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Amrando · 21-09-2011, 16:36

regarding mobile data on trains: (sorry to 'derail' the thread)

I have a friend who was formerly an engineer with Qualcomm. His explanation was fairly basic, but practical. The problem is that cellular networks' tower handoffs are not designed to happen seamlessly (fast enough) to handle 'driveby' transmissions at 300kmh. When driving at 100-150kmh, your phone is in contact with two towers simultaneously long enough for the two to converse with each other and 'handoff' the call from old to new. However at 300kmh (ICE), or 350kmh (TGV/Shinkansen) or god forbid 800kmh (aircraft overhead) your phone is in negotiation with too many towers at once. This is the 'real' reason why you are told to shut off your cellphone while flying. Because each phone creates a huge footprint of negotiations to transmit on the ground with the towers it passes over, and causes too much 'overhead'

for the cellular providers.

	(#5)
Amrando (Offline) Junior Member Newbie Posts: 7 Join Date: 06 Sep 2011 Country:	21-09-2011, 16:36 regarding mobile data on trains: (sorry to 'derail' the thread) I have a friend who was formerly an engineer with Qualcomm. His explanation was fairly basic, but practical. The problem is that cellular networks' tower handoffs are not designed to happen seamlessly (fast enough) to handle 'driveby' transmissions at 300kmh. When driving at 100-150kmh, your phone is in contact with two towers simultaneously long enough for the two to converse with each other and 'handoff' the call from old to new. However at 300kmh (ICE), or 350kmh (TGV/Shinkansen) or god forbid 800kmh (aircraft overhead) your phone is in negotiation with too many towers at once. This is the 'real' reason why you are told to shut off your cellphone while flying. Because each phone creates a huge footprint of negotiations to transmit on the ground with the towers it passes over, and causes too much 'overhead' for the cellular providers.