Airborne mobile phone

[Henry Hallam]

I'd like to talk to anyone who has had success using a mobile phone to either make calls or send text messages from relatively high altitudes, say above 3000-4000ft. The safety issue of interference with avionics is not relevant - I am part of a team building an unmanned helium balloon that will reach about 80,000ft and due to Ofcom rules we are not allowed to have any kind of ham radio transceiver onboard, and can't afford a satellite phone. Telemetry is important so we have a GPS location to find the payload after it lands!

At the moment it looks like the only option is a GSM mobile and we will communicate with the electronics in the payload either over SMS or a slow dialup data connection. This has been done once before and the SMSes stopped coming through higher than a couple thousand feet, though they returned after it landed safely. But 3 hours or so is a long time to wait when you don't know where your payload is so we would much prefer to be able to get a signal through while it's in the air.

I've heard various ideas about why phones don't work at altitude, mainly they fall into two camps:
1. The base stations only send out the signal in a horizontal direction.
2. The phone sees too many base stations and this somehow confuses it.

I'd really like to hear from anyone who thinks they know the definitive answer to this. I've read reports that phones were indicating a full "four bars"/whatever of signal strength but not being able to make calls, which would suggest option 2. Maybe this could be solved by a directional antenna pointing straight down to reduce the number of stations "seen"? Of course it would compromise the ability to get any signal after landing...

Any ideas?

[QDMQDMQDM]

'A friend's phone' doesn't work above about 2.5K feet agl. I thought it was where the signals were directed, rather than the number of base stations confusing the phone. There's no point wasting power sending signals high into the air where no-one will be using them.

Talk to the mobile companies.

QDM

[4SPOOLED]

A mobile phone base station is just like any tranmitter. It works on radio waves and the waves are transmitted in all directions including the vertical componant into space just as HF/VHF/UHF

A Base sation has a range of up to 20km horizontally depending on the terrain as the receiving handset needs line of site to communicate with the base station. 20km's is roughly 66,000ft. CDMA transmissions can be greater. However it also has alot of signifigence where the base sations transmitters are aimed. Simple geometry on the angles and signal strengths on your local tower should be able to solve this problem.

With no terrain and obstacles one would think that the reception gained in the vertical componant rather than the horizontal. I have also spoken on my phone on decent at 6000ft.

Hope this helps

4S

[Sky Wave]

I understood the problem with using mobiles at altitude is that it causes network confusion because the mobile is in range of soooo-many base stations. I don't think the operators will be too impressed by the idea.

I could have been completely misinformed tho.

[footpad6]

I've heard various ideas about why phones don't work at altitude, mainly they fall into two camps:
1. The base stations only send out the signal in a horizontal direction.
2. The phone sees too many base stations and this somehow confuses it.



Both of the points above are correct.
1. The networks are designed and optimised to give coverage to the greatest number of population.

2. GSM networks use frequency re-use (I believe the UK networks work on about 8 frequencies) and the network is designed so that the Base Stations (telephone masts) using the same frequency are not going to intefere with each other. This leads to the scenario when at altitude of the User Equipment reporting four bars but in fact what it is experiencing is interference.

I think that using GSM or UMTS mobile phones for what you are trying to achieve isn't the way forward.

Have you thought about PMR446 ( unlicensed radio). Some of the commercial producers might actually have what you require off the shelf.

Rgds,

FP6

[OpenCirrus619]

As far as I know the reason that the phone stops working as you get higher is that it can "see / be seen" by more than 1 cell on the same frequency. The phone network sees this as a possible cloned phone - how else could the same phone be talking to 2 cells at the same time? The spacing of cells using the same freq. is worked out so that a phone ON THE GROUND cannot suffer this problem.

If you are, for example, close to London you will find problems with using the phone once you get a few hundred feet up (many low powered cells / higher density of re-use of frequencies). On the other hand if you fly over, for example, the middle of Dartmoor then you can get much higher before you get logged off the network.

OC619

[strafer]

Why don't you send up a manned ballon instead? That way, you could tie two empty cans to the ends of an 80,000ft long piece of string and communicate using that?

However, it a may be a bit nippy at that height, so the person going up should probably pack a jumper.

