[FI] VR laser-treating windows to improve wifi reception

[MoominAndChips]

VR aims to improve train Wi-Fi by laser-treating carriage windows

Last year, VR invested five million euros in a more efficient Wi-Fi connection – with no discernible improvement.

yle.fi

Given that the wifi signal should be coming from within the train, I assume this is about the cellular connection the wifi links to. How does etching the glass help, and why not have an external antenna?

 

[stuving]

VR aims to improve train Wi-Fi by laser-treating carriage windows

Last year, VR invested five million euros in a more efficient Wi-Fi connection – with no discernible improvement.

yle.fi

Given that the wifi signal should be coming from within the train, I assume this is about the cellular connection the wifi links to. How does etching the glass help, and why not have an external antenna?

Yes, the headline confused WiFi with mobile phone data - quite common these days. In the text, it says:

On Friday, the company unveiled its latest plan, saying it will laser-engrave train windows as a means of facilitating access to internet base stations as trains roll past them.

According to VR, mobile phone reception is hampered by the poor permeability of radio signals into train cars, and their rapid movement past telecom operators' base stations.

Laser engraving burns patterns onto train windows, which should improve the ability of data and phone signals to penetrate the train interior.

The windows are metallised to reduce solar heat gain, with the side effect of blocking radio waves. Quite a lot of work has been done on this idea of cutting narrow gaps into the metal layers to let radio waves through while keeping most of the low emissivity benefits. The most popular design appears to be a grid of engraved lines at about 2 mm spacing to form small squares. If the radio screening effect is large, it should be possible to get rid of much of that signal loss.

The process does have drawbacks, though. Screening of the WiFi bands helps to protect the inside of the carriage from any signals outside. In theory the etched pattern could be designed to still block those bands and pass other radio bands, but as the bands are very close I doubt that would work well. And all these newly exposed edges of the metallisation layers will allow oxygen and moisture get in and corrode the metal, so shortening the life of the window. Making low-e windows with a suitable pattern from new will allow those edges to be protected.

 

[rf_ioliver]

Funny, but they mean 5G/4G signals not Wifi.

Actually VR's onboard Wifi isn't too bad and Finland's 5G/4G density is very good. The are plans to increase the base stations along the tracks - not just for passenger convenience either. The problems you start getting are more to do with interference between base stations, though since 4G the way the spectrum and signal power levels are managed is much more sophisticated, and then getting the other necessary infrastructure to those base stations. After that you're into other problems such as cell handover, signal interference (25kV power lines don't help), roaming and all the other fun of managing mobile communications.

I just love Joakim Strand's (Finnish MP) comparison of Earth-Moon communications in 1969 with modern day cell infrastructure....<sigh>

 

[MarcVD]

As a side question, anyone around knows how 4G/5G signal reception in automobiles work today ? I remember very well old mobile phones (think Nokia 3310 and the like) having a special connector for the car kit that would link to an outside antenna. No such connector anymore on any smartphone today. But cars still have an outside antenna, like a shark fin or integrated in the rear windshield. How does that work and could the same technology be used in a rail vehicle?

 

[rf_ioliver]

Typically modern phones and modern base stations rely upon significant improvements in radio technology since the early 1G/2G years. Also the density of base stations has increased somewhat too, plus the way base station handover is managed, signal strength, optimisation (MIMO antennas) etc.

Now it is possible that your phone is connecting to the car's Wifi, which is then routed over a (most likely 4G) or 5G connecting - at least my Passat can do this, but VW's Infotainment system software is just really really bad, so I let the phone work on its own connection. Also, I think VW charge for this service, and it isn't cheap.

