Planes & Cell phones

On Wed, 21 Apr 2004 00:53:13 +0000, James Robinson wrote:

Greg Copeland wrote:

On Tue, 20 Apr 2004 16:35:03 -0500, FUji wrote:

Huh? Maximum output of most handheld cell phones is 0.6 watts with the old
in-car and bag phones going up to 3 watts. It can't output more than it's
maximum no matter how far you are away from the tower. The radius of
interference from 0.6 watt phones transmitting from inside an aluminum can
would be rather small. And it's a little hard to imagine a plane full of
people with bag phones.

I thought I might just toss this out there. I quickly looked. I did not
have any trouble finding modern, handheld phones, with 2-watts output.
So, I think it's safe to say that we know for sure it's at least 2-watts.

Both of my run-of-the-mill Nokias have a maximum transmit power of 600
mW. They are two different digital/analog models.

Well, that's an interesting point. I know if I leave my phone on in the
air, it tends to degrade to analog mode (dual band phone). While I am
aware the digital mode uses far less power (just didn't realize that
little), perhaps the 5-watt maximum number is representative of phones
operating in analog mode? I dunno. That's my best guess.

"Greg Copeland" wrote in message
news
On Tue, 20 Apr 2004 16:35:03 -0500, FUji wrote:

Huh? Maximum output of most handheld cell phones is 0.6 watts with the
old
in-car and bag phones going up to 3 watts. It can't output more than
it's
maximum no matter how far you are away from the tower. The radius of
interference from 0.6 watt phones transmitting from inside an aluminum
can
would be rather small. And it's a little hard to imagine a plane full
of
people with bag phones.

I thought I might just toss this out there. I quickly looked. I did not
have any trouble finding modern, handheld phones, with 2-watts output.
So, I think it's safe to say that we know for sure it's at least 2-watts.


0.7 watts is the maximum that is considered "safe" for handheld use by
medical experts. Any more than that gets your brain frying, so they say.
;-)

I've had cell phones for fifteen years (novatel, motorola, mitsubishi, etc.)
and all the handhelds except the ericssons were 0.6 watts. The ericssons
were only 0.5 watts! Way back then I remember if you complained about bad
reception with a handheld they'd tell you to "upgrade" to a transportable.

Any links or names of the ones you found?

On Tue, 20 Apr 2004 20:14:23 -0500, FUji wrote:

"Greg Copeland" wrote in message
news
On Tue, 20 Apr 2004 16:35:03 -0500, FUji wrote:

Huh? Maximum output of most handheld cell phones is 0.6 watts with the
old
in-car and bag phones going up to 3 watts. It can't output more than
it's
maximum no matter how far you are away from the tower. The radius of
interference from 0.6 watt phones transmitting from inside an aluminum
can
would be rather small. And it's a little hard to imagine a plane full
of
people with bag phones.

I thought I might just toss this out there. I quickly looked. I did not
have any trouble finding modern, handheld phones, with 2-watts output.
So, I think it's safe to say that we know for sure it's at least 2-watts.


0.7 watts is the maximum that is considered "safe" for handheld use by
medical experts. Any more than that gets your brain frying, so they say.
;-)

I've had cell phones for fifteen years (novatel, motorola, mitsubishi, etc.)
and all the handhelds except the ericssons were 0.6 watts. The ericssons
were only 0.5 watts! Way back then I remember if you complained about bad
reception with a handheld they'd tell you to "upgrade" to a transportable.

Any links or names of the ones you found?

http://www.hazardousareadirect.com/P...EX-HANDY04.htm
http://www.phonemerchants.com/poda3wadubac.html

All I did was a quick google and this was the first one that popped up.
It says, 2 watts, 1 watts, and 1 watts for it's maximum output for the
three supports networks. It is a tri-band phone.