[footpad6]

.. - / ... / -... -... -... -... .-.. --- --- -.. -.-- / -.-. --- .-.. -.. / ..- .--. / .... . .-. . / ..--.. /


And the above would be an example of the data stream returned!:bored:

[IO540]

I have frequently used a mobile phone airborne, mostly for text messages but I have also managed to get internet access using the basic 9.6k GSM data capability.

It tends to work at low levels, below say 3000ft. Very occassionally it works at 7000ft or so.

The signal strength indication doesn't tell you much because you are potentially tying up a number of base stations and the system spends a while working out which you should be connected to, which makes the comms slow and unreliable despite the apparently good signal.

GPRS you can forget, I have found.

For this baloon application, I would investigate some things

1. For a one-off thing, doing it illegally should be fine. Pick some amateur radio frequency; a lot of them are used for digital data (modern radio hams use keyboards and PCs) and if you use that, especially at very low power, it won't be noticed.

2. Contact one of the weather baloon operations and ask them what they do. They launch them twice a day, to 100,000ft or so, and they have telemetry from onboard GPS, temperature and humidity sensors.

3. Look up the services which provide basic email services over shortwave, for sailors etc. This might be illegal but should work...

80k feet is about 12 miles which isn't very far, and a lot of other solutions would work just fine :O There are loads of license-free off the shelf radio modems for industrial telemetry which do that sort of distance. May not be legal but if this is a short-term requirement...

[Henry Hallam]

Thanks for all the replies. We are being sponsored by a university to do this and we do intend to launch more than one balloon, so we're trying to do things "by the book". If it were just me, I'd stick a 5W radio modem on there and be done with it ;)

The weather balloon operators have a specific frequency allocated to them which we are apparently not allowed to use. We're going to pursue this a bit further, it does seem a bit ridiculous.

Have thought about a license-free PMR radio. It might be stretching the range of the stock transceivers you can buy (they're only 500mW and you're not allowed to attach a higher gain antenna) but we will do some experiments. They're only supposed to be used for speech but we could have a speech synthesizer on the balloon and just use a few different tones for the uplink, there aren't really that many messages that we need to get to the balloon - principally just "cut down and open the parachute before you fly over the sea". Downlink is more important.

Part of the problem is that the range has to be more than just 80,000ft. I'd like to be able to talk to the balloon within about a 30 mile radius of it on the ground. There also has to be a bit of margin for things like using the ground station in a car rather than on top of a hill. I offered to rent a C172 and fly chase but I think the rental costs would end up being more than building a new balloon!

Anyway it looks like mobiles from that kind of altitude are a no-go. We'll still carry one to hopefully get a message through on landing but I'll look into PMR446 a bit more.

Cheers, Henry

p.s. "Why don't you send up a manned ballon instead?" well, the larger of the balloons we've got can take a man to 25000ft or so, I did think about wearing a wooly jumper and a parachute. Oxygen? pah, I'll hold my breath.

[drauk]

This might sound (and be) silly, but what about WiFi? WiFi works really well if it has uninterrupted line-of-sight. In South Africa I have used an Internet Connection from the roof to a repeater a few miles away half way up a mountain and from there about 30 miles or so.

Other advantages are that you'd be using cheap hardware, no transmission costs, it's easy to do data (given that's what it is made for), it's legal, etc.

The downside would be that once the balloon comes back down below a certain altitude (you can do the maths) you'd lose line of sight and all communications. But if you didn't lose it until late enough you'd have a pretty good idea where it is. And you could always revert to GSM + SMS once it was back on the ground.

[Henry Hallam]

Were you using very high-gain/highly directional antennas for the WiFi? There is a bit of a problem with aiming with the balloon swinging about. But that's a good idea, thanks. We're going to do a couple of experiments with a tall hill and a light aircraft.

[drauk]

I never saw what was at the other end of the connection, though second-hand I was told it was just commodity wi-fi hardware. On our office roof was a directional antenna but it can't have be that directional give that it was just "pointed in that general direction". I think you'd have to try it and see.

[IO540]

There is no regulation on the receiver antenna gain.

Can wifi be used airborne? I would be quite suprised.

I can't believe people don't just stick an off the shelf radio modem on this thing... they come with RS232 or RS485 ports, all done for you.

