Mal wrote:


"Tuno" wrote in message
oups.com...
I'm a Verizon customer, and the only place I've been able to get my
phone to work in a glider above pattern altitude is in areas where SMS
does not work. Maybe that will change someday ...

-ted/2NO


Does the GPRS work at altitude.


Here is a simple overview of the factors for marginal
GSM coverage. I hope it's useful and not too boring.


Wether or not you'll get a signal depends mostly on the basestation
antenna radiation pattern. The operators normally use directional
antennas, covering the ground of the cell only.

Some of that gets reflected upwards, but that coverage is patchy.
There are of course situations where a basestation has been pointed
skywards (e.g. illuminating the side of a mountain), so in some rare
parts of the sky GSM works well.

Now, SMS uses the GSM control channel, the one which is also used
to establish a call. This channel has a very simple protocol, very
much like humans do radio communication - listen and if nobody else
talks, talk.

It only takes a small patch of coverage for an SMS to get through.
Also, as others have pointed out, the phone will hold a SMS until
it finds such a patch.

For a phone call proper, you need essentially uninterrupted coverage
for the duration of the call. In principle, if an SMS can get through
you can start a call, but it could be extremely short.

GPRS is a data transfer protocol which uses the spare channel capacity,
anything which is not used for calls. Since it's a packet based
protocol (each like very large SMS), it has a slightly better chance
of "getting through" than a phone call.

However, since the packets are larger, the patch of coverage must
last longer. Also, the system will only retry for a few seconds
before giving up. SMS will retry all week is it has to.

Among other things, GPRS is used to transfer the bulk of data
for MMS (pictures, video clips, etc.).


Iwo