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Old 1st Apr 2012, 23:29   #1 (permalink)
 
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High Altitude Mobile Phone Reception

I know this is not a Computer/Internet question, but I thought this was probably the best place to ask it.

I've just landed in Hong Kong after a flight from Los Angeles, which flew over Kamchatka and Korea enroute.

I had dutifully turned off my mobile phone but I had forgotten to turn off my second phone and I was surprised to see when I looked at it, that I had a "welcome" SMS message from a Russian phone carrier and that my phone had set itself to the Seoul time-zone.

Is it normal to be able to connect in this way from such high altitudes?
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Old 2nd Apr 2012, 09:29   #2 (permalink)
 
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Not normal but as you had your phone on for over 10 hours, it's also not that surprising you caught one or two rogue signals.
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Old 2nd Apr 2012, 10:13   #3 (permalink)
 
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It IS normal that you can connect. Part of the reason for turning mobiles off for the trip is the sheer number of cell sites your phone can potentially register to during the trip (it causes problems for the providers).
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Old 3rd Apr 2012, 01:58   #4 (permalink)
 
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M-B,

I think it is NOT normal to connect, which is why I posted the question. I have left my phone on occasionally before and have never seen this behaviour.

Looking at the antenna lobe patterns for cell phone towers, with the primary lobe being horizontal, it really surprises me that any connection was made. I have tried in the past to use a cell/mobile phone from low altitude in a lightplane, with very poor results.
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Old 3rd Apr 2012, 06:07   #5 (permalink)
 
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India Four Two,

Multipath propagation perhaps ?

Afterall, text messages etc. don't need much of a signal for long to work.

There is a brief discussion of it in a mobile specific context in the Nokia GSM Air Interface & Network Planning Training Document I just happened to stumble accross !

Last edited by mixture; 3rd Apr 2012 at 08:18.
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Old 3rd Apr 2012, 23:44   #6 (permalink)
 
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Quote:
Looking at the antenna lobe patterns for cell phone towers, with the primary lobe being horizontal, it really surprises me that any connection was made. I have tried in the past to use a cell/mobile phone from low altitude in a lightplane, with very poor results.
I've had a similar result with the Australian GSM phone system in my recreational flying - not that I've used it much. (Rec flying is for fun not for phones). However once when I really did need it at about 8,000ft, it was useless. Full scale signal strengths on the meter, but the network unavailable tone was all I could get. When I had descended to about 4,000 ft, and thought to check again, it worked perfectly. I wondered whether at the greater altitude, signals from local cells (below) were being swamped by those on the near horizon, and that these may have been too far away to meet the timing loop requirements of GSM, something which I had encountered before in the GSM regime - both in the air and on the ground.

Nowdays I'm in the 3G system, but I haven't had the chance or the need to see what happens there in the air. I suppose I should sometime, just in case it's important one day.
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Old 4th Apr 2012, 01:09   #7 (permalink)
 
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Quote:
Afterall, text messages etc. don't need much of a signal for long to work.
mixture, yes that occurred to me too.

Doing a bit of Googling, I stumbled upon these two interesting papers that are pertinent to this subject:

Airborne Cell Phone Performance

Electromagnetic interference with aircraft systems


Quote:
I suppose I should sometime, just in case it's important one day.
FOR,
Based on my experience in Canada and New Zealand, there is an expectation by ATC that pilots will use mobile phones in the event of comms failure. I wonder how well that works in practice?
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Old 4th Apr 2012, 02:10   #8 (permalink)
 
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Thank you for the links I42; both very interesting indeed.

f_o_r
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Old 4th Apr 2012, 06:10   #9 (permalink)
 
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FullOppositeRudder,

Quote:
I wonder how well that works in practice?
A couple of snippets from a previous thread on the subject.....

Quote:
Even used it to call ops before now while sat in the hold. My experience has been that over a certain speed the network just can't catch up!
Quote:
The F.O. managed to get an SMS away at 35,000' when his mobile phone briefly picked up a signal. It wasn't a reliable signal though.
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Old 4th Apr 2012, 07:18   #10 (permalink)
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Quote:
Based on my experience in Canada and New Zealand, there is an expectation by ATC that pilots will use mobile phones in the event of comms failure. I wonder how well that works in practice?
- I have not visited recently but it used to be a procedure published on the LSGG plates. "In event of ... call xxxxx".
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Old 4th Apr 2012, 16:21   #11 (permalink)
 
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On the odd occasion that I've accidentally left mine on, and discovered it at cruise altitude, it has never had a signal. I think it disappears around 15 to 20 thousand feet.

In the R/T failure scenario, I assume it would be used at lower levels to talk to approach controllers, or the D&D cell (in UK).
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Old 4th Apr 2012, 18:09   #12 (permalink)
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Quote:
I think it disappears around 15 to 20 thousand feet.
- wrong! I have received a 'Welcome to 'XXX' (Athens network) when overflying at 390 having forgotten to turn my phone off - and wondering what all the strange noises were on the R/T!
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Old 7th Apr 2012, 00:01   #13 (permalink)
 
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As has been mentioned earlier in the thread, t is possible to get the occasional multipath reflection. However, the antennae on cellphone masts are designed for horizontal propagation, and are very inefficient indeed at communicating with high-flying aircraft.
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Old 3rd Aug 2012, 12:56   #14 (permalink)


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Side lobe cell comms.

If you happen to pass through one of a cell site's side lobes you could communicate until you punched out of it. If you happened to know the location of the ground site, and you did some pre-flight planning you could orbit the ground site (inside that side lobe) and communicate until you ran out of fuel. Might not want to do this over the US of A.
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Old 5th Aug 2012, 11:18   #15 (permalink)
 
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Text messages received

My other Pilot has Blackberry, and is always ON.

He receives most of his E Mails in flight this way.

Our DEP message is always on his BB before we land.

So there is some benefit.

Glf
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Old 5th Aug 2012, 13:33   #16 (permalink)
 
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Is newer better?

Slight thread drift.

I'm not really sure that newer is better.

Reference digital TV: When there is tropical storm activity in the local area two of the major networks become very intermittent with pixelisation of the video signal and clicking sound effects. It nearly blows my (expensive) surround sound system speakers apart.

Reference mobile phone reception: I used to regularly cancel SAR via mobile phone at 1500 ft in a very remote location in CDMA days. FA chance of doing that now with 3G.

Back to the original thread, sometimes whilst flying in remote areas my phone will report a service provider of 999 999 instead of Telstra in the service provider field. Does anyone know what this means? Free calls maybe??

Last edited by Two_dogs; 5th Aug 2012 at 13:34.
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Old 5th Aug 2012, 18:20   #17 (permalink)

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There are some technical effects, too. I'm sure Googoo will reveal much more than I know.

In the UK, cellphone aerials are set to work horizontally and below. If there's reflection from something on the ground, then the signal may go up as well. The problem when the aerials worked with aircraft at altitude was that the airborne phone would access multiple towers and confuse the system. Some countries have a setup whereby a small number of towers have an upward-pointing aerial for aircraft - I think the USA is one such.

Straight GSM works on time-division multiplex, which sets an effective distance limit of about 20km, after which your returning signal is outside your timeslot. Although you may have a signal indication, you can't actually use it. Some rural sites have longer time slots, which increase the maximum range.
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