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Cell Phones In The Air?
jumbledInTheHead writes "Are you ever annoyed when someone near you talks unnecessarily loud on their cell phone? Or even worse, when it is in a tight, enclosed space and you can't walk away? The problem is about to get worse the next time you take a flight; the FAA is considering removing the ban on cell phone use on airlines."
Actually, the problem is that it's really easy to get a signal, because you have a clear shot to a crap load of cells at the same time while you are up in the air.
As a private pilot, I always leave my cell phone on when I fly VFR. (So far I haven't flown into any mountains due to navigational system confusion.)
The only way that I can get my phone to work is to descend very low in a rural area. If I'm up more than about 2000' AGL, then the phone doesn't work. I figure that it gets confused because it probably sees a dozen towers with strong signals.
Commercial aircraft would probably have to install special equipment to receive the signal inside of the airplane and then connect to the phone network directly.
Ha, ha! Nobody ever says Italy.
> Actually, the problem is that it's really easy to get a signal,
> because you have a clear shot to a crap load of cells at the
> same time while you are up in the air.
This is the big problem. If they use the existing cellular infrastructure, this will greatly increase interference and make voice quality even worse than it is today for everybody.
For existing cell phone towers, any cell phone in the air will be likely above the antenna mid-line. Since most antennas have a down-tilt of around 3-degrees (so they point slightly towards the ground), any coverage above the mid-line will be from one of the normally minimized antenna nodes that point up.
Antenna manufacturers try to make these nodes small because it's just wasted energy. One would rather have that energy pointed to where the traffic is. So the cell phones that are in the air will have moderate to poor signal strength which will require the cell phone and the base station radio to transmit at their highest power settings. For the base station, that's not too bad, but for the cell phone, you're suddenly going to have this giant source of interference because the phone will be broadcasting at its full power setting from nearly two miles above the surface. Since voice quality is indirectly proportional to the level of the noise floor in an area, cell phones service will get even worse.
However, the article talks about how they'll mitigate this. Airlines will install very small, low power base stations called "Picocells" aboard the plane. Thus, the cell phone will communicate with this nearby base station, reducing power levels significantly and minimizing the interference effect.
However, this will do nothing to mitigate the annoyance of listening to the person next to you screaming on their cell phone because they can't hear their voice over the roar of the engine.
Insert simplistic political, ideological, or personal proselytization here.
As a more "socially acceptable" alternative, you could just use your cell phone (even if you're not calling for real) and start shouting at it "yeah, the flight is nice but there's an idiot next to me that just won't shut up, I was trying to sleep and all he does is to yell at his cell phone as if everyone cared about his boring life..." and the like... :)
You're correct in that multi-path governs cellular communications, particularly for spread spectrum systems like IS-95 CDMA. However, wouldn't the fact that the device is flying above the skyline with no objects for the signal to bounce off of minimize multi-path effects? It's almost free air space with no obstructions when you're pointed at an airplane.
The only real way to be sure is to take field measurements, but I am pretty sure that this would be a Rician model (line of sight with multipath) with a fairly big Doppler shift. My reasoning is that since the mainlobe of the antenna is horizontal or pointing downward, it will pick up building and ground reflections. Since they are doing picocell and retransmitting, then can precompensate for the Doppler, though, by measurements on pilot channel. This topic has come up several times on comp.dsp. The general consensus was that the LOS component really helps things more than you think.
(S(SKK)(SKK))(S(SKK)(SKK))
I thought the reason you couldn't use a phone on the plane actually had more to do with FCC regulations than FAA ones.
Cell phones work by assigning a particular set of frequencies to a particular geographic area, and then reusing those frequencies further away where there is no chance for interference (phones that use spread spectrum work more or less the same way, only the frequency separation is more dynamic). When you take a phone operating within such an arrangement and suddenly raise its altitude a few thousand feet, it can suddenly be present in many, many cells. This causes interference in every cell where the phone is not actually communicating with that cell's tower.
I have heard of plans to put micro-cells aboard planes. Such micro-cells would instruct the phones to use low enough power that this wouldn't happen. THAT is a much different scenario, but I wonder how many different modulation types (and therefore customer populations) will be able to be handled by such a scheme. Those who aren't covered by a cell in the plane should not be using their phones for the technical reasons described above.
As for whether people can talk on a phone or not, I fail to see the distinction between talking on a phone and talking to a person next to you. I've seen drivers distracted by their fellow passengers with equal frequency to drivers distracted on a phone. I've seen loud, obnoxious boors talking way too loud to people 3 feet away with equal frequency to the same boors shouting into a phone. What's the difference? Rudeness is the same whether technology is involved or not.
Having trouble with the fellow next to you talking too loudly? A cell phone user cussing out their employee? Here's a nutty thought: Ask them politely to keep their voice down. Now, I know that sounds a little wacky to those of you who would rather hang back silently judging, but let me tell you I have tried it many times successfully. It requires a little known ability called courtesy, but with practice, you may be able to acquire this skill, too. Good luck, and welcome to the wonderful world of talking to strangers!