I have heard that communication using mobile phones begins to degrade when used on a vehicle moving at speeds above 200 km/hr due to doppler effect as described here (p-22). How is this limitation overcome in airplanes. What is the specific technology used to overcome this limitation.
I can't pass judgment on the 120 km/hr limitation on cell phones as I feel that is certainly not true. The frequency and speed of EM mobile waves in the 900MHz+ spectrum are far too high to be affected by the Doppler affect.
But, you are right, there are limitations of using cell phones in airplanes.
This has nothing to do with the Doppler effect. Cellphones do not work in airplanes because commercial airliners can fly at altitudes up to 40000 feet ASML (FL 400). This is much too far and too high for the cell phone's weak radio transmitter to receive any signal from cellphone network tower located on the ground. So if the airplane is on its final approach on landing in a dense, urban area, chances are that your cell phone will be able to catch some signal from the network towers on the ground. This is with reference to the fact that passengers on board Flight 93 were able to contact their families just before their plane hit the Twin Towers at an altitude of around 1000 feet. This paper has some very good information taking in account ground speeds and altitudes for cell phone performance.
However, that's not too say that it is impossible to make phone calls from airplanes when they are at cruising at high altitudes. While it isn't something you can do with your own cell phone, most international, long range aircraft feature a pay-to-use phone facility which uses the airplane's powerful satellite radio transmitter to function as a satellite phone to make phone calls.