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FCC Says No to Mobile Phones on Airplane
GayBliss writes "CNN is reporting that the FCC has decided to keep a rule in place that would ban mobile phone usage on airplanes. The FAA has a similar ban, but for different reasons. 'In an order released Tuesday, the agency noted that "insufficient technical information" was available on whether airborne cell phone calls would jam networks below. [...]Unlike the Federal Aviation Administration, which bans the use of cell phones and other portable electronic devices for fear they will interfere with navigational and communications systems, the FCC's concern is interference with other cell phone signals on the ground.'"
Cellphones were used effectively by passengers and cabin crew during the 9/11 hijackings, apparently without messing up ground communications.
Logically, if it's a technical problem using a cellphone from a plane, it would also be a problem using it from the top of a tall building. In a metropolitan area, the top of a skyscraper would be "line of sight" to hundreds of cellphone towers.
Paid Q&A/Research
Aircraft communications and navigation typically take place at VHF frequencies, between 108-132MHz. Voice communication is almost always AM in this frequency range.
Cell phones ~824-894MHz (traditional cellular) ~1900MHz (PCS - Sprint, Verizon, et al) - In the United States, anyway.
Regardless, the issue isn't interference with Avionics and communication, but the implications it would have on the cell network with one handset being able to reach (interfere with) hundreds of towers at one time.
"[H]earing only one side of a conversation makes it more noticeable and intrusive." (Sorry, no full article without paying, unless you're at an .edu with access, but the abstract pretty much sums it up.)
I agree with the researchers' conclusions. A full conversation usually stays in the background for me. Hearing one side is very jarring and I can't ignore it. I wish cellphones would be banned on airplanes, period, even when on the ground; the key difference between an airplane and a train/a building/the street is that in an airplane you can't get away.
Perhaps "rediculous", but, yes, that is the valid concern.
One of the ways that cellular providers reuse the spectrum is by dividing the landscape into . . . "cells". There are arrays of antennas in these cells that communicate with the instruments in the area. Additional spectral efficiency is gained by subdividing the cells and only using the antenna array pointing in your direction to communicate with your phone. The landscape is modeled as a 2-d environment for these purposes. The cell networks take all this landscape into account when they deploy their systems. If you want to use an additional component of altitude to the mix, you'd need different antenna arrays and you'd need to re-layout the whole mess. For these reasons, the FCC does not allow cell phone use in planes, helicopters, balloons, etc. As you say, it's a straight shot from an airplane to cell towers below -- including towers that you couldn't "see" (radio-wise) if you were on the ground directly below.
I am not a crackpot.
People talk louder on cell phones. It's not just half of a conversation. It's HALF OF A CONVERSATION!!!!!
Alternative Theory
The official crash report does not mention cell phone activity as a primary cause of the crash, and instead attributes it to pilot error.[9] However, a separate investigation into the cause of the crash showed that the autopilot system malfunctioned at the same time that a passenger's cell phone on board the plane received an SMS message and another received a call. After this information was made public, a number of countries that had previously been reluctant to do so outlawed cell phones on flights (including Switzerland).[10][11][12] Some passengers on any given flight are likely to forget to turn off their mobile devices[13], therefore it is unlikely this explanation is a likely cause.
("Crossair Flight 498." Wikipedia, The Free Encyclopedia. 8 Mar 2007, 18:16 UTC. Wikimedia Foundation, Inc. 4 Apr 2007 <http://en.wikipedia.org/w/index.php?title=Crossai r_Flight_498&oldid=113623260>.)
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
is basically that cell phones are designed for short-range communication (to the nearest base station).
As roaming between cells is designed to appear seamless, the handover to the next station would have to happen before the station one is currently connected to goes out of range (so the process is started when signal quality drops below a certain threshold). The next hop station is the one with the strongest signal.
This works fine on the ground, however in the air, the distance to the base stations is a lot greater, so it is not as easy to determine the best station for a handover, plus the high velocity has people enter and leave the cells pretty quickly. Being reachable via cell phone means that you have to establish an association to the nearest base.
