cellphones???

abripl wrote:

Others should not have their calls dropped no more than if a person is
calling from top of a hill or in a good position seeing different
towers. A cell phone "dialogs" with every tower in sight and ties up
only ONE channel on each.

Not so. The system designer will ensure that every cell within line of sight of
hills or other high spots is using a different set of frequencies. It is only
when the caller is in line of sight of cells relatively far away (usually 40 to
60 miles) that the call will cause conflicts.

George Patterson
I prefer Heaven for climate but Hell for company.

George Patterson wrote:

abripl wrote:

Others should not have their calls dropped no more than if a person is
calling from top of a hill or in a good position seeing different
towers. A cell phone "dialogs" with every tower in sight and ties up
only ONE channel on each.


Not so. The system designer will ensure that every cell within line of sight of
hills or other high spots is using a different set of frequencies. It is only
when the caller is in line of sight of cells relatively far away (usually 40 to
60 miles) that the call will cause conflicts.

There are algorithms built into the cell selection and re-selection
process that mitigate against interference but if the base station
receiver can't decode the uplink channel from the mobile then you have a
problem.

To achieve a usable BER (Bit Error Rate) and acceptable frame loss to
set up and maintain calls, all cellular and PCS networks, whether they
are CDMA, GSM, TDMA, etc. are designed to a specific C/I+N ratio
(Carrier to Interference plus Noise) rather than S/N (Signal to Noise).

No operator has as much spectrum as they would like and the principal
goal is to lay out the system for maximum frequency "reuse."

Over the years this has led to reduction of base station antenna heights
(few antennas are more than 100' high in an urban system) and down
tilt antennas.

Thus, any given channel may be "reused" 10-100 times in a given city.

The system design presumes the mobile units to be no higher than the
building heights. Any co-channel energy that the unintended base
station receiver hears from aircraft will reduce the C/I+N ratio and may
lead to dropped calls in that cell.

Perhaps more simply,regardless of protocol, if you can't hear your
messages over the interference it does not matter how strong the signal
is, you can't decode it.