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Onboard GSM repeater

I know the legal aspects of that but has anybody any experience with using a gsm repeater onboard an aircraft to allow at least some data communication?
I know that a typical gsm repeater has two antennas – one external – connecting with a distant gsm station – other – internal – creating a local gsm signal.
Those antennas have to be separated which is difficult in our case.
My idea is to use some kind of repeater which only creates a wifi signal, not gsm.
I think that being able to receive TAFs, METARs when flying on flight levels is a great safety feature.
That would actually require a wifi/gsm router which has external, powerful gsm module. Small antenna could be inserted in one of the drain hole in the aft bottom fuselage.
Just loose thinking.
Any ideas?
Of course a satphone could also solve all those problems.

Poland

Compared to just using a mobile terminal, a plain rod antenna through a drain hole is only a workaround for signal attenuation by the fuselage but not for anything else, so the gain will be minimal. However, one can take advantage of the fact that all base stations are below the aircraft, and that seeing too many base stations will impair cellular connectivity rather than improve it. So, it makes sense to use a directional antenna (say, 6 dB gain), pointing it downwards. A flat-shaped directional antenna can be installed instead of an inspection cover on the bottom surface of the wing. Also, a wired data connection will be better than Wi-Fi, although this restricts your choice of terminals.

LKBU (near Prague), Czech Republic

The difficulties of receiving GSM/4G/LTE data in the flight levels is not only down to the antenna. The networks seems to detect your distance and they are at least to some degree even actively shutting down such connection which harm their network, you also have doppler effects if you go fast enough etc. In the end you can use your iPhone as far as it works and if you want to start spending money on more capabilities go for a satellite option as that is the only thing which currently works.

www.ing-golze.de
EDAZ

Sebastian_G wrote:

The networks seems to detect your distance and they are at least to some degree even actively shutting down such connection which harm their network, you also have doppler effects if you go fast enough etc.

The distance to base station is limited to some 35 km, so it should not be an issue.
“Connections harming the network” are mostly those spanning too many base stations, so a directional antenna should help by limiting the number of stations in sight.
Doppler effect should not be an issue either, the standards do allow for that and mobile phones work in high-speed trains going faster than typical SEP aircraft.

LKBU (near Prague), Czech Republic

The signal level is not an issue.

I can fly across France, FL100, and have a strong signal say 50% of the time, but zero connectivity on both data and GSM (SMS), 99.99% of the time. What is happening? I don’t know, and those who do know are most definitely not going to be posting about it openly, but it seems obvious that the networks there are globally (globally for France) blacklisting any device which is seen by too many towers. Same in Belgium. Zero. France has improved somewhat in recent years…

Other countries may do the same but probably to a lesser degree.

We have done this in other threads years ago but one mention is here. It has been known for a long time that if you can control the radio in the phone directly (not possible unless a phone is rooted, not least because you would be running it contrary to GSM network compliance requirements; Nokia used to have a dedicated ROM-micro chip for their GSM interface to ensure this, but modern phones have the GSM code all under the one RTOS) then you can get connectivity in these situations, for short packets at least. For a non rooted phone you can achieve “something” by turning the “airline mode” on and off (possible from within user app code, I think) which forces a re-register and you can get a fresh bit of “connectivity” before getting blocked again. AFAIK nobody has brought such a product to market which does any of this, and requiring a rooted phone is a major hassle these days especially in the IOS market.

The key in making 3G/3G/SMS work airborne to some extent is to use short packets, and ensure only short packets will ever be sent (which is why all the telegram bots become useless when airborne the instant a bigger object is sent or received) and this means

  • no internet access (DHCP in any case takes far too long, relative to how long you have before the network cuts you off)
  • running your own server

Over the years a lot of people have implemented private wx sites, which get the wx, strip off the adverts around it, and present either just text (tafs and metars etc) or just a graphic of a few k (wx radar, IR, etc). People I have known have also implemented tafs and metar servers which run over GSM (you connect an old Nokia phone to a serial port on a PC) and that is probably the least-bad way because GSM (SMS) is the baseline (a GPRS/3G/4G session is started as a GSM data call, by dialing ATDT*99#) but there is no solution which is really reliable, due to the networks trying to kill it.

