Mike, Colchester asked:
If you were to use a mobile phone on an aeroplane, what would happen if you were passing between base stations at 500mph?
Chris - It wouldn’t really matter from a radio point of view because radio is moving at the speed of light which is considerably faster than 500 miles an hour. It’s whether the network could actually keep up with the very rapid transition between the different cells.
Actually, if it was a GSM mobile phone network then the system can't cope with your distance to the base-station changing too quickly. I don't have the specification document to hand, but I believe the upper limit is around a couple of hundred km/hour.
That's very interesting Techmind. It never even crossed my mind that speed could be a factor, but it makes a lot of sense now.
Most commercial wireless systems are designed to cope with relative speeds of up to 70mph with an acceptable level of deteriation in quality. Some are only designed to cope with up to 50kph however; it depends on the application and what the acceptable Bit Error Rate is (if digital) or a more woolly measure of sound quality if analog. However, all these specifications are based on the deteriation being due to "fading" rather than timing problems related to Doppler effects. It is to do with the way the radio copes with moving between areas where the received signals may be cancelled by interference to areas where the signal is OK (or even reinforced) by interference. There are computer models used (called fading models) that emulate such effects and wireless systems have to pass such tests (TU-50 is an example). The problems are related to the terrain as well as the movement which is usually irrelevent in a plane for example.
To answer Geezer's challenge :-)...
Doppler shift also matters. GSM will not work above 250km/h, LTE has limit of 350km/h. Pavel, Mon, 15th Dec 2014