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Garmin handheld aviation GPS business - the end?

Martin wrote:

What datalink are you using? AFAIK it’s not allowed to transmit on the frequencies used by mobile phones while airborne which rules out the most convenient solution (a workaround is to have a picocell on board, AIUI phone should then adjust it’s output power and it won’t threaten to disrupt the terrestrial network anymore, but that still requires some link with the ground).

Datalink manufacturer is: Samsung. :)
Perhaps I’m a bit of a simpleton… If it is proven that it causes no interference for commercial aircraft, why would it magically cause any for GA? The only interference I’ve ever experienced is when a call is coming in, I can hear the “blip blip” in my headset, as it causes a momentary burst on the radio. Absolutely minimal, and unless you’re flying in a quiet area, you’d likely not even hear it… I like it because I can always tell when a call or text is coming, as the blip-blip sound occurs before the phone starts alerting.

I take it you turn your phone off before every flight, and don’t ever forget it in your pocket. Of course you do! Just like all of us angel pilots do… ;0)

Peter wrote:

Above 5000ft or so it gets much more random and really cannot be relied on at all.

Exactly my experience in both the US and Europe.

Last Edited by AF at 03 Jul 16:39

AF wrote:

If it is proven that it causes no interference for commercial aircraft, why would it magically cause any for GA?

This isn’t about your aircraft, it’s about the network. AIUI the issue is that the transmissions can reach more cell towers from altitude (compared to transmitting from the ground) which could cause problems as the network wasn’t designed for this. And we’re talking about transmitting in a licensed spectrum and the hardware AIUI isn’t certified for this (there are probably some fines for this). That’s why you’re supposed to turn off GSM/ UMTS/ LTE/ etc. transceivers at all times. People will still be instructed to do it (it has nothing to do with aviation but with telecommunications and it won’t change in the foreseeable future without the aircraft being appropriately equipped).

I often have my phone in the airplane mode even on the ground, just to ignore the world that’s not immediately around me. Forgetting is always a possibility, but I don’t want to risk causing damage to a network operator, that could get very expensive (and devices do identify themselves, tracking you down should be realistic although I don’t know much about the protocols used, what is typically logged, etc.).

Martin wrote:

AIUI the issue is that the transmissions can reach more cell towers from altitude (compared to transmitting from the ground) which could cause problems as the network wasn’t designed for this.

I’d be curious to know what happens when one hikes mountains and reaches multiple cell towers from the same peak…
I get two towers simultaneously upstairs at home. If I walk to one side of the house, I receive one tower, another side… different tower.
Half-way between, the towers don’t blow up ;)

The worst that can happen is that the towers either duplicate transmission, or I lose connectivity. Can’t imagine a doomsday scenario there… but I get the point. An A380 with 500 people makes a massive difference.

That being said, I can’t say I fly fast enough to cause any real harm. There are times I’ve been faster on the Autobahn than flying…
But I acknowledge that you’re accurate wrt the technical bits and the helpfulness of everyone not breaking the rules…

Last Edited by AF at 04 Jul 22:43

Martin, I think this multiple towers thing was perhaps a problem in olden times. I know a number of people in the technical side of mobile and modern networks cope just fine. You really don’t have to turn it off and there would be tens of thousands of live cell phones in the air at any point in time. I have never heard of anyone being fined.

EGTK Oxford

AF wrote:

I’d be curious to know what happens when one hikes mountains and reaches multiple cell towers from the same peak

Since you’re still on the ground, they should consider mountains in the design and testing. I didn’t say more than one, but more than you would from the ground. Even a high-rise building hardly compares. I think one issue was interference on the random access channel (or RACH, if you will).

Of course I know the world won’t end if you do it. I would just prefer not to do it as part of normal operations. I’m no saint, but in this case the cost for compliance seems acceptable to me. I’m not saying what others should do, not my business.

JasonC wrote:

Martin, I think this multiple towers thing was perhaps a problem in olden times.

I know that things move forward and interference management is advancing as well. But AFAIK at least in 3G networks, this was still seen as a problem that needs solving (airliners need that picocell anyway, you won’t get a signal at 30k feet, even that posed potential problems say a ten years ago; I remember reading a paper about it from ETSI). And the regulations AFAIK still don’t allow it.

Circumstantially, I think this problem was solved many years ago – by locking out phones which have too many connections.

That is why, when flying, you often get a strong GSM signal but no connectivity whatsoever; not even for SMS. But if only one thing works it will be SMS, definitely not internet (GPRS/3G/4G).

This is another area where 4G has an edge (no pun intended). The lockout is nowhere near as aggressive as on 3G. Probably because 4G has a lot more bandwidth, and if a network can make money out of people texting on airliners, it’s all good.

People who know the business don’t want to discuss the measures taken. I know a guy who works in it and he is saying nothing…

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Circumstantially, I think this problem was solved many years ago – by locking out phones which have too many connections.

Anecdotically, I can add that this has happened to me a few times on high speed trains (TGV in France), that my phone wouldn’t want to connect to any network until I switch it off and on again. But never in the air. And I find it very useful to be able to get METARs or a current radar image at times.

I think another part of the solution being applied is to point the antenna beams towards the ground and actually limit their vertical radiation cone towards the sky. If now we could get some well dispersed antennas deliberately pointing only upwards to “catch” signals from above…

Lots of different factors here.

Being in sight of multiple cells is a non-issue unless the distance between those cells is greater than the frequency reuse distance – meaning that you could be in sight of two cells on the same interfering frequency. The reuse distance varies – smaller in higher populated areas that require more capacity. In a hilly area the cell size can be designed to cater for this.

3G and 4G are less sensitive to this anyway because they reuse frequencies differently to GSM.

The high speed train example is probably due to the 250kph speed limit for GSM. This is because there is a limit to how quickly the timing advance can be adjusted to match the change in distance from the base station. This will be a big factor in the air too – you need to be flying abeam a base station, not to/from it, to minimise the relative velocity.

Virtually all base station antenna have a downward inclination, so are not particularly sensitive to airborne devices.

You may not get service in the air but you certainly will not break the network either. If this were really a problem, it would be impossible to get network service underneath the approach to a busy airport.

Last Edited by at 05 Jul 12:08

Peter wrote:

I think this problem was solved many years ago – by locking out phones which have too many connections

How would that solve interference?

Peter wrote:

if a network can make money out of people texting on airliners, it’s all good

Of course it’s desired, that’s why it’s researched (I think it was researched as far back as 1988, perhaps even further). But try asking your carrier (or regulator) if it’s OK.

Rwy20 wrote:

I can add that this has happened to me a few times on high speed trains

That should be due to speed. Speed limits are common for wireless technologies, e.g. WiMAX has one as well.

Rwy20 wrote:

I think another part of the solution being applied is to point the antenna beams towards the ground and actually limit their vertical radiation cone towards the sky. If now we could get some well dispersed antennas deliberately pointing only upwards to “catch” signals from above…

That’s because they aren’t designed to cater to devices that are airborne. IIRC there was a system that did exactly this (it wasn’t GSM compatible, you needed dedicated equipment), reception was supposed to be into the thirties but they shut it down for insufficient interest (you can bet it wasn’t cheap).

ortac wrote:

unless the distance between those cells is greater than the frequency reuse distance

Exactly.

But you can have phones on in flight now there are aircraft based cells. On Etihad just now you can make and receive calls on their network. If interference was a problem it wouldn’t be allowed.

EGTK Oxford
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