If you're on a train then there are quite a few options (also applies to home, car etc) - on-train Wifi will aggregate everything and route it over 4G/5G (even satellite is possible), you can do the same with a base station (eNB, gNB in 4G or 5G parlance) and aggregate from there, or just let your phone connect to the nearest/most suitable base station. One issue with the local base stations (eg: one in each carriage) is that they'll be provisioned on a per-operator basis, and you get into roaming agreements etc, so some phones will be rejected because they're using the wrong operator. Another option is that the train company sets itself up as a private operator and routes calls from there to the public operators. Not particularly hard to do, but maintenance is a problem and antennas and the rest of the base station equipment isn't cheap. The issue with these ways is still of course getting sufficient bandwidth (and signal reliability) from the train to the rest of the telecoms network, which requires good cell coverage.

 

[MarcVD]

Another option is that the train company sets itself up as a private operator and routes calls from there to the public operators. Not particularly hard to do, but maintenance is a problem and antennas and the rest of the base station equipment isn't cheap. The issue with these ways is still of course getting sufficient bandwidth (and signal reliability) from the train to the rest of the telecoms network, which requires good cell coverage.

As far as l know the replacement of GSM-R, FRMCS, has a provision for that.

 

[rf_ioliver]

FRCMS is much more modern; to FRCMS, GSM-R is just an application. GSM-R itself is getting to be a bit of a nightmare, particular with interference from other radio channels. For example, Finland did not move to GSM-R because of this (amongst other issues, eg: the Sr1 locomotives act like giant antennas themselves).

 

[Bletchleyite]

UK Stadler units have this etching, you can barely see it but if you look for it you can.

 

[jpl]

The windows of public transportation vehicles sometimes have a low-emissivity coating which is basically a thin metal oxide layer designed to block infrared radiation and reduce heat transfer. One disadvantage is that it can block radio waves as well. What I think is that the laser cuts break the Faraday cage allowing the radio waves to pass through.

Speaking of radio stuff. During years 2004-2006, Finland's railways did move from analogue VHF radio to the system called RAILI which used GSM-R technology but it was short lifed. From the summer 2019 Finland has been using VIRVE for railway radio communications. It is a government network based on TETRA technology and is used by various departments such as Police, Ambulance and Fire & Rescue. There have been talks to scrap the TETRA and use commercial 4G/5G mobile networks instead.

The first line to be equipped with ETCS (Lielahti)-Suoniemi-Rauma/Pori is going to use FRMCS as railway radio even though FRMCS is not fully specified yet. So there will be kind of pre-FRMCS without constructing their own network - they will be relying on commercial operators 4G/5G networks instead. The ETCS level transition from NTC to L2 is planned between Siuro and Suoniemi instead of Lielahti as commuter trains run to Nokia and those units will not receive ETCS onboard units.

 

[AdamWW]

UK Stadler units have this etching, you can barely see it but if you look for it you can.

Best not to. Once you've seen it, it's harder to ignore....

 

[rf_ioliver]

Speaking of radio stuff. During years 2004-2006, Finland's railways did move from analogue VHF radio to the system called RAILI which used GSM-R technology but it was short lifed. From the summer 2019 Finland has been using VIRVE for railway radio communications. It is a government network based on TETRA technology and is used by various departments such as Police, Ambulance and Fire & Rescue. There have been talks to scrap the TETRA and use commercial 4G/5G mobile networks instead.

The first line to be equipped with ETCS (Lielahti)-Suoniemi-Rauma/Pori is going to use FRMCS as railway radio even though FRMCS is not fully specified yet. So there will be kind of pre-FRMCS without constructing their own network - they will be relying on commercial operators 4G/5G networks instead. The ETCS level transition from NTC to L2 is planned between Siuro and Suoniemi instead of Lielahti as commuter trains run to Nokia and those units will not receive ETCS onboard units.

The GSM-R implementation suffered from a lot of technical problems - mainly due to interference from the adjacent bands. TETRA on the other hand has a lot of nice features for reliable communication, but it is getting old and VIRVE phones aren't exactly cheap either. Much easier to put all that into the 5G application space. FRMCS is evolving - it is a big area; I've worked on aspects of it.