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patcat88

join:2002-04-05
Jamaica, NY
kudos:1

2 edits
reply to rradina

Re: it really has nothing to do with the aircraft....

said by rradina:

Help me understand how that solves the problem. It might if the antenna and all aloft devices automatically use a different frequency. If not, how does a parabola stop the regular cell antennas from hearing airborne devices? Even if it was huge, in an attempt to block vertically transmitted signals from the tower's normal antennas, it wouldn't stop reflected signals.

Phone sees stronger sky facing antenna, not 90 degree weak edge of ground aimed sector antennas. Phone locks onto sky facing channel/psuedochannel (CDMA) antenna, reverse link power control lowers the phone's transmit power, end of problem. All cellphone networks have interference, the question is how much. The sky facing antennas do frequency reuse just like ground aimed ones.

»en.wikipedia.org/wiki/Frequency_···cy_reuse

The problem isn't new and its been solved years ago. Take a ferry or drive a car over a long causeway/viaduct in a heavily populated metro area, with skyscrapers. Your phone will see 100s of towers. Does your phone drop or loose service while on the ferry or driving on the suspension bridge? NO.

The BSS can figure out when a phone is seeing too many towers, and steer all the phones in the bay (water) to a particular channel/tower that is reserved for open water bay phones. A phone can not switch towers without the tower's/network's permission.

»en.wikipedia.org/wiki/Radio_reso···nagement

rradina

join:2000-08-08
Chesterfield, MO
If this works, why haven't they done this? Every aircraft has several (possibly half the phones) accidentally or purposely left on during flight. Theoretically, these phones are transmitting at maximum power trying to find cell towers. Wouldn't that unnecessarily cause a lot of interference for ground-based traffic? Wouldn't the industry want to solve it the way you suggested?

Crookshanks

join:2008-02-04
Binghamton, NY

2 edits
reply to patcat88
said by patcat88:

Take a ferry or drive a car over a long causeway/viaduct in a heavily populated metro area, with skyscrapers. Your phone will see 100s of towers.

Urban areas have very few macro cells that provide long range coverage. Micro and pico cells are far more common. The macro cells are used to service fast moving (e.g., phones in cars, on the train, etc.) or more distant mobiles, while the rest are directed to micro/pico cells that serve a much smaller footprint. In your scenario the phone would not hear more than a handful of towers, as it would quickly move out of range of the micro and pico cells.

said by patcat88:

A phone can not switch towers without the tower's/network's permission.

Cellular networks are divided into paging areas. Your mobile does not notify the network when it switches to a different base station within the same paging area, it only tells the network when it moves into a new paging area. The cellular network has no idea which specific base station an idle mobile is listening to, and it may well be listening to more than one at a time in a CDMA network. Asking for permission for every single base station hand off while idle would consume a lot of power.

The network can command a mobile to switch channels or base stations, but the mobile does not have to request permission to move between base stations while idle. An idle mobile doesn't even have its receiver turned on a majority of the time, it wakes up every so often to check for pages, then goes back to sleep. This is another power saving feature, and one of the reasons why LTE can be such a battery hog -- getting low latency requires keeping the receiver on more than older technologies.

Crookshanks

join:2008-02-04
Binghamton, NY
reply to rradina
Phones don't transmit while looking for towers, they only transmit during initial registration and when moving between paging areas. Short bursts of communications don't have much of an impact on the overall signal-to-noise ratio of the network. The problem only becomes apparent when the phone is transmitting with a full duty cycle, e.g., while in a call, or engaged in a large data upload.

As for why they don't do it the way he wants, because it would be a foolish waste of money? Retrofitting every single base station in the country and sacrificing precious spectrum to service mobiles on airlines makes no sense. Pico/femtocells on the aircraft would be the way to solve this "problem", if the industry and airlines were so inclined.