Cringely: Wi-Fi in the Sky

Boiled Frog writes "In Cringely's latest article, he describes his plan to test a wi-fi connection between his house and his plane using two LinkSys 802.11g routers. He plans to experiment with various antennas to see which works the best."

Mesh in the Air

[bromoseltzer]

The interesting point here is that there are a lot of aircraft in the sky at any time. With a small WiFi-like box in each one, you've got a dandy mesh network. It is independent of land lines and satellites, so it is a new kind of connectivity. Whether there's any application other than aviation support isn't clear to me. The bandwidth wouldn't give you much video for the passengers, etc.

-mse

Warflying...

[taubman]

Sorry Bob, someone beat you to it. [airshare.org]

But i'd still be interested to see the results of a bi-directional test..

Re:Cringe-ly

[delcielo]

For the most part, I agree with you.

He's poo-pooing research into the matter by saying that it doesn't prove anything; and yet he's not giving any evidence that it's not true.

He does have the priviledge under Part 91 to do this in his own plane, though. The thing is, his homebuilt small plane probably has better insulation on the wiring than a mid-80's airliner. Also, he probably doesn't fly his little homebuilt on autopilot much (if it's even equipped with one) whereas an airliner spends most of its time being flown by the flight director (fancy autopilot), which is the component that we're really worried about, as it will follow a failed instrument without question, as opposed to analyzing whether or not the indications make sense. So, in the end, he won't really have proven anything regarding the RF interference issue on aircraft.

Finally, I'm not going to spend $1000 having an A&P mechanic install my $100 wifi router in my airplane. If I could just slap it in myself, that would be one thing; but with an airplane you're going to need a Form 337 approval at least, if not an STC (Supplemental Type Certificate). No big deal on the 337. It just takes time and thus money. That's money I'll be spending just help the wifi cloud when I happen to be flying? Uhh, I'll pass.

estimating range vs. altitude

[Anonymous Coward]

The crude, fast, and suprisingly useful approximation for line-of-sight as a function of height: range=(sqrt(2*height)) where range is in miles and height is in feet. Inverse-square losses will eat into your link budget, but you'd be suprised... 2 watt satellites in orbits @ 300Km can be heard with handheld scanners. I suspect he'll want to use an antenna with modest gain and a hemispherical pattern... a K5OE patch feed for 2.4GHz ought to be good enough, but just don't expose that thing to 100 KIA+ airspeeds.

Re:Cringe-ly

[div_2n]

It isn't too hard to figure out:

1) There are in-plane phones that charge your out the ass to use them. Cell phones kind of bypass that. It isn't surprising that they don't allow cell phones in-flight.

2) I have read that cell companies say that the phones would confuse the cell network due to being able to "see" so many towers. I don't buy that as I have used my cell on top of a 250ft tower on top of a tall mountain well within the range of at least 10 cell towers. No problem as far as I could see.

3) When the terrorists took over the planes in 2001, passengers were using cell phones to make calls while the planes were going. The pilots were NOT professionals. They had enough training to steer them into buildings and that is about it. They didn't crash because of cell phones being used. Hmmmm.

You can bet that cell phones are not a danger to make planes crash. That isn't the reason they are banned. You can bet on that.

Re:Mesh in the Air

[LWATCDR]

Actually not there is not a lot of airplanes in the sky at any one time.
Find someplace away from an Airport and just look up. Odds are pretty good that you will not see any planes. No planes no signal no mesh.

I really like the idea of inexpensive datalinks to aircraft. It would be great if you could just add an 802.11b/g to each VOR station. Light aircraft could have the advantage of weather radar, voip, and even a display showing every other aircraft near them.
The idea of using them as an ad hoc mesh just will not work.

What I would like to see try is placeing 802.11b APs on rural TV station towers as a way to provid low cost Broadband.
Just an idea mind you but I wonder how far of a shot you could get.

Handoff

[ozmanjusri]

A few years ago, I was doing some contract work for a company that does the installs for some of the GSM base stations here in Australia.

During a conversation with one of the techs the subject of the ban on mobile phones came up. His comment was that the phone transmitters are too low powered to affect the plane's systems, but that if 300 passengers on a plane travelling at 400kmh+ all had phones on, the handover process from cell to cell would be swamped and there would be a trail of crashed cellular base stations behind each passenger plane.
Better than crashing the planes, but still enough of a problem to insist on a ban on phones, and if you want people to co-operate, linking their cooperation to their own safety is about as good an incentive as you're going to get.

A light plane travelling at 200kph won't cause the same problem, so nobody worries about enforcing the ban for them.

Re:Mesh in the Air

[TheSync]

At 5,000 feet, air-to-gound line of sight is 100 miles, aircraft-to-aircraft line of sight is 200 miles. Most urban areas will probably have at least one aircraft within 100 miles at any point!

As proof-of-concept, listen to VHF air frequencies, you will hear 20-30 planes over a few minutes.

I have worked space station MIR with a 5 watt handheld VHF transmitter, which is about 100 miles away.

My impression is that if all commercial airline planes carried mesh network devices that could emit a few watts, urban areas could probably have near 100% mobile digital coverage, the question being just how much bandwidth would be available, which would be a cost/benefit ratio based on how complex the devices in the planes need to be.

It also would stress the mesh routing algorithms!

Re:Cringe-ly

[ba_hiker]

I am a private pilot and HAVE had a tape recorder/player in the cockpit cause significant interference on a navigation insturment in the cockpit. Durring a flight from San Luis Obispo to Santa Barbara the navi reciever indicated an errror when homing to the Gaviota VOR. The error was about 15 deg. The conditions were vfr and there was no safty-of-flight problem.

the real issue, i suspect, is RFI and the amount of intercell interference.

There are only 329 frequencies in the low (VHF) cell band and some 500 or so in the upper (UHF) band. No cell can use the same freq as another cell within some specified distance. Because of this the avarage cell can only use a small number of them (I remember somehing like less than 40 for the vhf band) to prevent RFI.

the cell companies hire engineering firms to calculate the interference and calculate cell sizes, antena siting, and transmitter power (at the base station). Many areas are saturated, the maximum number of cells are installed with the lowest power transmiters and directiona antanas. the cells in a region (for a carrier, which is allocated a set of frequencies) communicate and decide what cell gets what frequencies now.

A cell phone in an airplane will blank that frequency from all of the cells that it is detected in. So some 330 calls from aircraft over san franciusco, for instance, could block all the vhf (old style analog phone) in the whole bay area!

the same holdes for the newer phones, but with the fancier multiplexing schemes used the calculations are more difficult and probablistic (ie: 650 calls at once have a 50% chance of blocking all the UHF/digital cells in the above case).