The second link is a power amplifier which cranks output up to 3-watts.
Keep in mind, just bacause a phone may output less than maximum power,
doesn't have to mean they are not allowed to output higher. Perhaps we're
playing with semantics here. Perhaps the maximum allowed is 5-watts? And
most phones output less? I dunno. At any rate, right off the bat, I
didn't have any trouble finding a phone that has a maximum output of
2-watts.

FUji wrote:

The switching is done in a fraction of a second. The most that would happen
is a dropped call.

Not true. If you are a few thousand feet up, using one of the phones that uses the
old 800 MhZ bands, you will hit multiple cells which use the same radio frequency
set. The problem is not switching so much as it is interference with other calls. If
the ground equipment has the capability of detecting this interference (Motorola used
to do this), then you've blocked that frequency pair at every cell within range and
reduced their capacity by one call. If it can't detect and correct the problem, your
conversation may "step on" someone else's call.

If you are on the ground, you will only be able to reach one cell that uses the
frequency set you're using and there is no problem.

Now, if you have one of those "personal communication systems" (AKA "PCS phones"),
you will not have this problem in the air. These phones use frequency sets in the 900
MhZ range, use different technology, and are legal to use in the air. Of course,
non-professionals call them "cell phones", so you get all sorts of confusion there.
Some of them also use the old system for backup when they can't complete a call using
the PCS network, so you really have to check your manual.

This topic has been extensively discussed here for over 15 years that I know of. Back
when it mattered a lot more than it does now.

George Patterson
This marriage is off to a shaky start. The groom just asked the band to
play "Your cheatin' heart", and the bride just requested "Don't come home
a'drinkin' with lovin' on your mind".

Greg Copeland wrote:

I thought I might just toss this out there. I quickly looked. I did not
have any trouble finding modern, handheld phones, with 2-watts output.

They almost certainly are not cell phones. Probably PCS.

George Patterson
This marriage is off to a shaky start. The groom just asked the band to
play "Your cheatin' heart", and the bride just requested "Don't come home
a'drinkin' with lovin' on your mind".

"Greg Copeland" wrote in message
news
On Tue, 20 Apr 2004 16:35:03 -0500, FUji wrote:

The switching is done in a fraction of a second. The most that would
happen
is a dropped call.

People forget that cell switching is not magical. And it's certainly is
not zero cost. I must admit I do not fully understand everything that
goes on, but I am sure it's not as simple as you imply. Everytime a call
switches cells, it creates lots of work for the cell network to make sure
only a single tower handles that call. So, while it may take a fraction
of a second from a given phone and a given tower, there is lots going on
behind the scenes. Worse, instead of it going on with one, two or maybe
three towers, now it's causing a flurry of on twenty or more (highest
estimates I've read) towers. Let's also not forget that each tower can
only process and multiplex n-number of signals at a given time. DSPs,
just like your CPU, does have finite capacity. During cell switching, as
I understand it, this finite resource is being used on each tower in
contact with the phone. So, to say, "it causes all sorts of problems on
the cell network", does seem like a spot on statement to me.


True. I oversimplified it. A dropped call is all the users would
experience.

Even though it is theoretically possible to overload the processing
capability, I doubt that it is really a significant problem in the real
world.

For example, a group of people standing at the top of the CN Tower using
their phones would be line-of-sight to almost every cell tower in the
Toronto area. The system would select the best tower and lock on.

A better example that includes moving: People on their phones driving
through downtown NYC. A densely populated area would need more towers with
closer spacing. With all the buildings acting as giant reflectors we now
have multipath signals from many towers as well as phones. If the system
can lock onto thousands of phones under these conditions, a couple of 747's
with about half of the people on phones would be minor.

As some pilots who used their phones in the air have reported, they have to
lower their altitude to get a signal. Regardless of what the reports say,
hitting twenty towers with such a low wattage is highly unlikely.

On Tue, 20 Apr 2004 20:59:28 -0500, FUji wrote:

Even though it is theoretically possible to overload the processing
capability, I doubt that it is really a significant problem in the real
world.