And this is where it starts to get ridiculous. A plane with 300 people on board means that there are 300-epsilon phones constantly associating with base stations, and once they are done, they are already leaving for the next cell. With a GSM network, that happens over one or two 9600 baud signalling channels (basically time slots) that these 300 phones plus all the people on the ground compete for. In most parts of Europe, normal signalling traffic (which includes SMS) is so bad that two channels are constantly reserved for it, and that is without people on planes. I doubt other cell phone systems scale much better.
Battery is the other scalability problem. An 8 hour drive across Germany eats about a third of my cell phone battery, with reassociation happening every two minutes (yay for cell phone noise in the radio). Having the phone on a plane requires higher power levels, so I suspect my phone would run out of battery after two or three hours anyway.
So the entire thing is pointless. Cell phone technology was not made for that.
I'm sure the no cell phone rules originated when cell phones (bag phones) were 5-7 watts, which is a pretty respectable output to be having near sensitive equipment. Phones haven't been that powerful in a long time, these days they are typically in the .3 - .7 watt range. You would think that wouldn't be enough to cause a problem, but it can. During my pilot training I could always tell when my instructor had a call. At first she thought I was just being weird everytime I told her she had a call, but when we got back to the ground she'd see that she had. I could always tell, because I could hear it over my headset in the pilot seat. For whatever reason she couldn't hear it from the copilot seat. I could even tell the difference between a call, a text, or a voice message alert depending on the interference noise that I heard. Of course the phone was all of five feet from the antenas and radios.
Now before you get all "but on a passenger plane we're in the back no where near the cockpit!", I'll tell you another story about something we had going on for a while at my last base. I'm an aircraft maintainer by trade, a pilot just for fun. Two years ago the crews were flying test missions and kept having problems with their radios. They kept hearing a Mexican radio station through their headsets, this is not entirely unusual considering the base was in southern California and the radios can pick up music stations. The odd thing was that the radios were turned off and they were hearing it over the intercom. The intercom on an aircraft routes all of the various radios, warning alerts, etc into the crew's headsets, it's not just for talking on the aircraft. While this sort of thing is usually funny and sporatic at it's worst, this time it stopped being so, because it was continuous and eventually go loud enough to distract the crew when trying to talk to each other, other aircraft, or traffic control. It took a long time for the engineers to figure out what was going on since it was occuring on more than one type of aircraft. Turns out some of our test equipment was picking up the signal bleeding it in through the power bus. The equipment that was causing the problem wasn't even a radio, it just turns out that it inadvertantly acted like one.
So don't get so worked up thinking it's just some grand conspiracy to sell more air phone minutes or keep you from listening to some tunes. Considering how fast technology changes and how many devices are going wireless there is just no way they can keep up with testing every single device to make sure it won't cause a problem.
I can tell you first hand that GSM phones intefere very badly with aircraft COM radios. It happened to me while intercepting the localiser on approach to my local airfield, and the inteference completely obliterated any chance at communication with ATC. Fortunately, my friend (who was actually the pilot flying - fortunately, I'm also instrument rated because it was a dark, rainy night, so I could take over and continue the approach) found his phone fairly quickly and shut it off. If you own a GSM phone, you'll be familiar with the sound of the inteference, because you can hear it on any nearby radio.
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Line of sight, it takes very little signal to get that far. You're only talking a little less than two miles distance, and ham radio operators have gone much farther on very low signal levels. Frequency also enters into it of course, lower ones will go much better than higher, but still - two miles is nothing.
That said, the aluminum skin of the aircraft is going to interfere and cut the signal strength. And the antennas for most cell sites are designed for maximum gain looking horizontally and slightly downward so they should be pretty deaf to signals from above.
Hmm...
I'm willing to bet that it's not at all statistically uncommon for 20 or 30 callers in a high user density area with good coverage to be equidistant from their surrounding towers on the ground at any one time.