There is always a bit of a problem with anything that needs a protocol, e.g. wifi or bluetooth. The slightest thing goes wrong and the connection goes down the pan. One-way transmission is a lot easier and can be done with simple AM modulation of a carrier. If the data rate is low one can use very low power and a high gain narrow band receiver to recover the signal.

I would pick some shortwave frequency and transmit very slow AM data at very low power. Recovery is easy and nobody will ever pick it up by accident.

This stuff is plain daft. A PC motherboard radiates far more than a lot of regulated equipment.

[jammydonut]

Have you investigated Iridium Satelite phones?

[Dimensional]

Mate:

I'm at your university (TC, Cantab) and could be of assistance as I've got what is probably an acceptable licence to OfCom -- drop me a PM.

-D

[Whopity]

due to Ofcom rules we are not allowed to have any kind of ham radio transceiver onboard,
Of course if you had a FCC Licence, Offcom rules would not apply to you! ever thought of that! All you would need is the Captains permission. Or use the balloon frequency 122.475MHz.
Using mobile phones in an aircraft infringes the terms of the phone providers licence!
The aircraft radio licence also includes the use of 455.475 - 455.850MHz and 460.775 - 461.225 MHz.
What about PMR? thats used from aircraft by the traffic spotters!

[wingman863]

I was using mine at about 3000ft two weeks ago and had a bit of a problem aquiring an initial signal when I turned it on. Once it was active, text messages were able to be sent but the timing became a bit dodgey. I got a load of messages at the same time a few minutes after landing which I should have got in the air. I didn't make any voice calls though. At lower levels of about 1500, it seems to work better in my experience. I don't know whether me keeping my phone on for the whole of the flight might have made things easier in terms of aquiring the initial signal.

I certainly wouldn't recommend using phone on a normal network. Seems a bit unreliable. Have you tried contacting the CAA (are you in the UK?) or the relavant people to ask for advice?

I doubt they would say yes, but if you asked a mobile network to set up a temporary transmitter for you and emphasise that its for a university, education, supporting the community (blah blah blah corporate responsibility crap), they might agree to help. I think they do this sort of thing for big events like concerts. You could ask them to point it towards the heavens and you might get a reliable signal. The baloon moving might be a problem though.

[Floppy Link]

Do you have to launch the balloon in the UK???
Got back from Cyprus having forgotten to turn the aircraft mobile off and found a message saying "Welcome to Serbia" - we were about 36000ft or so when we flew over that region...

[Henry Hallam]

Theoretically we don't have to launch in the UK but the total budget for the first balloon is £1k so realistically we're limited to the local area. For similar reasons I don't think setting up a dedicated mobile phone transmission tower is a practical possibility... certainly much less feasible than persuading Ofcomm to let us fly a ham transceiver. We're more than willing to get ham licenses but even with one you're not allowed "any unmanned stations". We're looking at going down the commercial license route for later ballons but I think that involves real money and real hassle.

Whopity, not sure what you mean about using an FCC license? That would be difficult to get and almost certainly not valid here. Or are you joking about flying on an FAA PPC :P

Yeah we are looking into PMR, 40 miles or so (the range we'd like) might be pushing it even with line-of-sight but worth a try.

Jamydonut, unfortunately an Iridium phone costs about £800 which is 80% of the total budget... but that is probably what we'll use for later balloons which may be aloft for weeks at a time and will go a long way from home.

IO540, I'd love to stick an industrial radio modem on it but I can't find any license-free ones which offer that sort of range, even in free air. They all seem to be limited to 100mW.

[Cat.S]

Why not hire an Iridium? You can get one for 9$ a day from the company below- (They're based in UK, though charge in US $.)
http://www.mobalrental.com/satellite.asp

[Henry Hallam]

hm.. I wonder if their $6/day "loss protection" covers the balloon landing in a lake ;)
But, I suppose the most we'd have to pay is the cost of the phone, and if we'd bought one and lost the balloon then we'd have paid that much anyway. So it's a pretty good idea, thanks!

[Genghis the Engineer]

On a different tack, what about aircraft VHF?

Whilst continuous transmission on an in-use frequency would clearly be unacceptable, if there is an airfield in your vicinity with separate tower, approach and ground frequencies - can you negotiate temporary "loan" of the frequency for a few hours at a time when it wouldn't be in use? (E.g. the ground frequency at a time when the airfield happens to be closed to traffic and is only using the approach frequency?)

G