It happens on the time. Capacity planning is part of their job. It's
just that proper planning by the various carriers tend to hide this fact.


For example, a group of people standing at the top of the CN Tower using
their phones would be line-of-sight to almost every cell tower in the
Toronto area. The system would select the best tower and lock on.

Right, which means they are not changing towers and are only using the
resources of a single tower.


A better example that includes moving: People on their phones driving
through downtown NYC. A densely populated area would need more towers with
closer spacing. With all the buildings acting as giant reflectors we now
have multipath signals from many towers as well as phones. If the system
can lock onto thousands of phones under these conditions, a couple of 747's
with about half of the people on phones would be minor.

That's really part of a capacity planning issue, IMO. If you were to
figure out the average call density, it would probably be fairly sparse.
After all, only so many cars can fit in a given area. Now then, if you
have a plane with 250 people and half those are using their phone, that's
an extra 125 calls on each tower that is now suddenly passing from tower
to tower. That's a HUGE difference in capacity in a very short period of
time.


As some pilots who used their phones in the air have reported, they have to
lower their altitude to get a signal. Regardless of what the reports say,
hitting twenty towers with such a low wattage is highly unlikely.

If it's reasonable to assume a ground based user can get two to three
towers at any given time, I don't think it's hard to easily imagine two,
three or even four times that since you're in the air with much fewer
obstructions (less scatter, direct, and father los), especially since
there is a much higher chance that your phone is operating at or near its
maximum output. Granted, chances are you not in a rural area if you're
hitting that many towers. But, just for the sake of argument, let's say
it's less. Is using use two or three times your normally alloted capacity
fair on the carriers? With enough phones in use at any given time, I can
easily imagine it playing heck with their capacity planning.

x-no-archive: yes
"G.R. Patterson III" wrote:


Now, if you have one of those "personal communication systems" (AKA "PCS phones"),
you will not have this problem in the air. These phones use frequency sets in the 900
MhZ range, use different technology, and are legal to use in the air.

Not 900 Mhz in the US. Perhaps you meant to say 1900 Mhz range.

Tim Baron wrote:

Not 900 Mhz in the US. Perhaps you meant to say 1900 Mhz range.

You're correct, of course. The 900 MhZ band is for pagers and such.

George Patterson
This marriage is off to a shaky start. The groom just asked the band to
play "Your cheatin' heart", and the bride just requested "Don't come home
a'drinkin' with lovin' on your mind".

Greg Copeland wrote:

The general theory on modern cell phones in flight, goes like this:
The FCC also has a ban because when you're in flight, you're always at
least 6-8 miles away from the nearest cell tower. You end up communicating
with too many towers and bogging down the network.

No, you could be right beside the nearest tower. In general, any tower within about
20 miles of you will be able to receive you when you're on the ground (unless
something's blocking the signal). To eliminate conflict between calls, towers that
are neighbors use different frequency sets. When you make a call, the control system
polls all of the towers that can "hear" you and tells the closest one to accept the
call. That tower tells your phone what frequency pair to use. After that, only that
tower can "hear" your phone. If you move too far away, the control system will poll
all the towers again and have your phone switch frequencies.

Unfortunately, there aren't enough radio frequencies to allow every tower to use a
unique set, so there will probably be several towers between 30 and 60 miles from you
that use the same set of frequencies that your phone is using. They can't hear you
'cause they're too far away.

Now take off. As soon as you get 500' up, some of these towers can hear your phone.
If these towers are using the same frequency pair for other calls that your phone is
using, your call will bleed into those conversations. Some hardware systems can
detect conflicts like this and have other phones change frequencies. This hardware,
however, will log the ID of the phone that's causing the trouble, and you may get a
service termination notice.

The system designers carefully design the network to prevent call conflict due to
things like skyscrapers. Skyscrapers rarely move, however.

George Patterson
This marriage is off to a shaky start. The groom just asked the band to
play "Your cheatin' heart", and the bride just requested "Don't come home
a'drinkin' with lovin' on your mind".