I want to send/receive data to/from a balloon carrying some sensor. Initially balloon will be tight to a rope and will rise gradually in human control. It will send altitude, temperature, humidity, windspeed, GPS data via GSM/GPRS module to a control computer and to a mobile phone on the ground. It will also receive some remote control commands through the same communication channel.
- How high the balloon can rise before GSM/GPRS signal vanishes? - Is there a legal altitude limit for GSM/GPRS operation? - Which GSM/GPRS modules you would recommend for the balloon and for the computer (please consider price and locality as Australia)? - Do you know any similar project or any open project which can help me to learn more on GSM/GPRS data communication?
I believe GSM has a 15km range, which would put anything over 50,000ft out of range. However, I do recall reading a study conducted outside the USA (due to FAA regulation) shortly after the 9/11 attacks to determine the success rate of placing mobile calls on commercial flights - I recall they found at altitude (although I can't remember exact figures or have a link for you) the success rate was extremely low (less than
10%) over a sample data of several thousand calls - which apparently was used to feed conspiracy theorists rubbish about that plane that crashed in the middle of nowhere, and its passengers apparently called their relatives from their cell phones, so who knows if said study was truely accurate.
NextG apparently has 4x the range of GSM (or so goes the sales pitch), but alot of the blokes on aus.comms.mobile don't like it.
Who knows, that information may be helpful. At least its some research pointers for you.
No idea about AU law, I do recall Mythbusters tackling the issue of cell phones on planes who pointed out that in the USA its illegal under FAA regulation on any passenger aircraft. Mostly because the equipment, such as navigations & communications need to be tested to ensure they are sufficiently shielded from interferance. I really don't think there would be legal restrictions on a balloon, but a high altitude you will need flight clearance.
Nup, but you may be interested in packet radio as an alternative - with a radio license its free on amatuer bands and can provide several thousand kilometer ranges. Although the bandwidth is typically compariable to dialup modem, but that should be plenty sufficient for the data you stated. I suggest you see some aus.radio groups for info about that ;)
** You are going to run foul of the laws of Australia.
Tethered balloons must NOT be flown to a height of more than 300 feet (
100m ) above the ground without a special permit from the Civil Aviation Safety Authority ( CASA) - plus you must be at least 4km away from ANY airport.
Also, the balloon must remain 500 feet below cloud at all times and be flown only when there is perfect visibility.
If it's in a populated area then the mobile network operators might get upset, and it is probably also illegal.
They may get upset because normally your line-of-sight (strong) signal gets obstructed by hills and the curvature of the earth, and so the operator can re-use the same frequency for many base stations that are not adjacent cells to each other. This works as long as a mobile phone is not in the coverage area of two base stations that use the same frequency at the same time. Reusing frequencies means that they to bill several customers simultaneously using frequency spectrum that they only paid for once.
If you transmit from a high altitude, you may have line of sight to several base stations that all receive on the frequency that you're transmitting, and your signal would interfere with the signals from other handsets on that frequency even though those handsets are a long way away from your location. That means that using this particular frequency, the operator can only bill one customer at a time (you) and they are not making a good return on purchasing that frequency.
Chris is actually correct. The original reason the FCC banned cellular phones in any aircraft or balloon, was to prevent harmful interference to terrestrial cellular systems. The original ban did not consider the potential impact on aircraft navigation or communication systems.
When in the air, the distance to the cell tower causes the cell phone to operate at maximum power, and this cause co-channel interference. The current push is to have a pico cell installed in an aircraft, and this will allow the phone to operate at minimum power levels, and prevent interference to the ground based networks.
If cellular phones where that dangerous to the operation of aircraft, do you really think that we would even be allowed to take them onboard? Plenty of people "forget" to turn them off.
No, cellular phones adjust their output power to suit the current cell. For small cells, the phones and the cell will operate at very low power levels. This allows many phones to operate in a small area at the same time while only using a limited number of channels.
The inverse square law is the *exact* problem with cellular phones on aircraft. When in the air, the distance from the cellular phone to the cell towers on the ground is fairly equidistant, over a large footprint on the ground. All the towers will receive the phone's signal at a similar strength. This will cause interference with existing calls over a large area on that channel. This is why the FCC and ACMA prohibit the operation of cellular phones in an airborne aircraft.
When the cellular phone is on the ground, the tower closest will typically take control, the phone will adjust its power level down, and towers further away will have a much weaker signal (due to the inverse square law).
Obviously they never taught about cellular phones at toaster repair school.
I dont know about GSM, but with CDMA, when it operates in a city area (mostly full or near full signal all the time) the battery will last for about 4 days. When in country areas with low or no reception, the battery will go flat in a day or less.
I always assumed that the phone raised its transmission power to maintain the connection in poor signal conditions, thus draining the battery faster ?
It is as you would say "complete bollocks", as mobiles do *not* operate at max power all the time. They change their output power as needed to maintain the required signal the tower the mobile has connected to.
Now usually you are right but this time you are not, and I can prove it. Read the specification:
For GSM phones see page 12 of this:
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For 3G phones, see page 22 of this document:
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Anyway my first post did not mention the handset transmit power control setting, I was referring to the fact that terrain and the curvature of the earth help operators to be able to reuse frequencies at closer distances than would be possible if handsets had line-of-sight to all basestations in a city, like on a balloon. This would be true even if maximum transmit power were always used.
And as usual, insulting people will not make you right.
Actually David, Phil is quite right, but ambiguous. All of the time, *some* phone will be operating at full power. Just not *all* phones, *all* the time. You *both* failed to communicate clearly.
** Not to anyone who can read English an follow a context.
** What I wrote said there are lotsa mobiles phones, all over the country, running at max power, at any time of day.
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