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| I think it's definitely possible with GSM technology, and it was one of the things that looked like a 'stretch' in the film.
The reason cellphones are banned on aeroplanes is more down to the fact that causes the networks a lot of problems because reception is too good. Once you are a few kms up, your phone becomes visible to a load of different basestations at once (clear line of sight to them), as opposed to maybe one or two when you're on the ground.
This gives you an excellent chance of making a call but can cause problems with the routing software that the mobile networks use to figure out which cell you're 'in' and whether or not you are moving from one cell to another. To the network it looks like you are in multiple cells at once and moving rapidly into other multiple cells. If planeloads of people were whizzing around up there, registered on your network, there would be plenty of problems.
And before someone says that the plane is a faraday cage acting to block reception, haven't you ever seen people switch on and use their phones in the plane on the ground after it has parked on the stand? They work perfectly. Once when my plane was delayed on the ground in Zuerich the pilot gave permission to use phones and everyone was calling with no problems.
Of course, the US uses a different standard for mobile phones but I'd be very surprised if it didn't work in a very similar way.
Gav | |
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Interesting post, I have not tried or tested this theory of yours, so I cant prove you wrong, but I have worked abit with GSM Networking and you have pointed out some of the key functions of GSM. Firstly lets break down the handovers
Sector - Sector
BTS - BTS
BSC - BSC
MSC- MSC
GSM Network - PSTN
Now the handover between Sector or Cells takes 0.8 secs, BSC and MSC handovers are outside or behind the Cell handover so they dont affect the Call that much. The handover takes place between Sector/Cell when the signal strength is reduced and the next strongest signal snatchs it up, however the system is designed to hang on for a long as possible before handing over. The Handy does not need line of sight to function, as RF works on refraction and reflection, so unless the dimensioning is top banana you'll always have a dropped call ( have you heard the 'boing' in someones voice? thats the 'A' bit going on the signal frame between your handy and the Sector antenna).
On most Cell sites the Sectors run on a power set based on the dimensioning. So urban sites will function upto 3ks +/- and rural possibly upto 110ks +/-. By dimensioning we're talking traffic loading and surrounding Topoligy for Cell coverage. In a nutshell, the more population, the more handys, more calls, the more cells, although in difficult terrain with low pop, the cells are more powerful to cope, but the siting is based on Microwave LOS so you have workable transmission for the network connectivity.
Lets also remember a SIM is tied down to a network and will only function on the VLR, once you have, as Elvis would say " now left the building".
Now heres where it gets interesting, I'll phrase it outside the tech terms. I worked (as the teaboy) on a testing phase with a company to see how fast we could get the cells to handover, and the functionality (we were testing with the german ICE 3 train), and we got to a point in speed that the cells just lock down, the speed of the call is so quick that the handover sequence as explained in layman terms above, just freaks out and locks down. However the network I was on is a special private Network, so this problem was solved (I cant say how, I wish I could but Im bound by contract). But put it this way, the best way to understand the system you have invented is rather than wait for faults is too generate the fault and rectify.
Now sectorization is designed to work on refraction & relection, this means bouncing a signal of things (building etcs) to get coverage. The 'frezonal' signal is 'aimed' on an azimuth and tilt, that is calculated for best coverage. So with this in mind, you will also bounce the signal off the ionisphere. So in effect you have, against the technologys design ' Total coverage BABY'.
Now back to Gavs point, yes there is a problem with handovers, the process although fast does have its limitations, now a plane does 550kmh or whatever, but lets take into account the physical nature of the planes speed to the relevence of the earths surface .... er look up at a jet, does it go fast? no coz its just cruising along and looks slow, but its really doing the goose after burners pants.
So, Gavs got a good point, almost spot on to be precise
Gav, US has CDMA, we have TDMA, difference is the coding and timing. They always have to be different
