody is about.
I shall take the exact route indicated on post 1 & see if my music is broken/cut out for 4 metres.

If it is broken & the concourse is deserted, as I expect it will be, then Iceblue’s suggestion, post 12, is wrong in explaining the Liverpool Street Bluetooth phenomena as being too many Bluetooth users in the area.
So watch this space........unless I oversleep!

Place your bets.

 

[tellytype]

2.4 gigs is horribly congested & unregulated. I'm at STP on Thursday with a Spectrum Analyser, if someone reminds me I'll take a plot of just how bad the noise is in that part of the spectrum in public places (or just about anywhere populated) these days.

 

[43066]

It’s purely down to interference, due to the number of Bluetooth users in the area.

Bluetooth operates over 40 channels, and transmits packets (tiny pieces of data) over one channel at a time, but constantly and randomly changing the channel in use.

Should two nearby (<10m) devices attempt to send a packet on the same channel at the same time, they will likely interfere with each other and cause the data received to be incorrect. The receiving side detects when data is incorrect and can rerequest the data from the sender, with some level of packet loss a normal and expected part of Bluetooth use. This happens in fractions of a second and is completely unnoticeable to the user.

The problem is where there are high concentrations of people in relative proximity like a station concourse, a much higher proportion of channel collisions will be happening causing too many packets to be lost such that error correction can’t keep up, causing the interruptions to audio as reported here.

Makes sense - exactly the same thing happens at London Bridge when it’s busy.

 

[Islineclear3_1]

It’s purely down to interference, due to the number of Bluetooth users in the area.

Bluetooth operates over 40 channels, and transmits packets (tiny pieces of data) over one channel at a time, but constantly and randomly changing the channel in use.

Should two nearby (<10m) devices attempt to send a packet on the same channel at the same time, they will likely interfere with each other and cause the data received to be incorrect. The receiving side detects when data is incorrect and can rerequest the data from the sender, with some level of packet loss a normal and expected part of Bluetooth use. This happens in fractions of a second and is completely unnoticeable to the user.

The problem is where there are high concentrations of people in relative proximity like a station concourse, a much higher proportion of channel collisions will be happening causing too many packets to be lost such that error correction can’t keep up, causing the interruptions to audio as reported here.

This is my understanding too, especially if there is a WiFi transmitter in the area as this uses up a lot of the spectrum. I think that any delay in sending data packets causes signal buffering and a resultant drop in signal level but I stand to be corrected. Also, Bluetooth wasn't designed to send large packets of media data originally but maybe this has changed now?

 

[MrJeeves]

Actually you do get a significant amount of bounce, and digital signals can use the extra data received as a result of bounces to rebuild a transmission that would otherwise be too weak or corrupted.

It stretches further than that even... devices can use these extra bounces to transmit and receive extra data through something called multi-path propagation.

 

[VauxhallandI]

I did the walk at 8am today, the interference was directly below the TV.

Not as bad as some other times however it was quieter than usual.

 

[dgl]

Some devices can be quite electrically noisy, emitting a ton of interference. I've noticed that in some of the caravans at work if I put the lights on (circular LED sealed units) my DAB radio will start to have reception problems.
Also any signal of a high enough power can swamp out a receiver, even the wanted one. Whilst devices will have filters to block out unwanted frequencies they can only block signals out so much, once enough unwanted signal(s) are present any filters become redundant and the device can no longer distinguish between the wanted and unwanted signals.

As for signals bouncing off things, that can be very much an issue and causes multipath interference, more of a problem with analogue signals but it's not gone away. Caused ghosting on analogue TV where two (or more) identical signals were received at different times.

 

[Ediswan]

Caused ghosting on analogue TV where two (or more) identical signals were received at different times.

For fun, you could do the maths, work out the path difference, then try and figure out where the bounce was occuring.

625 line analogue TV signals are much more interesting than DVB
Started out as B&W
Then found a way to add colour
Then found a way to add 'teletext'
Then found a way to add stereo sound
All while remaining compatible with the original B&W receivers

 

[dosxuk]

Is there a catering outlet nearby? Microwave ovens operate on the same frequency range and can generate a fair bit of RF noise in their vicinity (not anywhere near enough to cook you, but enough to cause errors on signal reception).

 

[yoyothehobo]

At Leeds station there is an area near the gate line on platform 8 which stretches across to 9-11 platforms. Is always there so i assume its a fairly constant source of interference, but could be just about anything to be honest.

 

[VauxhallandI]

Is there a catering outlet nearby? Microwave ovens operate on the same frequency range and can generate a fair bit of RF noise in their vicinity (not anywhere near enough to cook you, but enough to cause errors on signal reception).

Not in the case of Liverpool St. As you pass the food outlet there is no interferenc. It really happens at the point of greatest volume in the whole building