The Golze ADL products do it properly, by using Iridium, but they have the same above limitations i.e. no internet access and they run everything from their own server so they control the data size. Highly reliable and great value at ~€25/month. I have the ADL150.

I played with this stuff some years ago and spent a lot of time on it. The Thuraya satphone system works not too badly and on their 50kbps “GMPRS” you can get “internet” over it (well, you can run telegram over it, and emails, until somebody sends you a 1MB email and then you can forget it until you land ) but Thuraya is run by an outfit which as I found out many times is not interested in delivering customer service to infidels

@byteworks may know more.

I suppose one could build a system which knows where the towers are and points a directional antenna at them, one at a time

Administrator
Shoreham EGKA, United Kingdom

I think you may also have issues with latency – cell towers are designed to have a horizontal radiation pattern (after all, all your users are on the ground) so it may be the case you get the best signal-to-noise ratio only with distant towers, as the angle between the ground and your aircraft from a distant tower is shallow (but steep to a close in tower). Cell sites need very precise timing (they have atomic clocks – usually rubidium frequency standards) to work, and if there’s too much distance between you and the tower, latency may be an issue. This is just a guess, I really don’t know very much about the cell network other than fairly generic info!

I think this would also be an issue with a directional antenna on the plane pointing down as the original suggestion – you’re not going to get a very strong signal from nearby towers with a steep angle to the plane.

The easiest solution would be to fly at around 2000’ or below, after all, cell sites must have to be able to deal with people walking on the local hills, which at least around here are about 2000’ tall, so you’d look no different to someone driving up the mountain road :-)

Andreas IOM

Peter wrote:

I can fly across France, FL100, and have a strong signal say 50% of the time, but zero connectivity on both data and GSM (SMS), 99.99% of the time. What is happening?

The signal strength only says how strong a signal your phone receives from the cell tower – not how strong a signal the tower receives from your phone…

I don’t know, and those who do know are most definitely not going to be posting about it openly

Why on earth would they not!?

ESKC (Uppsala/Sundbro), Sweden

Peter wrote:

The Golze ADL products do it properly, by using Iridium, but they have the same above limitations i.e. no internet access and they run everything from their own server so they control the data size. Highly reliable and great value at ~€25/month. I have the ADL150.

What Golze plan are you getting for 25 EUR/mo? Looking at their services page https://www.ing-golze.de/service.jsp the monthly plan is 39.50 EUR/mo.

EGBJ and Firs Farm, United Kingdom

The signal strength only says how strong a signal your phone receives from the cell tower – not how strong a signal the tower receives from your phone…

The two are supposed to be balanced, roughly. The phone listens all the time, and every ~10 mins connects. The TX power is set, in 256 steps, according to the RX signal strength, to a max of ~400mW (for a normal handheld phone; more for a fixed device like a PCMCIA modem etc).

Why on earth would they not!?

For the reason I posted These are the mechanisms to protect the networks.

What Golze plan are you getting for 25 EUR/mo?

No idea. Maybe something old…

BTW I used to have one of the repeaters mentioned in the OP – we live in the countryside and 90% of the UK has almost no signal These things are illegal to use, but not quite illegal for chink vendors to sell on Ebay… they arrive labelled as “HI-FI amplifier” They also don’t really work, because you need one amplifier channel for each frequency, and AFAIK none of the products does more than 1 or 2. I took one apart and it is fairly obvious how it works. Really primitive; worked for voice + SMS, not for data. Building a repeater which actually works properly is a lot more complicated; it has to decode the packets and probably buffer them. The old half-duplex repeater problem…

Administrator
Shoreham EGKA, United Kingdom
EGTR
23 Posts
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