In fact, as the system explicitly allows you to skip from tower to tower in search of the best signal, I'm also willing to bet that the system was, in fact, designed with this in mind and will simply queue your call.
Caution: May contain nuts.
Well, a little understanding of how the cell phone networks work would help here... The number of channels (frequencies, if you will) available to a single cell site is limited. Let's say that Verizon is assigned (by the FCC) sufficient bandwidth to have 100 simultaneous calls in the city of Phoenix. Now, they could (like the Television stations) place a gigantic antenna on the top of the biggest mountain in the city, thus covering an area of, say, 100 miles radius. They would only be able to have 100 customers talking at a time; not a very good situation. So, Verizon gets smart. They put 1000 antennas around the city, on very short towers so each one covers, say, 1 mile. Now each of these antennnas can support 100 customers talking at a time, and Verizon can now have 100,000 customers talking simultaneously. With some overlap on the towers, Verizon can tell that you're driving towards the edge of the coverage of one tower, and seamlessly tell your phone to change channels and start talking to a new tower. Ever had your call dropped while driving along? Probably because the tower you were coming into range of was full, or there was a software glitch in the handoff to the new tower. Now, let's assume you are flying over Phoenix, talking to the wifey about what the rugrats did today. The channel that you're using cannot be reused by any of the 1000 cell towers in the city, because all of the cell towers have a clear line-of-sight to your airplane. You have just taken up cell phone bandwidth equivalent to 1000 customers. That's why the FCC is concerned. /frank
And the worms ate into his brain.
If that's their main concern then I believe it's unfounded in reality. For the uninitiated, here's a quick resumé of how cell phones work...
When a cellphone connects to a tower to transmit a call it gets one of a couple of possible responses:
a) If the tower has no relay slots free for the call it sends a 'fail' response and your phone automatically tries another tower. If your phone gets above a certain number of 'fail' responses, it will just give up with a 'no service' error.
b) If the tower has a free slot the call is connected. In this case, the phone will either stay connected to that tower until the termination of the call, or until the signal drops below a certain threshold (range), whichever happens soonest. When the signal level drops below an acceptable level you'll get passed on to the tower with the 2nd strongest signal, etc, ad infinitum.
Now it's important to realise that your phone connects initially to the tower with the strongest signal, but that needn't necessarily be the closest tower. If you're flying at 30,000ft above a grid of towers, the tower you connect to will be decided not only on signal strength but also on available slots, so not everyone on the plane will connect to the same tower. If there are no relay slots available you simply will not connect. Fears of disconnecting other users by your sudden appearance on the network are unfounded, as slots are served on a 'first come, first served' basis. We already do this every day travelling by train, or by car on the interstate.
Logically though, a plane travelling through a cell with 300 passengers making calls at 500mph would be less disruptive than a train travelling through the same cell with 300 passengers making calls at 120mph, as their calls would get handed over to other towers sooner, freeing relay slots as it passes.
If there's any potential bottleneck, it's during 'registration', whereby every 7 seconds or so your phone sends 'hello, I'm phone $model $IME $serial_no belonging to $network, can I connect?' and waits for a response from the cell towers, but as this handshake takes mere milliseconds I cannot see even this presenting a problem.
Caution: May contain nuts.
Insightful? wtf?
It's quite evident you have no experience of avionics. After 9 years repairing aircraft radio, intercom and nav aids I can tell you with absolute authority that all airborne electronic equipment is securely grounded, from the copper braided sleeve running up the pilots' headset cord to the 8 inch copper straps between the ac generators and the airframe.
Hell, in our test bay we'd have banks of vhf radios in for repair or test, stacked up along a bench. Some would be on full 400w ssb transmit tests into dummy loads while those alongside would be hooked up to oscilloscopes measuring bfo drift, and there wouldn't be as much as a stray spike on the scope.
Aircraft electronics are *designed* to be robust, else they wouldn't get the damn accreditation in the first place.
Caution: May contain nuts.